New evidence for the existence of southern sea otters (Enhydra lutris nereis) in Baja California, Mexico

Genomic analyses reveal range‐wide devastation of sea otter populations

“…Rodriguez-Jaramillo & Gendron, 1996) and the population is currently classified as endangered (Norma Oficial Mexicana, 2010). A previous study that analysed 318 bp of the mitochondrial control region of the two samples used in this study (Schramm et al, 2014) did not have the resolution to determine if these otters were recent migrants from California (Hatfield, 2005;Rathbun et al, 2000) or were survivors of the historical population. We found that the two individuals we sampled are probably migrants or the descendants of migrants from California, representing a southward expansion of the population, rather than survival of the original Baja California sea otter population.…”

“…Sea otters were sampled from the Kuril Islands (KUR, n = 13), Commander Islands (COM, n = 45), Aleutian Islands (AL, consisting of Attu, Amchitka and Adak Islands, n = 21), south central Alaska (AK, n = 19), California (CA, n = 7) and Baja California (BC, n = 2). All samples derive from sea otter research expeditions from 1974 to 1994 (Supplemental Methods; Figure 1a; Figure S1A-C; Table S1), except for the two recent (2008)(2009)(2010)(2011) samples recovered from stranded individuals from Baja California (Schramm et al, 2014) (Table S1; Figure S1D). Three historical Californian samples, excavated from coastal shell middens and dating from ~1500-200 years ago, were also analysed (Supplemental Methods; Figure 2a; Table S2).…”

“…Sea otters were formally protected in 1911 by the International Fur Seal Treaty, and populations have increased and been reintroduced into southeast Alaska, British Columbia, Washington State and southern California where they had been fully extirpated (Jameson et al, 1982). Sea otters in Baja California, Mexico, were declared probably extinct due to the fur trade (Kenyon, 1969), but there have continued to be sporadic sightings in the region (Gallo‐Reynoso & Rathbun, 1997; Schramm et al, 2014). The recent history of sea otter populations provides a unique model for species decline, because rarely are bottlenecks so uniform and near‐concurrent across an entire species distribution.…”