Stock Enhancement and Carrying Capacity of Blue Crab Nursery Habitats in Chesapeake Bay

Abstract

Declining populations of the blue crab, Callinectes sapidus, may be suitable for enhancement with hatchery-reared juveniles. For three years, field experiments were conducted to determine if shallow, unvegetated, marsh-fringed nursery habitats in lower Chesapeake Bay are below carrying capacity and thus capable of supporting additional juvenile crabs. The field experiments included sampling of wild and hatchery-reared juvenile blue crabs and their major benthic prey, and manipulative experiments to assess the survival of juvenile crabs and the abundance of benthic prey in enhanced and control coves. Densities of the clam Macoma balthica, a major prey of the blue crab, were initially high in enhanced coves and decreased to a level equivalent to that in control coves by the end of the experiment, but always remained well above a low-density threshold. Survival of juvenile crabs was lowest where clam densities were highest, suggesting that alternative prey did not deter predation on juvenile crabs, but instead led to higher densities of cannibalistic crabs through bottom-up control. Crab densities correlated with densities of major benthic prey and prey density never dropped below a low-density threshold. Marsh-fringed nurseries are apparently below carrying capacity for the blue crab and could be enhanced through the release of hatchery-reared juveniles.

Keywords:

• clams
• benthos
• bottom-up control
• alternative prey
• carrying capacity
• Callinectes sapidus

ACKNOWLEDGEMENTS

Thanks to collaborations with the University of Maryland Biotechnology Institute, Center of Marine Biotechnology (Y. Zohar, A. Place, O. Zmora, and staff), Smithsonian Environmental Research Center (A. H. Hines, E. Johnson, and staff), and North Carolina State University (D. Eggleston), as well as contributions from many VIMS students and staff, NSF REU interns, and Virginia Governor's School High School interns. We are grateful to Senator Barbara Mikulski and NOAA, Chesapeake Bay Office, for funding. This is contribution #2815 from the Virginia Institute of Marine Science.