Killer Whales Serve as Sentinels for Ocean Pollution
Black and white killer whales frolicking on Canada's Pacific coast have become symbols of nature's wild beauty. But orcas have also become sentinels for humankind's contamination of the planet.
Despite international efforts to control them, polychlorinated biphenyls (PCBs) and many other contaminants persist in the environment. And Dr. Peter S. Ross of the Institute of Ocean Sciences (IOS) at Sidney, British Columbia (B.C.), has found that “killer whales rank among the world's most contaminated marine mammals.”
British Columbia's killer whale populations face severe pressures. COSEWIC, the authoritative Committee on the Status of Endangered Wildlife in Canada, classes the 80-odd “southern residents” in B.C. waters as endangered. The agency lists the 200 or so northern residents and another 200 “transient” killer whales as threatened.
Factors in the decline include low genetic diversity, and loss of food as salmon stocks shrank in the 1990's. As well, the very people who admire killer whales and want to see them up close can disrupt their lives and reproduction by boat traffic and noise.
Below these problems lies another, insidious threat: high levels of endocrine-disrupting chemicals found in their bodies are weakening the whales' ability to reproduce and stay healthy. Dr. Ross is investigating key questions for killer whales. Where do the contaminants come from? How do they affect marine mammals? How well or poorly are regulatory efforts or source controls working?
Dr. Ross's work clothes sometimes include hiking boots, kneepads, and a hockey helmet. That's when he's jumping from a boat's bow onto barnacle and kelp-covered rocks, capturing young harbour seals. He and colleagues grab the seal by the hind flippers, weigh it and determine the sex, take a blood sample and a small (6 millimetre) plug of flesh, sterilize the cut, tag the seal, and let it go.
The samples go first to a portable field lab, then back to IOS. There, researchers analyze flesh and blood every which way, looking for contaminants new and old.
Why sample harbour seals if the most pressing conservation concern is killer whales? The harbour seal has a similar physiology and immune system. Sampling them is less disruptive than taking more dart biopsies from killer whales. The abundance of harbour seals, with 130,000 of them in B.C., lets the researchers pick out animals of a consistent age, 4-5 weeks, which gives more reliable data.
Finally, harbour seals face their own threats from contaminants. Peter Ross notes that “authorities in northern Europe in the late 1980's thought that because population numbers had risen, harbour seal stocks had recovered. Then a virus wiped out 60 per cent of them. Contaminants had weakened their immune system.”
Although generally less contaminated than their European counterparts, harbour seals on the west coast also suffer from persistent organic pollutants (POPs) such as DDT, PCBs, dioxins, and furans. These dissolve in the animal's fats, circulate through its body, and can damage the endocrine (hormone-producing) system and other functions.
Industrialized countries have long banned DDT, PCBs and other persistent toxics. Canada helped lead the way to the international Stockholm Convention of 2001, controlling a dozen major POPs. And Canada and other countries offer financial aid for developing nations phasing out POPs. (Meanwhile, compounds known as PBDEs, used as fire retardants in many products, have become a cause of concern.)
So how are the contaminants still getting into the marine food chain? Some developing countries still use POPs, which can enter the sea directly or from the atmosphere. And POPs produced decades ago in developed countries continue to circulate in the sea. Still others are newly entering the marine food chain as they leach out from old industrial sites and dumps.
“Often the contaminant path is hard to pin down,” Dr. Ross says. “POPs can travel long distances in the atmosphere, and then enter lower levels in the food web – bacteria, algae, zooplankton, fish – before whales or seals ingest them. But in some cases we can track down the source.”
The interconnected waters of southern British Columbia and northern Washington state provide a key example. Checking harbour seals throughout the area, Dr. Ross found that PCB levels in their flesh decreased as he went from south to north. The findings point to Puget Sound, a large arm of the sea within Washington State, as a prime source of PCB contamination from old industrial residues.
Dr. Ross often collaborates with American scientists on transboundary mammals, and with Canadians including Dr. John Ford, also of Fisheries and Oceans Canada (DFO), and other researchers from universities and the federal Department of Environment.
Whether contaminants originate nearby or far away, B.C.'s killer whales pick them up by eating coastal prey. Salmon, a major food source, migrate inshore from distant ocean waters, bringing few toxics with them. Species such as rockfish, which spend their lives closer to the coast, carry more contaminants.
The prey's position in the food chain also makes a difference. Transient killer whales dine on seals, sea lions, porpoises, and other mammals that have already accumulated toxins from lower levels of the food chain. Thus, the transient whales are more at risk for toxic effects than their resident, fish-eating cousins.
“Contaminants don't act as a rapid poison,” Dr. Ross says, “but weaken the whales' ability to survive diseases or other stresses.
“In southern B.C. and northern Washington state, we've got about seven million people, as against 80-some killer whales in the local southern resident population. In sharing killer whale habitat, citizens of this region can act as partners with government and industry when they consider their responsibilities in light of household cleaners, pesticides, vehicle use and other lifestyle choices. By protecting streams, rivers and our coastal waters, we can help ensure the survival of salmon and killer whales into the future.”