Tagging Basking Sharks

[ music and water rushing ] [ music ] My name's Heidi Dewar. I'm a fisheries research biologist at the Southwest Fishery Science Center in La Jolla. The group that I work with works on highly migratory species. And typically most of the sharks we work on are blue, mako, and thresher sharks. Recently, though, we got the exciting opportunity to start a project on basking sharks. Basking sharks are the second-largest shark in the ocean. They're slightly smaller than whale sharks. They reach up to 30 to 40 feet. And like the largest whales and sharks and rays they're filter feeders. So they're feeding on copepods largely, but probably also fish eggs and other small organisms. So if you see them, they could be potentially big and imposing, but they're actually pretty docile, and they have itty-bitty teeth. You don't have to worry about them, they're not going to filter you to death. [ music ] We are trying to collect as much information on basking sharks as we can. What we'd really like to know is what their preferred habitat is, what makes basking shark habitat, or what conditions are necessary to set up basking shark food. So to address those questions, we started a basking shark tagging program, and this is a towed satellite tag that's secured just under the dorsal fin of the shark. And it floats at the surface, and when the shark's close enough to the surface, the tag transmits the location to satellites. So we get information on their movements that way. Another great thing about these tags is if the shark doesn't come to the surface and you don't get those intermittent transmissions, it still will pop off after a period of time. A little pin here corrodes and the tag comes to the surface, and then transmits log data or data that's been recorded on the tag over the course of the deployment. So far, we have put out three of these tags off of San Diego and heard from all of them. We're also collaborating with people up at Stanford and they put a fourth tag on. [ music ] So basking sharks are named basking sharks because most of the time when people see them in coastal waters, they're up close to the surface, probably feeding on surface slicks, areas where water currents bring together lots of nice food for them to filter. What we've found with our satellite tags is that if they go offshore, their behavior completely changes. These two are really the longest and the most interesting. This was the fish that went down off the coast of Baja. But it didn't go as far offshore, and it came to the surface daily, so still acting like a basking shark. But this shark that went over to Hawaii, after it left those coastal waters, it didn't come to the surface at all. And what we think it was doing is down at depth following this mass of fish and squid and crustaceans that move up and down daily, that we call the deep scattering layer. So it's not foraging on surface slicks as we see near the coastal environment but instead has a completely different foraging behavior offshore, which is not something we knew about before. [ music ] We've got the tagging work that we're doing. In addition to that, we've been trying to go back in time and look at historic sighting records, but then also do a better job of collecting current sighting records. So we have a pretty extensive outreach program. We've got some lovely stickers and cards and magnets that we've been trying to distribute to people that are out on the water: dive boat operators, whale-watching vessels, recreational fishermen. So we're trying to sort of reach out into the community to get more eyes on the water to help us find them. We use that information both so that we know when to try to launch an effort to go put tags out as well as to just get some sense for when they're here so that we can try to get a sense also for why they're here, and what those patterns are like.