PCB concentrations from river otter scat collected at latrine sites (geometric means, lipid weights) along the Green-Duwamish River. Left of green vertical line represents Lower Duwamish Waterway. Red horizontal line denotes published threshold for adverse effects on river otters. Graph pulled from Otter Spotter website.

PCB concentrations from river otter scat collected at latrine sites (geometric means, lipid weights) along the Green-Duwamish River. Left of green vertical line represents Lower Duwamish Waterway. Red horizontal line denotes published threshold for adverse effects on river otters. Graph pulled from Otter Spotter website.

Otter poop has the inside scoop

Researchers at the Woodland Park Zoo have been examining otter scat to measure the amount of pollutants in the Duwamish River, along with other parts of Washington.

The North American river otter may be cute, but they are also “top predators” in the Duwamish River and are vulnerable to biomagnification of pollutants in the aquatic ecosystem. This means researchers are able to use them as “biomonitors” that integrate information about the health and quality of the environment they live in by examining their scat.

The Woodland Park Zoo has a program called “Otter Spotter,” which informs the public about river otters in the area and community members can help with otter research.

According to Michelle Wainstein, field conservation associate at the Woodland Park zoo, the Otter Spotter program is basically a “community science program,” community members in Washington can — and should — report any otter sightings. This program came about because there was a lack of otter research.

“As we were putting together some of the other otter research work that we were doing, we discovered something that was surprising to us, which is that there is no basic population distribution data for river otters in the state. We felt that as a major basic data gap and so this was one of the ways to address that data gap,” Wainstein said.

The program according to Wainstein, is a “really simple” online platform that allows community members to report an otter spotting. She said there are a series of questions that they are prompted to answer and then that information goes onto a real-time map that shows where the otters were spotted. There are almost 800 sightings submitted so far, including some in Tukwila, Maple Valley and Covington.

Wainstein said according to the Otter Spotter map, there have been three otter sitings in the Maple Valley area and then a couple dozen in the Duwamish River, which turns into the Green River. Big Soos Creek runs right through the Green river, and also connects with Jenkins Creek, giving otters ins and outs around the Covington area.

Since otters are top predators in the river, they are great for researching pollutants in the river.

“What we have been learning with some of the other research that we have been doing, is they can tell us a lot about the health of our watersheds and I think they maybe don’t provide a direct service to us, like species that we harvest, but they certainly are playing a really valuable role in the ecosystem. They are great ways to understand how healthy our ecosystems are, their watersheds in particular,” she said.

In her findings (for the Green river and Duwamish river in particular), Wainstein said there are “surprisingly high levels of contaminants” in the river. She said the further up river you go — i.e. further away from the big cities like Tukwila and Seattle — the less contaminants there are.

“We find around where the Duwamish turns into the Green (River), we find a pretty quick drop off to low levels of contamination and that level stays pretty low all the way to pretty near the Howard Hansen Dam,” Wainstein said.

She said this is good and bad at the same time. The cleaner part of the river is reflected well in the otters. The bad part is the otters living in the lower part of the Duwamish are picking up a “tremendous” amount of pollutants from the prey they are eating in that area.

Most of what is causing otters to absorb any of these pollutants has almost nothing to do with them being the water itself, but has to do with what they are eating.

“Some invertebrates and even fish through their gills can pick up soluble contaminants. Mostly, what’s happening is benthic animals (animals that live on, in or near the seabed), or the ones that are kind of buried in the sediment or that are filtering sediment to eat, are picking up those pollutants that are attached to those sediments and then something is eating a small fish and then a larger fish is eating those smaller fish, and then otters are eating those different larger species of fish,” Wainstein said. “As the pollutants make their way up the food chain, they go through this process called ‘bioaccumulation.’ They concentrate as this organism eats it. The pollutants sort of get stuck in their fatty tissues, they don’t get excreted.”

From what they can tell from the research that has been done so far on otter scat, it appears the high levels of contaminants do not have a really drastic effects on the otters in terms or reproduction or survival, according to Wainstein. Since the research has been noninvasive, she said it is hard to tell if this is truly accurate or not. Looking at scat or watching an otter on a camera does not allow the researchers to tell if there are “sub-lethal” effects in the pollutants or not.

“That would likely involve more invasive work, which is something we don’t want to do at the moment in terms of having to trap and sample otters directly. So there is a chance that isn’t something obvious that we see,” she said. “The good news it that despite what we’ve (people have) done to the environment, we seem to have some resilient species that are making a living. On the flip side, they are carrying these really heavy pollutant burdens and they probably have some effect. They’re probably not as healthy as they could be.”

To do more for the otters in the community, report any otters that you spot in the area and take advantage of resources that are available through King County, according to Wainstein.

To visit the Otter Spotter website, go to https://www.zoo.org/otters.


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