# Endangered and Threatened Wildlife and Plants; Designation of Critical Habitat for the Gulf Sturgeon

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A02-13620

## Record

- **Collection:** Federal Register
- **Document type:** Proposed Rule
- **Published:** June 6, 2002
- **Citation:** 67 FR 39107

## Text

DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
RIN 1018-AI23
DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
50 CFR Part 226
[Docket No. 0202522126-2126-01; I.D. 052002A]
RIN 0648-AQ03
Endangered and Threatened Wildlife and Plants; Designation of Critical Habitat for the Gulf Sturgeon

AGENCY:

Fish and Wildlife Service, Interior, and National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Commerce.

ACTION:

Proposed rule.

SUMMARY:

We, the Fish and Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS), collectively “the Services,” propose to designate critical habitat for the Gulf sturgeon (
Acipenser oxyrinchus desotoi
), a threatened species listed under the Endangered Species Act of 1973, as amended (Act). We propose 14 geographic areas among the Gulf of Mexico rivers and tributaries as critical habitat for the Gulf sturgeon. These 14 geographic areas (units) encompass approximately 2,544 river kilometers (rkm) (1,580 river miles (rmi)) and 6,042 square kilometers (km
2
) (2,333 square miles (mi
2
)) of estuarine and marine habitat.

Critical habitat identifies specific areas that are essential to the conservation of a listed species, and that may require special management considerations or protection. If this proposal is made final, section 7(a)(2) of the Act requires that Federal agencies ensure that actions they fund, permit, or carry out are not likely to result in the destruction or adverse modification of critical habitat. The regulatory effect of the critical habitat designation does not extend beyond those activities funded, permitted, or carried out by Federal agencies. State or private actions, with no Federal involvement, are not affected.

Section 4 of the Act requires us to consider the economic and other relevant impacts of specifying any particular area as critical habitat. We hereby solicit data and comments from the public on all aspects of this proposal, including data on the economic and other impacts of the designation.

DATES:

Comments:
We will accept comments until September 23, 2002.

Public Hearings:
We have scheduled four public hearings for this proposal. We will hold public informational meetings prior to each public hearing at the hearing location. The public information sessions will start at 5:00 p.m. and end at 6:30 p.m.. The formal public hearings will start at 7:00 p.m. and end at 9:00 p.m. on the dates indicated:

(1) August 19, 2002, Live Oak, FL

(2) August 20, 2002, Defuniak Springs, FL

(3) August 21, 2002, Biloxi, MS

(4) August 22, 2002, Kenner, LA

All comments received during the comment period, both written and presented at public hearings, will receive equal consideration.

ADDRESSES:

Comments:
If you wish to comment, you may submit your comments by any one of several methods:

(1) You may submit written comments and information to the Panama City Field Office, addressed to Patty Kelly, U.S. Fish and Wildlife Service, 1601 Balboa Avenue, Panama City, FL 32405.

(2) You may hand-deliver written comments to the Panama City Field Office, at the above address, or fax your comments to 850/763-2177.

(3) You may send comments by electronic mail (e-mail) to
gulfsturgeon@fws.gov.
For directions on electronic filing of comments, see the “Public Comments Solicited” section.

Comments and materials received, as well as supporting documentation used in the preparation of this proposed rule, will be available for public inspection, by appointment, during normal business hours at the above address.

Public Hearings

(1) Suwannee River Water Management District, 9225 C.R. 49, Live Oak, FL 32060.

(2) City of Defuniak Springs, 71 U.S. Highway 90 West, Chautauqua Building, Museum Room, Defuniak Springs, FL 32433.

(3) J.L. Scott Marine Ed Center, 115 Beach Boulevard, Biloxi, MS 39530.

(4) Hilton New Orleans Airport, 901 Airline Drive, Kenner, LA 70062.

FOR FURTHER INFORMATION CONTACT:

Patty Kelly, FWS, at the above address (telephone 850/769-0552, extension 228; facsimile 850/763-2177) with questions concerning units 1 to 7; or Stephania Bolden, NMFS, at 9721 Executive Center Drive North, St. Petersburg, FL 33702-2449, (telephone 727/570-5312; facsimile 727/570-5517) with questions concerning units 8 to 14.

SUPPLEMENTARY INFORMATION:

Background

The Gulf sturgeon (
Acipenser oxyrinchus
(=
oxyrhynchus
)
desotoi
), also known as the Gulf of Mexico sturgeon, is an anadromous fish (ascending rivers from the sea for breeding), inhabiting coastal rivers from Louisiana to Florida during the warmer months and overwintering in estuaries, bays, and the Gulf of Mexico. It is a nearly cylindrical primitive fish embedded with bony plates or scutes. The snout is greatly extended with four barbels in front of the mouth and the suction type mouth is located beneath the head. The upper lobe of the tail is longer than the lower lobe. Adults range from 1.8 to 2.4 meters (m) (6 to 8 feet (ft)) in length, with adult females larger than males. The Gulf sturgeon is distinguished from the geographically disjunct Atlantic coast subspecies (
A. o. oxyrinchus
) by its longer head, pectoral fins, and spleen (Vladykov 1955, Wooley 1985).

Distribution and Status

Historically, the Gulf sturgeon occurred from the Mississippi River to Tampa Bay. Its present range extends from Lake Pontchartrain and the Pearl River system in Louisiana and Mississippi east to the Suwannee River in Florida. Sporadic occurrences have been recorded as far west as the Rio Grande River between Texas and Mexico, and as far east and south as Florida Bay (Wooley and Crateau 1985, Reynolds 1993).

In the late 19th century and early 20th century, the Gulf sturgeon supported an important commercial fishery, providing eggs for caviar, flesh for smoked fish, and swim bladders for isinglass, a gelatin used in food products and glues (Carr 1983). Gulf sturgeon numbers declined due to overfishing throughout most of the 20th century. The decline was exacerbated by habitat loss associated with the construction of water control structures, such as dams and sills, mostly after 1950. In several rivers throughout its range, dams have severely restricted sturgeon access to historic migration routes and spawning areas (Boschung 1976, Wooley and Crateau 1985, McDowell 1988).

On September 30, 1991, we listed the Gulf sturgeon as a threatened species under the Act (16 U.S.C. 1531
et seq.
) (56 FR 49653). Other threats and potential threats identified in the listing

rule included modifications to habitat associated with dredged material disposal, de-snagging, and other navigation maintenance activities; incidental take by commercial fishermen; poor water quality associated with contamination by pesticides, heavy metals, and industrial contaminants; aquaculture and incidental or accidental introductions; and the Gulf sturgeon's slow growth and late maturation. The Gulf sturgeon listing rule and the Gulf Sturgeon Recovery/Management Plan (FWS
et al.
1995), which was approved by the Services and the Gulf States Marine Fisheries Commission, provide a more detailed discussion of the reasons for the species' decline and threats to surviving populations.

The Gulf Sturgeon Recovery/Management Plan (FWS
et al.
1995) recommended that genetic studies be done to determine geographically distinct management units. Some work in this regard has been completed (Waldman and Wirgin 1998), but we have not formally adopted management units at this time. For purposes of this proposed rule, we have used the term subpopulation to subdivide the Gulf sturgeon population based on geography, degree of connectedness, and genetic interchange (Lande and Barrowclough 1987). Seven subpopulations are described below.

Feeding Habits

Gulf sturgeon feeding habits in freshwater vary depending on the fish's life history stage (
i.e.
, young-of-year, juvenile, subadult, adult). Young-of-year Gulf sturgeon remain in freshwater through early February feeding on aquatic invertebrates and detritus (Mason and Clugston 1993, Sulak and Clugston 1999). Juvenile feeding is believed to be widely distributed, exploiting scarce food resources throughout the river, including aquatic insects (
e.g.
, mayflies and caddisflies), worms (oligochaetes), and bivalve molluscs (Huff 1975, Mason and Clugston 1993). Mason and Clugston (1993) found that subadult and adult Gulf sturgeon collected during June and October do not feed in fresh water.

Many reports indicate that adult and subadult Gulf sturgeon fast and lose up to 30 percent of their total body weight while in fresh water, and then compensate the loss during winter feeding in the sea (Carr 1983, Wooley and Crateau 1985, Clugston
et al.
1995, Morrow
et al.
1998a, Heise
et al.
1999a, Sulak and Clugston 1999, Ross
et al.
2000). Gu
et al.
(2001) tested the hypothesis that Gulf sturgeon do not feed significantly during their annual residence in fresh waters by comparing stable carbon isotope ratios of tissue samples from subadult and adult Suwannee River Gulf sturgeon and their potential fresh water and marine food sources. A large difference in isotope ratios between fresh water food sources and fish muscle tissue suggests that Gulf sturgeon do not feed significantly in fresh waters. The isotope similarity between Gulf sturgeon and marine food resources strongly indicates that this species relies almost entirely on the marine food web for its growth (Gu
et al.
2001).

Once Gulf sturgeon leave the river, having spent at least 6 months in the river fasting, we presume that they immediately begin feeding. Upon exiting the rivers, Gulf sturgeon are found in high concentrations near their natal river mouths. Lakes and bays at the mouths of the river systems where Gulf sturgeon occur are important because they offer the first opportunity for Gulf sturgeon exiting their natal rivers to forage. Gulf sturgeon rely almost entirely on estuarine and marine food for their growth (Gu
et al.
2001). Gulf sturgeon must be able to consume sufficient quantities of prey while in estuarine and marine waters to regain the weight they lose while in the river system and to maintain positive growth on a yearly basis. In addition, reproductive Gulf sturgeon require additional food resources to obtain sufficient energy necessary for reproduction (Fox
et al.
in press, Murie and Parkyn pers. comm. 2002).

Adult and subadult Gulf sturgeon, during marine and estuarine periods, are thought to forage opportunistically (Huff 1975), primarily on benthic (bottom dwelling) invertebrates. Gut content analyses have indicated that the Gulf sturgeon's diet is predominated by amphipods, lancelets, polychaetes, gastropods, shrimp, isopods, molluscs, and crustaceans (Huff 1975, Mason and Clugston 1993, Carr
et al.
1996b, Fox
et al.
2000, Fox
et al.
in press). Gulf sturgeon from the Suwannee River subpopulation are known to forage on brachiopods (D. Murie and D. Parkyn, University of Florida (UF), pers. comm. 2002); however this is not a documented prey of other subpopulations. Ghost shrimp (
Lepidophthalmus louisianensis
) and the haustoriid amphipod (
Lepidactylus
sp.) are strongly suspected to be the most important prey for adult Gulf sturgeon over 20 kilograms (kg) (44 pounds (lb)) (Heard
et al.
2000, Fox
et al.
in press). This hypothesis is based on the following evidence—(1) Gulf sturgeon have been consistently located and observed actively feeding in areas where numerous burrows similar to those occupied by ghost shrimp exist (Fox
et al.
2000) and with high densities of both ghost shrimp and haustoriid amphipods (Heard
et al.
2000), (2) the digestive tracts of two adult Gulf sturgeon that died during netting operations contained numerous ghost shrimp (Fox
et al.
2000), (3) stomach contents of a 30 kg (67 lb) sturgeon taken in the upper portion of Choctawhatchee Bay contained more than 100 individual haustoriid amphipods and 67 ghost shrimp (Heard
et al.
2000), and (4) one-third of 157 sturgeon guts analyzed by Carr
et al.
(1996b) contained exclusively brachipods and ghost shrimp.

Reproduction

Gulf sturgeon are long-lived, with some individuals reaching at least 42 years in age (Huff 1975). Age at sexual maturity for females ranges from 8 to 17 years, and for males from 7 to 21 years (Huff 1975). Gulf sturgeon eggs are demersal (they are heavy and sink to the bottom), adhesive, and vary in color from gray to brown to black (Vladykov 1963, Huff 1975, Parauka
et al.
1991). Chapman
et al.
(1993) estimated that mature female Gulf sturgeon produce an average of 400,000 eggs. Habitat at egg collection sites consist of limestone bluffs and outcroppings, cobble, limestone bedrock covered with gravel and small cobble, gravel, and sand (Marchant and Shutters 1996, Sulak and Clugston 1999, Fox
et al.
2000). A dense matrix of gravel or cobble is probably essential for Gulf sturgeon egg adhesion and the sheltering of the yolk sac larvae, and is a habitat the adults apparently select (Sulak and Clugston 1999). Other substrates identified as possible spawning habitat include marl (clay with substantial calcium carbonate), soapstone, or hard clay (W. Slack, Mississippi Museum of Natural Science, pers. comm. 2002; F. Parauka, FWS, pers. comm. 2002). Water depths at egg collection sites ranged from 1.4 to 7.9 m (4.6 to 26 ft), with temperatures ranging from 18.3 to 22.0 degrees Celsius (°C) (64.9 to 71.6 degrees Fahrenheit (°F)) (Fox
et al.
2000). Laboratory experiments indicated optimal water temperature for survival of Gulf sturgeon larvae is between 15 and 20°C (59 and 68°F), with low tolerance to temperatures above 25°C (77°F) (Chapman and Carr 1995).

Sulak and Clugston (1999) suggested that sturgeon spawning activity in the Suwannee River is related to the lunar phase of the moon, but only after the water temperature has risen to 17°C (62.6°F). Fox
et al.
(in press) however, found little evidence of spawning associated with lunar cycles within the Choctawhatchee River system.

