Effects of gear modifications in a North Atlantic pelagic longline fishery: A multiyear study

PLoS One. 2023 Oct 19;18(10):e0292727. doi: 10.1371/journal.pone.0292727. eCollection 2023.

Abstract

The threat of population declines caused by pelagic longline fisheries in the Atlantic has increased the concern to find strategies that minimize the bycatch and mortality of non-target marine animals. Gear modification, such as the use of circle hooks instead of conventional J-hooks, has been identified as an effective bycatch reduction strategy in different pelagic longline fisheries around the world. This study aimed to verify the effectiveness of the use of circle hooks by quantifying catch rates, relative size selectivity, and anatomical hooking position for the most common target species (swordfish, Xiphias gladius, and blue shark, Prionace glauca), and some bycatch species (loggerhead sea turtles, Caretta caretta, and shortfin mako, Isurus oxyrinchus) caught by the Azorean longline fishing fleet. The trial was conducted for five consecutive years (2000-2004) using eight different types of hooks. In general, the blue shark catches using circle hooks were significantly higher compared to J (Mustad 9/0). The circle hooks also showed high probabilities of catching juvenile blue sharks. Conversely, the circle hooks were efficient in reducing the loggerhead sea turtle bycatch and were related to fewer catches of small sea turtle individuals. The use of circle hooks was also associated with reduced swordfish catches compared to J (Mustad 9/0), and the effect of hook types on length at capture was only significant for Circle (L. & P. 18/0-CLP18) and Ringed Tuna (RT). No significant differences were observed comparing hook type to either catch rates or size selectivity for shortfin mako. Additionally, circle hooks were more likely to lodge in the mouth than in deeper anatomical positions, when compared to J (Mustad 9/0), for the four species analysed. The present study demonstrated that the use of circle hooks could mitigate the impact of the pelagic longline fisheries in the Azores by decreasing the bycatch of sea turtles and reducing animal injuries caused by deep hooking.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Conservation of Natural Resources
  • Fisheries
  • Humans
  • Sharks*
  • Tuna
  • Turtles*

Grants and funding

The US National Marine Fisheries Service (NOAA) funded the contracts to Alan B. Bolten and Karen A. Bjorndal at the Archie Carr Center for Sea Turtle Research, University of Florida: Phase 1 (2000, NA96FE0393), Phase 2 (2001, NA16FM1378), Phase 3 (2002, NA16FM2589), Phase 4 (2003, NA03NMF4540204), Phase 5 (2004, NA04NMF4540318). This work was also conducted within the framework of the project COSTA, Consolidating Sea Turtle conservation in the Azores (US Fish and Wildlife Service, Marine Turtle Conservation Fund, n° F15AP00577, F16AP00626, F17AP00403, F18AP00321; Archie Carr Center for Sea Turtle Research through funds from Disney Conservation Fund; Regional Directorate for Fisheries of the Regional Government of the Azores). FDL was supported by the PO AÇORES 2020 (ACORES-01-0145-FEDER-000121 “Ocean Biometrics) funding program. FV was supported by the Investigator Programme of the Fundação para a Cıência e Tecnologia (FCT, CEECIND/03469/2017, CEECIND/03426/2020). This work also received national funds through the FCT – Foundation for Science and Technology, I.P., under the project UIDB/05634/2020 and UIDP/05634/2020 and through the Regional Government of the Azores through the initiative to support the Research Centers of the University of the Azores and through the project M1.1.A/REEQ.CIENTÍFICO UI&D/2021/010. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.