With two reported collisions between humpback whales and vessels so far this whale season, state and federal officials yesterday reminded boaters and other ocean users to take appropriate steps to avoid such incidents.

One reported collision occurred Jan. 10 on the north Kona coast, and another was off of Waikiki on Jan. 27, said Jeff Walters, co-manager of the 1,400-square-mile Hawaiian Islands Humpback Whale National Marine Sanctuary. Both incidents involved small tour boats and were reported by the operators, he said.

One collision is believed to have involved a calf, and it appears in both cases the whales swam away, said David Schofield, marine mammal response coordinator with the National Oceanic and Atmospheric Administration Fisheries Service. The collisions are still under investigation by the Fisheries Service and NOAA Office of Law Enforcement.

Walters and Schofield yesterday emphasized that boaters need to be careful.

"It's important to avoid collisions for at least two different reasons: One is conservation of the animal because it is an endangered species," Walters said. "And the other one is public safety. These are 40-ton animals. Even a medium-sized boat hits that kind of object in the water and there could be human injuries and vessel damage."

On Christmas Day 2003, a 3-year-old boy suffered fatal injuries when the whale-watching boat he was on struck a humpback whale off Diamond Head. The next month, a Maui man was knocked unconscious when his 18-foot fishing boat struck a whale.

Two reported collisions so far this season is not unusual, with collisions averaging five to seven a year, Schofield said. There were six reported collisions in each of the last two whale seasons.

But that underscores the fact that there are many whales in Hawaiian waters this time of year, Schofield said. Up to 10,000 humpback whales visit Hawai'i from November through May, with a "super" peak season from January through March, Walters said. The population growth rate is about 7 percent a year, "quite significant for a natural population," he said.

Walters said boaters must heed basic collision-avoidance guidelines: Always post a dedicated lookout in addition to the captain, watch the vessel speed, and never leave the helm.

"Be ready to react at any moment, and also take some time to understand your environment, understand the waters that you're working in and learn how to spot whales," Walters said. "You need to look for blows and breaches. Always scan out ahead of you. Even the slightest odd wave or wrinkle in the water that looks out of the ordinary, that could be a whale, so you need to carefully steer away from that."

Schofield also recommended using propeller guards.

"This is basically a school zone for whales," Schofield said. "You wouldn't drive your car 60 miles an hour through a school zone when the light is flashing yellow, so we need you to slow down out there because there's a lot of kid whales out there right now. A lot of keiki whales."

Schofield also said there have been two instances of entangled whales this season. The reports came in too late for officials to get to either whale, but one is still in the area, he said. There were six entanglements last season, and in four of those cases experts were able to remove the gear, he said.

He encouraged boaters to report an entangled whale immediately.

Reach Lynda Arakawa at larakawa@honoluluadvertiser.com.