Newswise — In a recently published study on June 29 in PLOS ONE, scientists investigating the endangered southern resident killer whales have made a noteworthy observation: the prevalence of skin disease within this population has shown a significant increase. The researchers carefully documented a consistent rise in the presence of interconnected gray patches and gray targets on the whales' skin over the period from 2004 to 2016. Despite lacking a definitive understanding of the underlying cause, the authors of the study express concern about this trend.
Having eliminated potential environmental factors such as fluctuations in water temperature or salinity as contributing factors, the researchers propose a compelling hypothesis. They suggest that the most plausible explanation for this phenomenon is the presence of an infectious agent, with the rising occurrence of skin lesions potentially indicating a compromised immune system in the whales.
This worrisome development adds yet another substantial threat to the well-being of the southern resident killer whale population, which already grapples with a multitude of challenges.
Thousands of photos, invaluable data
Leading the research is Joseph K. Gaydos, a wildlife veterinarian and the science director for the SeaDoc Society, which operates under the School of Veterinary Medicine at the University of California, Davis. Gaydos, along with a team of collaborators, conducted an analysis using an extensive collection of digital photographs spanning more than a decade. These photographs, obtained by the Center for Whale Research for identification purposes, encompassed nearly 20,000 individual whale sightings in the Salish Sea, providing invaluable data for remotely assessing the health of these endangered creatures.
Since 1976, the Center for Whale Research has been conducting photographic identification surveys of the southern resident killer whales in the Salish Sea, capturing clear images of each individual. During the evaluation of these images, biologists noticed occasional and transient abnormal skin changes in the whales. However, these skin changes had not been systematically characterized or monitored over time for research purposes.
The examination of these photographs unveiled six distinct skin disease syndromes, with none of them being linked to mortality. Nevertheless, the unexpected steady increase in the occurrence of the two most common lesions raised concerns. Understanding the presence and significance of these skin changes in the southern resident killer whales is vital for assessing their overall health and determining their potential impact on population recovery.
This small and endangered population, specializing in fish-eating salmon, traverses coastal and inland waters from southeastern Alaska to California. They are socially organized into three pods: J, K, and L. With fewer than 75 individuals remaining, the population faces a critical threat. Previous studies have primarily focused on identifying causes of mortality and scoring body conditions, leaving a significant knowledge gap regarding the role of health in impeding population recovery.
Gaydos expressed surprise at the dramatic increase in the prevalence of these skin lesions, stating, "Before we looked at the data, we had no idea that the prevalence of these skin lesions were increasing so dramatically. It's worrisome. Now we need to try and isolate the potential infectious agent."
Insight for an endangered species
Photographic identification serves as a noninvasive method for studying skin disorders and their patterns within a population, but it does not provide direct identification of specific causes. Nevertheless, it remains a valuable tool for assessing the general health of animals, especially when capture-release health assessments are not feasible.
The research conducted represents a notable advancement in comprehending the epidemiology of skin changes in the southern resident killer whales. The findings underscore the importance of ongoing monitoring and research efforts aimed at unraveling the underlying causes and understanding the health implications of these skin changes. Ultimately, these endeavors aim to contribute to the conservation and recovery of this endangered population, highlighting the significance of continued investigation in this field.
In addition to the SeaDoc Society, the collaborative effort involved researchers from numerous institutions, including the Center for Whale Research, British Columbia’s Animal Health Center, NOAA’s Northwest Fisheries Science Center, San Diego Zoo Wildlife Alliance, SeaWorld Parks and Entertainment, the Vancouver Aquarium, Wild Orca, and others.
For more information, read the study, “Epidemiology of skin changes in endangered Southern Resident killer whales (Orcinus orca)” in PLOS ONE.
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