MA'ALAEA, Maui — A humpback whale calf was injured when it was struck by a Maui whale-watching boat with 70 schoolchildren aboard but appeared to be "swimming and acting normally" afterward, a fisheries official said yesterday.

National Oceanic and Atmospheric Administration staff found and checked on the baby whale, noting injuries on its head and pectoral fin. Staff members plan to continue monitoring the whale's condition, said NOAA fisheries spokeswoman Wende Goo.

The collision occurred at about 10 a.m. Thursday when a mother whale and calf surfaced by the Pacific Whale Foundation's 65-foot Ocean Spirit, according to Greg Kaufman, the foundation's president. He said no one spotted the pair before the collision. The boat was headed toward Kaho'olawe at about 15 mph.

Two to five whale-boat collisions are reported each year in Hawai'i, but many suspect that number is only a fraction of all collisions because some boaters are afraid to report the incidents for fear of prosecution.

Jane Mori, a fifth-grade teacher at the Carden Academy of Maui, said 32 fifth-, sixth- and seventh-graders from the Pukalani school were on the boat along with a group from St. Joseph's School in Makawao. Kaufman said a total of 89 people were aboard.

"We were watching whales in the distance for some time and we were just starting to cruise around to look for more whales when a mother and calf just popped up right in front of the boat. All of a sudden there was this grinding noise and we looked off the back of the boat and all you saw was blood over the water," Mori said.

She described the impact as a jolt. "It felt like we hit a rock, like we were on a reef, but we were out in the middle of the ocean. It was horrible," she said.

No one was thrown to the deck or otherwise hurt, Mori said. However, she added, "A lot of the children were crying and the adults were shaking. It was pretty devastating."

NOAA's Office of Law Enforcement is investigating the collision. The animals are protected by the Endangered Species Act and the Marine Mammal Protection Act. Vessels are required to maintain a distance of at least 100 yards from humpbacks, but that is not always possible because of the whales' unpredictable behavior.

Deputy special agent Marc Cline of NOAA said investigations into whale-boat strikes also look at possible negligence by the boat operator, but that is rarely the case.

"Who would want to hit a whale on purpose? It's almost always accidental," Cline said. "People just want to see them."

An estimated 5,000 humpback whales visit Hawai'i annually to socialize, mate and calve in the Islands' warm, shallow waters. The majority of whales arrive by mid-December and most leave by April.

Kaufman said male "escort" whales were nearby at the time of the collision, indicating the mother-calf pair may have been under pursuit and trying to evade aggressive suitors.

"We've seen more and more situations where mothers with calves swim toward boats when they are being pursued by males, and this was one of those unfortunate situations where the whale misguessed where the boat was heading," he said.

After the collision, which Kaufman described "as a little bump," the mother and calf were seen swimming away and exhibiting normal behavior.

The vessel, captained by Doug Hunt, sustained damaged to its rudder and was out of commission yesterday.

Mori said the collision appeared to be unavoidable. "We weren't pursuing them. They just came up and it happened," she said.

The Pacific Whale Foundation conducted a question-and-answer period with the children to allay some of their concerns about the incident, Mori said.

The foundation is active in efforts to reduce whale-boat collisions and has developed guidelines for vessel operators to use during humpback whale season. Kaufman said a key recommendation is to go no faster than 15 knots — about 15 mph — to minimize damage to the boat and whale in the event of a strike.

"From Dec. 1 to May 15, you have to drive your boat completely different," said Kaufman, comparing it to slowing your car in a school zone.

"It's shocking to believe that a whale would surface right under your boat. Every boater thinks they'll have a chance (to avoid a collision)," he said.

Among the recent whale collisions are a Jan. 17 incident in which a whale-watching boat hit a humpback off Kaua'i, and a similar collision Jan. 2 off Maui. No one was injured in either collision.

In December 2003, a whale-watch boat struck a humpback off Diamond Head, killing a 3-year-old boy who hit his head on a railing from the force of the impact.

On Jan. 5, 2004, a Maui fisherman was knocked unconscious when his 18-foot boat struck a humpback whale as he was returning to Kahului Harbor.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.