The Provincetown-based nonprofit group reported Friday that about 100 whales are concentrated near the western shore of Cape Cod Bay and near the entrance to the Cape Cod Canal .
The animals are feeding below the surface of the water and aren't easily visible to boaters. The center advises that the animals are vulnerable to collisions with ships and asks that boaters take precautions.
Charles "Stormy" Mayo, senior scientist with the center, called the whale cluster "an exceptional concentration of an extremely rare animal."
The North Atlantic right whale population is about 500.