Fiskeriforskning has completed a preliminary study, the main goal of which was to map relevant behavioural activity of farmed cod in cages.
As a result, measures are being taken to reduce the danger of escape and to develop preventive operation routines for farming of cod.
The test has shown that cod behave differently than e.g. salmon. While the salmon seems to stay in cages with small holes for a long time, the cod will quickly discover this, head for the hole, and a short time later, swim out.
Determined escape
As expected, there is a good connection between the densities of cod in a cage and how many escape per time unit. Cod do not escape "accidentally", but swim with determination through the hole in the linen net. The scientists have neither proved nor disproved whether the cod are able to make holes in the net, but demonstrated that even with small holes, the cod will escape the cage.
"Because the cod's behaviour increases the danger of escape, it is important to gain more knowledge about this if the profitability in future cod farming is going to be secured", says Scientist Kåre Aas, who has been responsible for the testing.
Preventive measures
The study shows that escape prevention must be achieved through technical changes, adapted surveillance and increased knowledge about the cod's normal behaviour in cages. Technical improvements are an obvious development in the supplier industry, and new constructions are continuously being introduced.
It is also necessary to frequently inspect the bags to reveal holes and wear and tear.It should be studied whether new types of linen have properties that make them better suited than those that are in use today. If it is shown that cod are able to make holes in the net, there should be requirements for both breaking stress and tolerance to chewing.
All fish that escape from cages can have environmental consequences and cause big financial losses for the owner. Cod farming is still in its infancy, with an annual production in 2003 of approximately 2,000 tonnes. Calculations show, however, that future production has the possibility of reaching the level of salmonids.
The project "Cod that escape, a behavioural study in cages" is carried out by Norfra Cod AS in Storfjord Municipality on assignment from Innovasjon Norge.
