# Endangered and Threatened Wildlife; 90-Day Finding on a Petition To List 10 Species of Giant Clams as Threatened or Endangered Under the Endangered Species Act

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2017-13275

## Record

- **Collection:** Federal Register
- **Document type:** Proposed Rule
- **Published:** June 26, 2017
- **Citation:** 82 FR 28946

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
50 CFR Parts 223 and 224
[Docket No. 170117082-7082-01]
RIN 0648-XF174
Endangered and Threatened Wildlife; 90-Day Finding on a Petition To List 10 Species of Giant Clams as Threatened or Endangered Under the Endangered Species Act

AGENCY:

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

ACTION:

90-day petition findings, request for information, and initiation of status review.

SUMMARY:

We, NMFS, announce our 90-day findings on a petition to list ten species of giant clam as endangered or threatened under the U.S. Endangered Species Act (ESA). We find that the petition presents substantial scientific or commercial information indicating that the petitioned action may be warranted for seven species (
Hippopus hippopus, H. porcellanus, Tridacna costata, T. derasa, T. gigas, T. squamosa, and T. tevoroa
). Accordingly, we will initiate status reviews of these seven giant clam species. To ensure that the status reviews are comprehensive, we are soliciting scientific and commercial information regarding these species. We find that the petition did not present substantial scientific or commercial information indicating that the petitioned action may be warranted for the other three petitioned giant clam species (
T. crocea, T. maxima,
or
T. noae
).

DATES:

Information and comments on the subject action must be received by August 25, 2017.

ADDRESSES:

You may submit comments, information, or data, by including “NOAA-NMFS-2017-0029” by either of the following methods:

•
Federal eRulemaking Portal:
Go to
www.regulations.gov/#!docketDetail;D=NOAA-NMFS-2017-0029,
click the “Comment Now” icon, complete the required fields, and enter or attach your comments.

•
Mail or hand-delivery:
Office of Protected Resources, NMFS, 1315 East-West Highway, Silver Spring, MD 20910. Attn: Lisa Manning.

Instructions:
NMFS may not consider comments if they are sent by any other method, to any other address or individual, or received after the comment period ends. All comments received are a part of the public record and NMFS will post for public viewing on
http://www.regulations.gov
without change. All personal identifying information (
e.g.,
name, address, etc.), confidential business information, or otherwise sensitive information submitted voluntarily by the sender will be publicly accessible. NMFS will accept anonymous comments (enter “N/A” in the required fields if you wish to remain anonymous).

FOR FURTHER INFORMATION CONTACT:

Lisa Manning, NMFS, Office of Protected Resources (301) 427-8403.

SUPPLEMENTARY INFORMATION:

Background

On August 7, 2016, we received a petition from a private citizen, Dr. Dwayne W. Meadows, Ph.D., requesting that we list the Tridacninae giant clams (excluding
Tridacna rosewateri
) as endangered or threatened under the ESA. The ten species of giant clams considered in this finding are the eight
Tridacna
species, including:
T. costata, T. crocea, T. derasa, T. gigas, T. maxima, T. noae, T. squamosa,
and
T. tevoroa
(also known as
T. mbalavauna
); and the two
Hippopus
species:
H. hippopus
and
H. porcellanus.
The petitioner also requested that critical habitat be designated for Tridacninae species that occur in U.S. waters concurrent with final ESA listing. The petition states that Tridacninae giant clams merit listing as endangered or threatened species under the ESA because of the following: (1) Loss or curtailment of habitat or range; (2) historical and continued overutilization of the species for commercial purposes; (3) inadequacy of existing regulatory mechanisms to safeguard the species; (4) other factors such as global climate change; and (5) the species' inherent vulnerability to population decline due to their slow recovery and low resilience to threats.

ESA Statutory Provisions and Policy Considerations

Section 4(b)(3)(A) of the ESA of 1973, as amended (16 U.S.C. 1531
et seq.
), requires, to the maximum extent practicable, that within 90 days of receipt of a petition to list a species as threatened or endangered, the Secretary of Commerce make a finding on whether that petition presents substantial scientific or commercial information indicating that the petitioned action may be warranted, and promptly publish the finding in the
Federal Register
(16 U.S.C. 1533(b)(3)(A)). When we find that substantial scientific or commercial information in a petition and in our files indicates the petitioned action may be warranted (a “positive 90-day finding”), we are required to promptly commence a review of the status of the species concerned, which includes conducting a comprehensive review of the best available scientific and commercial information. Within 12 months of receiving the petition, we must conclude the review with a finding as to whether, in fact, the petitioned action is warranted. Because the finding at the 12-month stage is based on a significantly more thorough review of the available information, a “may be warranted” finding at the 90-day stage does not prejudge the outcome of the status review and 12-month finding.

Under the ESA, a listing determination may address a “species,” which is defined to also include subspecies and, for any vertebrate species, any distinct population segment (DPS) that interbreeds when mature (16 U.S.C. 1532(16)). A joint NMFS-U.S. Fish and Wildlife Service (USFWS) policy clarifies the agencies' interpretation of the phrase “distinct population segment” for the purposes of listing, delisting, and reclassifying a species under the ESA (“DPS Policy”; 61 FR 4722; February 7, 1996). A species, subspecies, or DPS is “endangered” if it is in danger of extinction throughout all or a significant portion of its range, and “threatened” if it is likely to become endangered within the foreseeable future throughout all or a significant portion of its range (ESA sections 3(6) and 3(20), respectively; 16 U.S.C. 1532(6) and (20)). Pursuant to the ESA and our implementing regulations, the determination of whether a species is threatened or endangered shall be based on any one or a combination of the following five section 4(a)(1) factors: The present or threatened destruction, modification, or curtailment of habitat or range; overutilization for commercial, recreational, scientific, or educational purposes; disease or predation; inadequacy of existing regulatory mechanisms; and any other natural or manmade factors affecting the species' existence (16 U.S.C. 1533(a)(1), 50 CFR 424.11(c)).

ESA-implementing regulations issued jointly by NMFS and USFWS (50 CFR 424.14(b)) define “substantial information” in the context of reviewing a petition to list, delist, or reclassify a species as the amount of information that would lead a reasonable person to believe that the measure proposed in the petition may be warranted. When evaluating whether substantial information is contained in a petition,

we must consider whether the petition: (1) Clearly indicates the administrative measure recommended and gives the scientific and any common name of the species involved; (2) contains detailed narrative justification for the recommended measure, describing, based on available information, past and present numbers and distribution of the species involved and any threats faced by the species; (3) provides information regarding the status of the species over all or a significant portion of its range; and (4) is accompanied by the appropriate supporting documentation in the form of bibliographic references, reprints of pertinent publications, copies of reports or letters from authorities, and maps (50 CFR 424.14(b)(2)).

At the 90-day stage, we evaluate the petitioner's request based upon the information in the petition including its references, and the information readily available in our files. We do not conduct additional research, and we do not solicit information from parties outside the agency to help us in evaluating the petition. We will accept the petitioner's sources and characterizations of the information presented, if they appear to be based on accepted scientific principles, unless we have specific information in our files that indicates the petition's information is incorrect, unreliable, obsolete, or otherwise irrelevant to the requested action. Information that is susceptible to more than one interpretation or that is contradicted by other available information will not be dismissed at the 90-day finding stage, so long as it is reliable and a reasonable person would conclude that it supports the petitioner's assertions. Conclusive information indicating the species may meet the ESA's requirements for listing is not required to make a positive 90-day finding. We will not conclude that a lack of specific information alone negates a positive 90-day finding, if a reasonable person would conclude that the unknown information itself suggests an extinction risk of concern for the species at issue.

To make a 90-day finding on a petition to list a species, we evaluate whether the petition presents substantial scientific or commercial information indicating the subject species may be either threatened or endangered, as defined by the ESA. First, we evaluate whether the information presented in the petition, along with the information readily available in our files, indicates that the petitioned entity constitutes a “species” eligible for listing under the ESA. Next, we evaluate whether the information indicates that the species at issue faces extinction risk that is cause for concern; this may be indicated in information expressly discussing the species' status and trends, or in information describing impacts and threats to the species. We evaluate any information on specific demographic factors pertinent to evaluating extinction risk for the species at issue (
e.g.,
population abundance and trends, productivity, spatial structure, age structure, sex ratio, diversity, current and historical range, habitat integrity or fragmentation), and the potential contribution of identified demographic risks to extinction risk for the species. We then evaluate the potential links between these demographic risks and the causative impacts and threats identified in ESA section 4(a)(1).

Information presented on impacts or threats should be specific to the species and should reasonably suggest that one or more of these factors may be operative threats that act or have acted on the species to the point that it may warrant protection under the ESA. Broad statements about generalized threats to the species, or identification of factors that could negatively impact a species, do not constitute substantial information that listing may be warranted. We look for information indicating that not only is the particular species exposed to a factor, but that the species may be responding in a negative fashion; then we assess the potential significance of that negative response.

Many petitions identify risk classifications made by non-governmental organizations, such as the International Union for the Conservation of Nature (IUCN), the American Fisheries Society, or NatureServe, as evidence of extinction risk for a species. Risk classifications by other organizations or made under other Federal or state statutes may be informative, but such classification alone may not provide the rationale for a positive 90-day finding under the ESA. For example, as explained by NatureServe, their assessments of a species' conservation status do “not constitute a recommendation by NatureServe for listing under the U.S. Endangered Species Act” because NatureServe assessments “have different criteria, evidence requirements, purposes and taxonomic coverage than government lists of endangered and threatened species, and therefore these two types of lists should not be expected to coincide” (
http://www.natureserve.org/prodServices/statusAssessment.jsp
). Thus, when a petition cites such classifications, we will evaluate the source of information that the classification is based upon in light of the standards on extinction risk and impacts or threats discussed above.

Analysis of the Petition

General Information

The petition clearly indicates the administrative measure recommended and gives the scientific and, in some cases, the common names of the species involved. The petition also contains a narrative justification for the recommended measures and provides limited information on the species' geographic distribution, habitat use, and threats. Limited information is also provided on population status and trends for all but a couple of species. The introduction of the petition emphasizes that giant clam species have not been evaluated by the IUCN since 1996, and more recent information provides evidence of significant population declines of all giant clam species range-wide, with increasing threats. The petition then provides general background information on giant clams as well as some limited species-specific information where available. Topics covered by the petition include giant clam taxonomy, natural history, descriptions of
Tridacna
species (descriptions of
Hippopus
species are absent), geographic range, habitat descriptions, life history (including growth and reproduction), ecology (including their symbiotic relationship with zooxanthellae and their ecological role on coral reefs), population structure and genetics, and abundance and trends. A general description of threats categorized under the five ESA Section 4(a)(1) factors is provided and is meant to apply to all of the petitioned clam species. This section discusses the following threats: Coral reef habitat degradation (including sedimentation, pollution, and reclamation), subsistence and commercial harvest by coastal and island communities for local consumption as well as sale and export for the meat, aquarium and curio trades, inadequacy of existing regulatory mechanisms to safeguard the species, and impacts of climate change (including bleaching and ocean acidification). A synopsis of and our analysis of the information provided in the petition and readily available in our files is provided below.

Species Description

Giant clams are a small but conspicuous group of large bivalves that are members of the cardiid bivalve subfamily Tridacninae (Su
et al.,
2014). They are the largest living marine

bivalves found in coastal areas of the Indo-Pacific region, and are frequently regarded as important ecological components of coral reefs, especially as providers of substrate and contributors to overall productivity (Neo and Todd 2013). The most recent information suggests there are 13 extant species of giant clams, 10 of which are considered in this 90-day finding, including 8 species in the genus
Tridacna
—
T. crocea, T. derasa, T. gigas, T. maxima, T. noae, T. squamosa, T. costata
(formerly
T. squamosina
) and
T. tevoroa
(formerly
T. mbalavauna
), and 2 species in the genus
Hippopus
—
H. hippopus
and
H. porcellanus.

