About 400 Spinner Sharks Form Massive School South of Block Island — Possible Sign of a Northward Shift

Researchers photograph an estimated 400 spinner sharks near Block Island

Aerial photos from an August survey captured an unusually dense school of an estimated 400 spinner sharks roughly 10 miles south of Block Island, the Rhode Island Department of Environmental Management (DEM) reported. Teams from the DEM’s Division of Marine Fisheries and the Anderson Cabot Center for Ocean Life at the New England Aquarium were conducting a flight to monitor North Atlantic right whales when the aggregation was spotted.

Spinner sharks (Carcharhinus brevipinna) are typically associated with warmer waters off the Carolinas and Florida, but scientists are increasingly documenting them farther north as ocean temperatures rise. The DEM and Aquarium researchers used morphological features visible in the photographs — such as body shape and fin proportions — plus the sharks' schooling behavior to identify them as spinners, though officials noted sandbar sharks (which also form groups) remain a possibility.

"I was very surprised because I have never seen an aggregation that large," said Sonja Feinberg, an aerial observer with the Anderson Cabot Center. "At first it just looked like a group of about 30, but the more we circled, the more we realized there could have been hundreds."

Orla O’Brien, the aerial survey team lead and a research scientist at the Anderson Cabot Center, said this is the first time her team has documented such a tightly packed spinner shark aggregation. The team previously recorded a large gathering of more than 1,000 basking sharks in November 2013.

The sighting follows a separate September 1, 2024, encounter when local fisherman Capt. Carl Granquist caught, measured, filmed and released a 24-inch spinner shark just south of Charlestown. The juvenile had a partially healed umbilical scar, indicating it was a young-of-the-year and raising questions about whether spinner shark nursery habitat is shifting northward or whether the individual had dispersed a long distance.

That juvenile encounter motivated a paper in the Journal of Fish Biology authored by Joshua Moyer, Jon Dodd and Stephen Kajiura, which highlights the unexpected northern presence and discusses the implications for reproduction and range. As of Nov. 7, researchers at the Atlantic Shark Institute said their work on spinner sharks in northern waters is ongoing and that it remains unclear whether spinners are now giving birth farther north.

The Florida Museum of Natural History describes spinner sharks as slender, gray-bronze sharks named for their dramatic aerial "spinning" behavior when feeding: they swim through baitfish schools while rotating along their axis and sometimes breach and spin high above the surface. Spinner sharks typically reach about 6.4 feet and have been linked to 16 unprovoked, nonfatal attacks in the International Shark Attack File; their teeth are adapted for seizing small prey, so bites are usually minor.

During the same August aerial survey the DEM also recorded three minke whales, 14 fin whales and one humpback whale. Officials emphasized the sharks are not predators of whales and primarily forage on fish; it is unclear whether the shark school and the whales approached one another during the survey.

Why this matters

Large northern aggregations of a typically southern species could indicate ecological shifts driven by warming oceans, changes in prey distribution, or alterations in nursery habitat. Continued aerial surveys, field sampling and genetic studies will be important to confirm species identity, determine whether reproduction is occurring locally, and understand the broader ecological consequences.