Flexibility for fuelling reproduction in a pelagic ray (Mobula eregoodoo) suggested by bioenergetic modelling.

This study investigated the measurements of energy density and bioenergetic modelling for a pelagic ray, Mobula eregoodoo, to estimate its relative allocation to various bodily processes and especially reproduction. The data revealed M. eregoodoo uses up to 21.0% and 2.5% of its annual energy budget on growth and reproduction, respectively. During pregnancy, females depleted energy reserves in the liver, which, along with their biennial reproductive cycle, aligns with general theory that ectotherms are capital breeders and thus build energy reserves before reproduction. Nonetheless, the reduction in energy reserves did not account for all reproductive costs, and therefore, gravid females supplement reproductive costs through energy derived from the diet, according to an income-breeding strategy. These characteristics imply that M. eregoodoo exhibits some flexibility in fuelling reproduction depending on energy availability throughout the reproductive cycle, which may be prevalent in other elasmobranchs. The data represent the first estimates of both the metabolic costs of gestation in elasmobranchs and the relative cost of reproduction in rays. Energy costs and plasticity associated with highly variable reproductive strategies in elasmobranchs may influence long-term population viability under a rapidly changing environment.

Powering Ocean Giants: The Energetics of Shark and Ray Megafauna.

Shark and ray megafauna have crucial roles as top predators in many marine ecosystems, but are currently among the most threatened vertebrates and, based on historical extinctions, may be highly susceptible to future environmental perturbations. However, our understanding of their energetics lags behind that of other taxa. Such knowledge is required to answer important ecological questions and predict their responses to ocean warming, which may be limited by expanding ocean deoxygenation and declining prey availability. To develop bioenergetics models for shark and ray megafauna, incremental improvements in respirometry systems are useful but unlikely to accommodate the largest species. Advances in biologging tools and modelling could help answer the most pressing ecological questions about these iconic species.

The influence of ontogenetic diet variation on consumption rate estimates: a marine example.

Consumption rates are the foundation of trophic ecology, yet bioenergetics models used to estimate these rates can lack realism by not incorporating the ontogeny of diet. We constructed a bioenergetics model of a marine predatory fish (tailor, Pomatomus saltatrix) that incorporated high-resolution ontogenetic diet variation, and compared consumption estimates to those derived from typical bioenergetics models that do not consider ontogenetic diet variation. We found tailor consumption was over- or under-estimated by ~5-25% when only including the most common prey item. This error was due to a positive relationship between mean prey energy density and predator body size. Since high-resolution diet data isn't always available, we also simulated how increasing dietary information progressively influenced consumption rate estimates. The greatest improvement in consumption rate estimates occurred when diet variation of 2-3 stanzas (1-2 juvenile stanzas, and adults) was included, with at least 5-6 most common prey types per stanza. We recommend increased emphasis on incorporating the ontogeny of diet and prey energy density in consumption rate estimates, especially for species with spatially segregated life stages or variable diets. A small-moderate increase in the resolution of dietary information can greatly benefit the accuracy of estimated consumption rates. We present a method of incorporating variable prey energy density into bioenergetics models.