‘Best practice’ branch line configuration and deployment method to maximize hook sink rates to reduce interactions with seabirds in pelagic longline fisheries
Adding weight to lines to expedite gear sink rates is the most effective method of reducing seabird mortality in longline fisheries. Line weighting is not only very effective in reducing mortality but virtually guarantees compliance by industry to weighting requirements. This is because in many fisheries weight is embedded in gear (e.g., integrated weight demersal longlines and leaded swivels in pelagic gear). Once embedded, weighting regimes are difficult or impossible to change when vessels are at sea in the absence of on-board scientific observers.
The relationships between a) gear design and the sink rates of baited hooks, and b) sink rates and seabird mortality are critically important to efforts to reduce the incidental take of seabirds in longline fisheries. In demersal longline fisheries there is a considerable body of evidence dealing with both of these relationships (see Appendix). Hitherto, comparable information for pelagic longline fisheries has been lacking. Given that reducing seabird by-catch in pelagic longline fisheries is a critical step to improving seabird conservation, and that line weighting is important in reducing interactions with fishing gear, the dearth of relevant information in the published literature for pelagic longline fisheries is remarkable. This opinion, in essence, was expressed at the first meeting of the SBWG in 2007 and is one of the main reasons for the increase in research activity in pelagic longline fisheries in the past two years. The results of this research mean it is now possible to present scientific advice on what constitutes 'best practice' for pelagic gear configuration and deployment methods to minimise contact with seabirds in coastal (domestic) pelagic longline fisheries.