Sea ranching of Atlantic cod (Gadus morhua L.):: Effects of release strategy on survival

Several releases of 1-group cod were performed in order to reveal any effects of release strategies on survival in the sea. All cod were length measured and tagged with external anchor tags before release. In the first experiment, two different release methods were investigated. One group was released in shallow water (0 to 2 m) close to the shoreline, while the second was released in deeper water (10 to 20 m) further from the shoreline. The experiment was performed twice, at two different locations. In the second series of releases, the objective was to determine the effects of fish size at release, time of year, distance from a cormorant roost and treatment of the cod (conditioning, predator training or both) prior to release. A total of 44000 cod were released in six batches, at two release sites and three points in time between January and June. Neither the release method nor prerelease treatment seemed to influence survival significantly. Recaptures from fishermen ranged from 2.9 to 10.5% in Experiment 2, proportional to the date of release and fish size at release and also depending on release site. Cormorants and shags were major predators on the released cod. The percentage of the tags used in Experiment 2 that were found at the roost varied between 1.8 and 7.1%, and was lower at later release dates; it was also inversely proportional to fish size at release and proximity to the roost.