With humpback whale populations rising, marine mammal specialists are asking the Hawai'i boating public to steer clear of potentially dangerous and costly encounters with the large animals.

The risk of collisions or harassment is greatest during the peak of the humpbacks' seasonal visits — from January to March — and prompted state and federal agencies to schedule workshops to educate boaters. The first workshop is tonight in Hawai'i Kai.

A new brochure also will be mailed to commercial boaters to reinforce legally allowable practices and acceptable maneuvers when they approach humpback whales. Federal laws require boaters to stay 100 yards away from whales, while helicopters and airplanes may go no lower than 1,000 feet above the whales.

An estimated 6,000 to 10,000 whales a year migrate to Hawai'i to give birth and nurse their calves. Their numbers are increasing by about 7 percent a year.

Officials with the Hawaiian Islands Humpback Whale National Marine Sanctuary and the state Department of Land and Natural Resources' Division of Aquatic Resources are concerned about the increase they have seen in collisions. There were six collisions during the 2005-06 whale season, up from four in the previous season.

"That's a reminder that that's one of the major threats to these animals," said Edward Lyman, marine mammal response manager for the sanctuary. "We want to remind the ocean users that there are certain things they can do."

The tips are there to help mariners as well, he said.

"You do not want to run into a 45-foot animal, a 40-ton animal," he said. "It's going to cause serious injuries to the people in the boat as well, maybe even fatalities."

One simple suggestion: Go slower.

"The calves are very difficult to see at the surface and they are at the surface quite a bit and frankly they just may not know any better."

Reach Mike Gordon at mgordon@honoluluadvertiser.com.