Gillnet bycatch increases risk of regional extirpation for tufted and horned puffins

In coastal Alaska, the nearshore distributions and foraging depths of diving seabirds such as tufted and horned puffins ( Fratercula cirrhata and F. corniculata ) overlap with salmon set gillnet (“setnet”) fisheries. Additive mortality from bycatch in setnets poses a threat to puffin populations that breed in the Kodiak Archipelago of Alaska. We estimated mean annual puffin exposure to setnet bycatch using spatially explicit setnet fishing permit-days and modeled puffin at-sea abundances for the years 1995 to 2021. Using setnet bycatch mortality scenarios based on available fishery observer data, we then simulated population dynamics at Archipelago (regional) and salmon management district (local) scales. Simulations projected extirpation probability across 50 years using mean at-sea abundances from 2002 and 2005 as initial population sizes. Models suggested an increase in 50-year probability of regional extirpation in the Kodiak Archipelago for tufted puffins from 7%, when bycatch mortality was absent, to 33% to 40% in scenarios of 100 to 200 individuals bycaught annually. For horned puffins, 50-year probability of regional extirpation increased from 14%, when bycatch mortality was absent, to 31% to 40% in scenarios of 15 to 30 individuals bycaught annually. Local (district-level) extirpation was >50% probable in most salmon management districts in the Kodiak Archipelago. We conclude that bycatch mitigation for salmon set gillnet fisheries, especially within the Northwest Kodiak District where exposure was greatest, could improve conservation outcomes for puffins. Assessments of exposure and potential mortality for other diving seabird species throughout coastal Alaska may reveal similar population-level impacts.