Norwegian hook designs improve catch efficiency in the Adriatic bottom longline fishery

Abstract

The present study reports the results of investigations conducted during 2006-2007 of the bottom longline fishery in the Southern Adriatic Sea. The study investigated the rigging of the line and the material used. These investigations specifically compared the catch efficiency of the traditionally used J-shaped hook to hooks with innovative design that are commonly used in the Norwegian costal longline fishery. Fishing trials were conducted using a commercial fishing boat operating in areas with two different bottom morphologies (rocky and muddy bottom). Species abundance of the catches in the two areas were compared. The working hypothesis was that the innovative hooks, characterized by a point toward the line of pull (i.e., Mustad: EZ-Baiter, Wide Gap, Wide Gap Eyed), perform better than the traditional hook whose point is parallel to the line of pull (i.e., Mustad: Round Bend Sea). A variant of the traditional J-shaped hook, characterized by an offset-angle (Mustad: Kirby) was also tested. The elasmobranch species (Squalus acanthias 26 % and Raja clavata 13 %) were the most abundant species on rocky bottom, followed by Pagrus pagrus (13 %). These species were hardly present on muddy bottoms where Merluccius merluccius dominated (48 %). The EZ-Baiter and Wide Gap hooks had the highest catch efficiency in terms of biomass of fish caught. They also gave the highest income. The Wide Gap Eyed hook performed the worst as it was not suitable for the baiting operations. The EZ-Baiter and Wide Gap hook were more efficient than the Round Bend Sea hook on both bottom morphologies. The results suggest that the EZ-Baiter hook performed better than Wide Gap hook on rocky bottom, while the Wide Gap performed better on muddy bottom. The Kirby hook did not improve the catch efficiency compared to the Round Bend Sea. It was concluded that introduction of the Norwegian hook designs could improve the efficiency and income of the Italian bottom longline fishery without large investments.