# Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Shortfin Mako Shark (Isurus oxyrinchus) as Threatened or Endangered Under the Endangered Species Act

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2022-24493

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** November 14, 2022
- **Citation:** 87 FR 68236

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[Docket No. 221103-0232; RTID 0648-XR116]
Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Shortfin Mako Shark (Isurus oxyrinchus) as Threatened or Endangered Under the Endangered Species Act

AGENCY:

National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Department of Commerce.

ACTION:

Notice of 12-month finding and availability of status review document for the shortfin mako shark (
Isurus oxyrinchus
).

SUMMARY:

We, NMFS, have completed a comprehensive status review under the Endangered Species Act (ESA) for the shortfin mako shark (
Isurus oxyrinchus
) in response to a petition from Defenders of Wildlife to list the species. After reviewing the best scientific and commercial data available, including the Status Review Report, we have determined that listing the shortfin mako shark as a threatened or endangered species under the ESA is not warranted.

DATES:

This finding was made on November 14, 2022.

ADDRESSES:

The Status Review Report associated with this determination, its references, and the petition can be accessed electronically online at:
https://www.fisheries.noaa.gov/species/shortfin-mako-shark#conservation-management.

FOR FURTHER INFORMATION CONTACT:

Adrienne Lohe, NMFS Office of Protected Resources, 301-427-8442.

SUPPLEMENTARY INFORMATION:

Background

On January 25, 2021, we received a petition from Defenders of Wildlife to list the shortfin mako shark (
Isurus oxyrinchus
) as a threatened or endangered species under the ESA. The petition asserted that the shortfin mako shark is threatened by four of the five ESA section 4(a)(1) factors: (1) the present or threatened destruction, modification, or curtailment of its habitat or range; (2) overutilization for commercial and recreational purposes; (3) inadequacy of existing regulatory mechanisms; and (4) other natural or manmade factors.

On April 15, 2021, NMFS published a 90-day finding for the shortfin mako shark with our determination that the petition presented substantial scientific and commercial information indicating that the petitioned action may be warranted (86 FR 19863). We also announced the initiation of a status review of the species, as required by section 4(b)(3)(A) of the ESA, and requested information to inform the agency's decision on whether this species warrants listing as endangered or threatened under the ESA. We received information from the public in response to the 90-day finding and incorporated the information into both the Status Review Report (Lohe
et al.
2022) and this 12-month finding.

Listing Determinations Under the ESA

We are responsible for determining whether species are threatened or endangered under the ESA (16 U.S.C. 1531
et seq.
). To be considered for listing under the ESA, a group of organisms must constitute a “species,” which is defined in section 3 of the ESA to include any subspecies of fish or wildlife or plants, and any distinct population segment (DPS) of any species of vertebrate fish or wildlife which interbreeds when mature (16 U.S.C. 1532(16)). On February 7, 1996, NMFS and the U.S. Fish and Wildlife Service (USFWS; together, the Services) adopted a policy describing what constitutes a DPS of a taxonomic species (“DPS Policy,” 61 FR 4722). The joint DPS Policy identifies two elements that must be considered when identifying a DPS: (1) The discreteness of the population segment in relation to the remainder of the taxon to which it belongs; and (2) the significance of the population segment to the remainder of the taxon to which it belongs.

Section 3 of the ESA defines an endangered species as any species which is in danger of extinction throughout all or a significant portion of its range and a threatened species as one which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range (16 U.S.C. 1532(6), 16 U.S.C. 1532(20)). Thus, in the context of the ESA, we interpret an “endangered species” to be one that is presently in danger of extinction. A “threatened species,” on the other hand, is not presently in danger of extinction, but is likely to become so in the foreseeable future. In other words, the primary statutory difference between a threatened and endangered species is the timing of when a species is in danger of extinction, either presently (endangered) or in the foreseeable future (threatened).

Under section 4(a)(1) of the ESA, we must determine whether any species is endangered or threatened as a result of any one or a combination of any of the following factors: (A) the present or threatened destruction, modification, or curtailment of its habitat or range; (B) overutilization for commercial, recreational, scientific, or educational purposes; (C) disease or predation; (D) the inadequacy of existing regulatory mechanisms; or (E) other natural or manmade factors affecting its continued existence (16 U.S.C. 1533(a)(1)). We are also required to make listing determinations based solely on the best scientific and commercial data available, after conducting a review of the species' status and after taking into account efforts, if any, being made by any state or foreign nation (or subdivision thereof) to protect the species (16 U.S.C. 1533(b)(1)(A)).

Status Review

To determine whether the shortfin mako shark warrants listing under the ESA, we completed a Status Review Report, which summarizes information on the species' taxonomy, distribution, abundance, life history, and biology; identifies threats or stressors affecting the status of the species; and assesses the species' current and future extinction risk. We appointed a biologist in the Office of Protected Resources Endangered Species Conservation Division to compile and complete a scientific review of the best available information on the shortfin mako shark, including information received in response to our request for information (86 FR 19863, April 15, 2021). Next, we convened an Extinction Risk Analysis (ERA) Team of biologists and shark experts to assess the threats affecting the shortfin mako shark, as well as demographic risk factors (abundance, productivity, spatial distribution, and diversity), using the information in the scientific review. The Status Review Report presents the ERA Team's professional judgment of the extinction risk facing the shortfin mako shark but makes no recommendation as to the listing status of the species. The Status Review Report is available electronically (see
ADDRESSES
). Information from the Status Review Report is summarized below in the Biological Review section, and the results of the ERA from the Status Review Report are discussed below.

The Status Review Report was subject to independent peer review as required by the Office of Management and Budget Final Information Quality Bulletin for Peer Review (M-05-03; December 16, 2004). The Status Review

Report was peer reviewed by three independent specialists selected from the academic and scientific community with expertise in shark biology, conservation, and management, and specific knowledge of shortfin mako sharks. The peer reviewers were asked to evaluate the adequacy, appropriateness, and application of data used in the Status Review Report, as well as the findings made in the “Assessment of Extinction Risk” section of the report. All peer reviewer comments were addressed prior to finalizing the Status Review Report.

We subsequently reviewed the Status Review Report, its cited references, and peer review comments, and conclude the Status Review Report, upon which this 12-month finding is based, provides the best available scientific and commercial information on the shortfin mako shark. Much of the information discussed below on the species' biology, distribution, abundance, threats, and extinction risk is attributable to the Status Review Report. Following our review of the Status Review Report and consideration of peer review comments, we conclude, however, that the ERA Team's foreseeable future of 25 years for the shortfin mako shark is not adequately justified. Each of the three peer reviewers recommended evaluating the species' risk of extinction over a longer time horizon. Based on these peer review comments and our review of the ERA Team's selection of 25 years as the foreseeable future, we have completed an independent determination of the foreseeable future (see Extinction Risk Analysis). For this reason, while we rely on the ERA Team's assessment of the species' present risk of extinction, we have supplemented the assessment of the species' risk of extinction within the foreseeable future. We have also independently applied the statutory provisions of the ESA, including evaluation of the factors set forth in section 4(a)(1)(A)-(E), our regulations regarding listing determinations,
1

and relevant policies identified herein in making the 12-month finding determination.

1
On July 5, 2022, the United States District Court for the Northern District of California issued an order vacating the ESA section 4 implementing regulations that were revised or added to 50 CFR 424 in 2019 (“2019 regulations,” see 84 FR 45020, August 27, 2019) although making no findings on the merits. On September 21, 2022, the U.S. Court of Appeals for the Ninth Circuit granted a temporary stay of the district court's July 5 order. As a result, the 2019 regulations are once again in effect, and we are applying the 2019 regulations here. For purposes of this determination, we considered whether the analysis or its conclusions would be any different under the pre-2019 regulations. We have determined that our analysis and conclusions presented here would not be any different.

Biological Review

Taxonomy and Species Description

The shortfin mako shark belongs to the family Lamnidae in the order Lamniformes, the mackerel sharks (ITIS 2021). Lamnid sharks are littoral to epipelagic with broad distributions in tropical to cold-temperate waters (Compagno 1984). They are fast-swimming and have a modified circulatory system to maintain internal temperatures warmer than the surrounding water (Compagno 1984). The shortfin mako shark belongs to the genus
Isurus
and only has a single living cogeneric species, the longfin mako shark (
Isurus paucus
). The species is relatively large, reaching a maximum total length (TL) of about 445 centimeters (cm) (Weigmann 2016), and has a moderately slender, spindle-shaped body with a conical snout (Compagno 1984). Its pectoral fins are narrow-tipped and moderately broad and long (considerably shorter than the length of the head) as compared to the very long pectoral fins of the longfin mako shark, which also has a less pointed snout and dusky underside (Compagno 1984; Ebert
et al.
2013). The first dorsal fin is large and the second is very small and pivoting (Compagno 1984). The upper and lower lobes of the caudal fin are of nearly equal size, which is reflected in the genus name
Isurus
from the Greek words for “equal tail.” The teeth are large and bladelike without serrations, and the tips of the anterior teeth are strongly reflexed (Compagno 1984). The dorsal surface of the body is dark blue and the ventral side is white (Compagno 1984).

Distribution

The shortfin mako shark is a globally distributed pelagic species, occurring across all temperate and tropical ocean waters from about 50° N (up to 60° N in the northeast Atlantic) to 50° S and across a range of marine habitats (Rigby
et al.
2019; Santos
et al.
2020). Compagno (2001) provides the following description of the species' global distribution: in the western Atlantic, the species occurs from the Gulf of Maine to southern Brazil and possibly northern Argentina, including Bermuda, the Caribbean, and the Gulf of Mexico. In the eastern Atlantic, the range spans from Norway, the British Isles, and the Mediterranean to Morocco, Azores, Western Sahara, Mauritania, Senegal, Côte d'Ivoire, Ghana, southern Angola, probably Namibia, and the west coast of South Africa. In the Indo-Pacific basin, the species is found from the east coast of South Africa, Mozambique, Madagascar, Mauritius and Kenya north to the Red Sea, and east to Maldives, Iran, Oman, Pakistan, India, Indonesia, Viet Nam, China, Taiwan, North Korea, South Korea, Japan, Russia, Australia (all states and entire coast except for Arafura Sea, Gulf of Carpentaria and Torres Strait), New Zealand (including Norfolk Island), New Caledonia, and Fiji. In the central Pacific, the shortfin mako shark occurs from south of the Aleutian Islands to the Society Islands, including the Hawaiian Islands, and in the eastern Pacific, from southern California (and sometimes as far north as Washington State) south to Mexico, Costa Rica, Ecuador, Peru, and central Chile. Rare observations outside of this range have also been made, for example in waters of British Columbia (Gillespie and Saunders 1994).

Habitat Use

The shortfin mako shark is known to travel long distances in and between open ocean, continental shelf, shelf edge, and shelf slope habitats (Rogers
et al.
2015b; Santos
et al.
2021), making extensive long-distance straight-line movements of several thousand kilometers (km) (Francis
et al.
2019). From traditional dart and fin tagging data, maximum recorded time at liberty is 12.8 years, and the maximum straight-line distance between tag and recapture localities is 3,043 nautical miles (5,636 km) (Kohler and Turner 2019). Shorter-term electronic tagging results from several studies indicate that the species commonly makes roundtrip migratory movements of more than 20,000 km, with one individual found to undertake an extended migration of 25,550 km over a period of 551 days (Rogers
et al.
2015b; Francis
et al.
2019). While the species has also demonstrated fidelity to small geographic areas on or near continental shelves and coastal areas of high productivity, this fidelic behavior is rarely observed in the open ocean (Rogers
et al.
2015b; Corrigan
et al.
2018; Francis
et al.
2019; Gibson
et al.
2021). Recent research demonstrates that the species regularly switches between these states of activity (
i.e.,
resident or fidelity behavior state and traveling state), spending nearly half their time (44-47 percent) in residency and slightly less than half their time (35-42 percent) in transit (Rogers
et al.
2015b; Francis
et al.
2019). It is unknown whether these behavioral states are tied to specific behaviors such as feeding or breeding. Furthermore, this behavioral switching may be affected by factors including

environmental variation, spatial areas of sampling, or biotic factors; therefore, these findings may not be representative of the entire species, especially across time and space.

