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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. 

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. 

Fishery observer data from Japanese longline vessels targeting southern bluefin tuna, was used to determine if there were differences in seabird avoidance between two types ("WCPFC type" and "Light type") of tori-lines.  There was no signficant difference between the two tori-lines for either the nominal catch rates of albatross or the per-capita catch rates.  Therefore both types of tori-line have similar seabird avoidance effects and the "Light type" may be more practical in areas with difficult weather and oceanic conditions.

Four parts of the tori-pole were tested for their effectiveness in reducing the incidental catch of albatross in the Japanese southern bluefin tuna longline fishery.  Observer data were used to test 1. bird line material, 2. streamer material, 3. bird line length and 4. pole height above sea surface.  The effectiveness of tori-poles in reducing albatross interactions increased with a longer bird line, but there was no difference in the effectiveness between the different bird line materials, type of streamer material or pole height above the sea surface.  

The use of blue-dyed bait (both squid and fish) as a means to reduce seabird interactions with pelagic longline fishing gear was tested during Japanese longline fishery survey cruises off South Africa in the Southern Ocean.  The incidental catch of seabirds was lower for both blue-dyed squid and fish baits compared to non-dyed baits. The catch per unit effort (CPUE) of albatrosses decreased when blue-dyed squid and fish baits were used during all years of the study.  The CPUE of petrels was lower during two years when blue-dyed bait was used.  The CPUE of the target southern bluefin tuna was also reduced during all three years when blue-dyed bait was used, except in 2003 when blue-dyed fish bait was used.  A second experiment, testing the use of tori lines and blue-dyed bait (both types) resulted in no interactions with seabirds.

The use of blue-dyed bait (both squid and fish) as a means to reduce seabird interactions with pelagic longline fishing gear was tested during Japanese longline fishery survey cruises off South Africa in the Southern Ocean.  The incidental catch of seabirds was lower for both blue-dyed squid and fish baits compared to non-dyed baits. The catch per unit effort (CPUE) of albatrosses decreased when blue-dyed squid and fish baits were used during all years of the study.  The CPUE of petrels was lower during two years when blue-dyed bait was used.  The CPUE of the target southern bluefin tuna was also reduced during all three years when blue-dyed bait was used, except in 2003 when blue-dyed fish bait was used.  A second experiment, testing the use of tori lines and blue-dyed bait (both types) resulted in no interactions with seabirds.

Hybrid streamer lines with weighted and unweighted branch lines were tested for their effectiveness in reducing seabird interactions with longline gear during the 2010 tuna joint venture fishery in the South African EEZ.  Weighted branch lines with hybrid streamer lines dramatically reduced seabird attacks, secondary attacks and mortalities and had a minimal effect on fish catch.  Bird mortalities on weighted branch lines were reduced by 86% compared to unweighted branch lines.  Primary attack rates were four times lower on weighted branch lines. In addition, no seabird attacks occurred between two streamer lines, suggesting that streamer lines flown in pairs are highly effective at preventing attacks.  The average tuna catch was almost the same on both types of branch lines, but weighted branch lines tangled on themselves three times more often than unweighted branch lines.

Tests were conducted aboard pelagic longline vessels fishing off the coast of Uruguay, to determine the effect of hook type (circle hook vs J-hook) on the catch and length composition of target and non-target species.  Both American and Spanish style longlines were used during these experiments.  American style longlines consist of a 3.6 mm polyamide monofilament mainline with polyamide or polyester buoys lines 9-36 m long.  Spanish style longlines consist of 5-mm polyethlene multifilament mainline with buoy lines (similar in thickness and material to mainline) 12-18 m long.  On the American style longlines, albacore tuna and shortfin mako shark catches were significantly higher on circle vs J-hooks. Catches of other tunas and sharks (blue and porbeagle) were also higher on circle hooks, but were not significantly higher.  There was no significant difference in the catches of seabirds or sea turtles between the two types of hooks on the American style longlines.  On the Spanish style longlines, albacore tuna catches were also significantly higher on circle compared to J-hooks, and there was a significant decrease in pelagic stingray catches on circle hooks.  No significant difference in the catch rates of seabirds or sea turtles was seen between the two types of hooks on this type of longline.  There was no significant difference in the length distribution for any species between the two hook types on either type of longline.  There were also no significant differences between hook types for any hooking location of incidentally caught sea turtles.

A modified longline system with a net sleeve and weight on the secondary vertical line was tested in the Chilean Patagonian toothfish fishery. A net sleeve that deploys to cover the fish/hook when hauled and a weight were attached to the vertical hook line. The net sleeve significantly reduced depredation of fish by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus). The weighted line also was able to reduce seabird bycatch deaths to zero.  

The Patagonian toothfish longline fishery in the Southwest Atlantic suffers from depredation of fish by sperm whales and high bycatch rates of seabirds. This study assessed depredation and seabird bycatch using a modified longline with an "umbrella" net sleeve system with stones for faster sinking. The "umbrella-and-stones" system was effective for preventing bycatch and appeared to restrict depredation, but catches were significantly reduced.