The growth of fish farming industries in Ireland has led to a number of environmental concerns, in particular that of escapees from farmed fish cages.
Impact on Native Fish Stocks
Escaped fish have been shown to have detrimental effects on native fish stocks, due to competition for resources, spread of disease, and alteration of genetic diversity due to hybridisation (McGinnity et al., 2003; Read and Fernandes, 2003). These issues are putting further pressures on an already declining wild fish stock in Irish waters.
Stock losses from fish farming facilities can occur in relatively low concentrations due to repeated ‘trickle’ losses, or higher concentrations due to large scale events (damage to facilities caused by adverse weather conditions, boats and predator attacks ) (Thorstad et al., 2008).
Farmed fish varieties will vary morphologically in a number of ways that could affect wild and native stocks. In the case of salmonoids for example, farmed species have visible abnormalities of the ‘snout and opercula, and of the dorsal, caudal and paired ventral fins’ (Thorstad et al., 2008, p.34). Variations in size and morphology are some of the reasons why farmed escapees pose a number of threats to wild species especially due to hybridisation. Domestication and trait selection can have an effect on farmed stock in a number of ways including growth rate and body size which in turn can have adverse effects on their rate of survival, temperature tolerance and disease resistance. Studies have also shown farmed juveniles to be less risk averse when confronted with predators unlike native or wild stocks which will also affect survival rates (Einum and Fleming, 1997).
A number of measures have been taken to mitigate the issues and concerns surrounding farmed escapees in Europe and in particular Ireland. Licencing requirements for fish farm operators in the Republic of Ireland are such that annual reports must be submitted on the number of farmed salmon escapees. Furthermore, since 1991, routine checks have been conducted on salmon catches from commercial landings and fish dealers for the presence and incidence of farmed salmon species, in particular those caught using drift nets. Continued reporting in this manner may help to mitigate issues surrounding escapees and provide necessary information to help establish methodologies to reduce the potential risks going forward. Further methods to identify and monitor escaped farmed stocks include:
- Morphology and scale characters
- Biochemical methods based on carotenoid content or stable isotopes
- Visual markers after intra-abdominal vaccination
- Genetic methods
From a financial standpoint, escaped individuals represent a significant economic loss to the businesses involved. Damaged constructions, due to poor maintenance, bad weather and depredation, as well as the loss of stock, can result in losses in the region of hundreds of thousands each year.
In 2009 alone, the Irish aquaculture industry took a loss of almost €700,000 from the escape of 35,000 individuals (Jackson et al., 2015). Losses like these can hardly be described as sustainable, and pose a serious threat, both to the marine environment, and to the coastal communities reliant upon this form of income.