Chapter 9. Assessing and Managing the Impacts of Marine Salmon Farms on Wild Atlantic Salmon in Western Scotland: Identifying Priority Rivers for Conservation

  1. Derek Mills MSc, PhD, FIFM, FLS
  1. J.R.A. Butler1 and
  2. J. Watt2

Published Online: 20 NOV 2007

DOI: 10.1002/9780470995495.ch9

Salmon at the Edge

Salmon at the Edge

How to Cite

Butler, J.R.A. and Watt, J. (2003) Assessing and Managing the Impacts of Marine Salmon Farms on Wild Atlantic Salmon in Western Scotland: Identifying Priority Rivers for Conservation, in Salmon at the Edge (ed D. Mills), Blackwell Science Ltd., Oxford, UK. doi: 10.1002/9780470995495.ch9

Editor Information

  1. Atlantic Salmon Trust

Author Information

  1. 1

    Spey Fishery Board Research Office, 1 Nether Borlum Cottage, Knockando, Morayshire, AB38 7SD, Scotland, UK

  2. 2

    Lochaber and District Fisheries Trust, Arieniskill Cottage, Lochailort, Iny ernes shire, PH38 4LZ, Scotland, UK

Publication History

  1. Published Online: 20 NOV 2007
  2. Published Print: 7 JUL 2003

ISBN Information

Print ISBN: 9780632064571

Online ISBN: 9780470995495



  • marine salmon farms;
  • wild atlantic salmon;
  • western scotland;
  • sea lochs;
  • interb reeding



This chapter contains sections titled:

  • The Scottish salmon farming industry became established in the early 1980s. However, impacts of farm salmon on wild Atlantic salmon (Salmo salar) were not predicted and many farms were located near the mouths of rivers. This paper assesses 38 salmon rivers in the centre of the west coast salmon farming zone, and compares the status of stocks in those with and without salmon farms in their sea lochs. Juvenile surveys carried out at 230 sites in 35 rivers in 1997, 1999 and 2001 revealed that rivers with farms had 62-82% and 44-62% lower mean abundances of salmon fry and parr, respectively, and the differences were statistically significant. Calibration of juvenile abundance indices against smolt counts at two rivers with fish traps demonstrated that 86% of predicted smolt runs were depleted in rivers with farms, versus 26% in rivers without farms. Severe stock collapses were evident in 14 (50%) of rivers with farms, where only remnant populations remain. Applying the NASCO Rivers Database classifications, nine of these are considered ‘threatened with loss’, and five may be ‘lost’. In 1990-2001 escaped farm salmon were significantly more prevalent for rod catches in rivers with farms (mean 9%) than in those without (mean 2%), resulting in a greater threat of genetic introgression. Epidemics of sea lice (Lepeophtheirus salmonis) found on sea trout (Salmo trutta) suggest that salmon smolts emigrating from sea lochs with farms are also suffering lethal infestations. It is proposed that in sea lochs with farms the combined effects of genetic introgression and lice infestation have suppressed smolt survival rates to < 8% during the 1990s, resulting in stock collapse. Invoking the requirements of the Habitats and Birds Directives, and NASCO's ‘precautionary principle’, the 15 largest and potentially most genetically diverse salmon rivers on the west coast are identified. Measures are proposed to avoid further deleterious effects of marine salmon farms on these rivers, including the establishment of exclusion zones in their sea lochs.