Taxonomy

Giant clam taxonomy (family Cardiidae, subfamily Tridacninae) has seen a surge in new species descriptions in recent decades (Borsa
et al.,
2015a), and there is some disagreement in the literature regarding the validity of some species. Two giant clam species considered in this 90-day finding have been only recently described (
T. tevoroa
and
T. costata
), but have been shown to be junior synonyms of species described decades before (
i.e., T. mbalavuana
and
T. squamosina,
respectively; Borsa
et al.,
2015a). Another species,
T. noae,
has been the subject of debate in terms of its validity as a species. However,
T. noae
has been recently resurrected from synonymy with the small giant clam,
T. maxima,
after additional molecular and morphological evidence supported the taxonomic separation of the two species (Su
et al.,
2014).

Range and Distribution

Modern giant clams are distributed along shallow shorelines and on reefs in the Indo-West Pacific in the area confined by 30° E and 120° W (
i.e.,
from South Africa to beyond French Polynesia) and between 36° N and 30° S (
i.e.,
from Japan in the North to Australia in the South; Neo
et al.,
2015) and excluding New Zealand and Hawaii, although there are reports that at least two species have been introduced in Hawaii (
T. derasa
and
T. squamosa;
bin Othman
et al.,
2010). Although most extant giant clams mainly occur within the tropical Indo-Pacific region, three species (
T. maxima, T. squamosa
and
T. costata
) are found as far west as East Africa or the Red Sea (Soo and Todd 2014). Of all the giant clam species,
T. maxima
has the most cosmopolitan distribution, which encompasses nearly the entire geographical range of all the other giant clam species. On the other side of the spectrum, the more recently described
T. costata, T. tevoroa,
and
H. porcellanus
have the most restricted geographical ranges (bin Othman
et al.,
2010).

Anecdotal reports by SCUBA divers and data from Reef Check (an international non-governmental organization that trains volunteers to carry out coral reef surveys) include records of giant clams beyond previously defined geographical boundaries, extending their known occurrence to near Cape Agulhas, South Africa. Giant clam distribution is not uniform, with greater diversity found in the central Indo-Pacific (Spalding
et al.,
2007). A couple of recent sources have extended the known ranges of a couple of species. For example, Gilbert
et al.
(2007) documented the first observation of
T. squamosa
in French Polynesia, extending the species' range farther east than previously reported. Likewise, in our files, we found evidence that
T. tevoroa
has recently been observed in the Loyalty Islands of New Caledonia, whereas it was previously thought to be restricted to Tonga and Fiji (Kinch and Teitelbaum 2009). The petition claims that several of the species occur (or historically occurred) in the United States and its territories or possessions, including:
T. derasa, T. gigas, T. maxima, T. squamosa,
and
H. hippopus.
The rest of the petitioned clam species have strictly foreign distributions. The NMFS Coral Reef Ecosystem Program (CREP) conducts routine Reef Assessment and Monitoring Program surveys in U.S. territories, but their comprehensive monitoring reports only include general information on
Tridacna
clams, not at the species level.

Habitat

The petition cites Soo and Todd (2014), stating that giant clams are markedly stenothermal (
i.e.,
they are able to tolerate only a small range of temperature) and thus restricted to warm waters. Based on the broad latitudinal and depth ranges of some giant clam species, they each likely have varying ranges of temperature tolerance, possibly similar to that of other coral reef associated species. Although giant clams are typically associated with and are prominent inhabitants of coral reefs, this is not an obligate relationship (Munro 1992). Giant clams are typically found living on sand or attached to coral rock and rubble by byssal threads (Soo and Todd 2014), but they can be found in a wide variety of habitats, including live coral, dead coral rubble, boulders, sandy substrates, seagrass beds, macroalgae zones, etc. (Gilbert
et al.,
2006; Hernawan 2010).

Life History

The exact lifespan of tridacnines has not been determined; although it is estimated to vary widely between eight to several hundred years (see original citations in Soo and Todd 2014). Little information exists on the size at maturity for giant clams, but size and age at maturity vary by species and geographical location (Ellis 1997). In general, giant clams appear to have relatively late sexual maturity, a sessile, exposed adult phase and broadcast spawning reproductive strategy, all of which can make giant clams vulnerable to depletion and exploitation (Neo
et al.,
2015). All giant clam species are classified as protandrous functional hermaphrodites, meaning they mature first as males and develop later to function as both male and female (Chambers 2007); but otherwise, giant clams follow the typical bivalve mollusc life cycle. At around 5 to 7 years of age (Kinch and Teitelbaum 2009), giant clams reproduce via broadcast spawning, in which several million sperm and eggs are released into the water column where fertilization takes place. Giant clam spawning can be seasonal; for example, in the Central Pacific, giant clams can spawn year round but are likely to have better gonad maturation around the new or full moon (Kinch and Teitelbaum 2009). In the Southern Pacific, giant clam spawning patterns are seasonal and clams are likely to spawn in spring and throughout the austral summer months (Kinch and Teitelbaum 2009). Once fertilized, the eggs hatch into free-swimming trochophore larvae for around 8 to 15 days (according to the species and location) before settling on the substrate (Soo and Todd 2014; Kinch and Teitelbaum 2009). During the pediveliger larvae stage (the stage when the larvae is able to crawl using its foot), the larvae crawl on the substrate in search of suitable sites for settlement and metamorphose into early juveniles (or spats) within 2 weeks of spawning (Soo and Todd 2014). Growth rates after settlement generally follow a sigmoid (“S” shaped) curve, beginning slowly, then accelerating after approximately 1 year and then slowing again as the animals approach maturity (Ellis 1997). These rates are usually slow and vary amongst species.

Feeding and Nutrition

According to Munro (1992), giant clams are facultative planktotrophs, in that they are essentially planktotrophic (
i.e.,
they feed on plankton) but they can acquire all of the nutrition required for maintenance from their symbiotic algae,

Symbodinium.
Nutritional requirements and strategies vary significantly by species. For example,
T. derasa
is able to function as a complete autotroph in its natural habitat (down to 20 m), whereas
T. tevoroa
only achieves this in the shallower parts of its distribution (10 to 20 m).
Tridacna gigas
shows a different strategy, comfortably satisfying all apparent carbon requirements from the combined sources of filter-feeding and phototrophy (Klumpp and Lucas 1994). In fact, Klumpp
et al.
(1992) showed that
T. gigas
is an efficient filter-feeder and that carbon derived from filter-feeding in Great Barrier Reef waters supplies significant amounts of the total carbon necessary for its respiration and growth.

Giant Clam Status and Abundance Trends

The petition does not provide historical or current global abundance estimates for any of the petitioned clam species; rather, the petition cites a number of studies that document local extirpations of various giant clam species in particular areas to demonstrate that all species of giant clams are currently declining, or have declined historically, within their ranges. We assess the information presented in the petition, and information in our files, regarding each of the petitioned species in individual species accounts later in this finding.

ESA Section 4(a)(1) Factors

The petition indicates that giant clam species merit listing due to all five ESA section 4(a)(1) factors: Present or threatened destruction, modification, or curtailment of its habitat or range; overutilization for commercial, recreational, scientific, or educational purposes; disease or predation; inadequacy of existing regulatory mechanisms; and other natural or manmade factors affecting its continued existence. We first discuss each of these threats to giant clams in general, and then discuss these threats as they relate to each species, based on information in the petition and the information readily available in our files.

Threats to Giant Clams

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

The petition contends that all giant clam species are at risk of extinction due to habitat destruction. The petitioner cites Foster and Vincent (2004) and states that: “Giant clams inhabit shallow coastal waters which are highly vulnerable to habitat degradation caused by various anthropogenic activities.” While we agree that highly populated coastal areas are subject to anthropogenic impacts (
e.g.,
land-based sources of pollution, sedimentation, nutrient loading, etc.), the reference provided by the petitioner refers to habitat degradation as a threat to seahorse populations, with no information provided in this reference specific to giant clams. The petition also asserts that because giant clams are associated with coral reefs, that all species of giant clams face all of the “regular” threats that coral reefs generally face, including coral reef habitat degradation, sedimentation and pollution. The petition cites Brainard
et al.
(2011), a status review report that was prepared by NMFS for 82 coral species under the ESA, as evidence of habitat destruction issues throughout the range of the petitioned giant clam species. While this status review report thoroughly describes issues related to coral reef habitat degradation in general, it does not discuss giant clams, nor does it provide any substantial evidence regarding a link between coral reef habitat degradation and negative population-level impacts to any of the petitioned giant clam species throughout their ranges. Further, the petition itself notes that while giant clam species are generally associated with coral reefs, it is not an obligate relationship. In fact, surveys in many areas suggest that adults of most species of giant clams can live in most of the habitats available in coralline tropical seas (Munro 1992), with observations of giant clam species inhabiting a diverse variety of habitats (
e.g.,
live coral, dead encrusted coral, coral rubble, seagrass beds, sandy substrates, boulders, macroalgae zones, etc.; Gilbert
et al.,
2006; Hernawan 2010). Additionally, while the petition describes the ecological importance of giant clams to coral reefs, the petition does not provide any information demonstrating the importance of pristine coral reef habitat to the survival of giant clam species.

Finally, the petitioner also notes evidence from the South China Sea that 40 square miles (104 sq km) of coral reefs have been destroyed as a result of giant clam poaching, with an additional 22 square miles (57 sq km) destroyed by island-building and dredging activities. The petitioner notes that the main target during these poaching activities is
T. gigas,
because its large shell is considered a desirable luxury item in mainland China. Although directed poaching of giant clams would fall under the threat of overutilization, the means of poaching (
e.g.,
explosives, tools of various sorts, and/or dragging and pulling to remove giant clams from the surrounding habitat) clearly has impacts to coral reef habitat as well. However, it is unclear how the loss of coral reefs in the South China Sea may impact the status of giant clams throughout their ranges, and aside from
T. gigas,
the petition provides no species-specific information regarding habitat destruction for the other nine petitioned species.

Therefore, while the information in the petition suggests concern for the status of coral reef habitat generally, its broadness, generality, and speculative nature, and the lack of connections between the threats discussed and the status of the giant clam species specifically, means that we cannot find that this information reasonably suggests that habitat destruction is an operative threat that acts or has acted on each of the species to the point that they may warrant protection under the ESA. Broad statements about generalized threats to the species, or identification of factors that could negatively impact a species, do not constitute substantial information that listing may be warranted. We look for information indicating that not only is the particular species exposed to a factor, but that the species may be responding in a negative fashion; then we assess the potential significance of that negative response and consider the significance within the context of the species' overall range. In this case, generalized evidence of declining coral reef habitat is not evidence of a significant threat to any of the individual petitioned species to infer extinction risk such that the species may meet the definition of either threatened or endangered under the ESA.

In addition to habitat degradation as a result of various anthropogenic activities, the petition contends that climate change related threats, including ocean warming and ocean acidification, are operative threats to all giant clam species and the coral reef habitat they rely on. The petitioner cites Brainard
et al.
(2011) and NMFS' proposed and final rules to list numerous reef-building corals under the ESA (77 FR 73219; December 7, 2012 and 79 FR 53852; September 10, 2014) as substantial information to support these claims. While we agree with the petitioner that coral bleaching events have been increasing in both intensity and geographic extent because of climate change, and the information in the petition suggests concern for coral reef ecosystems, we disagree with the petitioner's broad and generalized

application of this information to the status of giant clams.

