Killer whales are truly unmistakable with their striking black-and-white coloration. However, when viewed more closely, the Southern Resident killer whales’ skin is not uniformly colored, with scratches and scars from social encounters. However, concern is growing about other wounds that result in temporary and more permanent skin coloration changes. Could these be signs of skin disease?
A team of four veterinarians (two pathologists specializing in marine mammals and two with expertise in cetacean clinical medicine) examined historic photographs to look for changes in skin condition over time and assess whether there is evidence of a link between skin disease and poor health in this endangered population.
What was the study?
These specialists analyzed 18,697 high-resolution dorsal fin identification photographs taken between 2004 and 2016 by the Center for Whale Research to look for wounds (lesions). They categorized them into six distinct disease types.
They reported, “One or more of the three most prevalent skin lesions were noted in 99% of the whales alive at some point during the study period.”
What were these three most commonly seen skin lesions?
Gray patches, found on otherwise black skin, were the most commonly noted lesion in 27% of all photos and were present in all age groups, from calves to postmenopausal females.
Gray patches could be small or large and appear on any body parts visible in these images. By comparing individual whales over time, the team could see that “the lesions were dynamic and expanded and contracted in size over time.”
The team suggested that these patches could be due to edema—swelling caused by too much fluid trapped in the body’s tissues. Alternatively, it could reflect an increase in skin cells, indicating an inflammatory response or disease.
In 24% of the photos, gray targets were the second most common lesion. These circular lesions are lighter in the center than at their edges. Like grey patches, targets appeared on various body parts of whales of all ages, including newborns.
By looking at subsequent photos of individuals with grey targets, some evidence suggests that they may develop into grey patches. However, it is unclear if these are two distinct diseases or the development of a single disease over time.
The team described the third most common lesion (11.4% of images) as ‘pinpoint black discoloration.’ These were often associated with rake (teeth) marks.
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What are the possible causes of these skin diseases?
These most widely seen lesions could be due to poxvirus, a virus in the same family as smallpox. Their susceptibility to this disease-causing virus could reflect the depressed status of their immune system.
These skin diseases could also be another symptom of poor body condition, usually associated with insufficient Chinook salmon.
What do these findings show?
The study’s authors noted, “Most strikingly, there was a strong increase in lesion prevalence from 2004 through 2016 in all three pods.”
However, without knowing the cause of disease or how it develops, together with its relationship to factors such as the decline of Chinook salmon, and the increase of environmental contaminants, the authors believe it’s vital to learn more to understand the impact of these skin diseases on this fragile population’s health.
They concluded, “These skin lesions are considered an expression or manifestation of disease process and seem to be increasing in all three pods, and the possible relationship between these lesions and decreasing immune-competence is concerning.”
As Wild Orca collects research photographs of individuals present when collecting samples as part of our Health Monitoring Program, we will continue to work with our colleagues and co-authors of this paper to provide evidence of new skin diseases or changes to skin conditions.
Our work to understand the health of individuals, and this entire population, to inform policy change is vital if we are to prevent their extinction.
