Preliminary results of the LL-sharks project: A comparison of wire versus monofilament leaders in the Portuguese pelagic swordfish fishery in the SW Indian Ocean
The effects of traditional nylon monofilament versus wire leaders in a commercial longline fishery targeting swordfish (Xiphias gladius) in the South West Indian Ocean were compared, based on total of 82 longline experimental sets conducted on a commercial vessel that deployed equal number of nylon monofilament and wire leaders (total of 82,656 hooks baited with squid). A higher number of taxa were caught on wire leaders, which also showed higher (13%) catch rates in number for sharks and particularly for the blue shark (Prionace glauca). In contrast, nylon monofilament leaders showed higher bite-offs rates (389%) than wire leaders. These results are probably due to the fact that species with sharp teeth could escape the longline by biting through the nylon leaders. The total retained catch value per unit of effort (VPUE) did not change between leader materials. Thus, banning wire leaders could be an effective way of reducing bycatch, particularly of sharks, that fishers may be keen to adopt. However, these results seem to be fishery specific and VPUEs are highly dependent on market fluctuations. Therefore, more studies are required for a thorough assessment of this shark bycatch mitigation measure.