Threats: Marine pollution

Publication - April 8, 2008
For hundreds of years, oceans have been seen as vast expanses, rendering humans and their impact puny in comparison. We have plundered their depths, thinking that the fish could never run out, and allowed millions of tonnes of garbage to flow into their waters like drops in a bucket.

We were wrong. The human impact on the world’s oceans has created a crisis situation. Today oil spills, sea dumping, agricultural, urban and industrial run-off, ocean mining and marine debris are spread all over the globe and untouched ocean no longer exists. Land based sources are estimated to account for about 44 per cent of the pollutants entering the sea and atmospheric inputs account for an estimated 33 per cent. By contrast, maritime transport accounts for only about 12 per cent.

Large-scale oil spills resulting from accidents at sea are devastating for local wildlife, beaches, tourism and fisheries, but the fact is, small oil spills happen every day. From routine boat and car maintenance to offshore drilling and relatively minor ship spills, our dependence on oil is spreading into our oceans. The impact of oil spills big or small depends on the sensitivity of the location, the type of oil, and where the weather takes it. A recent accident off the northeast coast of Vancouver Island tipped a truck with 10,000 litres of diesel oil into the Robson Bight Ecological Reserve, a killer whale sanctuary. The truck is intact 350 metres below sea level, a ticking time bomb in a sensitive habitat set aside to protect against exactly this sort of problem.

But it is not just oil that is spoiling our oceans. Domestic sewage, industrial discharge, urban runoff, accidents, explosions, sea dumping, agricultural fertilizers and pesticides, mining and radioactive discharges flow into our oceans, tainting every level of the food chain. The beluga whale population in the St. Lawrence estuary is infamous for the level of toxins found in their bodies. The St. Lawrence estuary drains some of the most industrialized regions of the world, the Great Lakes. The St. Lawrence valley is also home to extensive agriculture. St. Lawrence belugas have the highest rates of cancer of any cetaceans, making up half of all known cases in the world. Dead belugas are routinely found to have a high number of tumours and lesions and are so contaminated with mercury, lead, PCBs, DDT and other toxins that their bodies are treated as toxic waste.

The impacts of pollution vary. Nutrients from fertilizers and pesticides used in industrial agriculture are often washed into waterways and out into the ocean. Excess nutrients stimulate plankton blooms, which are also caused by natural upwellings of nutrient-rich cold water. While these blooms are sometimes harmless, toxic red or brown blooms can be harmful to molluscs and fish, and cause outbreaks of paralytic shellfish poisoning in humans. But even non-toxic green blooms can be harmful. As large blooms die and decay, they use up oxygen in the water, creating ‘creeping dead zones’ (CDZ) where there is not enough oxygen dissolved in the water to sustain marine life. PEI has been struggling with alarmingly regular fish kills (large-scale deaths) in their rivers. Since 1994, no less than 27 fish kills have been linked to agricultural runoff, including large numbers of juvenile salmon and trout, which are vital to PEI’s lucrative sports fishery.

Trashing our oceans