A whale that has been cruising the waters off Wai'anae during the past week has been identified as a female sperm whale rather than an out-of-season humpback.

Whale researcher Joe Mobley, of the University of Hawai'i's West O'ahu campus, said that he would be skeptical of any report of a humpback in Hawai'i in August, since their normal season here is November to May. He confirmed his suspicions on seeing photographs taken by boater Chuck Babbitt of Kane'ohe, who saw the whale near Wai'anae on Saturday.

"Most folks might confuse them, but there's no question that animal is a sperm whale," Mobley said.

He noted skin color and texture, body conformation, and a unique feature that's visible in one photo. Unlike humpbacks, sperm whales have their blowholes off-center, and their spouts shoot forward and to the left.

Jeff Walters, co-manager of the Hawaiian Islands Humpback Whale National Marine Sanctuary, agreed.

"The spout is definitive," he said. "It has to be a sperm whale."

Mobley said sperm whales aren't common in Hawai'i waters, and they tend to remain in deep water, searching for squid, their primary food. Sperm whale females, which can grow to 30 to 50 feet long, remain year-round. That's within the size range of adult humpbacks as well.

Male sperm whales can grow to 50 to 70 feet in length and are around the Islands from February to April. Mobley said that during an aerial survey for whales in February 2004, he photographed the biggest sperm whale he has ever seen, a massive 70-footer off Kaua'i.

Boater Babbitt said he was fishing off Makaha Saturday when he noticed a whale spouting repeatedly. He had a good camera with him, and photographed it. Babbitt said he is an amateur whale-watcher and was certain the animal he saw was a sperm whale.

"Actually, Saturday was pretty amazing for marine mammals off of Wai'anae," he said. "We also saw two separate pods of pilot whales and two pods of what are either pygmy killer whales or melonheaded whales," he said.

Boater Eric Clark, fishing the same day aboard the "Indigo," said he also saw a whale that was "breaching, and re-entered the water with its tail high in the air."

"It was midway up to Ka'ena Point from Ko Olina, about five miles offshore," he said. "It was near a large school of pilot whales, which were a little farther east and closer to shore."

Mobley said sperm whales are known to breach, but do so rarely.

"I wish I'd seen it," he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.