The analysis of stable isotopes and fatty acids

What have the whales eaten?

Researchers can collect faeces samples or analyze the stomach contents of a carcass to determine the diet of a cetacean species. Yet, these techniques are limited; they only provide information on what the whale ingested in its most recent meals. Two other techniques exist to help researchers acquire a better understanding of what whales eat: the analysis of stable nitrogen (N) and carbon (C) isotopes and the analysis of fatty acids contained in baleen and other whale tissues.

Interrogating witnesses

When a fin whale comes ashore along the St. Lawrence, a team led by Véronique Lesage (MLI-DFO) is dispatched to locate key "witnesses"—baleen, skin, blubber and muscle samples—that are subsequently "interrogated" back at the laboratory. Additionally, a large-rorqual biopsy programme provides skin and blubber samples from living animals. These "witnesses" reveal the diets of rorqual whales and how they evolve over time.

Stable isotopes

This analysis consists of measuring the abundance of stable isotopes ¹³C and ¹⁵N in relation to the more common forms of these elements, ¹²C and ¹⁴N. These “signatures” provide information on the type of prey ingested (plankton or fish) and on the region where the sampled animal fed (Gulf or Estuary). Results from the analysis of skin and muscle samples reveal what the rorqual whale ate in the two months leading up to the sampling. Baleen, on the other hand, is a veritable archive of the 10 to 15 years preceding an animal’s death: the further from the gum line the sample, the further back in time the researchers travel!

Fatty acids

An extensive diversity of fatty acid chains can be found in marine ecosystems. Every animal species has its own, unique, diet dependent fatty-acid signature. By comparing fatty acids found in a whale’s blubber layer with those found in potential prey, it is possible to determine which prey species the whale consumed.

Discover related projects linked to the analysis of stable isotopes and fatty acids:

Other techniques