Bird-scaring lines do not deter shearwaters from Mediterranean longliners in calm conditions; night setting the best option

Verónica Cortés (Institut de Recerca de la Biodiversitat (IRBio), Universitat de Barcelona, Spain) and Jacob González-Solís have published in the on-line/open-access journal PLoS One on seabird mitigation trials conducted on Mediterranean longliners.

The paper’s abstract follows:

“High numbers of seabirds are killed annually worldwide in longline fisheries. In the Mediterranean, this mortality is seriously affecting the viability of seabird populations, in particular of the three endemic shearwaters. Even so, there is currently no specific seabird mitigation requirements for the longline fleet operating in this area. From 2013 to 2014, we assessed the efficiency and practical applicability of four mitigation measures on artisanal demersal longliners targeting European hake (Merluccius merluccius) in the western Mediterranean: night setting, tori line, weighted lines and artificial baits. We performed fifty-two pairs of experimental (with the tested mitigation measure) and control settings (without any measure), and compared their effects on seabird interactions and fish catches. In addition, we estimated the longline sink rates and the seabird access area to baited hooks in different longline configurations. Night setting reduced bycatch risk without affecting target and non-commercial fish catches. The tori line may have reduced the bycatch risk by displacing bait attacks beyond the end of the line, but at this distance shearwaters could still access to the baits and the streamers did not deter birds under calm wind conditions. Weighted lines increased sink rate, but it resulted in only a minor reduction of the seabird access window to baited hooks and led to some operational problems during the setting. Artificial baits substantially reduced commercial catches. Moreover, the seabird access to the baited hooks was influenced by the longline configuration, the setting speed and the relative position to the floats and weights. So far, night setting stands out as the best mitigation measure for reducing bycatch levels without compromising target catches in demersal longliners. Ideally, these results should be confirmed in longliners targeting species other than European hake.”

An Yelkouan Shearwater Puffinus yelkouan caught on a Mediterranean longline hook, photograph by Vero Cortés

Reference:

Cortés, V. & González-Solís, J. 2018. Seabird bycatch mitigation trials in artisanal demersal longliners of the Western Mediterranean. PLoS One doi.org/10.1371/journal.pone.0196731.

John Cooper, ACAP Information Officer, 17 May 2018