Physiological Thresholds in the Context of Marine Mammal Conservation.

There is growing evidence of the adverse effects of global environmental change on marine mammals, particularly in terms of changes in abundance, distribution, habitat use, migratory phenology, feeding habits, risk of infectious diseases, bioaccumulation of contaminants, declines in reproductive success, and reductions in genetic diversity. These anthropogenic stressors have led to an evident conservation crisis: a quarter of the extant marine mammal species that have been assessed and now considered at risk of extinction. However, we still know very little about the subtle, subclinical effects of environmental stressors on various aspects of physiology that could impacts their survival and long-term fertility, or that could impact the performance of future generations. This chapter argues for the need of considering physiological thresholds when examining how drivers of global environmental change can impact marine mammal populations. It also poses questions regarding our understanding of individual phenotypic plasticity and resilience of species in the face of environmental stressors, particularly under abrupt and unpredictable environmental changes. Specifically, I present evidence of how drivers of environmental change can exert effects at different levels of biological organization to influence the viability of individuals and populations, and discuss which aspects of environmental change could be the most likely to shift the physiological thresholds of different marine mammal species. Finally, the chapter identifies areas of further research in marine mammal conservation physiology in the current context of global environmental change.