The vertical distribution of shortfin mako sharks is related to numerous environmental variables, including water temperature, dissolved oxygen (DO) concentration, time of day, prey availability, and lunar phase. The species typically occupies waters ranging between 17 °C and 22 °C (Casey and Kohler 1992; Nasby-Lucas
et al.
2019; Santos
et al.
2020, 2021), though it has a broad thermal tolerance and has been shown to also occupy waters from 10 °C (Abascal
et al.
2011) to 31 °C (Vaudo
et al.
2017). Like other lamnid sharks, the shortfin mako shark has counter-current circulation and is a red muscle endotherm, meaning that it can maintain the temperature of its slow-twitch, aerobic red muscle significantly above ambient temperature (Watanabe
et al.
2015). Red muscle endothermy allows the species to tolerate a greater range of water temperatures, cruise faster, and have greater maximum annual migration lengths than fish without this trait (Watanabe
et al.
2015). The high energetic cost of endothermy is suggested to be outweighed by benefits such as increased foraging success, prey encounter rates, and access to other seasonally available resources (Watanabe
et al.
2015). The routine metabolic rate and maximum metabolic rate of shortfin mako sharks is among the highest measured for any shark species (Sepulveda
et al.
2007), which may explain why the shortfin mako shark typically inhabits waters with DO concentrations of at least 3 milliliters per liter and avoids areas of low DO (Abascal
et al.
2011). Individuals primarily occupy the upper part of the water column, but dive to depths of several hundred meters (m) (as deep as 979.5 m reported by Santos
et al.
(2021)), allowing them to forage for mesopelagic fishes and squid, though dives may have other functions including navigation (Holts and Bedford 1993; Francis
et al.
2019). There is evidence that illumination from a full moon causes shortfin mako sharks to move into deeper water in pursuit of prey (Lowry
et al.
2007). “Bounce” or “yo-yo” diving behavior, in which individuals repeatedly descend to deeper water and then ascend to shallow depths, has been regularly observed in both adults and young-of-the-year (YOY) (Sepulveda
et al.
2004; Abascal
et al.
2011; Vaudo
et al.
2016; Santos
et al.
2021). This type of diving behavior may be associated with feeding, behavioral thermoregulation, energy conservation, and navigation (Klimley
et al.
2002; Sepulveda
et al.
2004). Tagging studies have shown that the species typically spends more time in deeper, colder water during the daytime, and moves to shallower, warmer waters at night (Holts and Bedford 1993; Klimley
et al.
2002; Sepulveda
et al.
2004; Loefer
et al.
2005; Stevens
et al.
2010; Abascal
et al.
2011; Nasby-Lucas
et al.
2019). These diel vertical migrations are typically attributed to the pursuit of prey. However, other studies indicate no significant changes in vertical distribution between daytime and nighttime (Abascal
et al.
2011, Santos
et al.
2020). Larger individuals can dive to deeper depths than smaller individuals (Sepulveda
et al.
2004), and juveniles specifically tend to spend much of their time in shallower, warmer water (Holts and Bedford 1993; Nosal
et al.
2019).

There is some evidence that certain ocean currents and features may limit movement patterns, including the Mid-Atlantic ridge separating the western and eastern Atlantic (Casey and Kohler 1992 using conventional tagging data from 231 recaptured shortfin mako sharks over a 28-year period; Santos
et al.
2020 using satellite telemetry for 41 shortfin mako sharks over a period of between 30 and 120 days), and the Gulf Stream separating the North Atlantic and the Gulf of Mexico/Caribbean Sea (Vaudo
et al.
2017 using satellite telemetry for 26 shortfin mako sharks over a period of 78-527 days). However, conventional tagging data indicates that movement does occur across these features. Data from the NMFS Cooperative Shark Tagging Program (n=1,148 recaptured shortfin mako sharks) over a 52-year period show evidence of the species crossing the Mid-Atlantic Ridge demonstrating exchange between the western and eastern Atlantic (Kohler and Turner 2019). In fact, individual shortfin mako sharks (n = 104) that made long distance movements (>1,000 nautical miles) while at liberty for less than one year were primarily tagged off the coast of the U.S. Northeast and were recaptured in the Gulf of Mexico, Caribbean Sea, mid-Atlantic Ocean, and off Portugal, Morocco, and Western Sahara (Kohler and Turner 2019). In the Pacific, tagging data supports east-west mixing in the north and minimal east-west mixing in the south (Sippel
et al.
2016 using conventional tagging data from 704 recaptured shortfin mako sharks since 1968; Corrigan
et al.
2018 using satellite telemetry data of 13 individuals over a period of 249-672 days). Trans-equatorial movement appears to be uncommon based on tagging studies (Sippel
et al.
2016; Corrigan
et al.
2018), but tagged shortfin mako sharks have been recorded crossing the equator (Rogers et al. 2015a; Santos
et al.
2021).

The locations of mating grounds and other reproductive areas are not well known for the shortfin mako shark, although the distribution of the youngest age classes may indicate potential pupping and nursery areas. Casey and Kohler (1992) observed YOY shortfin mako sharks offshore in the Gulf of Mexico, hypothesizing that pups are born offshore in the Northwest Atlantic to protect them from predation by large sharks, including other makos. Bite marks observed on mature females caught in the Gulf of Mexico may have resulted from mating behavior, indicating that the area may also be a mating ground (Gibson
et al.
2021). The presence of mature and pregnant females in the Gulf of Mexico provides further support that this may be a gestation and parturition ground for the species. However, fisheries data suggests that pupping is geographically widespread in the Northwest Atlantic given that neonates are widely distributed along the coast of North America and largely overlap with the distribution of older immature sharks and adults (Natanson
et al.
2020). Excursions of tagged shortfin mako sharks towards the shelf and slope waters of the Subtropical Convergence Zone, the Canary archipelago, and the northwestern African continental shelf, as well as aggregations of YOY shortfin mako sharks in these areas, may indicate that they serve as pupping or nursery grounds in the Northeast Atlantic (Maia
et al.
2007; Natanson
et al.
2020; Santos
et al.
2021). In the Eastern North Pacific, the Southern California Bight has been suggested as a nursery area as roughly 60 percent of the catch here is made up by YOY and 2- to 4-year-old juveniles (Holts and Bedford 1993; Rodríguez-Madrigal
et al.
2017; Nasby-Lucas
et al.
2019). Farther south, the presence of many juveniles and some neonates near fishing camps in Baja California, Mexico, suggests that the area between Bahía Magdalena and Laguna San Ignacio may also be a nursery ground for the shortfin mako shark (Conde-Moreno and Galvan-Magana 2006). Presence of small immature shortfin mako sharks off Caldera, Chile, suggests that this may be a pupping or nursery area for the Southeastern Pacific (Bustamante and Bennett 2013). The temperate waters of the south-west Indian Ocean have been shown to host high concentrations of

neonates and adults, suggesting that this area may be a nursery ground (Wu
et al.
2021). Further, pregnant females have been observed in coastal waters off South Africa, strengthening the evidence that this area may be used for pupping or as a nursery (Groeneveld
et al.
2014).

Diet and Feeding

The shortfin mako shark is a large, active predator that feeds primarily on teleosts and also consumes cephalopods, other elasmobranchs, cetaceans, and crustaceans (Stillwell and Kohler 1982; Cortés 1999; Maia
et al.
2006; Gorni
et al.
2012). It is estimated that shortfin mako sharks must consume 4.6 percent of their body weight per day to meet their high energetic demands (Wood
et al.
2009). Based on the shortfin mako shark's diet, the species has a trophic level of 4.3 out of 5.0 (tertiary consumers have a trophic level over 4.0, while plants have a trophic level of one), one of the highest of 149 species examined by Cortés (1999) and comparable to other pelagic shark species such as common and bigeye thresher sharks (
Alopias vulpinus
and
Alopias superciliosus
), the salmon shark (
Lamna ditropis
), and the oceanic whitetip shark (
Carcharhinus longimanus
) (Bizzarro
et al.
2017). Rogers
et al.
(2012) found evidence that the species targets specific prey despite high prey diversity; however, stable isotope analysis indicates that the species is a generalist predator (Maya Meneses
et al.
2016). The degree of prey selectivity in any given individual's diet is likely strongly correlated with prey availability, with prey being consumed as encountered.

The specific diet of the shortfin mako shark varies by life stage, geographic location, season, and oceanic habitat. In the Northwest Atlantic, bluefish (
Pomatomus saltatrix
) are a major inshore prey item for the species and have been estimated to make up 77.5 percent of diet by volume (Stillwell and Kohler 1982), and more recently, 92.6 percent of diet by weight (Wood
et al.
2009). In the northeast Atlantic, teleosts made up over 90 percent of the species' diet by weight, and Clupeiformes and garpike (
Belone belone
) are common prey (Maia
et al.
2006). In the South Atlantic, teleosts are also dominant in the shortfin mako shark's diet (including
Lepidocibium flavobruneum, Scomber colias,
and Trichiruridae), while cephalopods of the orders Teuthida and Octopoda are also consumed (Gorni
et al.
2012). In the northeast Pacific along the west coast of the United States, jumbo squid (
Dosidicus gigas
) and Pacific saury (
Cololabis saira
) are the two most important prey items, and other frequent teleost prey includes Pacific sardine (
Sardinops sagax
), Pacific mackerel (
Scomber japonicus
), jack mackerel (
Trachurus symmetricus
), and striped mullet (
Mugil cephalus
) (Preti
et al.
2012). By contrast, YOY and juvenile shortfin mako sharks off Baja California Sur, Mexico, largely consume whitesnout searobin (
Prionotus albirostris
), Pacific mackerel (
S. japonicus
), and a variety of small squids (Velasco Tarelo 2005). As they age, larger teleost species and squids more commonly found in offshore pelagic waters become increasingly important, as evidenced by stable isotope analysis (Velasco Tarelo 2005). A large female shortfin mako shark recreationally caught off the coastline of the Southern California Bight was found to have eaten a California sea lion,
Zalophus californianus,
an event that does not appear uncommon based on previously documented pinnipeds in the stomachs of large shortfin mako sharks (Lyons
et al.
2015). Shortfin mako sharks in the Indian Ocean prey on teleosts (
Trachurus capensis
and
S. sagax
), elasmobranchs (
Rhizoprionodon acutus
and
Carcharhinus obscurus
), and cephalopods (
Loligo
spp.) (Groeneveld
et al.
2014). The dominant prey of shortfin mako sharks caught in coastal bather protection nets in the southwest Indian Ocean were elasmobranchs, while the diet of shortfin mako sharks caught in offshore longlines was dominated by teleosts (Groeneveld
et al.
2014). As the size of individuals caught in coastal bather nets was significantly greater than those caught in offshore longlines, Groeneveld
et al.
(2014) suggest that larger prey attracts larger mako sharks to coastal waters.

Size and Growth

Shortfin mako sharks are long-lived, and are estimated to reach maximum ages of at least 28-32 years based on vertebral band counts validated by bomb radiocarbon and tag-recapture studies (Natanson
et al.
2006; Dono
et al.
2015). Longevity in the Pacific has been estimated as high as 56 years (Chang and Liu 2009; Carreon-Zapiain
et al.
2018). There is uncertainty in the use of vertebral band pair counting to determine age as some authors find evidence for or assume annual growth band deposition periodicity (Cailliet
et al.
1983; Campana
et al.
2002; Ardizzone
et al.
2006; Bishop
et al.
2006; Semba
et al.
2009; Dono
et al.
2015; Liu
et al.
2018) while others find evidence for the deposition of two growth band pairs each year for either all (Pratt Jr. and Casey 1983) or their first five years of life (Wells
et al.
2013). Kinney
et al.
(2016) used the recapture of an oxytetracycline-tagged adult male to validate annual band deposition in adult shortfin mako sharks, inferring that juveniles experience more rapid growth and, therefore, exhibit biannual band pair deposition. In addition, there is evidence that vertebral band pair counts do not accurately reflect age in older, large individuals (Harry 2018; Natanson
et al.
2018). Due to inconsistent information on vertebral band deposition in the Pacific, the International Scientific Committee for Tuna and Tuna-like Species (ISC) Shark Working Group's 2018 stock assessment of shortfin mako sharks in the North Pacific treated data from the western North Pacific as having a constant band pair deposition rate and data from the eastern North Pacific as having a band pair deposition rate that changes from two to one band pairs per year after age 5. The 2017 stock assessment of North and South Atlantic shortfin mako sharks conducted by the International Commission for the Conservation of Atlantic Tunas (ICCAT) assumed annual band pair deposition based on Natanson
et al.
(2006).

