Bringing Ecology, Behavior, and Physiology Together to Inform Conservation Efforts for a Declining Fur Seal Population

Elizabeth McHuron1, Noel Pelland2, Katie Luxa3, Kirstin Holsman4, Rolf Ream5, Tonya Zeppelin6 and Jeremy Sterling6, (1)University of Washington, Seattle, United States, (2)University of Washington, Seattle, WA, United States, (3)University of Washington, WA, United States, (4)National Oceanic and Atmospheric Administration, Alaska Fisheries Science Center, Seattle, WA, United States, (5)Alaska Fisheries Science Center, National Marine Mammal Laboratory, Seattle, WA, United States, (6)NOAA Alaska Fisheries Science Center, Marine Mammal Laboratory, Seattle, WA, United States
Food availability is a key concern for the conservation of marine top predators, particularly during a time when they face a rapidly changing environment and continued pressure from commercial fishing activities. The eastern stock of northern fur seals, which breeds in the eastern Bering Sea, has experienced an unexplained population decline since the mid-1990s. Dietary overlap with the largest US fishery for walleye pollock in combination with changes in maternal foraging behavior and pup growth has led to the hypothesis that food limitation may be contributing to the population decline. We used existing physiological, ecological and behavioral datasets generated by long-term research efforts to develop a bioenergetic model to estimate energy intake from May - December in six target years, which was combined with diet data to quantify prey consumption. Mean individual energy intake ranged from 438,000 kcal (juveniles) - 3,301,000 kcal (adult males), which resulted in population-level prey consumption estimates of 304,687 - 572,760 tons. Pollock comprised between 42 – 81% of this consumption, with young and fishery-sized pollock consumed in all years at levels comparable to other pollock predators. Results indicate that to increase pup growth to levels observed in a growing fur seal population, lactating females would need to increase energy intake by 5% day sea-1, which may be difficult to achieve given they are currently consuming 27% of their body weight day sea-1. Alternatively, reductions in metabolic overhead would allow females to increase pup growth without increases in energy intake, but this is unlikely to occur without localized increases in prey abundance. This study contributes to the conservation of northern fur seals by providing insight into the conditions that may facilitate population growth as well as a pathway to incorporate fur seal pollock predation into multi-species pollock stock assessment models.