Spawning in the Suwannee River occurs during the general period of spring high water, when ionic conductivity and calcium ion concentration are most favorable for egg development and adhesion (Sulak and Clugston 1999). Fox
et al.
(in press) found no clear pattern between timing of river entrance and flow patterns on the Choctawhatchee River.

Atlantic sturgeon (
A. oxyrhynchus
) exhibit a long inter-spawning period, with females spawning at intervals ranging from every 3 to 5 years, and males every 1 to 5 years (Smith 1985). It is believed that Gulf sturgeon exhibit similar behavior, as male Gulf sturgeon are capable of annual spawning, and females require more than one year between spawning events (Huff 1975, Fox
et al.
2000).

Fresh Water Habitat

In the spring (March to May), adult and subadult Gulf sturgeon return to their natal river, where sexually mature sturgeon spawn, and the population spends until October or November (6 to 8 months) in fresh water rivers (Odenkirk 1989, Foster 1993, Clugston
et al.
1995, Fox
et al.
2000). During their early life history stages, sturgeon require bedrock and clean gravel or cobble substrate for eggs to adhere to and for shelter for developing larvae (Sulak and Clugston 1998). Young-of-year appear to disperse widely, using extensive portions of the river as nursery habitat. They are typically found on sandbars and sand shoals over rippled bottom and in shallow, relatively open, unstructured areas. This dispersion may be an adaptation to maximize scarce food resources (Randall and Sulak 1999). Clugston
et al.
(1995) reported that young Gulf sturgeon in the Suwannee River, weighing between 0.3 and 2.4 kg (0.7 and 5.3 lb), remain in the vicinity of the river mouth and estuary during the winter and spring.

Adult Gulf sturgeon spawn in upper river reaches. On some river systems such as the Pascagoula River and Apalachicola River, adult and subadult Gulf sturgeon remain near the spawning grounds throughout the summer months (Wooley and Crateau 1985, Ross
et al.
2001b). However, in other rivers Gulf sturgeon spawn and move downstream to areas referred to as summer resting or holding areas. Adults and subadults are not distributed uniformly throughout the river, but show a preference for these discrete areas usually located in lower and middle river reaches (Potak
et al.
1995). Often, these resting areas are located in close proximity to springs throughout the warmest months of the year, but not located within a spring or thermal plume emanating from a spring (Clugston
et al.
1995, Potak
et al.
1995, Foster and Clugston 1997). These resting areas are also often located in deep holes or shallow areas along straight-aways ranging from 2 to 19 m (6.6 to 62.3 ft) deep (Wooley and Crateau 1985, Morrow
et al.
1998a, Ross et al. 2001a and b, Craft
et al.
2001, Hightower
et al.
in press). The substrates consisted of mixtures of limerock and sand (Clugston
et al.
1995), sand and gravel (Wooley and Crateau 1985, Morrow
et al.
1998a), or just sandy substrate (Hightower
et al.
in press).

River flow may serve as an environmental cue that governs both sturgeon migration and spawning (Chapman and Carr 1995). If the flow rate is too high, sturgeon in several life-history stages can be adversely affected. Data describing the sturgeon's swimming ability in the Suwannee River strongly indicated that they cannot continually swim against prevailing currents of greater than 1 to 2 m per second (3.2 to 6.6 ft per second) (Wakeford 2001). If the flow is too strong, eggs might not be able to settle on and adhere to suitable substrate (Wakeford 2001). Flow velocity needs for age zero sturgeon may vary depending on substrate type. Chan
et al.
(1997) found that age zero Gulf sturgeon under laboratory conditions exposed to water velocities over 12 centimeters per second (cm/s) (4.7 inches per second (in/s)) preferred a cobble substrate, but favored water velocities under 12 cm/s (4.7 in/s) and then utilized a variety of substrates (sand, gravel, and cobble). Natural surface and groundwater discharges influence a river's characteristic fluctuations in volume, depth, and velocity (Leitman
et al.
1993, Albertson and Torak 2002).

Gulf sturgeon require large areas of diverse habitat that have natural variations in water flow, velocity, temperature, and turbidity (FWS
et al.
1995, Wakeford 2001). Change in temperature is one of the most important factors in initiating sturgeon migration (Wooley and Crateau 1985, Chapman and Carr 1995, Foster and Clugston 1997) (see the “Migration” section for temperature ranges). Laboratory experiments show that Gulf sturgeon eggs, embryos, and larvae have the highest survival rates when temperatures are between 15 and 20°C (59 and 68°F). Mortality rates of Gulf sturgeon gametes and embryos are highest when temperatures are 25°C (77°F) and above (Chapman and Carr 1995) (see “Reproduction” section for more detail). Researchers have documented temperature ranges at Gulf sturgeon resting areas between 15.3 and 33.7°C (59.5 and 92.7°F) with dissolved oxygen levels between 5.6 and 9.1 milligrams per liter (mg/l) (Morrow
et al.
1998a, Hightower
et al.
in press).

In comparison to other fish species, sturgeon have a limited behavioral and physiological capacity to respond to hypoxia (insufficient oxygen levels) (Secor and Niklitschek 2001). Basal metabolism, growth, consumption, and survival are sensitive to changes in oxygen levels (Secor and Niklitschek 2001). Temperatures greater than 20°C (68°F) amplify the effect of hypoxia on sturgeon and other fishes (Coutant 1987). In laboratory experiments, young shortnose sturgeon (
A. brevirostrum
) (less than 77 days old) died at oxygen levels of 3.0 mg/l and all sturgeon died at oxygen levels of 2.0 mg/l (Jenkins
et al.
1993). Data concerning the temperature, oxygen, and current velocity requirements of cultured sturgeon are being collected. Researchers plan to use this information to develop detailed information on water flow requirements of wild sturgeon throughout different phases of their fresh water residence (Wakeford 2001).

Estuarine and Marine Habitat

Subadult and adult Gulf sturgeon spend cool months (October or November through March or April) in estuarine areas, bays, or in the Gulf of Mexico (Odenkirk 1989, Foster 1993, Clugston
et al.
1995). Studies of subadult Gulf sturgeon (ages 4 to 7) in Choctawhatchee Bay found that 78 percent of tagged fish remained in the bay the entire winter, while 13 percent ventured into a connecting bay. Possibly 9 percent spent some time in the Gulf of Mexico (FWS 1998). Adult Gulf sturgeon are more likely to overwinter in the Gulf of Mexico, with 40 percent of the tagged adults presumed to have left Choctawhatchee Bay and spent extended periods of time in the Gulf of Mexico (Fox and Hightower 1998a). In contrast, Gulf sturgeon from the Suwannee River subpopulation are known to migrate into the nearshore waters, where they remain for up to two months and then depart to unknown feeding locations in the open Gulf of Mexico (Carr
et al.
1996b, Edwards
et al.
in prep.).

Subadult Gulf sturgeon show a preference for sandy shoreline habitats with water depths less than 3.5 m (11.5 ft) and salinities less than 6.3 parts per thousand (Parauka
et al.
in press). Fox and Hightower (1998a) found that adult Gulf sturgeon monitored in Choctawhatchee Bay use some of the same habitats as subadults. Some subadult Gulf sturgeon use seagrass

habitats in Choctawhatchee Bay. However, the majority of tagged fish have been located in areas lacking seagrass (Parauka
et al.
in press). Adult Gulf sturgeon also have not been frequently found in areas containing seagrass, which were concentrated in the western portion of the bay.

Craft
et al
. (2001) found that Gulf sturgeon in Pensacola Bay appear to prefer shallow shoals 1.5 to 2.1 m (5 to 7 ft) and deep holes near passes. Unvegetated, fine to medium-grain sand habitats, such as sandbars, and intertidal and subtidal energy zones resulting in sediment sorting and a preponderance of sand support a variety of potential prey items including estuarine crustaceans, small bivalve mollusks, and lancelets (Brim pers. comm. 2002, Menzel 1971, Abele 1986, American Fisheries Society 1989).

Habitats used by Gulf sturgeon in the vicinity of the Mississippi Sound barrier islands tend to have a sand substrate and an average depth of 1.9 to 5.9 m (6.2 to 19.4 ft). Preliminary data from bottom samples taken in these barrier island areas show that all samples contain lancelets (
Branchiostoma
). Since lancelets are a documented prey of Gulf sturgeon, it is likely that Gulf sturgeon are feeding along the sand substrate at barrier island passes (Ross
et al
. 2001a). Gulf nearshore (less than 1.6 km (1 mi)) unconsolidated, fine-medium grain sands, including natural inlets and passes from the Gulf to estuaries, support crustaceans such as mole crabs, sand fleas, various amphipod species, and lancelets (Brim pers. comm. 2002, Menzel 1971, Abele 1986, American Fisheries Society 1989).

Estuary and bay unvegetated “mud” habitats having a preponderance of natural silts and clays support burrowing and deep burrowing crustaceans, such as ghost shrimp, small crabs, also various polychaete worms, and small bivalve mollusks (Brim pers. comm. 2002, Menzel 1971, Abele 1986, American Fisheries Society 1989). Gulf sturgeon are found in these areas and since these are known food sources, it is assumed that Gulf sturgeon are also feeding in these areas.

Migration

Migratory behavior of the Gulf sturgeon varies by sex, maturity, water temperature, and river flow. Male Gulf sturgeon generally enter the rivers earlier in the spring and move greater distances than females; ripe (in reproductive condition) males and females enter the river earlier than nonripe fish (Fox
et al
. 2000). Adults and subadults begin moving from the estuaries, bays, and Gulf of Mexico into the coastal rivers in early spring (
i.e.
, March through May) when river water temperatures range from 16.0 to 23.°C (60.8 to 73.4°C) (Huff 1975, Carr 1983, Wooley and Crateau 1985, Odenkirk 1989, Clugston
et al
. 1995, Foster and Clugston 1997, Fox and Hightower 1998, Sulak and Clugston 1999, Fox
et al
. 2000). Some research supports the theory that spring migration coincides with the general period of spring high water (Sulak and Clugston 1999), while observations on other rivers systems do not support this theory (Fox
et al
. in press).

Fall downstream migration from fresh to saltwater begins in September (at about 23°C (73.4°F)) and continues through November (Huff 1975, Wooley and Crateau 1985, Foster and Clugston 1997). During the fall migration from fresh to saltwater, Gulf sturgeon may require a period of physiological acclimation to changing salinity levels, referred to as osmoregulation or staging (Wooley and Crateau 1985). This period may be short (Fox
et al
. in press) as sturgeon develop an active mechanism for osmoregulation and ionic balance by age one (Altinok 1997). On some river systems, timing of the fall migration appears to be associated with pulses of higher river discharge (Heise
et al
. 1999a and b, Ross
et al
. 2000 and 2001b, Parauka
et al
. in press).

Sturgeon ages 1 through 6 remain in the mouth of the Suwannee River over winter. In late January through early February, young-of-the-year Gulf sturgeon migrate down river for the first time (Sulak and Clugston 1999). Huff (1975) noted that juvenile Gulf sturgeon in the Suwannee River most likely participated in pre- and post-spawning migrations, along with the adults.

Findeis (1997) describes sturgeon (Acipenseridae) as exhibiting evolutionary traits adapted for benthic cruising. Tracking observations by Sulak and Clugston (1999), Edwards
et al
. (in prep.), and Fox
et al
. (in press) support that individual fish move over an area until they encounter suitable prey type and density, at which time they forage for extended periods of time. Individual fish often remained in localized areas (less than 1 km
2
(0.4 mi
2
) for extended periods of time (greater than two weeks) and then moved rapidly to another area where localized movements occurred again (Fox
et al
. in press). It is unknown precisely how much benthic area is needed to sustain Gulf sturgeon health and growth, but because Gulf sturgeon have been known to travel long distances (greater than 161 km (100 mi)) during their winter feeding phase, significant resources must be necessary. These winter migrations are an important strategy for feeding and for occasional travel to non-natal rivers for possible spawning and genetic interchange. Bays and portions of Gulf of Mexico waters adjacent to the lakes and bays near the mouths of the rivers where Gulf sturgeon occur are believed to be important for feeding and/or migrating (for increased gene flow and, therefore, increased genetic stability among subpopulations).

When temperature drops occur that are associated with major cold fronts, researchers of the Escambia, Yellow, and Suwannee River subpopulations have been unable to locate adult Gulf sturgeon within the bays (Craft
et al
. 2001, Fox
et al
. in press, Edwards
et al
. in prep.). It is hypothesized that the cold fronts disperse sturgeon to more distant foraging grounds. It is currently unknown whether Gulf sturgeon undertake extensive offshore migrations, and further study is needed to determine whether important winter feeding habitat occurs in farther offshore areas.

Sulak and Clugston (1999) describe two hypotheses regarding where adult Gulf sturgeon may overwinter in the Gulf of Mexico to find abundant prey. The first hypothesis is that Gulf sturgeon spread along the coast in nearshore waters in depths less than 10 m (33 ft). The alternative hypothesis is that they migrate far offshore to the broad sedimentary plateau in deep water (40 to 100 m (131 to 328 ft)) west of the Florida Middle Grounds, where over twenty species of bottom-feeding fish congregate in the winter (Darnell and Kleypas 1987). Available data support the first hypothesis. Evaluation of tagging data has identified several nearshore Gulf of Mexico feeding migrations, but no offshore Gulf of Mexico feeding migrations. Telemetry data document Gulf sturgeon from the Pearl River and Pascagoula River subpopulations migrate from their natal bay systems to Mississippi Sound and move along the barrier islands on both the barrier island passes (Ross
et al
. 2001a, Rogillio
et al
. in prep.). Gulf sturgeon from the Choctawhatchee River, Yellow River, and Apalachicola River have been documented migrating in the nearshore Gulf of Mexico waters between Pensacola and Apalachicola Bays units (Fox
et al
. in press, F. Paruka pers. comm. 2002). Telemetry data from the Gulf of Mexico mainly show sturgeon in depths of 6 m (19.8 ft) or less (Ross
et al.
2001a, Rogillio
et al
. in prep., Fox
et al
. in press, F. Paruka pers. comm. 2002).

