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Avoiding Sea Lice

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Humans consume more than 100 million tons of fish per year, and nearly half of that is farmed fish. In some ways farming is good; we’ve been overfishing many species in the wild. But aquaculture facilities also bring a host of problems. In some places, coastal wetlands and mangrove forests have been destroyed to make way for fish farms. They can also pollute the near-shore environment. The shallow, still water and concentrated excrement from fish provides an ideal breeding ground for sea lice; salmon are particularly vulnerable to the parasites.

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New technology is allowing a different kind of fish farming. Massive frames, more than 100 meters in diameter and about 68 meters high, are submerged several miles offshore and stocked with young fish. The structures are exposed to strong ocean currents that keep their water cleaner and better oxygenated than that of farms nearer to the coastline. The cages can be equipped with all sorts of equipment, such as cameras and oxygen sensors, as well as feeding tubes that can be placed at different depths. Rather than sprinkling food on the surface of the water as you might do in a fish tank—and as near-shore farms usually do—the feeding tubes force the fish to swim deeper to feed, which kills most of the sea lice.

Smaller open-ocean “aquaculture nets” are already deployed at various places throughout the world, but these large structures—each with a volume greater than that of St. Peter’s Basilica, as this article points out—are on a different scale entirely. Each can house up to a million and a half salmon. Norway is acquiring six of them in an attempt to triple its farmed fish production by 2030.

Have you had experience with aquaculture in your area—in particular, has it either degraded water quality, or itself been affected by pollutants in stormwater runoff? SW_bug_web

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  1. In addition to the problems associated with high concentrations of pathogens in fish farms that are connected to waters that also support wild fish populations there are genetic concerns as well. Salmon sub-species have, over millennia, adapted to unique environmental factors of their particular environment. Farmed salmon, when part of the larger aquatic ecosystem that includes wild, native salmon, are likely to mix genetically with the wild population and weaken their resistance to the particular environmental challenges of their spawning streams. Most wild pacific salmon species are already on either the threatened or endangered species list. To do anything that further reduces their survival rate is unconscionable. For those reasons, it is imperative that ALL fish farms be located where they have no reasonable possibility of becoming connected to the native environment. The ocean is a wildly unpredictable environment, and to think that it’s possible to account for, and maintain the necessary precautions to prevent an accident from happening is unrealistic. There is a lot of positive potential for the aquaculture industry, i.e. reduced energy cost per unit, predictable harvests, concentrated production close to consumer markets. All of these cost factors make it economically viable, even if they have additional up front costs of constructing the facilities where they can’t harm wild salmon. Before I order salmon in a restaurant, I ask where it was sourced. If it’s not wild caught from a sustainably managed fishery I order something else. That will change only if fish farms can do a better job of stewardship.

  2. Whole Foods Market works with Norway’s deep water salmon farms. Fish from these farms seem to have much less grey flesh next to the skin; salmon’s grey flesh contains the highest mercury level and probably should not be eaten regularly. Wild salmon is presently out of season, so that which is in stores has been frozen. Some years ago, Craig Claiborne stated in his NY Times column that previously frozen fish, when thawed and cooked, looses its protein content. Has this ever been verified?

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