Killer Whale

They have been located by local fishermen.

 Nauru Fisheries and Marine Resources Authorities Geographic Information System Officer Klaus Jacob said with Nauru being in the period of the La Niña season, it has resulted in having colder ocean or sea surface temperatures.

NFMRA believes these particular whales tend to adapt to such cold temperature.

Orca killer whales are friendly by nature, however, local fishermen have been reminded not to attempt to catch or threaten them.

The four-metre male orca was first spotted two weeks ago near the river's mouth, but made its way dozens of miles upstream towards the city of Rouen.

A plan to guide it back to the sea using sound stimuli failed, and experts concluded it was seriously ill.

The authorities had been preparing to euthanise the animal but activists say it died of natural causes.

Environmental campaign group Sea Shepherd tweeted that the orca's corpse was found at 11:48 local time (09:48 GMT) on Monday.