BYCATCH AND BEACHED BIRDS: ASSESSING MORTALITY IMPACTS IN COASTAL NET FISHERIES USING MARINE BIRD STRANDINGS

In most of the world's coastal fisheries, bycatch of marine birds is rarely monitored, and thus the impact on populations is poorly known. We used marine bird strandings to assess the impact of entanglement in Pacific Northwest coastal net salmon fisheries. We compared the magnitude and species composition of fisheries-associated strandings (FAS) to baseline data collected at beaches monitored by citizen-science programs in Washington State and British Columbia, and to seabirds salvaged from gillnets during observer programs. Carcass encounter rates were 16.4 carcasses/km [95% confidence interval (CI): 11.2 to 21.7] for FAS and 1.00 carcasses/km (95% CI: 0.87 to 1.14) for baseline data. Declines in fisheries effort were associated with decreasing FAS, although declines in at-sea seabird abundance may also be at play. Common Murres Uria aalge comprised most of the carcasses in both the FAS (86%) and bycatch studies (71%). Although the total count of murre FAS represented a small fraction (1.3%-6.6%) of baseline mortality accumulated for the Salish Sea over the same period, murre FAS added 0.2%-2.9% to annual mortality rates. Considering the effects of other natural and anthropogenic mortality agents on murres in the region, this species might benefit from further protection. Given the complexity of salmon fisheries management and the ubiquitous distribution of seabirds in the Salish Sea, we recommend the comprehensive adoption of gillnet gear modification to reduce seabird bycatch, a solution that may prove to be beneficial for the vitality of seabird populations and of the fishing industry.