Migratory strategies of juvenile northern fur seals (Callorhinus ursinus): bridging the gap between pups and adults.

In species exhibiting differential migration by sex and age, understanding what differences exist, and the adaptive reasons for these differences is critical for determining how demographic groups will respond to environmental variability and anthropogenic perturbations. We used satellite-telemetered movement and diving data to investigate differential migration and its ontogeny in a highly migratory North Pacific Ocean predator, the northern fur seal (Callorhinus ursinus; NFS), with a focus on understudied juvenile (1- to 2-year-old) animals. We instrumented 71 juvenile NFS in two years (2006-07 and 2007-08) at three major North American breeding sites and compared their migratory strategies with pups and adults.

Evaluating exposure of northern fur seals, Callorhinus ursinus, to microplastic pollution through fecal analysis.

Environmental microplastics are widely documented in marine life and bioaccumulation may present risks to marine predators. Investigations of microplastics in marine mammals are increasing, though none have examined animals routinely consumed by humans. Here, we investigate microplastic exposure in the northern fur seal (Callorhinus ursinus), a species consumed by humans, using fecal material.

Fortuitous encounters between seagliders and adult female northern fur seals (Callorhinus ursinus) off the Washington (USA) coast: upper ocean variability and links to top predator behavior.

Behavioral responses by top marine predators to oceanographic features such as eddies, river plumes, storms, and coastal topography suggest that biophysical interactions in these zones affect predators' prey, foraging behaviors, and potentially fitness. However, examining these pathways is challenged by the obstacles inherent in obtaining simultaneous observations of surface and subsurface environmental fields and predator behavior. In this study, migratory movements and, in some cases, diving behavior of 40 adult female northern fur seals (NFS; Callorhinus ursinus) were quantified across their range and compared to remotely-sensed environmental data in the Gulf of Alaska and California Current ecosystems, with a particular focus off the coast of Washington State (USA)--a known foraging ground for adult female NFS and where autonomous glider sampling allowed opportunistic comparison of seal behavior to subsurface biophysical measurements.

Evidence of localized resource depletion following a natural colonization event by a large marine predator.

For central place foragers, forming colonies can lead to extensive competition for prey around breeding areas and a zone of local prey depletion. As populations grow, this area of reduced prey can expand impacting foraging success and forcing animals to alter foraging behaviour. Here, we examine a population of marine predators, the northern fur seal (Callorhinus ursinus), which colonized a recently formed volcanic island, and assess changes in foraging behaviour associated with increasing population density.

Population structure as revealed by mtDNA and microsatellites in northern fur seals, Callorhinus ursinus, throughout their range.

Background: The northern fur seal (Callorhinus ursinus; NFS) is a widely distributed pinniped that has been shown to exhibit a high degree of philopatry to islands, breeding areas on an island, and even to specific segments of breeding areas. This level of philopatry could conceivably lead to highly genetically divergent populations. However, northern fur seals have the potential for dispersal across large distances and have experienced repeated rapid population expansions following glacial retreat and the more recent cessation of intensive harvest pressure.

Development and application of DNA techniques for validating and improving pinniped diet estimates.

Polymerase chain reaction techniques were developed and applied to identify DNA from >40 species of prey contained in fecal (scat) soft-part matrix collected at terrestrial sites used by Steller sea lions (Eumetopias jubatus) in British Columbia and the eastern Aleutian Islands, Alaska. Sixty percent more fish and cephalopod prey were identified by morphological analyses of hard parts compared with DNA analysis of soft parts (hard parts identified higher relative proportions of Ammodytes sp., Cottidae, and certain Gadidae).

Extreme weather events influence dispersal of naive northern fur seals.

Since 1975, northern fur seal (Callorhinus ursinus) numbers at the Pribilof Islands (PI) in the Bering Sea have declined rapidly for unknown reasons. Migratory dispersal and habitat choice may affect first-year survivorship, thereby contributing to this decline. We compared migratory behaviour of 166 naive pups during 2 years from islands with disparate population trends (increasing: Bogoslof and San Miguel Islands; declining: PI), hypothesizing that climatic conditions at weaning may differentially affect dispersal and survival.

Sex steroid concentrations and localization of steroidogenic enzyme expression in free-ranging female northern fur seals (Callorhinus ursinus).

Recent precipitous population declines in northern fur seal (Callorhinus ursinus) and other Alaskan pinniped populations are due in part to reduced fecundity and have emphasized deficits in basic reproductive knowledge of these species. Following estrus and mating, fertilized female pinnipeds experience an obligatory delayed implantation lasting several months and non-pregnant (pseudopregnant) females are indistinguishable by sex steroid levels during this time. The current study examined circulating steroid concentrations and ovarian expression of key steroid-synthesizing enzymes in northern fur seals to identify changes associated with embryonic implantation, data necessary for estimating early pregnancy rates of the population.