On an overcast July day, four biologists in a skiff are speeding across the waters of Sumner Strait near Wrangell in Southeast Alaska. They're following a group of harbor porpoises to learn more about the distinct populations of these animals in Southeast waters. They're looking at stock structure - a stock is a group of animals that interbreeds and interacts, distinct from other groups of the same species. They're looking at two stocks of harbor porpoises in Southeast, those in the Sumner strait area, and those in Icy Strait and Glacier Bay, about 200 miles northwest.
Genetic tests of tissue reveal the relatedness between individuals - but how do you get a tissue sample from a fast-swimming, skittish marine mammal like a harbor porpoise? These biologists are pioneering a new method called fluke prints. A fluke print is a water sample taken immediately after the porpoise surfaces for a quick breath of air. A two-liter sample of water is scooped from the surface of the ocean right where the porpoise was swimming. The water is filtered immediately and the filter paper is stored - analysis can be done any time in the next few months. The animals shed a tiny amount of skin, but it's enough to provide what's known as environmental DNA. This eDNA can identify the animals to the specific stock, and provides insights into the stock structure - and the gene flow between those different stocks of harbor porpoise in Southeast Alaska and beyond.