Search The Database

An excluder grate (grid) was tested in the silver hake trawl fishery in Massachusetts Bay to determine it's effectiveness in reducing spiny dogfish bycatch.  The effects of color (white or black), angle and direction of the 50 mm spaced grids were investigated through video observations and data collection.  The number of spiny dogfish caught in trawls with the excluder grate were greatly reduced for all gear configurations, while the number of target species caught remained within typical commercial quantities.  Over 88% of spiny dogfish were excluded by the grate regardless of color or gear configuration.  There were no observed differences in the behavior of spiny dogfish between gear configurations or grate colors.

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.

Analyses of the Hawaiian pelagic longline fishery were conducted to determine what factors, including hook type (J or circle) and location (sea mount v open ocean), have impacted the catch of both target and bycatch species.   Standardized catch rates for all tuna species as well as for blue and oceanic whitetip sharks were significantly higher when the wider circle hooks were used.  However, shortbill spearfish and striped marlin catch were significantly lower when circle hooks were used.  No differences in catch rates between the two hook types were seen for bigeye thresher sharks or swordfish.  The average swordfish lengths were significantly larger when circle hooks were used, while average lengths for bigeye and skipjack tunas were significantly smaller.  There was no difference in the average length between the two hooks types for yellowfin or albacore tunas, spearfish or marlins. In addition, the change from J hooks to circle was likely a factor in decling sea turtle bycatch rates. 

Experiments were conducted aboard Korean pelagic longline vessels to determine if there were differences in the catch rates of target (tuna and billfish) and bycatch (sharks and other bony fish) species between 3 types of hooks; 4.0 traditional tuna hook (J-4), size 15 circle hook (C15) and size 18 circle hook (C18).  Within the target group significant differences between catch rates were only found between the J-4 and C18 hooks.  In the bycatch species group, significant differences were found between J4 and C15 and between J4 and C18.  Overall, the large circle hook (C18) had the lowest catch rates for tunas and other fish, while small circle hooks (C15) had the lowest catch rates for billfish and sharks.  Any differences in the length of fish caught by the individual hooks were minimal.

Two types of excluder devices, one with exclusion bars and one with exclusion rings, were fitted at the entrance to fyke nets to determine their efficiency in reducing turtle bycatch.  In addition, the efficacy of an escape chimney, compared to a net with a large hole, was tested.  The exclusion device with bars across the net significantly reduced turtle catch rates.  Fish catch rates were not impacted by either excluder device.  All turtles were able to escape through the escape chimney, while the majority of fish (88%) were retained.  In comparison, 60% of turtles and 77% of fish were able to escape through the a large hole in the net.  The escape chimney was therefore the most effective at avoiding turtle bycatch while retaining fish.

This Handbook aims to:detail the design, operation and use of hoppers (back deck water tanks/sorting devices) in trawl fisheries across Australia;enable the sharing of industry knowledge on hoppers amongst fishers from all Australian trawl fisheries;provide readily accessible information to fishers on the use and application of hoppers;>facilitate the broader adoption among trawl fisheries of best practice use of hoppers. In fisheries where hoppers are not yet widely used but may be useful, help stimulate the development and uptake of new and suitable hopper designs; and provide a tool to inform and educate the general community, fisheries and environmental managers about the initiatives developed and adopted by Australian trawl fisheries to reduce the impacts of trawling on the aquatic environment, and to work towards achieving sustainable operating practices and improved economic efficiency.This handbook is primarily a technical handbook for fishers. It is also however, a useful resource for others interested in the environmental management of Australian trawl fisheries.