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Behavioral Ecology of Cetaceans: The Relationship of Body Condition with Behavior and Reproductive Success
Dr. Patrick Miller | University of Saint Andrews
The risk of harm to marine mammals from underwater noise is an important environmental and regulatory issue faced by the Department of Defense (DoD). In this one-year limited-scope study, the objectives were to test the ability to make key measures needed to study the role of body condition in the behavior and reproduction of toothed and baleen cetaceans, the Northern bottlenose whale (Hyperoodon ampullatus) and the humpback whale (Megaptera novaeangliae).
The approach was to collect animal-attached tag data, photographs, and tissue samples during three research trials in Canada and Norway and from opportunistic sources. The key analyses conducted in the study were carried out to evaluate the ability to perform the full study. The primary proposed indicator of total body lipid store was body density. This was measured via analysis of hydrodynamic performance when the animals were gliding (moving without active stroking). Measures of lipid concentration in blubber and body shape using laser photogrammetry were evaluated as possible approaches to cross-validate the tag-based measure of body density. Pregnancy status was evaluated using hormone analysis of progesterone, and nursing status was evaluated using observations of calves associated with subject whales. Tag data was used to describe foraging effort, and predator playbacks were conducted to simulate predator presence.
Every one of the complex suite of measures was successfully carried out in at least one of the target species. Body density of three tagged bottlenose whales was successfully calculated. Insufficient time was available in the study period to also complete analyses of body density for humpbacks, but this project was able to identify substantial levels of gliding and evaluate challenges to measure body density in this shallower-diver. Laser photogrammetry was conducted with both species, and the ability to measure some body dimensions was confirmed. However, girth is difficult to measure from a small boat, so alternative approaches to photographically assess body condition were proposed, particularly use of a high-resolution underwater scanning sonar. Lipid content in blubber samples was successfully measured in a number of sub-studies that evaluated variation in lipid content as a function of location on the body, depth in the blubber, and blubber thickness itself. This project demonstrated the ability to measure lipid content of remotely collected biopsy samples, but variation by blubber depth and location on the body appears to differ by species. Biopsy tips of 60-100mm were found to be appropriate to measure lipid content across the entire blubber layer, but full blubber-depth biopsy samples are recommended to provide an estimate of blubber thickness at the sampling location. While neither photogrammetry nor lipid content in remotely-collected biopsy samples are themselves ideal estimators of total body lipid content, they are feasible to conduct and are potentially useful techniques to validate the estimate of total body density from analysis of glides recorded by tags. This project successfully measured progesterone levels in biopsy samples and detected it within non-invasively collected blow expirate samples. Visual observations indicated none of the subjects were traveling with a calf. The high-resolution tags recorded a complex suite of measures that can be used to quantify foraging effort, energetic status, and anti-predator behavior. Playback of killer whale sounds to humpback whales was also successfully conducted.
This limited-scope study demonstrated that, with some refinement in approach, it is indeed feasible to conduct all of the necessary components of a study of the role of body condition in the behavioral ecology of free-ranging cetaceans. While the work remains challenging, a two-tiered study focusing on the role of body condition on the foraging and anti-predator behavior of Northern bottlenose whales and the role of body condition in the reproductive life history of the baleen humpback whale is recommended.