They are usually loners. So why are they gathering in groups, one reported to include 1,400 of them?"
Other than their size, they're not a threat to humans.
Groups of basking sharks ranging from as few as 30 to nearly 1,400 individual animals have been observed aggregating in waters from Nova Scotia to Long Island. While individual sightings are fairly common, seeing large groups is not. The reason why the animals congregate has not been clearly determined, and observations of these aggregation events are relatively rare.
More @ Basking sharks gather in large groups off northeast US coast: Group sightings are fairly rare
