It’s hard to think small in Alaska. The largest of the United States is home to North America’s highest mountain range. It’s a place where undammed rivers run more than 1000 kilometers, glaciers collapse into the ocean, and polar bears roam.
Daniel Schindler, however, is here hunting for something the size of a grain of rice. Crouching in tiny Allah Creek, hemmed in by alders and smeared in blood, he grasps a rotting sockeye salmon carcass and nearly decapitates the fish with a stroke of a carving knife.
With tweezers, he delves into a cavity of creamy goo tucked behind the brain and plucks out a sliver of what looks like bone. It is an otolith, a bit of calcium carbonate that sits within the inner ear and acts like an internal gyroscope, helping the fish orient its movements.
Schindler, an aquatic ecologist at the University of Washington in Seattle, holds the white fleck up to the sunlight. “For some reason, picking otoliths is a very therapeutic activity,” he says, as a cluster of scarlet-sided sockeye thrashes by in the shin-deep water, frantically searching for their spawning grounds.
Chemical isotopes trapped in the otolith, which forms layers like tree rings as it grows, tell the story of the salmon’s birthplace and life. Between 2 and 5 years ago, the sockeye hatched in this creek, a tiny corner of the sprawling network of freshwater lakes and streams along Alaska’s Bristol Bay. The fish headed out to sea and finally returned to its birthplace to spawn and die.
For the rest of this article: https://www.sciencemag.org/news/2019/09/how-salmon-scientist-got-hooked-battle-over-world-s-largest-gold-mine