Masters Thesis

Ecological factors influencing stress in northern river otters (Lontra canadensis)

Baseline levels of stress hormones are necessary for maintaining physical homeostasis in mammals. Excessive amounts of stress, however, can cause serious pathologies. Chronic effects of stress include increased susceptibility to infectious diseases due to suppressed functioning of the immune system, diminished growth rates, protein loss, neuron cell death and inhibited reproduction. A myriad of external factors including unhealthy, human-induced environmental conditions as well as naturally occurring fluctuations in resources, habitat attributes, health and sociality have the potential to cause deleterious changes in stress response in mammals. I validated a non-invasive enzyme immunoassay (EIA) for use in river otters (Lontra canadensis) and used these techniques to evaluate stress hormone concentrations extracted from feces of northern river otters in coastal northern California. I assessed how stress was correlated with anthropogenic and socioecological factors. Fecal samples were collected from river otter latrines at seven coastal river otter activity centers. I evaluated the relative importance of several ecological variables including location (as a surrogate for river otter activity center contamination level), water turbidity, water temperature variation, diet, parasite presence and scat grouping size (as an index of conspecific interactions or group size) as predictors of cortisol stress hormone concentrations of the river otters using AICc and multiple regression. The best fit model included location, turbidity, diet and parasite presence which explained 23% of the variation in stress response observed in this coastal river otter population. When the variables were assigned to one of two a priori models, anthropogenically influenced environmental conditions (location and turbidity) or socioecological variables (diet and parasite presence) and compared using multiple regression, the socioecological variables contributed more than twice as much to variations in stress levels than the anthropogenic variables. These results suggest that a complex combination of human induced and naturally occurring pressures are associated with physiological stress levels in this population of river otters. Indirect measures of river otter population health gained utilizing these techniques can be useful to help establish the ecological status of aquatic ecosystems that may affect many other wildlife species, as well as nearby human communities.

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