You are what you eat, so eat well! The use of stable isotope analysis to determine the trophic ecology of balaenopterid whales

Dr. Sean Todd holds the Steven K. Katona Chair in Marine Science at College of the Atlantic, and directs Allied Whale, the college’s marine mammal research group, as well as the college's Marine Mammal Stranding Response Program. Dr. Todd has been involved in marine mammal research and rescue for over 18 years, initially working in Newfoundland, Canada as a member of, and later as Coordinator of a large whale disentanglement team. During this time Dr. Todd was also involved in research efforts to mitigate stranding and entanglement of large whale species, and he was one of the first researchers to complete a comprehensive assessment of the trophic ecology of balaenopterid whales using stable isotope analysis. Since moving to the United States Dr. Todd has continued to focus his research in trophic ecology, and has recently completed a similar assessment for the Gulf of Maine. He currently sits on the Board of Scientific Advisors for the American Cetacean Society, as well as the Marine Environmental Institute.

Large whales can be sampled in situ through the delivery of a biopsy dart that typically obtains skin and some blubber. This relatively non-invasive methodology has provided researchers with tissues that permit a variety of analyses, including molecular-based investigations, contaminant load assessments, hormone measurements, and studies of diet and trophic ecology, on a per individual basis. In this paper I review biopsy-based trophic investigations that examine a whale’s storage tissues for records of assimilated diet through the detection of chemical signatures that are unique to the prey consumed. Stable isotope analysis, for example, assesses the ratio of certain species of stable isotope (for example, 15-Nitrogen or 13-Carbon) to their more common counterparts, ratios that remain remarkably stable and therefore diagnostic throughout the processes of consumption, assimilation, and storage within a consumer, and beyond if that consumer in turn becomes prey for higher-level consumers.

Assessment of stable isotope ratios, in conjunction with the collection and collation of other variables commonly taken during biopsy sampling protocols such as location (in time and space), species, individual identification, gender, behavioral status, reproductive status, etc., can be a valuable tool in examining variations in trophic ecology. In particular, longitudinally-based assessments have demonstrated changes in whale foraging behavior over years that may be linked to cyclical, oceanographically-driven changes in ecosystem productivity.