In the quiet waterways and marshlands of the Chesapeake Bay, North American river otters have long been elusive denizens, their secretive lives woven into the fabric of this vital estuarine ecosystem. Despite their longstanding presence along the Atlantic coast of the United States, the intricate details of how these semi-aquatic mammals interact with their environment remain shrouded in mystery. Intriguingly, recent experimental research conducted by a team of ecologists and parasitologists in Maryland has begun to peel back the layers of the river otters’ daily existence, revealing complex feeding behaviors, habitat preferences, and their entanglement with a diverse array of parasites. The findings, published in the prestigious journal Frontiers in Mammal Science, promise to redefine our understanding of these charismatic creatures and their ecological roles within a subestuary of the Chesapeake Bay.
The study emerged from a curious observation: a peculiar, watery fecal deposit found on a dock at the Smithsonian Environmental Research Center’s campus featured vividly red parasitic worms. This odd finding piqued the interest of Dr. Katrina Lohan, head of the Coastal Disease Ecology Laboratory and a leading parasite ecologist. Recognizing the potential significance, Dr. Lohan and her graduate student, Calli Wise, launched an extensive field investigation to characterize the diet and parasite load of river otters via their scat, or feces. Over an eleven-month period, Wise systematically collected samples from 18 active river otter latrines, gathering an average of 28 scats per latrine, carefully handling each sample with sterile tools to prevent DNA contamination.
River otter latrines serve as more than mere toilets; they function as social hubs where otters engage in scent-marking, communication, feeding, playing, and resting. These sites often manifest as patches of flattened vegetation near water bodies, sometimes accentuated by woody debris or manmade structures like docks and staircases. Notably, five of the latrines examined in this study were located directly on human-modified features such as docks and boardwalks, highlighting the otters’ adaptability and their interface with human environments along the Chesapeake shoreline.
To decode the contents of the latrine samples, researchers employed a dual-method analytical approach combining microscopic examination with metabarcoding — a sophisticated genetic sequencing technique that identifies prey species and parasite DNA fragments based on unique molecular markers. This technology allowed the team to bypass the limitations of traditional diet analysis, which relies solely on morphological identification of prey remains, and to uncover cryptic dietary components and parasites that might otherwise be overlooked.
The analysis revealed that river otters consume a remarkably diverse diet that spans aquatic and terrestrial taxa. Central to their nutrition were fish species, including invasive common carp and white river crayfish, as well as native crustaceans such as the American blue crab. Occasional consumption of amphibians and waterfowl further illustrated their opportunistic foraging strategies. The presence of invasive species in their diet not only underscores the otters’ ecological plasticity but also suggests their potential role in controlling non-native populations that may disrupt native food webs.
Beyond prey identification, the metabarcoding analysis uncovered the presence of numerous parasites within the otters’ prey items, predominantly targeting teleost fish — a vastly diverse group of ray-finned fishes. Some parasites appeared to infect the otters directly, while many others likely undergo complex life cycles involving intermediate hosts before reaching the otters as definitive hosts. This intricate parasitic network highlights the otters’ position as apex predators embedded within multifaceted disease ecology dynamics.
These findings raise fascinating ecological implications. The consumption of parasitized prey suggests that river otters could be indirectly influencing parasite transmission cycles, perhaps acting as agents culling infected individuals from fish populations. Such predation on diseased hosts might drive evolutionary pressures on prey species, affecting their genetic variance and disease susceptibility over time. Additionally, otters might be shaping parasite community composition, thereby impacting the broader ecosystem health.
The research also broaches public health concerns. Several parasites detected in the otter scats possess zoonotic potential, meaning they could infect humans, who share mammalian susceptibilities with river otters. Consequently, otters might serve as “disease sentinels,” biological indicators that reflect the presence of pathogens and parasites in aquatic environments frequented by humans. Monitoring otter health and parasite burdens could thus provide early warnings of emerging health risks in coastal and freshwater ecosystems.
However, the study faced notable challenges. Limitations in current genetic databases impeded the definitive identification of some parasite sequences, indicating substantial gaps in our molecular knowledge of aquatic parasites. Furthermore, the inability to link individual otter scats to specific animals constrained resolutions regarding individual dietary patterns and parasite loads, which could inform assessments of otter population health and social behavior.
Despite these constraints, the integration of advanced molecular techniques with ecological fieldwork represents a powerful toolkit for unraveling complex wildlife disease dynamics and trophic interactions. This approach exemplifies how interdisciplinary studies in wildlife ecology and disease ecology can illuminate the invisible threads binding predators, prey, parasites, and human activity within shared landscapes.
The reverberations of this research extend beyond academic circles. By enhancing understanding of otter ecology and their role in pathogen transmission, conservation strategies can be better tailored to safeguard otter populations and their habitats amidst escalating anthropogenic pressures. Furthermore, appreciating otters as integral components in controlling invasive species and disease spread lends additional impetus to preserving their natural environments.
In sum, the North American river otter emerges as a keystone species whose feeding habits and parasitic relationships paint a richly textured portrait of ecological interplay in Chesapeake Bay’s subestuaries. Through integrated field observation and cutting-edge genetic analysis, this groundbreaking study sheds light on the covert lives of otters, revealing them as vital players shaping aquatic ecosystem health and potentially serving as beacons in monitoring environmental and public health. As the research frontier advances, such insights will be pivotal in navigating the intertwined fates of wildlife, ecosystems, and human communities in an era of rapid environmental change.
Subject of Research: Animals
Article Title: North American river otters consume diverse prey and parasites in a subestuary of the Chesapeake Bay
News Publication Date: 14-Aug-2025
Web References:
http://dx.doi.org/10.3389/fmamm.2025.1620318
Image Credits: Credit: C. Wise
Keywords: North American river otters, Chesapeake Bay, river otter diet, parasite ecology, metabarcoding, invasive species, aquatic parasites, animal behavior, ecosystem health, disease ecology, wildlife conservation, zoonotic diseases
