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Summary: Bird-scaring lines, underwater setting and line shooters all reduced the incidental capture of seabirds, with bird-scaring lines being the most effective. These mitigation measures also reduced bait loss and increased the catch rates of target species.

Summary: The use of light torilines (made with nylon monofilament branch lines and streamers made from other light material) on pelagic longlines reduced the incidental capture of seabirds by 64%. The capture of target species, including swordfish and blue sharks, was increased by 32% and 15.1% respectively when light torilines were used.

Summary:

In northern hemisphere trawl fisheries, little is known about the extent of cable strike seabird mortality or techniques to mitigate it. We compared the rate of heavy seabird strikes by third-wire cables and warps, using three mitigation measures compared to a control of no mitigation. Experiments were conducted aboard two catcher-processor vessels targeting walleye pollock (Theragra chalcogramma) in the eastern Bering Sea: one that rendered offal into fish meal and fish oil (Vessel R) and one that minced offal prior to discharge (Vessel M). More birds attended Vessel M, but the rate of seabird cable strikes was higher on Vessel R due to the greater aerial extent of its cables. Streamer lines significantly reduced heavy seabird strikes by both cable types regardless of discharge characteristics. Reducing the aerial extent of third wires also reduced third-wire strike rates, but this method was less effective than streamer lines. Warp booms designed to divert seabirds from warps failed to reduce seabird warp strikes, but this technique could be improved. These results show for the first time that seabird strikes with modern third-wire trawl sonar cable systems can be reduced through mitigation or gear modification and that warp strikes can be mitigated with techniques similar to those found successful in southern hemisphere fisheries. 

Summary:

Experiments using squid dyed with Brilliant Blue dye were undertaken aboard tuna longline vessels off East Cape, New Zealand, to determine the dyed baits ability to reduce the incidental capture of seabirds.  Significant differences in catch rates between bait types were observed when all species were combined and for seabird mortality, but the authors identified problems with the statistical design, which make the results not very convincing and therefore inconclusive.  In addition, at sea observations of seabird behavior during the deployment of the longline gear, suggest the dye did not effectively camouflage the bait.  Instead the authors suggest seabirds may reject the blue dyed bait due to its color after either seeing it or investigating it through pecking and/or eating.

Summary:

The use of blue-dyed squid bait on pelagic longlines was tested to determine its ability to reduce both surface and subsurface interactions with seabirds.  In addition, blue-dyed fish bait was tested for its ability to reduce seabird strikes at the surface. Blue-dyed squid bait reduced seabird interactions by 68% compared to non-dyed squid bait when the longline was submerged, and only 3-8% of the blue-dyed squid bait were struck at the surface, compared to 75-98% of non-dyed squid bait.  Around 48% of blue-dyed fish bait was struck at the surface during the first two days of the trial, and 90% were struck over the last three days of the trial.

Summary:

Two types of streamer lines, a "light" with short streamers and a "hybrid" with mixed long and short streamers, were tested in the Japanese joint venture tuna fishery that operates in the South African EEZ.  The authors also looked at differences in catch rates between weighted and unweighted branchlines. The mean total attack rate was similar for each design but diving birds attacked further astern in response to both tori line types compared to surface foraging birds.  The "hybrid" line did not allow attacks by divers within 50 m but the "light" line allowed attacks through out all distances astern monitored. Surface foragers did not attack within 0-25 m of the "hybrid" line or at distances greater than 100 m of the "light" line.  Catch rates of birds were higher on unweighted compared to weighted branchlines.  Catch rates of fish were not significantly different between the two branchline types at night or during the dawn.

Summary:

Two types of streamer lines, a "light" with short streamers and a "hybrid" with mixed long and short streamers, were tested in the Japanese joint venture tuna fishery that operates in the South African EEZ.  The authors also looked at differences in catch rates between weighted and unweighted branchlines. The mean total attack rate was similar for each design but diving birds attacked further astern in response to both tori line types compared to surface foraging birds.  The "hybrid" line did not allow attacks by divers within 50 m but the "light" line allowed attacks through out all distances astern monitored. Surface foragers did not attack within 0-25 m of the "hybrid" line or at distances greater than 100 m of the "light" line.  Catch rates of birds were higher on unweighted compared to weighted branchlines.  Catch rates of fish were not significantly different between the two branchline types at night or during the dawn.

Summary:

Differences in sink rates of baited hooks attached to mainelines and set under varying degrees of tension, were tested aboard pelagic longlines off eastern Australia.  Three mainline configurations were tested 1. surface set tight with no slackness astern, 2. surface set loose with two seconds of slack astern and 3. deep set loose with seven seconds of slack astern.  Baited hooks on tight mainlines reached depth almost twice as quickly (5.8 s) compared to those on the two loose mainline configurations (9.9 s and 11 s).  The loose configurations therefore allows increased availability of baited hooks to seabirds.  It was hypothesized that the propeller turbulance slowed the sink rates. The authors suggest that unless the mainline can be set to avoid propeller turbulence, mainline deployed with a line shooter (to reduce sea bird interactions) for deep setting should not be accepted as an effective detterent to seabirds.

Summary:

Experiments were conducted aboard pelagic longline vessels off the east coast of Australia to determine the effects of different bait species (blue mackerel, yellow tail mackerel and squid), live and dead bait, weight of leaded swivels (60 g, 100 g and 160 g) and leader length (2 m, 3 m and 4 m distances between leaded swivel and hook) on the sink rates of hooks.  Live bait sank more slowly than dead bait, increasing the exposure of hooks to seabirds but the sink rates of individual live bait species were very variable.  With respect to dead bait, those on the 160 g leaded swivel with a distance of 2 m leader length had the fastest sink rate, while the 60 g swivel on the 4 m leader length had the slowest.  Overall, small changes to the weight of leaded swivels and the length of the leader are not likely to subtantial reductions in seabird mortality.

Summary:

Four types of tori-lines (long streamer, light streamer, hybrid streamer and modified light streamer) were tested for their ability to reduce seabird bycatch on commercial longline fishing vessels in the north Pacific Ocean.  Two experiments were undertaken 1) determine the frequency of bycatch of Laysan albatross for each tori-line and 2) determine mean rate of attacks for tori-lines.  In experiement 1, the mean number of seabirds appearing and the catch per unit effort (for seabirds) was not statistically different between the four tori-lines.  In experiment 2, seabird attack rates (Laysan albatross and shearwater) were not statistically different nor were bycatch rates of Laysan albatross among the four tori-line types.