Salas y Gómez Expedition: How to Tag a Shark

Colleagues and marine biologists Alan Friedlander and Jim Beets of the University of Hawaii have brought satellite tags to track the wanderings of Salas y Gómez’s Galapagos sharks. Before they can tag them, they have to catch them, a days-long undertaking that requires teamwork, experience, patience, chum, quick reflexes–and a little luck. (Kids, don’t try this at home.)
Alan Friedlander and Jim Beets program a tag to detach two months after being attached to a shark, rise to the surface, and transmit data about the animal’s movements.
By Alan Friedlander, US Geological Survey and University of Hawaii
We tag sharks to find out where they go.
When it comes to migration, there’s a lot of variability within shark species. Some may move a bit, a lot may be homebodies, but then you find the odd fish that swims hundreds and hundreds of kilometers away from the spot where you tag it. Like the Polynesian voyagers who found and settled Easter Island, sharks can be incredibly good navigators.
To tag the sharks, we first have to catch them. We chum them in, which means we put bait in the water to lure the sharks up close to the surface. On our latest try a lot of sharks came up close to the surface. At one point by Scott’s Reef near dusk this evening, we probably had 50 to 70 sharks surrounding the boat, which is very impressive. But most of them were fairly small–a meter to a meter and a half – and probably less than two years of age. That could signal that there was fishing here recently and a lot of the larger sharks were removed.
Jim Beets, Alan Friedlander, and Dave McAloney invert a shark beside the Zodiac to calm it before measuring and possibly tagging it.
The tagging process is pretty straightforward but well coordinated. Once we see lots of sharks around the boat, we put baited hooks in the water. (We’ve filed the barbs down on the hooks so we can easily take them out of the sharks without harm when we’re ready to release them.) We hook the fish, bring them alongside the boat, put a rope around their tails, grab their pectoral fins, and turn them over. They go into what’s called tonic immobility, a state of torpor where they become more relaxed, calm down, and are much easier to handle.
After several unsuccessful hours fishing for sharks to tag south of Salas y Gómez, the team heads north to Scott’s Reef, hoping for better luck there.
At that point, we measure them and determine their gender and age. Externally, you can see whether a shark is male or female because the males have claspers. We’ll measure the claspers and see if they’re calcified or not to determine the sharks’ maturity.
Then if the shark is large enough, we’ll attach a satellite tag via a tether below the dorsal fin in the shark’s shoulder. That’s a good spot to anchor the tag without injuring the shark or hindering its movement. After that, we roll it back over and–in a fairly well-choreographed exercise, when possible–we remove the hook, remove the tail rope, and the person holding the pectoral fin lets go of the shark all at about the same time. The shark swims away and, we hope, collects data for us over the next few months.
Michel Garcia grabs a video camera in an underwater housing and prepares to snorkel with dozens of hungry Galapagos sharks.
We were able to find a few sharks large enough to hold a pop-off satellite tags. We program the tag to detach from the shark and float to the surface at various intervals: two months, four months, and six months after we attach them to the sharks. When they pop off, they transmit information to us via satellite tracking where the sharks have gone. A light sensor on the tag uses angles of the sun to give us some idea of latitude and where the shark traveled.
The sharks’ migration patterns have significant implications for management of the new marine park. If they’re moving between Salas y Gómez and Easter Island, then the protected area may have to be expanded, it may not be large enough. If sharks go outside, there are international implications. For example: One of the Galapagos sharks we tagged during the Cocos Island, Costa Rica expedition in 2009 ended up in Colombian waters.
Fishing for a shark large enough to tag, Dave McAloney, Enric Sala, and Carlos Gaymer toss baited lines in the water shortly before sunset at Scott’s Reef.
Most of these sharks are small, and we know that in general, small sharks move less than large sharks. If there were large sharks here, we would conjecture that they would be moving larger distances. There’s not been a lot of work done on Galapagos sharks so far, except up in the Northwestern Hawaiian Islands. What work has been done shows that, although there is some movement observed between islands, many of them stay put. We won’t know about these sharks, though, until we start getting back information from the tags. Even then, with have a limited number of tags–we’re only deploying three –we’ll only be able to determine so much. But at least it’s a start.
Photos by Ford Cochran
The science team will share frequent updates and media from the expedition, including photographs, videos and links to Google maps, here on the National Geographic News Watch blog. You can also follow the expedition on Google Earth by clicking on the blue ship icon located where the expedition begins near Easter Island, roughly 2,000 miles (3,300 km) northwest of Santiago, Chile. (Make sure the “Places” layer is turned on).
National Geographic and Oceana are members of Mission Blue
View all dispatches from the Salas y Gómez expedition here

Changing Planet