Abstract
Preventing farmed fish from escaping sea cages is a major challenge for developing sustainable aquaculture practices. In this study, the individual behaviour of Atlantic cod Gadus morhua to inspect and bite the net was investigated in 4 replicate multi-patch experiments, using underwater video techniques and behavioural event recording. The experimental system in - cluded a tank enclosure where cod were presented with 6 separate net panels: duplicate pairs of plain control nets and 2 different treatment panels. Four holes were made in the treatment panels, 3 of which were mended with different repair techniques including short and loose thread ends and contrasting colour repair threads. Behavioural effects of feed stimulants were studied before, during and after a feed source was placed outside the net. The cod inspected and bit the net sys- tematically, significantly focusing on loose threads or minor damage on the net, and the fish were capable of causing severe net damage within a few days. The observed behaviours were related to hunger level and feed stimulation, and increased significantly during times when a feed source was present outside the net wall. Few bites were observed, and almost no measureable damage was recorded to plain control panels and the area around unrepaired holes during the treatment. Repairs made with white and black threads, and loose, long ends were significantly more dam- aged than repairs made with short thread ends and threads of similar colour as the net. The exper- iments demonstrated how a behavioural approach might be used in interpretation of a practical problem in aquaculture, and the results will be useful in the development of technology and escape mitigation strategies.
Highlights
Prevention of escape through improvement of husbandry and technology, as well as implementation of efficient recapture programmes, will be important for the development of a sustainable Atlantic cod Gadus morhua farming industry
The individual behaviour of Atlantic cod Gadus morhua to inspect and bite the net was investigated in 4 replicate multi-patch experiments, using underwater video techniques and behavioural event recording
The observed behaviours were related to hunger level and feed stimulation, and increased significantly during times when a feed source was present outside the net wall
Summary
Prevention of escape through improvement of husbandry and technology, as well as implementation of efficient recapture programmes, will be important for the development of a sustainable Atlantic cod Gadus morhua farming industry. Our knowledge about ecological and genetic impacts of escaped farmed salmonids is increasing (e.g. Naylor et al 2005), while the knowledge of cod escapes is still sparse. Research has shown that escaped farmed cod are present on spawning areas for wild cod during the Aquacult Environ Interact 3: 1–9, 2012 spawning season and that wild and escaped cod are likely to interbreed (Uglem et al 2008, 2010, Meager et al 2009). Cod farming may result in genetic changes in wild cod populations in the same way as suggested for Atlantic salmon Salmo salar Escaped farmed cod may transmit pathogens to wild populations (Øines et al 2006) and increase predation pressure on wild salmon smolt (Brooking et al 2006) and other fish species
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