The southern sea otter is a threatened species under the Endangered Species Act, and population recovery has been slow and halting since near extirpation during the fur trade in the 18th and 19th centuries. Research has shown that the sluggish growth rate of the southern sea otter population is due to elevated mortality, with the highest rates of mortality occurring in newborn pups and juveniles during their first year post-weaning, and a disproportionately high mortality rate observed in prime-age females over the last 20 years. The increasingly high amount of adult female mortality has had a profound influence on the population trajectory of the southern sea otter and is currently a point of concern for population recovery.

Coincident with increased prime-age female mortality, there has been a pattern of these deaths frequently occurring immediately before or after pup weaning. One explanation for this pattern is that females, having recently weaned a pup, experience nutritional deficiencies and overall poor body condition that result in the inability to withstand compounding environmental or physiological stressors. Such stressors include, but are not limited to, mating trauma, infection, and disease. In adult female southern sea otters, this condition has been observed more frequently in recent years and is commonly referred to as “end-lactation syndrome”.

Our research suggests that the extraordinary cost of pup rearing for female sea otters is likely the driving force behind the reduction in female body condition over the course of lactation. In addition, in the center of the current southern sea otter range, where sea otters are in high abundance, prey/food is limited. Reduced prey availability appears to exacerbate poor female body condition at the end of lactation. It appears that female sea otters invest everything they can into their pups and that some wild sea otters may be pushing themselves to their physiological limits. Thus, in order to better understand this major source of female sea otter mortality, it is important that we have a reliable estimate of the energetic cost of lactation and pup rearing. This project is designed to investigate just that. Building off of our previous research, we have begun a new project measuring the cost of milk production in lactating adult female sea otters, which until recently was not possible. This project will result in a more accurate estimate of the total energetic cost of rearing young for adult female sea otters and aid in answering many questions surrounding end-lactation syndrome in sea otters.