Risk/opportunity:(from the Climate Change Risk Assessment for Scotland 2012):
MA30 Damage to cultured aquatic species
Narratives: Marine and coastal change
SCCAP theme: Natural environment
N3: Sustain and enhance the benefits, goods and services that the natural environment provides
There were 7 escape events from saltwater fish farms resulting in the loss of 318,096 fish. 300,000 of these were Atlantic salmon lost in a single weather event impacting on the Western Isles.
- A total of 2.5 million fish escaped due to bad weather between 1995 and 2015 from Scottish fish farms, of which 21% escaped during a single storm event in 2005.
- Although escape events are less likely to be the result of weather than a non-weather cause, when they are, they are far costlier and on average resulted in six times more fish escaping.
- The North-East Atlantic is predicted to experience increased storm activity but there is a lack of consensus on the future storm and wave climate.
Over 99% of the UK marine finfish aquaculture industry is concentrated in Scotland (Gubbins et al, 2013). Most of the stock rearing occurs in farm cages situated in coastal locations. The prediction of wind speeds and therefore storminess is very complex and still uncertain at this time. In general, the North-East Atlantic is predicted to experience increased storm activity (Leckebusch et al, 2006). If climate change increases the frequency and intensity of storms as projected, farm cages will be more likely to get damaged, leading to increased numbers of fish farm escapes and greater economic losses. Storm frequency and intensity are important on two levels; for current practices based in more inshore areas and for future practices which may involve expansion of the industry into more offshore areas and by definition more exposed locations.
In addition to the economic losses due to fish farm escapes there is also the risk of impact on the surrounding ecosystem, including hybridisation with wild populations and competition for food and habitat.
The Scottish finfish aquaculture industry is largely made up of salmonid farms (Atlantic salmon [Salmo salar] and Rainbow trout [Oncorhynchus mykiss]) with some Brown trout [Salmo trutta].
There were seven escape events during 2015 from saltwater fish farms resulting in the loss of 318,096 fish. The majority (300,000 or 94%) of these were Atlantic salmon lost in a single weather event resulting in escapes from a farm in the Western Isles (Table 1).
Table 1 Scottish seawater fish farm escapes due to weather in comparison to all escape events
Escape events due to weather
Escaped fish due to weather
Number of escape events
Proportion of all escape events (%)
Number of escaped fish
Proportion of all escaped fish (%)
There is now legislation making it compulsory to report all fish farm escapes (Aquaculture and Fisheries (Scotland) Act 2007). In addition, the industry’s Code of Good Practice, coupled to recently agreed technical standards for marine cage fish farms should contribute to an overall reduction in escapes. It is expected that these standards will be introduced into legislation.
 There were no escape events in 2015 from freshwater farms resulting in any fish being recorded as escaping
A total of 2.5 million fish escaped between 1995 and 2015 due to bad weather from all Scottish fish farms, with 2 million of these being from saltwater farms. One storm event in 2005 resulted in losses from eight different farms and the overall loss of half a million fish, with approximately 160,000 of those being from salt water farms.
Figure 1 Weather related escape events and numbers of fishing escaping from saltwater fish farms in Scotland (1995-2015)
The number of events and number of fish escaping as a result is extremely variable and there has been no significant trend over this 20-year period (Figure 1).
Although weather related events represented just 19% of all escape events from seawater fish farms, these accounted for over 60% of the total number of fish which escaped (Table 1).
Table 2 Average number of fish escaping from an escape event in Scottish seawater fish farms (1995-2015)
Mean number of fish escaping per incident
In summary, Table 2 shows that although weather related events were less likely to occur during this period than non-weather events (e.g. as a result of human error, wear and tear or predation), they were far costlier when they did and on average resulted in six times more fish escaping.
 In total 4.3 million fish escaped during the same period, including those due to bad weather
The prediction of wind speeds and therefore storminess is very complex and still uncertain at this time. The uncertainty increases when you try and predict regional differences, such as those in Scotland. However, forecasts project an increase of up to 10% in the 20-year return period daily mean wind speeds in some seasons in Scotland (Gubbins et al 2013). In general, the North-East Atlantic is projected to experience increased storm activity (Leckebusch et al, 2006). In the short term, climate change is unlikely to have a significant effect on the farmed marine fish industry (MCCIP, 2012). However, if legislation and technical standards for fish farms fail to track the potential changes in storm frequency and intensity then the risks of escapes will continue or even increase. This will be particularly significant if the farmed finfish sectors expand into more exposed offshore locations.
Although the implications of storm events on fish farms is clear, there is a lack of consensus on future storm and wave projections and it is unclear how the fish farm industry might respond.
The number of escapes is highly variable and does not have a significant relationship to the fluctuations in the size of the industry (Figure 2)
Figure 2 Fish farm escapes as a proportion (%) of total production numbers
A long-term increase in escapes or escape events due to bad weather would imply the industry is vulnerable to the increasing storm frequency and intensity and the industry and/or legislation is failing to adapt to the changing environment. However, this data could be confounded by other factors such as malpractice, actions of predators and equipment failure.
Greater industry responsibility/awareness and the legislation making it compulsory to report all fish farm escapes are likely reasons for the reduction in escapes. However, capacity to police and implement existing legislation is still a limiting factor. Recently agreed technical standards for marine cage fish farms should contribute to an overall reduction in escapes and it is expected that these standards will be introduced into legislation.
 Total production numbers calculated by adding the numbers harvested year 0, 1 & 2 for each year
Legislation making it compulsory to report all fish farm escapes was only introduced in 2012 (Aquaculture and Fisheries (Scotland) Act 2007), therefore it is not clear to what extent escapes prior to this date went unreported.
Comparative total production figures are based on Atlantic salmon alone (total production numbers calculated by adding the numbers harvested year 0, 1 & 2 for each year). Fish farming of other species accounts for just approximately 3% of total tonnage, therefore only salmon production numbers were used. Production data did not distinguish between fresh and seawater farms, therefore comparison figures present data on escapes from all (freshwater and sea water) farms as well.
Published escape data contained inconsistent entries for numbers of fish escaping and therefore it was necessary to adjust fish escape numbers to enable analysis (e.g. conversion of text to numerical data, use of a midpoint figure where a range was given etc.)- see methodology for more detail.
Gubbins, M., Bricknell, I. & Service, M. (2013) Impacts of climate change on aquaculture. MCCIP Science Review 2013, 318-327, doi:10.14465/2013.arc33.318-327.
Leckebusch, G.C., Koffi, B., Ulbrich, U., Pinto J.G., Spangehl, T. & Zacharias, S. (2006) Analysis of frequency and intensity of European winter storm events from a multimodel perspective, at synoptic and regional scales. Clim. Res., 31, 59-74.
MCCIP (2012). Marine Climate Change Impacts on Fish, Fisheries and Aquaculture. (Eds. Frost M, Baxter JM, Buckley PJ, Cox M, Dye SR & Withers Harvey N) Summary Report, MCCIP, Lowestoft, 12pp.
MCCIP Report Cards and Scientific Reports - http://www.mccip.org.uk/annual-report-card/2013.aspx
Taylor, M. & Kelly, R. (2010) Assessment of Protocols and Development of Best Practice Contingency Guidance to Improve Stock Containment at Cage and Land-based Sites Volume 1: Report. pp 74. ISBN: 978-1-907266-30-0
Initial development of this indicator: Andrew Blight (MASTS)
Marine Scotland Policy and Marine Scotland Science for advice
Marine Climate Change Impacts Partnership (MCCIP)