With regard to climate change related threats to coral reef habitat, NMFS' final rule to list 20 species of reef-building corals (79 FR 53852; September 10, 2014) explains that exposure and response of coral species to global threats varies spatially and temporally, based on variability in the species' habitat and distribution. The vast majority of coral species occur across multiple habitat types, or reef environments, and have distributions that encompass diverse physical environmental conditions that influence how that species responds to global threats. Additionally, the best available information, as summarized in Brainard
et al.
(2011) and the coral final rule (79 FR 53852; September 10, 2014), shows that adaptation and acclimatization to increased ocean temperatures are possible; there is intra-genus variation in susceptibility to bleaching, ocean acidification, and sedimentation; at least some coral species have already expanded their ranges in response to climate change; and not all species are seriously affected by ocean acidification. In fact, some studies suggest that coral reef degradation resulting from global climate change threats alone is likely to be an extremely spatially, temporally, and taxonomically heterogeneous process. These studies indicate that coral reef ecosystems, rather than disappear entirely as a result of future impacts, will likely persist, but with unpredictable changes in the composition of coral species and ecological functions (Hughes
et al.,
2012; Pandolfi
et al.,
2011). We have additional information regarding climate change impacts and predictions for coral reefs readily available in our files, which indicates a highly nuanced and variable pattern of exposure, susceptibility, resilience, and recovery over regionally and locally different spatial and temporal scales, with much uncertainty remaining. The literature underscores the multitude of factors contributing to coral response to thermal stress, including taxa, geographic location, biomass, previous exposure, frequency, intensity, and duration of thermal stress events, gene expression, and symbiotic relationships (Pandolfi
et al.,
2011; Putman
et al.,
2011; Buddemeier
et al.,
2012; Sridhar
et al.,
2012; Teneva
et al.,
2012; van Hooidonk and Huber, 2012). Evidence suggests that coral bleaching events will continue to occur and become more severe and more frequent over the next few decades (van Hooidonk 2013). However, newer multivariate modeling approaches indicate that traditional temperature threshold models may not give an accurate picture of the likely outcomes of climate change for coral reefs, and effects and responses will be highly nuanced and heterogeneous across space and time (McClanahan
et al.,
2015).

In addition to bleaching, the petitioner similarly implies that ocean acidification is a threat to giant clam habitat (
i.e.,
corals and coral reefs). The petition cites Brainard
et al.
(2011) and states: “ocean acidification threatens to slow or halt coral growth and reef building entirely if the pH of the ocean becomes too low for corals to form their calcite skeletons.” The petition further states that bioerosion of coral reefs is likely to accelerate as skeletons become more fragile because of the effects of acidification. However, aside from these broad and generalized statements regarding the potential impacts of ocean acidification to giant clam habitat (based largely on information regarding ocean acidification impacts to corals and coral reefs), the petition provides very limited information regarding species-specific impacts of ocean acidification for most of the petitioned giant clam species. Additionally, as with coral bleaching, Brainard
et al.
(2011) and the coral final rule (79 FR 53852; September 10, 2014) show that adaptation and acclimatization to ocean acidification are possible, there is intra-genus variation in susceptibility to ocean acidification, and not all species are seriously affected. The previous discussion regarding spatial and temporal variability regarding how coral species respond to increasing temperature also applies to how corals respond to impacts of ocean acidification. Despite the generally high-ranking global threats from climate change, including coral bleaching and acidification and considerations of how these threats may act synergistically, only 20 of the 83 petitioned coral species ultimately warranted listing under the ESA. This underscores the fact that reef-building corals exist within a wide spectrum of susceptibility and vulnerability to global climate change threats. Thus, at the broad level of coral reefs, the information in the petition and in our files does not allow us to conclude that coral reefs generally are at such risk from ocean acidification effects as to threaten the viability of the petitioned giant clam species.

Finally, the petition provided no information or analysis regarding how changes in coral reef composition and function because of climate change pose an extinction risk to any of the petitioned giant clam species. This is particularly important given that giant clams do not have an obligate relationship to coral reefs and, like corals, occur in a wide variety of habitats that encompass diverse physical environmental conditions that influence how a particular species responds to global threats. Broad generalizations regarding climate change related threats and their impacts cannot be applied as an equivalent threat to corals and coral reef associated species. In cases where the petitioner provided relevant species-specific information regarding climate change impacts, we consider this information in further detail below in the individual species accounts.

Overutilization for Commercial, Recreational, Scientific, or Educational Purposes

The petition describes several activities that may be contributing to the overutilization of giant clams in general. The petition notes that harvest of giant clams is for both subsistence purposes (
e.g.,
giant clam adductor, gonad, muscle, and mantle tissues are all used for food products and local consumption), as well as commercial purposes for global international trade (
e.g.,
giant clam shells are used for a number of items, including jewelry, ornaments, soap dishes).

The petition discusses a number of commercial fisheries that operated historically, including long-range Taiwanese fishing vessels and some local fisheries that developed in the 1970s and 1980s (
e.g.,
Papua New Guinea, Fiji, Maldives). According to Munro (1992), historical commercial fisheries appear to have been limited to long-range Taiwanese fishing vessels, which targeted the adductor muscles of larger species (
e.g., T. gigas
and
T. derasa
). This activity reached its peak in the mid-1970s and then subsided in the face of depleted stocks, strong international pressures, and improved surveillance of reef areas (Munro 1992). In response to declining activities by the Taiwanese fishery and continuing demand for giant clam meat, commercial fisheries developed in Papua New Guinea, Fiji, and the Maldives. For example, the Fijian fishery, which was exclusively for
T. derasa,
landed over 218 tons over a 9-year period, with the largest annual harvest totaling 49.5 tons in 1984. The petition cites Lewis
et al.
(1998) in stating this level of harvest is “thought to have removed most of the available stock,” but the authors actually stated that in 1984-85 there were still abundant populations on various reefs in the windward (Lau, Lomaiviti)

islands but subsequent commercial harvest has considerably reduced these numbers. Because of these rapidly depleting local stocks, government authorities closed the fisheries (Munro 1992). The petition also noted historical commercial overutilization of giant clams (
i.e., T. gigas
and
T. derasa
) in Palau. Hester and Jones (1974) recorded densities of 50
T. gigas
and 33
T. derasa
per hectare at Helen Reef, Palau, before these stocks were “totally decimated by distant-water fishing vessels” (Munro 1992), although no further information or citations are provided to better describe the decimation. The petition discusses a few other studies that document historical overutilization of giant clams in various locations, including Japan, Philippines, Malaysia, and Micronesia (Okada 1997; Villanoy
et al.,
1988; Tan and Yasin 2003; and Lucas 1994, respectively). Thus, it is clear that in some locations, giant clams, particularly the largest species (
T. gigas
and
T. derasa
), have likely experienced historical overutilization as a result of commercial harvest. However, it should be noted that the large majority of the information provided in the petition points to selective targeting of the largest giant clam species, with limited information on many of the other petitioned giant clam species. Therefore, we cannot conclude that overutilization is contributing equally or to the same extent to the extinction risk of all giant clam species. Thus, any individual studies and species-specific information are discussed and analyzed in further detail in the individual species accounts below.

In terms of current and ongoing threats of overutilization to giant clams, the petition emphasizes the threat of the growing giant clam industry in China, largely the result of improved carving techniques, increased tourism in Hainan, China, the growth in e-commerce, and the domestic Chinese wholesale market (Larson 2016). The petition also cites McManus (2016) to note concerns that stricter enforcement of the trade in ivory products has diverted attention to giant clam shells. The petition points out that the giant clam (
T. gigas
) is the main target for international trade, as this species' shell is considered a desirable luxury item, with a pair of high quality shells (from one individual) selling for upwards of US $150,000. Therefore, the high value and demand for large
T. gigas
shells may be a driving factor contributing to ongoing overutilization of the species. However, aside from
T. gigas,
the petition provides very limited information regarding the threat of international trade to the other nine petitioned giant clam species. Based on the information presented in the petition and in our files, we acknowledge that international trade may be a threat to some species (
e.g., T. gigas
), but we cannot conclude that international trade is posing an equivalent threat to all of the petitioned species, as it is clear that some giant clam species are more desirable and targeted more for international trade than others. A more detailed analysis of available species-specific trade information presented in the petition and in our files can be found in the individual species accounts in later sections of this notice.

Although the petition does not mention aquaculture and hatchery programs, we found some information in our files on numerous giant clam aquaculture and hatchery programs throughout the Indo-Pacific, with several species being cultured in captivity for the purpose of international trade and restocking/reseeding programs to enhance wild populations. Currently, a variety of hatchery and nursery production systems are being utilized in over 21 Indo-Pacific countries (Teitelbaum and Friedman 2008), with several Pacific Island Countries and Territories (PICTs) across the Pacific using giant clam aquaculture and restocking programs to help enhance wild populations and culture clams for commercial use/trade. For example, the Cook Islands cultures giant clams at the Aitutaki Marine Research Center and exported 30,000 giant clams from 2003 to 2006 for the global marine aquarium trade (Kinch and Teitelbaum 2009). In 2005, the Palau National Government established the Palau Maricultural Demonstration Center Program to conduct research on giant clam culture and to establish community-based giant clam grow-out farms. This program has helped establish 46 giant clam farms throughout Palau, with over two million giant clam `seedlings' distributed (Kinch and Teitelbaum 2009). At least 10 percent of all giant clams from each farm are also kept aside to spawn naturally in their own ranched enclosures, thus reseeding nearby areas. In addition to being used to reseed areas in Palau, the program exported approximately 10,000 cultured giant clams each year from 2005 to 2008 to France, Germany, Canada, the United States (including Guam and the Federated States of Micronesia (FSM)), Korea, and Taiwan. Other major producers of cultured giant clams for export include the Republic of the Marshall Islands, Tonga, and the FSM, producing an approximate average of 15-20,000 pieces of clams per year (Kinch and Teitelbaum 2009). Therefore, the international trade of giant clams is complex, with many facets to consider, including the increasing influx of cultured giant clams into the trade. We acknowledge that the success of these restocking programs have been variable and limited in some locations (Teitelbaum and Friedman 2008); however, given the foregoing information, we cannot conclude that international trade poses an equal extinction risk to all of the petitioned giant clam species. In cases where the petition did provide species-specific information regarding commercial trade, we consider this information, as well as what is in our files, in the individual species accounts below.

Disease and Predation

The petition states that predation is not likely a threat to giant clam species, as there is no evidence to suggest that levels of predation have changed or are unnaturally high and affecting the status of giant clam populations. We could also find no additional information in our files regarding the threat of predation for any of the petitioned clam species.

The petition asserts that because diseases have been documented in a number of species and have likely increased in concert with climate change, they cannot be ruled out as a threat. The petition presented some limited information on diseases (
e.g.,
impacts of protozoans and parasitic gastropods on giant clams and other bivalves on the Great Barrier Reef of Australia), but did not provide any species-specific information regarding how diseases may be impacting giant clam populations to the point that disease poses an extinction risk to any of the petitioned clam species. We could also not find any additional information in our files regarding the threat of disease for any of the petitioned clam species. Therefore, we conclude that the petition does not provide substantial information that disease or predation is a threat contributing to any of the species' risk of extinction, such that it is cause for concern.

Inadequacy of Existing Regulatory Mechanisms

The petition claims existing regulatory mechanisms at the international, federal, and state level to protect giant clams or the habitat they need to survive are inadequate. The petitioner asserts that not only are local and national laws inadequate to protect

giant clams, but that international trade and greenhouse gas regulations are also inadequate. We address each of these topics separately below.

Local and National Giant Clam Regulations

The petitioner notes that there are some laws for giant clams on the books in certain locations, but only discusses regulations from the Philippines and Malaysia and a separate issue of illegal clam poaching in disputed areas of the South China Sea. The petition acknowledges that all species of giant clam in the Philippines are protected as endangered species under the Philippine's Fisheries Administrative Order No. 208 series of 2001 (Dolorosa and Schoppe 2005), but states that despite this law, declines of giant clams continue. However, the only study presented on abundance trends since the law was implemented in 2001 was conducted on one reef (Tubbataha Reef; Dolorosa and Schoppe 2005). Dolorosa and Schoppe (2005) specifically stated that they could not conclude a continuous decline of tridacnids was occurring because the much lower density observed in their study was based on data taken from a single transect. Prior to the study conducted by Dolorosa and Schoppe (2005), the only quantitative information presented was from studies conducted in the 1980s and 1990s (Villanoy
et al.,
1988; Salazar
et al.,
1999). Therefore, based on the foregoing information, we cannot conclude that the aforementioned fisheries law is inadequate for mitigating local threats to giant clams and slowing or halting population declines in the Philippines. However, illegal poaching for some species does seem to be an issue in some areas of the Philippines, notably in the protected area of Tubbataha Reef National Marine Park. For example, hundreds of giant clams (
T. gigas
) were confiscated from Chinese fishermen who poached in the Park in the early 2000s (Dolorossa and Schoppe 2005), indicating that regulatory mechanisms (
e.g.,
the protected area) may not be adequate to protect that highly sought after species.

