Egg sampling confirmed that Suwannee River Gulf sturgeon Acipenser oxyrinchus desotoi, a subspecies of Atlantic sturgeon A. o. oxyrinchus use the same spawning site at river kilometer (rkm) 215 from the mouth of the river each year. Forty-nine eggs were recorded in 1995, and 368 were recorded in 1996. Spawning began 4-7 d after the March new moon in both years and lasted 10-11 d; in 1996, a second 10-d spawning round began on the April new moon. Developmental synchrony among eggs recovered suggested several discrete spawning events in both years. Total eggs deposited for three 1996 sampling days was estimated as 405,600-711,000/d, approximating the fecundity range of a large female Gulf sturgeon. Eggs were found only in the southern half of the river, an area with surface currents of 0.5-1.5 m/s and numerous eddies producing reverse bottom currents of 0.1-0.5 m/s. Egg substrate consisted of bedrock limestone thinly overlain by fine sand and densely distributed elliptical gravel 2-10 cm in diameter. Eggs were found predominantly in depths of 2-4 m at water temperatures of 17-21ЊC, conductivities of 50-100 S, and dissolved oxygen levels exceeding 5.0 mg/L. The Cody Scarp, 15 rkm above the spawning ground, may mark the upstream limit of spawning areas in the river. Three 2-4month-old riverine juveniles (82-115 mm total length, TL) collected are the smallest yet captured from any river. Data for 18 riverine age-0 juveniles (to 350 mm TL) suggest that this stage lasts 6-10 months, terminating with migration of fish to the river mouth in January-February. Less than 2% of 461 juveniles captured at the estuarine river mouth (1990)(1991)(1992)(1993) were under 350 mm TL. Riverine age-0 fish were collected over long shallow stretches (typically Ͻ4 m deep) of relatively barren sand (rkm 12-238).

Gulf sturgeon spawn on portions of three sites in the upper Suwannee River, which may appropriately be described as spawning reefs. The same areas are utilized from year to year. Habitat factors important in spawning site determination include gravel/cobble substrate, the presence of eddy fields, a neutral to slightly alkaline pH, and an empirically observed range in calcium ion content (6-18 mg/L Ca+, corresponding to a conductivity range of 40-11OpS).Eggs are deposited contagiously within a small area (< 10,000 m2) with very little scatter, suggesting little if any current drift. They are not found from samplers on immediately adjacent sand substrate. The broadcast spawner model does not seem to fit the Gulf sturgeon. Spawning begins 4-7 days after the March new moon, with water temperature above 17.0 oC, and extends for 9-23 days as discrete events involving individual females. Spawning may continue, if water temperature remains below 21-22oC. The total annual pool of spawning females in the Suwannee population is estimated at 80 individuals. Young of the year utilize open sand habitat away from shoreline and vegetated habitat. They disperse widely, and occur over freshwater reaches from rkm 10-237

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Soft‐bodied annelids, arthropods, and occasionally globular molluscs were primary foods of the threatened Gulf sturgeon Acipenser oxyrinchus desotoi collected from the mouth upriver to kilometer 221 of the Suwannee River, Florida, in 1988–1990. In spring, large subadults and adults that immigrated from the estuary had fed primarily on lancelets, brachiopods, amphipods and other crustaceans, polychaetes, and gastropods. Small Gulf sturgeons that remained near the mouth of the river during spring fed on epibenthic and hyperbenthic amphipods and grass shrimp and on isopods, oligochaetes, polychaetes, and chironomid and ceratopogonid larvae found in the intertidal zone, Subadults of more than 5 kg and adults in the freshwater middle river reaches between km 55 and 221 essentially fasted during the summer and fall. Gulf sturgeons in the Suwannee River were indifferent to abundant potential freshwater foods and apparently had stored sufficient nutrient reserves while in the estuary. A presumably young‐of‐year or year‐old Gulf sturgeon captured in summer at the most upriver site (km 221) had fed on aquatic insects and oligochaetes. Most Gulf sturgeons of all sizes had ingested detritus or biofilm.

The movements of 67 Gulf sturgeon Acipenser oxyrinchus desotoi equipped with radio transmitters were monitored in the Suwannee River, Florida, from March 1989 through August 1992. The objectives of this study were (1) to determine the seasonal movement patterns and distribution of Gulf sturgeon while in freshwater, (2) to document relationships between water temperature and Gulf sturgeon movement, and (3) to determine whether springs were used as thermal refugia by these fish. Gulf sturgeon were detected entering the river from mid-February through April; they moved upstream at an average speed of 3.5 km/d to areas where they remained until October or November. Gulf sturgeon moved no more than 0.6 river km (on average) upstream or downstream from their established summer area. Gulf sturgeon began leaving the Suwannee River from mid-September through early November and moved downstream at an average speed of 6.2 km/d; all fish returned to the Gulf of Mexico by early December. Water temperatures associated with spring and fall migrations averaged 22.1 °C (range, 16.0-28.0°C) and 21.3°C (range, 16.9-26.8°C), respectively. Gulf sturgeon were frequently close to springs throughout the warmest period, but none were located within a spring or the thermal plume emanating from a spring.