The juvenile monk seal RJ16, nicknamed Kahuluokalae, died Friday of what experts believe may have been a severe infection.

“Kahulu,” as he was known to his local admirers, was one of four monk seals born in 2017. He was found floating listlessly in an undisclosed location on Christmas Day and was brought to the National Oceanic and Atmospheric Administration Inouye Regional Center’s monk seal treatment facility on Dec. 28.

X-ray and ultrasound tests found no sign of trauma or evidence that the seal had ingested a fish hook or other foreign body. A blood test did indicate an infection of unknown origin.

A NOAA report said the seal received intensive medical care, including nutrition, fluids, vitamins and a broad range of medications several times a day.

“Though the expert NOAA tea did everything they could, they were unable to save this very ill seal,” the NOAA stated in a Friday update.

The cause of death remains undetermined pending the results of further diagnostic tests.