Gulf Sturgeon Spawning Migration and Habitat in the Choctawhatchee River System, Alabama±Florida

Transactions of the American Fisheries Society 129:811±826, 2000 q Copyright by the American Fisheries Society 2000 Gulf Sturgeon Spawning Migration and Habitat in the Choctawhatchee River System, Alabama±Florida DEWAYNE A. FOX North Carolina Cooperative Fish and Wildlife Research Unit, Department of Zoology, North Carolina State University, Raleigh, North Carolina, 27695-7617, USA JOSEPH E. HIGHTOWER* North Carolina Cooperative Fish and Wildlife Research Unit, U.S. Geological Survey, Biological Resources Division, Department of Zoology, North Carolina State University, Raleigh, North Carolina, 27695-7617, USA FRANK M. PARAUKA U.S. Fish and Wildlife Service, Field Of®ce, 1612 June Avenue, Panama City, Florida 32405, USA Abstract.ÐInformation about spawning migration and spawning habitat is essential to maintain and ultimately restore populations of endangered and threatened species of anadromous ®sh. We used ultrasonic and radiotelemetry to monitor the movements of 35 adult Gulf sturgeon Acipenser oxyrinchus desotoi (a subspecies of the Atlantic sturgeon A. oxyrinchus) as they moved between Choctawhatchee Bay and the Choctawhatchee River system during the spring of 1996 and 1997. Histological analysis of gonadal biopsies was used to determine the sex and reproductive status of individuals. Telemetry results and egg sampling were used to identify Gulf sturgeon spawning sites and to examine the roles that sex and reproductive status play in migratory behavior. Fertilized Gulf sturgeon eggs were collected in six locations in both the upper Choctawhatchee and Pea rivers. Hard bottom substrate, steep banks, and relatively high ¯ows characterized collection sites. Ripe Gulf sturgeon occupied these spawning areas from late March through early May, which included the interval when Gulf sturgeon eggs were collected. For both sexes, ripe ®sh entered the Choctawhatchee River signi®cantly earlier and at a lower water temperature and migrated further upstream than did nonripe ®sh. Males entered the Choctawhatchee River at a lower water temperature than females. Results from histology and telemetry support the hypothesis that male Gulf sturgeon may spawn annually, whereas females require more than 1 year between spawning events. Upper river hard bottom areas appear important for the successful spawning of Gulf sturgeon, and care should be taken to protect against habitat loss or degradation of known spawning habitat. The Atlantic sturgeon Acipenser oxyrinchus the Gulf States Marine Fisheries Commission comprises two disjunct subspecies along the At- 1995). lantic and Gulf coasts: the Gulf of Mexico form, Historically, Gulf sturgeon supported substan- A. o. desotoi (hereafter referred to as Gulf stur- tial commercial and limited sport ®sheries in Flor- geon) and the allopatric East Coast form, A. o. ida (U.S. Commission of Fish and Fisheries 1902; oxyrinchus (hereafter referred to as Atlantic stur- Burgess 1963; Smith and Clugston 1997). Overall, geon). Gulf sturgeon have one of the southernmost commercial ®sheries showed many signs of over- distributions of sturgeon worldwide (Bemis and exploitation. Catches declined rapidly in most ar- Kynard 1997). Historically, Gulf sturgeon ranged eas, and in 1984 the state of Florida ended harvest throughout the Gulf of Mexico from Louisiana to in all state waters. This was followed in 1991 by Charlotte Harbor, Florida. However, populations Federal designation of Gulf sturgeon as a threat- have been severely reduced or extirpated through- ened species. In an effort to prevent future declines out much of their range and present distribution is and to bolster the current Gulf sturgeon population from east of the Mississippi River to the Suwannee levels, the U. S. Fish and Wildlife Service and the River, Florida (U.S. Fish and Wildlife Service and Gulf States Marine Fisheries Commission com- pleted a Recovery/Fishery Management Plan for the subspecies. The plan identi®ed a need to collect * Corresponding author: [email protected] information on Gulf sturgeon habitat requirements Received December 22, 1998; accepted December 27, 1999 (U.S. Fish and Wildlife Service and the Gulf States 811 812 FOX ET AL. Marine Fisheries Commission 1995). This plan collection of fertilized eggs (Kempinger 1988; speci®cally cites the need for information regard- LaHaye et al. 1992). Sturgeon eggs in benthic ®sh ing the location, timing, and characteristics of es- intestines have been used to identify spawning sential spawning habitat. Recently, genetically dis- sites for the Chinese sturgeon A. sinensis (Zhong- tinct subunits of Gulf sturgeon were identi®ed Ling and Yan 1991). Atlantic sturgeon spawning throughout the Gulf of Mexico (Stabile et al. sites have been identi®ed by use of