ANAHOLA, Kauai — Two endangered Hawaiian monk seals, including one initially thought to have been shot last year in Kauai likely drowned after getting trapped in fishing nets, officials said Wednesday.

The findings, which were based on post-mortem exams, underscored the often difficult task of determining specific causes of death of marine mammals in an ocean environment.

The release of the necropsy results was delayed by staffing and other limitations due to the COVID-19 pandemic.

This juvenile male Hawaiian monk seal tagged as RL52 was found dead last year after apparently getting trapped in a fishing net. Courtesy: NOAA Fisheries

The seals were found dead in September and November on the beach near Anahola Beach Park. The carcass of a third monk seal found in December was too severely decomposed to determine the cause of death, according to the Hawaii Department of Land and Natural Resources.

The unusually quick succession of deaths raised suspicions, leading the National Oceanic and Atmospheric Administration to begin an investigation. It also offered a reward of up to $20,000 for information leading to the arrest and conviction of anyone responsible.

The NOAA and the DLNR, which share responsibility for investigating monk seal deaths, said the seals found in September and November were in good condition and their stomach contents suggest they had recently eaten.

The postmortems found no evidence of underlying disease or signs of injuries. “But fluid in the seals’ lungs suggested they struggled to breathe before death,” NOAA said in a press release.

“Taken together, these findings strongly suggest that both seals died from being held underwater in a net and unable to breathe,” it added.

The agency also explained why it “initially suspected and stated” that the juvenile male seal tagged RL52, which was found in September, had been struck by gunfire.

Holes found in the carcass “closely resembled shotgun injuries,” NOAA said. But “X-ray imagery and examination of the underlying blubber and muscle tissue showed no evidence of shotgun injuries or other trauma.”

Correction: An earlier version of this story said the second seal was believed to have been beaten to death in November. The NOAA said fisheries officials have not stated, suggested, nor received any information that a seal was beaten.

NOAA did not address reports that the seal found in November, which it said was an untagged juvenile female, had been beaten to death.

The Hawaiian monk seal is one of the most endangered seal species and is protected under the Endangered Species Act and Hawaii state law, meaning it is illegal to harass, harm, pursue, hunt, shoot, wound, kill, trap or otherwise harm them.

Entanglement in fishing nets has emerged as one of the most lethal risks to the seals.

A study released last year in the Journal Marine Mammal Science found that and other human-related causes including shootings and beatings were responsible for more than half of the 114 deaths of seals that occurred in the main Hawaiian Islands between 1992 and 2019.

Seals occasionally drown for natural reasons or get caught by other ocean debris. But NOAA said “lay gill nets are the more reasonable explanation based on past net drowning history in Hawaiʻi and recent reports of lay gill nets set at night in the vicinity.”

DLNR rules set limits on use of the nets, spelling out how long they can be and requiring that they not be left unattended for more than a half hour after being set.

“These monk seal deaths are, yet again, terrible and unnecessary losses,” said Suzanne Case, DLNR’s chair.

A Hawaiian monk seal found dead on the beach near Anahola Beach Park in Kauai. Courtesy: National Oceanic and Atmospheric Administration

The nets were made of monofilament nylon and “are imported modern fishing gear that is indiscriminate and deadly and have been banned elsewhere in the United States,” Case said. She added that DLNR is “in discussions regarding how best to ensure seals and turtles are protected given ongoing drownings in lay nets.”

All marine mammals are susceptible to drowning if they are trapped underwater and exhaust their air supplies.

“While the vast majority of fishers in Hawaii continue to practice safe, sustainable and pono fishing methods, some continue to fish recklessly, with devastating impact on native and endangered species,” DLNR said in a separate press release.  “This is particularly common with lay gill net fishers.”

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