Cod_ A Biography of the Fish That Changed the World - Mark Kurlansky [63]
Although farming cod is a new field and salmon farming is firmly established, Martin claims cod would be far easier to farm. Salmon have a delicate scale structure and are prone to infections, whereas cod tolerate handling and are disease resistant. Also, salmon do not like to be crowded into a pen, whereas cod have a herding social structure.
Fish farming—everything from salmon to mussel—is becoming a bigger industry every year. Farming starts out well enough. After the Petty Harbor experiment, Martin set up several pens, fattening the cod with mackerel, herring, and capelin. This probably produced excellent fish, but at the time of the moratorium he had gone out of business with a debt of one million Canadian dollars. Commercially successful fish farms reduce operating costs by feeding pellets of pressed fish meal rather than wild bait fish. In the case of salmon, they are also fed artificial coloring to give them the pink tint they acquire in the wild from eating crustaceans. Gastronomically, a wild salmon and a farmed salmon have as much in common as a side of wild boar has with pork chops.
Not only gastronomes but also scientists have deep concerns about fish farming. Pen-reared cod have a phenomenal growth rate. They are much bigger at a given age than wild northern stock. Cod doubles its size in a year anyway, but a hatchery cod can quadruple its size in the same period. Since size determines fecundity, pen raising and releasing would appear to be a way to rebuild stocks. But this is a dangerous business.
The idea of releasing farmed fish into a wild stock frightens scientists because man does not select fish in the same way nature does. If a cod was not disease resistant, did not know how to avoid predators, lacked hunting or food-gathering skills, had a faulty thermometer and so did not produce the antifreeze protein or the ability to detect a change in water temperature that signals the moment to move inshore for spawning, this cod would not survive in the wild. But it would survive in a pen, and if it had other characteristics that were particularly well suited for farm life, the defective fish would flourish and possibly even dominate. If it then reproduced with a wild fish, it would pass its “bad genes” to their offspring.
Christopher Taggart, fisheries oceanographer at Dalhousie University in Halifax, compared farmed fish to purebred dogs and thoroughbred horses: “Most purebred dogs carry genetic defects like bad hips. Thoroughbred horses break a leg if you look at them. It is a byproduct of selecting. Try to produce a dog with thick fluffy fur that is a good swimmer and it ends up to also have bad hips. If the dog bred in the wild, you would produce a wolf population with bad hips.”
The genetic consequence of fish farming are still unknown. The assumption—the hope—for fish that live their entire life cycle in pens is that they never escape into the wild to mingle with the species. But this accident has happened. Worse, some hatcheries produce young for the purpose of releasing and enhancing the wild stock.
New England salmon hatcheries released so many fry into the wild that by 1996, only an estimated 500 Atlantic salmon in New England still had the diverse genetic characteristics of the wild species.
The central issue to the survival of a species is how to maintain its diversity—the wide range of genetic characteristics that gives a species the ability to adapt to the many challenges of life in the world. Scientists have no way of knowing, but can only hope, that the tiny reduced population of surviving northern stock carry the full range of traits once presented in the gene pool of a population of