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Do farmed salmon threaten wild populations?

Salmon species.

Salmon species.

Millions of escaped domestic salmon could overwhelm genetic pool of wild fish

Staff Report

FRISCO — Farmed salmon represent a clear threat to wild populations based simply on the sheer numbers of domesticated fish that escape their pens. Millions  of farmed salmon escape captivity each year, potentially with huge consequences for the genetics of wild populations, according to a new study from the University of East Anglia.

The researchers concluded that, while farmed salmon are genetically different to their wild counterparts, they are just as fertile. With full reproductive potential to invade wild gene pools, farmed salmon should be sterilized, the study concluded.

“Around 95 per cent of all salmon in existence are farmed, and domestication has made them very different to wild populations, each of which is locally adapted to its own river system,” said lead researcher, Professor Matt Gage.
“Farmed salmon grow very fast, are aggressive, and not as clever as wild salmon when it comes to dealing with predators. These domestic traits are good for producing fish for the table, but not for the stability of wild populations.

“The problem is that farmed salmon can escape each year in their millions, getting into wild spawning populations, where they can then reproduce and erode wild gene pools, introducing these negative traits.

The scientists say that, to avert problems, farmed salmon should be sterilized, as is common with farmed rainbow trout. But the aquaculture industry has not embraced this technology yet because of fears that triploids don’t perform as well in farms as normal diploid fish, eroding profits.

“We know that recently-escaped farmed salmon are inferior to wild fish in reproduction, but we do not have detailed information on sperm and egg performance, which could have been affected by domestication. Our work shows that farm fish are as potent at the gamete level as wild fish, and if farm escapes can revive their spawning behaviour by a period in the wild, clearly pose a significant threat of hybridisation with wild populations.”

Researchers used a range of in vitro fertilization tests in conditions that mimicked spawning in the natural environment, including tests of sperm competitiveness and egg compatibility. All tests on sperm and egg form and function showed that farmed salmon are as fertile as wild salmon – identifying a clear threat of farmed salmon reproducing with wild fish.

“Some Norwegian rivers have recorded big numbers of farmed fish present – as much as 50 per cent. Both anglers and conservationists are worried by farmed fish escapees which could disrupt locally adapted traits like timing of return, adult body size, and disease resistance.

“Salmon farming is a huge business in the UK, Norway and beyond, and while it does reduce the pressure on wild fish stocks, it can also create its own environmental pressures through genetic disruption.

This research was funded by the Natural Environment Research Council (NERC) and the Royal Society.

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