But the boats involved in past collisions have been significantly smaller and slower than the 400-ton Hawaii Superferry, which travels at a speed of 37 knots, Kaufman said.

"Any vessel can hit a whale, from a canoe to a battleship," Kaufman said. "When you start looking at a vessel like Hawaii Superferry, in its class and size, it approaches 100 percent lethality."

It was the seventh day on the witness stand for Kaufman, who was called to testify as a whale expert by Maui Tomorrow, the Sierra Club and Kahului Harbor Coalition. The three environmental groups are challenging the Superferry's operation without an environmental assessment of ferry-related improvements at Kahului Harbor, The Maui News reported.

Second Circuit Judge Joseph Cardoza is hearing testimony before deciding whether to continue a ban on Superferry operations until an assessment is done.

Kaufman's cross-examination was expected to continue when the hearing resumes at 9:30 a.m. Monday.

On Friday, Superferry lawyer Bruce Lamon questioned Kaufman about studies reporting collisions between whales and boats in Hawai'i waters and how close the collisions were to the Superferry's route.

Of incidents reported from 1975 to 2003, Kaufman said the closest collision occurred in Ma'alaea, about 16 miles from the Superferry's northern route. While 22 collisions were reported during the period, Kaufman said, many of them involved boats that weren't moving when they were bumped by whales.

After the court hearing, Kaufman said he wasn't asked about other whale-vessel collisions that have occurred since the study was done. He said 17 "whale strikes" with vessels have been reported from 2003 through the last whale season ending this year, with some occurring in the area of Superferry operations.

Kaufman said the largest Pacific Whale Foundation boat is a 65-foot catamaran that would travel at an average speed of 8 knots during whale-watching trips. By comparison, he said, the Hawaii Superferry is 355 feet long and travels at 37 knots.

"In the last three years in Hawai'i, there has not been a fatal strike because it's involving small boats moving at slow speeds," Kaufman said.

Also during testimony, Kaufman said a study indicated that, in 93 percent of whale-vessel collisions, operators didn't see whales before they surfaced in front of vessels.

"We are simply not getting any forewarning," Kaufman said. "These whales are popping up in front of the vessel, and they're striking them. The point is you need to slow down and as you slow down, the likelihood of collisions decrease."

During the hearing Friday, Lamon also questioned Kaufman about the possibility that humpback whales could be removed from endangered species classification based on reports indicating increasing humpback whale populations in the North Pacific.

Based on an estimated whale population of 15,000 before 1905, Lamon said the humpback whale could be subject to "delisting" from the endangered species list when its numbers reached 9,000. Kaufman said the humpback whale population is estimated at 11,600 to 15,000 in the North Pacific.

"We all can be happy about the recovery of humpback whales so far," Lamon said.

Attorney Isaac Hall, representing the environmental groups, objected, saying Kaufman had testified that humpback whales weren't being "delisted."

Kaufman said questions have surfaced about whether the pre-1905 population was underestimated. In addition, he said, research is under way to better understand the movement and breeding of humpbacks.