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Ageing Sharks

August 24, 2019

NOAA Fisheries The Science behind Ageing Sharks Introducing Nancy Kohler, Chief of NOAA Fisheries Apex Predators Program One of the most important things to find out about a shark is how fast they grow and how old they are when they mature. Introducing Lisa Natanson, Shark Ageing Expert Lisa shows us how she ages a shark. Lisa measures and weighs the shark. She removes the backbone. So as part of our research, we try to age the sharks. Similar to counting tree rings on a tree to see how old they are — you can do that with a shark backbone. Part of it is to find out if one ring means one year. And there’s different ways that we can validate that. What we do is when we go on the research cruises, we’ll inject them with oxytetracycline, which parts a mark on the backbone. So we know that timeframe when we actually tagged the fish. And when that fish is recaptured, we take a look at the backbone, and we can count the rings between the time we tagged it and the time it was recaptured. And that basically validates if there’s two rings and it’s been at liberty for two years, then that would validate that it’s one ring per year for that shark. And that’s so important to us to help age the fish. Unlike bony fish where they can count rings on the otoliths, I mean, for the sharks, the only real hard part that we do is to use the backbone. Why is ageing important? You need to know how old the sharks are; you need to know how long they live; you need to know what age they mature because of long-term sustainability. We are setting quotas and bag limits to catch these fish, and we want to make sure that there’s enough around in order for people to fish and catch them forever. Lisa’s next project . . . the backbone of a 1,300 pound, 12-foot long shortfin mako shark. Age to be determined . . . NOAA Fisheries CREDITS & COPYRIGHT Blacktip reef shark footage- PAUL BROWN, NATIONAL PARKS SERVICE Music – KILLER TRACKS

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