United states department of interior bureau of ocean energy management

3.3Atlantic Sturgeon (Gulf subspecies)

3.3.1Description of the Species

The Atlantic sturgeon (Gulf subspecies) (Acipenser oxyrinchus desotoiis) an anadromous fish (migrating seasonally between fresh and salt water) that range primarily from the Suwannee River in Florida to the Mississippi River in Louisiana (Morrow et al. 1996). Atlantic sturgeon are light to dark brown with a pale underside (USFWS and GSMFC 1995). Sturgeon have elongate, fusiform bodies covered by naked skin imbedded with bony plates or scutes. The average adult Atlantic sturgeon ranges in length from 4 to 7 ft (120 - 225 cm) and weights exceeding 300 lbs (135 kg); size varies according to gender, age, and spawning condition (USFWS 1980; Huff 1975). The largest recorded Atlantic sturgeon was caught at Cow Horn Reef near the mouth of the Mississippi River in September 1936 and had a weight of 503 lbs (228.2 kg) and a length of 9 ft (274 cm) (Reynolds 1993). Females live longer than males and continue to grow with age, consequently they are larger and heavier than males (Huff 1975). Sexual maturity is reached between 8 and 17 years (females) and 7 to 21 years (males) (Huff 1975). Atlantic sturgeon are long lived and may live to at least 42 years (Huff 1975).

The diet of juvenile (2.2 to 4.4 lbs [1 - 2 kg]) sturgeon includes brackish-water amphipods, chironomid larvae, certapogonid larvae, aquatic insects, and small bivalves. Arthropods, annelids, and mollusks are consumed by juvenile sturgeon in rivers and adults in estuaries. Macroinvertebrates, such as dipteran larvae, amphipods, isopods, small grass shrimps, and annelids are key prey species of 2.2 to 22 lbs (1 - 10 kg) Atlantic sturgeon feeding in river mouths. Subadults (22 to 42 lbs [10 - 19 kg]) also consume mud or ghost shrimp. Adult sturgeon in estuaries and coastal areas primarily consume amphipods, polychaetes, lancelets, gastropods, isopods, brachiopods and shrimp (Mason et al. 1993; Carr et al. 1996). Atlantic sturgeon generally eat soft-bodied foods, avoiding armored or spiny organisms. Organisms that are encrusted or have hardened tubes, such as polychaetes and corophiid amphipods, and bony fishes are less likely to be consumed (Mason et al. 1993). Inorganic and organic detritus is consumed incidentally by Atlantic sturgeon (Mason et al.1993). Non-spawning sturgeon may feed longer in the estuaries and bays than spawning adults before moving into the rivers (Fox et al. 2000).

The USFWS and NMFS have joint responsibility regarding consultation for this species. The USFWS is responsible for consultations that occur in riverine habitat and in estuarine habitats with the Department of Transportation, the Environmental Protection Agency (EPA), the U.S. Coast Guard (USCG), and the Federal Emergency Management Agency (FEMA). The NMFS is responsible for consultations that occur in the marine environment and in estuarine habitats with the Department of Defense (DOD), the U.S. Army Corps of Engineers (USACE), the Bureau of Ocean Energy Management (BOEM), and any other Federal agencies not mentioned here.

3.3.2Species Habitat and Distribution

Atlantic sturgeon live in the estuaries and coastal shelf regions of the GOM during cooler months (October to March). In March and early April, adult sturgeon begin migrating into freshwater rivers to spawn. Non-ripe adults, juveniles, and subadults also migrate, but generally move into the rivers days to months after spawning adults. Sexually mature, ripe males, and females enter rivers when surface water temperatures reach 62 to 70^o F (Carr et al. 1996). Male sturgeon in the Choctawhatchee Bay in Florida enter the river earlier than female sturgeon and migrate farther upstream (Fox et al. 2000). Males remain at the spawning grounds longer than females. Ripe sturgeon entered the Choctawhatchee River earlier and moved significantly further upstream than non-ripe fish. After spawning, males and females return to the lower river and reside with non-ripe sturgeon in summer holding areas until the fall migration. After hatching, age-0 fish remain in riverine habitats through January and age-1 fish move into the estuaries in February (Sulak and Clugston 1998).

