EFFECT OF STERN-SETTING TUNNEL ON THE SINK RATE OF INTEGRATED WEIGHT LONGLINE (IWL)

This paper describes a new vessel modification to allow setting of longlines via a stern-setting tunnel, and the proposed experimentation to evaluate this method's effect on the sink rate of demersal integrated weight longline (IWL). The stern setting tunnel consists of an elongated steel tube, built in to the longliner during a dry-dock refit. The tube angles downwards from where the line exits the baiting machine, which is positioned in the aft section of the stern setting deck, to the exit point at the water line on the vessel's transom. The exit point of the tube is understood to be slightly off-centre towards the downward-swing side of the propeller. The sink rate of IWL longlines, conforming to the CCAMLR standard specified in conservation measure 24-02, is planned to be tested in a series of sets using time-depth recorders during current sea-trials and approximately three weeks of fishing in the New Zealand ling fishery. To evaluate the effects of the stern-tunnel method, the sink rates will be compared to similar vessels using IWL and the same setting machinery but setting conventionally over the stern. The sink rate tests are not expected to be completed until just before the WG-IMAF meeting and it is intended that the results will be tabled separately at the meeting commencement.