Development of mitigation strategies for inshore fisheries
Introduction
This report provides information about the inshore demersal longline fleet, including fishing practices and mitigation techniques. It also investigates the line sink rates using time-depth recorders. Published 2010.Download the publication
MIT 2009/01 Development of mitigation strategies for inshore fisheries (PDF, 868K)
Background papers
Summary
Port visits were carried out to characterise the inshore bottom longline fishery and discuss seabird interactions and mitigation measures with skippers.
Gear employed by the smaller inshore bottom longline vessels fell into three groups, two of which worked ‘clip on’ gear. These vessels could be further split by target species: those targeting ling or bluenose worked heavier gear with larger hooks than those targeting snapper. A further group of vessels used an automatic lining system. Within these groupings there was further gear variation, most notably due to the combination, size and spacing of weights and floats added to the line.
Mitigation measures currently in use are simple, low tech and perceived by fishers to be effective under the right circumstances. Night-setting and tori lines were the most commonly employed mitigation.
Areas where further work is needed were identified and possible mechanisms for improving mitigation devices and practices were highlighted.
Time-depth recorders (TDRs) were used to measure sink rates of bottom longlines from six vessels. Sink times showed considerable variation and were in the order of 20 – 60 seconds to 5m and a further 30 - 70 seconds to sink another 10m. When vessel speed was considered TDRs had generally sunk to at least 5m once 100m behind the vessel and to 15m depth 200m behind the vessel.
Increasing the amount of weight on the line increased sink rate, most appreciably below 5m. Recommendations to increase sink rate include the use of closely spaced regular sized weights and careful deployment of intermediate surface floats.