Release strategies for estuarine species with complex migratory life cycles: Stock enhancement of Chesapeake blue crabs (Callinectes sapidus)

Responsible stock enhancement requires rigorous experiments to develop release strategies that account for movement of all life-history stages among habitats across inshore-offshore and estuarine gradients. However, crab stock enhancement research to date has focused primarily on hatchery production, with only limited field assessments of the efficacy of releases to increase the target population. This paper summarizes ongoing research to develop effective release strategies for hatchery-reared juveniles to augment the spawning biomass of Chesapeake Bay blue crabs, which has declined 80% in 15 years and appears to be recruitment limited. Our release experiments focused on three factors: (1) components of preparation and release, which included life stage and size at release, pre-release conditioning to minimize differences between hatchery and wild crabs, and micro-habitat and micro-timing of release; (2) stocking variables, particularly seasonal timing of release and stocking density; and (3) site selection and coordination, including release macro-habitat and location of release sites along environmental gradients, emphasizing coordination of release site and fishing pressure with migration corridors linking nurseries to spawning areas. In the first 5 years of research, we demonstrated that small (1,000-10,000) cohorts of hatchery reared, 20 mm, 7th-instar juvenile blue crabs can be tagged and released into small (1-10 ha) coves, and that these cohorts can be followed successfully to quantify growth, survivorship, and productivity of the enhanced population. We also determined the timing and routes of migration using a tag-reward system with the cooperation of fishers. Our multifaceted research strategy provides a model for responsible approaches to stock enhancement of other species with complex migratory life cycles.