Do leaded swivels close to hooks affect the catch rate of target species in pelagic longline? A preliminary study of southern Brazilian fleet.

Citation
Gianuca D, Peppes FV, Cesar JH, et al (2013) Do leaded swivels close to hooks affect the catch rate of target species in pelagic longline? A preliminary study of southern Brazilian fleet. In: Agenda Item 2. ACAP, La Rochelle, France, 1-3 May, p 12
Abstract

This paper is also published by ICCAT as SCRS/2012/099

The interaction between foraging seabirds and baited hooks during setting operations is responsible for high levels of albatross and petrel mortality, as well as reducing the fishing efficiency of the longline due to bait loss. Experiments indicate that 60 g placed no more than 3 m from the hook is likely to achieve optimal sink rates to reduce seabird interactions. However, some fishermen believe that alterations to traditional gear decrease the catch rate of target species, especially tuna. Over nine cruises, 92 sets and 87,098 hooks were observed to compare the catch rate of target species on lines with leaded swivels placed at 2 m and 5.5 m from the hooks. The catch of 3,868 fish from 16 taxa was recorded.

For the main target species, the difference between the total CPUE of branch lines set with swivels placed at 2 m and 5.5 m from the hook were equal or less than one fish per 1,000 hooks, except for T. albacares for which the CPUE using 2 m leaders was around three fish per 1,000 hooks higher than when using 5.5 m leaders. The Generalized Linear Model analysis shows that there is no significant difference between the effects of 2 m or 5.5 m leaders on the catch rate of target species. The results of the present study support a growing body of evidence that placing line weights closer to the hooks does not negatively affect the catch rate of target species in pelagic longline.

Recommendations
1. There is no evidence that leaded swivels positioned close to hooks (e.g. about 2 m) reduce the catch rate of target species in southern Brazilian pelagic longline fisheries.
2. More studies on the potential effects of line weighting regimes on catches of targeting species should be conducted in other pelagic longline fleets in order to understand this issue globally.