Abstract

The southern sea otter (Enhydra lutris nereis) has been listed as “threatened” under the Endangered Species Act (ESA) since 1977.¹ Despite periods of slow growth and range expansion since the early 20th century, the population has recently ceased growing appreciably and mortality events have occurred. A collaborative and multidisciplinary effort is underway to determine what forces are limiting the recovery of these animals

Introduction

The limited ability of the southern sea otter population to recover to levels that would allow delisting appears to be the result of adult (particularly prime-age female) mortality, a large proportion of which apparently results from diseases, parasites, and intoxications. At this time, it is critical to link what we know about pathology and epidemiology of these sea otters with what is known about their ecology. This is being done by collaborative examination of extensive databases, risk analysis, and by observation of instrumented living animals which are periodically captured and sampled for markers of health and often, eventually recovered and examined by pathologists when they die.

Methods

Approximately 80 southern sea otters have been surgically implanted with temperature sensitive VHF radio transmitters and time-depth recorders (TDRs) at three study sites along the California central coast. Animals are tested for general health, IgG levels, genetic diversity, disease and contaminants exposure, and other factors. Many of these animals have been intensively observed and extensive ecological data including time activity budgets, habitat utilization, food habits and prey preferences, variations in core body temperature, social interactions, and movement have been recorded. The TDRs are recovered from many otters that die, or those that are recaptured, and the core body temperature, exact time and depth to which animals dive is retrieved from the archival tags. This information is compared to ecological observations and correlated with measures of health, disease, and contaminant exposure. For animals that die, and their bodies are recovered, pathologic observations as to cause of death and additional laboratory data can be added into the dataset. Certain behaviors and activities, locations, and diet types appear to place animals at different levels of risk of exposure and/or at risk of dying from various causes.^2,3

Results and Discussion

We will present findings on several animals whose lives and deaths are typical and instructive. By using implanted physiologic monitoring devices, we have been able to link behavioral and ecological observations with epidemiologic risk factors and verify outcomes at postmortem examination. This integrated program is allowing us to gather unprecedented information about the life, health, and death of an otherwise hard-to-observe, free-ranging marine mammal. Some causes of significant mortality have apparent links to terrestrial sources of pollution³ and may represent outstanding examples of “pathogen pollution⁴.” Large-scale, multi-year, transdisciplinary studies (like those described) have the likelihood of providing sufficient biologic and biomedical data to support the potentially difficult regulatory and expensive policy decisions that may be required.

Literature Cited

1.  Ralls K, DeMaster DP, Estes JA. Developing criteria for delisting the southern sea otter under the U.S. Endangered Species Act. Conservation Biology. 1996;10:1528–1537.

2.  Kreuder C, Miller M, Jessup D, Lowenstine L, Harris MD, Ames J, et al. Patterns of mortality in the southern sea otter (Enhydra lutris) from 1998–2001. J Wildl Dis. 2003;39(3):495–509.

3.  Miller MA, Gardner IA, Paradies D, Worcester K, Jessup D, Dodd E, et al. Coastal freshwater runoff is a risk factor for Toxoplasma gondii infection of southern sea otters (Enhydra lutris nereis). International Jour Parasit. 2002;32:997–1006.

4.  Daszak P, Cunningham AA, Hyatt AD. Emerging infectious diseases of wildlife—threats to biodiversity and human health. Science. 2000;287:443–49.