Hawaii boaters have experienced more humpback whale and vessel collisions as the number of migratory leviathans increase, federal officials said last week.

During the 2001-2005 humpback whale seasons, there were one to four reports a year of whale-vessel strikes in Hawaii waters, while from 2006 to 2010 the numbers rose to between five and 11 a year, said Ed Lyman, a federal marine mammal response manager. Forty-eight whale-vessel strikes have occurred in those 10 years, he said.

From November through May, the seasonal migration from Alaska will bring an estimated 10,000 to 12,000 humpback whales to Hawaii waters — a large jump from the 1,000 estimated in 1978, scientists said.

The entire North Pacific humpback whale population, estimated at 20,000, has been increasing at a rate of 7 percent annually due to federal protections for the endangered species, scientists said.

More whales mean an increase in the probability of reported whale-vessel strikes, said Lyman, who is with the National Oceanic and Atmospheric Administration.

"There’s no speed limit in Hawaii waters," said Lyman, who works at the Hawaiian Islands Humpback Whale National Marine Sanctuary on Maui.

His advice: "You’d better go slower for your own sake."

An adult humpback is about the size of a bus, and it is federally listed as endangered with rules that give it the right of way.

Federal law requires boaters to maintain a distance of 100 yards from any humpback.

He said the increase in reports could also be partially due to improved communications with individuals and government agencies.

The humpbacks travel to Hawaii waters to calve their newborns, increasing the potential for a collision as the young learn to swim and dive.

A newborn whale surfaces and dives frequently, sometimes appearing suddenly near boaters.

The whale-watching industry generates more than $20 million annually in Hawaii, according to federal officials.

Akin to bird-watchers, whale-watchers have their annual gathering, volunteering to count the number of whales at sites on various islands.

Pacific Whale Foundation President Greg Kaufman, whose Maui-based organization started the first islandwide whale count in 1988, said the volunteers who gather at 14 sites on the Valley Isle on Feb. 26 have keen eyes and are patient.

"They’re really not there for the show. They’re there for the Zen of it," he said.

Kaufman said people plan their vacations around whale-watching season and sign up for the whale count a year in advance.

Kaufman said counts show an upward trend with an increase in sightings at Hookipa, Hana and Kapalua.

In addition to attracting visitors, the national marine sanctuary has been developing into a center for whale research since its establishment in 1997.

Sanctuary officials have become speakers at international research forums, including the "Splash Symposium" in Quebec in 2009, which brought scientists from around the world to present research papers on humpback whales.