Study looks at implications of salmon breeding

For the first time researchers will measure the fertilisation compatibility between farmed and wild salmon, and therefore the risk of farmed genes entering wild populations, which are in severe decline.

Wild Atlantic salmon stocks have fallen by more than 50pc, mainly through poorly-managed fisheries and deterioration of feeding and spawning habitats. But there are also serious ecological and genetic threats to wild populations from salmon farming, through the escape of farmed fish into wild salmon ecosystems.

The three-year study, which starts this month, has received funding of just over £330,000 from the Natural Environment Research Council. Much of the field work will be carried out at the Norwegian Institute of Nature Research and at hatcheries in Scotland.

Leading the team is Dr Matthew Gage, from UEA’s School of Biological Sciences.
“Salmon farming is a multi-million pound industry and takes the pressure off wild salmon as a food source. But the significant and increasing entry of farmed salmon into wild populations presents important problems for a species that is already of significant conservation concern,” he said.

“Ecologically, escaped fish can reduce the fitness of wild fish by competing for resources such as food, space and mates, or by disturbing spawning sites or passing on pathogens that can cause disease. Such repeated releases of new genetic strains into an already stressed wild population could lead to ‘genetic swamping’ and the complete dilution of wild genes.”

Currently, more than 95 per cent of Atlantic salmon in existence are of farmed origin. An estimated two million farmed salmon escape and enter the North Atlantic each year, equalling the number of wild fish. Farmed fish enter spawning populations, with an average of 11-35 per cent of salmon in Norwegian rivers of farmed origin.

Farmed fish present a major problem for wild Atlantic salmon because they compete for resources, but potentially more important is the introgression of domestically-selected farmed genes into wild populations, leading to loss of local adaptation.

Farmed salmon have undergone decades of intense selective breeding, including selection for faster growth and efficient feed conversion and increased aggression, giving them a reduced fitness compared with wild strains under selection from the wild.

Dr Gage said: “Our project will try and actually quantify the degree of fertilization compatibility at that all-important sperm and egg level. Farmed fish have been selected under very different regimes to wild fish so their relative fertility might have gone up or down. We hope to provide the objective information on fertilization compatibility between farmed and wild fish, and that could allow policy makers to make more informed decisions for both aquaculture and salmon conservation.

“Evidence shows that escaped farmed salmon tend to be less behaviourally successful at spawning in the natural environment than their wild counterparts, but we will be looking in detail at fertilization compatibilities between sperm and egg, and under competition between males of farmed and wild origins.

“The other exciting aspect of this project is that we will be able to address questions on the evolution of reproductive isolation, which is likely to evolve initially via reductions in sperm-egg compatibility.”