Fish are probably caught by the following means: they typically encounter the lead panel (20-mm mesh) of the trap (which is attached to the shore) and, while trying to swim around it, are led to the entrance of the trap, enter the heart and are led into the residence chamber. The wings and throat are made of 20-mm mesh, ensuring that the fish do not snag inside the net. Once deployed, the trap floats on the surface of the water and is anchored with seven anchors which give the net height stability, even in high currents such as those typically encountered at the study location. Depending
on the purpose of the study, the trap can be set to float at the surface in deep water (>5 m) by adding additional floats, or, in shallow water, can be made to rest upright on the sea-floor. The two types of deployment have been shown to function equally well. In the present study, the trap rested on the sea-bottom. During sampling, the trap was emptied every day by carefully hauling up the last compartment of the residence chamber so that the fish would enter a hand-held net. Care was taken to ensure that trout were not abraded against the trap chamber or the hand-held net during
transfer. To get an accurate assessment of the fish in this experiment, all fish were killed and assessed in the laboratory according to the method described in Finstad et al. (2000). A method to assess sea lice on live specimens is currently being devised. The sea trout collected from both gill-net and trap were put into plastic bags, killed by a blow to the head and bagged individually.