Shortfin mako sharks exhibit slow growth rates. Growth coefficient (K) estimates range from 0.043-0.266 year
−
1
in the Atlantic Ocean, 0.0154-0.16 year
−
1
in the Pacific Ocean, and 0.075-0.15 year
−
1
in the Indian Ocean (Pratt Jr. and Casey 1983, Ribot-Carballal
et al.
2005, Natanson
et al.
2006, Bishop
et al.
2006, Cerna and Licandeo 2009, Semba
et al.
2009, Groeneveld
et al.
2014, Liu
et al.
2018). Males and females have similar growth rates until a certain point, when male growth slows down compared to female growth. This has been estimated to occur at 7 years of age in the western and central North Pacific (Semba
et al.
2009), 11 years of age in the Northwest Atlantic (Natanson
et al.
2006), and 15 years of age (217 cm fork length (FL)) in the western South Atlantic (Dono
et al.
2015). Females ultimately attain larger sizes than males, as has been documented in other shark species (Natanson
et al.
2006). Maximum theoretical length in females is reported to be 370 cm TL in the western and central North Pacific (Semba
et al.
2009) and 362 cm TL in the eastern North Pacific (Carreon-Zapiain
et al.
2018). The maximum observed length for the species is 445 cm TL (Weigmann 2016), although Kabasakal and de Maddalena (2011) used photographs to estimate the length of a female caught off Turkey at 585 cm TL.

Age and size at maturity vary by geographic location. In general, males

and females reach maturity at approximately 6-9 and 15-21 years (Natanson
et al.
2006; Semba
et al.
2009), and at sizes of 180-222 cm TL and 240-289 cm TL (Conde-Moreno and Galvan-Magana 2006; White 2007; Varghese
et al.
2017), respectively. Additional information on growth and reproductive parameters for the species can be found in Table 1 of the Status Review Report.

Reproductive Biology

Shortfin mako sharks reproduce through oophagous (meaning `egg eating') vivipary, wherein, after depletion of their yolk-sac, the embryos develop by ingesting unfertilized eggs inside the mother's uterus and are born as live young (Stevens 1983; Mollet
et al.
2000). Estimates of gestation time vary from nine months to 25 months (Mollet
et al.
2000; Duffy and Francis 2001; Joung and Hsu 2005; Semba
et al.
2011) and litter sizes typically range from four to 25 pups (Mollet
et al.
2000; Joung and Hsu 2005; Semba
et al.
2011). Several studies find that litter size increases with maternal size (Mollet
et al.
2000; Semba
et al.
2011), though others find no evidence of this relationship (Joung and Hsu 2005; Liu
et al.
2020). Size at birth is approximately 70 cm TL (Mollet
et al.
2000). The reproductive cycle is estimated to take up to 3 years, with a potential resting period of 18 months (Mollet
et al.
2000). There is evidence that parturition (birth) occurs in late winter to mid-spring in both the Northern and Southern Hemispheres based on embryonic growth estimates (Mollet
et al.
2000; Semba
et al.
2011; Bustamante and Bennett 2013), though Duffy and Francis (2001) found evidence of parturition in summer. With regard to mating strategy, two studies have found genetic evidence for polyandry and multiple paternity within litters, though other mating strategies (
e.g.,
polygyny or monogamy) cannot be ruled out (Corrigan
et al.
2015; Liu
et al.
2020).

Population Structure and Genetics

Although certain ocean currents and features may limit movement patterns between different regions as discussed previously (see
Habitat Use
), several genetic studies indicate a globally panmictic (characterized by random mating) population with some genetic structuring among ocean basins.

Heist
et al.
(1996) investigated population structure using restriction fragment length polymorphism analysis of maternally inherited mitochondrial DNA (mtDNA) from shortfin mako sharks in the Northwest Atlantic (n = 21), central North Atlantic (n = 24), western South Atlantic (n = 23), eastern North Pacific (n = 30), and western South Pacific (n = 22). The North Atlantic samples showed significant isolation from other regions (p < 0.001) and differed from other regions by the relative lack of rare and unique haplotypes and high abundance of a single haplotype (Heist
et al.
1996). Significant differences in haplotype frequencies were not detected between the samples from Brazil, Australia, and California (Heist
et al.
1996). Haplotypes did not seem to be confined to specific regions, and the three most common haplotypes were found in all samples (Heist
et al.
1996). Clustering of mtDNA haplotypes did not initially support the presence of genetically distinct stocks of shortfin mako shark (Heist
et al.
1996); however, reanalysis of the data found significant differentiation between the South Atlantic and North Pacific samples (Schrey and Heist 2003) in addition to isolation of the North Atlantic.

A microsatellite analysis of samples from the North Atlantic (n = 152), South Atlantic (Brazil; n = 20), North Pacific (n = 192), South Pacific (n = 43), and Atlantic and Indian coasts of South Africa (n = 26) found very weak evidence of population structure (F
ST
= 0.0014, P = 0.1292; R
ST
= 0.0029, P = 0.019) (Schrey and Heist 2003). Pairwise F
ST
comparisons were not statistically significant after Bonferroni correction, though one pairwise R
ST
value (North Atlantic vs. North Pacific) showed significant differentiation (R
ST
= 0.0106, P = 0.0034). These results were insufficient to reject the null hypothesis of a single genetic stock of shortfin mako shark, suggesting that there is sufficient movement of shortfin mako sharks, and therefore gene flow, to reduce genetic differentiation between regions (Schrey and Heist 2003). The authors note that their findings conflict with the significant genetic structure revealed through mtDNA analysis by Heist
et al.
(1996). They suggest that as mtDNA is maternally inherited and nuclear DNA is inherited from both parents, population structure shown by mtDNA data could indicate that female shortfin mako sharks exhibit limited dispersal and philopatry to parturition sites, while male dispersal allows for gene flow that would explain the results from the microsatellite data (Schrey and Heist 2003).

Taguchi
et al.
(2011) analyzed mtDNA samples from the central North Pacific (n = 39), western South Pacific (n = 16), eastern South Pacific (n = 10), North Atlantic (n = 9), eastern Indian Ocean (n = 16), and western Indian Ocean (n = 16), finding evidence of significant differentiation between the North Atlantic, and the central North Pacific and eastern South Pacific (pairwise Φ
ST
= 0.2526 and 0.3237, respectively). Interestingly, significant structure was found between the eastern Indian Ocean and the Pacific Ocean samples (pairwise Φ
ST
values for Central North Pacific, Western South Pacific, Eastern South Pacific are 0.2748, 0.1401, and 0.3721, respectively), but not between the eastern Indian and the North Atlantic (Taguchi
et al.
2011).

Corrigan
et al.
(2018) also found evidence of matrilineal structure from mtDNA data, while nuclear DNA data provide support for the existence of a globally panmictic population. Although there was no evidence of haplotype partitioning by region and most haplotypes were found across many (sometimes disparate) locations, Northern Hemisphere sampling locations were significantly differentiated from all other samples, suggesting reduced matrilineal gene flow across the equator (Corrigan
et al.
2018). The only significant differentiation indicated by microsatellite data was between South Africa and southern Australia (pairwise F
ST
= 0.037, Φ
ST
= 0.043) (Corrigan
et al.
2018). Clustering analysis showed only minor differences in allele frequencies across regions and little evidence of population structure (Corrigan
et al.
2018). Overall, the authors conclude that although spatial partitioning exists, the shortfin mako shark is genetically homogenous at a large geographic scale. Taken together, results of genetic analyses suggest that female shortfin mako sharks exhibit fidelity to ocean basins, possibly to utilize familiar pupping and rearing grounds, while males move across the world's oceans and mate with females from various basins, thereby homogenizing genetic variability (Heist
et al.
1996; Schrey and Heist 2003; Taguchi
et al.
2011; Corrigan
et al.
2018).

Haplotype diversity in shortfin mako sharks has been found to be high in several studies. Heist
et al.
(1996) found 25 haplotypes among 120 individuals for an overall haplotype diversity of 0.755 and a nucleotide diversity of 0.347. Taguchi
et al.
(2011) found haplotype and nucleotide diversity to be 0.92 and 0.0070, respectively, across the global range of the species. Corrigan
et al.
(2018) detected 48 unique haplotypes among 365 individuals for a haplotype diversity of 0.894 ± 0.013 and found very low nucleotide diversity of 0.004 ± 0.003.

Demography

Natural mortality for shortfin mako sharks is low and was estimated by Bishop
et al.
(2006) at 0.14 and 0.15 year
−
1
for males and females, respectively. Chang and Liu (2009) calculated natural mortality at 0.077-0.244 year
−
1
for females and 0.091-0.203 year
−
1
for males in the Northwest Pacific. In the North Atlantic, natural mortality was estimated at 0.101 year
−
1
(Bowlby
et al.
2021). The generation time is estimated at 25 years (Cortés
et al.
2015; Rigby
et al.
2019).

In an analysis of productivity and susceptibility to longline fisheries in the Indian Ocean, Murua
et al.
(2018) calculated a population finite growth rate (λ) for shortfin mako sharks of 1.049 year
−
1
(1.036-1.061; Murua
et al.
2018). Liu
et al.
(2015) estimated values for λ of shortfin mako sharks off California to be 1.1213 ± 0.0635 year
−
1
and 1.0300 ± 0.0763 year
−
1
for those in the Northwest Pacific. As the species displays sexual dimorphism in size, growth rates, and size at maturity, Tsai
et al.
(2015) argue that the use of a two-sex demographic model more accurately estimates the probability of decline risk and, therefore, better informs management decisions. Further, as the mating mechanism of shortfin mako sharks affects the proportion of breeding females and has not been conclusively established, these scenarios (monogamous, polyandrous, polygynous) should be modeled as well (Tsai
et al.
2015). The authors report that in the Northwest Pacific, without fisheries-related mortality, values for λ were 1.047, 1.010, and 1.075 year
−
1
for females and 1.056, 1.011, and 1.090 year
−
1
for males in monogamous, polyandrous, and polygynous mating scenarios, respectively. Under fishing conditions at the time of the study, all values for λ dropped to less than one (0.943, 0.930, and 0.955 year
−
1
for females and 0.918, 0.892, and 0.939 year
−
1
for males in monogamous, polyandrous, and polygynous mating scenarios, respectively). Thus, population declines were expected regardless of the mating system modeled.

Productivity for the shortfin mako shark is quite low. In a recent analysis using six methods, Cortés (2016) determined that the intrinsic rate of population increase (r
max
) for Atlantic shortfin mako sharks ranged from 0.036-0.134 yr
−
1
. These values were among the lowest calculated from 65 populations and species of sharks (Cortés 2016).

Abundance and Trends

Currently, there is no estimate of the absolute global abundance of the shortfin mako shark; however, based on the age-structured assessments conducted by ICCAT (2017) and the ISC Shark Working Group (2018), current abundance is estimated to be one million individuals in the North Atlantic and eight million individuals in the North Pacific (FAO 2019). Comprehensive analyses based on available regional stock assessments and standardized catch-per-unit-effort (CPUE) data have been used by the International Union for Conservation of Nature (IUCN) to approximate trends for the species globally.

