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MIT2023-07A Novel seabird bycatch mitigation for floated demersal longline fisheries (PDF, 1,616K)

Summary

The introduction of mitigation standards and subsequent changes to regulations require fishers to sink demersal longlines to a depth of five metres within the aerial extent of the tori line. Previous experimental trials without hooks identified gear modifications to reduce sink times to depth for ‘floating’ demersal longlines set with multiple floats attached between widely spaced weights. In combination with tori line improvements these modifications were shown to meet regulations.

This project tested compliant gear configurations in a fishing context to examine their practicality, workability, and influence on catch rates compared to control gear set as per the skipper’s normal practice. Deployment of modified floats with a seven-metre rope between the float and the longline and a small weight on the longline was successful. Increased line weight size and reduced line weight spacing were also employed. These measures resulted in reduced times to depth and, in combination with tori lines providing coverage up to 90 m astern, met the regulated depth of five metres at the end of the tori line.

The use of more weight and modified floats resulted in a marginal increase in work load for the crew, but did not hinder setting or hauling operations. Modified floats performed well, did not frequently tangle with the longline or tori line, and proved simple to set and retrieve.

Poor and patchy catch rates precluded firm conclusions on the influence of experimental gear configurations. However, if necessary, options were identified to more precisely control the height hooks fish above the seabed whilst meeting regulations.

Publication information

Goad, D. 2024. Novel seabird bycatch mitigation for floated demersal longline fisheries. MIT2023-07A final report prepared by Vita Maris for the New Zealand Department of Conservation, Wellington. 22p.