Mysterious skin disease threatens endangered killer whales

In a groundbreaking study, researchers have identified an alarming increase in the prevalence of skin disease among endangered southern resident killer whales. This discovery, which has scientists deeply concerned, highlights the urgency to take measures to protect and conserve these majestic animals.

Published in the journal PLOS ONE, the study was focused on the analysis of over 20,000 digital photographs of killer whales captured in the Salish Sea from 2004 to 2016. The images provided an unexpected finding – the presence of gray patches and gray targets on the skin of these whales. 

Unidentified causes

Despite extensive research, the cause of the skin lesions remains unidentified. However, the ramifications of this observation could be far-reaching.

The study was led by Joseph K. Gaydos, a wildlife veterinarian and the science director for the SeaDoc Society, which is a program in the UC Davis School of Veterinary Medicine. 

“Before we looked at the data, we had no idea that the prevalence of these skin lesions was increasing so dramatically. It’s worrisome. Now we need to try and isolate the potential infectious agent,” said Gaydos.

The researchers were able to rule out environmental factors such as water temperature and salinity fluctuations that could have accounted for the increase in skin disease. The experts then theorized that an infectious agent might be the culprit, and the lesions could be indicative of the whales’ dwindling capacity to stave off diseases due to weakened immune systems.

Endangered population 

The revelation is alarming, as the fragile southern resident killer whale population is already grappling with numerous challenges to its survival. This population, which comprises fewer than 75 individuals, is unique. 

These fish-eating mammals, known for primarily consuming salmon, wander the coastal and inland waters stretching from southeastern Alaska to California. Their society is divided into three pods, named J, K, and L. However, what sets them apart is not just their dietary preferences but also their endangered status.

The Center for Whale Research has been carrying out photographic identification surveys of these whales since 1976. They amass clear images of each individual which serve as invaluable tools for remote health assessments. 

Skin changes studied for the first time

Interestingly, though the skin anomalies were sometimes observed in earlier pictures, they hadn’t been systematically analyzed or tracked for changes over time. The study discovered six different skin disease syndromes, and though none were directly associated with mortality, the consistent increase in two of the most common lesions was unforeseen.

Understanding these skin changes is paramount to evaluating the overall health of the southern resident killer whales and gauging their potential impact on population recovery. Given that the population numbers are critically low, every aspect of their health is a vital piece of the puzzle.

Though the photographic approach employed in the study offers a non-invasive method for studying skin disorders and their epidemiology, it falls short in identifying specific causes for these disorders. Nonetheless, it is an indispensable resource in understanding the broader health perspectives of these creatures, especially since capture-release health assessments are often impractical.

The research highlights the importance of continuous monitoring to clarify the causes and implications of these skin changes. For the southern resident killer whales, it is a race against time. 

This study is a collaborative effort involving 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, and Wild Orca.

Why are killer whales endangered?

Killer whales, specifically southern resident killer whales, face endangerment due to a variety of factors:

Food shortage

The southern resident killer whales primarily feed on Chinook salmon, but overfishing and habitat destruction have led to a decline in the Chinook population. This has caused a significant food shortage for the whales, impacting their nutrition, reproductive capacity, and overall health.

Pollution

The waters these whales inhabit are often polluted with toxins and contaminants such as PCBs (polychlorinated biphenyls), DDT (dichlorodiphenyltrichloroethane), and heavy metals. These pollutants accumulate in the whales’ bodies, leading to various health problems, including reproductive issues and weakened immune systems. This makes them more susceptible to diseases.

Noise and disturbance

Increased human activities such as shipping, boating, and naval exercises contribute to ocean noise pollution. These disturbances can interfere with the whales’ communication, hunting, and navigation by using echolocation. Chronic exposure to noise can lead to stress, which can further impact their health and reproductive success.

Climate change

Rising ocean temperatures and changes in ocean chemistry due to climate change can impact the entire marine food chain. It can cause shifts in the distribution and availability of prey, altering the killer whales’ feeding habits and potentially leading to malnutrition or starvation.

Incidental catch

Although not a primary threat, there’s also a risk of killer whales getting caught in fishing gear, leading to injury or death.

The combination of these factors poses a significant challenge to the survival and recovery of killer whale populations, necessitating ongoing conservation efforts.

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