River-Specific Fidelity

Stabile
et al
. (1996) analyzed Gulf sturgeon subpopulations from eight drainages along the Gulf of Mexico for genetic diversity. They noted significant differences among Gulf sturgeon stocks and suggested that they displayed region-specific affinities and may exhibit river-specific fidelity. Stabile
et al
. (1996) identified five regional or river-specific stocks (from west to east)—(1) Lake Pontchartrain and Pearl River, (2) Pascagoula River, (3) Escambia and Yellow Rivers, (4) Choctawhatchee River, and (5) Apalachicola, Ochlockonee, and Suwannee Rivers.

Tagging studies suggest that Gulf sturgeon exhibit a high degree of river fidelity. From 1981 to 1993, 4,100 fish were tagged in the Apalachicola and Suwannee Rivers. Of these, 860 fish (21 percent) were recaptured in the river of their initial collection. Only eight subadults (.002 percent) moved between rivers (FWS
et al
. 1995). Foster and Clugston (1997) noted that telemetered Gulf sturgeon in the Suwannee River returned to the same areas as the previous summer, suggesting that chemical cuing may influence distribution.

To date, biologists have documented a total of 21 Gulf sturgeon making inter-river movements from natal rivers. They are as follows—Apalachicola River to Suwannee River, six Gulf sturgeon (Carr
et al
. 1996b); Suwannee River to Apalachicola River, three sturgeon (Carr
et al
. 1996b, F. Parauka pers. comm. 2002); Choctawhatchee River to Apalachicola River, one sturgeon (F. Parauka pers. comm. 2002); Yellow River to Choctawhatchee River, three sturgeon (one adult female, one subadult female) (Craft
et al
. 2001); Yellow River to Louisiana Estuarine area, one female sturgeon (Craft
et al
. 2001); Escambia River to Yellow River, one mature female on spawning grounds (Craft
et al
. 2001); Suwannee River to Ochlockonee River, one sturgeon (FWS
et al
. 1995); Choctawhatchee River to Escambia River, one male sturgeon (Fox
et al
. in press); Choctawhatchee River to Escambia, one female sturgeon (Fox
et al
. in press); Pearl River (Bogue Chitto) to Pascagoula River, one sturgeon (Ross
et al
. 2001b); Choctawhatchee River to Pascagoula River, one subadult sturgeon (Ross
et al
. 2001b); and Pascagoula River to Yellow River, one sturgeon (Ross
et al
. 2001b). Tallman and Healey (1994) note that observed straying rates between rivers were not the same as actual gene flow rates, i.e. inter-stock movement does not equate to successful reproduction. The gene flow is low in Gulf sturgeon stocks, with each stock exchanging less than one mature female per generation (Waldman and Wirgin 1997).

Previous Federal Action

Federal action on the Gulf sturgeon began in 1982, when the fish was included as a Category 2 candidate species for listing in the FWS's vertebrate notices of review dated December 30, 1982 (47 FR 58454) and September 18, 1985 (50 FR 37958), and in the animal notice of review dated January 6, 1989 (54 FR 554). At that time, the FWS gave Category 2 designation to species for which listing as threatened or endangered was possibly appropriate, but for which additional biological information was needed to support a proposed rule. A status report on the Gulf sturgeon (Hollowell 1980) had concluded that the fish had been reduced to a small population due to overfishing and habitat loss. In 1988, the FWS completed a report on the conservation status of the Gulf sturgeon, which recommended listing it as a threatened species (Barkuloo 1988).

The Services jointly proposed the Gulf sturgeon for listing as a threatened species on May 2, 1990 (55 FR 18357). In that proposed rule, we stated that designation of critical habitat was not prudent due to the species' broad range and the lack of knowledge about specific areas used by the species. We published the final rule on September 30, 1991 (56 FR 49653) to add Gulf sturgeon to the list of threatened species, and included a special rule under section 4(d) of the Act to allow the take of Gulf sturgeon, in accordance with applicable State fish and wildlife conservation laws and regulations, for educational and scientific purposes, the enhancement of propagation or survival of the species, zoological exhibition, and other conservation purposes. In the final rule, we found that a critical habitat designation may be prudent but was not determinable. Section 4(b)(6)(C) of the Act provides that a concurrent critical habitat determination is not required with a final regulation implementing endangered or threatened status and that the final designation may be postponed for one additional year beyond the period specified in section 4(b)(6)(A), if a prompt determination of endangered or threatened status is essential to the conservation of the species, or critical habitat is not then determinable. We found that prompt determination of threatened status was essential to the conservation of the species and stated that we would make a final decision on designation of critical habitat by May 2, 1992. This decision, however, was not made.

On August 11, 1994, the Sierra Club Legal Defense Fund, Inc. (Fund), on behalf of the Orleans Audubon Society and Florida Wildlife Federation, gave written notice of their intent to file suit against the Department of the Interior for failure to designate critical habitat for the Gulf sturgeon within the statutory time limits established under the Act. The Fund filed suit on October 11, 1994 (
Orleans Audubon Society
v.
Babbitt,
Civ. No. 94-3510 (E.D. La)). Following a court order on August 9, 1995, granting the Fund's motion for summary judgement, the Services published a notice of decision on critical habitat designation for the Gulf sturgeon on August 23, 1995 (60 FR 43721). We determined that critical habitat designation was not prudent based on the lack of additional conservation benefit to the species.

On September 22, 1995, the Services and the Gulf States Marine Fisheries Commission approved the Gulf Sturgeon Recovery/Management Plan (FWS
et al.
1995). The recovery plan established the criteria that must be met prior to the delisting of the Gulf sturgeon. The recovery plan also identified the actions that are needed to assist in the recovery of the Gulf sturgeon.

On August 12, 1996, the plaintiffs filed a motion to add the Department of Commerce as a defendant in the lawsuit. The Fund amended their complaint to challenge the August 1995 “not prudent” determination. On October 30, 1997, the court granted the plaintiffs' motion for summary judgment, with relief restricted to a remand of the “not prudent” determination to the Services, requiring that the Services publish a determination on designation of critical habitat, based on the best scientific information available. On February 27, 1998, we published a notice of decision (63 FR 9967) on critical habitat designation for the Gulf sturgeon. We again determined that lack of additional conservation benefit from critical habitat designation for this species made such designation not prudent.

On December 18, 1998, the Sierra Club sued the Services challenging the new determination not to designate critical habitat for the Gulf sturgeon (
Sierra Club
v.
U.S. Fish and Wildlife Service et al.
CA No. 98-3788 (E.D. La.)). On January 25, 2000, the Court issued an order granting our motion for summary judgment and dismissing the complaint. The Sierra Club filed an appeal and, in March 2001, the United States Court of Appeals for the Fifth Circuit reversed the decision of the

District Court and instructed the District Court to remand the decision to us for reconsideration (
Sierra Club
v.
U.S. Fish and Wildlife Service, 245 F.3d 434
(5th Cir. 2001)). On August 3, 2001, the District Court issued an order directing us to publish a proposed decision concerning critical habitat designation for the Gulf sturgeon by February 2, 2002, and a final decision by August 2, 2002. Negotiation with the plaintiff resulted in an agreement to publish the proposed decision by May 23, 2002, and the final decision by February 28, 2003.

This proposal is the product of our reexamination of our 1998 prudency determination for the Gulf sturgeon. It reflects our interpretation of the recent judicial opinions on critical habitat designation and the standards placed on us for making a prudency determination. If additional information becomes available on the species' biology and distribution and threats to the species, we may reevaluate this proposal to designate critical habitat, including proposing additional critical habitat, proposing the deletion or boundary refinement of existing proposed critical habitat, or withdrawing our proposal to designate critical habitat.

Critical Habitat

Critical habitat is defined in section 3(5)(A) of the Act as (i) the specific areas within the geographic area occupied by a species, at the time it is listed in accordance with the Act, on which are found those physical or biological features (I) essential to the conservation of the species and (II) that may require special management considerations or protection; and (ii) specific areas outside the geographic area occupied by a species at the time it is listed, upon a determination that such areas are essential for the conservation of the species. “Conservation” is defined in section 3(3) of the Act as the use of all methods and procedures that are necessary to bring any endangered or threatened species to the point at which listing under the Act is no longer necessary.

In order for habitat to be included in a critical habitat designation, the habitat features must be “essential to the conservation of the species.” Such critical habitat designations identify, to the extent known using the best scientific data available, habitat areas that provide essential life cycle needs of the species (
i.e.,
areas on which are found the primary constituent elements, as defined at 50 CFR 424.12(b)).

Regulations at 50 CFR 424.02(j) define special management considerations or protection to mean any methods or procedures useful in protecting the physical and biological features of the environment for the conservation of listed species. If any areas containing the primary constituent elements are currently being managed to address the conservation needs of the Gulf sturgeon, they may not require special management or protection, and, therefore, may not meet the definition of critical habitat in section 3(5)(A)(i) of the Act.

When we designate critical habitat, we may not have the information necessary to identify all areas which are essential for the conservation of the species. Nevertheless, we are required to designate those areas we know to be critical habitat, using the best information available to us.

Within the geographic area of the species, we will designate only currently known essential areas. We will not speculate about what areas might be found to be essential if better information became available, or what areas may become essential over time. If the information available at the time of designation does not show that an area provides essential life cycle needs of the species, then the area will not be included in the critical habitat designation. Our regulations state that, “The Secretary shall designate as critical habitat areas outside the geographic area presently occupied by the species only when a designation limited to its present range would be inadequate to ensure the conservation of the species” (50 CFR 424.12(e)). Accordingly, when the best available scientific data do not demonstrate that the conservation needs of the species require designation of critical habitat outside of occupied areas, we will not designate critical habitat in areas outside the geographic area occupied by the species.

Section 4(b)(2) of the Act requires that we take into consideration the economic impact, and any other relevant impact, of specifying any particular area as critical habitat. We may exclude areas from critical habitat designation when the benefits of exclusion outweigh the benefits of including the areas within critical habitat, provided the exclusion will not result in extinction of the species.

Our Policy on Information Standards Under the Endangered Species Act, published on July 1, 1994 (59 FR 34271), provides guidance to ensure that our decisions are based on the best scientific and commercial data available. It requires that our biologists, to the extent consistent with the Act and with the use of the best scientific and commercial data available, use primary and original sources of information as the basis for recommendations to designate critical habitat. When determining which areas are critical habitat, information that should be considered includes the listing package for the species, the recovery plan, articles in peer-reviewed journals, conservation plans developed by States and Counties, scientific status surveys, studies, and biological assessments, unpublished materials, and expert opinion or personal knowledge.

Habitat is often dynamic, however, and populations may move from one area to another over time. Furthermore, we recognize that designation of critical habitat may not include all of the habitat areas that may eventually be determined to be necessary for the recovery of the species. Therefore, critical habitat designations do not signal that habitat outside the designation is unimportant or may not be required for recovery. Areas outside the critical habitat designation will continue to be subject to conservation actions that may be implemented under section 7(a)(1) of the Act and to the regulatory protections afforded by the section 7(a)(2) jeopardy standard and the section 9 of the Act take prohibition, as determined on the basis of the best available information at the time of the action. It is possible that federally funded or assisted projects affecting listed species outside their designated critical habitat areas could jeopardize those species. Similarly, critical habitat designations made on the basis of the best available information at the time of designation will not control the direction and substance of future recovery plans, habitat conservation plans, or other species conservation planning and recovery efforts if new information available to these planning efforts calls for a different outcome.

Prudency Determination

Section 4(a)(3) of the Act and implementing regulations (50 CFR 424.12) require that, to the maximum extent prudent and determinable, we designate critical habitat at the time a species is listed as endangered or threatened. Regulations at 50 CFR 424.12(a)(1) state that the designation of critical habitat is not prudent when one or both of the following situations exist: (1) The species is threatened by taking or other activity and the identification of critical habitat can be expected to increase the degree of threat to the species or (2) such designation of critical habitat would not be beneficial to the species.

In our February 27, 1998, notice of decision, we determined that the

designation of critical habitat was not prudent for the Gulf sturgeon because such designation would not be beneficial to the species. However, on March 15, 2001, the United States Court of Appeals for the Fifth Circuit determined that this “not prudent” determination was made erroneously, and ordered us to reconsider it (
Sierra Club
v.
U.S. Fish and Wildlife Service,
245 F.3d 434). Accordingly, we withdraw our previous determination that designation of critical habitat will not benefit the Gulf sturgeon.

In reconsidering whether designation of critical habitat for the Gulf sturgeon will be prudent, we find that designation will be clearly beneficial to the species. Critical habitat will primarily benefit the sturgeon through the Act's consulting mechanism under section 7 of the Act. If critical habitat is designated for the Gulf sturgeon, other Federal agencies will be required to consult with us on actions they carry out, fund, or authorize, to ensure that their actions will not destroy or adversely modify critical habitat. In this way, a critical habitat designation will protect areas that are necessary for the conservation of the species. It may also serve to enhance awareness within Federal agencies and the general public of the importance of Gulf sturgeon habitat and the need for special management considerations.

