Scientists are waiting for lab results to help determine what caused the recent death of three Hawaiian monk seals on Oahu.

The three seals — two adult females and one female pup — were all found dead on Oahu within the span of three days last week, according to the National Oceanic and Atmospheric Administration. As of now the cause of their deaths remains a mystery.

“Unfortunately, we will have to wait to get additional diagnostic tests,” said Michelle Barbieri, veterinarian of NOAA Fisheries’ Hawaiian Monk Seal Research Program. “The main one is microscopic evaluation of tissue. That’s standard. We do that with every monk seal that comes to us. That is our first path. … This doesn’t give us a guarantee, but we’re going to try.”

Hawaiian monk seal RK60, nicknamed Nani, was found dead floating offshore in Kaneohe Bay on May 15. She had been spotted at the bay May 2, and at that time was reported to be in good condition. On Wednesday a small but fully developed female seal pup was found dead in Laie.

On Thursday, Hawaiian monk seal RT10, nicknamed Ua Malie, was found dead on the shores of Kahuku on the North Shore.

Postmortem exams of the dead monk seals were conducted, according to Barbieri, but due to decomposition it was difficult to come to definitive conclusions. At this time NOAA does not think the deaths are due to a trend, pattern or common threat.

“We didn’t see any overt signs of trauma,” she said. “We didn’t see fishhooks, and we didn’t see signs of entanglement.”

It is possible that the pup could have been born dead, she said, and that it belonged to Ua Malie, based on where both were found.

Barbieri hopes that additional diagnostic tests will reveal more, but it could take four weeks or more to get the results from the microscopic evaluation back from the mainland. Once those results come in, then further samples might be sent out.

Nani was born on Rabbit Island off of Oahu and was 7 years old, Barbieri said. Nani gave birth to a female at Moku Iki islet off of Lanikai last summer. Ua Malie was 8 years old and frequented the North Shore.

Volunteers who kept track of Ua Malie said she was the mother of several seals, including Holokai, Lei Ola and Kahulu, the monk seal pup born last summer who died from an infection late last year.

While scientists know Kahulu died from an infection, according to Barbieri, the underlying cause remains unknown.

NOAA stepped up its surveillance of monk seals on Oahu starting Friday morning, in partnership with Hawaii Marine Animal Response, the field operations arm of nonprofit Hawaii Marine Mammal Alliance, to look for subtle abnormalities. So far, 16 seals have been assessed, and the team has not seen anything concerning so far, she said.

What the public can do is help to report sightings of seals as NOAA conducts extra surveillance in the days ahead. It is possible that Nani was observed “logging,” or floating listlessly, at Kaneohe Bay in the days leading up to the discovery of her body. Logging behavior is a possible symptom of a sick seal.

Pup season is also just getting started, according to Barbieri. The first two pups born in the main isles were on Hawaii island and Lanai, but several more have been born on Oahu and several more females are expected to give birth in the next few months, according to Barbieri.

“It’s been a healthy pup season,” she said. “So we’re optimistic, in that regard.”

Hawaiian monk seals (Neomonachus Schauinslandi) were listed as an endangered species in 1976 and are protected by both federal and state laws. As a general rule, NOAA recommends giving seals at least 50 feet of distance. Harassing, harming or killing any endangered species is considered a felony and can result in a fine up to $50,000 and five years in prison under state law.

An estimated population of 1,400 Hawaiian monk seals remains in Hawaii, with about 1,100 in the Northwestern Hawaiian Islands and 300 in the main Hawaiian Islands.

The public can report seal sightings to NOAA’s hotline at 888-256-9840.