It’s happening again. In what is becoming a summer tradition, shark sightings have been reported and many are in places that people are not used to seeing them: near shore.
People filmed a relatively small group of sharks feeding off Nantucket this month and there were about two dozen confirmed shark sightings on Cape Cod last weekend. In many cases, the prevalence of smart phone cameras and social media are merely allowing the public to catch up with what researchers have known for years: Sharks commonly inhabit coastal waters and will follow their prey near shore.
In New York, the historical presence of sand tiger sharks is well known, although reports of six bites in recent weeks is certainly unusual for that area. What’s causing this spate of shark activity so close to shore? It could be from increased numbers of bait fish, recovering shark populations, or habitat shifts due to climate change.
In some cases, this activity may be a positive sign, indicating that efforts to clean up coastlines and manage our fisheries are working. If that’s the case, we humans may need to update our perspective of the beach as the wide-open sea it is rather than a swimming pool. That is certainly the case along Cape Cod, where growing numbers of seals have attracted a recovering white shark population closer to shore in search of prey.
In other instances, seeing sharks in new places is not a conservation win, but may be a sign of changes in response to human-caused climate change. Seawater temperatures in the Gulf of Maine are rising faster than 90 percent of the global ocean, and although we can’t predict the precise impact this will have on sharks, we can safely say that more weird stuff will probably happen.
For instance, species such as blacktip sharks that used to be rare north of Cape Hatteras, are routinely migrating to New York during the summers. Bull sharks, which used to give birth only in Florida, have now established nursery areas as far north as North Carolina. These are two of the species that make Florida the “shark bite capital of the world,” and their ranges appear to be expanding north in response to warming waters.
So what are scientists in New England doing in response to these changes? We are deploying common technology and sharing data in an attempt to monitor shifting shark dynamics, and make sure the public has the most up to date information on shark activity.
Underwater listening stations and acoustic telemetry track tagged sharks whenever they swim within range of a receiver. The Massachusetts Division of Marine Fisheries, working with the Atlantic White Shark Conservancy, has about 80 underwater listening stations around Cape Cod to monitor the presence of more than 250 tagged white sharks. The New England Aquarium uses the same technology, with about 70 receivers in Nantucket Sound and offshore to the south. We have tagged nearly 150 sharks of nine species as part of a suite of projects that include studying the impact of offshore wind development on these highly migratory species.
In addition, the Conservancy’s Sharktivity app provides easy access to the latest shark locations as reported by the public, spotter plane pilots, and “live-buoys” that detect tagged sharks in real time.
The New England White Shark Research Consortium shares white shark detections and other biological data in order to maximize our knowledge of this species in an effort to improve public safety. Shark tags can also be detected by groups across the US East Coast and Gulf of Mexico, creating a network that can monitor their movements more widely.
Continuous, long-term monitoring is needed if we are to understand changes in shark population dynamics. Although our work will never eliminate the risk of being bitten, we believe that understanding shark movements and informing the public is our best bet for reducing shark bites.
Nick Whitney is a senior scientist at the Anderson Cabot Center for Ocean Life at the New England Aquarium. Greg Skomal is a senior scientist with the Massachusetts Division of Marine Fisheries.