A designation of critical habitat will provide Federal agencies with a clearer indication as to when consultation under Section 7 of the Act is required, particularly in cases where the action would not result in direct mortality, injury or harm to individuals of the species (
e.g.,
an action occurring within the critical habitat area when or where the Gulf sturgeon is not present). The critical habitat designation, in describing the essential features of the habitat, will also help determine which activities conducted outside the designated area are subject to section 7 consultation (
e.g.,
activities that may affect essential features of the designated area). For example, disposal of waste material in water adjacent to a critical habitat area may affect an essential feature (water quality) of the designated habitat and so would be subject to the provisions of section 7.

A critical habitat designation will also assist Federal agencies in planning future actions because it establishes, in advance, those habitats that will be given an additional review in section 7 consultations. This is particularly true in cases where there are alternative areas that would provide for the conservation of the species and the success of the action. With a designation of critical habitat, potential conflicts between Federal actions and listed species can be identified and possibly avoided early in the agency's process.

It is true that we are already working with Federal and State agencies, and private individuals and organizations, in carrying out conservation activities for the Gulf sturgeon, such as conducting population surveys and assessing habitat conditions. It is also true that these entities are fully aware of the distribution, status, and habitat requirements for the Gulf sturgeon, as they are currently known. However, as discussed above, some additional educational and informational benefit will result from designation.

Though the identification of known spawning habitat in this proposed rule may increase illegal harvest, we currently have no knowledge that illegal harvest is or has been an issue with the Gulf sturgeon. Since the States of Louisiana, Mississippi, Alabama, and Florida have deemed harvest illegal since the 1980s, and we found no records of illegal harvest during our literature review or in discussions with researchers, we have found no evidence that identification of Gulf sturgeon critical habitat would increase the degree of threat to the species. Therefore, we propose that designation of critical habitat is prudent for the Gulf sturgeon.

Methods and Criteria Used To Identify Critical Habitat

As required by section 4(b)(2) of the Act and its implementing regulations (50 CFR 424.12), this proposal is based on the best scientific information available concerning the species' present and historical range, habitat, biology, and threats. In preparing this rule, we reviewed and summarized the current information available on the Gulf sturgeon, including the physical and biological features that are essential for the conservation of the species (see “Primary Constituent Elements” section), and identified the areas containing these features. The information used includes known locations; our own site-specific species and habitat information; State-wide Geographic Information System (GIS) coverages (
e.g.,
land ownership, bathymetry (the measurement of depths of water in oceans, seas, and lakes), and estuarine substrates); the final listing rule for the Gulf sturgeon; recent biological surveys and reports; peer-reviewed literature; our recovery plan; discussions and recommendations from Gulf sturgeon experts; and information received during Gulf sturgeon recovery meetings. The Gulf Sturgeon Recovery/Management Plan (FWS
et al.
1995) contains valuable biological information, and it is cited throughout this document. However, the state of our knowledge regarding Gulf sturgeon biology and distribution has changed markedly since publication of the recovery plan for this species. The recovery criteria put forth in this recovery plan were deemed preliminary and may now warrant revision in light of new information. As a result of recent research and survey efforts directed towards this species, substantial portions of the biological information presented in the recovery plan are now dated or obsolete. Thus, although the recovery plan is a valuable source of information, it is not the final authority on the natural history and distribution of this species.

In the past, we had assumed, based on the information available at the time, that unoccupied habitat would be necessary for the recovery of the Gulf sturgeon. Since approval of the recovery plan in 1995 and our 1998 not prudent finding, we have collected new biological information on this species. We have analyzed what is necessary for the conservation of the Gulf sturgeon, as described above, and based on the best scientific information available at this time, we have determined that unoccupied habitat is not essential to the conservation of the Gulf sturgeon.

Determining the Scale of the Proposed Designation

We first evaluated the Gulf sturgeon in the context of its current distribution throughout the historic range to determine what portion of the range must be conserved to ensure recovery of the species. We considered several factors in this evaluation—(1) Maintaining overall genetic integrity and minimizing the potential for inbreeding, (2) retaining potential evolutionary importance at the margins of the species' range by protecting the eastern- and western-most subpopulations, (3) decreasing the extinction risk of a subpopulation by protecting adjacent subpopulations that can provide a rescue effect, if needed, (4) avoiding the potential for subpopulation extirpation from environmental catastrophes, and (5) protecting sufficient habitat to support full recovery of the species.

The historic range of the Gulf sturgeon included nine major rivers and several smaller rivers from the Mississippi River, Louisiana, to the Suwannee River, Florida, and in marine waters of the Central and Eastern Gulf of Mexico, south to Tampa Bay (Wooley and Crateau 1985, FWS
et al.
1995).

Seven of these major river systems continue to support reproducing subpopulations. These include (from west to east)—the Pearl, Pascagoula, Escambia, Yellow/Blackwater, Choctawhatchee, Apalachicola, and Suwannee Rivers.

Gulf sturgeon is listed as a single Distinct Population Segment (DPS) throughout its range (see policy 61 FR 4722). However, this species exists as several subpopulations with limited mixing. The Gulf Sturgeon Recovery/Management Plan (FWS
et al.
1995) noted the importance of identifying and maintaining genetic integrity and diversity during restoration efforts on Gulf sturgeon. A severe loss of genetic variability often leads to a noticeable decline in the fitness of a species (Soulé 1987). Evidence suggests that peripheral subpopulations are often genetically and morphologically divergent from central subpopulations (Lesica and Allendorf 1995). Distinct traits found in peripheral subpopulations may be crucial to the species, allowing adaptation in the face of environmental change (Lesica and Allendorf 1995, Allendorf
et al.
1997). In light of these considerations, we determined that the inclusion of stocks or subpopulations from both the eastern and the western margins of the current range were necessary to protect the potential evolutionary importance of those subpopulations (Scudder 1989, Lesica and Allendorf 1995, Young and Harig 2001).

While telemetry data indicate that Gulf sturgeon from one genetically distinct drainage occasionally enter another river and also mix during the winter months in estuarine and marine habitats, a genetic analysis of tissue samples concluded that Gulf sturgeon exhibit a strong natal river fidelity, with stocks exchanging less than one mature female per generation on the average (Waldman and Wirgin 1997). These low gene flow estimates strongly suggest that natural recolonization of extirpated subpopulations of Gulf sturgeon would proceed slowly (Waldman and Wirgin 1997). Semi-isolated subpopulations are more vulnerable to the effects of demographic and environmental population fluctuations (Forney and Gilpin 1989, Wahlberg
et al.
1996).

Gene flow estimates usually were higher between adjacent stocks, suggesting that migrants from semi-isolated subpopulations are exchanged chiefly with neighboring subpopulations (Waldman and Wirgin 1997). The loss of any intermediate subpopulations by a single environmental catastrophe could seriously limit a species' recovery (Kautz and Cox 2000, Young and Harig 2001). In light of this, we determined that it is necessary to propose as critical habitat rivers used by subpopulations evenly spaced between the western- and eastern-most limits of the current range. To ensure conservation of the species, subpopulations must be geographically located so that existing subpopulations could serve as sources of sturgeon emigration, albeit at a slow rate (Waldman and Wirgin 1997), to adjacent rivers as their subpopulations increase and so that they can provide a rescue effect if an adjacent subpopulation is extirpated (Brown and Kodric-Brown 1977, Hanski and Gyllenberg 1993, Young and Harig 2001).

Designating critical habitat for only a few subpopulation units, or for units not spaced in a manner that allows fish to exchange with other subpopulations, could increase the vulnerability of the species due to isolation of subpopulations. Protection of a single, isolated, minimally viable population risks the extirpation or extinction of a species as a result of harsh environmental conditions, catastrophic events, or genetic deterioration over several generations (Kautz and Cox 2000). To reduce the risk of extinction through these processes, it is important to establish multiple protected subpopulations across the landscape (Soulé and Simberloff 1986, Wiens 1996).

Because of these considerations, we reached the conclusion that this proposal should include critical habitat units within the major river systems that support the seven currently reproducing subpopulations (FWS
et al.
1995) and associated marine habitats. These river systems include (from west to east)—the Pearl, Pascagoula, Escambia, Yellow/Blackwater, Choctawhatchee, Apalachicola, and Suwannee Rivers. We believe that with proper protection and management, these units collectively represent habitat necessary to provide for the conservation of the species. The number, distribution, and range of Gulf sturgeon subpopulations included in these units is necessary to protect and sustain this species' genetic integrity and diversity and to provide a rescue effect, if needed. We believe that these seven river systems, with their associated estuarine and marine environments, represent habitat that is essential for the conservation of the Gulf sturgeon.

Assessing Specific Habitat Areas Essential to the Conservation of Gulf Sturgeon

Once we determined that the proper scale of the proposed critical habitat designation should cover the area occupied by the seven reproducing subpopulations, we evaluated which habitats used by those seven subpopulations are essential to their conservation. To conduct this evaluation, we assessed the critical life history components of Gulf sturgeon as they relate to habitat. Gulf sturgeon use the rivers for spawning, juvenile feeding, adult resting, and staging, and to move between the areas that support these components. Gulf sturgeon use the lower riverine, estuarine, and marine environment during winter months primarily for feeding, and more rarely, for inter-river migrations.

We then investigated what types of habitat support these life history components and where these areas of habitat are located. We evaluated empirical data, published and unpublished literature, and solicited the views of experts. These habitat components are described in the “Primary Constituent Elements” section of this proposed rule. We identified known or presumed spawning sites in each of the seven river systems. Some spawning sites have been conclusively identified; others are presumed due to the presence of suitable habitat. We identified known or presumed sites used for resting or staging. We identified areas where subadult and adult Gulf sturgeon occur during winter to feed. These areas are primarily in the marine or estuarine environment; young-of-year and juveniles feed mostly in the riverine environment. As a component of the above identifications, we gathered all available data on locations and habitat use of marked (tagged) fish.

To determine which areas should be proposed as critical habitat, we then evaluated where the necessary constituent elements of Gulf sturgeon habitat intersected with areas known to be used by both marked and unmarked fish. Detailed location data, where available, is included with each proposed unit description in the “Critical Habitat Unit Descriptions” section of this proposed rule. Because most of the sturgeon species' upstream movement is for spawning (Bane 1997; J. Hightower, U.S. Geological Survey (USGS)-Biological Resources Division, pers. comm. 2002), we have determined that the proposal should include areas as far upstream as the furthest known or presumed spawning site. Therefore, in rivers where spawning sites have been confirmed, the proposed units extend upstream to a geographically identifiable point such as a river confluence above those sites. In areas where spawning sites are presumed but not confirmed, we have included river reaches that contain the primary

constituent elements necessary for spawning (
e.g.
, appropriate substrate, and water quality and quantity), if those areas occur within close proximity of Gulf sturgeon historic and/or current sightings or captures, and if they are still accessible to sturgeon (
e.g.
, not blocked by dams). The proposed riverine critical habitat units include areas that continue to offer at least periodic passage of Gulf sturgeon to known and presumed spawning sites. Successful reproduction and recent recruitment have been documented in each riverine unit by eggs, larvae, and/or juveniles, or by a mixed age structure. We are proposing to protect spawning habitats from a catastrophic occurrence by including both the main stem spawning sites and at least one tributary site.

We have included riverine habitat from the river mouth up to and including spawning grounds in order to provide sufficient habitat necessary for the other riverine life stages of Gulf sturgeon while they reside in the riverine habitats. Habitat necessary for these life stages includes habitat for summer resting or staging areas, juvenile feeding, entire young-of-year life cycle, passage throughout the river, and passage into and out of estuarine habitat. All of the selected areas are known to be used by Gulf sturgeon for some portion of their life cycle.

Subadult and adult sturgeon use estuarine and marine areas for feeding and passage between river systems. Designation of critical habitat units encompassing estuaries and bays adjacent to the riverine units discussed above would protect unobstructed passage of sturgeon from feeding areas to spawning grounds. In evaluating the estuarine and marine areas, we first reviewed where Gulf sturgeon from the seven adjacent riverine units have been documented by telemetry relocations and tag returns from incidental captures. We also considered areas for which we have Gulf sturgeon sightings and targeted and incidental capture records. When available, we reviewed habitat data (
e.g.
, bathymetry, substrate type, and benthic organisms) associated with these estuarine and marine systems and compared these data with studies pertaining to the habitat requirements and preferences of Gulf sturgeon. We also evaluated data for evidence of critical migratory pathways between the river systems and the adjacent bays and Gulf of Mexico that allow Gulf sturgeon to travel to important feeding areas, as well as allow for the occasional travel to non-natal rivers for possible spawning and genetic interchange. Where documented interchanges have occurred, but no telemetry data exist to identify the migratory path used (
e.g.
, between the Pascagoula River and Yellow River, the Pascagoula and Choctawhatchee River, and between Suwanee River and Apalachicola River), we have not proposed a migration route. We then assessed the Gulf sturgeon's overall use of estuarine and marine waters and delineated specific critical habitat boundaries.

Migration and feeding may take place via the Gulf Intracoastal Waterway (GIWW) in some of the proposed units. Portions of the GIWW that consist primarily of excavated land cuts and canals have been excluded from this designation because they were not available historically, and, therefore, are not considered to be evolutionarily significant.

