Tire “dummies” can help conservationist track dead sea otters

By Joshua Rapp Learn

Researchers found that dead sea otters drift the same way as car tires cut in half.
©NPS Photo/ Kaitlin Thoresen

What does a sea otter and half a car tire have in common? They both float to the same places.

Researchers looking for a way to better track possible sea otter (Enhydra lutris) deaths in the event of oil spills have found a cheap way to follow the right tides.

“We found these car tires had very similar drift patterns to actual carcasses,” said Mike Harris, a senior environmental scientist with the California Department of Fish and Wildlife’s Office of Spill Prevention and Response. and a co-author of a study published recently in Marine Mammal Science.

His now retired co-author Jack Ames first developed the idea in the mid-1990s when these tests were actually conducted, partly in response to the Exxon Valdez oil spill disaster that occurred off the coast of Alaska in 1989. A relatively smaller oil spill in 1992 off Avila Beach in California resulting from a pipeline break led to the death of a handful of sea otters. Ames wanted to find a way to track how many of the federally threatened animals died as a result of the spill and for future spills.

“One of our primary responsibilities is responding to wildlife impacted by oil spills,” Harris said. “Part of that is not only the immediate response, but trying to develop some measure about the impact of the spills. To do that you have to have some estimate of mortality.”

Ames found that dead sea otters, after they come out of rigor mortis, often float in a similar shape as a car tire cut in half. The otters’ backs aim skyward and their front and back flippers hanging downward in a rough crescent shape.

The tires didn’t float quite as well as the sea otter carcasses, though, so they added first Styrofoam, then later 4-inch square blocks of wood to the tires, so they would float similarly to the otters, catching about the same amount of wind and current.

“In the scheme of things it was a relatively inexpensive way to develop dummies,” Harris said.

They then put these “car tire dummies” into the water alongside sea otter carcasses, all equipped with telemetry tracking devices, and found they had similar drift patterns.

While Ames never got around to publishing his findings, Colleen Young, also with the CDFW, rounded up the data on his findings together with additional expertise on modeling drift and statistics.

Harris said that it’s fortunate that there hasn’t been an oil spill in California waters since this tool was developed, but that it remains a possible tool available to wildlife managers in the event of a future catastrophe.

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society. Contact him at jlearn@wildlife.org with any questions or comments about his article.

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