A whale-watching boat hit an adult humpback whale off Kaua'i Tuesday in the latest accident involving the whale-watching industry and the animals that are the focus of its business.

Mike Killary, acting assistant special agent in charge at NOAA Fisheries, said a whale-watch vessel with 49 people aboard was returning to port after a regular whale-watching cruise about noon Tuesday, traveling at about 17 mph when the boat hit the whale in a glancing strike. He would not identify the company involved in the collision.

"It appears at first glance that the whale surfaced in front of them," Killary said. The boat immediately cut power and its crew observed as the whale came up to breathe. It appeared uninjured. No one on the boat was injured and the vessel was not damaged, he said.

Killary said the case remains under investigation, but he said there did not appear to be any criminal aspect to the incident.

After an incident earlier this month in which a humpback whale and a whale-tour vessel collided near Maui, personnel for the Hawaiian Islands Humpback Whale National Marine Sanctuary posted improved yellow, black and white signs at small boat harbors around the islands.

The signs warn boaters to be vigilant during the whale season.