According to a recent study led by Rosamond Naylor of Stanford University, cultured fish now make up half of the fish and shellfish consumed globally. In other words, half the fish we eat now come from farms as opposed to being caught wild in the sea – in excess of 50 million metric tons of it.
This is a landmark for the global aquaculture industry, which has tripled in size since 1995. The growth has in part been driven by burgeoning demand for the long-chain omega-3 fatty acids found in oily fish such as salmon, which according to the US National Institutes of Health are effetive at reducing the risk of cardiovascular disease.
Such growth in fish farming over extractive fishing methods is surely a good thing? At face value farming fish sounds great. You’re not harvesting wild fish stocks, there’s no bycatch and you don’t have the inconvenience and cost of sailing the high seas, yet you still meet demand for heavily impacted fish like salmon and tuna.
Unfortunately it’s not that simple. The fish we farm of course need to be fed on something, and the general solution has been to feed them wild fish harvested from the sea, which in turn puts significant strain on marine resources as considerable amounts of other fish (eg. anchovies, sardines) are harvested from the sea to make fishmeal.
Currently up to 5 pounds of wild fish are required to produce a single pound of farmed salmon. Not over efficient or ecologically sound…
Additionally, the high densities of fish in farms facilitates transmission of diseases and makes them vulnerable to outbreaks. Essentially the fish farms may then act as pathogen reservoirs that infect the surrounding local population of wild fish to detrimental effect. For instance, in British Columbia the potential extinction of pink salmon is feared by some scientists due to infestations of parasitic sea lice caught from their cultured counterparts.
In order for the growing aquaculture industry to maintain its contribution to global fish supplies and truly represent a viable alternative to the age old methods of hooks and nets, it is going to have to find ways of reducing its dependance on wild fish stocks without also disrupting the surrounding ecology.
One method Naylor et al. suggest is to reduce the amount of fish oil in the diet of farmed salmon, since apparently a reduction of only 4% would translate to only 3.9 pounds of fishmeal being required to produce 1 pound of salmon, instead of the aforementioned 5 pounds.
Other avenues currently under investigation include protein from grain and livestock byproducts, as well as extracting omega-3 oils from single celled organisms and genetically modified plants.
Unfortunately simply farming fish that are vegetarian is currently not an ecologically viable alternative as farmers tend to use some fishmeal to increase yield, and due to the sheer volume of vegetarian fish being cultured around the globe these farms presently use 50% more fishmeal than salmon and prawn farms combined. Eliminating fishmeal from their diets would therefore go a long way toward making these vegetarian fish farms more environmentally sound.
In the US a proposed Offshore Aquaculture Act is calling for reduction in the use of fishmeal and oils, but of course careful regulation of any imposed legislation will be required for it to prove effective.
In principal fish farms seem a great alternative to traditional fishing methods, but as the industry booms it may simply exacerbate existing issues of overfishing wild stocks, unless alternative, more ecologically sound sources of nourishment for the farmed fish can be found.
Undoubtedly the next crunch question will be whether potential altertanitves are sufficiently cost effective to be adopted by the aquaculture industry…