In the 2019 IUCN Red List assessment, Rigby
et al.
estimated a global population trend using the following data sources: (1) the 2017 stock assessments conducted by ICCAT for the North and South Atlantic, (2) the 2018 stock assessment conducted by the ISC Shark Working Group for the North Pacific, (3) standardized CPUE data for the South Pacific from Francis
et al.
(2014), and (4) a preliminary stock assessment in the Indian Ocean by Brunel
et al.
(2018). Individual trends by region are discussed below. Using Just Another Red List Assessment (JARA) (Winker
et al.
2018; Sherley
et al.
2019), a Bayesian state-space tool for trend analysis of abundance indices, Rigby
et al.
(2019) found that the species is declining in all oceans other than the South Pacific, where it is increasing, with the steepest population declines indicated in the North and South Atlantic. Due to the unreliable stock assessment in the South Atlantic (discussed further below), Rigby
et al.
(2019) considered the North Atlantic stock assessment to be representative of the South Atlantic for the trend analysis. However, this may have inaccurately represented the extent of decline in the South Atlantic; the North Atlantic has experienced the largest known degree of decline across the species' range, and while there is some possibility that the South Atlantic has a similar stock status, the 2017 stock assessment does not support that conclusion, and accordingly, ICCAT has not taken comparable regulatory action for the species in the South Atlantic. A global trend was estimated by weighting each region's trend by the relative size of each region. To standardize the time period over which the trends were calculated, JARA projected forward the amount of years without observations that it would take to reach three generation lengths. The overall median population reduction was estimated at 46.6 percent, with the highest probability of 50-79 percent reduction over three generation lengths (72-75 years). Because available datasets for each region cover different time periods and have different durations, the timeframe of this trend is not a comparison between two specific years, but rather a standardized timeframe of three generation lengths. Trends indicated by Rigby
et al.
(2019) do not always align with abundance and trend indicators from other sources, as discussed below. The JARA framework used by Rigby
et al.
(2019) has been described as inappropriate for this long-lived, sexually dimorphic species because it only uses mean annual trends in the population over the assessment period and does not consider size or age structures of the population over recent decades (Kai 2021a). Available information on abundance and trends by region is discussed below. Stock assessments provide information on the status of a stock, with results presented using the terms “overfished” and “overfishing.” Specific to the context of the Magnuson-Stevens Fishery Conservation and Management Act (MSA), a stock or stock complex is considered “overfished” when its biomass has declined below minimum stock size threshold (MSST), defined as the level of biomass below which the capacity of the stock or stock complex to produce maximum sustainable yield (MSY) on a continuing basis has been jeopardized (50 CFR 600.310(e)(2)(E)-(F)). Overfishing occurs whenever a stock or stock complex is subjected to a level of fishing mortality or total catch that jeopardizes the capacity of a stock or stock complex to produce MSY on a continuing basis (50 CFR 600.310(e)(2)(B)). While the stock assessments referenced in this finding do not define “overfished” and “overfishing” using the exact language above, they use the two terms with equivalent meanings. It is important to note that the terms “overfished” and “overfishing” do not have any specific relationship to the terms “threatened” or “endangered” as defined in the ESA. While a stock that is overfished is not able to sustain an exploitive fishery at MSY (
i.e.,
the highest possible annual catch that can be sustained over time), there is a significant difference between a stock that is overfished and a stock that is in danger of extinction. A stock will become overfished long before it is threatened with extinction, and can be stable at biomass levels that do not support MSY. Similarly, one goal of the MSA (and fisheries management organizations) is to “rebuild” overfished

stocks to biomass levels that will support MSY. This level can be significantly above the biomass levels necessary to ensure that a species is not in danger of extinction. Thus, evidence of declining abundance that threatens the ability of the fishery to provide MSY are relevant, but not dispositive of a threatened or endangered species determination. Therefore, while available information about whether specific stocks are overfished or experiencing overfishing is relevant to and considered in our ESA extinction risk analysis, the fact that a stock may be considered “overfished” or experiencing “overfishing” does not automatically indicate that any particular status is appropriate under the ESA. Stock assessments, which provide information for determining the sustainability of a fishery, are based on different criteria than status reviews conducted under the ESA, which provide information to assess the likelihood of extinction of the species. When conducting a status review under the ESA, we use relevant information from available stock assessments, such as levels of biomass and fishing mortality, and apply the ESA's definitions of threatened and endangered species to the information in the record using our standard tools of ESA extinction risk analysis. As part of our ESA extinction risk analysis, when examining whether overutilization for commercial purposes is a threat to the species, we consider whether the species has been or is being harvested at levels that contribute to or pose a risk of extinction to the species.

North Atlantic Ocean

The most recent stock assessment by ICCAT indicates a combined 90 percent probability that the North Atlantic stock is in an overfished state and is experiencing overfishing (ICCAT 2017). The nine model runs used in this assessment generally agreed, indicating that stock abundance in 2015 was below biomass at maximum sustainable yield (B
MSY
) (ICCAT 2017). The age-structured stock assessment model estimates historical declines in spawning stock fecundity (SSF, defined as the number of pups produced in each year) from 1950 (unfished condition) to 2015 at 50 percent and recent declines (from 2006 to 2015) at 32 percent (FAO 2019). All assessment models were consistent, and together indicated that the North Atlantic shortfin mako shark has experienced historical declines in total biomass of between 47-60 percent, and recent declines in total biomass of between 23-32 percent (FAO 2019). Projections conducted in the 2017 assessment using a production model estimated that for a total allowable catch (TAC; in this case, TAC refers to all sources of mortality and is not limited to landings data) of 1,000 metric tons (t), the probability of the stock being rebuilt and not experiencing overfishing (biomass (B) > B
MSY
, and fishing mortality (F) < fishing mortality at MSY (F
MSY
)) was only 25 percent by 2040 (one generation length).

In 2019, the ICCAT Standing Committee on Research and Statistics (SCRS) carried out new projections for North Atlantic shortfin mako shark through 2070 (two generation lengths) using an integrated model (Stock Synthesis) at the Commission's request. The 2019 update to the stock assessment projects that even with a zero TAC, the North Atlantic stock would have a 53 percent probability of being rebuilt (SSF > SSF
MSY
) and not experiencing overfishing (F < F
MSY
) by 2045, and that regardless of TAC (including a TAC of 0 t), the stock will continue declining until 2035 (ICCAT 2019). Projections showed that a TAC of 500 t has a 52 percent probability of rebuilding the stock, with overfishing not occurring, by 2070. The projections indicated that realized TAC must be 300 t or less to ensure that the stock will be rebuilt and not experiencing overfishing with at least a 60 percent probability by 2070 (ICCAT 2019). These TAC options with associated time frames and probabilities of rebuilding were presented to the Commission; however, given the vulnerable biological characteristics of this stock and these pessimistic projections, to accelerate the rate of recovery and to increase the probability of success, the SCRS recommended that the Commission adopt a non-retention policy without exception.

The 2017 stock assessment and 2019 update to the stock assessment present more accurate and rigorous results than the prior 2012 assessment. The 2012 assessment overestimated stock size, underestimated fishing mortality, and suggested a low probability of overfishing (ICCAT 2019). Input data and model structure changed significantly between the 2012 and 2017 ICCAT stock assessments: catch time series start earlier (1950 vs. 1971 in the 2012 assessment), some biological inputs have changed and are sex-specific in the 2017 assessment, and additional length composition data became available (ICCAT 2017). In addition, the CPUE series have been decreasing since 2010, which was the last year in the 2012 assessment models (ICCAT 2017). Finally, the age-structured model in the 2017 stock assessment more accurately captured the time-lags in population dynamics of a long-lived species than the production models used in 2012.

The IUCN's JARA trend analysis for the North Atlantic region relied on the 2017 ICCAT stock assessment. Trend analysis of modeled biomass estimated a median decline of 60 percent in the North Atlantic based on annual rates of decline of 1.2 percent between 1950 and 2017 (Rigby
et al.
2019), which is consistent with the decrease in total biomass (60 percent) obtained from Stock Synthesis model run 3 from the 2017 ICCAT stock assessment.

There is no stock assessment available for shortfin mako sharks in the Mediterranean Sea. Ferretti
et al.
(2008) compiled data from public and private archives representing sightings, commercial fisheries, and recreational fisheries data in the western Mediterranean Sea and used generalized linear models to conduct a meta-analysis of encounter trends. Long-term combined trends for shortfin mako shark and porbeagle (
Lamna nasus
) in the Mediterranean Sea indicate up to a 99.99 percent decrease in abundance and biomass since the early 19th century, though there was considerable variability among datasets due to geography and sample size (Ferretti
et al.
2008). While shortfin mako sharks spanning a broad range of sizes (suggesting breeding/pupping in the region) are occasionally reported as bycatch in swordfish and albacore longline fisheries (Megalofonou
et al.
2005), or in other artisanal or commercial fisheries (Kabasakal 2015), from the eastern Mediterranean Sea, no reliable estimates of abundance are available for this region.

Overall, the best available scientific and commercial information indicates that the North Atlantic shortfin mako shark population has experienced historical declines in biomass of between 47 and 60 percent, and declines will continue until at least 2035 regardless of fishing mortality.

South Atlantic Ocean

Results of the most recent ICCAT stock assessment for shortfin mako sharks in the South Atlantic indicate a high degree of uncertainty (ICCAT 2017). One model (Just Another Gibbs Sampler emulating the Bayesian production model) estimated that the stock was not overfished (B
2015
/B
MSY
= 1.69-1.75) but that overfishing may be occurring (F
2015
/F
MSY
= 0.86-1.07). Two runs from this model indicate a 0.3-1.4 percent probability of the stock being overfished and overfishing occurring, and a 29-47.4 percent probability of the stock not being overfished but

overfishing occurring, or, alternatively, the stock being overfished but overfishing not occurring, and a 52.3-69.6 percent probability of the stock not being overfished and overfishing not occurring (ICCAT 2017). The Just Another Bayesian Biomass Assessment (JABBA) model results indicated an implausible stock trajectory and were, therefore, not relied upon for management advice. The Catch-only Monte-Carlo method (CMSY) model estimates indicate that the stock could be overfished (B
2015
/B
MSY
= 0.65 to 1.12) and that overfishing is likely occurring (F
2015
/F
MSY
= 1.02 to 3.67). Considering catch scenarios C1 (catches starting in 1950 in the north and 1971 in the south, as reported in the March 2017 ICCAT shortfin mako data preparatory meeting) and C2 (alternative estimated catch series based on ratios (method described by Coelho and Rosa 2017), starting in 1971), Catch-only Monte-Carlo method model estimates indicated a 23-89 percent probability of the stock being overfished and overfishing occurring, a 11-48 percent probability of the stock not being overfished but overfishing occurring, or alternatively, the stock being overfished but overfishing not occurring, and only a 0-29 percent probability of the stock not being overfished and overfishing not occurring. Generally, while CPUE exhibited an increasing trend over the last 15 years, both catches and effort increased contrary to the expectation that the population is expected to decline with increasing catch (FAO 2019). This inconsistency caused the ICCAT working group to consider the assessment highly uncertain, and they conducted no projections for the South Atlantic stock. Nevertheless, the combined assessment models found a 19 percent probability that the stock is overfished and is experiencing overfishing, a 48 percent probability of the stock not being overfished but overfishing occurring, or alternatively, the stock being overfished but overfishing not occurring, and a 36 percent probability that the stock is not being overfished or experiencing overfishing (ICCAT 2017). The assessment also notes that, despite uncertainty, in recent years the stock may have been at, or is already below, B
MSY
, and fishing mortality is already exceeding F
MSY
. Based on the uncertainty of the stock status, combined with the species' low productivity, the ICCAT working group concluded that catches should not increase above average catch for the previous 5 years, about 2,900 t (ICCAT 2017; FAO 2019). There is a significant risk that the South Atlantic stock could follow a trend similar to that of the North Atlantic stock given that fishery development in the South Atlantic predictably follows that in the North, and that the biological characteristics of the stock are similar. The 2019 update to the stock assessment (ICCAT 2019) therefore reiterates the recommendation that, at a minimum, catch levels should not exceed the minimum catch in the last 5 years of the assessment (2,001 t with catch scenario C1).

In addition to the ICCAT stock assessment, standardized catch rates in South Atlantic longlines indicate steep declines in the average CPUE of shortfin mako shark between 1979-1997 and 2007-2012 (Barreto
et al.
2016). However, the methodologies used in this study have several caveats and limitations, including the standardization analysis being applied individually to each of the time series and the use of different variables. Therefore, the results are not directly comparable between the different time periods and cannot be used to infer the total extent of decline over the entirety of the time series (FAO 2019).

Overall, despite high uncertainty in abundance and trends for the species in this region, the best available scientific and commercial data indicate that there is a 19 percent probability that the population is overfished and is experiencing overfishing, and in recent years the stock may have been at, or is already below, B
MSY
and fishing mortality is already exceeding F
MSY
.

North Pacific Ocean

The most comprehensive information on trends for shortfin mako sharks in the North Pacific comes from the 2018 ISC Shark Working Group stock assessment, which found that the North Pacific stock was likely not in an overfished condition and was likely not experiencing overfishing between 1975 and 2016 (42 years) (ISC Shark Working Group 2018). This analysis used a Stock Synthesis model that incorporated size- and age-specific biological parameters and utilized annual catch data from 18 fleets between 1975 and 2016, annual abundance indices from five fleets for the same period, and annual size composition data from 11 fleets between 1994 and 2016 (Kai 2021a). This assessment determined that the abundance of mature females was 860,200 in 2016, which was estimated to be 36 percent higher than the number of mature females at maximum sustainable yield (MSY) (ISC Shark Working Group 2018). Future projections indicated that spawning abundances were expected to increase gradually over a 10-year period (2017-2026) if fishing mortality remains constant or is moderately decreased relative to 2013-2015 levels (ISC Shark Working Group 2018). Using results from the ISC stock assessment, historical decline in abundance (1975-1985 to 2006-2016) is estimated at 16.4 percent, and a recent increase (2006-2016) is estimated at 1.8 percent (CITES 2019).

