Human activities are threatening the world's oceans. According to author Peter Weber*, land-based human activities account for more than three-quarters of these threats. Many wastes originate in our own backyards, even thousands of kilometres from the coast. They travel to the oceans through sewer pipes and surface waterways, and on atmospheric currents. Whether we live in Vancouver or Saskatoon, Timmins or Truro, our actions can hurt—or help—our threatened oceans.
Here is a brief summary of threats to ocean health.
Three-quarters of the threats to marine wildlife and habitats are caused by human activities far from the coast. For example:
- Canadian cities flush hundreds of billions of litres of untreated sewage into rivers, lakes, and oceans each year.
- Plastic trash is as harmful to marine organisms as oil spills, toxic waste, and heavy metals.
- Ocean waters contain thousands of different toxic chemicals from industries, farms, and households across the country.
- Urban communities flush up to 30 million litres of oil into aquatic ecosystems each year, as ordinary people carelessly pour waste oil down the drain.
Sewage from domestic wastewater is often discharged into waterways, totally or partially untreated. This can lead to bacterial and viral contamination of shellfish, turning them into a lethal last meal for a diner. The resulting closure of a clam or oyster fishery can economically devastate a coastal community.
Persistent Organic Pollutants (POPs) represent a class of chemicals (including DDT, PCBs, dioxin) that poison the water and accumulate in food chains to cause tumours, deformities, loss of reproductive capability, and even death in plants and animals, including humans. The pesticides we put on our lawns and crops contribute POPs to the environment, as do industrial chemicals from landfill sites. Transported by waterways, the atmosphere and ocean currents, POPs affect ocean wildlife like beluga whales, fish, and polar bears thousands of kilometres away.
Heavy metals like mercury and cadmium cause problems similar to POPs. They enter the environment mainly through mining and smelting operations, coal burning electricity generators, and pulp and paper manufacturing.
Oil can kill aquatic life if ingested or absorbed through the skin. It also damages fur and feathers and smothers aquatic habitats and beaches. Ships and oceanic oil rigs, as well as land-based sources like domestic storm sewers, dump oil into the ocean.
Ocean litter; particularly plastic, chokes and entangles wildlife such as sea turtles, whales, dolphins, and seals who often mistake it for food. Litter may be dumped directly by ships or cities, or washed into waterways from poorly managed waste-disposal sites.
Coastal habitat destruction is a growing concern. As human coastal communities grow, homes, harbours, resorts, and recreational facilities encroach on critical coastal habitats like salt marshes, beaches, and estuaries. Even small developments add up to chip away at our most productive and important marine habitats—the edges where shore and ocean meet.
Inland habitat loss is also a major issue. It occurs as we drain marshes for agriculture, build condos and marinas along shorelines, dam rivers, and misplace landfill sites. Many endangered marine animals use inland habitats as migratory stop-overs or for breeding purposes, such as harlequin ducks (fast-flowing water) and whooping cranes (wetlands deep within the continent). Salmon on all coasts spawn in coastal rivers. These habitats are critical, even when the animals may not stay long.
Overfishing is pushing many of the world's commercially important fish stocks into decline. Large, highly mechanized commercial fishers are simply taking too many fish. As global ship traffic increases, more and more ocean creatures (whales, dolphins, manatees, sea turtles) fall victim to accidental collisions with boats or propellers.
Global climate change is a threat to all ecosystems, marine and terrestrial. The evidence is overwhelming that we contribute hugely to this process by burning fossil fuels and using chemicals in manufacturing.
The accidental international transport of alien organisms, such as plankton, crustaceans, pathogens, and parasites in the bilge water of large freighters is causing huge biological alterations, both in coastal waters and throughout inland watersheds. Some well-known examples are the sea lamprey and zebra mussels, both of which have had considerable impact on the Great Lakes ecosystem.
*Weber, Peter. Abandoned Seas: Reversing the Decline of Oceans. WorldWatch Institute.
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