Analysis of stable isotopes and fatty acids

What did the whales eat?

mno-BPJ090823_2051-grm-e1360768335554-300x220

  • Humpback whale surface feeding
  • Photo credit: © GREMM

To understand the diet of a cetacean species, researchers can collect a sample of its feces or analyze the stomach contents of a carcass. These two techniques have their limitations however, only revealing what the whale has ingested during its last few few meals. Two techniques are used to obtain a better idea of what whales eat: nitrogen (N) and carbon (C) stable isotope analysis and analysis of the fatty acids contained in whale baleen and other tissues.

Witnesses to question

When a whale is stranded on the shores of the St. Lawrence, the team of Véronique Lesage (MLI-DFO) travels to the scene to collect important “witnesses” that will subsequently be “questioned” in the lab: baleen and skin, fat, and muscle samples. Further, skin and fat samples can be obtained from living animals as part of a large rorqual biopsy program. These “witnesses” will reveal the diet of the rorquals and its evolution over time.

Stable isotopes

This analysis consists of measuring the abundance of stable isotopes 13C and 15N compared to the more common forms of these elements, 12C and 14N. These “signatures” allow to glean information on the type of prey ingested (e.g. plankton or fish) and on the region where the animal has fed (e.g. Estuary or Gulf). The measurements obtained in the skin and muscle samples are a reflection of what the whale has eaten in the previous two months. As for the baleen, it is a veritable archive of the 10-15 years preceding the animal’s death: the farther we move away from the gum, the farther back we go in time!

Fatty acids

A great diversity of fatty acid chains exists in marine ecosystems. Each animal species has a fatty acid signature that is unique and that depends on its diet. By comparing the fatty acids found in a whale’s blubber layer with those found in its potential prey, we can determine the species that it has consumed.