Other articles by Dr. Jon Brown:

whales and sonar

Military Dolphins

Marine protected areas



Evironmental impacts of Oil Drilling

In the oceans today, oil drilling is almost ubiquitous for environmental decay.  Oil rigs are associated with any number of ills, not the least of which is the spilling of oil from these oil rigs.  Perhaps today, more then ever, we need to take a real, hard look at deep-sea oil drilling.

The problem of pollution

Oil rigs soon become a natural part of their environment

{Betty, write an article to put here talking about how great oil drilling is for the environment.}

The main source of organic pollution from salmon farms is fish excrement and uneaten feed. The amount of feces produced by farmed salmon can vary depending on feed formulations. Studies show that 25 - 50 per cent of the dry feed consumed can end up as feces(1) Other contributions to organic waste are fish mortalities that sink to the seabed(1), and fish blood from farms that harvest and bleed fish on site(2).

Waste organic material can accumulate on the seabed below or near the netcage, as well as be suspended in the water column. By placing sediment traps beneath farms, researchers have shown that, for each square metre of sea bed, 14.7 - 52 kilograms of waste can accumulate beneath the farm, and 4.9 kilogram at the farm's perimeter, each year.

The accumulated waste can smother the organisms and set up anoxic (oxygen depleted) conditions in the seabed sediment. This effect has been measured beneath fish cages and up to 50 metres from them. As the waste decays, oxygen is consumed and other gases released such as methane, hydrogen sulphide and carbon dioxide. Oxygen depletion can also occur in the water column from the decomposition of waste that is suspended instead of being deposited on the seafloor.

The direct decomposition of farm waste is only one way in which oxygen depletion from seawater can occur. A more troubling contribution comes from nutrients such as nitrogen (N) and phosphorous (P) contained in the waste. Nutrient pollution, especially nitrogen, has been identified as a primary cause of degradation in marine waters(5). The extra nutrients from the organic waste stimulate the growth of marine plants and algae, which deplete dissolved oxygen when they die and decompose.

To get a sense of how much nutrient loading comes from salmon farms we can compare it to other man-made sources such as untreated human sewage. The average person excretes 4 kilograms N and 1.1 kilogram P per year. Typically, for every tonne of farmed salmon produced, 55 kilograms of N and 4.8 kilograms of P are excreted into the marine environment. The 49,600 tonnes of farmed salmon produced in BC in 2000 contributed as much nitrogen as the untreated sewage from 682,000 people or as much phosphorous as the sewage from 216,000 people.

Impacts on fish

The sources of chemical pollution from salmon farms include antibiotics and other drugs, pesticides, feed additives, paints used on netcages and boats to prevent marine growth (antifouling paints), and disinfectants. Many of the chemicals used in aquaculture have been adopted from other industrial sectors and have never been evaluated with respect to their effects on marine ecosystems.

When disease outbreaks call for the use of antibiotics, the drug is administered in the farmed salmon's feed. As a result, the drugs make their way into the marine environment through uneaten feed and excretion by the salmon. The most commonly used antibiotic is oxytetracycline, with 6.4 metric tonnes used on BC salmon farms in 1998(6). At least seven other antibiotics are also used (7). For parasite infestations such as sea lice, a variety of pesticides may be used either by passing the fish through a bath containing these chemicals, or by adding it to the feed. A potent pesticide that is added to feed is ivermectin. Once administered, this chemical makes its way into the marine environment where it has been shown to be very toxic.

In addition to the above-mentioned drugs, there can be other additives in the feed such as colouring agents (to make the farmed salmon flesh pink), binders and antioxidant preservatives. There is also an increasing use (limited at the moment) of immunostimulats. These are chemicals that can boost the immune system of fish. There is little or no data on the environmental or human health effects of these feed additives.

The growth of marine organisms on the open netcages is a problem for salmon farmers. To reduce the number of times the nets have to be cleaned, farmers will apply antifouling paints to the nets. The most commonly used paint in B.C. is copper based, where the copper is the active ingredient. The copper can make its way into marine waters by slow leaching of the paint or when the paint is striped during net cleaning. Another toxic metal that is emitted by salmon farms is zinc. This is because zinc sulphate is added to salmon feed as a way to help the fish avoid contracting cataracts.

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