NOAA Fisheries Service is investigating the recent death of an endangered Hawaiian monk seal on Moloka'i as a deliberate killing.

An adult male monk seal was discovered dead on Monday, southeast of Kaunakakai, said David Schofield, with NOAA's Pacific Island Regional Office's marine mammal response program.

A necropsy of the seal on Tuesday determined that it had been killed intentionally, Schofield said.

It was the third known case this year in which a seal was killed at human hands in the main Hawaiian Islands. The other two killings occurred on Kaua'i.

The National Oceanic and Atmospheric Administration, which has jurisdiction for enforcing the Endangered Species Act for ocean mammals, is not releasing details about how the Moloka'i seal was killed, so as to not hinder its investigation, Schofield said.

The seal was a known resident of Moloka'i and was considered by scientists to have been in his 20s, robust and in good health, Schofield said. The animal was easily identifiable because one of his rear flippers was amputated sometime before 2005.

Moloka'i resident Leimana Naki told George Peabody of the Molokai Advertiser-News that he found the carcass outside the reef breakers and towed it to shore with his kayak.

Peabody said Naki is a caretaker of the Kahinapohaku Fishpond who is active in caring for the Moloka'i nearshore environment.

This year on Kaua'i, two Hawaiian monk seals have been deliberately killed, alarming conservationists who are working hard to preserve the rare seals, which are found only in Hawai'i. The wild population of the seals is 1,200 or less and dropping 4 percent a year.

One of the Kaua'i seal-killing cases was solved when 78-year-old Charles Vidinha pleaded guilty to shooting a seal at Pila'a Beach on Kaua'i's northeast shore.

Vidinha was sentenced to 90 days in federal prison and fined $25. The lightness of the sentence angered many, since the potential fine for killing an endangered species is up to $50,000. Vidinha alleged he didn't mean to kill the seal, just scare it away.

NOAA's Office of Law Enforcement recently offered a $5,000 reward for information leading to the arrest and conviction of whoever killed a 5-year-old male seal on Kaua'i's west side in April. The Kaua'i Surfrider chapter has offered an additional $3,000 reward in that case.