\u201cWe started this research when a colleague sent me an email about some weird-looking, watery poo that she found at the dock on our campus. In the poo was a fire engine red worm,\u201d says senior author Dr Katrina Lohan, head of SERC\u2019s Coastal Disease Ecology Laboratory. Wildlife cameras confirmed that a North American river otter<\/a> (Lontra canadensis) \u2013 a semiaquatic mammal endemic to North America \u2013 was the culprit.<\/p>\n Over the following 11 months, graduate researcher Calli Wise collected scat from 18 otter latrines, averaging 28 samples per site, along a 12km stretch of the shoreline of the Rhode River, a subestuary of Chesapeake Bay. <\/p>\n \u201cScats usually smelled strongly of fish and were full of scales or crustacean shells,\u201d Wise says. But further analysis was needed to work out exactly what was in the otter poop, so the researchers took the samples to the lab.<\/p>\n Clues in the scat<\/p>\n In the lab, the team used metabarcoding (a DNA-based technique for identifying multiple species within a mixed sample, such as scat) and microscopy to examine what the otters had eaten and what parasites their meals carried. <\/p>\n \u201cWe found evidence of invasive species like common carp and white river crayfish in river otters\u2019 diet,\u201d explains Wise, who says they also discovered evidence of other fish species and crustaceans, including American blue crabs, as well as ducks and amphibians<\/a>.<\/p>\n The researchers also identified the parasites<\/a> (though they weren\u2019t able to clearly identify all parasites), then matched these as best they could to the hosts they were most likely to infect. <\/p>\n Many of the parasites found are known to infect teleost fish, a diverse group of ray-finned fishes that are the main prey of river otters. \u201cIt is possible that river otters, like other top predators, wouldn\u2019t be able to find enough food to eat without parasites,\u201d Lohan says.<\/p>\n![\"Scat](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2025\/08\/Scat-found-on-dock-scaled.jpeg\")
Otter latrine at a dock in Chesapeake Bay. Credit: C. Wise
\n![\"River](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2025\/08\/River-otter.jpeg\")
Camera traps confirmed the scat belonged to North American river otters. Credit: C. Wise.<\/p>\n