Robert Aguilar

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

Abstract 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 fa...

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.

Importance of blue crab life history for stock enhancement and spatial management of the fishery in Chesapeake Bay

Due to over-harvesting and habitat degradation, spawning stock abundance and biomass of the Chesapeake Bay blue crab (Callinectes sapidus) has declined over 80% in the last 15 years. In addition, only a small portion (11–22%) of the spawning stock migrates successfully to the historic spawning areas of the lower estuary. As a result, recent management goals to decrease harvests and increase spawning stock biomass have been adopted by the different Chesapeake Bay regulatory agencies. The crisis has also prompted an experimental assessment of the potential for stock enhancement to increase the number of spawners. While much of the current stock enhancement work has focused on assessing the competency of hatchery-reared individuals and identifying key processes that optimize survival and growth of juveniles to maturity, less attention has been paid to examining factors that influence the long-term efficacy of stock enhancement efforts. Here we discuss important interactions between blue crab life history, stock enhancement efforts, and management options available to increase the standing stock of mature females in Chesapeake Bay. We propose the establishment of migration corridors to protect female blue crabs when they undergo the long-distance migration after mating to lower Bay spawning areas.

Assessment of River Herring Spawning Runs in a Chesapeake Bay Coastal Plain Stream using Imaging Sonar

AbstractRecent declines in anadromous river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) have been documented in much of their range using fishery-independent spawning run counts. A lack of rigorous long-term run counts and demographic data for Chesapeake Bay spawning stocks resulted in the declaration of unknown stock status in a 2012 stock assessment and made it difficult to evaluate responses to conservation and restoration efforts. The objectives of the present study were to (1) conduct the first spawning run counts of river herring in the Choptank River, Maryland, since the run counts performed over a 2-year period in 1972 and 1973, (2) evaluate population structure and dynamics, and (3) identify environmental variables associated with run timing. Spawning runs of Alewives and Blueback Herring were recorded from March 10 to June 4, 2014, using imaging sonar and processed manually to produce hourly run counts of fish with TLs ranging from 200 to 350 mm. A total of 1,659,09...

Prevalence of the pathogenic crustacean virus Callinectes sapidus reovirus 1 near flow-through blue crab aquaculture in Chesapeake Bay, USA

Understanding the ecology of diseases is important to understanding variability in abundance, and therefore management, of marine animals exploited commercially. The blue crab Callinectes sapidus fills a crucial benthic-pelagic niche in Atlantic estuarine ecosystems and supports large commercial fisheries in both North and South America. In the USA, pre-molt blue crabs are typically held in short-term shedding (ecdysis) facilities to produce soft-shell crabs of increased value. However, mortality rates in these facilities are high and commonly associated with the pathogenic C. sapidus reovirus 1 (CsRV1). To assess whether crab mortalities in these facilities might increase CsRV1 prevalence in wild crab populations, tissue sampled from crabs collected over 2 summers either near to or far from shedding facilities using flow-through water systems were tested by reverse transcription quantitative PCR (RT-qPCR) for the presence of CsRV1 RNA. In support of our hypothesis, PCR data identified the probability of detecting CsRV1 in wild crabs sampled close to shedding facilities to be 78% higher than in crabs sampled from far sites. PCR detections were also 61-72% more probable in male crabs and 21% more likely in male and female crabs over the minimum landing size. As the prevalence at which CsRV1 was detected varied within seasons, among locations and between years, blue crab migration and/or population fluctuations appear to also be involved.