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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 field. On a broader scale, such studies also contribute to determining whether stock enhancement is possible in the case of the Chesapeake blue crab.

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Abstract:In certain cases of severely depleted fishery stocks, combining stock enhancement with traditional management techniques may be a useful way of returning stocks to an exploitable size. The Chesapeake Bay stock of blue crabs (Callinectes sapidus) has declined over the past decade and appears to be recruitment-limited, making it an appropriate candidate for enhancement efforts. This study serves as a first step in determining whether large-scale enhancement of blue crab stocks is feasible. Four hatchery-raised cohorts of 4000 -10 000 (25 000 in total) juvenile (6-30 mm carapace width, 58-70 days old) crabs were released in upper Chesapeake Bay coves. Sixty days after release, these crabs constituted 22%-79% of all crabs in the hatchery-crab size range (corresponding to an enhancement level of 28%-366%). Crabs released earlier in the summer reached maturity at the age of 6 months, younger than their wild counterparts. Estimated survivorship to maturity was 16%-20% for early-released crabs and 5-15% for latereleased crabs. Late-released crabs, like wild crabs, had to overwinter before becoming mature. Our study suggests ways to improve success of hatchery-raised individuals that can be broadly applied across taxa. The results also contribute specifically to determining whether large-scale stock enhancement is possible in the case of the Chesapeake Bay blue crab.Résumé : Chez certains stocks fortement réduits, la combinaison de mesures d'amélioration des stocks et de méthodes de gestion courantes peut être utile pour rétablir les stock à une taille exploitable. Le stock de crabes bleus (Callinectes sapidus) de la baie de Chesapeake a décliné au cours de la dernière décennie et semble limité par des problèmes de recrutement; c'est donc un bon candidat pour les efforts d'amélioration des stocks. Notre étude constitue une première étape pour déterminer si une amélioration du stock de C. sapidus à grande échelle est possible. Quatre cohortes de 4 000 à 10 000 (total de 25 000) jeunes (largeur de carapace, 6-30 mm; âge, 58-70 jours) crabes de culture ont été relâchés dans les anses supérieures de la baie de Chesapeake. Soixante jours après l'ensemencement, ces crabes représentaient 22-79 % des tous les crabes des classes de taille des crabes de culture, ce qui correspond à un niveau d'amélioration de 28-366 %. Les crabes relâchés plus tôt au printemps atteignent la maturité à l'âge de 6 mois, donc plus rapidement que les crabes sauvages. La survie à la maturité est estimée à 16-20 % chez les crabes relâchés tôt et à 5-15 % chez les crabes relâchés tard. Les crabes relâchés tard, tout comme les crabes sauvages, doivent passer l'hiver avant d'atteindre la maturité. Notre étude suggère des méthodes pour augmenter le succès d'individus élevés en culture qui sont largement applicables à d'autres taxons. Nos résultats contribuent aussi de façon spécifique à évaluer si des améliorations de stock à grande échelle sont possibles chez le crabe bleu de la baie de Chesapeake.[Traduit par la Rédaction] Davis et al. 122