The IUCN Red List Assessment for global shortfin mako shark also used the ISC assessment to model the average trend in the North Pacific stock over three generation lengths (72 years) and indicated a median decline of 36.5 percent based on annual rates of decline of 0.6 percent from 1975-2016 (Rigby
et al.
2019). A comprehensive comparison of the assessments by the ISC and the IUCN (Kai 2021a) describes JARA (applied by Rigby
et al.
2019) as a useful tool in extinction risk assessments for data-poor pelagic sharks, but inappropriate for the relatively data-rich North Pacific shortfin mako shark. The assessment by IUCN used only the mean annual trends in the population over the assessment period estimated from Stock Synthesis, and did not consider size or age structure of the population over recent decades. Kai (2021a) concludes that the results of the ISC's assessment of current and future status of North Pacific shortfin mako shark are more robust and reliable than those of the IUCN, and finds a median decline of the population trajectory of 12.1 percent over three generation lengths with low uncertainty.

The ISC Shark Working Group's 2021 indicator-based analysis for shortfin mako sharks in the North Pacific used time series of catch, indices of relative abundance (CPUE), and length-frequency data from multiple fisheries over the time period 1957-2019 to monitor for potential changes in stock abundance since the 2018 benchmark assessment. Catch of shortfin mako shark in 2019 was the second highest value for the last decade, and the scaled CPUEs indicated a stable and slightly increasing trend in the four major fleets (U.S. Hawaii longline shallow-set, Taiwan longline large-scale, Japan research and training vessels, and Mexico observer for longline) (ISC Shark Working Group 2021). The Working Group concluded that there were no signs of major shifts in the tracked indicators that would suggest a revision to the current stock assessment schedule for shortfin mako shark is necessary (ISC Shark Working Group 2021). The next stock assessment is scheduled for 2024.

Observer data from the Western and Central Pacific Fisheries Commission (WCPFC) indicate that longline catch rates of mako sharks in the North Pacific declined significantly by an average of 7 percent (95 percent confidence interval (CI): 3-11 percent) annually between 1995 and 2010 (Clarke
et al.
2013). However, these data represent trends for both longfin and shortfin mako sharks combined, and the performance of the standardization model was poorer than for other studied shark species, making the estimated trend less reliable. There were also variable size trends for mako sharks in the North Pacific, with females showing significant increases in median length in one region (Clarke
et al.
2013). In an updated indicator analysis using the same data, Rice
et al.
(2015) noted that the standardized CPUE trend looked relatively stable between 2000 and 2010, but no inference was possible for the last 4 years (2010-2014) due to data deficiencies in some years.

Kai
et al.
(2017) analyzed catch rates in the Japanese shallow-set longline fishery in the western and central North Pacific from 2006-2014, finding an increasing trend since 2008. However, fishery-independent logbook data collected from Japanese research and training vessels in the western and central North Pacific (mainly 0-40° N and 130° E-140° W) from 1992-2016 showed a decreasing catch rate since 2008 (Kai 2019). The opposing trends indicated by fishery-dependent and -independent data in this region may be due to factors such as differing areas of operation, differing gear types, underreporting by both data sources, and differing model structures applied to the data (Kai 2019). Additionally, standardized CPUE estimates from 2011-2019 in the Japanese longline fleet operating in the North Pacific Ocean showed a stable trend from 2011 to 2016, with a slight decline after 2016 (Kanaiwa
et al.
2021). The authors note that observer coverage in the fleet is low (1.7-3.0 percent in certain areas) and that these results may not represent the overall trend for the North Pacific stock of shortfin mako shark (Kanaiwa
et al.
2021).

Results from stock assessments and standardized CPUE trends from observer data are more comprehensive, robust, and reliable than trends from fishery logbook data. Therefore, we find that the best scientific and commercial information available indicates that shortfin mako sharks in the North Pacific are neither overfished nor experiencing overfishing, and the population is likely stable and potentially increasing despite evidence of historical decline and indications of recent decline in fishery-independent datasets.

South Pacific Ocean

In the South Pacific, longline catch rates reported to WCPFC did not indicate a significant trend in abundance of mako shark (shortfin and longfin combined) between 1995 and 2010 (Clarke
et al.
2013). In an updated indicator analysis, standardized CPUEs for the mako shark complex show a relatively stable trend in relative abundance, with low points in 2002 and 2014, though the 2014 point is based on relatively few data and should be interpreted with caution (Rice
et al.
2015). In New Zealand waters, logbook and observer data from 1995-2013 analyzed by Francis
et al.
(2014) indicate that shortfin mako sharks were not declining, and may have been increasing, over the period from 2005-2013. More recently, an analysis of the data did not result in statistically significant trend fits for two of the data series; those that were significant were increasing (Japanese South 2006-2015, Domestic North 2006-2013, and Observer Data 2004-2013) (FAO 2019). Trend analysis of modeled biomass indicates a median increase of 35.2 percent over three generation lengths based on estimated annual rates of increase of 0.5 percent from 1995-2013 (Rigby
et al.
2019). In sum, the best scientific and commercial information available indicates that shortfin mako sharks in the South Pacific have an increasing population trend.

Indian Ocean

Only preliminary stock assessments using data-limited assessment methods have been conducted for the shortfin mako shark in the Indian Ocean, with few other stock indicators available. Catch data are thought to be incomplete for several reasons: landings do not reflect the number of individuals finned and discarded at sea, shortfin mako sharks are not sufficiently specified in catch data and are often aggregated with other species, shortfin mako shark may be misidentified as longfin mako shark, and recorded weight may often refer to processed weight rather than live weight (Bonhommeau
et al.
2020). These factors were a significant consideration in our evaluation of the species. With these caveats in mind, a preliminary assessment by Brunel
et al.
(2018) was carried out based on CPUE estimates from Portuguese (2000-2016) and Spanish (2006-2016) swordfish and tuna longline fleets operating in the Indian Ocean Tuna Commission (IOTC) Convention area. Results from two models (a Bayesian Schaefer-type production model and another model analyzing the trends of catches) indicate that the stock is experiencing overfishing (F
2015
/F
MSY
= 2.57), but is not yet overfished (B
2015
/B
MSY
close to one) (Brunel
et al.
2018). However, there were considerable uncertainties in the estimates and conflicting trends in biomass between the two models used. Nonetheless, trajectories showed consistent trends toward both overfished and subject to overfishing status (Brunel
et al.
2018). Using the results of the Schaefer model from Brunel
et al.
(2018), historical decline (1970-1980 to 2005-2015) was estimated at 26 percent, recent decline (2005 to 2015) was estimated at 18.8 percent, and future 10-year decline was projected at 41.6 percent from the historical baseline (1970-1980 to 2015-2025) (CITES 2019). A trend analysis for modeled biomass in the Indian Ocean using Brunel
et al.'
s assessment indicates a median decline of 47.9 percent over three generation lengths based on annual rates of decline of 0.9 percent from 1971-2015 (Rigby
et al.
2019).

A more recent preliminary assessment using updated catch and CPUE indices also indicates that the shortfin mako shark in the Indian Ocean is experiencing overfishing but is not overfished (Bonhommeau
et al.
2020). This assessment uses nominal catch of shortfin mako shark as reported to the IOTC (1964-2018) and scaled CPUEs from Japan (1993-2018), Spain (2001-2018), Taiwan (2005-2018), and Portugal (2000-2018). Bonhommeau
et al.
(2020) used JABBA and CMSY models, both of which gave results that were generally consistent with the previous assessment: that the stock is currently undergoing overfishing and is not overfished.

In a separate study, Wu
et al.
(2021) analyzed standardized CPUE trends using observer records and logbook data from 2005-2018 for the Taiwanese longline fishery in the Indian Ocean, which was the second largest shortfin mako shark-catching nation in the region in 2019. The standardized CPUEs indicate a gradual decrease between 2005 and 2007, followed by a sharp increase in 2008, a slow decline between 2008 and 2015, and another increase between 2015 and 2018 (Wu
et al.
2021). However, Wu
et al.
(2021) note that the rapid increases in CPUEs between 2007 and 2008 and later between 2015 and 2017 may be unrealistic for the stock biomass of such a long-lived species, and suggest that the results may be due to increased reporting by skippers and observers.

Logbook data from Japanese longliners operating in the Indian Ocean from 1993-2018 indicate that abundance of shortfin mako shark decreased from 1993-2009, and increased slightly since then (Kai and Semba 2019). Standardized CPUE has risen after 2008 in Portuguese and Spanish longline fleets as well (Coelho
et al.
2020; Ramos-Cartelle
et al.
2020), although these data sets were included in the preliminary stock assessment conducted by Bonhommeau
et al.
(2020). In the Arabian Sea CPUE data suggest variable abundance and little evidence of significant population reduction (Jabado
et al.
2017). Fishing pressure in this region is high, and because the species has high susceptibility to pelagic fisheries, Jabado
et al.
(2017) estimated that over the past 3 generations the population has declined 20-30 percent, with future declines expected over the next 3 generations. Results from these studies may reflect partial stock status in the Indian Ocean, but may not have sufficient spatial coverage to be indicative of the entire stock status.

In sum, the best available scientific and commercial information indicates that shortfin mako shark population in the Indian Ocean is experiencing overfishing but is not yet overfished, and recent increasing CPUE trends are indicated in Spanish, Portuguese, and Taiwanese longline fleets. Catch data have the potential to be substantially underestimated and the recent increases in CPUE from these fleets may not reflect trends in abundance.

Summary

Overall, while abundance estimates for the shortfin mako shark are not available for all regions, the stock assessments available for the North Atlantic and North Pacific Oceans indicate current numbers of about one million and eight million individuals, respectively (FAO 2019). These estimates were generated by the FAO Expert Advisory Panel, which extracted these numbers using the age-structured assessments conducted by ICCAT (2017) and the ICS Shark Working Group (2018). Rigby
et al.
(2019) conducted a trend analysis of shortfin mako shark abundance indices using the 2017 ICCAT stock assessment in the Atlantic, the 2018 ISC Shark Working Group stock assessment in the North Pacific, a preliminary stock assessment for the Indian Ocean (Brunel
et al.
2018), and a CPUE indicator analysis from New Zealand for the South Pacific (Francis
et al.
2014). Due to the unreliable stock assessment in the South Atlantic, Rigby
et al.
(2019) considered the North Atlantic stock assessment to be representative of the South Atlantic for the trend analysis. However, this may have inaccurately represented the extent of decline in the South Atlantic for reasons described above. This assessment estimates the overall median population reduction for the global shortfin mako shark population at 46.6 percent, with the highest probability of 50-79 percent reduction over three generation lengths (72-75 years) (Rigby
et al.
2019), although the JARA framework used by Rigby
et al.
has been described as inappropriate for this species as it only uses mean annual trends in the population over the assessment period and does not consider size or age structure of the population over recent decades (Kai 2021a).

Population decline has been indicated in the North Atlantic with high certainty, and abundance is likely to continue declining until at least 2035 even in the absence of fishing mortality (ICCAT 2019). In the North Pacific, while there is evidence of historical decline, recent assessments indicate that the stock is neither overfished nor experiencing overfishing, and the population is likely stable or potentially increasing (ISC Shark Working Group 2018). Although a stock assessment has not been completed for shortfin mako sharks in the South Pacific, the best available scientific and commercial data and analyses indicate an increasing population trend (Francis
et al.
2014; Rigby
et al.
2019). Abundance of the shortfin mako shark in the South Atlantic and Indian Oceans is not as clear, given significant uncertainties in the data available from these regions. The most recent stock assessments of shortfin mako sharks in the South Atlantic has a high degree of uncertainty, and indicate a combined 19 percent probability that the stock is overfished and experiencing overfishing (ICCAT 2017). Preliminary assessments in the Indian Ocean indicate that the population is experiencing overfishing but is not yet overfished (Brunel
et al.
2018; Bonhommeau
et al.
2020).

Extinction Risk Analysis

In evaluating the level of risk faced by a species and deciding whether the species is threatened or endangered, we must consider all relevant data and are required under the ESA to base our conclusions on the best scientific and commercial data available. In evaluating and interpreting the best available data we also apply professional judgment. We evaluate both the viability of the species based on its demographic characteristics (abundance, productivity, spatial distribution, and diversity; see McElhany
et al.
(2000)), and the threats to the species as specified in ESA section 4(a)(1)(A)-(E).