This proposed designation includes a significant portion, but not all, of the species' historic range. The fourteen proposed critical habitat units include riverine main stems and in some cases tributaries, distributaries (a river branch flowing away from the main stem in the floodplain) and adjacent estuarine and marine areas that contain one or more of the primary constituent elements essential for the conservation of the Gulf sturgeon (see “Primary Constituent Elements” section). The omission of some historically occupied river drainages and estuarine and marine areas from this proposed critical habitat designation does not diminish their individual or cumulative importance to the species. Rather, it is our determination that the seven riverine units with known spawning and seven associated estuarine and marine units included in this proposed rule include the habitats essential for the conservation of the Gulf sturgeon. With unobstructed passage in the estuarine and marine habitat, the subpopulations within the proposed designated critical habitat units may eventually populate presently unoccupied coastal river systems or augment adjacent surviving small subpopulations.

Although the Mobile River Basin is the largest Gulf of Mexico drainage east of the Mississippi River, it has been extensively impounded and modified for navigation. Further, there have been relatively limited reports of captures and no evidence of reproduction of Gulf sturgeon from that system for many years. Gulf sturgeon have been reported from other river systems. Some of these other systems historically supported a commercial fishery (
e.g.
, Mobile River, Ochlockonee River) and some may support small reproducing subpopulations (
e.g.
, Techefuncte River, Ochlockonee River, Mobile River); however, there is no recent documented spawning and we have no evidence at this time that these systems are essential to the conservation of the species. Therefore, we have not proposed them as critical habitat.

The data available to us are insufficient to support a determination that Lake Maurepas, Breton and Chandeleur Sounds, the Mississippi River Delta, St. Louis, Biloxi, Mobile, Perdido, St. Andrews, St. Joseph, Ochlockonee, or Apalachee Bays are essential to the conservation of the species. Records within the majority of these bays are relatively scarce. Although some Gulf sturgeon from the seven subpopulations may occasionally use these bays for winter feeding, there are insufficient data to support these bays' regular winter use or importance and no documented spawning. Therefore, we have not proposed these bays for designation as critical habitat.

The amount of research and status surveys conducted on many subpopulations is limited. Because of the limited availability of data specific to each river system and specific to the Gulf sturgeon's use of the marine environment, we are aware that habitat other than that identified in this proposed rule may later be found to be essential to the conservation of Gulf sturgeon. To the extent feasible, we will continue, with the assistance of other Federal, State, and private researchers, to conduct surveys, research, and conservation actions on the species and its habitat in areas designated and not designated as critical habitat. If additional information becomes available on the species' biology, distribution, and threats, we will evaluate the need to designate additional critical habitat, delete or reduce critical habitat, or refine the boundaries of critical habitat. Gulf sturgeon surviving in, or moving to rivers that are not being proposed for critical habitat will continue to receive protection under the section 7 of the Act jeopardy standard and the section 9 of the Act prohibitions on take (see “Critical Habitat” section).

Primary Constituent Elements

In accordance with sections 3(5)(A)(i) and 4(b)(1)(A) of the Act and regulations at 50 CFR 424.12, in determining which areas to propose as critical habitat, we are required to base critical habitat determinations on the best scientific data available and to focus on those physical and biological features (primary constituent elements) that are essential to the conservation of the species and that may require special management considerations or

protection. Such requirements include, but are not limited to, space for individual and population growth and for normal behavior; food, water, air, light, minerals, or other nutritional or physiological requirements; cover or shelter; sites for breeding, reproduction, and rearing of offspring; and habitats that are protected from disturbance or are representative of the historical geographical and ecological distribution of a species.

Based on the best available information, primary constituent elements essential for the conservation of the Gulf sturgeon include the following:

(1) Abundant prey items, such as detritus, aquatic insects, worms, and/or molluscs, within riverine habitats for larval and juvenile life stages; and abundant prey items, such as amphipods, lancelets, polychaetes, gastropods, ghost shrimp, isopods, molluscs and/or crustaceans, within estuarine and marine habitats for subadult and adult life stages.

(2) Riverine spawning sites with substrates suitable for egg deposition and development, such as limestone outcrops and cut limestone banks, bedrock, large gravel or cobble beds, marl, soapstone, or hard clay;

(3) A flow regime (
i.e.
, the magnitude, frequency, duration, seasonality, and rate-of-change of freshwater discharge over time) necessary for normal behavior, growth, and survival of all life stages in the riverine environment, including migration, breeding site selection, courtship, egg fertilization, resting, and staging, and for maintaining spawning sites in suitable condition for egg attachment, egg sheltering, resting, and larval staging;

(4) Water quality, including temperature, salinity, pH, hardness, turbidity, oxygen content, and other chemical characteristics, necessary for normal behavior, growth, and viability of all life stages;

(5) Sediment quality, including texture and other chemical characteristics, necessary for normal behavior, growth, and viability of all life stages; and

(6) Safe and unobstructed migratory pathways necessary for passage within and between riverine, estuarine, and marine habitats.

Need for Special Management Consideration or Protection

An area designated as critical habitat contains one or more of the primary constituent elements that are essential to the conservation of the species (see “Primary Constituent Elements” section), and that may require special management considerations or protection. Various activities in or adjacent to each of the critical habitat units described in this proposed rule may affect one or more of the primary constituent elements that are found in the unit. These activities include, but are not limited to, those listed in the “Effects of Critical Habitat” section as “Federal Actions That May Affect Critical Habitat and Require Consultation.” For example, riverine spawning sites for Gulf sturgeon must be relatively sediment-free for successful egg development and may need best management practices implemented in the watershed upstream to prevent an excessive accumulation of sediment in these areas. None of the proposed critical habitat units is presently under special management or protection provided by a legally operative plan or agreement for the conservation of the Gulf sturgeon. Therefore, we have determined that the proposed units may require special management or protection.

Proposed Critical Habitat Designation

The areas proposed for designation as critical habitat for the Gulf sturgeon provide one or more of the primary constituent elements described above. Tables 1 and 2 summarize the location and extent of proposed critical habitat. All of the proposed areas require special management considerations to ensure their contribution to the conservation of the Gulf sturgeon. The boundaries of proposed critical habitat units are described generally below.

Table 1.—Approximate Linear Distance of the Proposed Riverine Critical Habitat Units for the Gulf Sturgeon
[Main stems are listed first and tributaries are indented]

Critical habitat unit river systems
State

River
kilometers

River
miles

1. Pearl (East, West, and all distributaries)
Louisiana/Mississippi
616
383

Bogue Chitto

153
95

2. Pascagoula
Mississippi
130
81

Leaf

164
102

Bowie

24
15

Chickasawhay

232
144

Big Black Creek

10
6

3. Escambia Florida/Alabama

93
58

Conecuh

128
79

Sepulga

11
7

4. Yellow
Florida/Alabama
136
84

Blackwater

18
11

Shoal

13
8

5. Choctawhatchee
Florida/Alabama
224
139

Pea

92
57

6. Apalachicola
Florida
172
107

Brothers

23
14

7. Suwannee
Florida
286
178

Withlacoochee

19
12

Total

2,544
1,580

Table 2.—Approximate Area of the Proposed Estuarine and Marine Critical Habitat Units for the Gulf Sturgeon

Critical habitat unit estuarine and marine systems
State

Kilometers
2

Miles
2

8. Lake Borgne
Louisiana/
718
277

Little Lake
Mississippi/
8
3

Lake Pontchartrain
Alabama
763
295

Lake St. Catherine

26
10

The Rigolets

13
5

Mississippi Sound

1,879
725

MS near shore Gulf

160
62

9. Pensacola Bay
Florida
381
147

10. Santa Rosa Sound
Florida
102
39

11. Near shore Gulf of Mexico
Florida
442
171

12. Choctawhatchee Bay
Florida
321
124

13. Apalachicola Bay
Florida
683
264

14. Suwannee Sound
Florida
546
211

Total

6,042
2,333

Critical Habitat Unit Descriptions

The river reaches within units 1 to 7 proposed as critical habitat lie within the ordinary high water line. As defined in 33 CFR 329.11, the ordinary high water line on non-tidal rivers is the line on the shore established by the fluctuations of water and indicated by physical characteristics such as a clear, natural line impressed on the bank; shelving; changes in the character of soil; destruction of terrestrial vegetation; the presence of litter and debris; or other appropriate means that consider the characteristics of the surrounding areas.

The downstream limit of the riverine units is the mouth of each river. The mouth is defined as rkm 0 (rm 0). Although the interface of fresh and saltwater, referred to as the saltwater wedge, occurs within the lower-most reach of a river, for ease in delineating critical habitat units, we are defining the boundary between the riverine and estuarine units as rkm 0 (rm 0).

Regulatory jurisdiction in coastal areas extends to the line on the shore reached by the plane of the mean (average) high water (MHW) (33 CFR 329.12(a)(2)). All bays and estuaries within units 8 to 14, therefore, lie below the MHW lines. Where precise determination of the actual location becomes necessary, it must be established by survey with reference to the available tidal datum, preferably averaged over a period of 18.6 years. Less precise methods, such as observation of the “apparent shoreline,” which is determined by reference to physical markings, lines of vegetation, may be used only where an estimate is needed of the line reached by the mean high water.

The term 72 COLREGS is defined as demarcation lines which delineate those waters upon which mariners shall comply with the International Regulations for Preventing Collisions at Sea, 1972 and those waters upon which mariners shall comply with the Inland Navigation Rules (33 CFR 80.01). The waters inside of these lines are Inland Rules waters and the waters outside the lines are COLREGS waters. These lines are defined in 33 CFR 80, and have been used for identification purposes to delineate boundary lines of the estuarine and marine habitat Units 8, 9, 11, and 12.

Unit 1. Pearl River System in St. Tammany and Washington Parishes in Louisiana and Walthall, Hancock, Pearl River, Marion, Lawrence, Simpson, Copiah, Hinds, Rankin, and Pike Counties in Mississippi

Unit 1 includes the Pearl River main stem from the spillway of the Ross Barnett Dam, Hinds and Rankin Counties, Mississippi, downstream to where the main stem river drainage discharges at its mouth joining Lake Borgne, Little Lake, or The Rigolets in Hancock County, Mississippi, and St. Tammany Parish, Louisiana. It includes the main stems of the East Pearl River, West Pearl River, West Middle River, Holmes Bayou, Wilson Slough, downstream to where these main stem river drainages discharge at the mouths of Lake Borgne, Little Lake, or The Rigolets. Unit 1 also includes the Bogue Chitto River main stem, a tributary of the Pearl River, from its confluence with Lazy Creek just upstream of its crossing with Mississippi State Highway 570, Pike County, Mississippi, downstream to its confluence with the West Pearl River, St. Tammany Parish, Louisiana. The lateral extent of Unit 1 is the ordinary high water line on each bank of the associated rivers and shorelines.

The majority of recent Gulf sturgeon sightings in the Pearl River drainage have occurred downstream of the Pools Bluff sill on the Pearl River, near Bogalusa, Washington Parish, Louisiana, and downstream of the Bogue Chitto sill on the Bogue Chitto River in St. Tammany Parish, Louisiana. Between 1992 and 1996, 257 Gulf sturgeon were captured from the Pearl River system (West Middle River, Bogue Chitto River, East Pearl River, and West Pearl River). The subpopulation was estimated at 292 fish, of which only 2 to 3 percent were adults (Morrow
et al.
1998b). The annual mortality rate was calculated to be 25 percent. Preliminary results from captures between 1992 and 2001 suggest a stable subpopulation of 430 fish, with approximately 300 adults (Rogillio
et al.
in prep.). These Pearl River distributaries are used for migration to spawning grounds, summer resting holes, and juvenile feeding. Gulf sturgeon have been captured in all of these distributaries and all are proposed as critical habitat.

The presence of juvenile Gulf sturgeon (1 to 4 years old) in the Pearl River system indicates successful spawning at some location in the Pearl River system. It is believed that the only suitable habitat for spawning for the Pearl River subpopulation of Gulf sturgeon occurs above the sills on the Pearl River and the Bogue Chitto River with access to these areas only during high flows (Morrow
et al.
1996, Morrow
et al.
1998a). Bedrock and limestone outcropping that are typical of Gulf sturgeon spawning areas in other systems do not occur here. However, within the Pearl drainage, spawning areas likely include soapstone, hard clay, gravel and rubble areas, and undercut banks adjacent to these substrates (W. Slack pers. comm. 2001). Although the Pools Bluff sill blocks

upstream movement on the Pearl River during periods of low water, potential spawning sites have been identified upstream of the sill at various locations between Monticello, Lawrence County, Mississippi, and the Ross Barnett Dam spillway, Hinds and Rankin Counties, Mississippi (F. Parauka pers. comm. 2002). Gulf sturgeon have also been recently reported as far upstream as Jackson, Hinds County, Mississippi (Morrow
et al.
1996, Lorio 2000). The Ross Barnett Dam upstream of Jackson prevents sturgeon movement further upstream at all flow conditions. Identified suitable spawning habitat, presence of juvenile fish, and documented adult captures support our inclusion of the Pearl River up to the spillway of the Ross Barnett Dam.

