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  1. #1
    Fish&Fly
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    Escaped farmed Atlantic salmon replace the original salmon stock in the River Vosso

    Escaped farmed Atlantic salmon replace the original salmon stock in the River Vosso, western Norway

    by

    H. Sægrov, K. Hindar, S. Kålås and H. Lura
    ICES Journal of Marine Science: Journal du Conseil 1997 54(6):1166-1172; doi:10.1016/S1054-3139(97)80023-9
    © 1997

    Eggs and alevins were collected from 36 redds in the River Vosso in late March 1996. The redds had been made by 20 individual female Atlantic salmon and 12 female brown trout. Species-specific allozyme variation was used to distinguish trout from salmon and egg size and pigment analyses were used to distinguish farmed from wild salmon females. Nine (45%) of the 20 female salmon spawners in the sample were of confirmed farmed origin, because their offspring contained synthetic astaxanthin which is an additive to commercial fish feed. Most of the remaining female salmon were also likely to have been farmed escapees because only about half of the actual farmed spawners can be identified by their astaxanthin content due to intake of carotenoids from natural food sources. The estimated peak spawning for both confirmed and putative farmed females was 32 d earlier than peak spawning of wild females. Egg survival was high and similar to previous estimates for wild and farmed salmon in the River Vosso. Based on the astaxanthin content in sampled eggs and the time of peak spawning it is concluded that most Atlantic salmon fry that hatched in the River Vosso in 1996 were produced by escaped farmed females. The frequency of redds made by farmed females was in accordance with their estimated representation (81%) in the population of spawners during autumn 1995.

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  2. #2
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    It is frightening to witness how quickly feral farm salmon overran this once great salmon river and wiped out the famous inhabitants forever.
    At least DNA science has advanced sufficiently to identify, and hopefully convict, any future culprits.

    http://www.imr.no/english/__data/pag...news_19_07.pdf by Øystein Skaala - Retur: Havforskningsinstituttet, Postboks 1870 Nordnes, NO-5817 Bergen, Norway



    "The debate over the potential genetic effects of escaped farmed salmon on wild salmon goes back for more than 20 years. As early as the 1980s, large numbers of escaped salmon were being registered in the sea and in a number of wild salmon stocks. With the aid of new DNA methods, we can now study salmon stocks and how these change as a result of escapes; studies that would have been impossible only a few years ago."

    Successful practical application:
    In autumn 2006, local fishermen in the Romsdalsfjord in western Norway reported a sudden increase in catches of escaped salmon, although no escapes in that area had been reported to the Directorate of Fisheries.
    When asked, none of the fish farmers in the area said that they had lost fish. In collaboration with IMR, the Directorate of Fisheries collected samples from all the seacages in the region. Samples were taken from a total of 16 sea-cages in seven farms. DNA was also extracted from 29 of the escapees and was typed for 15 genetic markers.
    The results showed that none of the 29 escapees could be matched to 12 of the 16 sea-cages, but that 20 of the 29 escapees (69%) matched the genotypes of the salmon in one specific sea-cage; i.e. a very clear signal. The police authorities concluded that the results were sufficiently strong to warrant a full investigation of the owner of that particular sea cage.

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