Nursery and Grow‐Out Strategy Optimization in Bay Scallop Argopecten irradians Aquaculture

Abstract

The northeastern United States once had a robust and profitable wild bay scallop Argopecten irradians commercial fishery that generated revenue for fishermen and quality seafood for regional consumption. Since the 1980s, bay scallop landings have been declining due to overfishing, habitat loss, and coastal water quality degradation. There is potential for bay scallop aquaculture to fill the void left by the decline of the wild fishery. However, further investigation into optimizing growth and survival in the nursery, grow‐out, and overwintering phases is needed. Growth and survival as related to stocking density were investigated during the nursery phase using a floating downweller system. Over the 6‐week nursery period, survival, growth, and food availability were documented in relation to flow rates and initial stocking densities. Initial bay scallop stocking density largely predicted mean bay scallop growth rates (mm/d) over the 6‐week observation period but had little impact on survival. At the end of the observation period, bay scallops were moved out of the nursery system to three different grow‐out locations on Cape Cod. At each location, bay scallops were stocked into three surface gear types (floating bags of two different mesh sizes [6 or 9 mm] or hanging trays) and bottom cages to investigate grow‐out phase strategies. In exposed, high‐energy environments, the surface gear was susceptible to damage, and bay scallop growth rates and survival were impacted. In low‐energy environments, growth rates and survival were similar between surface and bottom gear. In both low‐ and high‐energy environments, bay scallop growth rates (mm/d) declined significantly once temperatures dropped below 15°C. Observed growth rates and survival in the configurations examined in this study indicate that bay scallop farming on New England shellfish farms is viable.

Scoping Bay Scallop Restoration in Rhode Island: A Synthesis of Knowledge and Recommendations for Future Efforts

“…Parasites, such as the pea crab, have long been known to infect bay scallops and can cause reduced growth and impaired reproduction (Kruczynski 1972, Bologna & Heck 2000. In addition, whereas disease has always been a threat to natural populations, the relatively high density of bay scallops in planted populations results in restored bay scallop populations being more susceptible to pathogens, and bay scallops grown in bottom gear are more susceptible to parasites compared with those kept in surface gear (Karlsson 1976, Tobi & Ward 2019. Pollution and upstream runoff can introduce new pathogens to bodies of water (Getchell et al 2016), and the release of hatchery-reared scallops into a wild population poses the risk of introducing new pathogens into a system.…”

“…In addition, stocking density is a primary consideration when keeping scallops in cages (Leavitt et al 2010b). Overcrowding of scallops can result in high levels of food competition, decreased growth rates, as well as physical injuries and/or death (Rhodes & Widman 1984, Leavitt et al 2010b, Tettelbach et al 2015, Tobi & Ward 2019. A cover of approximately 50% of cage surface area is generally recommended to limit the effects of overcrowding (Leavitt et al 2010b), which means many enclosures are necessary to effectively grow-out a sufficient number of scallops.…”

“…This strategy focuses on protecting young scallops during vulnerable life history stages and attempts to increase the chances that a scallop will survive and grow to adulthood. Spat collector bags, which collect pelagic scallop larvae just prior to settlement, increase the surface area on which scallops can settle, and they can also serve as artificial "nurseries" for grow-out by providing protection from predation (Fegley et al 2009, Tobi & Ward 2019. In North Carolina, southern bay scallops have been successfully collected and grown in spat bags deployed in their natural environments beyond the size at which scallops typically detach from settlement surfaces, and at which they are less vulnerable to extreme predation (Fegley et al 2009, Carroll et al 2010.…”