The effect of leaded swivel position and light toriline on bird attack rates in Brazilian pelagic longline

Citation
Gianuca D, Peppes FV, Cesar JH, et al (2011) The effect of leaded swivel position and light toriline on bird attack rates in Brazilian pelagic longline. In: Agenda Item 1. ACAP, Guayaquil, Equador, p 18
Abstract

The incidental capture of albatrosses and petrels in pelagic longline fisheries has been well documented (Brothers 1991, Brothers et al. 1999, Baker and Wise 2005, Jimenes et al. 2008), including in Brazilian waters (Neves and Olmos 1998, Bugoni et al. 2008). This incidental captures, as well as in demersal longline, trawl and trow fisheries are the primary responsible for populations declines to threatened levels of most albatrosses and several petrels species (Weimerskirch et al. 1997, Croxall et al. 1998, Lewison and Crowder 2003). The seabirds are attracted to the longline operation by bait and offal discard, and the mortalities occur when lines are being sets and the birds attacks the baited hooks, then becoming hooked and drown.
The use of bird scaring lines (torilines) is a widely used method for reducing theses seabird mortalities, and the efficiency of the toriline should be improved when combined with another mitigation measure. Modifying fishing gear to increase sink rate, and consequently decrease the exposure of baited hooks, is an effective mitigation measure in the demersal longline fisheries (Robertson et al. 2006, Drietrich et al. 2008), and the same should be applied to pelagic longline. Motivated by this premise, Robertson et al. (2010) carried out an experiment assessing the effect of different branch lines configuration and type of bait on sink rate of baited hooks. This author find, in experimental conditions, that initial sink rates of baited hooks are increased by placing leaded swivels close to the hooks.
The aim of this study, conducted during real fishing conditions on board vessels from the Brazilian pelagic longline fleet was: (1) determine the sink rates of baited hooks of branch lines with 60-75 g leaded swivels positioned 2 m from the hook (mitigation design) and 5.5 m from the hooks (preferred by industry), (2) test the performance of the Brazilian light toriline combined with swivels positioned 2 m from the hook for reducing seabird attack rates, and (3) determine and compare the catch rate of target species by the two branch lines configuration.