The Bogue Chitto sill, located on the Bogue Chitto River near its confluence with the Pearl River, also hinders movement of Gulf sturgeon upstream of the sill except during high water flows. Suitable spawning habitat occurs within the Bogue Chitto upriver of the sill (F. Parauka pers. comm. 2002, W. Slack pers. comm. 2001) and juvenile, adult and subadult Gulf sturgeon have been documented on the Bogue Chitto River as far upstream as McComb, Pike County, Mississippi (D. Oge, Department of Environmental Quality, pers. comm. 2002; F. Parauka pers. comm. 2002; W. Slack pers. comm. 2001). We, therefore, have proposed as critical habitat the main stem of the Bogue Chitto River upstream of Quins Bridge (Mississippi State Highway 570) to its confluence with Lazy Creek.

Unit 2. Pascagoula River System in Forrest, Perry, Greene, George, Jackson, Clarke, Jones, and Wayne Counties, Mississippi

Unit 2 includes all of the Pascagoula River main stem and its distributaries, portions of the Bowie, Leaf, and Chickasawhay tributaries, and all of the Big Black Creek tributary. It includes the Bowie River main stem beginning at its confluence with Bowie Creek and Okatoma Creek, Forrest County, Mississippi, downstream to its confluence with the Leaf River, Forrest County, Mississippi. The Leaf River main stem beginning from Mississippi State Highway 588, Jones County, Mississippi, downstream to its confluence with the Chickasawhay River, George County, Mississippi is included. The main stem of the Chickasawhay River from the mouth of Oaky Creek, Clarke County, Mississippi, downstream to its confluence with the Leaf River, George County, Mississippi is included. Unit 2 also includes Big Black Creek main stem from its confluence with Black and Red Creeks, Jackson County, Mississippi, to its confluence with the Pascagoula River, Jackson County, Mississippi. All of the main stem of the Pascagoula River from its confluence with the Leaf and Chickasawhay Rivers, George County, Mississippi, to the discharge of the East and West Pascagoula Rivers into Pascagoula Bay, Jackson County, Mississippi, is included. The lateral extent of Unit 2 is the ordinary high water line on each bank of the associated rivers and shorelines.

Subpopulation estimates, calculated from sturgeon captures in 1999 and 2000 in the summer holding areas on the Pascagoula River, range between 162 and 216 individuals (Heise
et al.
1999a, Ross
et al.
2001b). Due to the sampling technique, these estimates are based primarily on large fish and do not account for juvenile or subadult fish (S. Ross, University of Southern Mississippi (USM), pers. comm. 2001).

Gulf sturgeon spawning on the Bowie River was confirmed via egg collection in 1999 (Slack
et al.
1999, Heise
et al.
1999a). This is the only confirmed spawning area in the Pascagoula River drainage. Downstream, the Bowie River is sometimes used as a summer holding area (Ross
et al.
2001b). Gulf sturgeon have been documented using the area above the known spawning habitat (Reynolds 1993, W. Slack pers. comm. 2002). Additional suitable spawning habitat has been identified in this upstream reach (F. Parauka pers. comm. 2002), and since Gulf sturgeon have rarely been documented upstream of spawning grounds, we have also included the 19 rkm (12 rmi) of river reach upstream of the confirmed spawning grounds. Confirmed use for spawning and use as a summer holding area support the inclusion of the Bowie River as proposed critical habitat.

Documented sightings of Gulf sturgeon and identified suitable spawning habitat upstream to Mississippi State Highway 588 (Reynolds 1993, W. Slack pers. comm. 2002, F. Parauka pers. comm. 2002), confirmed use as a migration corridor, and confirmed use by juvenile Gulf sturgeon (W. Slack pers. comm. 2002) support the inclusion of the Leaf River as proposed critical habitat.

Documented sightings of Gulf sturgeon using the Chickasawhay River (Miranda and Jackson 1987, Reynolds 1993, Ross
et al.
2001b) upstream to Quitman (Ross
et al.
2001b), and the presence of apparently suitable spawning habitat at Quitman (F. Parauka pers. comm. 2002), support the inclusion of this river reach as proposed critical habitat for spawning, migration, and juvenile feeding. We have included the suitable spawning habitat located within .8 rkm (.5 rmi) upstream of Mississippi State Road 512 and have extended the proposed designation 9 rkm (5.5 rmi) upstream to the confluence with Oaky Creek for ease of identification.

Gulf sturgeon use the West and East distributaries of the Pascagoula River during spring and fall migrations (Ross
et al.
2001b). Summer resting areas have been consistently documented on Big Black Creek and on the Pascagoula River (Ross
et al.
2001a and b). Confirmed use for migration and/or summer resting areas and probable feeding use by juveniles support our inclusion of these river reaches.

Unit 3. Escambia River System in Santa Rosa and Escambia Counties, Florida and Escambia, Conecuh, and Covington Counties, Alabama

Unit 3 includes the Conecuh River main stem beginning just downstream of the spillway of Point A Dam, Covington County, Alabama, downstream to the Florida State line, where its name changes to the Escambia River, Escambia County, Alabama, and Escambia and Santa Rosa Counties, Florida. It includes the entire main stem of the Escambia River downstream to its discharge into Escambia Bay and Macky Bay, Escambia and Santa Rosa Counties, Florida. All of the distributaries of the Escambia River including White River, Little White River, Simpson River, and Dead River, Santa Rosa County, Florida are included. The Sepulga River main stem from Alabama County Road 42, Conecuh and Escambia Counties, Alabama, downstream to its confluence with the Conecuh River, Escambia County, Alabama, is also included. The lateral extent of Unit 3 is the ordinary high water line on each bank of the associated lakes, rivers and shorelines.

Sufficient data are not yet available to estimate historic or current subpopulation sizes of the Escambia River drainage subpopulation. Collection and tagging of Gulf sturgeon, monitoring, and eventual subpopulation estimates are in the initial phases on the Escambia River in Florida and the Conecuh River in Alabama.

Suitable spawning habitat (Parauka and Giorgianni in prep.) and a reported larval sighting (N. Craft, Department of Environmental Protection (DEP), pers. comm. 2001), just below the Point A Dam (221 rkm (137 rmi) on the Conecuh River support inclusion of critical habitat upstream to the Point A Dam. The Point A Dam prevents sturgeon movement further upstream at all flow conditions. In addition, spawning has

been confirmed between rkm 161 and 170 (rmi 100 and 105.6) (Craft
et al.
2001) on the Conecuh River. The use of the river main stem for spawning, adult resting areas, juvenile feeding and resting, and the use for migration to these sites supports our inclusion of the Escambia/Conecuh River main stem as proposed critical habitat for the Escambia River subpopulation of Gulf sturgeon.

Historic sightings reported from the 1910s and 1920s, and as recently as 1991, have been documented in Escambia County, Alabama, on the Sepulga River (Reynolds 1993). Estes (1991) describes the Sepulga as having smooth rock walls, and long pools with stretches of rocky shoals and sandbars. We included the Sepulga River reach upstream to Alabama County Road 42, Escambia County, Alabama, because it has suitable spawning habitat and documented sightings.

We believe it is most likely that Gulf sturgeon use the Escambia River main stem and all the distributaries for exiting and entering the Escambia/Conecuh River. Gulf sturgeon have been documented to use distributaries near the river mouth within other systems (
e.g.,
Suwannee, Pearl, and Pascagoula River systems) for migration into and out of riverine habitat. We, therefore, have included all distributaries on the Escambia River system (
i.e.,
White River, Little White River, Simpson River, and Dead River) in Unit 3.

Unit 4. Yellow River System in Santa Rosa and Okaloosa Counties, Florida and Covington County, Alabama

Unit 4 includes the Yellow River main stem from Alabama State Highway 55, Covington County, Alabama, downstream to its discharge at Blackwater Bay, Santa Rosa County, Florida. All Yellow River distributaries (including Weaver River and Skim Lake) discharging into Blackwater Bay are included. The Shoal River main stem, a Yellow River tributary, from Florida Highway 85, Okaloosa County, Florida, to its confluence with the Yellow River, is included. The Blackwater River from its confluence with Big Coldwater Creek, Santa Rosa County, Florida, downstream to its discharge into Blackwater Bay is included. Wright Basin and Cooper Basin, Santa Rosa County, on the Blackwater River are included. The lateral extent of Unit 4 is the ordinary high water line on each bank of the associated lakes, rivers and shorelines.

The USGS conducted a subpopulation study in the Yellow River system during the spring (May to July) and fall (October) of 2001. Based on the capture of 98 fish in the spring and the capture/recapture of 94 fish that fall, the USGS estimated the subpopulation to consist of 580 Gulf sturgeon of 1 m (3.3 ft) or greater in size (M. Randall, USGS, pers. comm. 2001). This estimate excludes fish younger than 3 to 4 years of age.

Five distinct limestone outcrops have been documented as possible spawning sites on the Yellow River, between rkm 43 and 134 (rmi 26.7 and 83.3) (Parauka and Giorgianni in prep.). Several sites consist of brittle marl and limestone, and others of porous limestone. The lowest downstream site (rkm 43 (rmi 26.7)) is a primitive rock revetment, a manmade structure with a fair amount of rock substrate (Craft
et al.
2001). In recent years, Alabama State biologists have observed young-of-year Gulf sturgeon near limestone outcrops 3.2 km (2 mi) south of Alabama State Highway 55 (136 rkm (84 rmi)) (Craft
et al.
2001), which confirms that reproduction is occurring within this subpopulation. The river upstream of Alabama State Highway 55 is shallow, sandy, and creek-like and, therefore, not believed suitable for spawning (M. Randall pers. comm. 2001; F. Parauka pers.comm. 2001; G. Morgan, Conecuh National Forest, pers. comm. 2001). Preliminary surveys located four potential summer resting areas on the Yellow River main stem (Craft
et al.
2001). Recent fish captures and the confirmation of spawning at the furthest upstream spawning habitat location near Alabama State Highway 55 support our inclusion of the Yellow River main stem to Alabama State Highway 55 (136 rkm (84 rmi)) as proposed critical habitat for the Yellow River subpopulation of Gulf sturgeon.

The inclusion of the Shoal River, from the Yellow River confluence upstream to the Florida Highway 85 bridge (13 rkm (8 rmi)) , is supported as proposed critical habitat because it is a confirmed summer resting area (Lorio 2000). The potential for distributaries Weaver River and Skim Lake to be used for migration to and from the Yellow River system (Craft
et al.
2001) supports their inclusion as proposed critical habitat. The current and historic use of deep holes by Gulf sturgeon on the Blackwater River main stem and between Wright Basin and Cooper Basin demonstrate the importance of this area for summer resting and staging (Reynolds 1993, Craft
et al.
2001) and support its inclusion as proposed critical habitat for the Yellow River subpopulation.

Unit 5. Choctawhatchee River System in Holmes, Washington, and Walton Counties, Florida and Dale, Coffee, Geneva, and Houston Counties, Alabama

Unit 5 includes the Choctawhatchee River main stem from its confluence with the west and east fork of the Choctawhatchee River, Dale County, Alabama, downstream to its discharge at Choctawhatchee Bay, Walton County, Florida. The distributaries discharging into Choctawhatchee Bay known as Mitchell River, Indian River, Cypress River, and Bells Leg are included. The Boynton Cutoff, Washington County, Florida, which joins the Choctawhatchee River main stem, and Holmes Creek, Washington County, Florida, are included. The section of Holmes Creek from Boynton Cutoff to the mouth of Holmes Creek, Washington County, Florida, is included. The Pea River main stem, a Choctawhatchee River tributary, from the Elba Dam, Coffee County, Alabama, to its confluence with the Choctawhatchee River, Geneva County, Alabama, is included. The lateral extent of Unit 5 is the ordinary high water line on each bank of the associated rivers and shorelines.

Preliminary estimates of the size of the Gulf sturgeon subpopulation in the Choctawhatchee River system are 2,000 to 3,000 fish over 61 cm (24 inches (in)) total length (F. Parauka pers. comm. 2001).

Biologists have located Gulf sturgeon within .8 rkm (.5 rmi) downstream of the Elba Dam, Coffee County, Alabama, on the Pea River (Lorio 2000) and have identified suitable spawning habitat from the Elba Dam to the Pea River mouth (Parauka and Giorgianni in prep., Zehfuss
et al.
in prep.). The Elba Dam prevents sturgeon movement further upstream at all flow conditions. This river reach has one confirmed spawning site, and Gulf sturgeon often use the lower reach for summer resting (Fox
et al.
2000, Hightower
et al.
in press). Suitable spawning and resting habitat, confirmed spawning, and young-of-year and juvenile feeding (F. Parauka pers. comm. 2001) support inclusion of the Pea River reach as proposed critical habitat.

Five spawning sites and seven resting areas have been identified on the Choctawhatchee River main stem between the river mouth (0 rkm (0 rmi)) and upstream to 150 rkm (93 rmi) (Hightower
et al.
in press, Zehfuss
et al.
in prep.). Biologists have identified suitable spawning habitat (limestone outcrops) periodically between 135 rkm (84 rmi) to the confluence of the West

Fork Choctawhatchee River and East Fork Choctawhatchee River (224 rkm (139 rmi)) (H. Blalock-Herod, FWS, pers. comm. 2002; Parauka and Giorgianni in prep.; Zehfuss
et al.
in prep.). Fox
et al.
(2000) located a male at 150 rkm (93 rmi) and another male in spawning condition near Newton (214 rkm (133 rmi)) on the Choctawhatchee River, 8 rkm (5 rmi) downstream of the confluence of the West Fork Choctawhatchee River and East Fork Choctawhatchee River. Since Gulf sturgeon rarely occur upstream of spawning grounds, we have included up to the confluence of West Fork Choctawhatchee River and East Fork Choctawhatchee River for ease of identification and with the probability of unconfirmed spawning grounds. Suitable habitat, confirmed spawning, and young-of-year and juvenile feeding support the inclusion of the Choctawhatchee River main stem as proposed critical habitat.