Methods

This section discusses the methods used to evaluate threats and the overall extinction risk to the shortfin mako shark. For purposes of the risk assessment, an ERA Team comprising biologists and shark experts was convened to review the best available information on the species and evaluate the overall risk of extinction facing the shortfin mako shark, now and in the foreseeable future.

According to regulations implementing section 4 of the ESA that were in place during the ERA Team's deliberations, which was consistent with our practice since 2009 in accordance with a legal opinion of the Solicitor of the United States Department of the Interior, “The Meaning of `Foreseeable Future' in section 3(20) of the Endangered Species Act” (M-37021, Jan. 16, 2009; referred to herein as “the 2009 M-Opinion”), the foreseeable future extends only so far into the future as we can reasonably determine that both the future threats and the species' responses to those threats are likely.
See
50 CFR 424.11(d). Under our longstanding practice we describe the foreseeable future on a case-by-case basis, using the best available data and taking into account considerations such as the species' life-history characteristics, threat-projection timeframes, and environmental variability. In addition, because a species may be susceptible to a variety of threats for which different data are available, or which operate across different time scales, the foreseeable future may not necessarily be reducible to a particular number of years and may not be defined the same way for each threat. Although the regulations were vacated and remanded without a decision on the merits on July 5, 2022, by the United States District Court for the Northern District of California, and that order has been temporarily stayed as of September 21, 2022, whether or not those regulations remain in place does not affect our understanding or application of the “foreseeable future.” The 2019 regulations merely codified the approach of our longstanding interpretation of this term in use prior to the issuance of these regulations (see 84 FR 45020, August 27, 2019), and the court did not make any findings on the merits that would call this approach into question. Thus, with or without the 2019 regulations, we would continue to apply an approach to the foreseeable future rooted in the 2009 M-Opinion.

In determining an appropriate foreseeable future timeframe for the shortfin mako shark, the ERA Team first considered the species' life history. The species matures late in life, with females estimated to mature at an age of 15-21 years and males at 6-9 years of age (Bishop
et al.
2006; Natanson
et al.
2006; Semba
et al.
2009; Groeneveld
et al.
2014). The species has high longevity of at least 28-32 years (Bishop
et al.
2006; Natanson
et al.
2006) and exhibits relatively slow growth rates and low productivity (Cortés
et al.
2015). The ERA Team also considered generation time for the shortfin mako shark, which is defined as the average interval between the birth of an individual and the birth of its offspring, and has been estimated at 25 years (Cortés
et al.
2015). Given the life history characteristics of the shortfin mako shark, the ERA Team concluded that it would likely take several decades for any conservation management actions to be realized and reflected in population abundance indices.

As the main threats to the species are overutilization in commercial fisheries and the inadequacy of regulatory measures that manage these fisheries (see Summary and Analysis of Section 4(a)(1) Factors below), the ERA Team then considered the time period over which they could reasonably predict the likely impact of these threats on the biological status of the species. The ERA Team took available projections for shortfin mako shark abundance into consideration: the 2019 ICCAT update to the stock assessment for the North Atlantic carried out projections over 2 generation lengths, or 50 years; the ISC Shark Working Group's 2018 stock assessment for North Pacific shortfin mako sharks used 10-year projections; and the IUCN Red List Assessment carried out projections based on available data to achieve a 3 generation length time frame using JARA.

In examining these projections and their respective confidence intervals, the ERA Team noted that uncertainty increased substantially after about one generation length in all cases across multiple regions of the species' range. The ERA Team noted that in the IUCN JARA projections conducted for shortfin mako sharks by region, uncertainty (
i.e.,
the difference between the median and confidence intervals) increased to 50 percent by 2030 for the South Pacific population (about 18 years projected), and 40 percent by 2040 for the Indian and North Pacific populations (about 25 years projected). Additionally, the ERA Team noted that ICCAT's report of the 2019 shortfin mako shark stock assessment update meeting emphasizes that the Kobe II Strategy Matrix (K2SM) used to provide scientific advice for the North Atlantic stock does not capture all uncertainties associated with the fishery and the species' biology. Specifically, ICCAT's SCRS stated that “the length of the projection period (50 years) requested by the Commission significantly increases the uncertainty of the results. Therefore, the Group advised that the results of the K2SM should be interpreted with caution,” (ICCAT 2019). As a result of this statement, the ERA Team considered the 50-year projection to have questionable scientific merit, with estimates over that time frame only provided because the Commission requested them. Given the concerns about uncertainty that were repeatedly highlighted by the SCRS (ICCAT 2019), the ERA Team concluded that the 50-year period was not an appropriate time period for the foreseeable future.

In addition to uncertainty in projected abundance trends, the ERA Team discussed the uncertainty associated with future management measures and fishing behavior across regions. ICCAT is currently the only major Regional Fishery Management Organization (RFMO) with management measures specific to shortfin mako sharks, and recently adopted a two-year retention ban for the species in the North Atlantic. The conservation benefit of this measure is uncertain, however, as it does not require fishermen to modify gear or fishing behavior that would reduce at-vessel or post-release mortality of the species. Further, management of the species after this two-year ban expires is unknown. Some of the top shortfin mako shark-catching nations in this region (Spain, Portugal, and Morocco) have very recently announced unilateral retention prohibitions for North Atlantic shortfin mako shark, although the effect these bans will have on the species is again unknown, even if they ultimately are well implemented. Although projections carried out in 2019 by ICCAT's SCRS indicate that the North Atlantic stock will continue declining until approximately 2035 regardless of fishing mortality, the effect on stock status beyond this varies greatly with fishing mortality levels. Beyond the North Atlantic and North Pacific (where fishing data is also considered robust), fishing harvest and, especially, at-vessel and post-release mortality data are less thoroughly documented, introducing considerable uncertainty in projections of fishery impacts past a few decades.

After considering the best available scientific and commercial information on the shortfin mako shark's life history, projected abundance trends, and current and future management measures and fishing behaviors, the ERA Team concluded that a biologically reasonable foreseeable future timeframe would be 25 years, or one generation length, for the shortfin mako shark. Because the main threats to the species are overutilization in commercial fisheries and the inadequacy of existing regulatory mechanisms to prevent overutilization in these fisheries, the ERA Team found that this timeframe would allow for reliable predictions regarding the likely impact of these threats on the future biological status of the species.

While we conclude that the ERA Team assembled the best scientific and commercial information, it is the role of the agency rather than the team to determine the appropriate application of the agency's interpretations of key statutory terms and of agency policy to the factual record, and to ultimately determine the species' listing status under the ESA. Based on the best available scientific and commercial information, we disagree with the ERA Team's conclusion that the foreseeable future extends only 25 years, or one generation length, and have determined that application of a 50-year time frame is more appropriate in this case generally, though for some individual threats our ability to predict the specific trends and the species' responses is less robust than for others. We agree that fisheries mortality and inadequate regulatory mechanisms to address this threat are, and will continue to be, the main threats to the species. While we also agree with the ERA Team's characterization of the shortfin mako shark's life history, we find this information to indicate that it would take more than one generation length for effects of conservation actions to be reflected in abundance indices. During peer review of the Status Review Report, reviewers noted that changes in threats and conservation measures for shortfin mako sharks might take decades to become visible in the mature population, and all three reviewers were of the opinion that a longer time horizon would be appropriate. We find that the ERA Team unnecessarily limited the length of the foreseeable future by relying on statistical confidence levels for projected population trends. The 2009 M-Opinion, which for over a decade has provided the basis for NMFS's interpretation of this term, states that “the foreseeable future for a given species is not limited to the length of time into the future for which a species' status can be quantitatively

modeled or predicted within predetermined limits of statistical confidence; however, uncertainties of any modeling efforts should be considered and documented.” Although, as the ERA Team noted, uncertainty in abundance projections increases with the length of projections, we have determined that we can use available projections, our knowledge of the species' life history, and predicted levels of fishing mortality to inform what is likely to be the status of the species in a given region over a longer timeframe. Also, although changes in threats (
i.e.,
fisheries removals) would be observable over a 25-year period, we do not find that this time period is sufficient to measure and understand the population-level response to these changes, which would only be observable over a longer time period given the species' late age-at-maturity (this was also noted by a reviewer during the peer review process of the Status Review Report). A 50-year timeframe would encompass the duration over which changes in productivity would be expected to occur and be measurable while also taking into account the considerable uncertainty in future management measures and population trends as described by the ERA Team. To conclude, we find that our knowledge of the species' life history and of the fisheries impacting the species allow us to reasonably determine the likely threats facing the species (overutilization for commercial purposes and the related inadequacy of existing regulatory mechanisms) and the species' likely response to these threats (reflected in abundance trends and other demographic factors) over approximately 50 years, or two generation lengths. We therefore consider the foreseeable future to extend 50 years (two generation lengths) rather than 25 years as determined by the ERA Team.

The ability to measure or document risk factors to a marine species is often limited, and quantitative estimates of abundance and life history information are often lacking altogether. Therefore, in assessing extinction risk of a species with limited data available from certain regions, it is important to include both qualitative and quantitative information. In assessing extinction risk to the shortfin mako shark, the ERA Team considered the demographic viability factors developed by McElhany
et al.
(2000) and the risk matrix approach developed by Wainwright and Kope (1999) to organize and summarize extinction risk considerations. The approach of considering demographic risk factors to help frame the consideration of extinction risk has been used in many of our status reviews (which can be accessed online at
http://www.nmfs.noaa.gov/pr/species
). In this approach, the collective condition of individual populations is considered at the species level according to four demographic viability factors: abundance, growth rate/productivity, spatial structure/connectivity, and diversity. These viability factors reflect concepts that are well-founded in conservation biology and that individually and collectively provide strong indicators of extinction risk. To some extent these factors reflect the impacts that the operative threats have already had or are having on the species.

Using these concepts, the ERA Team evaluated demographic risks by assigning a risk score to each of the four demographic risk factors. The contribution of each demographic factor to extinction risk was scored according to the following scale: 0—unknown risk, 1—low risk, 2—moderate risk, and 3—high risk. Detailed definitions of the risk scores can be found in the Status Review Report. The scores were then tallied and summarized for each demographic factor. The ERA Team discussed the range of perspectives for each of the factors and the supporting data upon which they were based. ERA Team members were then given the opportunity to revise scores after the discussion if they felt their initial analysis had missed any pertinent data discussed in the group setting.

The ERA Team also performed a threats assessment for the shortfin mako shark by evaluating each threat in terms of its contribution to the extinction risk of the species. The contribution of each threat to the species' extinction risk was scored on the following scale: 0—unknown risk, 1—low risk, 2—moderate risk, and 3—high risk. The scores were then tallied and summarized for each threat, and the ERA Team again discussed the range of perspectives before providing final scores. As part of the threats assessment, the ERA Team considered the synergistic and combined effects of the threats acting together as well as individually. It should be emphasized that the scoring exercise for both demographic risks and threats was simply a tool to help the ERA Team members organize the information and assist in their thought processes for determining the overall risk of extinction for the shortfin mako shark, and is a common and well-accepted feature of our species assessments.

Guided by the results from the demographic risk analysis and the threats assessment, the ERA Team members were asked to use their informed professional judgment to make an overall extinction risk determination for the shortfin mako shark. For this analysis, the ERA Team considered three levels of extinction risk: 1—low risk, 2—moderate risk, and 3—high risk. Detailed definitions of these risk levels are as follows: 1 = Low risk: A species is at low risk of extinction if it is not at a moderate or high level of extinction risk (see “Moderate risk” and “High risk” below). A species may be at a low risk of extinction if it is not facing threats that result in declining trends in abundance, productivity, spatial structure, or diversity. A species at low risk of extinction is likely to show stable or increasing trends in abundance and productivity with connected, diverse populations; 2 = Moderate risk: A species is at moderate risk of extinction if it is on a trajectory that puts it at a high level of extinction risk in the foreseeable future (50 years in this case) (see description of “High risk”). A species may be at moderate risk of extinction due to projected threats or declining trends in abundance, productivity, spatial structure, or diversity; 3 = High risk: A species with a high risk of extinction is at or near a level of abundance, productivity, spatial structure, and/or diversity that places its continued persistence in question. The demographics of a species at such a high level of risk may be highly uncertain and strongly influenced by stochastic or depensatory processes. Similarly, a species may be at high risk of extinction if it faces clear and present threats (
e.g.,
confinement to a small geographic area; imminent destruction, modification, or curtailment of its habitat; or disease epidemic) that are likely to create present and substantial demographic risks.

