basking shark
Three basking sharks are seen feeding at the edge of Dun Aonghasa, a pre-historic stone fort dated from 1100 BC on the remote Aran Islands in Galway, Ireland, May 13, 2016. REUTERS/Clodagh Kilcoyne

Basking sharks, who are known for their solitary lifestyle, were spotted in swarms of up to over a thousand along the northeastern United States, aerial surveys revealed. The result of the surveys baffled researchers, bring out theories about why basking sharks would congregate.

Leah Crowe, a field biologist at the National Oceanic and Atmospheric Administration's Northeast Fisheries Science Center, conducted the study along with his colleagues. The study, which was published in the Journal of Fish Biology, revealed about 10 sightings of large groups of basking sharks between 1980 and 2013 along the coast of Nova Scotia to Long Island. The aerial surveys were conducted to track endangered North Atlantic right whales.

"Aerial surveys provide a valuable perspective on aggregations and their potential functions, especially when coupled with environmental satellite and ship-based survey data," Crowe said.

The largest of the gathering was seen in November 2013 off southern New England where about 1,400 sharks congregated. Other shark species are known to gather for feeding, mating, and protection from predators.

For the record-breaking gathering, Crowe indicates that the group was likely feeding on zooplankton instead of mating. The study suggests these normally solitary species may have come together to reduce the drag caused by their open mouths during feeding, which further allows them to draft off each other to conserve energy.

However, "seeing them from the air is interesting, but it doesn’t tell us that much about the environmental factors," Crowe said.

"Although the reason for these aggregations remains elusive, our ability to access a variety of survey data through the North Atlantic Right Whale Consortium Database and to compare information has provided new insight into the potential biological function of these rare events," Crowe added. "The study also highlights the value of opportunistic data collection."

Basking sharks are relatively harmless to humans and can grow up to 32 feet in size. They spend about 90 percent of their time deep underwater, and only 10 percent at the surface, according to Dave Ebert, program director for the research center. This makes any sighting of basking sharks very valuable. While swimming slowly beneath the surface, basking sharks have their mouths open in a terrifyingly wide gape in order to filter the tiny organisms from seawater. Basking shark, the larger whale shark and the megamouth shark are the three shark species that eat plankton.