telemetry, cap- 1996); therefore, efforts must be taken to examine ture of larvae, collection of ripe individuals, and spawning habitat and life history characteristics analysis of reproductive hormones and metabolites within individual river systems. (Dovel and Berggren 1983; Van Eenennaam et al. Early efforts to delineate Gulf sturgeon spawn- 1996). ing locations were largely unsuccessful. Sampling Our primary objective was to delineate probable for eggs and larvae of Gulf sturgeon in the Su- spawning sites for Gulf sturgeon in the Choctaw- wannee River with 1-m plankton nets stationed hatchee River system of Alabama and Florida. This near the bottom produced neither, in spite of con- objective was to be addressed by tracking radio- siderable sampling (Huff 1975). In the Apalachi- tagged ®sh during the spawning season and by cola River, Florida, some incidental information deploying egg collectors in areas where telemetry on the location of spawning sites was derived by evidence indicated that adult ®sh were present. A the capture of three Gulf sturgeon larvae (Wooley secondary objective was to examine the role of et al. 1982). Recent efforts to delineate Gulf stur- sex and reproductive status on movement patterns geon spawning habitat have relied primarily on and habitat selection. arti®cial substrates to collect eggs (Marchant and Shutters 1996; Sulak and Clugston 1998). Over a Study Area 2-year period, collection of fertilized Gulf stur- The Choctawhatchee River originates in south- geon eggs at four discrete locations in the Suwan- eastern Alabama and ¯ows southward approxi- nee River provided the ®rst information regarding mately 280 km through Florida, eventually emp- the speci®c location and timing of spawning for tying into Choctawhatchee Bay (Figure 1). The this species (Marchant and Shutters 1996). These Choctawhatchee River drains a watershed in ex- ®rst insights provided a necessary starting point cess of 12,000 km2 and has an average discharge for more detailed studies. Recently, the collection of 198 m3/s, which makes it the third largest river of large numbers of eggs and detailed habitat char- in Florida (Bass et al. 1980). The watershed is acteristics of three Gulf sturgeon spawning loca- mostly agricultural or forested and has relatively tions has provided substantial new detail regarding low levels of urbanization, especially in the head- habitat characteristics within the Suwannee River waters. The Choctawhatchee River lacks a main- (Sulak and Clugston 1998; K. Sulak, U.S. Geo- stem impoundment, which makes it unique com- logical Survey-Biological Resources Division, pared with most other historical Gulf sturgeon riv- personal communication). ers. Two major tributaries contribute to the Choc- A combination of approaches have been used to tawhatchee River, the Pea River in the northern identify spawning sites for other sturgeon. Col- portion of the watershed and Holmes Creek, which lections of eggs and larvae with arti®cial sub- is the major tributary in Florida. The Pea River is strates, plankton nets, and beam trawls, combined located almost entirely within Alabama, and there with observations of spawning activity, have pro- is a run-of-the-river dam on the Pea River at river vided information regarding the spawning habitat kilometer (rkm) 191. requirements of white sturgeon A. transmontanus (McCabe 1990; Parsley et al. 1993; McCabe and Tracy 1994; Schaffter 1997). For shortnose stur- Methods geon A. brevirostrum, movement to and from Netting operations using multiple multi-®lament spawning sites has been characterized with telem- anchored gill nets (91.4±121.9 m long, 20±36 cm etry; the reproductive status of ®sh at hypothesized stretch mesh) were conducted within Choctaw- spawning sites was determined by visual inspec- hatchee Bay during late winter and early spring of tion, release of milt in males and movement pat- 1996 and 1997 (Figure 1). Nets were deployed terns (Buckley and Kynard 1985; Hall et al. 1991; perpendicular to the shoreline to maximize the in- Kieffer and Kynard 1993). Lake sturgeon A. ful- tercept area for migrating ®sh and were checked vescens spawning sites have been identi®ed by di- at 4-h intervals to minimize mortality risk. Sam- rect observation of spawning behavior and by pling was concluded when all transmitters had GULF STURGEON SPAWNING AND HABITAT 813 FIGURE 1.ÐLocation of Choctawhatchee River system and plotted maximum upstream relocation (in river ki- lometers or rkm from the mouth of the river) and reproductive status for individual female Gulf sturgeon for the 1996 and 1997 ®eld seasons. For ®sh captured in 1996 that returned in 1997, reproductive status in 1997 is unknown. been implanted within ®sh large enough to be sex- taining buffered 10% formalin for histological ually mature

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