The population of Chinook salmon in Alaska has declined dramatically in the past decade. Researchers are trying to figure out how to save the endangered species. Now a team of scientists led by Sean Brennan of the University of Alaska Fairbanks has identified an important chemical signature on the ear bones of Chinook salmon.
Salmon’s ear bone as growth rings, just like trees
The chemical tag could reveal where the fish are born, how they spend their first year of life, and the fish’s migration history. The ear bone, called otolith, grows layers as the Chinook salmon grows. The growth rings are produced throughout their life. According to a study published in the journal Science Advances, researchers can figure out where the fish lived by matching the chemical tags in otolith with the chemical tags of water in which they swim.
Each growth ring reflects the environment the salmon was swimming in at the time of its formation. The chemical tag comes from an isotope of an element called strontium, whose chemical structure varies depending on geography. It makes strontium a good marker for where the fish have been. Every summer, hundreds of thousands of Chinook salmon come from the ocean to the Nushagak River to spawn.
Chinook salmon spend the first year of life in the river
When the eggs hatch, they spend about a year in the river before migrating to the Bering Sea and Pacific Ocean. Scientists are working to determine the birth streams of adult Chinook salmon when they are caught in coastal fisheries. It will help them understand how environmental factors, movement, and freshwater habitat affect the fish’s survival.
The U.S. Geological Survey ecologist Christian Zimmerman said that this approach would help scientists map salmon productivity and understand how freshwater habitats affect the ultimate number of salmon. So far, they have been able to determine which parts of the Nushagak River produced most salmon. They also found that most of the salmon stayed in the same place for almost a year before migrating to the ocean.
Brennan’s techniques can also help researchers understand the behavior of other animals.