Shark Tagging Off To Slow Start: Fewer Seals? More Sharks Going To Canada?

CHATHAM – Although reports of shark sightings have appeared in the media since May, researchers did not make their first tagging trip until July 19 — and that happened not in Cape waters but off Scituate, where great white sharks were feeding off the carcass of a dead humpback whale.

State shark biologist Dr. Greg Skomal and colleagues from the Atlantic White Shark Conservancy have made two trips since, tagging two sharks off the Outer Cape Aug. 2 and three off Nauset on Monday, Aug. 5.

“Things are picking up, but still not peak season yet,” Skomal wrote in a text Tuesday.

As in the past few summers, white sharks seem to be arriving in large numbers in Cape waters later in the season, Skomal said.

“Really things didn’t ramp up until we got into August” last summer, he said, adding that the majority of taggings last year were made in September and October.

At this point there isn’t enough data to conclusively determine whether sharks are arriving later in the season on a consistent basis. “Every year is different and things can change quickly, which is why continued monitoring is so important,” Megan Winton, senior scientist with the AWSC, said in an email.

But, Skomal said, “It’s been slow.” Although there have been detections of previously tagged sharks on receiver arrays around the region — six in the past month, according to the AWSC’s Sharktivity app, compared to more than 100 sightings, many unconfirmed — “I wouldn’t say it’s a lot of fish,” he said. Eco tours also report that sightings have been “hit or miss,” he added.

“It’s not as consistent as it has been in 2018, 2019, 2020 or 2021,” Skomal said.

There could be a couple of factors at work. One is the number of seals in the region. Although there hasn’t been a recent full population study of the Cape’s gray seal population — the favorite meal of great white sharks — anecdotally, the numbers may be declining.

And an increase in great white shark sightings off the Canadian Maritime provinces, including some that were tagged off Cape Cod, could signal that some sharks are heading north, where there is an even larger seal population.

Wayne Davis, the spotter pilot who helps Skomal and his team locate sharks, said he’s noticed fewer seals in the several times he’s flown this summer.

“Places where there’s usually a great big herd,” such as the section of South Monomoy Island near an area referred to as “Shark Cove,” seems to be more sparse than usual.

“I counted at most a few hundred,” Davis said. “That’s like nothing.” He’s also noticed fewer seals at other locations where they tend to congregate, such as Nauset Inlet.

An aerial survey of the seal population hasn’t been done in several years, said Lisa Sette, manager of the seal research program at the Center for Coastal Studies in Provincetown. Seal haul-outs can change based on food distribution and other factors, she added.

Skomal noted that some sharks are heading to Nova Scotia and other northern coastal areas. “Some are bypassing Cape Cod, even though they’ve been coming here for years,” he said. Whether there’s a cause and effect at work isuncertain, he added.

“Cape Cod may be too challenging or a difficult environment for them in terms of conditions we’ve got for hunting seals,” he said. Sharks are “creatures of habit” and if they are successful hunting in a given location, “they will keep going back,” he said.

Researchers have a “very robust” amount of data on the Cape’s white shark population — there are over one million data points from tagged sharks “pinging” on acoustic receivers, Skomal said — and that information is being analyzed to tease out predictive models such as when sharks are likely to be here. It’s not easy, added Winton, since the raw data doesn’t account for all factors. The data is available to the public in the White Shark Logbook on the AWSC webpage.

Most of the acoustic tags that have been deployed have a battery life of about 10 years; Skomal has been tagging sharks for longer than that. Since 2010, more than 300 white sharks have been tagged.

“Twenty years ago, if you told me that we’d tag 300 sharks, I’d say you were crazy,” he said.