Gulf sturgeon are anadromous, spawning in freshwater and returning to the marine environment to feed. Herein, we document the marine distribution and timing of movement in and out of the marine environment of Gulf sturgeon natal to the Pascagoula and Pearl rivers (MS and LA). From 1999 to 2004, we attached sonic transmitters to 194 fish averaging 151 (MS) to 160 (LA) cm in fork length. We located 56 different Gulf sturgeon in the estuarine or marine environments, some multiple times. Fish were distributed nonrandomly, being found primarily in shallow water (mean=3.9 m) in barrier island passes. Benthic samples taken at Gulf sturgeon telemetry location sites were dominated by Florida lancelets, sand dollars, annelids, haustoriid amphipods, and mollusks-all docu-

Gulf sturgeon Acipenser oxyrinchus desotoi are federally listed as threatened, the principal reasons for population declines being habitat loss due to dams, overfishing, and water quality deterioration. The timing of freshwater migration and the locations and habitat features of spawning areas are undocumented for Gulf sturgeon in the Pascagoula River drainage. Our objectives were to identify and characterize spawning areas, determine spring movement patterns, and document homing fidelity by gill netting and radio‐tracking. Through collection and rearing of Gulf sturgeon eggs, we verified that the Bouie River north of Hattiesburg, Mississippi (250 river kilometers upstream from the mouth of the Pascagoula River), is a spawning area. We also documented homing fidelity in the Bouie River using radiotelemetry and capture data. Prolonged residence and overwintering of Gulf sturgeon were observed near the Bouie River spawning area. This behavior may be caused by the modified nature of this portion of the Bouie River, which includes deep, in‐channel gravel pits. Spawning habitat was located in an upstream reach that consisted of hard substrata and gravel with turbulent, high flow. The spawning area on the Bouie River and access to it are vitally important for this species in Mississippi.

Summary The anadromous Gulf sturgeon occurs along the north central coast of the Gulf of Mexico and is federally listed as threatened. We analyzed fine‐scale patterns of Gulf sturgeon population structure, focusing on the Pascagoula River drainage of Mississippi, in reference to movement patterns as determined via telemetry and capture data. We genotyped 361 Gulf sturgeon using eight microsatellite loci including samples from the Pascagoula, Pearl, Escambia, Yellow, Choctawhatchee, and Apalachicola river drainages. Pairwise FST estimates indicated that genetic structure occurs at least at the drainage level. The Pascagoula and Pearl rivers form a western group, demonstrating 100% bootstrap support for a division with drainages to the east. Assignment tests detected non‐natal genotypes occurring in all drainages. According to assignment tests, the Pascagoula supports an admixture of individuals, containing minimal influence from drainages to the east (2%) and substantial interaction with the Pearl River (14.1%). The occurrence of Pascagoula River fish in the Pearl was non‐reciprocal, observed at 1.1%. After accounting for non‐natal genetic diversity within the Pascagoula, there remained a disparity between a pooled Pascagoula group and the only documented spawning site within the drainage located in the Bouie River. We interpret this as an indication of a second genetic stock within the Pascagoula River drainage. Radio telemetry data suggest that spawning likely occurs in the Chickasawhay River, in areas isolated from the Bouie River spawning site by about 350 river kilometers. We emphasize the utility of integrating field and molecular approaches when delineating fine‐scale patterns of population structure in anadromous fishes.

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