Killer whales’ dietary preferences expose them to pollutants

Killer whales, known for their majestic beauty and power, are apex predators of the oceans. However, even these formidable creatures are not immune to environmental pollutants. 

A comprehensive study (the most extensive of its kind) on North Atlantic killer whales was recently published in ACS’ Environmental Technology journal, examining the levels of both old and newly emerging pollutants in the blubber of 162 individual whales. 

Persistent organic pollutants

Interestingly, the contaminant levels and associated health risks were more influenced by the whales’ diet than their geographical location – a discovery that can prove pivotal for conservation strategies.

Killer whales, or orcas, belong to the dolphin family and are found all over the globe. While they face disruptions in their hunting and communication due to marine vessel traffic, another significant threat looms: the persistent organic pollutants (POPs) in their surroundings. 

Such pollutants include chlorinated hydrocarbons and flame retardants, which, due to a phenomenon termed biomagnification, tend to accumulate in the fatty tissues of animals higher up in the food chain.

Orca populations 

Earlier investigations revealed that orca populations in the Pacific can have alarming levels of POPs in their blubber, leading to potential health concerns such as diminished immunity, hormonal disruptions, and reproductive complications. 

However, a knowledge gap persisted regarding North Atlantic orcas. To address this, a team of scientists led by McGill University in Canada set out to determine the contaminants in killer whales ranging from Eastern Canada to Norway.

How the research was conducted

The team harvested skin and blubber biopsies from over 100 free-roaming killer whales spanning the vast expanse of the North Atlantic Ocean, covering regions from Canada and Greenland to Iceland and Norway. 

They dissected half of each biopsy to probe for five categories of POPs, including polychlorinated biphenyls (PCBs). The remaining sample was employed to discern the animals’ dietary patterns. Their data yielded some striking insights.

What the researchers learned 

Orcas from the western North Atlantic demonstrated markedly elevated contaminant concentrations compared to their eastern counterparts. This trend defies previously noted POP patterns in other Arctic marine species.

Interestingly, dietary habits rather than geographic positioning accounted for this distribution. Orcas that fed primarily on fish registered the lowest POP concentrations. In contrast, those preying on marine mammals, such as seals or other whales, bore the highest levels.

Particularly alarming was that killer whales with a marine mammal-based diet exhibited PCB levels surpassing the critical threshold, indicating a pronounced risk of reproductive failure in females.

The readings for one particular POP, known as α-HBCDD, surpassed any prior records for marine mammals, notwithstanding its ban a decade prior.

Study implications 

The findings highlight the urgency of implementing stringent waste management practices to hinder contaminants from seeping into marine food webs, thereby impacting apex predators. 

The outcomes of this study stress the need of a call to action for safeguarding North Atlantic killer whales and their habitats.

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