When salmon farming involves placing metal or mesh net cages in the ocean to grow fish, this raises a lot of environmental questions. A summary of the problems that are associated with salmon farming in regards to the environment are below:
Sewage from farms pollutes surrounding waters.
Drugs are required to keep farmed fish healthy.
Escapes of farmed fish threaten native wild fish.
Net Loss: Salmon farming depletes other fish species.
Open net-cage salmon farming is currently one of the most harmful aquaculture production systems and poses environmental threats in all regions it is practiced.
The Environmental Impacts of Salmon Farming Include:
Sea lice are small marine parasites that naturally occur on several fish species. Open-net cage salmon are an easy meal for these parasites and infestations can occur. Salmon farms are often sited in sheltered bays, usually near wild salmon runs. During the Spring out migration, juvenile wild salmon will migrate past infected farms, encountering many more sea lice than they would normally. This can result in the death of the juvenile wild salmon and reduction of the overal stock.
Chemical Treatments: SLICE
To get rid of sea lice infestations, salmon farm companies use a pesticide called SLICE, it is administered through the feed. This toxic compound accumulates in the sediment below the net cages and can be swept away by ocean currents, contaminating other marine species, including shellfish.
There are four diseases that affect farmed salmon:
– Infectious Salmon Anaemia (ISA),
– Infectious Hematopoietic Necrosis (IHN),
– Bacterial Kidney Disease
These infectious diseases can impact wild salmon. Antibiotics are used in treatment which can contaminate the local marine environment.
Hundreds of thousands of salmon excreting in the confined area of a farm can cause a localized level of nutrient loading that may not be completely absorbed by the surrounding environment; hence, nutrient loading from salmon farms may be linked to algal blooms. These blooms are of concern because they reduce the amount of available oxygen in the water.
Marine Mammal Deaths
Open net-cages attract marine mammals who are natural predators of salmon. Whether a salmon farm obtains a license to shoot the mammals that threaten their stock or the creatures are ensnared and drowned in the nets surrounding open net-cages, as routinely takes place, the death of seals, sea lions, dolphins, porpoises and birds is a cost of farmed salmon production that is hidden from the consumer.
Due to storms on the oceans, accidents, human error or carelessness, fish farming equipment is often lost or abandoned. Un-recovered equipment like cables, chains and anchors remain on the bottom and can become a hazard to other mariners who may be traveling or anchoring near farm sites.
Waste Build Up On Ocean Floor
In open net-cage farming, the use of mesh nets means there is no way to prevent waste feed, which can be laced with antibiotics or pesticides, and fish feces from passing directly into the ocean.
The waste from the farmed fish can build up under the pens smothering portions of the ocean bottom, contaminating the marine ecosystem and depriving species of oxygen. Or the bulk of waste may be carried away from the farm site by ocean currents, but this too ends up collecting in another place and causing localized pollution.
Escapes & Alien Species
Atlantic salmon is the species that is typically farmed. In places like British Columbia, on the Pacific Coast, escaped Atlantic salmon can pose serious threats. Escapes have the potential to out-compete wild salmon for habitat and food and transfer disease and pathogens to wild salmon.
Salmon farmers often claim their industry is helping to “feed the world.” In truth, the salmon farming industry contributes to the pressures on already overstressed global wild fish stocks, can strain the food supply for people in poorer nations, and removes massive quantities of small fish from the ocean food chain.
Depending on the production region, 2-8 kilograms of wild fish are needed to produce one kilogram of farmed salmon.
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