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Sturgeons Atlantic Sturgeon Acipenser oxyrinchus Shortnose Sturgeon Acipenser brevirostrum Contributor: John W. McCord DESCRIPTION Taxonomy and Basic Description The Atlantic sturgeon, Acipenser oxyrinchus (Mitchell 1815) belongs to the sturgeon family, Acipenseridae. Atlantic sturgeon are among the longest-lived fish, with a life span approaching 50 years or greater. Sexual maturity is not obtained until age 8 to 20, with males maturing younger than females (ASMFC 1990 and 199
Transcript Sturgeons Atlantic Sturgeon  Acipenser oxyrinchus   Shortnose Sturgeon  Acipenser brevirostrum Contributor: John W. McCordDESCRIPTION Taxonomy and Basic Description  The Atlantic sturgeon,  Acipenser oxyrinchus  (Mitchell 1815) belongs to the sturgeon family,Acipenseridae. Atlantic sturgeon are among thelongest-lived fish, with a life span approaching50 years or greater. Sexual maturity is notobtained until age 8 to 20, with males maturing younger than females (ASMFC 1990 and 1998).The Atlantic sturgeon is also the largest fish inhabiting freshwaters on the Atlantic Coast, withfemales in South Carolina reaching about 2.5 m (8 feet) TL. Sexually mature female Atlanticsturgeon, often called ‘cows,’ may weigh several hundred kilograms or pounds. Mature maleAtlantic sturgeons, or ‘bucks,’ are generally smaller than females, rarely exceeding 1.8 m (6 feet)TL and 45 kg (100 pounds).Atlantic sturgeons, like other sturgeons, are shaped like sharks and have a deeply forked tail inwhich the upper lobe is longer than the lower. A single, small dorsal fin is located far back toward the tail and a single anal fin is directly beneath on the underside. Paired pectoral andpelvic fins srcinate immediately rear of the bony operculum and vent, respectively. The headextends forward into a snout that is pointed in juveniles and blunt and rounded in adults. Theprotrusible mouth is underneath and at the rear of the snout, and is preceded by a row of fourbarbels similar to those on catfishes. The mouth, the width of which is about one half thedistance between the eyes, does not bear teeth, but bony plates in the throat are used to crushfood items if necessary (Gilbert 1989; Vladykov and Greeley 1963). The skeleton is partlycartilaginous, with the skull and leading edges of the pectoral fins among the boniest structures.Structural support and protection are provided by thick, tough skin with three rows of bonyplates or scutes and much smaller scale-like ‘scutelets.’ The skin is generally rough, and gritty,not unlike that of a shark. Coloration is dark bronze to brownish above, lighter on the sides andwhite below (Gilbert 1989; J.W. McCord, SCDNR, pers. obs.).The shortnose sturgeon,  Acipenser brevirostrum (Lesueur 1818) is also classifiedin the Acipenseridae family. Adults are muchsmaller than adult Atlantic sturgeon, with‘cows’ reaching 1.2 m (47 inches) TL andreaching a maximum weight of perhaps 18 kg(40 pounds). Mature ‘bucks’ are generallysmaller than females, rarely exceeding 0.8 m(32 inches) TL and 7 kg (15 pounds). Theshortnose sturgeon is similar in shape and    physical characteristics to the Atlantic sturgeon. The snout is pointed only in young juveniles,and is broad, blunt and rounded in adults. The mouth is nearly as wide (70 percent) as is thedistance between the eyes, and wider than for Atlantic sturgeon of similar size (Gilbert 1989).The body is also protected by three rows of scutes, but compared to those of Atlantic sturgeon,the bony plates collectively cover less surface area and ‘scutelets’ are small and sparse. Theskin, though thick and tough, is less rigid than that of Atlantic sturgeon and is much smootherand often slimy or mucous-covered (J.W. McCord, SCDNR, pers. obs.). Coloration is generallybrownish above with pinkish or salmon tones, lighter on the sides, and white below. Because of this coloration, commercial fishers often refer to this species as ‘salmon sturgeon.’ Shortnosesturgeon are also long-lived fish, reaching age 55 (Dadswell 1979), but this species reachessexual maturity at an earlier age than Atlantic sturgeon. In the South, males may mature as soonas age two and females at age six (Dadswell et al. 1984).As indicated by the orientation of the mouth, both species of sturgeon are benthic feeders thatprimarily prey on invertebrates. Aquatic insects such as mayfly and midge larvae and smallcrustaceans predominate the juvenile shortnose sturgeon diets (Dadswell et al. 1984; Carlson andSimpson 1987), whereas mayfly larvae, amphipods and earthworms are most frequentlyconsumed by juvenile Atlantic sturgeon. Adults of both species consume mollusks, snails andamphipods (Van Den Avyle 1984; Dadswell et al. 1984; Haley 1998). Amphipods areparticularly abundant in the lower Edisto River near the fresh-brackish interface (J.W. McCord,SCDNR, pers. obs.); preliminary evidence indicates amphipods and polychaetes as prevalentdietary items for sturgeons in similar habitat in the Savannah River (B. Post, SCDNR, pers.comm., 2005). Status Both the Atlantic and shortnose sturgeons are identified with rankings of G3 and S3(NatureServe 2005), meaning that populations for both species are “vulnerable,” both globallyand in South Carolina. In general, populations of both species of sturgeon along the entireAtlantic Coast are reduced from historical levels for at least the past half-century (ASMFC 1990;ASMFC 1998; NMFS 1998). The Atlantic sturgeon was considered for listing under theEndangered Species Act (ESA) in 1998, but the National Marine Fisheries Service (NMFS)determined that listing was unwarranted. However, the gulf sturgeon (  Acipenser    oxyrinchus   desotoi ), a subspecies of the Atlantic sturgeon restricted to rivers and adjacent waters of the Gulf of Mexico, remains on the candidate list and is currently listed as “threatened” under the ESA.The shortnose sturgeon has been listed as “endangered” under the ESA since 1967 and theAmerican Fisheries Society deemed it “threatened” in 1989.POPULATION DISTRIBUTION AND SIZEAtlantic sturgeon historically ranged along the Atlantic coast from Labrador, Canada to the St.Lucie River, Florida (ASMFC 1990). The historical range of the shortnose sturgeon is verysimilar, from the St. John River, Canada to the St. Johns River, Florida (Vladykov and Greeley1963). Currently, both species are thought to be either very rare or extirpated from the extremesouthern portion of their ranges.  In South Carolina, Atlantic sturgeon and shortnose sturgeon both occur as relatively distinctpopulations by river system, as typical for anadromous fishes (Quattro et al. 2002; Wirgin et al.2000). There is a minimum of five populations (presumably for both species) in South Carolina:the Waccamaw-Pee Dee, Santee, Cooper, ACE Basin (Ashepoo, Combahee and Edisto Rivers)and Savannah River drainage basins. In addition, historical records indicate that Atlanticsturgeon occurred in the Coosawhatchie River (Smith et al. 1984), but current status is unknown.Since historical data relative to individual stock status are absent and current information isincomplete, the status of all stocks is poorly understood.In general, shortnose sturgeon stocks are more genetically isolated and dissimilar than areAtlantic sturgeon stocks, presumably because shortnose sturgeon are freshwater amphidromous,largely confined within each river basin (Kynard 1997; NMFS 1998) while Atlantic sturgeon aretruly anadromous and intermingle (Quattro et al. 2002).Historical data that relate directly to population size for South Carolina stocks are nonexistent,but historical distribution records and anecdotal information on abundance strongly indicate thatall populations of sturgeons in South Carolina are reduced from early 20 th century and previouslevels (USFWS 2001). The current status and trends in stock status over the past 25 years forboth sturgeons in South Carolina are based primarily on anecdotal information and short-termdatasets. Collectively, stock status of Atlantic sturgeon throughout the state was considered indecline based on trends of commercial landings in the early 1980s (Smith et al. 1984). Waccamaw-Pee Dee Basin : This large basin may currently provide sturgeon access to the vastmajority of their historical range of spawning and early nursery habitat, which was identified byMills (1826); low falls near the fall-line may have prevented further inland access except underhigh flows. Presumably, spawning of both Atlantic and shortnose sturgeon presently occurs overmore than 200 km (100 mi) of river mainstem in suitable channel habitats. Available dataindicate the presence of spawning stocks of both sturgeons in the basin, but the extent of basin-wide distribution and habitat utilization is largely unknown. Furthermore, relationships of individual tributary-specific sub-populations, should such exist, are unknown. Presumablyfishery impacts are below levels present through 1984, and current conditions should allowpopulations of both species to recuperate. Santee Basin : The Santee basin has the second largest drainage area and total discharge of allriver systems on the east coast of the United States (Hughes 1994). This large watershed hasbeen impacted by