Sturgeon return to the Gulf after the fall spawning period with dropping river temperatures. Sturgeon leave the rivers for winter marine habitats when river temperatures equal fall Gulf temperatures (usually late October or early November) and surface water temperatures are between 62 to 72^o F (Foster and Clugston 1997). Adult Atlantic sturgeon in the Suwannee River in Florida may remain in the lower river and adjacent estuary for several weeks of pre-migratory staging (from late November to early December; Sulak and Clugston 1999). Although it has been suggested that this staging period between fresh and salt water may be necessary for osmoregulation (Murphy and Skaines 1994), sturgeon in some rivers (e.g., the Pearl River in Louisiana) move through the river-bay interface rapidly with little time for acclimatization (Howard Rogillio, LDWF pers. comm. to USACE). By age one, Atlantic sturgeon have developed an active mechanism for osmoregulation and ion balance in euryhaline environments (Altinok et al. 1998).

The presence of the Florida peninsula led to the development of the subspecies in the Gulf; this speciation is maintained by the thermal barrier of the Gulf Stream around south Florida (Huff 1975). The Mississippi River may also limit movements in the Gulf east of the Mississippi River. Atlantic sturgeon have historically inhabited many larger tributaries east of the Mississippi River, including upstream of the Ross Barnett Dam on the Pearl River (Morrow et al. 1996). The present range of the Atlantic sturgeon within the GOM extends from Lake Pontchartrain and the Pearl River system in eastern Louisiana and western Mississippi east to the Suwannee River in Florida (USFWS and NMFS 2009). The largest GOM population of Atlantic sturgeon is in the Pearl River system. The East Timbalier and West Belle Pass project areas are not within the current known range of the Atlantic sturgeon.

3.3.3Status and Cause of Decline

The Atlantic sturgeon (Gulf subspecies) was federally listed as threatened throughout its range on September 30, 1991 and is also listed as a threatened species in Louisiana. The present range extends from east of the Mississippi River in Louisiana east to the Suwannee River in Florida.

On March 19, 2003, the USFWS and NMFS designated critical habitat for the Atlantic sturgeon in Louisiana, Mississippi, Alabama, and Florida (Federal Register Volume 68, No. 53). Portions of the Pearl and Bogue Chitto Rivers, Lake Pontchartrain east of the Lake Pontchartrain Causeway, Little Lake, The Rigolets, Lake St. Catherine, and Lake Borgne were designated critical habitat in Louisiana.

Historically, the Atlantic sturgeon supported commercial and recreational fisheries throughout most of their range from the Mississippi River east to Tampa Bay (U.S. Commission of Fish and Fisheries 1902, cited in Wooley and Crateau 1985). Atlantic sturgeon populations declined due to fisheries overexploitation (Barkuloo 1988), spawning habitat loss due to dam construction, and deterioration of water quality in natal rivers (Morrow et al. 1996). Around 1860, large-scale exploitation of Atlantic sturgeon began after it was discovered that smoked sturgeon could be substituted for smoked halibut and Atlantic sturgeon eggs could be made into high-quality caviar (Smith 1990). Sturgeon were harvested with gillnets, pound nets, otter trawls, harpoons, trammel nets, weirs, stake row nets, and seines (Huff 1975; Smith 1985; Van Den Avyle 1984; Smith and Clugston 1997). Sturgeon are vulnerable to gill nets and shrimp trawls, although turtle excluder devices (TEDs) may reduce bycatch in shrimp trawls. Poaching still occurs even though fishing is restricted (Collins et al. 2000). These fishing restrictions have not restored the population size, this may be due to reduced suitable spawning habitat. Dams and low water sills prevent spawning adults from moving to traditional spawning grounds. Low dissolved oxygen from eutrophication also contribute to spawning habitat degradation. Adults and subadults are not greatly affected by changes in salinity, dissolved oxygen, or high temperatures; however, eggs and larvae have low tolerance ranges (Collins et al. 2000). The shallow and productive habitats created and protected by barrier islands and headlands are essential for the Atlantic Gulf sturgeon to complete its life cycle. Further negative impacts or degradation caused by shoreline change could bring this species closer to extinction because the population is already significantly reduced and freshwater spawning habitats are extensively degraded.