The Humboldt County Sea Otter Mystery

Humboldt County California is about as far from the southern extent of the Northern sea otter (Enhydra lutris kenyonii) range, just north of  Grays Harbor in Washington State, as it is from the northern extent of the recognized range of the Southern sea otter (Enhydra lutris nereis), near Half Moon Bay in San Mateo County California. So when an adult male sea otter carcass was found near Eureka in Humboldt County about 4 months ago, the question was, was it a Northern or a Southern sea otter that had “gone walkabout” as the Australians say. The carcass of the “mystery otter” was sent to the CDFG Marine Wildlife lab in Santa Cruz where Dr. Melissa Miller examined him. It was an 8-9 year old male. It died acutely with no evidence of trauma, but unfortunately was badly decomposed. Further chemical and toxin testing may be conducted.

The question is of course of biological interest, but also of political interest. Southern sea otters in California were listed as “threatened” under the Endangered Species Act in 1977. The Northern sea otters that were transplanted to the Neah Bay area of Washington about that same time are not listed under ESA. The two subspecies are genetically distinct, but can certainly interbreed. So, would any offspring be protected under ESA or not ? Although a judge dismissed the suit, California fishing interests had at one time sued the US Fish and Wildlife Service claiming that Southern sea otters were not sufficiently distinct from the Northern to be listed. So what happens if they hybridize ?

It isn’t news that male sea otters “go walkabout” looking for new breeding territories, or who knows what else. Southern sea otters have traveled as far south as Baja, Mexico, one escapee from the San Nicolas Island transplant in the late 1980’s went to San Diego area, and other rare sightings have been reported in that area. Three years ago pictures surfaced of an otter in Long Beach Harbor  with the container terminal in the background.

Sea Otter in southern California waters

Sea Otter spotted in southern California waters (Credit: Krzysztof Szuszkowski)

But, the odd wandering male does not equal range expansion. Female sea otters do much less traveling. In fact they seldom move more than a few dozen kilometers up or down the coast once they reach maturity and start pupping. And, it is only when you have stable groups of females with pups and their attendant males move into an area, that you have range expansion. In fact, over the last 15 years, the occupied range of the southern sea otter population, from Half Moon Bay in the north to Gaviota in the south, has not really expanded substantially.

To the north, sightings of wandering male otters off the Marin headlands and around Pt. Reyes are fairly common. The extra-limital sea otter files kept by Brian Hatfield of USGS contain 8 sea otter sightings north of Cape Mendocino. The “Humboldt mystery otter” could even be one spotted near that Cape Medocino in October 2011 by NOAA staff, given that the Davidson current flows south to north and his body was rather decomposed when found at Gold Beach in near Eureka in January. Video documentation exists of a sea otter in Big Lagoon in Humboldt County as well. These sightings were not those of river otters (Lutris canadensis), a close relative with whom they can be confused. River otters quite frequently swim out into the ocean for short periods of time, so confusion of the two species is easy. Despite their very similar outward appearance, internally sea otters have many adaptations to life in the ocean, one being that their kidneys are lobed like those of a seal, where the river otter has a kidney that looks very much like ours.

Sea Otter in San Francisco Bay

Sea Otter spotted in San Francisco Bay (Credit: Sean Merrigan)

Another reason for the curiosity is that, should southern sea otters move north and start living in the waters off Marin, Napa, Sonoma, Mendocino and Humboldt counties, they could significantly reduce populations of red abalone. The remaining abalone sport fishery is highly prized by many and competition from otters would not be welcome. This has been a source of fear and speculation for decades. On the other hand, if sea otters do start to colonize the northern coast of California, they may reach numbers that allow them to be declared recovered under ESA sooner than if they don’t.

So, what’s the answer to the Humboldt County sea otter mystery ? Who was this wandering male ? Dr. Shawn Larson, Curator of Conservation Research/Animal Health Coordinator at the Seattle Aquarium says “Based on STRUCTURE a software program that assigns individuals to populations using multilocus genetic data like microsatellites, this individual, with 99% certainty, belonged to Enhydra lutris nereis, so it was a Southern sea otter.” So, it may or may not be a big deal. Stay tuned…..

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Seaotters.com is an education and outreach initiative dedicated to raising awareness about California's threatened sea otters and the role research plays in the species recovery and conservation. It's a collaboration of the Monterey Bay Aquarium, U.C. Santa Cruz, U.C. Davis, U.S. Geological Survey, U.S. Fish & Wildlife Service, California Department of Fish and Wildlife, among others. We're #WildforOtters! Are you?