Non-invasive fecal analysis to evaluate stress in vulnerable marine mammals

Abstract

A growing number of anthropogenic stressors have been found to impact marine mammals, leading to deleterious effects at both the individual and sometimes population-level. Hormones are an important facet of wildlife health, and can be used to quantify a range of anthropogenic stressors such as vessel noise, habitat disturbance, and pollution. Fecal analysis provides a non-invasive form of stress assessment that allows for evaluation of hormone levels, which can be utilized for marine mammal species whose feces float. Fecal analysis, mostly targeting the glucocorticoid hormone cortisol and its metabolites, has been widely employed in the terrestrial animal realm and is now being extended to marine systems. Here, we reviewed all known studies that have employed fecal analysis on threatened or endangered marine mammals. We found that large whales, both baleen and toothed, have been sampled comparatively more than other vulnerable marine mammal species, with no dolphin and few pinniped species being sampled. Non-invasive fecal analysis remains largely underutilized on vulnerable marine mammals due to logistical difficulties associated with obtaining marine fecal matter, coupled with logistical challenges associated with fecal processing. We opportunistically interviewed experts working with threatened or endangered marine mammal species that have not been targeted for fecal analysis to obtain information on whether or not those species would be potential candidates for fecal stress research. We then draw on various anthropogenic interactions that have been documented on vulnerable marine mammals that would warrant additional hormonal scat research to gain a better understanding of animal physiology and behavior. We chronicle the evolution of fecal analysis for cortisol as a viable technique for stress evaluation, and highlight future challenges and potential opportunities to expand this approach to studying other vulnerable marine mammals