Fecal Insights: How River Otters Help Us Understand Parasites and Ecosystem Health
With their large, expressive eyes and playful personalities, the North American River Otter is undeniably one of the cutest animals in the wild. Their sleek, waterproof fur and adorable whiskered faces give them an almost cartoonish charm, while their energetic, social behavior only adds to their appeal. Whether they are diving gracefully, splashing around in the water, or sliding on their bellies for fun, the otters’ lively antics are hard to resist.
Though their cuteness often steals the spotlight, these river otters are much more than just a charming species. Interestingly, their behavior and ecology actually make them valuable indicators of environmental health.
This concept served as the foundation for a Smithsonian scientist's project, which aimed to use river otters to study nearshore parasites and infectious diseases.
Led by Katrina Lohan, head of the Smithsonian Environmental Research Center’s (SERC) Coastal Disease Ecology Lab, the project intended to use river otters to detect health threats in the Chesapeake Bay, like zoonotic diseases. These diseases are caused by parasites, bacteria, and viruses that can infect both animals and humans, and can result in various health problems. Many scientists believe that as natural habitats are cleared and as coastal populations grow, there may be more interactions between humans and animals, potentially increasing the risk of wildlife transmitting diseases to humans.
This issue is particularly concerning in coastal areas, like the Chesapeake Bay—where SERC is headquartered. Coastal Ecosystems are some of the most biodiverse on Earth, yet they also support nearly 70 percent of the human population. The Chesapeake Bay Watershed, for example, spans six states and is home to more than 18 million people.
This issue is particularly concerning in coastal areas, like the Chesapeake Bay—where SERC is headquartered. Coastal Ecosystems are some of the most biodiverse on Earth, yet they also support nearly 70 percent of the human population. The Chesapeake Bay Watershed, for example, spans six states and is home to more than 18 million people.
But how exactly did Lohan plan on using these adorable creatures to study potential human health risks present in the Bay? Well, her lab tackled this task by diving into the less glamorous side of science—by analyzing their poop samples to uncover vital environmental clues.
Looking at poop samples, or scat, is an unintrusive way to study organisms while also generating vast amounts of information not only on the otters, but the ecosystem itself. Because river otters are apex predators in the Chesapeake Bay, and sit at the top of the food web, their scat can provide insights into predator-prey dynamics, prey diversity, food web interactions, and even how parasites move through the food web.
This is where the river otter's behavior became particularly convenient for the collection of scat samples.
As semi-aquatic animals, river otters are equally at home on land and in the water. They come ashore for a variety of behaviors, like using the bathroom, which they do in the same spot repeatedly. Scientists call this location a latrine. After setting up game cameras at these latrines, SERC staff observed that the otters also use these spots as social hubs, where they groom one another, eat, and strengthen social bonds. Lohan refers to the behaviors that happen in latrines as “poop parties”.
In the same location they party…. they also poop.Lohan planned to collect scat samples in order to determine the otters’ recent diet, and to identify any parasites infecting the otters or their prey. She had hoped these findings would allow her team to determine which areas of the bay contained parasites that posed risks to human health.
And though they did find several parasites that had the potential to harm human health, Lohan did not view this as the most significant finding in the dataset.
Instead, she discovered just how many parasites river otters are able to eat, without becoming infected themselves.
Lohan explains, “A lot of parasites are transmitted via fecal-oral contamination. This does literally mean that someone must eat poop to become infected—and this is why there is so much out there about handwashing [in humans]. River otters eat, poop, play, and even mate in these areas called latrines. This means that there is a lot of potential for fecal-oral transmission here.”
Despite frequently coming into contact with parasites, river otters were rarely infected by parasites and seemingly defied all the rules when it comes to parasite transmission.
“...they [river otters] are literally rolling in their poop,” said Lohan. “There is something going on that allows them to basically eat poop on a regular basis and be fine. It’s fascinating to me.”
Immunity to parasites gives river otters an advantage. Infected prey often experience a heightened immune response, which is energetically demanding and can make them weaker, slower, and easier targets for predators. For instance, a fish infected with parasites may struggle to keep up with its school and is more likely to be picked off by predators like the river otter.
Lohan and her team found that by preying on these weakened, infected individuals, otters gain an advantage in the food chain, demonstrating the unexpected benefits that parasites can offer and highlighting their complex role in ecosystems. While parasites may harm individual hosts, they also play an essential role in broader ecological processes like in food webs. In this way, parasites, though often overlooked, are a crucial force in maintaining the health of populations and communities, reinforcing Lohan’s assertion that “Parasites are incredibly important for every ecosystem.”
Ultimately, Lohan's work studying the North American River Otter has demonstrated that this charming creature is a shockingly adaptable animal that can not only help researchers track threats to public health, but also highlights the vast potential for further exploration in critical fields like parasite ecology.