The petitioner also notes that Malaysia's Department of Fisheries has listed giant clams as protected species, but cites Tan and Yasin (2003) as evidence that giant clams continue to decline despite this protective regulation. The petition provides no details regarding when this law was implemented or what specific protections it affords giant clams in Malaysian waters, nor could we find these details in the reference provided (Tan and Yasin 2003). Given that Malaysia represents a different proportion of each of the petitioned species' overall range, the potential inadequacy of regulatory mechanisms in Malaysia will be assessed and considered for each of the petitioned species in the individual species accounts below.

Overall, the discussion of inadequate regulatory mechanisms for giant clams at the national/local level by the petitioner focuses on Southeast Asia, without any information regarding regulatory mechanisms throughout large portions of the rest of the ranges of the species. However, we found regulations in our files in numerous countries throughout the tropical Pacific (
e.g.,
PICTs) and Australia regarding the harvest of giant clams. For example, size limits and complete bans on commercial harvest are the most commonly used fisheries management tools for giant clams throughout the PICTs (Kinch and Teitelbaum 2009). Several countries, including French Polynesia, Niue, Samoa, and Tonga, have size limits imposed for certain species. Some PICTs, such as Fiji and New Caledonia, both of which have active high volume tourist trades, allow up to three giant clam shells (or six halves) not weighing more than 3 kg to be exported with Convention on International Trade of Endangered Species of Wild Fauna and Flora (CITES) permits. Other PICTs, such as Guam and New Caledonia, have imposed bag-limits on subsistence and commercial harvest of giant clams. Papua New Guinea has imposed a ban on the use of night lights to harvest giant clams. There are also community-based cultural management systems in many PICTs like the Cook Islands where a local village or villages may institute
rahui,
or closed areas, for a period of time to allow stocks to recover (Chambers 2007). Finally, the following PICTs have complete bans on commercial harvest and export, with the exception of aquacultured species: FSM, Fiji, French Polynesia, Kiribati, Palau, Solomon Islands, and Vanuatu (Kinch and Teitelbaum 2009). Therefore, without any information or analysis as to how these regulatory measures are failing to address local threats to giant clams, we cannot conclude that there is substantial information indicating that regulatory mechanisms for all of the petitioned giant clam species are equally inadequate such that they may be posing an extinction risk to the species. Where more specific information is available for a particular species, we consider this information in the individual species accounts later in this finding.

Trade Regulations

The petition asserts that international regulations, specifically the CITES, are inadequate to control commercial trade of giant clam species. The petition explains that although all members of the Tridacninae family are listed under Appendix II of CITES, implementation and enforcement are likely not adequate and thus illegal shipments are not necessarily intercepted. However, the assertions regarding illegal shipments were made broadly about wildlife shipments in general, without providing any specific information or clear linkages regarding how CITES is failing to regulate international trade of each of the petitioned giant clam species. The petition cites a number of CITES documents and states that these documents “show wide disparities in yearly giant clam trade figures,” which suggest that some countries have failed to exert control on the clam trade (bin Othman
et al.,
2010). However, the petition did not provide any additional details explaining how these trade figures demonstrate a risk of extinction to any particular species.

Overall, the discussion of the inadequacy of CITES is very broad and does not discuss how the inadequacy of international trade regulations is impacting any of the petitioned species to the point that it is contributing to an extinction risk, with the exception of
T. gigas
and the growing giant clam industry in China. For example, the petition points out that the shape of the large giant clam shells (
T. giga
s) makes them highly desirable for making large, intricately carved scenes. In fact, the petition itself emphasizes that
T. gigas
is the main giant clam species targeted and poached in the South China Sea for this particular trade. Therefore, from the information in the petition and our files, it is clear that some giant clam species are more desirable and targeted for the international trade than others, and thus require more restrictive regulations to ensure their sustainability. As discussed previously in the
Overutilization for Commercial, Recreational, Scientific, or Educational
section above, we concluded that, for giant clams in general, the information in the petition and our files does not constitute substantial information that international trade is posing an equivalent threat to all of the petitioned giant clam species. Therefore, while we acknowledge that international trade may be a threat to some species, and existing regulations may be inadequate and warrant further investigation, the assertion that inadequate regulations for international trade is an equivalent

threat to all of the petitioned giant clam species is not supported.

Greenhouse Gas Regulations

The petition claims that regulatory mechanisms to curb greenhouse gas emissions and reduce the effects of global climate change are inadequate to protect giant clams from the threats climate change poses to the species and their habitat. The petition goes on to explain that climate change threats, including bleaching and ocean acidification, represent the most significant long-term threat to the future of global biodiversity. Information in our files and from scientific literature indeed indicates that greenhouse gas emissions have a negative impact to reef building corals (NMFS 2012). However, as we discussed in detail previously, beyond this generalized global threat to coral reefs, we do not find that the petition presents substantial information indicating that the effects of greenhouse gas emissions are negatively affecting the petitioned species or their habitat such that they may warrant listing under the ESA. In particular, the information in the petition and in our files does not indicate that the loss of coral reef habitat or the direct effects of ocean warming and acidification is contributing to the extinction risk of the petitioned species (refer back to the
Present or Threatened Destruction, Modification or Curtailment of its Habitat or Range
section above and the
Other Natural or Manmade Factors
section below). Therefore, with the exception of species for which species-specific information is available regarding negative responses to ocean warming or acidification, inadequate regulatory mechanisms controlling greenhouse gas emissions are not considered a factor that may be contributing to the extinction risk of the petitioned species.

Other Natural or Manmade Factors Affecting Its Continued Existence

Ocean Warming and Giant Clam Bleaching

The petitioner discusses the climate change-related impacts of ocean warming and giant clam bleaching as an extinction risk to all the petitioned giant clam species. In terms of giant clam bleaching, the petitioner argues that giant clams are like stony corals, in that the
Symbodinium
zooxanthellae in giant clams are subject to bleaching and other effects from high temperature. The petitioner provides a number of studies documenting giant clam bleaching in various locations, including the Great Barrier Reef in Australia and Southeast Asia. The petition then describes several studies on the physiological effects to giant clams from bleaching and ocean acidification, with the large majority of these studies conducted on
T. gigas.
However, while the petition provides some evidence that giant clams experience bleaching as a result of increased temperature, there is no discussion regarding how giant clams tolerate bleaching or the extent to which bleaching leads to mortality for the majority of the petitioned species. For example, the petition discusses a study by Leggat
et al.
(2003), in which the symbiotic zooxanthellae in
T. gigas
declined 30-fold during the 1998 global coral bleaching event, leading to a loss of the nutrition provided by zooxanthellae in ways very similar to the effects on stony corals; however, the petition failed to present any discussion or analysis as to how this stressor is linked to mortality of giant clams or population declines. In fact, the main conclusion of the Leggat
et al.
(2003) study states:

Despite this significant reduction in symbiont population, and the consequent changes to their carbon and nitrogen budgets, the clams are able to cope with bleaching events significantly better than corals. During the recovery of clams after an artificial bleaching event only three out of 24 clams died, and personal observations at Orpheus Island indicated that survival rates of bleached clams were greater than 95 percent under natural conditions. This is in contrast to reports indicating coral mortality in some species can be as great as 99 percent.

Therefore, although giant clams and stony corals can experience similar bleaching of their symbiotic zooxanthellae, this does not necessarily equate to analogous impacts of widespread bleaching-induced mortality from ocean warming. As discussed for another reef-dwelling organism in the orange clownfish 12-month finding (80 FR 51235), anemones also have symbiotic zooxanthellae, but literature on the effects of ocean warming on anemones show results that are not necessarily analogous with corals either, and in fact show high variability between and within species. Even individual anemones can show varying responses across different bleaching events. Although observed anemone bleaching has thus far been highly variable during localized events, the overall effect of bleaching events on anemones globally (
i.e.,
overall proportion of observed anemones that have shown ill effects) has been of low magnitude at sites across their ranges. In fact, only 3.5 percent of the nearly 14,000 observed anemones were recorded as bleached across 19 study sites and multiple major bleaching events (Hobbs
et al.,
2013). Based on this example, generalized statements about bleaching impacts to all organisms that have symbiotic dinoflagellates being analogous are not supported by the best available information.

Without species-specific information on how ocean warming-induced bleaching affects each of the petitioned giant clam species (
e.g.,
mortality rates and evidence of negative population level effects), we cannot conclude that bleaching caused by ocean warming may be acting equally on all of the petitioned species to the point that the petitioned action may be warranted. Where the petition provides some species-specific information regarding the effects of temperature-induced bleaching, we consider this information in more detail in the individual species accounts below.

Ocean Acidification

Similar to the effects of ocean warming, the petitioner discusses ocean acidification as a threat contributing to the extinction risk of all of the petitioned giant clam species. The petitioner asserts that the effects of ocean acidification will likely accelerate the bioerosion of giant clam shells and lead to their increased fragility. To support this assertion, the petition cites two studies. One study (Waters 2008) looked at cultured specimens of
T. maxima
in a lab experiment and found that
T. maxima
juveniles exposed to pCO
2
concentrations approximating glacial (180 ppm), current (380 ppm) and projected (560 ppm and 840 ppm) levels of atmospheric CO
2
(per the IPCC IS92a scenario) suffered decreases in size and dissolution, and this occurred below thresholds previously considered detrimental to other marine organisms in similar conditions. We discuss these results and implications in further detail in the
T. maxima
species account below.

The second study (Lin
et al.,
2006) did not specifically evaluate impacts of ocean acidification but instead involved mechanical tests on the shells of conch (
Strombus gigas
), giant clam (
T. gigas
), and red abalone (
Haliotis rufescens
) for a comparison of strength with respect to the microstructural architecture and sample orientation. The study found that although the structure of the
T. gigas
shell had the lowest level of organization of the three shells, its sheer size results in a strong overall system (Lin
et al.,
2006). The petitioner claims that because
T. gigas
has the lowest flexural shell strength relative to the two other types of shells tested, that any loss

of shell material or strength from the effects of ocean acidification may have a greater negative effect on giant clams than on other large molluscs. However, this statement is speculative, and no additional information or references were provided to support this claim.

Overall, while we agree that ocean acidification is likely to continue and increase in severity over time within the ranges of the giant clam species, resulting in various detrimental impacts, additional information in our files also underscores the complexity and uncertainty associated with the various specific effects of ocean acidification across the ranges of giant clams. There are numerous complex spatial and temporal factors that compound uncertainty associated with projecting effects of ocean acidification on coral reef associated species such as giant clams. Further, as explained in the final rule to list 20 reef-building coral species under the ESA (79 FR 53852; September 10, 2014), projecting species-specific responses to global threats is complicated by several physical and biological factors that also apply to the petitioned giant clam species. First, global projections of changes to ocean acidification into the future are associated with three major sources of uncertainty, including greenhouse gas emissions assumptions, strength of the climate's response to greenhouse gas concentrations, and large natural variations. There is also spatial and temporal variability in projected environmental conditions across the ranges of the species. Finally, species-specific responses depend on numerous biological characteristics, including (at a minimum) distribution, abundance, life history, susceptibility to threats, and capacity for acclimatization.

In this case, the petition did not provide sufficient information regarding the likely impacts of ocean acidification on specific giant clam species or their populations. Without any analysis of how ocean acidification may be negatively impacting each of the petitioned giant clam species (with the exception of
T. maxima
and
T. squamosa
), we cannot conclude that substantial information was provided to indicate effects of ocean acidification may be acting on all of the petitioned species to the point that the petitioned action may be warranted. In cases where the petition did provide species-specific information, we consider this information in further detail in the individual species accounts below.

