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The genetic consequences of species‐wide declines are rarely quantified because the timing and extent of the decline varies across the species' range. The sea otter (Enhydra lutris) is a unique model in this regard. Their dramatic decline from thousands to fewer than 100 individuals per population occurred range‐wide and nearly simultaneously due to the 18th–19th century fur trade. Consequently, each sea otter population represents an independent natural experiment of recovery after extreme population decline. We designed sequence capture probes for 50 Mb of sea otter exonic and neutral genomic regions. We sequenced 107 sea otters from five populations that span the species range to high coverage (18–76×) and three historical Californian samples from ~1500 and ~200 years ago to low coverage (1.5–3.5×). We observe distinct population structure and find that sea otters in California are the last survivors of a divergent lineage isolated for thousands of years and therefore warrant special conservation concern. We detect signals of extreme population decline in every surviving sea otter population and use this demographic history to design forward‐in‐time simulations of coding sequence. Our simulations indicate that this decline could lower the fitness of recovering populations for generations. However, the simulations also demonstrate how historically low effective population sizes prior to the fur trade may have mitigated the effects of population decline on genetic health. Our comprehensive approach shows how demographic inference from genomic data, coupled with simulations, allows assessment of extinction risk and different models of recovery. see also the Perspective by Julia M. Kreiner and Tom R. Booker [ABSTRACT FROM AUTHOR]

In the western region of the Baja California Peninsula, Mexico, four species of pinnipeds are found: the California sea lion (Zalophus californianus), the Guadalupe fur seal (Arctocephalus philippii townsendi), the Pacific harbor seal (Phoca vitulina richardii), and the northern elephant seal (Mirounga angustirostris). Their populations have changed in recent decades as a result of banning their commercial exploitation and government protection. These changes also have impacted their distribution, so it is necessary to have updated information. Herein, we present information about the distribution of the four species on a local scale, on 16 islands off the west coast of the Baja California Peninsula. These data were obtained from boat surveys during the winter and summer of 2009. The California sea lion and the northern elephant seal were found on all the islands except San Roque. New records for the northern elephant seal on the islands of Todos Santos Sur [South], San Jerónimo, and Asunción are presented. The Guadalupe fur seal was only found on Guadalupe Island and the San Benito Archipelago; however, it is now present in new areas on the island. This expansion is especially noticeable on the San Benito Este and Oeste [East and West] Islands. The harbor seal was found on all the islands in the study area except Guadalupe. This seal has only been recorded on the three San Benito islands in recent years. These changes in the distribution of the four species should be considered in future studies on abundance and other ecological topics, especially those concerning population growth and recolonization. [ABSTRACT FROM AUTHOR]

Harbour seals (Phoca vitulina) and northern elephant seals (Mirounga angustirostris) are the only phocid species found in Mexico. There is evidence that harbour seals at other latitudes exhibit non-migratory behaviour; however, there is lack of knowledge regarding this species' movements in Mexico. In contrast, elephant seal migrations to high latitudes are documented. In order to analyse this behaviour in harbour seals, hair samples (N = 19) were collected from weaned, or nearly weaned, pups on Natividad Island, Baja California (BC), during the 2013 breeding season (February). Lanugo samples (N = 20) were also collected from elephant seal pups on the San Benito Archipelago (60 km north of Natividad) during the same season, providing information on maternal foraging during the last 4-5 months before sampling. Of the two species, BC harbour seals had higher isotope values, reflecting their non-migratory behaviour. These differences may be due to the depleted base values in the higher latitude foraging areas used by northern elephant seals relative to the areas around Natividad frequented by harbour seals. A lower trophic position by elephant seals was considered but taken as an unlikely explanation for this variation. Bayesian analysis confirmed the distinction, with a low overlap value (0.4) and different isotopic spaces (Phoca: 0.5, Mirounga: 1.6). Building upon previous studies of the trophic ecology of the two phocids that inhabit the region, we provide new information by comparing the two species during the same season using the same tissue type sampled from individuals of similar age classes. [ABSTRACT FROM AUTHOR]

The article discusses a study which shows that Phoca vitulina concolor 74 (Pvc74) is sex linked in both species of elephant seals, from genus Mirounga. The study used DNEasy Blood and Tissue kit to extract DNA from skin samples of Northern elephant seals (NES). The study found that harbor seals show a modest degree of sexual dimorphism and that sex detection in the field is not always easy.