Genetic Effective Size in Populations of Hatchery‐Raised Red Drum Released for Stock Enhancement

Abstract

Genetic analysis of progeny from 13 spawning events occurring over a 2-week period in a Texas Parks and Wildlife Department (TPWD) hatchery for red drum Sciaenops ocellatus during the spring of 2002 and hatchery spawning and release records over the 2003 spawning season were used to estimate the average genetic effective size of an average spawn and an average hatchery-released population. The purpose of this study was to assess the potential for a Ryman-Laikre effect in the TPWD red drum stock enhancement program. Genetic analysis revealed that 16 of 27 dams (59.2%) and 16 of 18 sires (88.9%) spawned at least once. The average effective size (N e ) for a single spawn was 2.59, approximately 43% less than the maximum N e (4.55) predicted if all possible mating (dam 3 sire) combinations had occurred and family size per mating combination had been equivalent. The reduction in N e stemming from the actual number of mating combinations was approximately 34% and appeared to be due primarily to nonspawning dams; the reduction in N e generated by the actual variation in family size was approximately 9%. Spawning and release records at the TPWD hatchery indicate that in 2003 the number of released populations per bay or estuary ranged from 7 to 27. Using the average effective size (N e ) estimate for a single spawn (2.59), the estimated average effective size of all released fish per bay or estuary (N eR ) in 2003 ranged from about 28.5 to about 46.6. These values of N eR are less than the averages estimates of about 272 and 263 for the long-term (N eI ) and contemporaneous (N eV ) effective size, respectively, of red drum in bays and estuaries in the northern Gulf of Mexico and indicate a reasonable potential for a Ryman-Laikre effect. Approaches that might be employed to increase the N eR of TPWD-released fish and decrease the probability of a Ryman-Laikre effect are discussed.

Compromising genetic diversity in the wild: unmonitored large-scale release of plants and animals

“…Estimated N e for local populations is roughly 10 2 -10 3 compared to a census size on the order of 10 6 adults [70][71][72]. Individual broodstock programs typically use 40-200 adults [71][72][73], but non-random contributions of different parents leads to relatively low hatchery N e [69,71,72].…”

“…Individual broodstock programs typically use 40-200 adults [71][72][73], but non-random contributions of different parents leads to relatively low hatchery N e [69,71,72]. A detailed study of one Texas hatchery in one year estimated the hatchery N e to be 28-47 [71]. Hatchery fish had habitat usage similar to wild fish in Florida [74] but not in Texas [69].…”

A Genetic Assessment of a Red Drum, Sciaenops ocellatus, Stock Enhancement Program

“…The dissimilarity between decreases in N bc and N ec and corresponding reductions in genetic diversity metrics, when comparing this study to those based on semelparous species, is likely because red drum have about 35 year‐classes represented in the adult population, and so high proportions of stocked fish within a single year‐class typically have a small impact on the genetic diversity of the population. Similarly, Gold et al () also reported the potential of a Ryman–Laikre effect from stocking large numbers of red drum into a Texas estuary from small effective population sizes in the hatchery, but did not detect reductions in genetic diversity in the wild (Carson et al ). Ultimately, N bc and N ec are measures of the influences of stocking on the effective population size of individuals recruiting into the adult population.…”

Economic, ecological and genetic impacts of marine stock enhancement and sea ranching: A systematic review

“…No changes in genetic diversity of Pacific herring ( Clupea pallasii ) with spatiotemporal stable population structures were observed (Kitada et al., ; Kitada, Yoshikai, et al., ). The Texas red drum enhancement programme replaces ~25% of the broodfish with wild each year; nevertheless, the analysis suggested a potential R‐L effect (Gold, Ma, Saillant, Silva, & Vega, ; Karlsson, Saillant, Bumguardner, Vega, & Gold, ). In contrast, no effect on genetic diversity was reported in the stocked red drum population in the South Carolina (Katalinas, Brenkert, Darden, & Denson, ).…”