Individual Species Accounts

Based on the information presented in the petition and in our files, we made 10 separate 90-day findings, one for each of the petitioned giant clam species. We first address the seven species for which we have determined that the information presented in the petition and in our files constitutes substantial information that the petitioned action may be warranted (
i.e.,
positive 90-day finding). Because we will be addressing all potential threats to these species in forthcoming status reviews, we will only provide summaries of the main threat information in these species accounts as opposed to addressing every ESA (4)(a)(1) factor. Then, we address the remaining three species for which we determined that the information presented in the petition and in our files does not constitute substantial information that the petitioned action is warranted (
i.e.,
negative 90-day finding). In these species accounts, we address every ESA (4)(a)(1) factor individually.

Hippopus hippopus

Species Description

The petition does not provide any descriptive information for
H. hippopus.
We found some information in our files describing this species. Its shell exterior is off-white with a yellowish orange coloring and reddish blotches arranged in irregular concentric bands; the shell interior is porcelaneous white, frequently flushed with yellowish orange on the ventral margin, and the mantle ranges from a yellowish-brown, dull green, or grey (Kinch and Teitelbaum 2009). Maximum shell length for
H. hippopus
is 40 cm, but it is commonly found at lengths up to 20 cm. It can be found on sandy bottoms of coral reefs in shallow water to a depth of 6 m. Smaller specimens (up to about 15 cm in length) are often attached to coral rubble by their byssal strings, while large and heavy specimens are unattached and lack a byssus (Kinch and Teitelbaum 2009).

Life History

The petitioner provides some information on life history specific to this species. He cites Shelley (1989) who found second sexual maturity in
H. hippopus
at Orpheus Island, Great Barrier Reef, at a shell size of 145mm which equated to 2 years of age for males and 4 years of age for hermaphrodites of the species from the study area. He cites Stephenson (1934) and Shelley (1989) who reported that
H. hippopus
spawns in the austral summer months of December to March on the Great Barrier Reef, which is also supported by Munro (1992) who found spawning of
H. hippopus
to be restricted to a short summer season in the central region of the Great Barrier Reef. In Palau, Hardy and Hardy (1969) reported that
H. hippopus
spawned in June. In a detailed study of early life history in Guam, fertilized eggs of
H. hippopus
had a mean diameter of 130.0 μm (micrometers; 13 cm; Jameson 1976). According to the same study, settlement in Guam occurred 9 days after fertilization at a mean shell length of 202.0 μm (20.2 cm) for
H. hippopus.
Juveniles of
H. hippopus
in Guam first acquired zooxanthellae after 25 days and juvenile shells showed first signs of becoming opaque after 50 days (Jameson 1976).

Range, Habitat, and Distribution

The petition includes a range map for
H. hippopus
that was excerpted from bin Othman
et al.
(2010). bin Othman
et al.
(2010) note that data from Reef Check (
www.reefcheck.org
) indicate that there are populations of giant clams beyond the species-specific boundaries described by the references on which the range maps within bin Othman
et al.
(2010) are based, although no further detail is provided for any species. This applies to all species for which range maps based on bin Othman
et al.
(2010) are provided in this finding. The range map for
H. hippopus
provided in the petition does include several U.S. Pacific areas including Guam, Commonwealth of the Northern Mariana Islands (CNMI), and Wake Atoll. According to the petition,
H. hippopus
also historically occurred in Singapore (Neo and Todd 2012b and 2013) and the United States, although locations in the United States are not specified and no reference is provided.

EP26JN17.000

According to Munro (1992),
H. hippopus
occurs in the widest range of habitat types of all the Tridacninae species. This species is seemingly equally comfortable on sandy atoll lagoon floors or exposed intertidal habitats, and similar to
T. gigas,
which is found in many habitats (
e.g.,
high or low islands, lagoons, or fringing reefs; Munro 1992).

Population Status and Abundance Trends

Although an overall population abundance estimate or population trends for
H. hippopus
are not presented, the petitioner does provide some limited abundance information from various locations within the species' range. For example, the petition cites Tan and Yasin (2003) who state that giant clams of all species but
T. crocea
are considered endangered in Malaysia. The authors mention underwater surveys that reveal the “distribution of giant clams are widespread but their numbers are very low,” but there are no references provided by the authors to provide any more detail or support for this information, which makes it difficult to interpret this information for individual species. The only species-specific information for
H. hippopus
in this reference is that it occurs in Malaysian waters. The petition states that Brown and Muskanofola (1985) found that
H. hippopus
was locally extinct in Indonesia. Upon review of this reference, more specifically, the authors found many small shells of
H. hippopus
but no living specimens in their survey area of seven island transects in Central Java, Indonesia. The authors noted that because of time constraints, it was not possible to cover more than a very small proportion of the total area suitable for clam growth in Karimun Jawa. Thus, confining the survey to such a small area could have affected the results. Hernawan (2010) found small populations and evidence of recruitment failure in the six species found during a survey of Kei Kecil, Southeast-Maluku, Indonesia, including
H. hippopus.
The authors conducted giant clam surveys in nine sites out of the many thousands of islands that make up Indonesia. At another site in Indonesia, Eliata
et al.
(2003) reported an 84 percent decline in
H. hippopus
based on surveys of Pari Island from 1984 and 2003. This species is presumed nationally extinct in Singapore (Neo and Todd 2012a, 2013) and has been reported as extirpated from Fiji, Tonga, Samoa and American Samoa, Guam, the Mariana Islands, and Taiwan (Wells 1996a, Skelton
et al.
2002, Teitelbaum and Friedman 2008).

The petition presents three references from the Philippines on
H. hippopus.
Villanoy
et al.
(1988) states this species has been overexploited based on the export volumes of giant clam shells. The petitioner claims densities of
H. hippopus
declined by 97 percent in Tubbataha Reef Park in the Philippines from 1995-2005 based on a survey by Dolorosa and Schoppe (2005). However, upon closer review of this reference, the data in Dolorosa and Schoppe (2005) indicating a substantial decline in
H. hippopus
density was taken from a single transect; as such, the authors concluded that a continuous decline of the Tridacnids (including
H. hippopus
) could not be confirmed. Finally, Salazar
et al.
(1999) did a stock assessment of giant clams (including
H. hippopus
) in the Eastern Visayas of the Philippines and found most of the populations were made up of juveniles with insufficient numbers of breeders to repopulate the region, although this reference was unavailable for review. Notably, the petition cites Thamrongnavasawat (2001) as reporting that
H. hippopus
is considered extinct in Mo Ko Surin National Park in Thailand, although the bibliographic information provided for this reference did not allow us to access it for review.

While individually and collectively the studies discussed in this section represent a small portion of
H. hippopus'
total geographic range, localized declines and potential extirpations of this species in small areas are spread throughout its range and not confined to one area that may be disproportionately affected by some negative impact. Thus, the number and spatial distribution of localized severe

declines or extirpations in the context of the species' range may be contributing to an elevated extinction risk for this species such that it warrants further investigation.

Threats to
Hippopus hippopus

The petition presents three studies with species-specific information regarding threats to
H. hippopus.
Some historical information indicates that shells of
H. hippopus
(long extirpated in Fiji) occur in shell middens at the Lapita-era (1100-550 B.C.) settlements (Bourewa and Qoqo) along the Rove Peninsula in Fiji; the valve size and weight increase with depth (
i.e.,
age) in the midden, suggesting that human consumption contributed to its local disappearance (Seeto
et al.
2012). While this one piece of evidence does not constitute substantial information that overharvest may be acting or may have acted on
H. hippopus
as a species to the extent that it needs protection under the ESA, the threat of overexploitation will be evaluated in the status review. Blidberg
et al.
(2000) studied the effect of increasing water temperature on
T. gigas, T. derasa,
and
H. hippopus
at a laboratory in the Philippines.
Hippopus hippopus
experienced increased respiration and production of oxygen in elevated temperatures and was therefore more sensitive to higher temperature than the two other species tested. After 24 hours at ambient temperature plus 3 °C, however, no bleaching was observed for any of the species. While we acknowledge the potential for ocean warming to have an effect on this species, this was a limited experiment, the results of which are difficult to interpret in terms of the potential species-level or even localized impacts of physiological stress due to elevated ocean temperatures in the wild in the context of this assessment. While this one study does not constitute substantial information that climate change may be acting on
H. hippopus
as a species to the extent that it needs protection under the ESA, the impacts of ocean warming will be further evaluated for
H. hippopus
in the status review based on the best available information.

Finally, Norton
et al.
(1993) found two incidences of mortality in
H. hippopus
from rickettsiales-like organisms in cultured clams in the western Pacific, one in the Philippines and one in Kosrae. However, it is not uncommon among individuals cultured in close proximity to be afflicted with parasites or diseases that spread quickly (Norton
et al.,
1993). While this does not constitute substantial information that disease or parasites may be acting on
H. hippopus
as a species to the extent it needs the protections of the ESA, the threats of disease and parasites will be further evaluated in a forthcoming status review.

Conclusion

In conclusion, the information provided on threats for this species is limited and the individual studies by themselves are not substantial information indicating the petitioned action may be warranted for the species. However, the evidence presented of localized declines or extirpations in different parts of the species' range does suggest that one or more threats may be acting on the species throughout all or a significant portion of its range and the petitioned action may be warranted. The number and spatial distribution of localized severe declines or extirpations in the context of the species' range may be contributing to an elevated extinction risk for this species such that it warrants further investigation. The best available information on the species' overall status and all potential threats will be evaluated in a forthcoming status review to determine what has potentially caused these declines and extirpations.

Hippopus porcellanus

Species Description

The petition does not provide any descriptive information for
H. porcellanus.
We found some information in our files describing this species. Commonly known as the China clam,
H. porcellanus
grows to a maximum of 40 cm, but is commonly found up to 20 cm in shell length. The shell exterior is off-white, occasionally with scattered weak reddish blotches. The shell interior is porcelaneous white, more or less flushed with orange on the ventral margin, and the mantle ranges from a yellowish-brown, dull green or grey (Kinch and Teitelbaum 2009). This species can be distinguished from its congener,
H. hippopus,
by its smoother and thinner shells and presence of fringing tentacles at its incurrent siphon (Neo
et al.,
2015).

Life History

Aside from the information already discussed previously in the
Giant Clam Life History
section, the petition did not provide any life history information specific to
H. porcellanus,
nor could we find any additional information in our files on the life history of this species.

Range, Habitat, and Distribution

Hippopus porcellanus
has one of the most restricted geographic ranges of the petitioned giant clam species. The petition notes that the species only occurs in Palau, Indonesia, and the Philippines based on the IUCN assessment (Wells 1996); however, in the population abundance and trends section, the petition notes the endangered status of
H. porcellanus
in Malaysia, placing its occurrence there as well.

EP26JN17.001

H. porcellanus
can be found in shallow waters on sandy bottoms of coral reefs. Young specimens are often attached to coral heads via their byssus, whereas mature individuals lack a byssus and lay unattached on the substrate (Rosewater 1982).

Population Status and Abundance Trends

The petition does not provide an overall population abundance or trend estimate for
H. porcellanus
as a species throughout its range. The petition does, however, provide limited, localized information on the population status and abundance trends of
H. porcellanus,
with some information from Malaysia and the Philippines, but no species-specific information from other parts of the species' range, including Indonesia and Palau. As discussed in other species accounts, the petitioner cites Tan and Yasin (2003), who state that giant clams of all species but
T. crocea
are considered endangered in Malaysia. As noted previously, the authors mention underwater surveys that reveal that the “distribution of giant clams are widespread but their numbers are very low,” but the authors do not provide any references with any more detail or support for this information, which makes it difficult to interpret this information for individual species. The only species-specific information for
H. porcellanus
in this reference is that it is restricted to Sabah, Eastern Malaysia.

