A juvenile monk seal that died after it was spotted off Hawaii island having trouble breathing had ingested a fishhook, according to a necropsy conducted by the National Oceanic and Atmospheric Administration Fisheries.

Officials believe the hook was the cause of the monk seal’s death.

The hook lodged in the esophagus of the male monk seal, identified as RK68, and slowly migrated into the trachea. Scar tissue built up around the point of the hook, blocking the windpipe.

"It was slowly suffocating," said Charles Littnan, lead scientist of NOAA’s Hawaii Monk Seal Recovery Program.

RK68 was spotted Friday near Mahu­kona on the island’s northwestern shore. The Coast Guard flew the seal to Oahu for medical treatment, but the damage caused by the hook was too extensive, Littnan said.

He was taken to the Waikiki Aquarium on Friday, where scientists sedated him for an examination to determine the cause of his labored breathing. The monk seal stopped breathing and suffered cardiac arrest while scientists took X-rays.

Littnan said the mammal could have been hooked several weeks to several months ago. It was the first monk seal death of the year.

At a news briefing held Tuesday, William Aila Jr., director of the state Department of Land and Natural Resources, urged the public to report monk seal hookings as soon as possible with as much detailed information to allow officials to mobilize a recovery team.

A sighting of RK68 was observed several months earlier, but there were no outward signs of distress or confirmation the monk seal was hooked.

Hooking seals is beyond the control of fishermen, but they can report incidents when they occur, Aila said.

The necropsy also showed RK68 with healing fractured rib wounds. Littnan said the injuries were not related to the hooking.

The rib fractures probably happened when the mammal was younger and were caused by blunt force trauma, likely human-related, caused by kicking or hitting with a foreign object. K68 recovered from its rib fractures but subsequently got hooked, he said.

Another juvenile male monk seal, identified as RT12, was spotted Monday afternoon off Kauai with a fishing line hanging from its mouth. A veterinarian from Sea Life Park and NOAA staff performed minor surgery Tuesday morning and successfully removed a circle hook, typically used by shore casters, stuck in the seal’s tongue; the mammal was then released.

Officials say the number of monk seal hookings is increasing. Fifteen were reported in 2012; three resulted in deaths. Nine hookings were reported in 2011 with no deaths.

Killing or harassing a monk seal is a Class C felony, punishable by up to five years in prison and up to a $50,000 fine.

Regarding recent whale collisions in the islands, Elia Herman, state co-manager of the Hawaiian Islands Humpback Whale National Marine Sanctuary, said five confirmed whale-vessel collisions have occurred this year, and one incident is under investigation.

Juveniles or calves tend to get struck by vessels such as a tour boat, canoe or kayak. "Much like seals, some of this is going to be unavoidable. You’re going to have accidents, but how can we help prevent those. Go slow and keep a look out," Herman said.

To report a marine mammal in distress, call NOAA’s Marine Mammal toll-free hotline at 888-256-9840.