Managing Shark Populations in Alaskan Waters

September 12, 2019

NOAA Fisheries The Science Behind Monitoring Shark Populations in Alaskan Waters Hi, I’m Cindy Tribuzio. I work at the Alaska Fisheries Science Center in Juneau, Alaska. Aging and monitoring the growth of shark populations and of any fish populations is very important for stock assessment. In the Gulf of Alaska–in the Bering Sea Aleutian Islands we primarily study the Pacific sleeper shark, the salmon shark and the spiny dogfish. Those are our three main species for stock assessment. Humans should care about the fate of sharks because diversity is very, very important to the health of the entire planet. Theyr’e all uniquely evolved into their environment. The diversity of sharks is actually quite astounding and ecosystems really are like a puzzle– if you take out them out of the system, the whole balance of the system changes. It’s not stable anymore. Spotlight on Pacific Spiny Dogfish Research Spiny dogfish have been harvested off the West Coast and Alaskan waters for nearly 1,000 years starting with tribal fisheries. Today, they are mostly caught as bycatch in fisheries for halibut and groundfish. The spiny dogfish is actually a shark even though it doesn’t say shark in its name. Spiny dogfish are actually generalist feeders. I’ve seen them feeding on jellyfish, shrimp, squid, octopus, larger fish. They’re fairly common and they tend to travel in schools but they’re also only three feet long. They’re a pretty small species. Spiny dogfish are named because they have these two dorsal fins spines and the spine has an enamel gland on it that deposits this dark enamel coating and that has an annular variation, which is what we use to count the number of years on it. It’s like counting tree rings. Then there’s the vertebrae– which is like a spinal column but not quite– and the vertebrae are what we are investigating now for aging spiny dogfish. We have to dissect out the vertebrae from the animal. Clean it off. Trim off all the excess gunk and what-not. Then we put it through a multiple step staining procedure. Hemotoxylin is a vibrant purple color stain and that makes those dark bands really pop out so they’re a lot easier to catch and easier to see and then we mount it on a slide and start examining them under the microscope where we look for the banding pattern, start to take pictures and do image analysis on it. The dogfish sharks are believed to have been the most abundant shark species in the world. The tagging study has been going on for about five years now. What we have learned from just where the tags have released from the animals is that the dogfish are going all over the place. We’ve had dogfish go from basically near Dutch Harbor all the way down off the coast of Los Angeles in under nine months. They didn’t go around the coast as we would have expected. They went across the North Pacific out over the deep water. Clearly they’re doing a lot more moving than we previously believed. This does have an impact on stock assessment because these are not just Gulf of Alaska fish; they’re not just British Columbia fish; they’re not just West Coast fish; they are coast-wide and we have three, four very different management areas. So there’s larger implications just from a management perspective. Even though they are not a sought-after species, fisheries managers limit harvest as a precaution against overfishing. From biological perspective there’s a lot more life history going on with these animals than we believed. Most of the animals that went for these long distance swims were larger, female spiny dogfish. There’s so much to learn about all these animals. Spiny dogfish live 40 to 120 years. Females may live longer than males. Females reach sexual maturity at about 36 years of age. Males reach sexual maturity at about 20 years of age. NOAA Fisheries/ Copyright and credits

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