As many as six humpback whales were spotted in Boston Harbor on Wednesday, a rare sight in the congested shipping port. But the whales probably weren’t lost, according to Joseph Ayers, a professor at Northeastern’s Marine Science Center in Nahant, Massachusetts. They were probably just looking for a snack.

“There appear to be a lot of bait fish in the area right now, like pogies, and that seems to be attracting the whales,” he said. Ayers, who specializes in marine science and neurophysiology, said that whales are usually feeding whenever people see them close to shore.

Ayers said that in the past, he has seen humpbacks as close as “50 yards off the wharf in Nahant.” But while it might be normal for these whales to come close to shore, it’s not common for them to swim into Boston Harbor. In fact, Ayers said it could be quite dangerous.

“Boats are the biggest problem for whales. If a whale swims into the propeller of a boat, especially something as big as a shipping vessel, it could be deadly,” he said. Since the whale sightings earlier this week, the U.S. Coast Guard in Boston has warned boaters to be aware of the animals.

Boaters might be able to avoid whales by steering clear of large flocks of birds because, according to Ayers, “Whenever you see a flock of birds, it means there are fish around.” And where there are fish, there could be humpback whales.

Ayers speculated that these recently-spotted whales are looking for food based on their behavior. “The displays that they’ve been making are definitely feeding displays,” he said.

Humpback whales use a unique hunting method that involves blowing air bubbles around schools of fish. Once the fish are trapped in the air bubble rings, the whales swim up from below the fish and consume them.  

No one knows for certain what the whales are doing in Boston Harbor, but Ayers knows one thing for sure. “It’s their ocean, and they feed where they find food. It’s a very opportunistic lifestyle,” he said.