New research from the Smithsonian Environmental Research Center in Edgewater on river otter feces in the Chesapeake Bay makes revelations about the animal’s diet, the ecological role of parasites and how they are encroaching into human-populated areas.
Calli Wise, a biological research technician, and Dr. Katrina M. Pagenkopp Lohan, a senior scientist, were both heavily involved in the study for the center.
“We were just really surprised when we found river otters out on our dock, and started trying to go into literature to find out what was known about river otters in the Chesapeake Bay, and found nothing,” Lohan said. “So we know they’re here, and they are clearly an apex predator in our system, because there is no other predator that is larger than them that would consume them … so that really just got us to [go], ‘OK, what can we do to learn more about these really charismatic animals without having to capture and kill them?’”
To conduct the study, researchers braved ticks and thorns to find the places along the Rhode River in Edgewater where otters were relieving themselves, dubbed latrines. They found 18 locations, both in nature and on human-made structures such as docks and boardwalks, to collect samples. The samples were analyzed under a microscope, which revealed the genetic data of the food the otters ate.
“It’s a fish-based diet that’s already been consumed and digested and pooped back out and then left in the environment to collect, but we were really fortunate with extracting, actually, a pretty good result out of these really degraded samples,” Wise said.
Another difficulty was finding where in the food chain a piece of genetic data came from.
“There were a lot of things that were obvious to us that were clearly being consumed, right? So, like blue crabs, they’re eating blue crabs. We have them on video eating blue crabs. We know that that’s part of their diet. But then there were some insects and some fungi,” Lohan said. “So we kind of had to go, ‘Well, are these growing and attracted to the scat after it’s been deposited? Were they prey from something that they ate before they pooped it out?’ So teasing apart some of that ended up being pretty tricky.”
Samples were collected along the Rhode River over around nine months in 2021, mostly during the summer.
The analysis revealed a diverse diet rich in parasites. The scientists expected to find parasites, specifically ones using otters as their host. Instead, they found parasites that infected the prey and didn’t affect the otters much, which they call non-trophic, or non-prey-to-predator, transmission. The researchers concluded that, in potentially a multitude of ways, the parasites are making it easier for otters to catch their prey. How exactly is unclear; it could slow the prey down, change their behavior, or something else entirely.
“Oftentimes, we think of parasites as being really bad, and we want to get rid of parasites, but it turns out that they play really important ecological roles that are fundamental to many aspects of ecology. And in this case, they are fundamental to these river otters being able to catch enough food, which is obviously critical to them being able to stay in an environment,” Lohan, who has spent around a decade studying parasites and food webs, said.
The idea behind the study was that the otters were eating the Chesapeake Bay species without the cleaning or sanitation that humans do, like washing hands or cooking food before eating it, which researchers believed would lead them to find more parasites. They had hoped to find zoonotic parasites, which can be spread between animals and humans, and while they found some, they were unable to confirm exactly which species these were due to limitations with the data collection method used.
The findings that affect humans come from the location of the latrines. Researchers found river otters will do their business anywhere and are seemingly expanding further into urban areas, typically not considered good river otter habitats, like Baltimore’s Inner Harbor. Lohan stressed that despite the river otters’ cute appearance, they are still wild animals with sharp claws, and humans should avoid contact.
The study was released Thursday. Earlier this year, SERC appointed marine biologist and oceanographer Monty Graham as its director.
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