Off the coast of Hawaii in 2009, two fishermen caught an enormous grander blue marlin weighing in at 1,245 lbs and measuring 12.2 feet long. Conservationists wondered, how long does it take for these animals to reach this size? It turned out that the answer lies in tiny bones in the marlin’s ears, according to a new report.
Although the animal was huge, certain ear bones (called “otoliths”) are, in this animal, each the size of half a grain of rice. What’s special about otoliths, as opposed to other types of bones, is that the cells in otoliths don’t get slowly re-absorbed and replaced. Instead, the inside of the otolith is the same as it was the day the fish was born, and it slowly grows more bone around it, like the rings of a tree.
“This ear bone is actually more like a stone,” Allen Andrews, a research fisheries biologist at the National Oceanic and Atmospheric Administration (NOAA) told Newsweek. “It grows like a mineral. As the fish swims around in its environment from when it’s born to when it’s caught, it actually records a history of its environment.”
Jeff Sampaga, a biological science technician with NOAA fisheries, removed the otoliths from the enormous marlin head. Then Andrews analyzed them and found radiocarbon signatures in certain layers of the otolith. He knew that in the 1950s and 1960s, nuclear bomb testing took place all over the world and left an impact on the ocean, and that he could use that impact as a marker of time.