Commercial harvesting of sea cucumbers will remain illegal under new rules adopted late Friday by the state Board of Land and Natural Resources in response to a spike in collection of the seafloor dwellers.

But the new rules allow aquarium collectors to take up to 3,600 of the animals per year for the entire fishery. Harvests will be limited to waters off Oahu.

Inga Gibson, senior state director of the Humane Society of the United States, said the rules should have completely banned collection of the species until officials have scientific data to determine what is a sustainable take for the animals, rather than relying on numbers provided by aquarium collectors.

Alton Miyasaka, Department of Land and Natural Resources acting commercial fisheries program manager, said the department selected 3,600 as the cap because it was higher than the annual take of about 3,300 reported by aquarium collectors.

He said the demand for sea cucumbers declined after 2008, possibly because of the recession, and has leveled out. Without any sign of the animal’s depletion, there was no justification for reducing aquarium collectors’ take, he said.

“Once again there’s this big exception for the aquarium collection trade,” Gibson said. “It’s not based on science. You can’t determine the sustainability or the health of the reefs or animals just because this is the number of animals that has been collected.”

Miyasaka said the department does not know what is a sustainable catch limit for sea cucumbers, which is usually based on life history, modeling and other assessments. He said it can take up to three years to compile that information and that the department plans to consult with other experts to pinpoint that number.

He said experts suspect sea cucumbers around Hawaii live about seven years. Sea cucumbers play an important role in the ecology of the ocean, state officials say, cleaning debris and tilling the ocean floor to keep the seabed aerated and prevent algae from developing into a dense mat.

In May the commercial collection of the animals came to the attention of DLNR officials after a photo surfaced of a personal inflatable raft filled with sea cucumbers collected off Maui. The cucumbers were collected by one dealer who also collected cucumbers off Oahu, Miyasaka said.

He said the photo was “shocking” for some and prompted people to call DLNR. Other officials have said thousands of sea cucumbers had been collected off Waimanalo to be shipped to Hong Kong.

State officials have said the cucumbers were collected for medicinal purposes in Asian countries, where dried cucumbers are often pounded into a powder that is placed in a pill to treat inflammation and arthritis.

At the time, DLNR had no restrictions on collecting sea cucumbers because no commercial industry existed for the animals in the islands, likely because it’s not economical, Miyasaka said.

In response, DLNR established an emergency rule in June banning the commercial collection of sea cucumbers, except for aquarium collectors, Miyasaka said.

The adopted rules, which also allow individuals to gather a small harvest for personal use, must get final approval from the state attorney general’s office and Gov. David Ige.