Boston (CNN) -- What scientists say is the largest concentration of endangered right whales ever spotted in one location is giving researchers an unusually rich opportunity to study the animals and their feeding habits.
But the gathering, an annual affair in the chilly spring waters off Cape Cod Bay in Massachusetts, also raises the threat of boats striking the 70-ton mammals, according to the state Division of Marine Fisheries. The agency has posted an advisory to boaters urging them to be on the lookout for the whales and steer clear.
Scientists believe that there are only 450 right whales in the world but say the numbers have been slowly recovering since commercial whaling of the species was banned more than 70 years ago.
The more than 100 whales counted in the bay this month is the largest number recorded in one place, according to the Provincetown Center for Coastal Studies in Provincetown, Massachusetts.
"We're looking at an exceedingly rare animal in unusual numbers in one of their last critical habitats," Charles Mayo, a scientist at the center who studies right whales, said Friday.
Why so many in one place?
In a word, food, said Mayo. One way or another, the whales caught wind of a unusually rich repast of plankton available in the waters of the bay and arrived to take advantage of the easy dining, Mayo said. The plankton bloom often occurs, but it's been particularly rich and long-lasting this year for unknown reasons, he said.
There have been no boat strikes on the many whales contained in the bay's waters, said Dan McKiernan, deputy director of the state Marine Fisheries Division.
In fact, the last known fatal strike on a whale in the area happened in 1999, he said.
State and federal law makes it a crime to close within 500 yards of a right whale, according to the state Marine Fisheries Division.
Seeing so many right whales in the same place is encouraging for researchers, even though they are well aware that the species is on the road to recovery after dipping in the early 1900s to as few as a handful of breeding females and male suitors.
It's also a spectacle for the public, Mayo said. The whales feed on the surface and can be seen from shore, he said.
"Anytime you see a whale from the beach that's actually alive, it's pretty exciting," he said.
The whales should begin trickling out of the bay sometime in the next few days heading for deeper waters offshore, Mayo said.