Federal officials warn to exercise caution when driving vessels during humpback whale season, which lasts until May, as collisions have been increasing in the past several years.

"Be extra vigilant if you think there’s a whale around," said Ed Lyman, a resource protection manager for the Hawaiian Islands Humpback Whale National Marine Sanctuary.

Lyman said boaters should be prepared to respond if they see a whale nearby.

A federal rule requires vessels to maintain a distance of 100 yards from a humpback whale, and the state has imposed a ban on thrill crafts, such as Jet Skis in West and South Maui coastal waters during migratory season from Dec. 15 through May 15.

Lyman said there were 10 whale-vessel strikes in the 2012-13 season.

Vessel-whale collisions increased from between one to four per year in 2001-2005 to 11 per year in 2006-2010, according to scientists.

Lyman said it’s too early in the season to predict if the numbers will be more than last season.

The number of humpback whales, Megaptera novaeangliae, that frequent Hawaii has increased from an estimated 1,000 in 1979 to between 10,000 and 12,000 in recent years.

FEDERAL officials say the numbers are still well below the 15,000 to 20,000 before whaling in the 19th century.

Vessel owners say the increase in the number of humpbacks have contributed to an increase in whale-vessel collisions.

Whale behavior has also been changing, with the animals sometimes swimming and bumping into vessels, observers say.

Lyman offered several tips to avoid collisions, including the posting of additional dedicated lookouts during whale season.

He said going slower is better because it provides the animal and the vessel operator more time to detect and respond to each other to avoid contact.

He advised people at the helm to be prepared to take evasive maneuvers if necessary and to keep at least 100 yards away from humpback whales.

Lyman said the person at the helm should stop immediately if within 100 yards and use prudent seamanship to decide to either move away slowly or wait for the whale to move away.

Call the NOAA Hotline,  888-256-9840, if involved in a collision with a whale or to report any entangled or otherwise injured whales. Those without cellphones should hail the Coast Guard on VHF channel 16.