Abstract
AbstractHatchery supplementation programs have been implemented for several populations of American Shad Alosa sapidissima, which are declining across the species' native range due to disrupted access to spawning grounds, habitat degradation, and overfishing. The genetic impacts of stocking Pamunkey River‐origin larvae into the James River American Shad population since 1994 were investigated, and the effects were considered within a regional context by including American Shad populations from other Chesapeake Bay tributaries that also received interbasin stockings from various rivers over the same period. Levels of genetic diversity for microsatellite markers were high in all populations except the Susquehanna River population, which showed a significant decline in diversity between the 1990s and 2007. Before supplementation of James River American Shad, the James and Pamunkey River populations exhibited subtle standardized differentiation among groups (F′CT = 0.012), whereas differentiation was reduced after supplementation (F′CT = 0.007), indicating that supplementation contributed to homogenization of population structure within the two rivers. Chesapeake Bay tributaries also displayed higher levels of differentiation in the 1990s (F′CT = 0.063) than in contemporary, supplemented samples (F′CT = 0.004). Bayesian analyses of population structure among 1990s Chesapeake Bay samples only identified the Susquehanna River as having a distinguishable population, and no population structure was detected among samples collected in the late 2000s. In light of the fact that Chesapeake Bay American Shad populations are not rebounding in response to supplementation, our observation of reduced genetic differentiation among populations is a likely signal of substitution by hatchery‐origin fish rather than increasing natural recruitment. As such, spawning habitat improvement in conjunction with continued baywide fishing regulation may be a more beneficial strategy for restoring viable American Shad populations than continued reliance on supplementation.Received June 5, 2013; accepted February 3, 2014
Highlights
The American Shad Alosa sapidissima is an anadromous alosine clupeid with a North American native range extending from the Saint Johns River, Florida, to the Saint Lawrence River, Quebec (Leim 1924)
Some of the most intensive supplementation of American Shad populations in the species’ native range has been within Chesapeake Bay tributaries (Mansueti and Kolb 1953; ASMFC 2007), especially the Susquehanna River, in which supplementation was resumed in the 1970s and has included larvae from broodstock collected in the Columbia River, Chesapeake Bay rivers, and the Delaware, Hudson, and Connecticut rivers
The Pamunkey River population, and all of the Chesapeake Bay populations were consistent with those described by Hasselman et al (2013), who sampled American Shad that were collected in 2003–2006 from coastal rivers throughout the species’ entire native range, including Chesapeake Bay
Summary
The American Shad Alosa sapidissima is an anadromous alosine clupeid with a North American native range extending from the Saint Johns River, Florida, to the Saint Lawrence River, Quebec (Leim 1924). As. a result, numerous restoration programs have been initiated in multiple states, with the common goal of creating self-sustaining populations through harvest regulation, hatchery supplementation, and re-establishment of access to historical spawning grounds via dam removal or the construction of fish passage facilities (ASMFC 2007). Since the early 1990s, Virginia has initiated large-scale American Shad restoration efforts, and Maryland has expanded American Shad restoration and supplementation beyond the Susquehanna River and its tributaries (Hendricks 2003; Olney et al 2003) These restoration efforts include hatchery components (Supplementary Table S.1) in addition to habitat improvements and fishing regulation. A temporal genetic analysis of the James and Pamunkey River populations throughout multiple years of supplementation would (1) provide insight into whether genetic diversity of the James River population has changed over time, (2) provide information about the origin of untagged recruits returning to the James River, and (3) indicate whether levels of genetic differentiation between the James and Pamunkey River populations have increased or decreased
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