September 29, 2026 — Much like counting tree rings, scientists study fish ear stones—known as otoliths—to measure age and growth rates. These small, hard calcium carbonate structures sit in a fluid-filled pocket behind the fish’s brain, helping it balance and hear.
Beyond revealing age, otoliths act as natural recording devices. As a fish grows, its ear stones absorb trace elements from its diet and the surrounding water. By analyzing these elements scientists can:
- Determine what fish have eaten
- Trace their origins back to specific estuaries from which they hatched
- Track lifelong migrations
- Reconstruct decades of changing ocean chemistry
Every year at sea, fisheries observers and scientists aboard research surveys collect about 45,000 of these specimens. Back in Seattle, Alaska Fisheries Science Center researchers analyze more than 30,000 under microscopes to count annual growth rings. This steady stream of data feeds directly into stock assessment models, guiding efforts to sustainably manage U.S. fisheries. Over four decades, these routine surveys built an extraordinary legacy: an enormous archive of 2.5 million otolith pairs dating back to the 1960s. Today, they are housed at the University of Washington’s Fish Collection, a shared facility between the Burke Museum of Natural History and Culture and the School of Aquatic and Fishery Sciences.