Energy budget calculations indicate resource limitation in Eastern Pacific leatherback turtles

Resource availability constrains energy allocations to competing functions such as growth and reproduction, and thus influences animal life-histories and population dynamics. Leatherback turtles Dermochelys coriacea are critically endangered and exhibit physiological and life-history traits unique among marine reptiles. In addition, leatherback nesting populations in the North Atlantic (NA) are, on average, larger, produce more eggs, exhibit shorter remigration intervals (RIs, time between nesting seasons), and generally demonstrate more stable population trends than Eastern Pacific (EP) nesting leatherback populations. In order to compare energy requirements of inter-basin leatherback populations, we estimated costs associated with reproduction to calculate the energy budgets of leatherback populations from the EP and the NA. Our estimations illustrate that in contrast to reported trends in RIs of these populations (EP = 3.7 yr; NA = 2 yr), NA leatherbacks should require RIs between 1.5 to 4 times longer than their EP counterparts to accumulate sufficient energy to return to their nesting beaches for an entire reproductive season. These results indicate that resource limitation might lengthen RIs for EP leatherbacks compared to NA leatherbacks, thus decreasing the EP population's reproductive success and increasing its exposure to risk of fisheries-related mortality. We hypothesize that stochastic resource availability related to El Nino-Southern Oscillation (ENSO) is exacerbating the effects of high incidental fisheries mortality, resulting in plummeting EP leatherback populations. Therefore, management strategies for fisheries should allow little, if any, mortality of Pacific leatherbacks if there is to be any reasonable hope for recovery of this population.