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

Abstract

We quantified whether local populations of early juvenile blue crabs (J1–2) could be enhanced through the translocation of crabs to underutilized nursery habitats, and if enhancement success, survival, and potential impacts of stocked crabs on their benthic prey varied in a density-dependent manner. Using plankton nets, ∼143,000 blue crab megalopae were collected as they ingressed into Pamlico Sound, NC. Of these, ∼13,800 early juvenile blue crabs (J1–2 stages) were then stocked at potential nursery sites relatively far removed (32–70 km) from their initial settlement areas using a replicated before-after control impact (BACI) experimental design. On average, there was negative enhancement success (−34%) five weeks after local crab enhancement, and no evidence of density-dependent enhancement success, mortality, or impact on potential crab prey. Poor stocking success was likely due to pelagic emigration from enhancement sites relative to controls. Attempts to assess the feasibility of stocking blue crabs at local scales of small coves should (i) probably not consider J1–2 stages because of their apparent propensity to emigrate from these areas, or (ii) further assess the effects of geomorphology and wind fetch of release sites on density-dependent emigration.

Keywords:

• BACI
• blue crabs
• density-dependence
• stock enhancement
• translocation

ACKNOWLEDGEMENTS

We thank J. Harcke for use of her wet-laboratory at the North Carolina Aquarium on Roanoke Island for grow-out of megalopal stage blue crabs. We are grateful to P. Rudershausen, D. Moore, N. Reyns, and G. Bell for their expert assistance in the field. We thank Reiji Masuda and two anonymous referees for comments on a previous version of this manuscript. Funding was provided by the Blue Crab Advanced Research Consortium, Center of Marine Biotechnology, University of Maryland, and the North Carolina Blue Crab Research Program (02-STOK-02).