The petition asserts that
H. porcellanus
is overexploited and depleted in the Philippines based on Villanoy
et al.,
(1988) and Rubec
et al.,
(2001). Villanoy
et al.,
(1988) examined average size frequency distributions of giant clams harvested from the Sulu Archipelago and Southern Palawan areas from 1978 to1985, and determined that
H. porcellanus
was overexploited in the Philippines as early as the 1980s. The authors note that these findings have serious implications given that the Sulu Archipelago and Southern Palawan may be the last strongholds of all giant clam species occurring in Philippine waters. Rubec
et al.
(2001) more recently described
H. porcellanus
as “depleted,” but they did not provide any references or additional detail to help us determine what they meant by “depleted” or how this current information relates to historical abundance of the species in Philippine waters. Without any quantitative information on abundance trends of
H. porcellanus
in the Philippines since the 1980s, it is difficult to determine what the present status of the species is in this portion of its range. However, we note that because
H. porcellanus
has an extremely restricted geographic range, occurring in only three countries, overexploitation in the Philippines gives cause for concern and warrants further investigation.

While
H. porcellanus
also occurs in Indonesia and Palau, the petition did not provide any additional information regarding the species' status or abundance trends in these locations. The information provided by the petitioner for giant clams in Indonesia is from a location where
H. porcellanus
is not known to occur (
i.e.,
Kei Kecil, Indonesia). We could not otherwise find any information in our files from Indonesia or Palau regarding the status of
H. porcellanus
in these locations.

Overall, while the information presented in the petition is very limited regarding the species' current status and abundance trends throughout its range and would not in and of itself constitute substantial information, the species' range is significantly restricted. Therefore, given that the species only occurs in four countries, the information presented in the petition from the Philippines, albeit limited, gives cause for concern that the species may have an elevated extinction risk that warrants further investigation.

Threats to
H. porcellanus

The only species-specific information provided by the petition regarding threats to
H. porcellanus
is related to overutilization in the Philippines. As described in the
Population Status and Abundance Trends
section above, the

petitioner cited Villanoy
et al.
(1988) as evidence of overutilization of
H. porcellanus.
Villanoy
et al.
(1988) notes that giant clams have long been harvested by subsistence fishermen in the Indo-Pacific Region as a supplementary source of protein. Additionally, in some areas of the Philippines (
e.g.
Sulu Archipelago, Southern Palawan), giant clams are also harvested commercially for their shells. After examining average size frequency distributions of giant clams harvested from the Sulu Archipelago and Southern Palawan areas from 1978-1985, Villanoy
et al.
(1988) determined that
H. porcellanus
was overexploited in the Philippines as early as the 1980s, and is no longer commercially harvested. As noted previously, the Sulu Archipelago and Southern Palawan areas are thought to be the last strongholds of giant clams in Philippine waters. Therefore, the overexploitation of
H. porcellanus
as of the 1980s and its restricted range could have serious implications regarding the species' extinction risk. More recently, Rubec
et al.
(2001) similarly document that
H. porcellanus
has been depleted to such an extent that it is no longer commercially viable for harvesting in the Philippines.

Conclusion

In conclusion, the information provided on population abundance and threats for this species is limited and by itself would not be considered substantial information indicating the petitioned action may be warranted. The individual studies presented are not compelling evidence of species level concerns for reasons discussed above. However, given the species' extremely restricted range, combined with evidence of localized declines and historical overutilization in the Philippines, we find the information compelling enough to conclude that the petitioned action may be warranted. The best available information on the species' overall population status and all potential threats will be evaluated in a forthcoming status review.

Tridacna costata (T. squamosina)

Species Description

Tridacna costata
has been described only recently (Richter
et al.,
2008; bin Othman
et al.,
2010), but it has been shown to be a junior synonym of the previously described
T. squamosina
(Borsa
et al.,
2015a). This species of giant clam grows to 32 cm (Neo
et al.,
2015) and features 5-7 deep rib-like vertical folds, resulting in a zig-zag dorsal shell margin. According to Richter
et al.,
(2008), the mantle is most commonly a subdued brown mottled pattern; mantle margins are green with prominent “wart-like” protrusions and pale striations following mantle contour. These features (the pronounced rib-like vertical folds and the prominent wart-like protrusions on the mantle tissue) are the main diagnostic features that separate
T. costata
from its sympatric congeners. These features are conservatively present even in small clams <10 cm shell length (Richter
et al.,
2008).

Life History

The petition itself does not describe any species-specific life history information for
T. costata,
but we found some limited information in one of the references provided that suggests a narrow reproductive period. Richter
et al.
(2008) found marked differences in the seasonal times of reproduction between
T. costata
and its Red Sea congeners (
T. maxima
and
T. squamosa
). Specifically,
T. costata'
s reproductive period appears to be an early and brief period in spring, coinciding with the seasonal planktonic bloom (Richter
et al.,
2008). This narrow reproductive window may make
T. costata
particularly vulnerable to overfishing. The timing of
T. costata'
s reproduction combined with the small diameter of the ova (75 ±2 [SEM] μm) suggests a planktotrophic (
i.e.,
feeding on plankton) development of the larvae. This contrasts with the lecithotrophic (
i.e.,
yolk-feeding) and hence food-independent larval development in the summer-spawning
T. squamosa
and
T. maxima,
which also have much larger eggs (35 percent ±1 percent and 41 percent ±2 percent by volume, respectively; Richter
et al.,
2008).

Range, Habitat, and Distribution

Among giant clam species,
T. costata
has one of the most restricted geographical ranges, occurring only in the Red Sea. Richter
et al.
(2008) describes the species as occurring throughout the northeastern Gulf of Aqaba (type locality), Sinai coast, western Gulf of Aqaba, northern Red Sea, and Egyptian mainland down to Hurghada and Safaga.

EP26JN17.002

In a survey of giant clams in the Red Sea, Richter
et al.
(2008) noted that live specimens of
T. costata
were found exclusively in very shallow water including reef flats, seagrass beds, sandy-rubble flats, on slight depressions in barren rocky flats, or under branching corals or coral heads shallower than 2m. All clams were weakly attached to the substrate. Thus, unlike its Red Sea congeners
T. maxima
and
T. squamosa,
which have broad vertical ranges of distribution,
T. costata
is restricted to the reef top (Richter
et al.,
2008).

Population Status and Abundance Trends

Given the recent description of this species, information on its current population status and abundance trends is limited. However, one available study suggests a significant historical decline of the species. Results of surveys along the shores and well-dated emerged reef terraces of Sinai and Aqaba show that
T. costata
comprised >80 percent of giant clam stocks prior to the last interglacial period (122,000 to 125,000 years ago). Subsequently, the proportion of
T. costata
plunged to <5 percent in freshly discarded shell middens (Richter
et al.,
2008). Currently, the species is thought to represent less than one percent of the present giant clam stocks in the Red Sea. For example, in underwater surveys conducted in the Gulf of Aqaba and northern Red Sea, only 6 out of 1,000 live specimens belonged to the new species, with densities averaging 0.9 ±0.4 individuals per 1,000 m
2
. The highest numbers for the species occurred on offshore shoals in the Red Sea proper; however, adult broodstock was below detection in much of the study area (Richter
et al.,
2008). In fact, only 13 live individuals of
T. costata
were observed along the entire Jordanian Red Sea coast, which prevented collection of paratypes (Richter
et al.,
2008).

Threats to
T. costata

Based on the limited information in the petition, we determined that historical and ongoing overutilization may be a threat contributing to an elevated extinction risk for this species that warrants further investigation, particularly given the species' restricted geographic range and shallow depth distribution. In general,
Tridacna
stocks in the Red Sea have declined to less than 5 percent of their sizes in the 1980s and 1990s, largely due to artisanal reef-top gathering for meat and shells (Richer
et al.,
2008). Richter
et al.
(2008) notes that modern humans have likely been exploiting Red Sea mollusks for at least 125,000 years. Although natural disturbances may be responsible for variable rates of recruitment and mortality among the three Red Sea giant clam species, the substantial reduction in
Tridacna
size (equivalent to ~20-fold decrease in individual body mass and fecundity accompanying the species shift) strongly indicates overfishing (Richter
et al.,
2008). Further, given that
T. costata
is restricted to the shallow reef top (and thus more accessible to reef top gathering), it is likely that overutilization of the species has contributed to its significant decline. Therefore, we conclude that the petition presents substantial information that overutilization may be a threat contributing to an elevated extinction risk for this particular species.

Conclusion

Based on the above information, we find that the petition presents substantial scientific and commercial information indicating that the petitioned action of listing
T. costata
as threatened or endangered may be warranted. Its highly restricted range, reduced abundance, low productivity (due to its narrow reproductive periodicity), and the threat of overutilization for commercial purposes may be contributing to an elevated risk of extinction such that the petitioned action may be warranted. The best available information on the species' overall population status and all potential threats will be evaluated in a forthcoming status review.

Tridacna derasa

Species Description

The petition itself does not provide any descriptive information for
T. derasa.
Neo
et al.
(2015) report that
T. derasa
is the second largest species, growing up to 60 cm with heavy and plain shells, with no strong ribbing. According to Lewis
et al.
(1998), the maximum size recorded in Fiji, 62 cm, is well above that recorded by

Rosewater (1965, 51.4 cm) who, however, had access to only few specimens. Specimens greater than 50 cm in length are relatively common.

Life History

The petition presents very limited life history information for
T. derasa.
The optimal reproductive season for
T. derasa
sampled from Michaelmas Cay was from September/October to November/December (Braley 1988). Simultaneous hermaphroditism was found in 0 to 28 percent of sampled
T. derasa.
We found no additional life history information for this species in our files.

Range, Habitat, and Distribution

The petition does not provide a description of the geographic range for
T. derasa,
but it was included in the range map provided for most of the petitioned species. The map includes all of Malaysia, but Tan & Zulfigar (2003) report that
T. derasa
is restricted to Sabah, Eastern Malaysia. Wells (1996) noted that
T. derasa
has been introduced during various mariculture efforts in areas including the United States (
e.g.,
Hawaii) and the Federated States of Micronesia. bin Othman
et al.
(2010) reports
T. derasa
from Australia, Palau, Papua New Guinea (PNG), and the Philippines.
Tridacna derasa
is noted as an introduced species in the Cook Islands and Samoa (introduced for aquaculture purposes) and also reported from Fiji, FSM, the Marshall Islands, New Caledonia, Solomon Islands, Tonga, and Vanuatu (CITES 2009).

EP26JN17.003

Tridacna derasa
preferentially inhabits clear offshore or oceanic waters away from high islands with significant run-off of freshwater (Munro 1992). For example, it is not recorded from the Papuan Barrier Reef running along the south coast of PNG, nor from the fringing reefs of the north coast, but it does occur within a few miles of the southeast point of mainland PNG (Munro 1992). Large
T. derasa
were also commonly found at 10 to 20 m depth in the clear oceanic conditions of the windward islands and barrier reefs of eastern Fiji (Adams
et al.,
1988). Lewis
et al.
(1988) reported that:

T. derasa
has a curious NW-SE distribution across the Indo-Malayan region, and is not found east of Tonga or in equatorial areas east of Solomon Islands. In Fiji, the species is generally confined to clear oceanic outer lagoon areas, within the protection of well-developed barrier or fringing reefs. Occurring near the surface down to 25 m,
T. derasa
occurs in greatest density in the windward (eastern) islands of the Fiji group. Very high numbers (hundreds/hectare) are occasionally noted. It is rare or absent from high island fringing reefs and lagoons where salinity and water clarity are reduced by freshwater runoff, and from unprotected areas. Until a size of typically 30 cm is reached, the species is weakly byssally attached to coral pieces or rubble.

