Southern resident killer whale eating salmon.

Image Credit: Astrid Van Ginneken / Center for Whale Research

Newly identified toxic metal hot spots on the West Coast further threaten endangered killer whales and their key food source, a recent study shows.

Southern resident killer whales and the chinook salmon they depend on for survival are both already in a dangerous state of decline, said Ocean Wise research scientist Joseph Kim.

Less food and more boat traffic, noise and pollution all jeopardize the survival of the remaining 75 members that make up the unique population of killer whales. The orcas ply the coast from California to Alaska but primarily frequent waters around southern Vancouver Island, Washington state and Oregon in the U.S., and the Salish Sea on both sides of the border.

The majority of coastal chinook stocks in the whales’ core range are also struggling as a result of habitat destruction, overfishing and climate change. 

However, exposure to high levels of mercury, cadmium, lead and copper in critical habitats only compounds the concern and threats to the salmon and the orcas, Kim said.  

An extensive sediment survey from nearly 100 locations along the B.C. coast also assessed six toxic metals in areas where juvenile chinook live, feed and grow before heading out to sea, and the whales feed on the salmon.  

The source, mix and concentration of toxic elements in sediment can vary depending on a location’s conditions — like air and water currents and the types of human activities taking place, said Kim, the study’s lead author.  

Maps of concentration hot spots (top left to bottom) for mercury (Hg), cadmium (Cd), arsenic (As), nickel (Ni), copper (Cu), and lead (Pb) from recent coastal sediment research.

Image Credit: SUBMITTED

The research is part of the long-standing Ocean Wise Pollution Tracker program, the first coast-wide contaminant-monitoring program in Canada. 

The program aims to monitor the buildup of chemicals in the marine ecosystem over time to identify the source of the worst pollutants with risks to marine life and maps where they are found.

Victoria Harbour and Prince Rupert Harbour are the top toxic hot spots, with an overlap of problematic metals as well as other worrisome chemical contaminants, which are likely tied to industrial and urban activity in these highly populated areas, the tracker shows.

Lead levels in sediment were especially high in Prince Rupert and Victoria harbours compared to the rest of the coast, the recent study showed.

Victoria Harbour’s mercury levels are also high enough to likely harm small seabed creatures at the base of the food chain for salmon and, ultimately, whales. 

Victoria Harbour also has high levels of some toxic industrial chemicals used as flame retardants in things like plastic, textiles, manufactured goods and polystyrene foams in the construction industry that can get into the ocean by leaching from landfills or into wastewater systems, past research for the pollution tracker shows. 

Illustration showing how toxic pollutants can compound in the food chain of killer whales.

Image Credit: SUBMITTED

Relatively high concentrations of mercury were also measured in Burrard Inlet, Prince Rupert Harbour, and Haida Gwaii, according to Kim's latest study. 

“I can’t really say what comes from one specific source or another,” he said, adding contaminants can be a mix depending on the type of industrial and urban discharges. 

Mining, metal smelters, refineries, pulp and paper mills, sewage, stormwater, runoff from roads, ship traffic and corrosive paint on vessels can all build up contaminants.

Toxic metals also have natural sources that accumulate in coastal sediments — think forest fires, volcanoes or eroding bedrock.

Less-populated sites like Haida Gwaii, Vancouver Island's coast, Georgia Strait and B.C.’s north and central coasts are also hot spots for mercury, cadmium, arsenic, nickel, copper and lead, the study noted.

Sampling at the Bischof island chain near Haida Gwaii and Ardmillan Bay near Bella Bella had the highest concentrations of cadmium, also at levels likely to impact microscopic seabed marine life. 

It was a surprise to see such high levels in a remote area like Haida Gwaii, Kim said, adding the cadmium concentrations might be the result of a natural source for the metal. 

But cadmium is also tied to metal smelting and fuel burning and the wastewater is readily absorbed by plankton, with toxic effects throughout the food chain at high levels. 

However, many pollutants and toxic metals can often travel great distances on air and ocean currents and accumulate more in some spots than others, Kim added.

“The characteristics of the sediment and characteristics of the pollutants themselves can have a combined effect.” 

The levels of toxic metals in the study were compared against Canadian sediment quality guidelines to determine risks to salmon and whale habitat. 

The survival rate of juvenile chinook can drop due to toxic metals in the sediment where they reside and if they don’t die, these metals can accumulate in their bodies and affect the whales that eat them, Kim said. 

Toxic metals like mercury and other persistent contaminants can also build up in the endangered whales through nursing and be absorbed through the lungs or the skin. Mercury can build up in an orca’s liver and brain and cause anorexia, loss of co-ordination and death. 

Identifying where toxic metals build up, particularly from human activity, illustrates the need to curb the source of pollutants and possibly clean up operations to reduce the risks to chinook and the whales, the study concluded. 

— This story was originally published by Canada's National Observer.

News from © The Canadian Press, 2023