No sturgeon have been documented within Holmes Creek, except for the section that connects the Choctawhatchee River and Boynton Cutoff, north and south. We have included this river section of Holmes Creek because it acts as part of the Choctawhatchee River main stem. In 1994, Gulf sturgeon were captured during March and April at the mouths of Indian River, Cypress River, and Bells Leg, indicating that sturgeon probably use these distributaries as migratory corridors to and from the Choctawhatchee River main stem. All distributaries, including the Indian River, Cypress River, Bells Leg, and Mitchell River, are included as proposed critical habitat.

Unit 6. Apalachicola River System in Franklin, Gulf, Liberty, Calhoun, Jackson, and Gadsen Counties, Florida

Unit 6 includes the Apalachicola River mainstem, beginning from the Jim Woodruff Lock and Dam, Gadsden and Jackson Counties, Florida, downstream to its discharge at East Bay or Apalachicola Bay, Franklin County, Florida. All Apalachicola River distributaries, including the East River, Little St. Marks River, St. Marks River, Franklin County, Florida, to their discharge into East Bay and/or Apalachicola Bay are included. The entire main stem of the Brothers River, Franklin and Gulf Counties, Florida, a tributary of the Apalachicola River, is included. The lateral extent of Unit 6 is the ordinary high water line on each bank of the associated rivers and shorelines.

Based on mark/recapture studies conducted in 1998 and 1999 in the Apalachicola River downstream of Jim Woodruff Lock and Dam, the summer subpopulation of subadult and adult Gulf sturgeon was estimated to be between 270 and 321 individuals (FWS 1998, 1999). Seventy-one sturgeon were collected in the upper Brothers River, upstream of the Brickyard Cutoff and downstream of Bearman Creek between June and September 1999 (FWS 1999, Lorio 2000). Gulf sturgeon captured on the Brothers River have not been included in the Apalachicola River subpopulation size estimate although they are believed to be part of the subpopulation.

The Gulf sturgeon became restricted to the portion of the Apalachicola River downstream of the Jim Woodruff Lock and Dam upon the construction of the dam in the 1950s. Wooley
et al.
(1982) documented the capture of two Gulf sturgeon larvae on the Apalachicola River just downstream of the Jim Woodruff Lock and Dam, thereby confirming successful spawning up to the dam. Resting aggregations are often seen at the base of the dam. Seven potential spawning sites have been identified in the upper Apalachicola River between Highway 20 and the Jim Woodruff Lock and Dam (120 to 171 km (76 to 106 rmi)) (Parauka and Giorgianni in prep.). Suitable spawning and resting habitat, confirmed spawning, and young-of-year and juvenile feeding support inclusion of the Apalachicola River as proposed critical habitat.

The entire main stem of the Brothers River, a major tributary of the Apalachicola River, is also included as proposed critical habitat. Spawning has not been documented within this tributary, but an important resting area is located in the uppermost section of the Brothers River between Brickyard Cutoff and Bearman Creek (FWS 1999, Lorio 2000). Sturgeon use the lower Brothers River as a resting and possible osmoregulation area (staging) before migrating into the estuarine and marine habitats for winter feeding (Wooley and Crateau 1985). The Apalachicola River distributaries, including the East River, St. Marks River and Little St. Marks River, are included, based on information derived from other systems. Gulf sturgeon tend to use more than just the main stem for migration into and out of the river systems (
e.g.,
Suwannee, Choctawhatchee, and Pearl River systems).

Unit 7. Suwannee River System in Hamilton, Suwannee, Madison, Lafayette, Gilchrist, Levy, Dixie, and Columbia Counties, Florida

Unit 7 includes the Suwannee River main stem, beginning from its confluence with Long Branch Creek, Hamilton County, Florida, downstream to the mouth of the Suwannee River. It includes all the Suwannee River distributaries, including the East Pass, West Pass, Wadley Pass, and Alligator Pass, Dixie and Levy Counties, Florida, to their discharge into the Suwannee Sound or the Gulf of Mexico. The Withlacoochee River main stem from Florida State Road 6, Madison and Hamilton Counties, Florida, to its confluence with the Suwannee River is included. The lateral extent of Unit 7 is the ordinary high water line on each bank of the associated rivers and shorelines.

The Suwannee River supports the largest Gulf sturgeon subpopulation among the coastal rivers of the Gulf of Mexico (Huff 1975, Gilbert 1992). Sulak and Clugston (1999) reported 5,344 uniquely tagged Suwannee River sturgeons from 1986 to 1998. Multiple models using various age classes have been used to estimate the subpopulation size of Gulf sturgeon on the Suwannee River system. Chapman
et al.
(1997) estimated the subpopulation at 3,152 fish greater than age 6. Sulak and Clugston's (1999) estimate was 7,650 individuals greater than 61 cm (24 in) total length and older than age 2. Pine
et al.
(2001) estimated the Suwannee River subpopulation at 5,500 individuals ages 2 to 25. Based on intensive egg sampling efforts conducted between 1993 and 1998, Sulak and Clugston (1999) estimated that 30 to 90 female fish spawn per year.

Marchant and Shutters (1996) collected two Gulf sturgeon eggs in April 1993 on the Suwannee River. These were the first eggs reported from the wild for Gulf sturgeon. Between 1993 and 1998, three spawning sites were confirmed with the collection of Gulf sturgeon eggs on artificial substrate samplers (Marchant and Shutters 1996, Sulak and Clugston 1999). Young-of-year have been documented using between rkm 10 to 237 (rmi 6.2 to 147.3) on the Suwannee River main stem (Carr
et al.
1996a, Sulak and Clugston 1999). The young-of-year sturgeon located at rkm 237 (rmi 147.3), north of Interstate 75, by Sulak and Clugston (1999) was likely spawned in the river as far upstream as Big Shoals and was captured on its way downstream (M. Randall pers. comm. 2002). It is believed that the farthest upstream that sturgeon spawn during high water is Big Shoals, near White Springs, Hamilton and Columbia Counties, Florida, but adult sturgeon are probably unable to move upstream of Big Shoals (Huff 1975; K. Sulak, USGS, pers. comm. 2002; M. Randall pers. comm. 2002).

Suitable spawning habitat has been identified upstream to Big Shoals (Huff 1975; H. Blalock-Herod, FWS, pers. comm. 2002). Foster and Clugston (1997) located five major resting areas throughout the Suwannee River. A deep river bend and a shallow sandy section were characteristic features of the resting areas (Foster and Clugston 1997). Confirmed use for spawning, identified and probable spawning habitat upstream to Big Shoals, young-of year and juvenile feeding, and summer resting support the inclusion of the Suwannee River as proposed critical habitat. For ease of identification, the Suwannee River has been included upstream of Big Shoals .8 rkm (.5 rmi) to its confluence with Long Branch Creek.

Adult Gulf sturgeon sightings and suitable spawning habitat on the lower Withlacoochee River near Florida State Road 141, Hamilton and Madison Counties, Florida, support the inclusion of this area as proposed critical habitat. We have included shoals (5 rkm (3 rmi)) located just upstream of where sturgeon have been observed as possible spawning habitat, and have stopped at Florida State Road 6 (14 rkm (9 rmi)), upstream from the shoals, for ease of identification.

The Suwannee River branches near its mouth into the East Pass and West Pass. Gulf sturgeon adults use the East Pass and West Pass for emigration and immigration (Mason and Clugston 1993, Edwards
et al.
in prep.). The West pass is divided into two primary channels—Wadley Pass, connected to the Gulf of Mexico by a straight dredged channel across the northern portion of the Sound, and Alligator Pass, used by juveniles (Huff 1975), connected to the Gulf of Mexico by an undredged, natural channel. Confirmed use of the East Pass, West Pass, and Alligator Pass, and probable use of the Wadley Pass by adult and juvenile Gulf sturgeon for migration and feeding support the inclusion of all distributaries of the Suwannee River as proposed critical habitat.

Unit 8. Lake Pontchartrain, Lake St. Catherine, The Rigolets, Little Lake, Lake Borgne, and Mississippi Sound in Jefferson, Orleans, St. Tammany, and St. Bernard Parish, Louisiana, Hancock, Jackson, and Harrison Counties in Mississippi, and in Mobile County, Alabama

Unit 8 encompasses Lake Pontchartrain east of the Lake Pontchartrain Causeway, all of Little Lake, The Rigolets, Lake St. Catherine, Lake Borgne, including Heron Bay, and the Mississippi Sound. Proposed critical habitat follows the shorelines around the perimeters of each included lake. The Mississippi Sound includes adjacent open bays including Pascagoula Bay, Point aux Chenes Bay, Grand Bay, Sandy Bay, and barrier island passes, including Ship Island Pass, Dog Keys Pass, Horn Island Pass, and Petit Bois Pass. The northern boundary of the Mississippi Sound is the shoreline of the mainland between Heron Bay Point, Mississippi and Point aux Pins, Alabama. Proposed critical habitat excludes St. Louis Bay, north of the railroad bridge across its mouth; Biloxi Bay, north of the U.S. Highway 90 bridge; and Back Bay of Biloxi. The southern boundary follows along the broken shoreline of Lake Borgne created by low swampy islands from Malheureux Point to Isle au Pitre. From the northeast point of Isle au Pitre, the boundary continues in a straight north-northeast line to the point 1 nautical mile (nm) (1.9 km) seaward of the western most extremity of Cat Island (30°13′N, 89°10′W). The southern boundary continues 1 nm (1.9 km) offshore of the barrier islands and offshore of the 72 COLREGS lines at barrier island passes (defined at 33 CFR 80.815(c), (d) and (e)) to the eastern boundary. Between Cat Island and Ship Island there is no 72 COLREGS line. We therefore, have defined that section of the southern boundary as 1 nm (1.9 km) offshore of a straight line drawn from the southern tip of Cat Island to the western tip of Ship Island. The eastern boundary is the line of longitude 88°18.8′W from its intersection with the shore (Point aux Pins) to its intersection with the southern boundary. The lateral extent of Unit 8 is the MHW line on each shoreline of the included water bodies or the entrance to rivers, bayous, and creeks.

The Pearl River and its distributaries flow into The Rigolets, Little Lake, and Lake Borgne, the western extension of Mississippi Sound. The Rigolets connect Lake Pontchartrain and Lake St. Catherine with Little Lake and Lake Borgne. The Pascagoula River and its distributaries flow into Pascagoula Bay and Mississippi Sound.

This proposed unit provides juvenile, subadult and adult feeding, resting, and passage habitat for Gulf sturgeon from the Pascagoula and the Pearl River subpopulations. One or both of these subpopulations have been documented by tagging data, historic sightings, and incidental captures as using Pascagoula Bay, The Rigolets, the eastern half of Lake Pontchartrain, Little Lake, Lake St. Catherine, Lake Borgne, Mississippi Sound, within 1 nm (1.9 km) of the nearshore Gulf of Mexico adjacent to the barrier islands and within the passes (Davis
et al.
1970, Reynolds 1993, Rogillio 1993, Morrow
et al.
1998a, Ross
et al.
2001a, Rogillio
et al.
in prep., F. Parauka pers. comm. 2002). Substrate in these areas ranges from sand to silt, all of which contain known Gulf sturgeon prey items (Abele 1986, American Fisheries Society 1989, Menzel, 1971).

The Rigolets is a 11.3 km (7 mi) long and about 0.6 km (0.4 mi) wide passage connecting Lake Pontchartrain and Lake Borgne (U.S. Department of Commerce (USDOC) 2002). This brackish water area is used by adult Gulf sturgeon as a staging area for osmoregulation and for passage to and from wintering areas (Rogillio
et al.
in prep.). Lake St. Catherine is a relatively shallow lake with depths averaging approximately 1.2 m (4 ft), connected to The Rigolets by Sawmill Pass. Bottom sediments in Sawmill Pass are primarily silt, while Lake Catherine's bottom is composed of silt and sand (Barett 1971). Incidental catches of Gulf sturgeon are documented from Lake St. Catherine and Sawmill Pass (Reynolds 1993; H. Rogillio, Louisiana Department of Wildlife and Fisheries, pers. comm. 2002). Based on the proximity of Little Lake, Lake St Catherine, and Sawmill Pass to The Rigolets and Pearl River, we believe these areas are also used for staging and feeding and, therefore, are including them with the Rigolets as proposed critical habitat.

Rogillio (1990) and Morrow
et al.
(1996) indicated that Lake Pontchartrain and Lake Borgne were used by Gulf sturgeon as wintering habitat, with most catches during late September through March. Lake Pontchartrain is 57.9 km (36 mi) long, 35.4 km (22 mi) wide at its widest point, and 3 to 4.9 m (10 to 16 ft) deep (USDOC 2002). Morrow
et al.
(1996) documented Gulf sturgeon from the Pearl River system using Lake Pontchartrain (verified by tags) and summarized existing Gulf sturgeon records, which indicated greater use of the eastern half of Lake Pontchartrain. Although Rogillio
et al.
(in prep.) did not relocate any of their sonic tagged adult Gulf sturgeon in Lake Pontchartrain, H. Rogillio (pers. comm. 2002) believes the eastern part of this lake to be an important winter habitat for juveniles and subadults based on previous records. We believe that Gulf sturgeon feed in Lake Pontchartrain during the winter. The Lake Pontchartrain Causeway, twin toll highway bridges, extends 33.6 km (20.9 mi) across Lake Pontchartrain from Indian Beach on the south shore to Lewisburg and Mandeville on the north shore. Sediment data from Lake Pontchartrain indicate sediments have a

greater sand content east of the causeway (Barret 1976, Manheim
et al.
2002). Most records from Lake Pontchartrain are located east of the causeway, with concentrations near Bayou Lacombe and Goose Point, both on the eastern north shore (Reynolds 1993, Morrow
et al.
1996). Gulf sturgeon have also been documented west of the causeway, generally near the mouths of small river systems (Davis 1970). We have excluded the western half of Lake Pontchartrain, however, because we believe that the sturgeon using these areas are coming from these western tributaries and not the Pearl River.