The ERA Team adopted the “likelihood point” method for ranking the overall risk of extinction to allow individuals to express uncertainty. Following this method, each ERA Team member distributed 10 “likelihood points” across the three extinction risk levels, representing the likelihood that the species falls into each risk category. Each Team member had the ability to cast points in more than one category to account for uncertainty, and the points that each Team member allocated across the categories summed to 10. This method has been used in previous NMFS status reviews (
e.g.,
oceanic whitetip shark, Pacific salmon, Southern Resident killer whale, Puget

Sound rockfish, Pacific herring, and black abalone) to structure the ERA Team's thinking and express levels of uncertainty when assigning risk categories. After scores were provided, the ERA Team discussed the range of perspectives and the supporting data on which scores were based, and members were given the opportunity to revise scores if desired after the discussion. Likelihood points were then summed by extinction risk category. Other descriptive statistics, such as mean, variance, and standard deviation, were not calculated, as the ERA Team concluded that these metrics would add artificial precision to the results.

Finally, consistent with the appropriately limited role of the Team, the ERA Team did not make ultimate recommendations as to whether the species should be listed as threatened or endangered. Rather, the ERA Team drew scientific conclusions about the overall risk of extinction faced by the shortfin mako shark under present conditions and in the foreseeable future based on an evaluation of the species' demographic risks and assessment of threats.

Because we determined to adopt a different period of years as the “foreseeable future” for the shortfin mako shark after the ERA Team's work concluded, we also present our own assessment of extinction risk over the foreseeable future (50 years or two generation lengths) in a later section of this document alongside the ERA Team's results.

Demographic Risk Analysis

Abundance

The ERA Team assessed available abundance and trend information by region, including formal stock assessments, preliminary stock assessments using data-limited assessment methods, and standardized CPUE trends. There are no global abundance estimates available; however, using the formal stock assessments available for the North Atlantic and North Pacific, current abundance has been estimated at one million and eight million individuals, respectively (FAO 2019). Using the regional rates of change weighted by an area-based estimate of the size of each region as a proportion of the species' global distribution, the IUCN Red List assessment estimated global decline at 46.6 percent over three generation lengths, with the particular years covered varying by region (Rigby
et al.
2019). Although historical declines of varying degrees are evident across all oceans, current trends are mixed.

As discussed previously, the most recent stock assessment for shortfin mako shark in the North Atlantic indicates a combined 90 percent probability that the stock is in an overfished state and is experiencing overfishing (ICCAT 2017). The age-structured stock assessment model estimates historical declines in SSF from 1950 (unfished condition) to 2015 at 50 percent, and recent declines (from 2006-2015) at 32 percent (ICCAT 2017, FAO 2019). All nine assessment model runs were consistent, and together indicated that shortfin mako sharks in the North Atlantic have experienced historical declines (1950-2015) in total biomass of 47-60 percent, and recent declines (2006-2015) in total biomass of 23-32 percent (ICCAT 2017, FAO 2019). The 2019 update to the stock assessment projects that even with a zero TAC, there is a 53 percent probability that the North Atlantic stock will be rebuilt and not experiencing overfishing by 2045, and that regardless of TAC (in this case, TAC refers to all sources of mortality and is not limited to landings), the stock will continue declining until 2035 (ICCAT 2019). Overall, the ERA Team agreed that the findings from the stock assessment and projections were concerning. The ERA Team discussed how to appropriately interpret the stock assessment's focus on being rebuilt (SSF > SSF
MSY
) and without overfishing (F < F
MSY
) in the context of assessing extinction risk. As discussed previously in
Abundance and Trends,
while the fisheries management goal of rebuilding an overfished stock relates to achieving biomass levels that will allow for production of MSY, this can be significantly above the biomass levels necessary to ensure that a species is not in danger of extinction. While it will likely take decades for the stock to meet these fisheries management criteria (rebuilt and without overfishing), this does not indicate that the stock is at risk of becoming extirpated now or over the foreseeable future. Additionally, the ERA Team weighed the potential effects of the recent two-year North Atlantic shortfin mako shark retention prohibition on fishing mortality and abundance (ICCAT Recommendation 21-09, discussed in
Inadequacy of Existing Regulatory Mechanisms
below, which entered into force on June 17, 2022). As data for each fishing year is not reported until the following calendar year, the effect of this measure on fishing mortality will not be easily assessed until 2024 when the landings and discard data from 2023 can be analyzed. As noted above, the low productivity and slow population growth of shortfin mako shark may also mean that measurable impacts of this measure on abundance do not manifest for several years, when a new cohort enters the fishery. The Team concluded that there was significant uncertainty concerning both the effect of the measure and the future management of the stock after the two-year time period, and therefore did not significantly rely on any potential effect of the measure when drawing conclusions about the stock's abundance or trends.

We agree with the ERA Team's assessment of abundance and related considerations in the North Atlantic. We also recognize that without a substantial reduction in total fishing mortality (annual TAC of 500 t or less), it is unlikely that the stock will be rebuilt by 2070 (ICCAT 2019). Even if the spawning stock is not considered rebuilt by the stock assessment metric (SSF > SSF
MSY
), this does not necessarily mean that the stock will be in danger of being extirpated. However, given that fishing mortality is still high in this region (1,709 t in 2020) compared to even the greatest assessed TAC level (1,100 t), this level of removal will lead to continued declines. Unless aggressive management measures effectively reduce fishing mortality in this region, declines will likely continue throughout the foreseeable future (50 years). ICCAT has a demonstrated track record of taking multilateral actions to address data gaps and to respond to indications of declining stock status (see previous ICCAT measures specific to the stock in
Inadequacy of Existing Regulatory Mechanisms
below). The two-year retention prohibition adopted by ICCAT in 2021 is the most recent step that has been taken to conserve and manage this stock in line with the ICCAT Convention. ICCAT's track record would indicate that similar or additional measures are likely to be continued or taken, as needed, to ensure ICCAT's objectives of ending overfishing and rebuilding the stock to levels that support MSY are met. Recommendation 21-09 calls for the Commission to review the measure no later than the annual meeting in 2024 to consider additional measures to reduce total fishing mortality. Overall, we conclude that the best available scientific and commercial data indicate that the stock is overfished and experiencing overfishing, has experienced an estimated 50 percent decline in SSF from 1950 to 2015, and will continue decreasing until 2035 regardless of TAC.

The 2017 stock assessment for shortfin mako sharks in the South Atlantic indicated a high degree of

uncertainty. The combined assessment models found a 19 percent probability that the population is overfished and is experiencing overfishing (ICCAT 2017). The authors concluded that despite high uncertainty, in recent years the South Atlantic stock may have been at, or already below, B
MSY
and fishing mortality is likely exceeding F
MSY
(ICCAT 2017). Projections for the stock were not completed in 2019 due to high uncertainty. The ERA Team agreed that the best available scientific and commercial data indicate some degree of historical and ongoing population decline, but was unable to draw conclusions about the degree of decline due to the highly uncertain results of the 2017 stock assessment. We agree with the ERA Team's assessment of abundance in the South Atlantic.

The most comprehensive information on trends for shortfin mako sharks in the North Pacific comes from the 2018 ISC Shark Working Group stock assessment, which found that the North Pacific stock was likely not in an overfished condition and was likely not experiencing overfishing between 1975 and 2016 (42 years) (ISC Shark Working Group 2018). This assessment determined that the abundance of mature females was 860,200 in 2016, which was estimated to be 36 percent higher than the number of mature females at MSY (ISC Shark Working Group 2018). Future projections indicated that spawning abundance is expected to increase gradually over a 10-year period (2017-2026) if fishing mortality remains constant or is moderately decreased relative to 2013-2015 levels (ISC Shark Working Group 2018). Using results from the ISC stock assessment, historical decline in abundance (1975-1985 to 2006-2016) is estimated at 16.4 percent, and a recent increase (2006-2016) is estimated at 1.8 percent (CITES 2019). While the IUCN used the ISC assessment to model the average trend in the North Pacific stock over three generation lengths (72 years), resulting in a median decline of 36.5 percent (Rigby
et al.
2019), Kai (2021a) found a median decline of the population trajectory of 12.1 percent over three generation lengths with low uncertainty. The ERA Team concluded that despite evidence of historical decline, the best available scientific and commercial data indicate that shortfin mako sharks in the North Pacific are neither overfished nor experiencing overfishing, and the population is likely stable and potentially increasing. We agree with the ERA Team's conclusion.

Although a stock assessment is not available for shortfin mako sharks in the South Pacific, available information indicates that the population is increasing. Standardized CPUEs for the mako shark complex (
i.e.,
both shortfin and longfin mako shark) show a relatively stable trend in relative abundance, with low points in 2002 and 2014, though the 2014 point is based on relatively few data and should be interpreted with caution (Rice
et al.
2015). In New Zealand waters, logbook and observer data from 1995-2013 analyzed by Francis
et al.
(2014) indicate that shortfin mako sharks were not declining, and may be increasing, over the period from 2005-2013. More recently, trend estimations using data from these two studies (Francis
et al.
2014 and Rice
et al.
2015) did not result in statistically significant trend fits for two of the data series; those that were significant were increasing (Japanese South 2006-2015, Domestic North 2006-2013, and Observer Data 2004-2013) (FAO 2019). Trend analysis of modeled biomass indicates a median increase of 35.2 percent over three generation lengths (Rigby
et al.
2019). In sum, the ERA Team agreed that the best available scientific and commercial data for shortfin mako sharks in the South Pacific indicate an increasing population trend, and we agree with the ERA Team's conclusion.

Finally, in the Indian Ocean, preliminary stock assessments using data-limited assessment methods are available for shortfin mako sharks and indicate that the stock is experiencing overfishing, but is not yet overfished (Brunel
et al.
2018; Bonhommeau
et al.
2020). This means that while the stock is subjected to a level of fishing mortality that jeopardizes the stock's ability to produce MSY, biomass levels are still high enough that the stock is able to produce MSY on a continuing basis. Both preliminary assessments are considered highly uncertain due to limitations in catch data. Using the results of the Schaefer model from Brunel
et al.
(2018), historical decline (1970-1980 to 2005-2015) was estimated at 26 percent, recent decline (2005 to 2015) was estimated at 18.8 percent, and future 10-year decline was projected at 41.6 percent from the historic baseline (1970-1980 to 2015-2025) (CITES 2019). A trend analysis for modeled biomass in the Indian Ocean using Brunel
et al.'
s assessment indicates a median decline of 47.9 percent over three generation lengths (Rigby
et al.
2019). Recent increases in CPUE trends are indicated in Spanish, Portuguese, and Taiwanese longline fleets (Coelho
et al.
2020; Ramos-Cartelle
et al.
2020; Wu
et al.
2021), though it should be noted that these datasets were included in the assessment by Bonhommeau
et al.
(2020). Overall, the ERA Team concluded that the best available scientific and commercial data indicate some level of historical population decline and indicate that shortfin mako sharks are currently experiencing overfishing in this region. We agree with the ERA Team's conclusion.

The ERA Team considered the risk associated with abundance of the global species using the best available scientific and commercial information, summarized above. Reported landings represent a substantial underestimate of mortality resulting from fisheries interactions because they do not fully account for mortalities that result from fisheries interactions, including sharks that are discarded dead, finned, or that experience post-release mortality, and therefore there is some level of uncertainty in all available stock assessments and abundance indices, particularly so in the South Atlantic and Indian Oceans. However, stock assessments in the North Atlantic and North Pacific were considered robust by the ERA Team. Some degree of historical decline is indicated in all ocean basins, and population declines are ongoing in the North Atlantic. In the South Pacific, there are no available stock assessments, so the positive trends indicated here are based on available studies with limited geographic scope. Overall, there is no indication that global abundance has declined to the point that reproductive success of the species has declined or inbreeding has resulted, nor is there evidence of other depensatory processes associated with small populations. All ERA Team members agreed that the best available scientific and commercial information indicates that the species' abundance does not put it at risk of extinction currently. Several ERA Team members were of the opinion that declining abundance trends would likely contribute to the species' risk of extinction in the foreseeable future as they defined it; however, the majority of ERA Team members concluded that global abundance trends are unlikely to contribute significantly to the species' risk of extinction currently or in the foreseeable future as they defined it. We agree that this factor is not contributing significantly to the species' risk of extinction now.

