Genetic evaluation of American shad Alosa sapidissima restoration success in James River, Virginia

摘要

The American shad Alosa sapidissima has experienced severe declines throughout its native range due to habitat degradation, fragmentation, and over-fishing. Hatchery supplementation is often used for stock restoration, but the effects of supplementation on population structure and genetic diversity are rarely assessed. This study employed molecular markers to evaluate how supplementation of the James River American shad population with Pamunkey River origin larvae since 1994 has impacted genetic diversity and population structure. Population genetic parameters of other major Chesapeake Bay tributaries (Susquehanna, Rappahannock, Potomac, and Nanticoke) also were characterized. Prior to stocking, the James and Pamunkey populations exhibited subtle genetic differentiation, which was absent among post-supplementation samples, presumably due to the stockings. A similar situation was observed among other shad populations of Chesapeake Bay tributaries which were subtly differentiated in the 1990s but lacked any credible among-population differentiation among contemporary samples. Genetic diversity of the James River shad population was high prior to stocking, and remained high throughout years of intensive supplementation, yet the current population decline suggests that the James River shad population still has not recovered. Despite harvest curtailment, elimination of the ocean intercept fishery, and widespread supplementation efforts, Chesapeake Bay tributary American shad populations are collectively at their lowest levels in recorded history. Therefore, success of other restoration goals such as creation of fish passage in James River was investigated in a concurrent radio telemetry study to assess passage at Bosheru27s Dam fishway. Ninety-four American shad were radio-tagged on the spawning grounds below Bosheru27s Dam. Approximately one-half of the tagged shad were detected at the escapement receiver within 24 hours after tagging, and the average residence times of remaining shad were approximately one week. No tagged shad were detected above Bosheru27s Dam. These results imply that restricted passage through Bosheru27s Dam fishway may be an important factor in the failure of James River American shad to recover. Therefore, improving passage at migratory barriers such as Bosheru27s Dam, in conjunction with a continued Bay-wide fishing moratorium, may be more beneficial to shad restoration efforts in James and other Chesapeake Bay tributaries than continued supplementation.