There has been a great deal of controversy lately about the practice of fish-farming, with some stores going so far as to declare that the salmon they sell are wholly from wild sources.
There are a number of reasons for this backlash against farmed fish, some legitimate, others more the product of the fishing industry and their lobbyists.
Most fish-farms are either in shallow fjords and estuaries along the coast, or land-based in tanks. The coastal fish farms are the ones targeted, and while man of the concerns are valid, they are not often viewed in a larger context. However, let’s look at the concerns, and explore some possible solutions.
One of the biggest concerns is the proliferation of sea-lice in captive salmon populations, and the risk of it spreading to wild populations. Open-net farms in river estuaries are a concentrated population of salmon, and the parasites that feed on them. Any young salmon travelling down-river to the sea will have to pass through waters literally infested with sea lice larvae. While there are treatments that can control the parasites in the farms, they are of little use to the wild populations transiting through the farm areas. Controlling sea lice in the farms does help, but the sheer concentration in the limited waters of an estuary makes it difficult to stop the spread to wild fish.
Sea lice, especially on the younger fish, can easily kill them. They lack the size, strength, and thick skins to effectively resist any infestation. Canada’s Department of Fisheries and Oceans, however, disagrees. And state that there is no evidence to support the contention that farmed salmon stocks are responsible for the decline in wild salmon stocks, so there is no consensus on the sea-lice issue.
Open net salmon and trout farms are a source of other pollutants, though. There is the biological waste from the thousands of fish themselves, which can cause algal blooms and oxygen depletion, not to mention just being a pile of sludge that can over and suffocate sea floor life, contaminating other fish stock.s. The antibiotics and other chemicals used to treat the fish are another source of pollution and can lead to the breeding of resistant strains of bacteria and other organisms. Even the chemicals used to treat sea-lice can affect other crustaceans, and have the ability to accumulate in sediments.
Then there is the question of feed. Fish confined to net systems cannot feed on natural prey, so food has to be provided, typical some sort of fish meal, which is simply ground up fish. This fish has to come from somewhere., and is usually non-commercial fish and/or bycatch from commercial fisheries. Which is something like hunting rabbits to feed cows…
Off the coast of British Columbia, the majority of salmon in the farms are actually Atlantic salmon. Similar situations are found in fish-farms all over the world in regard to non-native populations. Sometimes, these fish escape, and this can impact the wild population is negative ways.
It is clear that coastal open-net fish farms are a substantial problem. This has to balanced out against the costs of open water fisheries. While some fisheries are managed in a sustainable fashion, the collapse of several fisheries over the last few decades, in particular the North Atlantic Cod fishery, makes it clear that many are not. Most fishing is done in an unsustainable fashion, effectively “strip-mining” the oceans.
There are solutions, however, that can manage the problems of fish-farms, and provide healthy stocks of fish for human consumption.
One solution is contained fish farm. Take the same fish farms, and wall them off to prevent a mixing of the farm water and the sea water. This contains waste, sea-lice, and any chemicals, but still has to deal with the water produced, and provide feed. It is possible that the waste could be collected and used for fertilizer.
Another solution, at least for salmon, is fresh-water fish farms. This controls disease and sea-lice, since sea-lice can’t live in fresh water, and requires much less surface area. However, the salmon from freshwater farms aren’t as large as sea-framed fish or wild stock, nor is the meat as pink. Consumer acceptance thus far has been minimal.
Another solution would be to create deep water farms, and build them with complete eco-systems. Grow kelp and phyto-plankton, and zoo-plankton. Have a few other species from the bottom of the food chain. Then some shellfish, intermediate species, and then whatever apex predators you wanted to cultivate. A deep-water site allows a much more ecological approach to fish farming, and requires little in the way of outside inputs.
Fish farms are potentially a valuable source of protein for a growing world, but there must be controls put in place to mitigate their environmental effects.