Mitigation Fact Sheets
This series of 14 Seabird Bycatch Mitigation Factsheets describe the range of potential mitigation measures available to reduce seabird bycatch in longline and trawl fisheries. The sheets assess the effectiveness of each measure, highlight their limitations and strengths, and make best practice recommendations for their effective adoption. They are designed to help decision-makers choose the most appropriate measures for their longline and trawl fisheries.
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This series of 14 Seabird Bycatch Mitigation Factsheets describes the range of potential mitigation measures available to reduce seabird bycatch in longline and trawl fisheries.
Streamer lines are the most commonly prescribed mitigation measures for longline fisheries and are regarded as one of the most effective known mitigation measures (a primary measure). Streamer lines are cheap, simple to use and do not require modification of the fishing gear.
Line weighting is an essential component of seabird bycatch mitigation strategies, being one of the more effective known mitigation measures (a primary measure). Best practice weighting regimes should result in rapid initial line sink rates that will reduce the likelihood of seabird bycatch.
Line weighting is an essential component of seabird bycatch mitigation strategies, being one of the most effective known mitigation measures (a primary measure). Best practice weighting regimes should result in rapid initial line sink rates that will reduce the likelihood of seabird bycatch. Integrated weight lines with lead beads in the core were developed to address this problem.
Seabirds are vulnerable to mortality on longline hooks during the short period between hooks leaving the vessel and sinking beyond the bird's diving range. The Chilean System was developed primarily to combat the problem of depredation by cetaceans, however, the configuration of the gear leads to very high initial hook sink rates, which results in near zero seabird bycatch rates.
Night-setting is one of the few mitigation measures that is equally applicable to both demersal and pelagic longline fisheries.
Seabirds are at greatest risk of becoming hooked and drowned when baited hooks are at, or within a few metres of, the surface. In theory, setting hooks below the surface of the water should greatly reduce the likelihood of catching seabirds. It should be noted that this is currently a secondary measure, as underwater setting cannot be used in isolation to reduce seabird bycatch.
Streamer lines are the most commonly prescribed seabird bycatch mitigation measures for longline fisheries. However, recent evidence shows that they are not fully effective unless combined with other mitigation measures. To reduce bycatch to negligible levels they must be used in combination with branchline weighting and night setting.
Line weighting is arguably the most effective known mitigation measure (a primary measure) and has been demonstrated to be a key component to all successful reductions in seabird bycatch in pelagic longline fisheries. It is recommended that it be used in combination with streamer lines and night setting.
Side-setting appears to be effective in the waters of the North Pacific where it was developed. The ability to generalise its use across other oceans, with a higher diversity of seabirds with greater diving capabilities and more demanding sea conditions, remains untested.
Blue-dyed bait is a measure under development and, while there are some promising results, there is some uncertainty about its long-term effectiveness at reducing seabird bycatch and the practicality of widespread application. Current evidence suggests that blue-dyed squid is effective but dyed fish bait is not.
This Fact-sheet covers technical issues associated with the use of bait casters and line shooters from the perspective of their use to improving fishing efficiency and ensuring that seabird bycatch is not increased by their use.
Seabirds are attracted to longliners during hauling to feed on discards, offal and spent bait. Birds can easily become hooked, in the bill, foot or wing, as the line returns to the surface or swallow hooks left in discards or bait. These interactions are rarely lethal at the time but the injuries sustained could have serious implications for the long-term survival of the individuals concerned.
In recent years, dedicated seabird observers on trawl vessels have identified significant bycatch problems. These fall into two categories, net entanglement (Fact-sheet 14) and collisions with cables, predominantly those used to tow the net (warp strikes), but also net monitoring equipment.
In recent years, dedicated seabird observers on trawl vessels have identified significant bycatch problems. These fall into two categories, collisions with the cables used to tow the net (Warp strike, Fact-sheet 13) and net entanglement.
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