LIHUE » An aggressive Hawaiian monk seal that officials planned to euthanize to protect pups is nowhere to be found.

A federal official spent a week looking for the animal at Kure Atoll in the Northwestern Hawaiian Islands, The Garden Island reported last week.

The National Oceanic and Atmospheric Association recently announced it would euthanize one, possibly two, adult males at the atoll to protect the critically endangered species. Those males were attacking other seals and holding pups and juveniles under water in an attempt to drown them.

The missing seal, KE18, attacked other seals last year and was more aggressive this year, said Charles Littnan, head of NOAA’s Hawaiian monk seal research program.

"The last two days we couldn’t find him at all, so it is possible that he had gone out to sea to forage," he said.

Officials will review options for dealing with the aggressive seal next year.

Moving the seals was eliminated as an option because doing so would just allow the seals to attack pups in their new location. An aquarium or research facility was not available to take them in.

The crew who went to Kure Atoll undertook the mission "sadly and with great regret," Littnan said.

Tim Robinson, program coordinator at the Hawaiian Monk Seal Watch Program, said it’s unpleasant to euthanize any endangered animal, but his group, made up of Kauai volunteers, supports NOAA’s decision.

"So the trade-off here is that by getting rid of these two guys they’re letting the young live," he said.

Kathleen Gobush, a research ecologist at the center, said the males are both "subordinate males." This means, unlike the dominant males at Kure, they don’t have mating partners and breeding opportunities.

Gobush said the animals may be displaying what she called "misplaced breeding aggression." The adult males have been scratching, biting and mounting the pups. In some cases, they’ve been corralling the small seals into the ocean and then holding them under water.

Ten of the 13 pups that weaned at Kure Atoll this year have been injured in these attacks over the past few months. Two are missing and feared dead.

About 100 monk seals live at Kure, 1,200 miles northwest of Honolulu inside the Papahanaumokuakea Marine National Monument.