Salmon farms provide much of the salmon in the market today. This is generally the Atlantic Salmon which is a completely different fish from the Pacific salmon in the last post. The farm raised salmon market is dominated by 4 large companies with a combined market share of about 75%. Farms grow salmon in submerged cages about the size of a small house which will contain thousands of fish. Some of them so crowded the fish can barely swim.
There are a number of issues created by salmon farming – many of which adversely affect the wild population. Because of the salmon needing both freshwater and saltwater, many of these farms are at the estuaries and mouths of large rivers.
Pollution is one of the key issues with salmon farming. The first type is organic pollution. A large farm of 200,000 fish releases waste products that are equal to the untreated sewage of a town of more than 50,000 people. This decomposition of waste products depletes oxygen in the water. The extra nutrients from the waste stimulates the growth of marine plants and algae well above natural levels, again depleting oxygen in the water. The waste sediment settles to the seabed and all of this can smother the other organisms that would normally be in the water and destroys any shellfish beds around.
The next problem is chemical pollution. With that many fish so close together, disease is a major problem which is managed via the introduction of antibiotics into the salmon’s feed. These drugs find their way into the marine environment. Toxic chemicals are used with the net cages. Cages are often painted with antifouling paints containing copper to prevent the growth on the metal nets minimizing the cleaning. The copper often gets stripped off as the nets are cleaned or slowly leach from the paint. Zinc is added to the feed to keep the salmon from getting cataracts which also finds its way into the environment. Pesticides are used to prevent problems like sea lice on the fish. These chemicals that are added are also very toxic.
Salmon are naturally white fleshed fish. Wild salmon get their color from the diet they eat in the wild, consuming smaller shrimp and krill. However, at the farm, the color is from artificial dyes added to the feed. The picture shows the range of dyes available from SalmoFan which allows farmers to choose just the right shade for their salmon.
It takes on average 2 1/2 pounds of smaller fish to produce 1 pound of farmed salmon. The fish are caught and fed to the larger salmon or turned into fish meal and fish oil to feed to the farmed salmon. As a result of this processing, farmed salmon has been found to have levels of PCB’s and other contaminates that are 10 times that found in wild salmon.
Most salmon pens are have open tops which allows a small percentage of the farmed salmon to escape. The farming industry refers to this as “leakage.” This creates many issues for the wild salmon. The farmed adult Atlantic Salmon tend to be more aggressive than their wild kin. These fish are carriers of sea lice, disease and other parasites which affects the wild population. As they are not native, especially to the Pacific rivers, they begin to take over. The New Brunswick river is a great example. In 1983, escapees were about 5.5% of the salmon population, by 1995, that percentage grew to 90%. Since almost all farmed salmon are from 40 original stocks which have been bred to be large, fast maturing adaptable and aggressive, the genetic diversity of the population has been greatly reduced.
Stay tuned – next post about the collision between wild salmon and farmed salmon and what we can do.