Escape-related behaviour of Atlantic cod,Gadus morhuaL., in a simulated farm situation

Abstract

Cultured ¢sh escaping from farms represent an economic loss as well as a potential problem for wild ¢sh populations. This study investigated the escape-related behaviour of farmed Norwegian coastal and northeast Arctic cod (NEAC), Gadus morhua L. Six groups of ¢sh were observed during three replicate trials in a large tank that was split into two equal parts by a net wall. The ¢sh could move freely through an opening in the net during the trials. Three groups were not fed during the trials. The ¢rst escape occurred shortly after producing the net opening (11 AE 10.5 min; mean AE standard deviation). Norwegian coastal cod were more prone to escape than the NEAC. A starvation period of 9 days increased the number of ¢sh on the escape side of the tank. Net biting and net inspection by the ¢sh were frequently observed, irrespective of whether the ¢sh were fed or not. The same ¢sh were repeatedly found on the escape side of the tank, but the propensity for recurrent escape behaviour was not related to genotype, feeding status or size. The results suggest that other factors, such as individual variation in boldness or exploration behaviour, could a¡ect the willingness to escape.

Spatiotemporal distribution of coastal and oceanic Atlantic cod Gadus morhua sub-groups after escape from a farm

“…Previous work has demonstrated that identically farmed adult NCC and NEAC differ with respect to disposition to pass through an opening in a net wall (Hansen et al 2008). Also, Salvanes et al (2004) documented behavioural differences between sub-groups of juvenile cod farmed in common-garden experiments.…”

“…In addition, genetic and other factors like hunger level, stocking density and environmental variation might affect the escape likelihood of cod. It has, for example, been shown that the 2 genotypes Norwegian coastal cod (NCC) and north-east Arctic cod (NEAC) exhibit a movement pattern within rearing tanks that might involve higher escape risk (Hansen et al 2008).…”

“…The proportion of cod escaping from farms is therefore higher than for salmon farming, where, at the end of each year, on average 0.2% of the number of fish in the farms was reported to escape from 2004 to 2009 (data from the Norwegian Directorate of Fisheries). The high escape risk of farmed cod is related to several factors; cod tend to bite holes in the net pen walls, they exhibit a swim pattern in the cages that involves a higher probability for finding holes in the net, and the technological and operational principles for cod farming in sea cages are principally developed for salmon and not for cod (Moe et al 2007, Hansen et al 2008). In addition, genetic and other factors like hunger level, stocking density and environmental variation might affect the escape likelihood of cod.…”

Behavioural indicators of welfare in farmed fish

“…A study on Atlantic cod, Gadus morhua, escaping from net cages revealed consistent individual differences between the fish escaping compared with nonescaping fish, with bold individuals being more willing to swim through small holes in the net, and thus escape more frequently than shy fish (Hansen et al 2008). These responses are generally linked with the learning ability of farmed fish.…”

Using purposeful inbreeding to reduce outbreeding depression caused by escaped farmed Atlantic cod

“…Given that farmed cod spawn in the cages, embryos with cultivated cod genes drift out of sea cages into the environment, escaping through spawning (Jørstad et al 2008, Jensen et al 2010). If they survive, they may interact with wild cod with possible negative implications, including competition for food and other resources, mating competition, and outbreeding depression (Hansen et al 2008). If the fish have been intensely selected for domestication, they can introduce domestic adaptations that disrupt local adaptations of wild cod (Hindar et al 1991).…”