Are The Cute Mammals Sea Otters Melting Your Heart

Sea otters are unusual among marine mammals in that they live outside of their zone of thermal neutrality and consequently have extremely high metabolic demands. As a result they require a high rate of food intake, up to 30% of their body weight per day, and they have limited capacity to cope with reduced food availability or additional physiological challenges. Moreover, a large proportion of their diet consists of filter-feeding benthic invertebrates, which tend to concentrate both contaminants and disease-causing pathogens that flow into near-shore waters from land.

The sea otter was hunted to extinction in southeast Alaska by fur traders in the 18th and 19th centuries. In the mid-1960's, 402 otters from the northern reaches of Alaska were re-introduced to their southern habitat, and by 1987 the population there had grown to about 3,500 animals. Kvitek was one of the first researchers in the late 1980's to record the expanding population. This rapid expansion, and the pervasive presence of toxic butter clams throughout southeast Alaska, provided Kvitek with the perfect opportunity to set up a comprehensive study . Through observation of the animals, collection of discarded sea otter prey, and sampling prey in areas yet uninhabited by otters, Kvitek hoped to determine whether the foraging behavior and distribution of sea otters under natural conditions was mediated by clam toxicity. Did seasonal toxic algal bloomsdetermine when and where sea otters settled and foraged?

In Summary

The Otter Project considers four factors when evaluating sea otter population status and the result of this year's survey is quite discouraging. It appears that the sea otter population could possibly continue to decline. Three of the four factors are Negative. For 2010, the factors indicated the following:

Spring survey: Mixed. The 3-year running average is down. The raw count for 2010 is up slightly from 2009 but still down from 2008 and 2007. Even though 2010 saw a very modest increase in the number of otters counted in the spring survey, there may be cause for concern as we saw the most significant drop in the 3-year running population average in over a decade.

Dead strandings: Negative. Through December 2010, the number of dead otters recovered was up from previous years.

Mortality by age-class: Negative. Significant increase in mortality of pups and immature otters. An increase in mortality also occurred in reproductive adult age classes this year.

Pup to independent ratio: Negative. The 2010 survey results showed a significant decrease in the pup to independent ratio compared to 2009. The 2009 survey results were the highest in two decades.

Not just otters but also people are potentially at risk from the parasite. People eat many of the same shellfish as otters. There has also been a documented outbreak of human toxoplasmosis in British Columbia, shown later to have been caused by contaminated drinking water, presumably from cat droppings.

Though a potentially serious human health threat, Toxoplasma gondii is only one of many waterborne protozoans that may be entering beach waters via runoff. A new California Sea Grant study is looking at one of the more worrisome of these, Cryptosporidium, widely regarded as one of the most significant causes of diarrhea in humans.

Leading the project are Rob Atwill, also at the School of Veterinary Medicine at Davis, and Conrad. Taking cues from sea otters, Atwill and Conrad are measuring pathogen levels in bivalves near outfalls of human and agricultural runoff, to track the upstream sources of pollution. Genetic tests are also being used to identify which animal species are the main sources of pathogen pollution. Wildlife, cattle, pets and people can spread Cryptosporidium.

The scientists are also working with dairies along the coast to test the degree to which management practices, such as planting vegetative buffer strips, can reduce pathogen pollution.