Resistance of aquaculture net cage materials to biting by Atlantic Cod (Gadus morhua)

Cod bite on aquaculture net cages has resulted in damages like frayed netting and holes, which in part can explain why cultured cod have escaped more frequently than salmon over the last years. We describe damages found on various netting materials subjected to cod bite through field experiments at commercial cod farms. Further, a method to test local cod bite resistance of traditional netting structures is suggested and initial results from a test jig prototype are given. Results from field experiments indicated that cod may have been attracted by types of netting that made it possible to draw filaments out of the twine, while stiff, coated netting structures and thick filaments showed no sign of bite damage during the test period. We concluded that netting materials for cod aquaculture must be resistant to cod bite or be repellent or uninteresting for cod. Based on the present findings, the better choice among the traditional netting materials seemed to be hard-laid netting materials, preferably with a primer that glues the filaments together.