Pilot evaluation of summer flounder stock enhancement potential using experimental ecology

Abstract

Stock enhancement is receiving increasing attention as a management tool to rebuild depleted fisheries. Unfortunately, proactive studies addressing the potential of stock enhancement to accomplish management goals prior to the implementation of enhancement efforts are uncommon. We outline an ecologically based, pilot protocol with which to address the potential of fisheries stock enhancement using hatchery-reared (HR) organisms, through trial releases coupled with laboratory and field experiments with juvenile summer flounder Paralichthys dentatus. Released HR fish did not persist in nursery habitats in which wild fish enjoyed relatively long residence times and high survival. Multiple lines of observations and evidence suggest that the relatively rapid disappearance of released HR fish was not a result of emigration. Caging and tethering trials, coupled with previously obtained behavioral data, suggest that the poor performance of HR fish in this study was a result of increased susceptibility to predation-induced mortality, as compared with wild fish. These results suggest that post-release survival of HR summer flounder might be increased by (1) improving methods of predator-conditioning, (2) releasing HR fish in sites that serve as natural refuges from predators, or (3) releasing fish at larger sizes. While poor post-release survival of HR summer flounder may limit the success of stock enhancement efforts with this species, we suggest that conclusions regarding the potential of stock enhancement as a management tool can only be made if biological information is coupled with economic information to predict economic costs associated with stock enhancement relative to costs associated with alternative management approaches.

Complexity affects habitat preference and predation mortality in postlarval Penaeus plebejus: implications for stock enhancement

“…Stock enhancement is one of the more expensive and least successful fishery management options available (Grimes 1998, Kellison et al 2003. To reduce the ecological uncertainties that often limit its success, a candidate release species' optimal habitat must be known together with this habitat's carrying capacity and how to minimize losses through predation (Rothlisberg 1998).…”

Generalized Predatory Impact Model: A Numerical Approach for Assessing Trophic Limits to Hatchery Releases and Controlling Related Ecological Risks

“…In addition, Tatara et al (2011) found that while the stocking of hatcheryreared steelhead parr (Oncorhynchus mykiss) into experimental streams led to an increase in the composite (hatchery-reared and natural) population, the emigration of natural steelhead parr led to an overall decrease in the abundance of natural recruits. Evidence of displacement arising from overstocking is rare in marine systems, potentially due to the complex experimental framework required to detect population and community changes in manipulated ecosystems (some good examples can be found in Leber et al, 1995;Kellison et al, 2003;Brennan et al, 2008;Eggleston et al, 2008). It should be noted, though, that if fish survive to reproduce, density dependence may arise, such as increased mortality or displacement in subsequent generations.…”

Pilot Evaluation of Early Juvenile Blue Crab Stock Enhancement Using a Replicated BACI Design

“…Multiple stock enhancement programs and pilot releases of hatchery-reared individuals appear to be successful (e.g., McEachron et al, 1994;Leber and Arce, 1996;Fushimi, 1998;Agnalt et al, 1999;Lenanton et al, 1999;Davis et al, 2005), whereas others suggest stock enhancement efforts are not or may not be logistically or economically advisable (Hilborn, 1998;Ottera 1999;Kellison et al, 2003;Kellison and Eggleston 2004). Because of the extensive effort necessary to estimate the success and possible ecological ramifications of stock enhancement, it is advisable to first address the likelihood of actually enhancing wild stocks using pilot studies, because failure at this stage would render future investigations of ecological and economic potential of stocking unnecessary (Kellison et al, 2003). If release scenarios determine that post-release survival of hatchery-reared organisms will achieve biological and economic goals (e.g., Kellison and Eggleston, 2004), then managers can focus on potential ecological impacts of release (e.g., Leber, 1995;McMichael et al, 1999).…”