Over the foreseeable future of 50 years that we have determined is more appropriate to apply for this species, we find that the best available scientific and commercial data indicate that the abundance factor is unlikely to significantly contribute to the species'

extinction risk. The shortfin mako shark population in the Pacific Ocean basin (a major segment of the global population) is likely to be stable and/or potentially increasing over this time period. Despite historical levels of decline (estimated at 47-60 percent reduction in total biomass) and likely continued decreases in the North Atlantic until at least 2035 (there is the potential for the population to begin rebuilding after this time with appropriate reduction of fishing mortality through management measures), as well as potential continuing population decreases of unknown degrees in the Indian and South Atlantic Oceans, we conclude that the best available scientific and commercial information indicates that global population abundance will not likely decline to the point that will put the species at risk of extinction over this timeframe.

Productivity

The shortfin mako shark exhibits high longevity (at least 28-32 years; Natanson
et al.
2006; Dono
et al.
2015), slow growth rates, late age at maturity (6-9 for males and 15-21 years for females; Natanson
et al.
2006; Semba
et al.
2009), long gestation (9-25 months; Mollet
et al.
2000; Duffy and Francis 2001; Joung and Hsu 2005; Semba
et al.
2011), and long reproductive cycles (3 years; Mollet
et al.
2000; Joung and Hsu 2005). Cortés (2016) determined that the intrinsic rate of population increase (r
max
) for Atlantic shortfin mako sharks ranges from 0.036-0.134 yr
−
1
. This was among the lowest values calculated from 65 populations and species of sharks. The ERA Team therefore concluded that the productivity of the species is quite low. The species also exhibits low natural mortality (0.075-0.244 yr
−
1
; Cortés 2016) and a long generation time (25 years; Cortés
et al.
2015). Together, the species' life history characteristics indicate that it is highly susceptible to depletion from exploitation or other high-intensity sources of mortality, and will recover slowly from declines brought on by such stressors. The ERA Team was largely in agreement that although this factor doesn't constitute a risk of extinction for the species currently, this factor would likely contribute significantly to the species' risk of extinction in the foreseeable future as they defined it, especially if exacerbated by impacts of fishing mortality and resulting declines in abundance. We agree that this factor is not contributing significantly to the species' risk of extinction now. Similarly, we find that the best available scientific and commercial data indicates that the shortfin mako shark's low productivity will likely contribute significantly to the species' extinction risk over the foreseeable future of 50 years that we have determined is more appropriate to apply for this species.

Spatial Structure/Connectivity

Shortfin mako sharks are globally distributed across all temperate and tropical ocean waters and utilize numerous habitat types including open ocean, continental shelf, shelf edge, and shelf slope habitats (Rogers
et al.
2015b; Corrigan
et al.
2018; Francis
et al.
2019; Rigby
et al.
2019; Santos
et al.
2020; Gibson
et al.
2021). This highly migratory species is capable of undertaking movements of several thousand kilometers (Kohler and Turner 2019; Francis
et al.
2019), and is able to make vertical migrations in the water column to several hundred meters depth (Santos
et al.
2021). As a red muscle endotherm, the species is able to regulate its body temperature, allowing it to tolerate a broad range of water temperatures (Watanabe
et al.
2015). Connectivity among ocean basins has been demonstrated by several genetic studies. Taken together, results of available genetic analyses suggest that female shortfin mako sharks exhibit fidelity to ocean basins, while males readily move across the world's oceans and mate with females from various basins, thereby homogenizing genetic variability (Heist
et al.
1996; Schrey and Heist 2003; Taguchi
et al.
2011; Corrigan
et al.
2018). The ERA Team unanimously agreed that, based on this information, this demographic factor is not likely to contribute significantly to the species' risk of extinction now or in the foreseeable future as they defined it. We agree that this factor is not contributing significantly to the species' risk of extinction now. Over the foreseeable future of 50 years that we have determined is more appropriate to apply for this species, we also find that this demographic factor is not likely to significantly contribute to the shortfin mako shark's risk of extinction because this factor is not currently negatively affecting the species' status and the best available scientific and commercial data suggests no basis to predict that this factor will change over the extended time horizon.

Diversity

In its consideration of the degree to which diversity (or lack thereof) might contribute to the extinction risk of the shortfin mako shark, the ERA Team evaluated available information on genetic diversity as well as diversity of distribution and ecology. Available genetic studies do not indicate that the species has experienced a significant loss of diversity that would contribute to extinction risk. In fact, haplotype diversity has been found to be high in several studies: 0.755 by Heist
et al.
(1996), 0.92 by Taguchi
et al.
(2011), and 0.894 by Corrigan
et al.
(2018). Nucleotide diversity has been found to be lower: 0.347 by Heist
et al.
(1996), 0.007 by Taguchi
et al.
(2011), and 0.004 by Corrigan
et al.
(2018). Genetic studies indicate a globally panmictic population, meaning that there is sufficient movement of shortfin mako sharks, and therefore gene flow, to reduce genetic differentiation among regions (Heist
et al.
1996; Schrey and Heist 2003; Taguchi
et al.
2011; Corrigan
et al.
2018). We found no evidence that gene flow, migration, or dispersal has been reduced. The species occurs across a variety of habitats and regions (Rogers
et al.
2015b; Rigby
et al.
2019; Santos
et al.
2020), and is able to consume a diversity of prey (Stillwell and Kohler 1982; Cortés 1999; Maia
et al.
2006; Gorni
et al.
2012); these characteristics protect against catastrophic events that may impact a certain region or prey species. For these reasons, the ERA Team unanimously agreed that it is not likely that this factor significantly contributes to the species' risk of extinction now or in the foreseeable future as they defined it. We agree that this factor is not contributing significantly to the species' risk of extinction now. Similarly, over the foreseeable future of 50 years that we have determined is more appropriate to apply for this species, we also find that this demographic factor is not likely to significantly contribute to the shortfin mako shark's risk of extinction because this factor is not currently negatively affecting the species' status and the best available scientific and commercial data suggests there is no basis to predict that this factor will change over the extended time horizon.

Summary and Analysis of Section 4(a)(1) Factors

As described above, section 4(a)(1) of the ESA and NMFS' implementing regulations (50 CFR 424.11(c)) state that we must determine whether a species is endangered or threatened because of any one or a combination of the following factors: the present or threatened destruction, modification, or curtailment of its habitat or range; overutilization for commercial, recreational, scientific, or educational purposes; disease or predation; the inadequacy of existing regulatory mechanisms; or other natural or manmade factors affecting its continued

existence. The ERA Team assembled the best available scientific and commercial data and evaluated whether and the extent to which each of the foregoing factors contributed to the overall extinction risk of the global shortfin mako shark population. We summarize information regarding each of these threats below according to the factors specified in section 4(a)(1) of the ESA.

The Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or Range

The shortfin mako shark is a highly migratory, pelagic species that spends time in a variety of open ocean and nearshore habitat types. The species is globally distributed from about 50° N (up to 60° N in the northeast Atlantic) to 50° S. While distribution is influenced by environmental variables including water temperature, prey distribution, and DO concentration, the shortfin mako shark is able to tolerate a broad thermal range and use a wide variety of prey resources. The ERA Team agreed that because shortfin mako sharks have a high adaptive capacity and do not rely on a single habitat or prey type, they are able to modify their distributional range to remain in an environment conducive to their physiological and ecological needs. Additionally, there is no evidence that range contractions have occurred, or that destruction or modification of their habitat on a global scale has occurred to such a point that it has impacted the status of the species. Therefore, the ERA Team concluded that the best available scientific and commercial information indicates that loss and/or degradation of habitat are not likely to be contributing significantly to the extinction risk of the shortfin mako shark now or in the foreseeable future as they defined it. We agree that this factor is not contributing significantly to the species' risk of extinction now. Because the contribution of habitat destruction, modification or curtailment to extinction risk is not likely to change from 25 to 50 years, we also find that this factor will not contribute significantly to extinction risk over the foreseeable future of 50 years that we have determined is more appropriate to apply for this species.

An analysis of potential threats posed by pollutants and environmental contaminants is carried out in
Other Natural or Manmade Factors Affecting its Continued Existence,
below, because this potential threat affects more than just the habitat or range of the species.

Overutilization for Commercial, Recreational, Scientific, or Educational Purposes

The best available information indicates that the primary threat facing the shortfin mako shark is overutilization in fisheries. The majority of the catch is taken incidentally in commercial fisheries throughout the species' range, and the species is often opportunistically retained due to the high value of its meat and fins (Camhi
et al.
2008; Dent and Clarke 2015). The species is targeted in semi-industrial and artisanal fisheries in the Indian and Pacific Oceans, and as a sportfish in several recreational fisheries, though recreational fisheries are thought to have minimal contribution to the species' overutilization in comparison to effects from commercial fisheries.

Global reported catches of shortfin mako shark have risen substantially since 1980. According to the Food and Agriculture Organization of the United Nations (FAO) global capture production statistics (accessible at
https://www.fao.org/fishery/statistics-query/en/capture/capture_quantity
), reported catch for shortfin mako shark in the period 2010-2019 totaled 128,743 t, up from 86,912 t in the period 2000-2009 and 29,754 t in the period 1990-1999. In the 2010-2019 time frame, reported landings in the Atlantic Ocean and adjacent seas totaled 61,673 t (~48 percent of global reported catch), in the Pacific Ocean totaled 43,927 t (~34 percent of global reported catch), and in the Indian Ocean totaled 23,143 t (~ 18 percent of global reported catch). Reported landings, however, represent a substantial underestimate of actual catch because they do not fully account for mortalities that result from fisheries interactions, including sharks that are discarded dead, finned, or that experience post-release mortality. For instance, Clarke
et al.
(2006) estimated that shark biomass in the fin trade alone is three to four times higher than catch reported in the FAO capture production data. Therefore, impacts of commercial fishing fleets on the shortfin mako shark are likely much greater than reported catch numbers suggest.

Data from across the species' range indicate that much of the catch of shortfin mako sharks in longline fisheries is composed of immature individuals (N Atlantic: Biton-Porsmoguer 2018, Coelho
et al.
2020a; S Atlantic: Barreto
et al.
2016; NW Pacific: Ohshimo
et al.
2016, Semba
et al.
2021; E Pacific: Furlong-Estrada
et al.
2017, Saldaña-Ruiz
et al.
2019, Doherty
et al.
2014; Indian: Winter
et al.
2020, Wu
et al.
2021). Exploitation of the juvenile life stage reduces the proportion of the population that survives to maturity to reproduce. Due to the late age-at-maturity of the species, many years are required before conservation actions may influence the spawning population. Additionally, abundance indices based on the part of the population that is most vulnerable to fisheries mortality (immature individuals) can be out of phase with those based on the abundance of the spawning stock (
e.g.,
CPUE and age-structured population models, respectively) for decades. For these reasons, the delay between identifying overutilization and addressing it can limit the effectiveness of mitigation and can make fisheries management for the shortfin mako shark difficult.

Rates of at-vessel mortality, or mortality resulting from interactions with fishing gear prior to being brought onboard (also known as hooking or capture mortality), vary by fishing practice and gear type. Campana
et al.
(2016) estimated fisheries mortality of shortfin mako sharks in Northwest Atlantic pelagic longline fisheries targeting swordfish and tuna, in which the majority (88 percent) of hooks used were circle hooks. The types of leaders or branch lines were not reported. Shortfin mako sharks were found to experience a mean at-vessel mortality rate of 26.2 percent, and another 23 percent of incidentally caught shortfin mako sharks were injured at haulback (Campana
et al.
2016). The proportion of shortfin mako sharks that experienced at-vessel mortality in pelagic longlines was significantly higher than that of blue sharks (
Prionace glauca
), likely because shortfin mako sharks have very high oxygen requirements, and their ability to ram ventilate—or continuously force water across their gills to breathe, typically by swimming at speed—is compromised once hooked (Campana 2016; Campana
et al.
2016). Data from Portuguese longline vessels targeting swordfish in the North and South Atlantic indicate at-vessel mortality rates of 35.6 percent for shortfin mako shark (Coelho
et al.
2012). This fleet uses stainless steel J hooks and both monofilament and wire branch lines (Coelho
et al.
2012). In the North Pacific, shortfin mako sharks incidentally caught in the Hawaii deep-set and American Samoa longline fisheries targeting tuna were found to experience an at-vessel mortality rate of 22.7 percent (Hutchinson
et al.
2021). Prior to May 2022, the Hawaii de

[Text truncated at 120,000 characters. The full text is on the page linked above.]

---

Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2022-24493. Public record. Not legal advice.