Mitigating seabird bycatch during hauling by pelagic longline vessels

Area of Science:

• Marine Biology
• Fisheries Science
• Conservation Biology

Background:

• Longline fisheries pose a significant threat to seabird populations globally.
• The Hawaii longline swordfish fishery has reduced seabird captures during setting, but 75% now occur during hauling.
• Understanding factors influencing haul captures is crucial for effective mitigation.

Purpose of the Study:

• To identify key factors affecting seabird bycatch rates during the hauling phase of the Hawaii longline swordfish fishery.
• To inform future mitigation strategies to reduce seabird captures during longline hauling.

Main Methods:

• Utilized observer data from the Hawaii longline swordfish fishery.
• Employed a generalized additive regression model with mixed effects to analyze catch rates.
• Assessed the significance of factors including albatross density, leader length, and year on haul catch rates.

Main Results:

• Albatross density during hauling and leader length were the most significant factors influencing haul catch rates.
• Increased albatross density and longer leaders were associated with higher standardized haul catch rates.
• A significant increasing temporal trend in catch rates was observed, potentially linked to increased local albatross abundance.

Conclusions:

• Reducing seabird access to hooks during branchline retrieval is critical for haul mitigation.
• Shorter leaders and heavier swivels are recommended to decrease bycatch.
• Mitigation efforts would disproportionately benefit Laysan albatrosses and offer opportunities to nearly eliminate local seabird bycatch.