Abstract
The southern sea otter (Enhydra lutris nereis) is listed as threatened under the Endangered Species Act (ESA) and is a "keystone species," one that strongly influences the abundance and diversity of the other species within its kelp forest ecosystem. Since 1995, the population has declined by approximately 10 percent. Because sea otters eat approximately 25 percent of their body weight per day in invertebrates, they may concentrate contaminants. They are vulnerable to marine pollutants, such as petroleum. They appear to be susceptible to a number of diseases and parasites that may have anthropogenic origins, and shellfish may serve as an intermediary for some of these infections. Many of the shellfish otters eat are harvested for human food. Thus, sea otters are a bioindicator and sentinel species for the health of nearshore marine ecosystems.
The performance of the California sea otter population is being driven by higher than expected adult mortality and, based on fresh postmortem examinations, 40-45 percent of mortality is due to infectious diseases and parasites. A comprehensive suite of ecological and biomedical investigations have been undertaken in California to determine what is happening to three representative subpopulations. These studies consist of capture, sampling and marking (with tags, VHF temperature sensitive telemetry, and TDR's--time depth recorders) and follow-up studies including periodic daily, seasonal and yearly movements; activity budgets and energy expenditures; foraging success and specialization. Biomedical investigations include defining and comparing baseline health, exposure to selected infectious diseases, contaminants and markers of immune function, and other selected studies. A regression modeling approach will be used to determine whether relationships exist between various demographic, behavioral, temporal and spatial characteristics and biomedical findings, health outcomes or mortality.
A parallel cooperative effort allows us to recover a high percentage of sea otters that die. This program has developed a 35-year database of results of more superficial examinations; for 10 years, a veterinary pathologist has examined a significant percentage of animals. These extensive datasets offer insights into life and death processes in sea otters in unprecedented detail. Several major causes of mortality appear to have anthropogenic connections and may be amenable to changes in regulations and enforcement or investment of resources in infrastructure development. Chemical and pathogen pollution investigations are yielding intriguing land-sea connections and have potential to explain the southern sea otter population decline. The overall goal is to improve the likelihood that sea otter populations will recover and that ecosystem health and services will be enhanced.