Finding Amelia

An unexpected call from an American marine biologist gave the Canadian journalist Karen Pinchin the lead of a lifetime. It was a Sunday afternoon in 2018 when Molly Lutcavage phoned Pinchin to share some astonishing news of a large fish and a yellow identity marker known as a spaghetti tag: the same bluefin tuna that Lutcavage had caught and released more than a decade earlier off of Cape Cod, Massachusetts, had been caught once again, this time near southern Portugal.

The transatlantic journey earned the bluefin the nickname Amelia, after the aviation pioneer Amelia Earhart, and prompted a scientific aha moment. For years, conventional wisdom separated North American and European populations of North Atlantic bluefin tuna, and since 1981 an international agreement had bisected the ocean into eastern and western zones for managing the fish stocks. We now know that line is “entirely...