Lake Pontchartrain connects by The Rigolets with Lake Borgne. Lake Borgne, the western extension of Mississippi Sound, is partly separated from Mississippi Sound by Grassy Island, Half Moon (Grand) Island and Le Petit Pass Island. Lake Borgne is approximately 14.3 km (23 mi) in length, 3 to 6 km (5 to 10 mi) in width and 1.8 to 3 m (6 to 10 ft) in depth (USDOC 2002). Most of Lake Borgne sediment is clay and silt (Barett 1971). Many Gulf sturgeon were anecdotally reported as taken incidentally in shrimp trawls in Lake Borgne 0.6 to 1.2 km (1 to 2 mi) south of the Pearl River between August and October from the 1950s through the 1980s (Reynolds 1993). There are twenty-two additional records of Gulf sturgeon in Lake Borgne (D. Walther, FWS, pers. comm. 2002). Known locations are spread out around the perimeter of the Lake, including at the mouth of The Rigolets, Violet Canal, Bayou Bienvenue, Polebe, Alligator Point, and at Half Moon Island (Reynolds 1993). We are proposing to include all of Lake Borgne as critical habitat.

The Mississippi Sound is separated from the Gulf of Mexico by a chain of barrier islands, including Cat, Ship, Horn, and Petit Bois Islands. Natural depths of 3.7-5.5 m (12 to 18 ft) are found throughout the Sound and a channel 3.7 m (12 ft) deep has been dredged where necessary from Mobile Bay to New Orleans (USDOC 2001). Incidental captures and recent studies confirm that both Pearl River and Pascagoula River adult Gulf sturgeon winter in the Mississippi Sound, particularly around barrier islands and barrier islands passes (Reynolds 1993, Ross
et al.
2001a, Rogillio
et al.
in prep.). Pascagoula Bay is adjacent to the Mississippi Sound. Gulf sturgeon exiting the Pascagoula River move both east and west, with telemetry recoveries as far east as Dauphin Island and as far west as Cat Island and the entrance to Lake Pontchartrain, Louisiana (Ross
et al.
2001a). Gulf sturgeon from the Pearl River subpopulation have been documented scattered between Cat Island, Ship Island, Horn Island, and east of Petit Bois Islands to the Alabama State line (Rogillio
et al.
in prep.). Gulf sturgeon have also been documented within 1 nm (1.9 km) off the barrier islands of Mississippi Sound. We, therefore, have included 1 nm (1.9 km) offshore of the barrier islands of Mississippi Sound. Habitat used by Gulf sturgeon in the vicinity of the barrier islands is 1.9 to 5.9 m (6.2 to 19.4 ft) deep (average 4.2 m (13.8 ft)), with clean sand substrata (Heise
et al.
1999b, Ross
et al.
2001a, Rogillio
et al.
in prep.). Preliminary data from substrate samples taken in the barrier island areas indicate that all samples contained lancelets (Ross
et al.
2001a). Inshore locations where Gulf sturgeon were located (Deer Island, Round Island) were 1.9 to 2.8 m (6.2 to 9.2 ft) deep and all had mud (mostly silt and clay) substrata (Heise
et al.
1999b) typical of substrates supporting known Gulf sturgeon prey.

Unit 9. Pensacola Bay System in Escambia and Santa Rosa Counties, Florida

Unit 9 includes Pensacola Bay and its adjacent main bays and coves. These include Big Lagoon, Escambia Bay, East Bay, Blackwater Bay, Bayou Grande, Macky Bay, Saultsmar Cove, Bass Hole Cove, and Catfish Basin. All other bays, bayous, creeks, and rivers are excluded at their mouths. The western boundary is the Florida State Highway 292 Bridge crossing Big Lagoon to Perdido Key. The southern boundary is the 72 COLREGS line between Perdido Key and Santa Rosa Island (defined at 33 CFR 80.810 (g)). The eastern boundary is the Florida State Highway 399 Bridge at Gulf Breeze, Florida. The lateral extent of Unit 9 is the MHW line on each shoreline of the included water bodies.

The Pensacola Bay system includes five interconnected bays, including Escambia Bay, Pensacola Bay, Blackwater Bay, East Bay, and the Santa Rosa Sound. The Santa Rosa Sound is addressed separately in proposed unit 10. The Escambia River and its distributaries (Little White River, Dead River, and Simpson River) empty into Escambia Bay, including Bass Hole Cove, Saultsmar Cove, and Macky Bay. The Yellow River empties into Blackwater Bay. The entire system discharges into the Gulf of Mexico, primarily through a narrow pass at the mouth of Pensacola Bay.

The Pensacola Bay system provides winter feeding and migration habitat for Gulf sturgeon from the Escambia River and Yellow River subpopulations. Over the past four years, researchers of the Florida Department of Environment Protection (FDEP) have conducted tracking studies in the Pensacola Bay system to observe Gulf sturgeon winter migrations. They have identified specific areas in the bays where Escambia River and Yellow River Gulf sturgeon collect, or migrate through, during the fall and winter season. These studies also identified two main habitat types where Gulf sturgeon concentrate during winter months. Movement is generally along the shoreline area of Pensacola Bay. Gulf sturgeon showed a preference for several areas in the bay, including Redfish Point, Fort Dickens, and Escribano Point, near Catfish Basin (FWS 1998, Craft
et al.
2001). Sandy shoal areas, located along the south and east side of Garcon Point, south shore of East Bay (Redfish Point area) and near Fair Point, appear to be commonly used, especially in the fall and early spring. During midwinter, common areas are in deep holes located north of the barrier island at Ft. Pickens, south of the Pensacola Naval Air Station, and at the entrance of Pensacola Pass. The depth in these areas ranges from 6 to 12.1 m (20 to 40 ft). Other areas where tagged fish were frequently located include Escribano Point, near Catfish Basin, and the mouth of the Yellow River. Previous incidental captures of Gulf sturgeon have been recorded in Pensacola Bay, Big Lagoon, and Bayou Grande (Reynolds 1993, Lorio 2000).

Unit 10. Santa Rosa Sound in Escambia, Santa Rosa, and Okaloosa Counties, Florida

Unit 10 includes the Santa Rosa Sound, bounded on the west by the Florida State Highway 399 bridge in Gulf Breeze, Florida. The eastern boundary is the U.S. Highway 98 bridge in Fort Walton Beach, Florida. The northern and southern boundaries of Unit 10 are formed by the shorelines to the MHW line or by the entrance to rivers, bayous, and creeks.

The Santa Rosa Sound is a lagoon between the mainland and Santa Rosa Island that connects Pensacola Bay in the west with Choctawhatchee Bay in the east. The Sound extends approximately 57.9 km (35.9 mi) along an east-west orientation, varying in width between 0.32 and 3.5 km (0.2 to 2.2 mi) (FDEP 1993). The Intracoastal Waterway transects the sound. The Santa Rosa Sound is proposed as critical habitat because we believe it provides one continuous migratory pathway between Choctawhatchee Bay, Pensacola Bay, and the Gulf of Mexico for feeding and genetic interchange. Within the last 3,000 years, periodic shoaling closed the opening of

Choctawhatchee Bay to the Gulf of Mexico. For many years, the Santa Rosa Sound provided the only way for Choctawhatchee River Gulf sturgeon to migrate to the Gulf of Mexico (Wakeford 2001). Recent locations of subadult and adult Gulf sturgeon within the Santa Rosa Sound confirm its present use by the Choctawhatchee River subpopulations (F. Parauka pers. comm. 2002, Fox
et al.
in press). The Escambia and Yellow River subpopulations may also use this area due to its close proximity. Gulf sturgeon have been located mid-channel and in shoreline areas in 2 to 5.2 m (6.6 to 17.1 ft) depths and sand substrate. The approximate length of the proposed critical habitat unit is 52.8 km (33 miles). Bridges were chosen as the eastern and western boundaries for ease in identification. Any portion of the sound not included in this unit is captured by the adjacent critical habitat units.

Unit 11. Florida Nearshore Gulf of Mexico Unit in Escambia, Santa Rosa, Okaloosa, Walton, Bay, and Gulf Counties in Florida

Unit 11 includes a portion of the Gulf of Mexico as defined by the following boundaries. The western boundary is the line of longitude 87°20.0′ W (approximately 1 nm (1.9 km) west of Pensacola Pass) from its intersection with the shore to its intersection with the southern boundary. The northern boundary is the MHW of the mainland shoreline and the 72 COLREGS lines at passes as defined at 30 CFR 80.810 (a-g). The southern boundary is 1 nm (1.9 km) offshore of the northern boundary. The eastern boundary is the line of longitude 85°17.0′ W from its intersection with the shore (near Money Bayou between Cape San Blas and Indian Peninsula) to its intersection with the southern boundary.

Unit 11 includes winter feeding and migration habitat for Gulf sturgeon from the Yellow River, Choctawhatchee River, and Apalachicola River subpopulations. Telemetry relocation data suggest that these subpopulations feed in nearshore Gulf of Mexico waters between their natal river systems (Fox
et al.
in press, F. Parauka pers. comm. 2002). Gulf sturgeon from the Choctawhatchee River subpopulation have been documented both east and west of Choctawhatchee Bay (F. Parauka pers. comm. 2002, Fox
et al.
in press). In the winter of 2001-2002, the USGS and FWS attached pop-up satellite tags to 20 Gulf sturgeon (12 from the Suwannee River, 4 from the Choctawhatchee River, 2 from the Apalachicola, and 2 from the Yellow River) to investigate winter feeding migrations in the Gulf of Mexico. Due to a design flaw, errors in attachment, or sturgeon's ability to successfully knock the tags off, the tags failed to report reliable data with only two exceptions. One of the Choctawhatchee-tagged Gulf sturgeon was located in Hogtown Bayou in Choctawhatchee Bay. This provided no new information, as we already knew that some adult Gulf sturgeon overwinter in this bayou. The other operating tag, however, was one that had been attached to a Yellow River Gulf sturgeon. Sonic tracking in the vicinity of that Yellow River Gulf sturgeon led to the relocation of other sonic tagged Gulf sturgeon. Sonic-tagged individuals from three different subpopulations (Choctawhatchee, Yellow, and Apalachicola Rivers) were relocated on multiple occasions in close proximity to one another, suggesting an important feeding area just offshore of Mexico Beach, Crooked Island East, and Crooked Island West over sand substrate. The data suggest that Gulf sturgeon from the Yellow River, Choctawhatchee River, and Apalachicola River remain within 1.6 km (1 mi) of the coastline between these river systems (F. Parauka pers. comm. 2002). Examination of bathymetry data along the Gulf of Mexico coastline between the Pensacola Bay and Apalachicola Bay reveals that depths of less than 6 m (19.7 ft), within which Gulf sturgeon are generally found, are all contained within 1 nm (1.9 km) from shore. Gulf nearshore substrate contains unconsolidated, fine-medium grain sands which support crustaceans such as mole crabs, sand fleas, various amphipod species, and lancelets (Menzel 1971, Abele 1986, American Fisheries Society 1989). Based on their direction of movement over time, it appeared these Gulf sturgeon were feeding in the nearshore Gulf of Mexico on route to their natal rivers. Given this information we are including the nearshore (up to 1 nm (1.9 km)) Gulf of Mexico waters between Pensacola and Apalachicola Bays.

Unit 12. Choctawhatchee Bay in Okaloosa and Walton Counties, Florida

Unit 12 includes the main body of Choctawhatchee Bay, Hogtown Bayou, Jolly Bay, Bunker Cove, and Grassy Cove. All other bayous, creeks, and rivers are excluded at their mouths/entrances. The western boundary is the U.S. Highway 98 bridge at Fort Walton Beach, Florida. The southern boundary is the 72 COLREGS line across East (Destin) Pass as defined at 33 CFR 80.810(f). The lateral extent of Unit 12 is the MHW line on each shoreline of the included water bodies.

Choctawhatchee Bay provides important habitat for maintaining the health of subadult and adult Gulf sturgeon as evidenced by a large number of Gulf sturgeon overwintering in the system (FWS 1997, 1998; Parauka
et al.
in press). The Choctawhatchee Bay offers a feeding area for both subadults and adults (FWS 1998, Fox
et al.
in press). Tagged subadults showed a preference for shoreline habitats which are predominated by sandy substrates, low salinity and water depths less than 3 m (10 ft) (FWS 1997, 1998; Parauka
et al.
in press). Most adult Gulf sturgeon were found in shallow water (2 to 4 m (6.6 to 13.1 ft)) with predominantly (greater than 80 percent) sandy sediment (Fox
et al.
in press). Ghost shrimp, a component of the sturgeon diet, are typically found in substrates ranging from sandy mud to organic silty sand (Felder and

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A02-13620. Public record. Not legal advice.