Influence of mariculture on winter sea duck distribution and abundance in south Puget Sound

Shellfish mariculture is a valuable and expanding industry in Washington State, in particular in South Puget Sound. Concurrently, long-term monitoring efforts throughout Puget Sound reveal varying levels of decline in a significant number of over-wintering sea duck species. However, reasons for these declines are unknown and the need for winter habitat assessments throughout Puget Sound is evident. The overlapping distributions of mariculture industry and marine bird use in nearshore environments identify a high probability of interaction. This study identified and evaluated associations of four sea duck species/groups, Bufflehead, Scoter, Goldeneye and Merganser, in relation to a changing mariculture landscape. Findings illustrate that shellfish mariculture in South Puget Sound is both expanding and intensifying; expanding almost 3 study sites annually by medium and large acreage operations and growing at an annual rate of 127 acres. Our results suggest that sea ducks exhibit species or group-specific responses to mariculture. Evaluating the location and intensity of mariculture operations in the South Puget Sound, Bufflehead and Scoter species abundances were positively associated with industry to different degrees. Only Bufflehead, however, maintained significant positive associations over time. Alternatively, Goldeneye and Merganser species abundances demonstrated negative associations with shellfish mariculture, however responses varied by intensity of culture operations. The influence of shellfish mariculture on winter sea duck populations is clear, however variability by species demonstrate that while industry may coexist or benefit some, can prove deleterious for others. This study highlights the complexity in defining spatially and temporally dynamic sea duck-mariculture relations. We recommend continued research to better understand species-specific habitat use and availability in relation to mariculture development and activity of winter sea duck populations in Puget Sound