Abstract
Salmonid farming affects both the environment and other industries, with impacts of wild fish attracted to fish farms being a major concern. Here, we summarized existing knowledge on the impacts of such aggregations around open-cage salmonid farms in Norway on the environ- ment and human activities and on the interactions of these impacts. Waste fish feed is considered the major cause for the attraction of wild fish to the cages. The aggregations of wild fish are rela- tively persistent and can affect the spatiotemporal distribution of several wild marine species. A change in diet by ingesting the high-energy waste feed available close to the cages may increase the energy stores of some of the attracted fish species, and perhaps also their fecundity, but whether this influences offspring viability is unknown. Changes in the distribution and physiology of the attracted fish can influence local fisheries in terms of resource availability and are probably also associated with the softer, lower-quality meat texture of wild fish caught close to salmonid farms. For fish farmers, the attraction of wild fish to the cages is advantageous because attracted fish eat a substantial amount of the waste feed before it can impact the benthos, and because large attracted fish prey on escaped farmed fish. However, movements of wild fish may play a role in the transfer of diseases, and wild fish may cause farmed fish to escape by damaging the net pens. Due to the complexity of interactions, a combined focus on the impacts of attracted wild fishes on the environment and human activities is warranted when developing future management and gover- nance strategies for salmonid aquaculture.
Highlights
Atlantic salmon Salmo salar farming is a major ecosystem modifying factor in coastal areas, with subsequent impacts on human activities (e.g. Maurstad et al 2007, Wiber et al 2012)
Salmon culture in open sea cages is a significant ecosystem modifying factor in the coastal zone, its ecological impacts in terms of attraction of wild organisms to farms have been studied only for a few of the many species that share the same environment as salmon farms
The ecological impacts of salmon farming due to attraction of wild marine fish species may not necessarily be solely negative or positive, but probably vary along a scale depending on many factors
Summary
Atlantic salmon Salmo salar farming is a major ecosystem modifying factor in coastal areas, with subsequent impacts on human activities (e.g. Maurstad et al 2007, Wiber et al 2012). The large aggregations of wild fish could affect the farming activity itself and potentially lead to adverse effects such as increased escape risk resulting from attraction of large predators which may damage the net cage wall, and through propagation of pathogens to wild fish (Sanchez-Jerez et al 2008, ArechavalaLopez et al 2013). We summarize the existing knowledge regarding the impacts of wild fish attraction to open-cage salmon farms on coastal ecology, human activities and their interactions (Fig. 1). The extent of the area around salmon farms within which wild fish are attracted has, to our knowledge, not been estimated, but it may be large, as noise and chemical cues can be detected by wild fish over relatively long distances. In the Aegean Sea, the spatial structure of wild fish around Sparidae fish farms was affected at a scale of 10 to 24 square n miles
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