The North American river otter (Lontra canadensis) and the North American mink (Neovisonvison) are important mesocarnivores and indicator species for riparian ecosystems. Monitoring of populations has focused predominantly on threats which may have implications for mortality, while the effects of highly prevalent sub-lethal stressors like parasites are broadly unknown. Macro-parasites have complex host-parasite-environmental relationships, including strong influences on biomass, host energetics, and behavior, that may affect food web topology. Mustelids require high calorie diets to maintain extremely fast metabolisms, meaning that even subtle effects on energetics could negatively affect individual fitness and population dynamics. We assessed the energetic (body) condition of river otter (Lontra canadensis, n=101) and mink (Neogale vison, n=58) in relation to parasitic infection by helminths (cestodes, nematodes, trematodes, and acanthocephalans) in Alberta and British Columbia. Gross necropsies were performed to determine overall health and energetic condition based on fat deposits (both internal and external), reproductive organ mass, liver somatic index (LSI), splenic mass index (SMI), and body mass index (BMI), compared against parasitic infection. We asked the question: are sub-lethal parasite infections an energetic burden on aquatic mammals in western Canada?
Multiple parasites were found, including some zoonotic species of concern (Versteriasp.), and novel infections of a marine acanthocephalan (Corynosoma strumosum) in coastal foraging mink and otter on Vancouver Island, which led to peritonitis and death in a juvenile mink. Most prevalent was infection by metacercaria (third larval stage) of Diplostomid (Digenea) parasites with over 80% of necropsied animals infected. Metacercariae burrowed into the intestinal or stomach wall, often migrating to the pancreas (most commonly), liver, kidneys, diaphragm, or abdominal musculature. Animals with moderate or severe infections showed classic signs of peritonitis and were in poorer condition, especially in terms of internal fat stores, than animals with mild or no infection. While many Diplostomids are generally not reported as serious threats to wild mammals, our findings show that parasitic infection can be a significant burden on the energetic condition of wild mammals. This is especially concerning for mustelids, which have high energetic demands. Continued monitoring of aquatic mammals, which are particularly susceptible to parasitic infection, is needed as this may have serious implications for individual health and population dynamics.