Evolutionary dependencies of marine mammals on their preferred prey species: a potential paradigm shift to guide fisheries management and conservation initiatives

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A nutritional consequence of the co-evolution between marine mammals and their prey appears to be that some potential prey species are no longer energy-rich enough to support the energetic needs of some species of marine mammals, while other marine mammals with lower energy requirements did not evolve high performing musculature, and have therefore adapted to survive on slower moving and generally lower quality prey. As such, fishing and ecosystem shifts that alter the relative abundances of high-energy and low-energy prey species can cause rapid changes in marine mammal numbers depending on which evolutionary pathway the marine mammals followedeven when high biomasses of potential prey species are present. This has been termed the “junk food” hypothesis. I propose to test the general applicability of the junk food hypothesis to marine mammals using bioenergetic models and regional time series of dietary information and population estimates. I will begin by comparing the food requirements of all marine mammals predicted by detailed bioenergetic models with those derived from generalized equations that scale consumption as a function of body mass. My expectation is that this will result in new generalized consumption equations for at least two categories of marine mammals separated by differences in the quality of prey they evolved to consume. I will also undertake a detailed spatial analysis of the population dynamics of marine mammals in the North Pacific relative to the 1975-1976 Oceanic Regime Shift when significant increases and decreases of fish and marine mammals occurred opposite to one another in the Gulf of Alaska and the California Current System. For the next 5 years, I will work with 4 graduate students and 5 undergraduates to formulate the models and build the necessary databases of abundances, distributions and diets for the intensively studied species of marine mammals, particularly in the North Pacific Ocean. I will also establish a complementary database on prey quantity, quality, composition, and distribution using data provided by PICES member countries (Japan, Korea, China, Russia, Canada and the United States). I expect the results to 1) establish trophic linkages and dependencies between marine mammals and their preferred prey species, 2) yield new generalized equations for estimating consumption by marine mammals, 3) test the applicability of the junk-food hypothesis as the major driver of marine mammal population dynamics, and 4) aid in predicting the spatial and temporal effects of climate change on consumption and distribution of marine mammals. The graduate students supported by this study will develop skills in programming, data analysis, and fisheries and marine mammal research; and will take part in international conferences, and in workshops and symposiums organized at PICES annual meetings to support this initiative.**