Orcas are one of the most intelligent and misunderstood predators in the world. Displaying that impressive dolphin intelligence, they were staples in ocean shows across the world where they performed stunts for large crowds. This increased captive populations and led to more orca human interactions. This unfavorable scenario earned them a reputation of being bloodthirsty and a ruthless killer 9due to a few unfortunate trainer-orca incidents). But, they are complex beings with high intelligence and emotional thresholds and they are imperative to a strong and sustainable marine ecosystem. 

Orcas are crucial to the marine food chain and healthy orca populations can be used to gauge ecosystem health. A new study from McGill University suggests that some Icelandic killer whales have very high concentrations of PCBs (polychlorinated biphenyls) in their blubber. This industrial chemical was found in a few samples but was completely absent in samples collected from orcas that belong to the same pod as the affected orca. 

PCBs are industrial chemicals that are banned from usage across several countries. They were found to have harmful effects when ingested several decades ago. Prolonged ingestion of PCB’s can affect the health of both humans and animals. They also degrade at an extremely slow pace. This allows them to remain in water bodies for years, much like other major pollutants like plastic. 

Methods of Study: 

The team collected blubber samples from orca pods they were following using gps tags. Orcas are abundant along the Icelandic coast and the 50 samples collected in the region showed incredible variations in the PCB levels, prompting further investigation. Orcas that are more dominant and part of larger and more successful hunting groups have a diverse range of prey to choose from including mammals such as seals, sea lions, small whales and smaller dolphin and porpoise species.  Smaller pods are restricted to a diet of fish like herring which are abundant in the region. 

The team found that samples collected from orcas that preyed on mammals showed . had concentrations of PCBs in their blubber that were up to 9 times higher on average than the killer whales that eat mainly fish. 

According to a media release by McGill University, this finding unexpectedly contradicts earlier research that had found relatively low levels of PCBs in Icelandic orcas. The researchers argue that future assessments of the state of killer whale populations should take into account a factor that has previously been overlooked: the individual variations in food sources that may lead to elevated health risks from PCB exposures for some individuals within populations of the world’s ultimate marine predator.

What This Means

“Killer whales are the ultimate marine predators and because they are at the top of the food web, they are among the most contaminated animals on the planet,” explains Melissa McKinney, an Assistant Professor in McGill’s Department of Natural Resource Sciences and the Canada Research Chair in Ecological Change and Environmental Stressors. She is the senior author on the study, which was published recently in Environmental Science and Technology.

“The concentrations of PCBs that we found in the whales that ate a mixed diet exceeded all known toxicity thresholds and are likely to affect both their immune and reproductive systems, putting their health at risk.”

The next step is to assess the proportion of marine mammals in the diets of these Icelandic and other North Atlantic orcas,” adds Anaïs Remili, the first author on the study and a Ph.D. candidate in McGill’s Department of Natural Resource Sciences. We also plan to put together a large dataset of contaminants in orcas across the Atlantic Ocean to contribute to their conservation efforts by quantifying potential health risks.

Impact of Findings

The data from the study, published in ACS Publications, assessed several organic pollutants which collect in the orcas blubber. There was a 300x (300-fold) variation in Polychlorinated biphenyl (PCB) levels between the least contaminated orca and the most contaminated orca In pods that feasted on a mixture of mammal and fish prey, the PCB levels were “6-to-9-fold greater in individuals with a mixed diet including marine mammals than in fish specialist individuals, whereas males showed PCB concentrations 4-fold higher than females.” 

The negative impacts of increased PCB concentration in marine mammals is well known. They cause negative impact on growth and also affect several generations of orca when a breeding female is exposed. Given PCBs have been identified as potentially impacting killer whale population growth and levels in mixed feeders specifically exceeded known thresholds, the situation could escalate very soon. 

The killer whales that ate a mixed diet of both sea mammals (such as seals, or other marine mammals such as porpoises) and fish (mainly herring) had concentrations of PCBs in their blubber that were up tp 9 times higher on average than the killer whales that eat mainly fish. This finding unexpectedly contradicts earlier research that had found relatively low levels of PCBs in Icelandic orcas. The researchers argue that future assessments of the state of killer whale populations should take into account a factor that has previously been overlooked: the individual variations in food sources that may lead to elevated health risks from PCB exposures for some individuals within populations of the world’s ultimate marine predator.

The researchers argue that future assessments of the state of killer whale populations should take into account a factor that has previously been overlooked: the individual variations in food sources that may lead to elevated health risks from PCB exposures for some individuals within populations of the world’s ultimate marine predator.

Significance of Findings

This discovery shows that a specific diet pattern contaminates orcas and could leave a lasting impact on current and future population health and numbers. To ensure the survival of the apex predators of the ocean, it is important to monitor their activity, which includes diet. To ensure that mammal hunting orcas are  healthy, the PCB levels must be monitored and future efforts should take this finding into account to identify potential orcas susceptible to PCB poisoning.