Sewage could be killing southern sea otter

A sudden rise in the death-rate of southern sea otters along the Californian coast, which means that they will soon become endangered, could be due to parasitic diseases from sewage outfalls, say scientists.


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According to the 19th February issue of The Scientist, southern sea otters may be suffering the first transference from the land to the sea of a disease causing a serious problem for a threatened species. Since 1995, the species, which had been making a slow recovery from only 50 individuals in 1915, has declined from 2,400 individuals to 2,000.

The problem could go much further than affecting just one species. “The otter is probably the one that’s going to be signalling the most to us about problems that we may be the cause of in the environment,” explains veterinarian Melissa A. Miller, a wildlife pathologist. “As a near-shore species with a high metabolic rate, they consume a lot of prey species, and they’re right there where wastewater is coming out both rivers and streams and sewage outfalls. So when we start seeing problems in sea otters that are things you would not expect to see in a healthy marine animal population, it’s a serious wake-up call for us.”

At least two parasites are thought to be involved in the infections that are killing the otters. “One is Toxoplasma gondii. If the parasite that we’re isolating out of these sea otters and harbour seals is the same as that from terrestrial animals and humans, then the only recognised definitive host for that parasite today is felids, basically any type of cat – bobcats, cougars, domestic and feral cats,” says Miller. The other isolated parasite and cause of disease and death in these marine animals is Sarcocystis neurona, only previously known to parasitise opossums.

According to David Jessup, senior wildlife veterinarian for the California Department of Fish and Game (CDFG) and supervisor of the Marine Wildlife Veterinary Care and Research Centre in Santa Cruz, the parasites are affecting the otters’ brains. Affected animals are often found alive, but suffering from seizures, and unable to hold food or to look after themselves.

As well as these two parasites, the sea otters appear to be succumbing to a number of other human-associated problems. “We’re getting the suspicion that there may be a number of organisms that are getting into the marine environment that are hard on sea otters.” said Jessup.

“We found one otter that died of Salmonella, another of [Escherichia] coli; both are pretty well recognised as being associated with faecal matter,” said Jessup. “Another otter examined at the National Wildlife Health Centre was found to have died of a Listeria septicemia.”

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