Over the past four years, summer shark sightings have become the norm off the outer beaches of Cape Cod. Now, Massachusetts researchers are finding their tagged sharks everywhere from Canada to the Gulf of Mexico. And the question remains: how many are there?
Last weekend, a dead minke whale drew at least two white sharks in Cape Cod Bay, forcing beach closures and an uncomfortable realization for many that the sharks aren’t only on the open-ocean beaches.
“It’s safe to assume sharks are everywhere,” said state shark biologist John Chisholm, noting that having sharks in Cape Cod Bay is a return to a much older norm. “Historically, you can dig up old photographs going back to the 1930s and 1920s of sharks that were caught in Cape Cod Bay.”
Still, even Chisholm was surprised by recent data showing that white sharks were frequenting Wellfleet Harbor. Chisholm and his colleagues have tagged 89 sharks with a technology used by a wide variety of marine biologists. A horseshoe crab researcher who had put receivers in Wellfleet Harbor picked up signals from five of the sharks Chisholm has tagged.
All five sharks were juveniles, and researchers speculate that they followed an abundance of fish into the harbor. Wellfleet sticks out into Cape Cod Bay, intercepting a counterclockwise current and acting like a fish trap. Four of the five visited the Harbor only briefly, but one has returned and spent a fair bit of time there.
Other sharks are also starting to show what researchers call site fidelity – returning to the same spots around the same time from year to year. But even the most faithful don’t stay in one spot for long. Sharks tagged near Cape Cod roam as far north as Newfoundland and as far south as the Gulf of Mexico.
“If you picture the Atlantic coast as a highway, these sharks are traveling that Atlantic highway and they’re stopping at Chatham on Cape Cod as a rest area, like the exit 6 Burger King on Rte. 6,” quipped Chisholm. “They’re stopping there to grab a bite to eat before they continue moving.”
If sharks are hungry travelers, grey seals are the burgers and fries. Around the world, from South Africa to Australia, seal haul-outs are white shark hotspots. Cape Cod has become the newest of those, with grey seals bouncing back after being almost eliminated by decades of intense hunting.
Just how many sharks there are remains an open question. Researchers have photographically identified 207 individuals, so far. They’re three years into a planned five-year population study, and they still encounter new individuals every time they go out looking.
For all the surprises and discoveries this summer, one of the most unusual aspects has been timing. Researchers are already seeing numbers – up to twenty sharks on any given day - not usually seen until September.
“This year is definitely different than the previous two years. There was an early spike, but now we’re starting to see it leveled off to where it usually is this time of year,” says Chisholm. “We’ll have to wait until September gets here to see what materializes.”