Federal officials are urging boat operators to be vigilant in Hawaiian waters after a humpback whale calf appeared to have been struck off Maalaea Bay on Maui.

Various vessel operators on Friday reported an injured calf, prompting an assessment by researchers from the Hawaiian Islands Humpback Whale National Marine Sanctuary and the Pacific Whale Foundation, according to a news release.

The Sanctuary concluded that the calf — which exhibited limited ability to swim — was likely suffering from blunt force injuries due to a boat strike.

“Behaviorally, it’s drooping a lot when you look at the images,” said Ed Lyman, the Sanctuary’s natural resource specialist. “Then there’s the light-colored skin, the lesions, and a notch, a potential wound on the dorsal ridge of the tailstock.”

While the Sanctuary is not 100% certain it was due to a ship strike, he said many indicators point that way.

It’s a reminder for all on the ocean to “keep a sharp eye out” and “go slower” during humpback whale season, he said. In the vicinity of the whales, data strongly suggests the transit speed should be 15 knots or less.

The “Go Slow, Whales Below” campaign urges boaters to reduce speeds to 15 knots or less when transiting, and 6 knots or less when approaching or departing from whales within 400 yards to help prevent collisions.

“It’s just a good reminder we are sharing the environment and the water with humpback whales,” said Jens Currie, chief scientist at the Pacific Whale Foundation. “So any time you head out on the water, you should be mindful of the whales, and be sure to keep a lookout of the whales below.”

Vessel size and speed can determine whether a whale survives or not, and numerous individuals have lived bearing the scars of previous injuries from boat strikes, he said.

Humpback whale season in Hawaiian waters — usually from November to May — is in full swing, with the peak between January to March.

Thousands of whales migrate from Alaska to the warmer waters of Hawaii each year to mate, give birth, and nurse their calves.

There are many mother-calf pairs currently in Maui waters, according to Lyman.

At least five other strike cases of whales have been reported, so far, he said. Some, including anotehr calf last week, bear visible injuries such as propeller scars.

Lyman, who was out on the water with his crew today, said he has not seen the injured whale calf again. The last sighting was on Saturday, when mother and calf were a few hundred yards off Maalaea Harbor.

Sightings of the calf can be reported to the NOAA Marine Wildlife hotline at 1-888-256-9840.