The growth of Scottish salmon (Salmo salar) aquaculture 1979–2016 fits a simple two-phase logistic population model

Abstract

Annual Scottish salmon production rose from 520 to 162,817 t over the years 1979–2016. This production growth is modelled using a logistic population model. Factors limiting production capacity include social, economic, regulatory and environmental factors (which change with time), while the growth in production is the product of changes in number of farms and productivity per farm. The model identifies fundamental differences occurring relatively abruptly around 1992. Pre 1992 the growth was extensive in nature with the number of farms increased exponentially (35% per year, 1979–1989) but productivity per farm increased relatively slowly (11% per farm per year) giving overall growth rate and with a relatively high 31.2% loss of fish. Since 1992 growth has been through intensification as the number of farms has fallen but productivity per farm increased rapidly in association with lower 20.3% loss of fish, which is in turn associated with a rapid uptake of antibacterial vaccine use. This simple model fails to predict a drop in production during 2004–2008 associated with a period of high exchange rate (£/$) and intense competition from Chile and Norway. After 2008, production resumes the pattern of increase predicted by the model as fitted from 1992 to 2003. Production is now approaching the historically fitted capacity, so further increase requires changes within the aquaculture industry that will increase carrying capacity such as increased productivity per unit biomass (better health, faster growth). For major increases in salmon production more substantial changes will be required, potentially offshore production will allow for more farms farm with larger biomasses, but this requires technical advances.