Limits to the use of contemporary genetic analyses in delineating biological populations for restocking and stock enhancement

Managers of restocking and stock enhancement programs have dual needs with respect to unit-stock identification: (1) identifying boundaries of genetically discrete stocks for responsible genetic management, and (2) delineating demographically discrete stocks. The reality, however, is that the temporal/spatial boundaries of genetic and demographic stocks may be discordant. Tagging data for the common snook, Centropomus undecimalis, show that there is little movement between Florida (FL) Gulf of Mexico and Atlantic waters. Nearly all snook from the Gulf inhabit a single estuary for their entire lives, whereas most Atlantic snook stray or emigrate much greater distances. A robust microsatellite DNA analysis of 1,300 specimens confirmed the genetic distinctiveness of Gulf and Atlantic stocks. Curiously, there was no evidence of genetic structure within the Gulf stock. Inferring demographic stock boundaries using genetic data alone could lead to the erroneous conclusion that releases in a single Gulf estuary would eventually influence catch rates along the entire Gulf coast. Alternative methods for unit-stock identification and careful consideration of their inherent limitations are needed to identify the area over which demographic benefits or genetic impacts from releases of cultured juveniles can be expected.