A Theoretical Approach To Assessing Annual Energy Balance In Gray Whales (eschrichtius Robustus)

• Main Author: Greenwald, Nathalie Lucie Elizabeth
• Format: Text
• Language: English
• Published: STARS 2005
• Subjects: energetic costs; BMR; gray whale; Eschrichtius robustus; model simulations; Biology; Bering Sea; Pacific
• Online Access: https://stars.library.ucf.edu/etd/329; https://stars.library.ucf.edu/cgi/viewcontent.cgi?article=1328&context=etd

While direct measurements of energetic demands are nearly impossible to collect on large cetaceans, comprehensive bioenergetic models can give insights on such parameters by combining physiological and ecological knowledge. This model was developed to estimate necessary food intake of gray whales, Eschrichtius robustus, of the Eastern North Pacific stock. Field Metabolic Rates (FMR) for gray whales were first estimated based on various assumptions (e.g. volumetric representation of gray whales, extent of their feeding season, and blubber depth distribution) using morphometric data, energetic costs, and food assimilation according to age and gender specific requirements. Food intake rates for gray whales of varying maturity and gender were then estimated based on FMR and caloric value of prey and compared to food intake rates of previous studies. Monte Carlo simulations and sensitivity analysis were performed to assess the model's predictions compared to observed field data from previous studies. Predicted average food intakes for adult male, pregnant/ lactating female, and immature whales were 475 ± 300, 525 ± 300 and 600 ± 300 kg d-1, respectively. Estimated blubber depths resulting from these food intakes were comparable to field data obtained from whaling data. Sensitivity analysis indicated food intake, from all parameters, as having the highest impact on the percent change in ending mass from a simulation. These food intake estimates are similar to those found in a previous study and fall within the range of food intake per body mass observed in other species of cetaceans. Though thermoregulation can be a factor in some cetaceans, it appears not to be an additional cost for gray whales as the present model's predicted lower critical temperatures for the whales (TLC) were below ambient temperatures. With temperatures increasing in the Bering Sea, the main prey of gray whales, ampeliscid amphipods, could be adversely affected, possibly resulting in increased food shortages leading to a surge in gray whale strandings.