STOCK STRUCTURE AND HOMING FIDELITY IN GULF-OF-MEXICO STURGEON (ACIPENSER OXYRINCHUS DESOTOI) BASED ON RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM AND SEQUENCE ANALYSES OF MITOCHONDRIAL-DNA

Efforts have been proposed worldwide to restore sturgeon populations t hrough the use of hatcheries to supplement natural reproduction and to reintroduce sturgeon where they have become extinct. We examined the population structure and inferred the extent of homing in the anadromo us Gulf of Mexico (Gulf) sturgeon (Acipenser oxyrinchus desotoi). Rest riction fragment length polymorphism and control region sequence analy ses of mitochondrial DNA (mtDNA) were used to identify haplotypes of G ulf sturgeon specimens obtained from eight drainages spanning the subs pecies' entire distribution from Louisiana to Florida. Significant dif ferences in haplotype frequencies indicated substantial geographic str ucturing of populations. A minimum of four regional or river-specific populations were identified (from west to east): (1) Pearl River, LA a nd Pascagoula River, MS, (2) Escambia and Yellow rivers, FL, (3) Choct awhatchee River, FL, and (4) Apalachicola, Ochlockonee, and Suwannee r ivers, FL. Estimates of maternally mediated gene flow between any pair of the four regional or river-specific stocks ranged between 0.15 to 1.2. Tandem repeats in the mtDNA control region of Gulf sturgeon were not perfectly conserved. This result, together with an absence of hete roplasmy and length variation in Gulf sturgeon mtDNA, indicates that t he molecular mechanisms of mtDNA control region sequence evolution dif fer among acipenserids.