Changing Winters: How overwintering strategy and temperature affect cultured oysters

Abstract

Oyster aquaculture is a vital part of the blue economy in Massachusetts. Continued growth of the industry, however, is limited by several factors, including a lack of recommendations tailored to the specific needs of growers in colder northern waters. In New England, oysters are often grown for at least two summers, requiring maintenance during at least one winter (overwintering). Winter can be an especially challenging time for growers, as extreme temperatures, winter storms, and ice can threaten both product and gear. To cope with these challenges, growers in Massachusetts adopt a variety of overwintering strategies for holding their oysters: in 1) bottom cages, 2) surface cages, or 3) removed from the water entirely and stored in underground pits (pitting). Adoption of a particular strategy is often based on site characteristics, but also on a farm or area’s historical growing practices. Importantly, these overwintering strategies expose oysters to vastly different environments, especially different temperatures and exposure to waterborne parasites and diseases, which may then carry over to affect oyster growth and health during the growing season. Choosing the most effective overwintering strategy is therefore a critical decision for growers. Moreover, winter conditions, especially sea surface temperatures, have changed rapidly in New England in recent decades and are likely to continue to change, further complicating decisions regarding overwintering. Despite the potential consequences of overwintering strategy on oyster growth and health, there is little quantitative data to support growers in making this important decision.

Our proposal will quantify the impact of overwintering husbandry practices and environmental conditions on oyster survival, growth, and parasite load. Our specific objectives are to explore how 1) overwintering strategy and 2) wintertime water temperatures affect oyster growth and health during the growing season on farms in Massachusetts. We will conduct a replicated experiment at three collaborating oyster farms in Massachusetts to deploy oysters in the field using the three established overwintering methods to quantify effects of overwintering practice. We will also explore how winter and summertime temperatures differ between overwintering strategies and farms and how they contribute to changes in oyster performance and health. Specifically, we will quantify oyster survival, tissue and shell growth, and prevalence and intensity of four common parasites that cause disease or reduce marketability. Our partner farms are located on both the South Coast and North Shore, encompassing multiple growing areas in Massachusetts. Our proposed research was developed from conversations with growers and will fill an urgent need for quantitative data that can be used to help the industry develop best management practices for overwintering. We therefore anticipate that our results will benefit growers in Massachusetts and throughout New England, allowing them to better understand the effects of winter conditions and husbandry choices on their yield, with the ultimate goal of supporting a best management practice (BMP) recommendation for overwintering for the Commonwealth and region. Our proposed work supports multiple WHOI Sea Grant Focus Area Priorities, including the growth of sustainable fisheries and aquaculture, adapting to and mitigating environmental changes, and enhancing environmental literacy and workforce development for Massachusetts residents.