An orca in St Heliers Bay, Auckland. New Zealand orcas are the only known group that regularly eat stingrays. (Credit: Getty)

The silent killer stalking orcas

  • BY Natalie Muller |
  • December 15, 2011

Killer whales may be top predators, but a little-known threat is putting them at risk.

KILLER WHALES ARE the most widely distributed marine mammals on earth. These skilled hunters sit right at the top of the aquatic food chain, and roam every ocean and just about every sea between the North and South poles. But while the distinctive cetaceans have little to fear in the way of predators, a silent threat has been seeping into their ecosystems for decades.

Persistent organic pollutants (POPs) such as the insecticide DDT, and polychlorinated biphenyls (PCBs) - which were found in coolant fluids for electrical equipment, paints, flame retardants and adhesives - were banned in many nations in the 1970s, but they're still tainting marine food webs.

This is bad news for killer whales, also known as orcas. As they sit at the top of the food chain, they're at high risk of accumulating high levels of contaminants in their blubber from the prey they eat. These chemicals bind to their fat and are virtually impossible to get rid of, interfering with hormones and weakening their immune and reproductive systems.

Orcas are 'toxic waste'

Studies have shown that orcas off the coast of British Columbia in Canada are among the most contaminated creatures on the planet, with up to 250 times the safe levels of POPs in their systems as humans do.

The concentration of pollutants in their blubber is so high their bodies can be considered as toxic waste when they die. In both Canada and Australia materials contaminated with more than 50 parts per million (ppm) of PCBs have to be treated and stored under special conditions, but the bodies of some killer whales have been found with 250ppm of PCBs in their blubber.

But scientists say there is a gap in the research about how southern hemisphere orcas, particularly off the coasts of Australia and New Zealand, are affected by these toxins. Despite the fact that these whales are found around our waters, "in Australia there has not been a single dedicated research study on killer whales," says Margie Morrice, a whale ecologist at Deakin University in Victoria. "We've certainly been trying to get funds over the past 15 years or so, but none have become available."

Killer whales in the eastern Aleutian Islands, Alaska. Orcas off the western coast of North America have staggering amounts of pollution in their blubber. (Credit: Robert Pittman/NOAA)

A widespread threat to orcas

Little is known about the size of Australia's orca populations, their movements or what they eat - let alone whether they have pollutants in their blubber. "We can only have some concept of what [the contaminant levels] might be from the examples of the northern hemisphere, but then we know that our population is quite different," says Margie, who also collects data for the Australian Orca Database.

Unlike the ecotypes in Canada, New Zealand's orcas tend to hunt sharks and rays, while in Australia they've been seen attacking anything from dolphins and humpback whales, to penguins and dugong.

"I suspect it doesn't matter how remote you go," says Dr Peter Ross, a research scientist at the Institute of Ocean Sciences in the Canadian city of Sidney, British Columbia. "There's little question that killer whales are vulnerable wherever they are, and that's just because of their long lifespans [they can live up to 100 years], the fact that they have trouble getting rid of these chemicals, and the fact that they're very high in the food chain."

Levels of toxins in orca blubber "alarming"

Dr Ingrid Visser, a whale biologist based on the Tutukaka Coast in New Zealand's Northland Region, has been collecting blubber samples for the first NZ study of pollutants in orcas. She is in the process of publishing the research, and says the levels of toxins are worrying.

"They are alarmingly high. They're not up there at the level of the British Columbia orcas, which are literally off the scale. But you can safely say that they have more pollutants than any other animal that's been examined in the Southern Hemisphere," she says.

Peter is spearheading the analysis of the NZ samples. He says more than 200 different chemicals were found in the blubber. One of the difficulties, however, is working out what impact the toxins are having on the NZ population, made up of fewer than 200 animals. Carrying out studies is tricky, because the animals rarely strand and because blubber tests are very expensive.

Peter says his captive-feeding studies of the more accessible harbour seals in British Columbia - which have a similar immune system to orcas - give a good indication of the impacts. "PCBs at moderate levels reduce reproduction, affects their immune system, it makes them more vulnerable to diseases and affects various hormone levels," he says.

This is a scary prospect for killer whale population numbers. Females only produce one calf every 4-5 years between the ages of 14 and 40. They also transfer a huge portion of the chemicals they accumulate to their offspring via the placenta and their milk. If females can't reproduce, they lose this chance to offload toxins.

Cleaning up the whale food chain

Banning DDTs and PCBs almost 40 years ago has gradually improved the health of the environment, Peter says. "We've estimated, on the basis of a life history-based model, that PCBs have declined in British Columbia killer whales by between 2.5 and 4 times since the early 1970s."

But Ingrid says the emergence of polybrominated diphenyl ethers (PBDEs) - a flame retardant currently being regulated against or phased-out worldwide  - is still a major concern. "From the chair that you're sitting on, to the car you drive, the TV you watch, [PBDEs] are in a lot of clothes...these flame retardants mimic the same issues as PCBs and DDTs," she says.

Ultimately, says Peter, it may take many years before the marine food web is free of these highly persistent chemicals. Tighter regulation, and more money for research into vulnerable species such as killer whales, is a good place to start.

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