Marine scientists are mystified by the death on Kaua'i of an apparently healthy young female Hawaiian monk seal.

"It does seem to be a mystery. Oftentimes you can find the smoking gun, but in this case, there was no obvious cause of death," David Schofield, NOAA's marine mammal response coordinator, said yesterday.

The 250-pound seal was found Feb. 3 in the wash of the waves on the western side of Hanapepe Bay. A necropsy performed Saturday by marine mammal veterinarian Bob Braun, assisted by Kaua'i marine conservation coordinator Mimi Olry, showed it appeared to have been a healthy animal that had recently eaten a meal of nenue, a reef fish.

Schofield said officials are awaiting the results of laboratory tests on the animal's tissues to identify toxins or other possible causes. One thought is that the seal might have suffered ciguatera poisoning from eating fish whose tissues are high in that neurotoxin.

The seal had been born on Miloli'i Beach on Kaua'i three years ago. It came to the attention of wildlife officials twice last year for having been hooked. In August, a hook in its mouth had affected its ability to eat, and the animal was emaciated. That hook was removed.

In December, the seal was hooked again, and wildlife officials removed a cable and float attached to the hook. The seal had lost the December hook on its own, Olry said, and this time its feeding did not appear to have been impaired.

"She looked great. She had a good blubber layer," she said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.