Newswise — The glacial Arctic Ocean was not a barren ice desert but a breeding ground for the evolution of cold adaptation in marine fish. This is the main conclusion of a new scientific publication from Stockholm University that examines small fish bones found in deep-sea sediments during an expedition aboard the Swedish Icebreaker Oden. “These tiny bones, the otoliths, provide a direct record of when and where fish occupied Arctic waters during major climate transitions”, says first author Julek Chawarski, who worked in the Department of Ecology, Environment and Plant Sciences at Stockholm University during the research project. Evidence of past vertebrate life Otoliths are small calcium carbonate structures in the inner ear of bony fish. They function as part of the fish’s balance and hearing organs, detecting movement, gravity, and sound vibrations. The otoliths were found during a research expedition to the Arctic, coordinated by Stockholm University, aiming to map today’s fish stocks using echo sounding and fish catches in the water column. “But when the first bottom samples arrived on deck, we immediately noticed a fish otolith”, says lead author of the study, Professor Pauline Snoeijs-Leijonmalm from the Department of Ecology, Environment and Plant Sciences at Stockholm...

A massive archive of otoliths—fish ear stones—reveals ocean history and fuels modern research.

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 An Archive Finds a Safe Home Across 40 years of research, Alaska Fisheries Science Center personnel, along with the North Pacific Observer Program, gathered otoliths from 83 different species. Their efforts span annual shelf and slope surveys from California to Alaska. They stretch across the Gulf of Alaska, the Aleutian Islands, the Bering Sea, and the Pacific sector of the Arctic Ocean. Around 2 million pairs of otoliths once sat inside a 1930s wooden airplane hangar that’s now part of NOAA’s Western Regional Center in Seattle. This created a major fire hazard for millions of ethanol-filled vials. In 2012, a National Science Foundation grant allowed NOAA...

A suite of bootstrap-based models and tools for analyzing fish stocks and aquatic populations. Designed for ecologists and fisheries scientists, it supports data from length-frequency distributions, tag-and-recapture studies, and hard structure readings (e.g., otoliths). See Schwamborn et al., 2019 for background. The package includes functions for bootstrapped fitting of growth curves and plotting.