A Hawaii Department of Land and Natural Resources news release accused 33 swimmers of “aggressively pursuing, corralling and harassing” the pod of dolphins — a violation of the Marine Mammal Protection Act, a federal law that in 2021 added extra protections for spinner dolphins in Hawaii. The species is particularly vulnerable to human activity in Hawaii’s bays, researchers say.

“It was just crazy to see,” Stephanie Stack, chief research biologist at the Pacific Whale Foundation, told The Washington Post. “Just the sheer number of people swimming directly at those dolphins … it’s pretty shocking.”

A Department of Land and Natural Resources spokesperson said the dolphins corralled by the swimmers were spinner dolphins. Officers with the department met the swimmers upon discovering them on patrol on Sunday morning and informed them of the violation before opening an investigation with the National Oceanic and Atmospheric Administration, according to the department’s news release.

Despite the federal protections, which prohibit swimmers or boats from approaching within 50 yards of a spinner dolphin in Hawaii, awareness about the harms of swimming near them still lags among the public, experts told The Post.

“It’s a tricky situation,” Stack said. “A lot of people feel entitled to swim with wildlife and to have this experience, and so it can be a controversial issue. I think we have to remember that it’s their home.”

Spinner dolphins partition their “home” into separate areas for sleeping and feeding, “kind of like a bedroom and dining room,” said Lars Bejder, director of the Marine Mammal Research Program at the University of Hawaii.

The dolphins gather in the daytime to sleep in sheltered bays like Hōnaunau Bay, a popular snorkeling destination on Hawaii Island where the 33 swimmers were spotted. They then venture out into deeper waters to feed at night, Bejder said. Avoiding swimmers in the day costs the dolphins energy and rest they need for hunting and breeding.

“If you go to bed at night, and if you have someone banging on the drums outside your bedroom window, you’re not going to be able to sleep very much, right?” he said.

Research has found a variety of ripple effects from human-induced disruption to spinner dolphins’ rest, including increased predation from sharks and decreased reproductive rates, Stack said. Dolphins also might abandon bays they used to frequent, she added.

“They’re under chronic stress,” she said. “Just like anything, they need rest.”

Spinner dolphins are not an endangered species, but Stack said precautionary efforts like the Marine Mammal Protection Act’s restrictions — and enforcement of those restrictions — are needed to ensure they don’t slip into a more precarious situation. Bejder added that authorities need the public’s buy-in and for tourists to resist expectations of swimming with dolphins.

“I think if you ask most local Hawaiians … they would agree,” Bejder said. “The vast majority of people will think that it’s good to leave these animals alone.”

A NOAA spokesperson did not comment specifically on the recent investigation but said violators of the law could face fines.

“NOAA urges members of the public to observe marine animals from a safe and respectful distance,” the spokesperson said.