Food, Glorious Food! Energy budget and reproductive potential of critically endangered leatherback turtles explored...

In ectotherms such as sea turtles, energy acquisition requires a combination of sufficient food resources and access to suitable temperatures. Leatherback turtles (Dermochelys coriacea) , though partially endothermic, are highly migratory and little is known about their energy acquisition. Existing knowledge is based on a few studies of juvenile leatherbacks in captivity that remained relatively small and did not reach sexual maturity while under observation. To bridge this gap, relevant physiological data have been extrapolated to the full lifecycle using Dynamic Energy Budget (DEB) theory. DEB theory provides the basis of mechanistic modeling presented here to (i) predict functional and life history traits for Northwest Atlantic (NWA) leatherback turtles, (ii) elucidate the effects of food availability and sea temperature on those traits, and (iii) use the model to predict traits for another (East Pacific, EP) population of leatherback turtles. Model simulations with warmer temperatures and more abundant food conditions (f≥0.882) led to younger age at puberty, larger size, and higher reproductive potential. Scaled food availability lower than f = 0.882, corresponding to a resource limitation of >15%, resulted in insufficient energy for leatherbacks to attain sexual maturity. Resource limitation hypothesized for the EP population was simulated as a 5% reduction in food availability, which, combined with a 1 °C warmer temperature possibly experienced by leatherbacks in the Pacific, successfully reproduced the observed data pattern. Namely, the model predicted that, under these conditions and while sharing the same physiological parameters as the NWA leatherbacks, the EP individuals would mature slightly earlier and at a similar size, would grow less after puberty (resulting in a smaller ultimate size), and would have a similar (seasonal) reproductive output as the NWA leatherbacks. Our findings highlight the need for a deeper understanding of the specific food and temperature conditions that individuals encounter along their migratory routes.