Being a mother comes with many cost regardless if you are human or animal. Sea otters have a relatively high cost in general due to the lengthy time (5 to 6 months) and energy mothers put into pup care and self maintenance. Recent research, published in 2016 in the Journal of Wildlife Diseases, has revealed that this cost may be deadly in Southern sea otters, Enhydra lutes neris. In a study led by Sarah Chinn and others they looked for end-lacation syndrome in postmortem female otters and how it relates to age, density of population, and time in reproductive cycle.
End-laction syndrome, ELS, is interior lesions due to the high energy costs of lactation and pup care after reproduction that normally results in mortality. It is characterized by an examination of adipose and muscle tissue, which those with ELS showing loss of both with visual damage as seen in Figure 1 below. In a sample of 108 female sea otters from California coast, researchers determined reproductive stage and then took into consideration other factors that could be a cause of mortality such as diet, co-infections, and current health. The five reproductive stages were as following: early pregnancy, late pregnancy, early pup car, late pup car, and weaning.
The results found that more than half of the sample had ELS with the cause of death being equally due to ELS as the primary cause or a major contributing factor. Though the majority of deaths occurred in sea otters who were either in the last two reproductive stage, this was expected because of the energy costs and trade-offs made by females to increase their pup’s survival during this time. In addition, age did play a major role in the results. They found that older otters were more likely than younger otters to care for their pups for longer periods to increase their reproductive fitness to pass down their genes. Younger otters in better health are less worried about this. Lastly, results showed that population size did contribute to the presences of ELS. High density of otters resulted in more competition and more energy required from female otters, which correlated with a higher ELS percentage due to females unable to compete with others for resources while taking care of their pups.
Overall this study shows how ELS is associated with sea otter mortality due to pup care. Mother sea otters must make tough choices regrading their own well being and/or their pup’s. This is important due to the behavioral choices that like humans, animals make in order to survive and reproduce. Future research hopes to use this knowledge to characterize ELS and study behavior of other populations of sea otters. However, since diagnostic is determined after death it is difficult to study how this effects behavior and reproductive choices in the wild. We are also left to question if ELS will eventually occur in all female otters if they live and reproduce long enough or if it will occur in otters across all reproductive stages and ages.
For the full research article click here.