Tracking Great White Sharks

Every summer, the waters off Cape Cod are visited by a number of great white sharks, studied by expert Dr. Gregory Skomal (GRS’06). Photo courtesy of KQED-QUEST

The photograph taken earlier this month of a kayaker looking over his shoulder as a shark’s dorsal fin cut through the water only a few feet behind him was splashed across newspapers and television screens within hours, raising concerns that great white sharks were coming in close to swimmers on Cape Cod. The photo, taken near Nauset Beach in Orleans, Mass., had officials warning people to use extreme caution while swimming at Cape Cod’s most popular beaches.

A few days later, a marine biologist made further headlines when he announced that the shark in the photo wasn’t a predatory great white after all, but only a fairly benign plankton-noshing basking shark.

The scientist was Dr. Gregory Skomal (GRS’06), a senior biologist at the Massachusetts Division of Marine Fisheries and one of the nation’s leading shark experts. Asked how he knew that the shark in question wasn’t a great white, Skomal says “the structure and shape of the fin, and eyewitness accounts regarding the shape, the coloration, and the behavior of the fish,” led him to identify it as a basking shark.

Skomal joined the state’s Marine Fisheries division in 1987 and currently heads up the Massachusetts Shark Research Program (MSRP), which studies the ecology, distribution, and relative abundance of sharks in local waters. In addition to fieldwork, the program aims to educate the public about sharks.

His work has spanned the globe, taking Skomal from the frigid waters of the Arctic Circle to coral reefs in the tropical Central Pacific. Much of his research is focused on the physiological stresses that captured sharks experience, which he measures using acoustic telemetry, satellite-based technology, and animal-borne imaging. He also studies the post-release survivorship and behavior of sharks.

Skomal is also an adjunct faculty member at the University of Massachusetts School for Marine Science and Technology in New Bedford, Mass., a guest investigator at the Woods Hole Oceanographic Institution in Woods Hole, Mass., and an adjunct scientist with the Center for Shark Research in Sarasota, Fla. He earned his PhD from Boston University in 2006.

The public may recognize Skomal (right) best from his frequent appearances in film and television documentaries, most notably the Discovery Channel’s Shark Week film Jaws Comes Home, which aired last year and featured Skomal investigating the reasons behind the return of great white sharks to the Cape. He attributes their presence to the recent explosion in the population of gray seals, a favorite great white prey, off the coast of Massachusetts.

BU Today spoke with Skomal about his research, why sharks return to the Bay State every summer, and how many sharks are likely to be found swimming near local beaches.

BU Today: Much of your research involves tagging great white sharks. How do you go about doing that and why is it so important?

Skomal: We use a unique process that we been using for the last three years, something called a harpoon tagging technique. In essence, it involves a traditional New England harpoon vessel, which has a tower and a very long pulpit in the bow. We tag the sharks while they are in the shallow waters off of Chatham and Monomoy Island, in water ten feet deep or less. The sharks are swimming freely, so we’re not catching them.

There are two kinds of tags that we are using. One is the kind that pops off the shark after a certain amount of time, a pop-up satellite tag. It collects all types of data about where the shark is swimming, and then at a date and time programmed by us, it pops off the shark, floats to the surface, and then transmits the compiled, archived data to a satellite, which then relays the data to me. We never get the tag back, but it tells us is a lot about the broad scale movements and behavior of the shark and, over a long time, its spatial scale.

The other tag we are using relies on an acoustic technology. We put pingers on the sharks, and they’re swimming in an area where we have a whole array of receivers, which can detect the signal of the tag on the shark and do a time stamp. This tells us where the sharks spend their time, where they come and go, when they arrive, when they leave.

What have you learned from the data you’ve gathered so far?

From our satellite-based tags, we’ve learned that the great white sharks are kind of like Cape Cod tourists. Maybe even like snowbirds, meaning they’re here in the summertime when things are nice and warm, and then in the winter they go south. Most sharks spend their time off the Atlantic coast of northern Florida. They’re really migrants that like to move north and south; there isn’t a lot of complexity to their migration. Most of them stay on the continental shelf, and a really simple pattern has emerged from our satellite tagging. From our acoustic tagging, we’re finding that the sharks come up here as early as late May and go back down south as late as December, so we’re getting an idea of their seasonal residency.

We’re trying to tease out patterns in their movements and fidelity to various sites. It certainly seems like the sharks prefer to be in the area from Chatham to the southern tip of Monomoy. They’re not moving extensively away from that, although they may be moving off shore. Now that we’re getting more and more sharks tagged, over the course of the next year or two we’re going to see some patterns emerge regarding their movements and how they may relate to time of day or even the tide. We don’t have that information yet.

How difficult is the tagging process?

It’s stressful and high anxiety because in essence you’re stalking a free-swimming shark in shallow water, and the movements of the shark are unpredictable. You’re basically trying to stalk a fish with a big boat, and that has certain levels of stress involved in it. But it’s fun, it’s exhilarating. Once the shark is correctly tagged, it’s very rewarding.

Any idea of how many great whites are typically in the waters off Cape Cod in the summer?

It’s hard to do that, because there’s no real formal survey we’re doing. The only way to get an accurate number is to tag them, and we try to tag as many as we can. We think we’re tagging some fraction of the shark population, but we don’t know what fraction it is. In 2011, we tagged eight sharks, and we don’t know if that’s a quarter of them or half of them—but at least we know there are eight different sharks. It’s probably safe to say we’re dealing with something in the order of less than 25 sharks.

You spent years in the field before deciding to pursue a PhD here at BU. What made you decide to do that?

I actually started working as a fisheries scientist back in 1987. I decided in 2000 to go back and get my PhD at BU, after getting a masters and working for many years. I’m a good example of someone who goes back after years of being a professional. Personally, I’m the kind of person who needs to grow continuously and expand my horizons. Getting my PhD was the next logical step.

Why do you love what you do?

It really has to do with the animals I study, which I find fascinating, and the field of science that I’m in. I conduct applied science, which means the data I collect can be implemented to manage and conserve sharks. My job changes all the time, and it’s always about new adventures. I like to push the envelope and go down roads that haven’t been traveled before. It’s a fascinating and amazing career.