Marine wildlife officials are urging boaters to watch their speed when cruising in Hawaiian waters following a second vessel strike of a humpback whale this season.

Ed Lyman, natural resource specialist with the Hawaiian Islands Humpback Whale National Marine Sanctuary, said the latest vessel strike was reported off Lahaina on Tuesday when an adult whale was spotted with a propeller slash on the leading edge of its tail.

He said there are an average of eight to 12 vessel strikes per year in Hawaii.

“We gotta be careful,” Lyman said. “We’ve got to share the water with the whales — for their sake and our sake.”

The message grows even more important as the humpback whale season begins to kick into high gear. Although whale season generally stretches from November to May, the peak is from January to March.

For years it has been illegal under federal law to approach within 100 yards of humpback whales. But in February, the state Department of Land and Natural Resources released a new set of voluntary recommendations for boaters operating around humpback whales.

The guidelines were based on the latest research on vessel-whale interactions, with input from the state, NOAA Fisheries, the Pacific Whale Foundation on Maui, tour operators, private boaters and community members. The recommendations include maintaining a maximum speed of 15 knots in waters of 100 fathoms or less when whales are present, and to proceed at a maximum approach and departure speed of 6 knots when watching a whale within 400 yards.

Jens Currie, chief scientist with Pacific Whale Foundation, said the research indicates the marine mammals react when boats come within 400 yards at speeds higher than 6 knots. The benefit of operating at lower boat speeds, he said, includes less disruptive engine noise.

“The research began in 2013, when we first set out to answer that question of what can we recommend as the best speed for boaters operating during whale-­viewing season,” Currie said when the guidelines were released.

Research also shows that collisions occurring at higher vessel speeds cause more whale deaths and serious injuries than collisions at slower speeds.

It has been estimated that more than 10,000 humpback whales travel from their summer feeding grounds in Alaskan waters to the warm and relatively shallow ocean around Hawaii to breed and give birth each winter.

Each year an estimated 40 whale-watch tour companies operate in the waters of Maui County alone. Add in fishing, recreational and other types of vessels, and the ocean can become quite crowded for humpback whales, officials say.

This season’s first vessel strike occurred in October, a self-reported incident that caused relatively minor damage, Lyman said.

Another one was thought to have occurred in early December, when a whale was spotted off Maui suffering from blunt-force injuries. The whale appeared to have severe spinal trauma, causing it to lose the ability to swim using its tail.

Researchers from the Pacific Whale Foundation responded to the incident, collected data to assess the whale’s health and injuries, and then were able to identify the animal from a global database of unique whale flukes or tails. The whale was known as “Moon” and had previously been sighted off northern British Columbia.

However, a photo of its fluke in late summer from the U.S. West Coast revealed that the whale’s injuries had already been inflicted, Lyman said.

During the previous humpback whale season in Hawaii, a dead whale calf was recovered Feb. 6 off Oahu near the Wailupe Peninsula. A postmortem exam determined the male calf was less than a week old and had been successfully nursing before suffering a traumatic brain injury, likely caused by a vessel strike, according to NOAA.

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Avoid whale-vessel strikes

>> Keep a sharp lookout. Look out ahead for “blows” (puffs of mist), dorsal fins, tails and other signs that whales may be present. Post at least one dedicated whale lookout in addition to the vessel operator from November through May.

>> Watch your speed. Maintain a maximum speed of 15 knots in waters of 100 fathoms or less when whales are present and proceed at a maximum approach and departure speed of 6 knots when watching a whale within 400 yards.

>> Stay at the helm. Keep hands on the wheel and throttle at all times and be ready to take action immediately to avoid a whale in your path.

>> Keep your distance. Federal regulations prohibit approaching within 100 yards of humpback whales in Hawaii waters.

>> Stop if too close. Stop immediately if within 100 yards of a humpback whale. Leave engines running and in neutral until the whale moves away.

>> Go around whales from behind. If whales are in your path, go around them from behind while maintaining more than 100 yards distance. Do not attempt to run out in front of whales to get past them.

>> Warn other vessels. If whales are spotted, use the appropriate VHF radio protocol or other means to alert other vessels.

>> Don’t assume whales can see you. Calves are especially vulnerable since they are curious and may not have learned to be wary of vessels.

>> Plan ahead. Be ready for delays in transit due to whale encounters. Avoid nighttime operations if possible.

>> Alert NOAA Fisheries. If involved in a whale collision or if you spot an entangled whale, call the NOAA Fisheries hot line at 888-256-9840. If a phone call is not possible, hail the U.S. Coast Guard on VHF channel 16.

Source: NOAA Fisheries