Monday, 21 October 2013

Environmental Catastrophe along a Norwegian River

Its starting to look like an Environmental Catastrophe along a Norwegian River called the Vikedalselva. Reports on the ground are coming through that a major escape of farmed salmon has infiltrated the river in large numbers. Local fishermen along the Vikedalselva are reporting that the media are not covering the story and feel the issue is being totally ignored by the authorities. Salmon ladders along the river have been closed to purge developing fish...


There has long been concern that escaped farmed salmon may harm the various wild fish populations through hybridisation and altering the gene pools of wild populations (Hansen et al. 1991).There are several problems that can arise in this connection. If the farmed salmon have different characteristics and adaptations from wild salmon populations, gene flow may cause the wild salmon populations to lose characteristics that are crucial in a natural environment, while they adopt more of the farmed salmon's characteristics.

On the other hand, if the escaped farmed salmon have less genetic variation than wild stocks, gene flow to the wild population will cause individual populations to lose variation (Tufto & Hindar). Variation is essential for two reasons (Hedrick, 2000), evaluated from both a short-term and a long-term perspective. A population that loses variation and thus becomes genetically uniform will be less resistant to disease and parasites. Or put another way: it is easier for a parasite to adapt to a population of genetically similar individuals (few polymorphic loci in the population and low heterozygosity) and where the individuals themselves have little variation (the individuals have few heterozygous loci).

Additionally, in theory some of the harmful, recessive alleles will increase in frequency and produce less viable individuals (inbreeding depression). Studies just out (Reed & Frankham, 2003) empirically show that there is a good connection between fitness and heterozygosity, population size and quantitative genetic variation. Heterozygosity explains about 20% of the variation in fitness. In the long term, a population with little polymorphism will not have as great an evolutionary potential as a population with a lot of genetic variation.

All escaped farmed fish will come from a small number of farmed populations, which will lead to different populations becoming more like one another. It has also been claimed that coadapted gene complexes may dissolve. The following is an attempt to clarify relevant concepts and summarise empirical studies.