Scientists studying endangered southern resident killer whales have observed a worrying increase in the prevalence of skin disease in this population.
In a new study, they document a steady increase in the occurrence of gray patches and gray targets on the whales' skin from 2004 to 2016.
The cause and significance of these lesions are unknown, but they may reflect a decrease in the whales' ability to fight disease.
What are the skin lesions and how are they detected?
OLIVIER MORIN/AFP via Getty Images
The study, published in the journal PLOS ONE, focused on the skin lesions of southern resident killer whales, a small and endangered population of fish-eating orcas that live in the coastal and inland waters of the Pacific Northwest, as per Phys.org.
These whales are socially structured into three pods: J, K, and L. The population is endangered, with fewer than 75 individuals remaining
The researchers analyzed a large collection of digital photographs spanning over a decade.
Photographs were obtained by the Center for Whale Research for identification purposes and included nearly 20,000 individual whale sightings in the Salish Sea.
The researchers used these photographs to remotely assess the health of these whales.
They found six different skin disease syndromes in the whales. The most common ones were gray patches and gray targets.
Gray patches are irregularly shaped areas of lighter pigmentation on the dorsal surface of the whale's body, while gray targets are circular areas of lighter pigmentation surrounded by darker pigmentation on the dorsal surface of the whale's body.
The researchers found that both gray patches and gray targets increased significantly over time, from less than 5% prevalence in 2004 to more than 20% prevalence in 2016.
They also found that these lesions were highly correlated, meaning that whales with one type of lesion were more likely to have the other type as well.
What are the possible causes and consequences of the skin lesions?
The researchers do not know what causes these skin lesions or what they mean for the whales' health and survival, as per Eurekalert.
They ruled out some potential environmental factors, such as changes in water temperature or salinity, as they did not find any correlation between these factors and the occurrence of lesions.
The hypothesis is that it is an infectious agent, such as a virus, bacteria, or fungus, that affects the skin of the whales.
They suggested that the increased occurrence of lesions may reflect a decrease in the ability of the whales' immune systems to combat disease. This could pose yet another significant threat to this already vulnerable population.
The researchers also speculated that these lesions may have social and behavioral implications for the whales.
They noted that some whales with lesions appeared to have reduced social interactions with other whales or avoided being photographed by researchers.
These experts wondered if these lesions may affect the whales' communication, recognition, or mating success, but they emphasized that more research is needed to understand the cause and significance of these skin lesions.
Collecting skin samples from live or dead whales with lesions for laboratory analysis, as well as monitoring the long-term health and survival of affected whales, is highly recommended by the experts for further analysis.
Moreover, they stressed the importance of protecting this population from other threats, such as noise pollution, vessel disturbance, prey depletion, contaminants, and climate change.
