Why Cape Cod is a global hotspot for great white sharks

50 years ago this summer, a young Steven Spielberg filmed “Jaws” on the scenic shores of Martha’s Vineyard. It’s a great movie, but it also cemented in the popular imagination that the great white shark is a killing machine, striking beach-goers with fear.

Now, as Discovery’s Shark Week makes its annual return, GBH’s All Things Considered host Arun Rath spoke with Greg Skomal about the hundreds of great whites who visit Massachusetts’ coast for the summer. Skomal is a marine biologist with the Massachusetts Division of Marine Fisheries and author of “Chasing Shadows: Unraveling the Mysteries of the Great White Shark.” What follows is a lightly edited transcript.

Arun Rath: To start off, for people who aren’t just ardent devourers of Shark Week the way that I am, give us a baseline about the number of sharks that are around locally. Cape Cod, in particular, is a hotspot in the summer, right?

Greg Skomal: Oh, it certainly is. Folks don’t usually think about sharks when they think about the Massachusetts coastline, but we get at least a dozen species that are seasonal visitors here. People do focus a little bit on the great white shark, which occur in fairly sizable numbers off our outer Cape beaches and have generated a lot of attention.

Rath: It makes me nervous to go into the water knowing that, once I saw that and watched the patterns of the sharks. But how much do we actually have to worry about them?

Skomal: Well, when we look at the incidents of shark bites, we can look at it statistically and say that it’s an incredibly low-probability event. I mean, we’ve heard all the cliches and analogies relative to lightning strikes and dog bites — and it’s true! The probability of being bitten by a shark is extremely low.

But we do caution swimmers when they’re in certain areas of Cape Cod, because there are great white sharks feeding in very close proximity to the shoreline on seals, which are very, very abundant there. So we say to folks: Understand that if you see seals in a specific area, you may be in a spot where white sharks are feeding, so take caution. Pay attention and know your own strengths and weaknesses in the water.

Rath: How close do they typically come to the shore?

Skomal: I think it surprises folks, but we’ve seen white sharks literally within feet of the shoreline. And it has a lot to do with the water depth. People tend to think of distance from shore, but think about your water depth in terms of distance from shore.

If you go down to the beach and the water drops off to five, six, seven, ten feet very close to the shoreline below, there could be a shark very close to the shoreline. But if you need to go out 50 yards to get to deep water, then it’s probably a pretty good guess that there’s not going to be a shark too close to the shore.

Rath: And where are the sharks coming from or returning from?

Skomal: One thing that our research has shown us using a variety of tagging technologies is that great white sharks we see off Cape Cod may be just seasonal visitors that go as far north as Newfoundland, Canada. Then when the water temperatures begin to cool in November and December, all these sharks — whether they’re in Canada, the Gulf of Maine or Cape Cod — will begin to migrate south. They’ll overwinter generally south of North Carolina — into South Carolina, Georgia, Florida, and even into the Gulf of Mexico.

Rath: It’s kind of amazing to think about that kind of distance. I mean, that’s pretty far.

Skomal: Oh, it’s an incredible distance and put it in the context of having to swim it and the fact that many of these sharks come back year after year after year. That’s incredible navigational skills, going to Cape Cod every summer and swimming there from a distance as far as Texas.

Rath: Then talking about that kind of distance and that amount of time, that’s also fast, right?

Skomal: Yeah, relatively quickly. They tend to avoid some of the mid-Atlantic states as they’re migrating north. So it’s not like they’re always close to the shoreline everywhere they go, it depends on their feeding strategy. That’s linked tightly to time of year.

They like to migrate to New England because we have a very robust seal population, and they love to feed on seals. Anywhere you look at white shark distribution on a global scale, you’ll see that they overlap with seals — and most of the seals that occur off the United States are in New England, as far north as into Canadian waters. It’s worth it for them to make this tremendous trip and travel these great distances so they can forage on the seals up here.

Rath: We’ve heard a lot about climate change affecting ocean temperatures. We actually have a big documentary coming out on NOVA about the Gulf of Maine in particular, and how that’s affected wildlife there. Have we seen any effects in terms of the great white migration movements? How are changing ocean temperatures affecting them?

Skomal: Oh, it’s a really good question and one we’re working on. We don’t have enough data as of yet. We know that, for example, on the California coastline, white sharks have shifted their distribution a little bit farther north as a result of what we think is associated with climate change. Here in New England, we know historically, white sharks have occurred as far north as Newfoundland. So the fact that we still see them off Canada doesn’t mean it’s a change in habitat use or change in distribution.

However, what we’re paying particular attention to is the timing of migration. We think climate change is likely to impact that because of more prolonged summers and a change in the duration of fall. Perhaps we’ll see the sharks arrive a little bit earlier and maybe stay a little bit later.

The other thing we’re paying attention to is: what happens to their forage base? In other words, what happens to the seals that these sharks are feeding on? As the Gulf of Maine continues to warm, the question I have is: what will happen to these seals in terms of their shifts in habitat use? Remember, they’ve got fur, they’ve got a thick blubber layer and their distributions are linked to temperature. If it gets too warm, they’re going to move north and they’re going to take the sharks with them.

Rath: Finally, we mentioned this year is the 50th anniversary of “Jaws’” filming and kind of the start of this shark mania. While it’s probably spread misinformation, you think about Shark Week now, it probably also means so much more research and money going into research. So I’m curious, as a marine biologist, on balance how do you feel about “Jaws”?

Skomal: Well, you know, if you read Chasing Shadows, my book, you’ll see that it was actually the movie Jaws that inspired me to become a marine biologist and I’m not alone. There’s a whole bunch of us all over the world that became shark biologists because of the movie “Jaws.” We were inspired by the character played by Richard Dreyfuss, Matt Hooper. And so, I look at “Jaws” as being inspirational for me.

But at the same time, I know that it really tapped into the fears that people have of sharks, and the media has continued to do that over the years. But what’s really refreshing to me, in the long haul, is I’ve also seen a shift in public attitudes — as folks perhaps replace some of this fear with fascination. I think I’m meeting more and more people each year that have a healthy respect for sharks and realize they’re important members of our marine ecosystem.