White Shark Population Study Enters Final Year

By: Alan Pollock

Topics: Sharks

A prototype real-time detector buoy for tagged sharks was tested out last summer, and hopefully will undergo more testing this season. FILE PHOTO

ORLEANS Though researchers don’t have firm numbers from 2017, it’s becoming clear that the number of individual white sharks off Cape Cod is substantial. Scientists are preparing to start the final year of the five-year population study this summer.

“There’s going to be a lot of sharks once this is all said and done,” shark researcher John Chisholm said. Chisholm is painstakingly reviewing thousands of underwater video clips taken during tagging expeditions in the past four years, identifying which individual sharks were spotted in each encounter. So far, more than 320 individual white sharks have been cataloged. “Almost every trip there’s a shark I don’t know,” he said.

Chisholm spoke at last week’s meeting of the regional white shark working group, which includes researchers, beach managers and first responders from around the Cape and South Shore. Leading the update on the research project was Greg Skomal, a shark biologist with the state’s Division of Marine Fisheries. With support and funding from the nonprofit Atlantic White Shark Conservancy, Skomal has been collecting shark data from three sources: weekly aerial surveys in the summer, acoustic receiver buoys that record when a tagged shark passes by, and their “mark recapture” tagging trips.

Last year, researchers made 31 tagging trips between June and October, making a total of 813 sightings – often of the same individual sharks as they moved up and down the coastline. Still, having analyzed video from each encounter, Chisholm said there were plenty of first-time sightings last year.

“It’s in the dozens of sharks,” he said.

Last year, the mark recapture survey identified a few sharks in June, more in July, and had peak sightings in August and October. September’s numbers were down, likely because researchers had to cancel seven trips because of unfavorable weather. “If we’re not out there, we’re not seeing sharks,” Skomal said.

The acoustic monitoring confirms a slight dip in shark activity last September, possibly related to a change in water temperature. But activity increases again, apparently peaking after Labor Day, when lifeguard coverage stops at most beaches.

“The hot spots continue to be the Outer Cape,” Skomal said. The tracking data shows that individual white sharks spend the summer months swimming north and south along the outer beach between Monomoy Point and Race Point in Provincetown. Skomal showed a computer animation with different colored dots – each representing a particular white shark – traveling up and down the coastline over the course of hours, days and weeks.

“What you see here is some real residency,” he said, with certain sharks staying off the outer beach for extended time periods, while others just pass through. “Some of these use it as a rest stop. Others get a room,” Skomal said. While the acoustic tags show this movement as sharks pass by the nearshore receiver buoys, satellite tags show that white sharks also routinely swim offshore.

The data suggests that there may be a general movement of sharks from the area of Monomoy Island north to Orleans and the Outer Cape in the later part of the summer.

Megan Winton, a research assistant working on the shark population study, said there’s no lack of information about white shark whereabouts during the study period.

“I’m up to my ears in data,” she said. Winton said she’s hopeful that some preliminary numbers from the 2017 research season will be ready at some point during the summer.

Most of the acoustic buoys were hauled ashore for the winter and will be returned to the water next month, Skomal said.

Last year also saw the first use of a prototype real-time shark monitoring buoy, which was stationed off Monomoy Island. The new technology worked well “until we got hit with bad weather,” Atlantic White Shark Conservancy Executive Director Cynthia Wigren said. The buoy washed ashore on the beach, and researchers hope to get it adjusted and back on station this summer, possibly joined by a second prototype receiver buoy.

Beach managers are keenly interested in real-time shark alerts, which would be useful in identifying some shark activity near bathing beaches or areas popular with boaters. But because the buoys only detect sharks that were previously tagged with acoustic transmitters, they are of limited value.

“Did it seem it was practical, that you could use that information from a public safety standpoint?” Orleans Natural Resources Director Nate Sears asked. Wigren said the real-time buoy did show potential to be useful, to a degree.

“Not every shark is tagged. The messaging around that, if it is used for public safety, is going to be significant,” she said.

While the five-year population study will come to a close after the 2018 season, there is already a plan for future research, Skomal said. In the years that follow, the study will focus on sharks’ fine-scale movements, in a bid to learn more about behavior like feeding and reproduction. Researchers hope to make use of new tags equipped with accelerometers that show shark movements in detail.

“We’re going to be fairly intensive on individual sharks, and move to a model that perhaps includes seals,” he said. This winter, researchers with the National Marine Fisheries Service and Woods Hole Oceanographic Institute tagged a number of seal pups. By tracking the movements of white sharks’ prime food source when they are off Cape Cod, they hope to better understand their hunting patterns, including how often they feed.

“Ultimately [we’re] trying to get a sense of bio-energetics,” he said.