Population Status and Abundance Trends

The petition does not provide estimates of population abundance or trends for
T. derasa;
however, the petition does provide some information on population status or trends from individual locations within the species' range. A small population of
T. derasa
(initial baseline survey counted 44 individuals) showed an annual mortality of 4.4 percent at Michaelmas Cay on the Great Barrier Reef between 1978 and 1985 (Pearson and Munro 1991). Rubec
et al.
(2001) notes that
T. derasa,
among other species, was depleted and no longer commercially harvestable in the Philippines, although the authors do not provide an original source of that information. Teitelbaum and Friedman (2008) refer to the extirpation of
T. derasa
in Vanuatu but do not provide a reference for that information. The authors also report that Vanuatu has a restocking program that includes
T. derasa.
Teitelbaum and Friedman (2008) report that the reintroduction of approximately 25,000
T. derasa
to Yap from neighboring Palau in 1984 resulted in only approximately 8 percent survival of the introduced

stock. However, these
T. derasa
matured, reproduced, and re-established viable populations on nearby reefs (Lindsay 1995). Surveys conducted by the Secretariat of the Pacific Community (PROC-Fish/C-CoFish programmes) noted the continued presence of
T. derasa
in Yap in low numbers in mid-2006.

The petitioner cites Tan and Yasin (2003), stating giant clams of all species but
T. crocea
are considered endangered in Malaysia. The authors mention underwater surveys that reveal “distribution of giant clams are widespread but their numbers are very low,” but the authors did not provide any references with any more detail or support for this information, which makes it difficult to interpret this information for individual species. Brown and Muskanofola (1985) found only one individual of
T. derasa
during a survey carried out in Karimun Jawa, a group of islands off the north coast of Central Java, Indonesia, surmising the species was essentially functionally extinct in this area. At another site in Indonesia, the petition cites Hernawan (2010), stating that they found small populations and evidence of recruitment failure in the six species found during a survey of Kei Kecil, Southeast-Maluku, including
T. derasa.
The authors conducted giant clam surveys in nine sites in this area. However, Indonesia encompasses thousands of islands and
T. derasa
occurs in other locations throughout Indonesia (Hernawan 2010). Therefore, these two studies represent a small sample of
T. derasa
abundance in Indonesian waters.

Hardy and Hardy (1969) did a seminal study of ecology of
Tridacna
in Palau in the 1960s where
T. derasa
and
T. gigas
made up the largest proportion of the standing crop biomass because of their size. Hester and Jones (1974) recorded densities of 50
T. gigas
and 33
T. derasa
per hectare at Helen Reef, Palau; the petition notes that this study was conducted before these stocks were “totally decimated by distant-water fishing vessels,” but provides no information or references to document this “decimation.”

While individually and collectively, the studies discussed in this section represent a small portion of
T. derasa'
s total geographic range, the small population sizes and extirpations of this species in small areas are spread throughout its range and are not confined to one or few areas that may be disproportionately affected by some negative impact. Therefore, the number and spatial distribution of small populations or local extirpations in the context of the species' range may be contributing to an elevated extinction risk for this species such that it warrants further investigation.

Threats to
T. derasa

Beyond the generalized threats to all giant clam species discussed above, the petition presents little information on threats to
T. derasa
specifically. According to Munro (1992), historical commercial fisheries appear to have been confined to long-range Taiwanese fishing vessels, which targeted the adductor muscles of the larger species (
e.g., T. gigas
and
T. derasa
). There are anecdotal claims in several of the references discussed above that harvest led to low population levels at certain study sites (
e.g.
Rubec
et al.,
2001, Teitelbaum and Friedman 2008, Tan and Yasin 2003, Brown and Muskanofola 1985, and Hernawan 2010), but none of those studies provide empirical evidence of declining trends or of potential causes of low population numbers. The petition cites Lewis
et al.
(1988), stating that the Fijian fishery for
T. derasa
landed over 218 tons over a 9-year period, with the largest annual harvest totaling 49.5 tons and which is “thought to have removed most of the available stock.” We find this to be a slight mischaracterization of what Lewis
et al.
(1988) state about
T. derasa
in Fiji based on 26 surveys between 1984-1987:

Tridacna derasa: Widespread throughout the group, but generally rare on the fringing reefs of the main islands where terrestrial influence is strong, and in the leeward islands (yasawas) where sheltered oceanic lagoons are generally wanting. In 1984-85, there were still abundant populations on various reefs in the windward (Lau, Lomaiviti) islands, but subsequent commercial harvest has considerably reduced these numbers. Isolated pockets still remain and should be protected. Densities on inhabited windward islands generally low, with remaining individuals in deeper water (10 m plus). Further commercial harvests for export should be prohibited.

According to CITES documents, commercial harvest for export is now prohibited in Fiji and the fisheries department cultures clams, including
T. derasa,
for restocking programs. Wild populations have been improving; currently reseeding occurs mostly in marine protected areas with 200 sites reseeded annually (CITES 2009). However, challenges remain for poaching at night.

A 2004 CITES trade review for
T. derasa
indicates that out of 11 countries where
T. derasa
is traded, one was assessed as “Urgent Concern” (Tonga), two as “Possible Concern,” and the remaining eight as “Least Concern.” The review also notes that international trade in
T. derasa
was reported from an additional 14 countries not selected for review and that for most countries no population monitoring seems to be in place and harvest and use of giant clams are inadequately regulated or not at all.

The petition cites Bliderg (2000), who studied the effect of increasing water temperature by 3 °C on cultured
T. derasa,
and several other species, for 24 hours. Results showed reduced gross production and decreased respiration of oxygen in response to the temperature increase however, different species of clams demonstrated different results, indicating different strategies for dealing with heat stress. None of the treated specimens exhibited any bleaching during the experiment. We acknowledge these results, but note they are not easily interpreted to determine potential individual or species level effects over time and/or space for
T. derasa.
The clams used in the experiment were cultured and not harvested from the wild. Cultured specimens are likely to experience much more uniform environments and are likely not acclimated to the common daily fluctuations in many environmental parameters experienced in the wild. As such, their responses to abrupt changes in their environment may differ from those of wild specimens. Given the heterogeneity of the species' habitat and current environmental conditions across its range, these results are not compelling evidence of a threat related to increased water temperature that is acting or will act on
T. derasa
to the extent that the petitioned action may be warranted.

Conclusion

In conclusion, the information provided on threats for this species is limited and by itself would not be considered substantial information indicating the petitioned action may be warranted. The individual studies presented are not compelling evidence of species level concerns for reasons discussed above, however, taken together they provide sufficient evidence such that further investigation is warranted. The evidence presented of small, localized populations or extirpations in different parts of the species range is compelling enough to conclude that the petitioned action may be warranted. The best available information on all potential threats to the species will be evaluated in a forthcoming status review to determine what has potentially caused the observed declines and extirpations, and the extent to which such declines have occurred.

Tridacna gigas

Species Description

Tridacna gigas
is the largest of all the giant clam species, growing to a maximum shell length of 137 cm, with weights in excess of 200 kg. However, the species is most commonly found at lengths up to 80 cm (Neo
et al.,
2015; Kinch and Teitelbam 2009). The shell exterior is off-white and is often strongly encrusted with marine growths. The shell interior is porcellaneous white, and the mantle is yellowish brown to olive green, with numerous, small, brilliant blue-green rings, particularly along the lateral edges (Kinch and Teitelbaum 2009). This species may be readily identified by its size and by the elongate, triangular projections of the upper margins of the shells (Lucas 1988).

Life History

In addition to the
Life History
section above on giant clams in general, the petition provided some species-specific life history information for
T. gigas.
The petition cited Braley (1988), who found that the optimal reproductive season for
T. gigas
sampled from Michaelmas Cay and Myrmidon Reef in Australia was October to February. Munro (1992) noted that spawning of
T. gigas
is restricted to a short summer season in the central region of the Great Barrier Reef. For
T. gigas,
von Bertalanffy growth parameter estimates include an asymptotic length (L∞) of 80 cm, growth coefficient (K) of 0.105, and a theoretical date of `birth' (t0) of 0.145 (Neo
et al.,
2015). According to Branstetter (1990), growth coefficients (K) falling in the range of 0.05-0.10/yr are for slow-growing species; 0.1-0.2 for a moderate-growing species; and 0.2-0.5 for a fast-growing species. Under these parameters, the giant clam
T. gigas
is considered a moderate-growing species. However, the petition notes that there are major differences between typical non-symbiotic bivalves and
T. gigas
regarding the relative allocations of energy to respiration and growth. For example, Klumpp
et al.
(1992) showed that
T. gigas
is an efficient filter-feeder and that carbon derived from filter-feeding in Great Barrier Reef waters supplies substantial proportions of the total carbon needed for respiration and growth.

Range, Habitat, and Distribution

Prior to the rapid escalation of the aquarium trade,
T. gigas
could be found throughout the shallow tropical waters of the Indian and Pacific oceans; however, the recent fossil record, together with historical accounts show that the range of
T. gigas
has been dramatically reduced (see the
Population Status and Abundance Trends
section below; Munro 1992; bin Othman
et al.,
2010). The species' range once extended from East Africa to Micronesia and Australia to Japan. Like other giant clam species,
T. gigas
is typically associated with coral reefs and can be found in many habitats, whether high- or low-islands, lagoons or fringing reefs (Munro 1992).

EP26JN17.004

Population Status and Abundance Trends

The petition does not provide overall estimates of population abundance or trends for
T. gigas.
The petition does provide several lines of evidence that
T. gigas
has experienced a number of local extirpations in various locations throughout its range. Munro (1992) reports that while relict stocks of
T. gigas
occur in Indonesian, Malaysian, and Philippines waters and possibly on the west coast of Thailand and in southern Burma, in most cases it appears that these stocks are functionally extinct because of the wide dispersal of the survivors, making successful fertilization unlikely. In a more recent survey from Indonesian waters,
T. gigas
was surprisingly found in Ohoimas, where it was previously believed to be extinct (Hernawan 2010). However, only four individuals were found in only one of nine sites surveyed. Additionally, several sources (Munro 1992; Teitelbaum and Friedman 2008; Kinch and Teitelbaum 2009) note

local extirpations of
T. gigas
have occurred in the Commonwealth of the Northern Mariana Islands, Federated States of Micronesia (Yap, Chuuk, Pohnpei, and Kosrae), Fiji, Guam, New Caledonia, Taiwan, Ryuku Islands (Japan), and Vanuatu. Neo and Todd (2012a, 2013) report that
T. gigas
is also nationally extinct in Singapore. In Australia, the
T. gigas
population from the Great Barrier Reef is essentially a relict population, consisting primarily of large adult clams; the lack of younger, faster-growing
T. gigas
clams is likely the reason for the species' low annual production of new biomass (Neo
et al.,
2015). Further, Kinch and Teitelbaum (2009) also report declining stocks of
T. gigas
across the three main island groups in Kiribati.

Thus, while quantitative abundance estimates are unavailable for
T. gigas
throughout its range, the numerous local extirpations of
T. gigas
documented across a large portion of its range may be contributing to an elevated extinction risk for this species such that it warrants further investigation.

Threats to
T. gigas

As noted previously, giant clams in general are considered a valuable fishery target in many countries, with uses for both local consumption and commercial trade. Based on information in the petition and our files, it is clear that
T. gigas
is the most heavily exploited species of all giant clams, which has likely led to its substantial declines and extirpations in a number of locations throughout its range. As discussed previously in the general threats section for giant clams, the petition emphasizes the threat of the growing giant clam industry in China, largely the result of improved carving techniques, tourism in Hainan, China, the growth in e-commerce, and the domestic Chinese wholesale market (Larson 2016). The petition also raises concerns that stricter enforcement of the trade in ivory products has diverted attention to giant clam shells (McManus 2016). The petition points out that the giant clam (
T. gigas
) is preferentially targeted for international trade due to its large size and because it is considered a desirable luxury item in China thought to confer supernatural powers and improve health. As noted previously, a pair of high quality shells (from one individual) can fetch up to US $150,000. Therefore, the high value and demand for large
T. gigas
shells may be a driving factor contributing to overutilization of the species.

