Researchers are hoping to understand why large groups of basking sharks, sometimes over 1,000 at a time are aggregating in waters from Nova Scotia to Long Island regularly.
In a recent study reported in the Journal of Fish Biology, researchers analyzed aggregations of basking sharks recorded off the northeastern United States coast to learn more about the phenomenon. Observations of these aggregation events are relatively rare. In almost 40 years of aerial surveys for right whales, ten large basking shark aggregation events were opportunistically recorded and photographed. Comparing this information with that collected in a number of earth-orbiting satellite and oceanographic databases and by the NEFSC’s ecosystem monitoring system, researchers obtained more insight into this behavior.
The researchers found the aggregations occurred in summer and fall when sea surface temperatures ranged between 55 and 75 degrees F. In the largest event, data was available to indicate there was a high concentration of zooplankton, the sharks’ primary food source, present.
“Aerial surveys provide a valuable perspective on aggregations and their potential functions, especially when coupled with environmental satellite and ship-based survey data,” said Leah Crowe, a protected species researcher at NOAA’s Northeast Fisheries Science Center and lead author of the study.
Ten large aggregations of basking sharks were identified between June 1980 and November 2013, ranging from 36 to at least 1,398 animals within an 11.5-mile radius of the central point in the aggregation. The largest aggregation ever recorded on the aerial survey was at least 1,398 animals photographed on November 5, 2013 in southern New England waters.
Basking sharks (Cetorhinus maximus) are the world’s second largest fish, growing as long as 32 feet and weighing more than five tons. They are highly migratory, slow-moving animals often sighted close to the surface with their large mouths open to filter zooplankton from seawater. They are considered passive and no danger to humans other than that posed by their large size and rough skin. They and the larger whale shark, along with the megamouth shark, are the three shark species that eat plankton.