A chemical signature discovered on the ear bones of Chinook salmon from the Bristol Bay region in Alaska could help scientists find out where the fish are born and uncover the mystery of how they live their first year of life.

The chemical signature would help scientists track the birth and migration history of the Chinook salmon, and it was found in the “otolith,” or the fish’s ear bone that is built up in layers throughout the life of a salmon, according to an International Business Times report. By examining the otolith, scientists would be able to compare chemical signatures within the ear bone with the water it lives in, as the signature comes from isotopes found in strontium, which can be found in bedrock, according to the report.

The water dissolves the strontium and releases it into the water, and the fish then picks it up, with the ions making their way to the ear bone. This makes each fish a “little recorder,” said Sean Brennan, who is the lead author of the study and a postdoctoral researcher at the University of Washington’s School of Aquatic and Fishery Sciences, according to a statement from the university. The chemical signatures tell scientists what environment the fish was swimming in when each layer was formed — which scientists can do because the signature doesn’t change even as it makes its journey from the bedrock to the otolith of the fish.

Brennan and his team made the findings by examining fish in the Nushagak River, where 200,000 Chinook salmon visit annually during the summer as they come in from the ocean to spawn in the tributaries of the river. Once the eggs hatch, salmon spend a year in the river before venturing out into the Bering Sea and the Pacific Ocean, according to the report.

By using this approach, scientists will be able to map the productivity of salmon to determine how their activities in the rivers affect the total number of salmon that make their way out to sea.