Scientists studying endangered southern resident orcas have noticed a steady increase of mysterious gray patches and gray targets (circular lesions which may appear on concentric rings – ed.) on the whales’ skin from 2004 to 2016. 

To date, researchers managed to identify six distinct types of lesions, with the two most common types being gray patches or targets. Some resemble tattooed skin.

They do not know the cause of the lesions and are worried that they could be due to underlying health problems in the struggling population.

After ruling out potential environmental factors, such as changes in water temperature or salinity, the authors hypothesize that the culprit could be an infectious agent. In addition, they suspect that the increased occurrence of these lesions may indicate a decrease in the whales’ immunity. 

The southern resident orcas are the smallest of the four communities of the exclusively fish-eating orca in the northeastern region of the North Pacific Ocean. Their ecotype received the name "resident," although there are other ecotypes also resident in the area. Only 75 southern resident orcas remain.