Documentary research of southern resident killer whales (Orcinus orca) revealed that there is a steady rise in the appearance of high correlated gray patches and gray targets on the animal's skin. The researchers ruled out potential environmental factors such as changes in temperature or salinity. They hypothesized that the most probable cause is an infectious agent and the whales' immune system is compromised by the increased occurrence of lesions.
This could pose another serious threat to the health of southern resident killer whale population which is already facing challenges.
Alarming Observation on an Endangered Animal
A team of collaborators led by wildlife veterinarian Joseph K. Gaydos from the University of California analyzed a large collection of digital photographs of killer whales from 2004 to 2016. The images, taken from the Center for Whale Research, include almost 20,000 individual whale sightings in the Salish Sea. It provides crucial information for the remote assessment of these endangered marine animal.
Since 1976, the facility has been conducting photographic identification surveys of the killer whales, gathering clear images of individual whales. While evaluating the captured images, scientists noticed the transient and persistent abnormal skin changes in these animals. However, the observed changes were never characterized systematically or tracked over time for health monitoring purposes.
The digital images revealed six various skin disease syndromes. None of the diseases is connected to mortality, but the steady increase in the two common lesions seems alarming. The photographic identification serves as a noninvasive approach in studying skin disorders, although it does not identify the specific causes.
The result of this study provides a significant insight into the epidemiology of skin changes in killer whales. The data gathered emphasize the need for consistent monitoring and investigation to reveal the causes and health impact of these skin changes, while contributing to the conservation of the endangered population.
Declining Population of Killer Whales
The southern resident killer whales, also known as 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 other ecotypes are also resident in the area.
The population of southern resident orcas showed periods of both growth and decline from 1973 to 2019. When the first population census was conducted, 66 whales were sighted in the area. It increased to 98 in 1995 and dropped to a count of 80 in 2001. At this point, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) designated the southern resident orcas as endangered. By December 2020, the animal species declined their population to only 74 individuals, the lowest count recorded in 40 years.
The recent declines in the killer whale population are attributed to the reduced availability of prey and other threats such as water pollution. The physical and acoustic disturbance from marine vehicles and other sources of noise are also seen as culprit.
Monitoring the population of southern resident killer whale is important because of their cultural, spiritual, and economical significance to the region. They are also viewed as an indicator species in the Salish Sea as the declining population of local killer whales could mean that there are stressors that might affect the whole marine ecosystem.
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