First-Year Survival of Northern Fur Seals (Callorhinus ursinus) Can Be Explained by Pollock (Gadus chalcogrammus) Catches in the Eastern Bering Sea

The Pribilof northern fur seal (Callorhinus ursinus) herd in the eastern Bering Sea has declined by ~70% since the 1970s, for elusive reasons. Competition for pollock (Gadus chalcogramma) with the commercial fishery has been suspected as a contributing factor, but no correlative relationship between fishing activity and fur seal population declines has heretofore been demonstrated. Here, we present evidence for a moderately strong inverse relationship between fishery catches of pollock and first-year survival of fur seals, based on three different approaches to evaluation. We suspect this relationship results from the dependence of lactating female fur seals on locating dense and extensive schools of pollock near the Pribilof Islands to efficiently provide nutrition for their pups, because the pollock fishery also targets these same schools, and when fished, the remnants of these schools are fragmented and dispersed, making them more difficult for fur seals to locate and exploit. Inadequately fed pups are less likely to survive their initial independent residence at sea as they migrate south from the Pribilof Islands in the fall. Our results imply that pollock catches above ~1,000,000 t within ~300 km of the Pribilof Islands may continue to suppress first-year survival of Pribilof fur seals below the estimated equilibrium survival value of 0.50, leading to continued decline of the population.

Antarctophthirus nevelskoyi n.sp. (Anoplura: Echinophthiriidae) - a new species of parasite of the Northern fur seal (Callorhinus ursinus L., 1758) at Tyuleniy Island, Okhotsk Sea, Russia

Aim. To perform a morphological study of seal lice (Anoplura: Echinophthiriidae) of the genus Antarctophthirus Enderlein, 1906 taken from Northern fur seals (Callorhinus ursinus L., 1758) at Tyuleniy Island, Okhotsk Sea, Russia).Material and Methods. Seal lice were collected from the nasal passages of Northern fur seal C. ursinus pups during a scheduled ecological and virological expedition to Tyuleniy Island in August 2017. Fourteen samples of seal lice (11 imago males, 1 imago female, 1 nymph of the 2nd age, 1 nymph of the 3-rd age) were stored in 70% ethanol at room temperature from the time of collection until the start of the study. Morphological features of the insects were studied using light and scanning electron microscopy and compared with the available data in the scientific literature.Results. Unique patterns of the arrangement of spines were found in the examined samples that is a sufficient species feature for representatives of this family and allows the identification of a new species of seal lice.Conclusion. A new species of seal lice, Antarctophthirus nevelskoyi n.sp., was identified and described and named after the famous Russian explorer of the Far East, Admiral Gennady Ivanovich Nevelskoy (18131876).

Prey composition impacts lipid and protein digestibility in northern fur seals (Callorhinus ursinus)

Pinnipeds have specific macronutrient (protein, lipid) requirements to satisfy physiological functions, yet little is known about how diet characteristics affect macronutrient digestibility. We measured relative and absolute lipid and protein digestibility in six female northern fur seals (Callorhinus ursinus (Linnaeus, 1758)) fed eight experimental diets composed variously of four prey species (Pacific herring, Clupea pallasii Valenciennes in Cuvier and Valenciennes, 1847; walleye pollock, Gadus chalcogrammus Pallas, 1814 (formerly Theragra chalcogramma (Pallas, 1814)); capelin, Mallotus villosus (Müller, 1776); magister armhook squid, Berryteuthis magister (Berry, 1913)). We quantified how digestibility was affected by proximate composition of the diet (% lipid or % protein), levels of food mass and macronutrient intake, and tested for any potential benefit of multi-species diets. Overall, digestibility of both protein and lipid were high across diets, although macronutrient retention of lipids (96.0%–98.4%) was significantly higher than protein (95.7%–96.7%) for all but the two highest protein diets. Increased levels of protein intake resulted in increased protein retention, but decreased lipid digestibility. There was no evidence that mixed-species diets provide greater macronutrient digestibility over single-species diets. The results suggest that high to moderate lipid diets are more beneficial to northern fur seals because they lead to increased levels of lipid retention without large decreases in protein digestibility. This raises concerns that dietary factors may be contributing to the population declines of northern fur seals in the Bering Sea.