damming to a greater extent than most basins on the Atlantic coast of NorthAmerica, with 88 percent of the river’s annual flow diverted into the Cooper River from 1942through 1985 (Kjerfve and Greer 1978). With the construction of the Santee-Cooper lakes(Moultrie and Marion) in the 1940’s, the vast majority of the Santee was closed to migratoryfishes. The navigational lock at Pinopolis Dam has been shown to be ineffective at passingshortnose sturgeon (Cooke et al. 2002; Timko et al. 2003). Fish passed at St. Stephen Dam arerecorded on videotape, and only four sturgeons have been passed at the St. Stephen Dam since1985 (D. Cooke, SCDNR, pers. comm., 2004). During the approximately 40 years since theimpoundment of the Santee River, average flows in the Santee River seaward of Wilson Damhave been greatly reduced from historical levels (Kjerfve and Greer 1978). Stocks of bothsturgeons were undoubtedly severely impacted over the four decades of generally low flows.  Surveys have recorded both adult shortnose sturgeon and juvenile Atlantic sturgeon in rather lownumbers through 2001 (Collins and Smith 1996; Cooke and Leach 2004a).A dam-locked population of shortnose sturgeon is present in the Santee-Cooper Lakes, withspawning apparently occurring at least into the Congaree River below Columbia (Collins et al.2003). Fish passage observations indicate that this population receives little genetic influx fromeither river. Sustainability of the population within the lakes is unknown, but dam-lockedshortnose sturgeon populations tend to be in poorer conditions than open river populations(Collins et al. 2003). The relationship of animals from this population to those in the Cooper andSantee Rivers is not yet clear, though a preliminary study shows animals within the lakes and inthe Cooper River to be genetically similar (Collins et al. 2003). The Cooper River : Several hundred adults are believed to inhabit the Cooper River andfertilized eggs have been collected below Pinopolis Dam (Cooke and Leach 2002). However,neither larvae nor juveniles have been collected and successful reproduction has not beenconfirmed (Cooke and Leach 2004b). The status and viability of sturgeon populations in theCooper River remains poorly understood, particularly for Atlantic sturgeon. The ACE Basin : The rivers that make up the pristine ACE basin remain unimpounded. Atlanticsturgeon likely spawn in both the Edisto and Combahee Rivers (Collins et al. 2000). Norecords exist for adult Atlantic sturgeon in Ashepoo River. Prior to 1994, there were very fewauthenticated records of shortnose sturgeon in the ACE basin and only one record in the lowerAshepoo River (Collins and Smith 1996; McCord 2003). The Savannah and Edisto Rivershortnose sturgeon populations are similar genetically (Quattro et al. 2002). Available evidencestrongly suggests that the current Edisto River shortnose sturgeon population has received amajor contribution from Savannah River animals and that the Edisto population has increasedover the past 10 to 15 years or more (McCord 2003). Otherwise, the current status of sturgeonstocks in the ACE Basin is poorly understood. If fishery-induced mortality was once the majorlimiting factor on populations of both species in the ACE Basin, current conditions shouldpromote population growth. Coosawhatchie and Ashley Rivers : These are small, coastal plain drainages. Atlantic sturgeonwere harvested commercially in the Coosawhatchie River in 1982 (Smith et al. 1984). Otherwise,there are no records for this area except reports of juvenile Atlantic sturgeon taken by shrimptrawls in lower Port Royal Sound. Several juvenile Atlantic sturgeon have been taken in theAshley River during shrimp trawl surveys (J. Jenkins, SCDNR, pers. comm.), but no otherrecords exist. There are no records for shortnose sturgeon in either of these rivers. The status of both the Atlantic and shortnose sturgeon is unknown for these small rivers. Savannah River : There are spawning populations of both Atlantic and shortnose sturgeon in theSavannah River (Hall et al. 1991; Collins and Smith 1996; Collins et al. 2002; Smith and Collins1998). However, the status of stocks is poorly understood and survival of juveniles andrecruitment to the adult population has been identified as a potential limiting factor in populationgrowth, particularly for shortnose sturgeon (Smith et al. 1992). According to historicaldistribution records much of the historically available spawning and nursery habitat for sturgeonsin the Savannah River remains accessible (USFWS 2001).
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