Í nýrri rannsókn vísindamanna við New York háskóla og fleiri háskóla kemur fram að til að framleiða eitt kíló af eldislaxi þarf fjögur til fimm kíló af villtum fiski. Þetta er mun hærri tala en eldisiðnaðurinn hefur haldið fram.
Í grein í vísindaritinu New Scientist segir aðalhöfundur rannsóknarinnar að eldi á ránfiski (carnivore) einsog laxi sé afar ósjálfbært.
Meðal afleiðinga eru að villtur uppsjávarfiskur, sem áður fór á matardiska íbúa í Vestur-Afríku og Suðaustur-Asíu, er nú bræddur í fiskolíu og mjöl og notaður í fóður fyrir eldislax.
„Líklega hefur notkun fiskimjöls og fiskolíu í eldisiðnaðinum verið vanmetið og jafnvel að miklu leyti,“ segir Stefano Longo við Háskólann í Gautaborg í viðtali við New Scientist, sem birtist nú í október.
Það er bókstaflega allt rangt við sjókvíaeldi á laxi. Dagar þessa iðnaðar eru taldir.
Niðurstöður rannsóknarinnar eru sláandi.
Í umfjöllun New Scientist segir:
It has been claimed that fish farming is a sustainable source of food that will help us feed the growing global human population while protecting wild fish populations – but this isn’t true.
“Fish farming is not a substitute for catching wild fish out of the ocean,” says Matthew Hayek at New York University. “In fact, it relies on catching wild fish out of the ocean.”
Hayek and his colleagues have shown that the amount of wild fish killed in order to feed farmed fish is between 27 and 307 per cent higher than previous estimates.
Farmed carnivorous fish eat multiple times more weight in wild fish caught from the ocean than is obtained by farming them, says Hayek. For instance, producing a kilogram of salmon may require 4 or 5 kilograms of wild fish.
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The result is that as the aquaculture industry expands, an increasing proportion of the global catch of wild fish is being fed to farmed fish.
This means that people in places such as South-East Asia and West Africa can no longer afford to buy fish because it is worth more as a source of fishmeal and fish oil for farmed fish, says team member Patricia Majluf at the conservation organisation Oceana.
Increasing the proportion of plant-based products in the diet of carnivorous fish, or raising omnivorous or herbivorous fish – such as tilapia, carp and catfish – creates a different set of problems. If plant-based food that could be eaten by people is fed to fish, more land and water is needed to produce food for fish, leading to issues such as deforestation.
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There are a number of reasons why Hayek’s team’s estimate for the amount of wild fish required to produce a given amount of farmed fish is so much higher than past assessments. One is that the team used a wider range of sources than previous studies, says Hayek, meaning it is less likely there is any statistical bias.The team also counted all the fish used to produce fishmeal or fish oil, not just those caught to feed farmed fish.
Finally, the team also estimated the number of fish killed but not brought to market. Unwanted species are often discarded from fishing boats but don’t usually survive. Seine nets are also sometimes left slightly open to let unwanted fish escape, but they are often injured and die.
The conclusion that the amount of wild fish that are killed to feed farmed fish is higher than previous estimates still stands, even disregarding these additional deaths, says Hayek. But counting them adds between 20 and 50 per cent to the total, he says.