River Otters, Sea Otters, and Toxoplasma gondii

Originally published as a letter to supporters, Winter 2007

At first glance, domestic cats and river otters seem worlds apart. One thrives in our marine waters, the other despises water. One often snuggles by us in our homes at night and the other avoids humans when possible. Recent SeaDoc research, however, has shown that like our own lives and the health of the marine ecosystem, these two animals are probably more intimately connected than most of us realize.

For several years we’ve been working to better understand what impacts the health of river otters in the Salish Sea. While the Pacific Northwest is fortunate to have a robust river otter population, more than 20 states are spending millions of dollars to bring back wild river otters. Maintaining our river otter population requires that we understand what impacts them and what we can do to prevent them from becoming endangered.

Disease is one important regulator of river otter populations and recent SeaDoc research revealed that a parasite called Toxoplasma gondii is one of the most common disease agents known to infect river otters in our region. In fact, 17% of river otters sampled had been exposed to this parasite. This SeaDoc Society work, which also includes other new information about river otter health, has just been published in the Journal of Wildlife Diseases. Interestingly, cats are the source of this parasite. In California, Toxoplasma gondii is a major cause of death for the threatened southern sea otter. Like in sea otters, T. gondii causes inflammation in the brain of river otters but just how many river otters are dying from this disease is still unknown.

How do cats transmit a parasite to river otters? A study in California showed that in the small communities of Cayucos, Los Osos and Morro Bay, feral cats were estimated to put 29.5 tons of feces into the environment annually, while owned cats defecating outdoors contributed an estimated 76.4 tons of feces. Feces deposited on land often travels to the ocean via fresh water and river otters are likely exposed when they drink fresh water running into the ocean or when they eat filter feeding bivalves like mussels that can concentrate the infective form of this parasite.

We impact the health of river otters and other marine wildlife in everything we do, even in the way we care for our pets. By being aware, we can make daily decisions that will benefit our marine wildlife and their ecosystem. For example, to reduce river otter exposure to Toxoplasma gondii you can spay or neuter your cat and help reduce unwanted feral cats. Allowing your cats to use an indoor litter box and disposing of feces in a landfill also will help. And our individual ability to help extends far beyond just how we care for our pets.

Your support of the SeaDoc Society is helping us better understand the connections between what we do on land and how it impacts river otters and other marine fish and wildlife and we thank you.

With Thanks,

Kirsten Gilardi & Joe Gaydos