Conclusion

Overall, we conclude that the information presented in the petition and our files provides substantial evidence that the petitioned action for
T. gigas
may be warranted. This species has likely experienced significant population declines and local extirpations in several locations throughout its range, likely due to historical and ongoing overutilization for commercial purposes and further investigation is warranted. The best available information on its overall status and all potential threats to the species will be evaluated in a forthcoming status review.

Tridacna squamosa

Species Description

Although the petition notes that
T. squamosa,
also known as the fluted clam, grows to 19 cm based on Neo
et al.
(2015), we find this information is in error. Neo
et al.
(2015) report shell lengths of up to 40 cm for the species, and information in our files suggests it is most commonly found at lengths up to 30 cm (Kinch and Teitelbaum 2009). The shell exterior is described as “greyish white, often with different hues of orange, yellow, or pink to mauve, and with the blade-like scales commonly of different shades or color” (Kinch and Teitelbaum 2009). The shell interior is porcelaneous white, occasionally tinged with orange, and the mantle is mottled in various mixes of green, blue, brown, orange, and yellow (Kinch and Teitelbaum 2009).

Life History

Aside from the general giant clam life history information already discussed previously in the
Giant Clam Life History
section, the petition provided little information specific to
T. squamosa. Tridacna squamosa
is a mixotroph whose photoautotrophic range is extended by heterotrophy. We found that
T. squamosa
reaches sexual maturity at sizes of 6 to 16 cm, which equates to a first year of maturity at approximately 4 years old (CITES 2004a).

Range, Habitat, and Distribution

Tridacna squamosa
has a widespread distribution across the Indo-Pacific, but is slightly more restricted than
T. maxima
(Munro 1992). Its range extends from the Red Sea and East African coast across the Indo-Pacific to the Pitcairn Islands. It has also been introduced in Hawaii (CITES 2004a). The species' range also extends north to southern Japan, and south to Australia and the Great Barrier Reef (bin Othman
et al.,
2010). This range description reflects the recent range extension of
T. squamosa
to French Polynesia as a result of observations by Gilbert
et al.
(2007). The petition notes that
T. squamosa
occurred in Singapore and the United States historically; however, there is no supporting reference or evidence provided of the species' occurrence in the United States or its territories.

EP26JN17.005

Tridacna squamosa
is usually found near reefs or on sand; it is found attached by its byssus to the surface of coral reefs, usually in moderately protected areas such as reef moats in littoral and shallow water to a depth of 20 m (Kinch and Teitelbaum 2009). This species tends to prefer fairly sheltered lagoon environments next to high islands; however,
T. squamosa
appears to be excluded by
T. maxima
in the closed atoll lagoons of Polynesia (Munro 1992). Neo
et al.
(2009) found that
T. squamosa
larvae, like many reef invertebrates, prefer substrate with crustose coralline algae.
Tridacna squamosa
is also commonly found amongst branching corals (staghorn,
Acropora
spp.; CITES 2004a)

Population Status and Abundance Trends

The petition provides limited some information regarding the species
'
population status and trends from Singapore, Samoa, and individual sites in Malaysia, Philippines, Indonesia, and Thailand.

The petitioner states that
T. squamosa
is functionally extinct in Samoa based on a study from western Samoa (Zann and Mulipola 1995). This study relied on a range of low technology methods developed for rapid environmental and fisheries assessments. Fisheries surveys were conducted via interviews and surveys of fishermen and households, and results were compared with commercial market landings from the Apia municipal fish market on the island of Upolu. From 1985 to1990, annual landings of all giant clams dropped from 10 metric tons to 0.1 metric tons and field surveys indicated that
T. squamosa
was so rare it was functionally extinct. The authors note that fishing effort also declined around 35 percent between 1983 and 1991, which is considered to be partially responsible for the declines in landings, although other factors likely contributed (
e.g.,
overfishing of inshore stocks, use of destructive fishing techniques, etc.). Information in our files suggests that this species has been the subject of restocking efforts in Samoa. Since 1988,
T. squamosa
has been trans-located from Palau, Tokelau, and Fiji to restock populations in Samoa under the Samoan Community-based Fisheries Management program (Kinch and Teitelbaum 2009).

In Singapore, Neo and Todd (2012a) surveyed 29 reefs, covering an estimated 87,515 m
2
and observed 28
T. squamosa
individuals, which was double the number observed in a 2003 survey of only 7 reefs and a little over 9,000 m
2
by Guest
et al.
(2008). However, Neo and Todd (2012a) estimate
T. squamosa
density to be 0.032 per 100 m
2
, which is five times lower than the 0.16 per 100 m
2
measured in 2003 (Guest
et al.,
2008). They go on to propose that habitat loss, exploitation, and or sediment have synergistically led to the endangered status of
T. squamosa
in Singapore's waters. Neo and Todd (2013) make a similar conclusion, stating that “the low density and scattered distribution of the remaining
T. squamosa
in Singapore are likely to significantly inhibit any natural recovery of local stocks.” However, the authors specifically make the point that the status of a species at a small scale (individual country or an island as may be the case for Singapore) is most often not representative of its global status. Any species, especially one with a large range like
T. squamosa,
will have variable statuses at smaller scales in different habitats due to a variety of factors. Singapore is a small and densely populated island nation known for particularly high anthropogenic impacts in its nearshore waters. The information in Neo and Todd (2012a 2012b and 2013) is informative for resource managers in Singapore and indicates a very low population and density of
T. squamosa.
However, it is unclear how the current information relates to historical abundance of this species at this location. In addition, it is not necessarily useful for assessing the global status of
T. squamosa
because Singapore is a very small proportion of the overall species' range and is not a representative environment of the rest of the species' range.

The petitioner cites Tan and Yasin (2003), stating that giant clams of all species but
T. crocea
are considered

endangered in Malaysia. As discussed previously, the authors of this study mention underwater surveys that reveal that the “distribution of giant clams are widespread but their numbers are very low.” However, there are no references provided by the authors to provide any more detail or support for this information, which makes it difficult to interpret this information for individual species. The only species-specific information for
T. squamosa
in this reference is that it occurs in Malaysian waters.

The petitioner cites Thamrongnavasawat
et al.
(2001) as saying
T. squamosa
are now considered “scarce” throughout Thailand. However, the link provided in the bibliography to access this reference was not functional, and we were otherwise unable to obtain and review this reference to determine what the authors meant by “scarce” or on what evidence this statement was based. However, the petitioner provides other studies from Thailand indicating that the species has likely undergone significant declines in this area. For example, Chantrapornsyl
et al.
(1996) documented heavy exploitation and local extirpation of
T. squamosa
in the Andaman Sea. Kittiwattanawong (1997) also concluded that
T. squamosa
was rare in the same area.
Tridacna squamosa
was also deemed “near extinct” in Mo Ko Surin National Park in Thailand (Dolorsa and Schoppe 2005).

Villanoy
et al.
(1988) examined average size frequency distributions of
T. squamosa
harvested from the Sulu Archipelago and Southern Palawan areas in the Philippines from 1978 to 1985, and determined that estimates of exploitation rates indicate that populations of these species are overexploited. The petitioner asserts that these findings have serious implications given that the Sulu Archipelago and Southern Palawan are thought to be the last strongholds of giant clams species occurring in Philippine waters. Dolorosa and Schoppe (2005) also report that
T. squamosa
had very low densities in surveys conducted in Tubbataha Reef National Marine Park in the Philippines. The authors note that because of the species' low settlement, survival and growth on live coral substrate, it would take hundreds of years for the stock to be re-established, particularly in isolated areas. However, the authors also note that the numbers seen at Tubbataha Marine Park are significantly lower than in other areas of the Philippines; therefore, the situation in the marine park may not be representative of the species' status across the Philippines as a whole (Dolorosa and Schoppe 2005). The petitioner also cited a stock assessment conducted in Eastern Visayas, in the Philippines (Salazar
et al.,
1999), which showed that while
T. squamosa
are common in the Samar Sea and San Pedro Bay, most of the giant clams surveyed were in the juvenile stage with no breeders left to repopulate the area. However, the Marine Science Institute (MSI) at the University of the Philippines has a long and successful record of rearing, having cultured giant clams to restore depleted supplies for the last 20 years. In fact, more than 40 sites have received cultured clams and MSI promotes giant clam farming as a sustainable livelihood with restocking activities occurring in collaboration with local groups (bin Othman
et al.,
2010).

As discussed previously, the petition also broadly states that all six giant clam species occurring in Indonesia, including
T. squamosa,
are experiencing recruitment failure based on a single study from Kei Kecil, Southeast-Maluku, Indonesia (Hernawan 2010). Hernawan (2010) conducted giant clam surveys in 9 sites; however, Indonesia encompasses thousands of islands and
T. squamosa
occurs in several other locations throughout Indonesia (Hernawan 2010). Thus, this study represents a very small sample of
T. squamosa
abundance in Indonesian waters, with no evidence provided to suggest that recruitment failure of
T. squamosa
is occurring throughout Indonesia.

Overall, given the extensive range of
T. squamosa,
the information provided in the petition is limited regarding the population status and abundance trends of the species throughout its range. While we acknowledge that in some locations (primarily Southeast Asia), abundance and/or density of
T. squamosa
may be low, the petition did not provide any information regarding the species' status from a large majority of its range. For example, in addition to countries in Southeast Asia,
T. squamosa
can be found throughout Oceania (
e.g.,
Australasia, Melanesia, Micronesia and Polynesia). The species also inhabits coastlines of the Indian Ocean and has a relatively cosmopolitan distribution in this region (bin Othman
et al.,
2010). Thus, no information was presented in the petition for an entire two thirds or more of the species' range (
i.e.,
Oceania (with the exception of Samoa), eastern Africa, and the Indian Ocean). However, a lack of information on its own does not mean the action may not be warranted if the lack of information itself may be considered a risk to the species. In this case, given that the only information we have indicates historical declines, low population levels, and notably local extirpations in some locations, we conclude that the information presented in the petition regarding the species' abundance and population trends is compelling enough to warrant further investigation in a forthcoming status review.

Threats to
T. squamosa

Given that
T. squamosa
is a large, free-living species of giant clam, it is easier to remove from the reef (Neo and Todd 2013), which makes it more susceptible to harvest for local consumption and/or commercial purposes. Some information (albeit limited) provided by the petition suggests that
T. squamosa
may be overexploited in some locations. As discussed earlier in the
Population Status and Abundance Trends
section for
T. squamosa,
estimates of exploitation rates from the Sulu Archipelago and Southern Palawan areas of the Philippines from 1978 to 1985 indicate that populations of
T. squamosa
were overexploited.

Information in our files indicates that
T. squamosa
is important in the subsistence fishery of Papua New Guinea. A commercial fishery for giant clams previously operated in the Milne Bay Province, whereby approximately 150 tonnes of giant clam adductor muscle were exported, as well as one large shipment of 16 tonnes of giant clam shells. However, this fishery has been closed since 2000 and we could not find any additional information in our files regarding the utilization of
T. squamosa
in Papua New Guinea. We also found some information regarding the reported functional extinction of this species in Samoan waters, and acknowledge that the significantly low density of
T. squamosa
in Samoa is largely attributed to overfishing (Kinch and Teitelbaum 2009); however, as noted previously, to mitigate low populations, restocking efforts have been underway in Samoa since the 1980s, and from 1998 to 2000, Samoa has seen the importation of several giant clam species, both larvae and ‘yearlings,’ for restocking purposes under the Samoan Community-based Fisheries Management program (Kinch and Teitelbaum 2009). Nevertheless, we cannot confirm whether this restocking program has been successful for
T. squamosa.

In terms of commercial trade, a significant trade review was conducted in 2004 for 27 countries that trade in

T.

squamosa

to identify potential areas of concern. Of the 27 countries reviewed, 24 were deemed to be of “least concern” for various reasons; the respective countries had either not reported any trade, or trade levels were minimal or export numbers were low. Two countries (Marshall Is

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2017-13275. Public record. Not legal advice.