Differences between hatchery-raised and wild blue crabs: Implications for stock enhancement potential

Stock enhancement of severely exploited, recruitment-limited fisheries has been controversial for several reasons, one of which is the lack of information about competency, competitiveness, and survivorship of hatchery-reared individuals released into the field. Because enhancement efforts have focused on finfish, even less information is available with which to assess enhancement potential of crustaceans. The Chesapeake Bay stock of blue crabs Callinectes sapidus has declined by more than 80% over the past 12 years and has exhibited recruitment limitation, leading to recent efforts to study the potential of enhancing populations with hatchery-reared juveniles. To assess how hatchery-raised juvenile blue crabs may fare after release into the Chesapeake Bay, we compared several aspects of hatchery and wild crabs. Hatchery crabs readily fed on natural prey, moved in the field similarly to wild crabs, and grew at rates similar to those of wild crabs; however, the two crab groups differed in other factors important to field survival. Prerelease and laboratory-held hatchery crabs had different carapace morphology (smaller spines) than wild crabs, though spine lengths increased to normal proportions by several weeks after release. Hatchery crabs did not initially bury in sediment as often as wild crabs, suggesting inexperience with an important predator escape response. Hatchery crabs were also,preyed upon at higher rates in the field than wild crabs. Conditioning experiments suggest that inexperience with sediment and low burial rates were not the main cause of higher predation. By identifying areas in which hatchery individuals may be relatively weak and deficits that can potentially be mitigated, studies such as this can lead to improving the success of hatchery-raised individuals in the held. On a broader scale, such studies also contribute to determining whether stock enhancement is possible in the case of the Chesapeake blue crab.