Southern Resident killer whales are endangered due to overfishing, habitat loss, and contaminants such as PCBs. A recent study analyzed the levels of toxic metals in sediment in the Salish Sea to assess their potential to impede the recovery of these endangered killer whales as they eat contaminated prey.
What was the study?
Scientists analyzed sediment collected from 98 sites along the British Columbia coast between 2018 and 2020 to “assess the habitat quality of Chinook salmon salmon and resident killer whales.”
From 36 chemical elements, they focused on six metals—mercury, cadmium, arsenic, nickel, copper, and lead—that settle in marine sediment and are inadvertently eaten by foraging animals. As predators catch contaminated prey, toxic levels build up, or ‘bioaccumulate,’ moving up the food chain to top predators.
Mercury, cadmium, copper, and lead are of “particular concern due to their toxicity even at low concentrations.” Several studies have previously found evidence of their bioaccumulation in Chinook salmon and killer whales.
A group Chinook salmon smolts.
What did they find?
In most regions, concentrations of these six toxic metals were above the current “sediment quality guidelines” set by the Canadian Government. Hotspot maps revealed areas of high contamination in Chinook salmon salmon salmon-rearing areas. In fact, Chinook salmon salmon chronically exposed to mercury, cadmium, copper, and lead have “increased mortality and reduced reproduction and growth.”
Of concern is that all six toxic metals were prevalent within the foraging areas of the Southern Resident killer whales in the Salish Sea, including harbors off the Strait of Juan de Fuca and in the Georgia Strait, home to the Port of Vancouver.
The scientists concluded that “current levels of sediment mercury, cadmium, arsenic, nickel, copper, and lead may pose a threat to Chinook salmon salmon and resident killer whale populations both directly and indirectly.”
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While some metals occur naturally, they are more ubiquitous today due to “mines, metal smelters and refineries, landfill leachate, sewage treatment plants, and urban run-off.” The study findings highlight the urgent need for cleanup operations—and prevention—to reduce the threat to salmon and killer whales from these toxic substances. As new contaminants of concern emerge, with evidence they transfer to calves before birth, interventions simply cannot wait.
