We are what we eat...that is more than just a metaphor. The food we eat gets incorporated into our body tissues. This allows us to learn about what an animal eats, not just by observing them, or looking through their poop, but by sampling tissues like skin.  This is particularly important for animals where it is hard to observe exactly what they are eating, or getting their poop, like many marine mammals. By using skin/blubber samples from biopsy darting researchers can look at the stable isotopes of Carbon and Nitrogen.  Every element has a certain number of istopes, which are naturally occurring variants of each element that differ in the number of neutrons in the atom. They occur in particular ratios at different trophic levels (level of the food chain) and regions. By looking at these istopes researchers can determine what and where an animal has eaten. In this paper researchers are looking at Eastern Pacific Gray whales (on the U.S. West Coast). Previously it was thought that they only ate in the Arctic, and did not eat at their breeding grounds in Baja California, Mexico. But observations of occassional feeding in other areas, like west of Vancouver Island, and at the breeding grounds raise questions. Join us as we learn about what these stable istopes from skin samples can tell us about the importance of different feeding areas to these whales, why this turns the table on what we have previously thought about their feeding habits, and why this information is so crucial for conservation. 

Paper freely available at: https://www.nature.com/articles/s41598-022-10780-1