Abstract
Abstract We report on the data from an extensive monitoring programme for the occurrence of escaped farmed Atlantic salmon (Salmo salar) in Norwegian rivers for 25 years. This monitoring started as a 3-year research programme in 1989 and was followed by management authorities to cover the proportional occurrence of escaped farmed Atlantic salmon in rivers during summer and autumn before spawning. Farmed salmon were distinguished from wild salmon by growth patterns in the scales. More than 362 000 salmon were registered by this programme. Here we present the historical data on escaped farmed salmon in catches 1989–2013 and a methodology for calculating averages across summer and autumn capture in rivers, across years and in regions, using weighted and unweighted observations. Catches of escaped farmed salmon show large spatial and temporal variation, with the early 1990s and early 2000s being periods of large influxes of farmed fish. Western Norway and parts of middle and northern Norway have shown particularly high incidences of escaped farmed fish. Because escaped farmed Atlantic salmon are competing and interbreeding with wild Atlantic salmon, as well as increasing the spread of disease-causing agents, they have become a major force driving the abundance and evolution of Atlantic salmon.
Highlights
Increased production of farmed Atlantic salmon (Salmo salar) worldwide and declining wild salmonid populations have caused concerns that salmon aquaculture is a major driver of abundance and viability of wild salmonid populations (Maitland, 1986; Fleming et al, 2000; McGinnity et al, 2003; Ford and Myers, 2008; Taranger et al, 2015; Forseth et al, 2017)
Farming of Atlantic salmon was made possible through inventions in the late 1960s and soon after emerged as a way of using the coastline for large-scale production of animal protein (Glover et al, 2017 and references therein)
After a strong build-up of production during the 1970s and 1980s and a demonstration that it was possible to produce farmed salmon at an acceptable market cost, fish farming was viewed as a relief to wild salmon populations, especially in oceanic, coastal and riverine areas with large fisheries
Summary
Increased production of farmed Atlantic salmon (Salmo salar) worldwide and declining wild salmonid populations have caused concerns that salmon aquaculture is a major driver of abundance and viability of wild salmonid populations (Maitland, 1986; Fleming et al, 2000; McGinnity et al, 2003; Ford and Myers, 2008; Taranger et al, 2015; Forseth et al, 2017). One concern relates to competitive interactions and interbreeding between escaped farmed and wild Atlantic salmon, another to increased transmission rates of fish disease agents (ICES, 2016). An article in VC International Council for the Exploration of the Sea 2019.
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