Summary
The Spanish system of longline fishing is used in a range of demersal and semi-pelagic fisheries throughout the southern hemisphere and has been the source of a large number of seabird fatalities. An experiment was conducted on a chartered Spanish-rig vessel to increase the sink rate of longlines to reduce interactions with seabirds. 2. The experiment examined the effect of setting speed, distance between line weights and the weight of the line weights on the sink rates of hook lines. 3. The most powerful effect was line weighting, which affected sink rate independent of setting speed and distance between weights. Distance between weights was also important, but its effect depended on setting speed. Overall, however, the effect of setting speed was minor and the principal determinants of sink rates were the mass of the weights and distance between the weights. 4. Based on published accounts of seabird mortality in Spanish system fisheries, 8 kg/30m is the preferred weighting regime to minimize interactions with seabirds. Sink rates from this regime are the fastest that can be expected from Spanish system gear without overly compromising fishing operations. Used in combination with bird scaring streamer lines and the slower setting speeds the weighting regime has the potential to reduce mortality of albatrosses and deep diving seabird species to very low levels.