Recently published photographs showing graphic injuries to two humpback whale calves off Maui are raising questions about how to make the ocean safer for the endangered animals during their winter visits.

So far this year there have been five confirmed whale-boat collisions in Hawai'i, four off Maui and one off Kaua'i. Two of the incidents are known to have injured baby whales.

Officials said the five known collisions are the most on record in any single year.

"We understand how upset the public is when they see these kinds of images. We try to deal with all these things with the best available information," said Naomi McIntosh, manager of the Hawaiian Islands Humpback Whale National Marine Sanctuary. "Whether there are too many boats and that is the cause of the collisions we're seeing, it's hard to definitely say."

A 2003 report compiled for the sanctuary found accounts of 22 whale-vessel collisions between 1975 and 2003. Only two incidents were reported between 1975 and 1984, six between 1985 and 1994, and 14 between 1995 and 2003.

Experts agree that one likely cause for the increase in collisions is the growing presence of humpback whales in Hawai'i. Estimates of the state's humpback population range from 5,000 to 10,000, with an estimated annual growth rate of 7 percent in recent years.

Despite public perception, officials say there hasn't been a significant increase in tour boats — responsible for three of this year's collisions — as the whale population has increased.

The size of Hawai'i's tour boat fleet has long been restricted under state Division of Boating and Ocean Recreation administrative rules that limit how many commercial permits are issued at each of the state's harbors. A maximum of 30 commercial boating permits are allowed at Maui's Ma'alaea Harbor and 29 at Lahaina Harbor, the state's busiest ports for whale-watch cruises. Twelve permits are allowed at Port Allen and 10 at Nawiliwili on Kaua'i; 15 at Wai'anae on O'ahu; and 120 at the Big Island's Honokohau Harbor, where gamefishing prevails.

Commercial boat use of Maui's Mala and Kihei boat ramps are limited to 15 permits each.

The permits do not specify the type of commercial activity, so it is impossible to know how many boats are engaged in whale-watching during the December-to-May season.

A July 2000 report to NOAA's Marine Sanctuaries Division, based on a survey conducted during the 1999 season, showed that 52 vessels were involved in whale-watch activities statewide, making 87 trips daily and carrying 370,000 passengers a year. Two-thirds of the activity occurred in Maui County waters.

The 1999 survey "provided a baseline for what was happening seven years ago. Today, if you look at the information and limiting factors, such as availability of harbor slips to dock boats and natural business competition, my guess is that the change in the number of boats is not that drastic," McIntosh said.

Whales are protected by myriad federal and state laws, including a rule that requires boats to stay at least 100 yards away. Prosecutions for whale harassment or encroachment are rare, since most encounters are accidental, occurring when whales surface unexpectedly or swim up to vessels.

McIntosh and other federal marine managers and researchers say educational outreach, not regulation, is the best way to reduce the risk of whale-vessel collisions. Signs have been posted at state harbors reminding boaters to proceed cautiously during whale season, and the sanctuary hosted a 2003 workshop on whale-boat collisions with participants from federal and state agencies and fishing, tour and shipping interests.

Researcher Marc Lammers of the Oceanwide Science Institute on O'ahu co-wrote the 2003 analysis of whale-vessel collisions. Like other scientists and marine protection officials contacted by The Advertiser for this story, Lammers was reluctant to call for a reduction in the whale-watch fleet or other new rules without first giving a boater outreach campaign a chance to reduce collisions.

"I would hesitate to come out with a total ban or hard-core speed restrictions. It's a thorny issue and there would be a lot of resistance. We should start with a combination of outreach and guidelines that give greater protection to the most vulnerable," he said.

Since certain areas within Hawaiian waters are known to be particularly thick with whales, Lammers suggested slower speed limits through those areas and extra protections for mother-calf pairs, which are more susceptible to collisions. These could include increasing approach distances to give the whales wider berth.

Jeff Mikulina, head of the Sierra Club's Hawai'i Chapter, said restricting the number of whale-watch boats or prohibiting them altogether should be included in a range of options when discussing ways to reduce collisions. Although there are few studies on the effects of ocean tourism on whales, Mikulina said "intuitively, there's an impact."

"My heart just sinks (at news of whale-vessel collisions) and you think, 'Why are these boats in the water during calving season, particularly when you can see the whales from shore,' " he said.

The July 2000 report noted "the majority of scientists and managers who work with marine mammals believe that whale watching is not inherently damaging to whales. The prevailing thinking about whale watching is that the opportunity to educate and inform passengers about whales and conservation issues more than balances what little harassment-related impacts there might be to individual animals."

Most whale-watch cruises provide an on-board naturalist to educate passengers about humpbacks.

"Watching humpbacks in their natural habitat is an awesome experience for our guests. However, we feel it's our responsibility to not only respect the humpbacks by keeping a safe viewing distance, but to also enlighten people about these magnificent creatures," said Ron Williams, president and CEO of Atlantis Adventures, which runs Navatek whale-watch cruises from Aloha Tower. Navatek has never had a whale collision, the company said.

Terry O'Halloran, chairman of the Hawaiian Islands Humpback Whale National Marine Sanctuary advisory council, said the panel has been looking at technological solutions, such as radar and sonar, that can pinpoint whale locations and provide real-time information to mariners. "But there isn't any silver bullet out there for this," he said.

"We're trying to find ways whales and boats can interact safely in sanctuary waters. That's our ultimate goal. Nobody who operates a boat wants to hit a whale," said O'Halloran, who has been involved in ocean tourism for 30 years on Kaua'i and represents business and commercial interests on the council.

NOAA's marine mammal response coordinator, Dave Schofield said propeller guards, used mostly by small boats, could be adapted to larger tour vessels to prevent serious injury to whales in a collision. Mandatory whale-avoidance classes for boaters is another idea, he said.