Southern Sea otter genetic assessment for range-wide population health

The Southern Sea Otter (Enhydra lutris nereis) was nearly extirpated during the late 19th century as a result of the fur trade. Following protection by the US federal government, southern sea otter populations have rebounded... [ view full abstract ]

The Southern Sea Otter (Enhydra lutris nereis) was nearly extirpated during the late 19th century as a result of the fur trade. Following protection by the US federal government, southern sea otter populations have rebounded from a small remnant population near Big Sur California. Tremendous effort has gone into monitoring the health and population size for the recovery of sea otters, however extensive genetic evaluation of California sea otters has not yet been undertaken. Genetic assessment of these otters can provide powerful insight into the health and stability of the population. We genotyped 1010 sea otters sampled over a twelve-year period at 38 genetic loci to determine the genetic structure of sea otters in California, test for population bottlenecks, calculate the effective population size, and determine the genetic diversity, as well as determine patterns in changes of genetic diversity over time. To date, this is the largest data set for southern sea otters and DNA loci evaluated (previous studies analyzed 350 or fewer otters and used 14 or fewer genetic loci). We found that sea otters in California had relatively little genetic structure and that genetic diversity remained relatively stable across sampling years. Bottleneck analysis found evidence for population bottlenecks in the past. Importantly, we found that the effective population size was lower than anticipated based on the census size of the population. This data set will also be used to assess genetic and pedigree associations with diseases causing morbidity and mortality in the population. These analyses will provide information on whether there are familial associations with mortality outcome. Our findings have important implications to the current status of the sea otter population and the potential for recovering and eventually removing federal protection of the species.