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.
Bycatch of Australian sea lions in rock lobster and shark gillnet fisheries is a key threat to the species. This report outlines and assesses methods for mitigating bycatch in these fisheries in South Australia. Gear modification was considered in the rock lobster fishery and spatial closures in the shark gillnet fishery. Spikes of different heights were tested to deter sea lions from entering rock lobster pots. Entry success significantly decreased with spikes extending high up into the collar (70 mm + from base) compared to other treatment and control pots.
A parallel haul method was used to determine the effectiveness of a square-mesh escape panel, installed in a bottom trawl, in reducing the bycatch of scup and other finfish bycatch species during the winter. The square-mesh escape panel reduced the average catches of scup by 78% and 79% and catches of black sea bass by 69% and 75% in weight and numbers respectively. The square-mesh escape panel was also effective in reducing catches of sublegal-size scup and black sea bass by 17% and 20% in weight and numbers respectively. However, catches of the target species, longfin sq
Tests with captive, as well as wild, juvenile sandbar sharks were undertaken to determine the effectiveness of electropositive metals in reducing the interactions with longline gear. Electropositive metals deterred feeding in groups of captive juvenile sharks, for a short period of time, and altered the swimming patterns of individuals when food motivation was not present. In the field, electropositive metals placed within 10 cm of the bottom longline hooks reduced the catch of sandbar sharks by around two thirds, compared to the catch on hooks with a placebo.
Tests were conducted on tuna longline fishing vessels in the eastern Pacific Ocean to determine if the use of J (size 4.0 traditional) or circle hooks (sizes 15, 16 and 18) and different bait resulted in differences in the catch rates of target and bycatch species. No significant differences in catch rates of the target species were found between hook types. Significant differences between J and circle hook size 15 and between J and circle hook size 16 were found in the bycatch species group (all species grouped together).
Bycatch reduction device prototypes ("RS_INP") (industrial and artisanal versions) were tested on vessels targeting shrimp in the Gulf of California to compare bycatch-to-shrimp ratios, catch efficiency, drag resistence indicators, fuel consumption rate and selectivity with traditional versions. The industrial version of the prototype reduced bycatch-to-shrimp ratios from 20-50% and shrimp production was not reduced. The artisanal prototype also reduced bycatch-to-shrimp ratios in trawl fishing gear but comparisons were difficult to make between drift gillnets.
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).
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.
Three codends 1. a control, 2. a simplified Nordmore-grid and 3. one with a radial escape section were tested aboard trawl vessels off New South Wales Australia, to determine the effects on the catch of bycatch and target species. The codend with a radial escape section and the simplified Nordmore-grid retained fewer school prawns by weight 11.5% and 4.6% resepectively, compared to the control net. The Nordmore-grid codend caught 50% fewer yellowfin bream than the radial escape section net and 55% fewer than the control net.
Monkfish in the US mid-Atlantic and northeast are targeted through sink gillnets that also capture Atlantic sturgeon. Large-mesh gillnets are required to fish seasonally using tie-downs as part of the Harbor Porpoise Take Reduction Plan. This study looked at the effects of tie-downs (control: 12 meshes x 30.5 cm stretch mesh with four mesh tie-downs, experimental: same, no tie-downs) on Atlantic stureon and marine mammal bycatch.
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.
Two types of tori-lines (tori-line and tori-line light streamer) were tested aboard commercial and research longline vessels in the western North Pacific to determine their effectiveness for seabird avoidance. The tori-line light streamer reduced bait-taking behavior (primarily Laysan albatross) and bycatch of seabirds (primarily Laysan albatross) compared to the tori-line. Therefore, the tori-line light streamer is a good option for avoiding seabird bycatch in this longline fishery.
Experiments were conducted in California to determine the effect of hook type (circle and J-type) on anatomical hook location and subsequent growth and mortality rates of white seabass. Juvenile white seabass were captured with 4/0 offset circle hooks, J-type hooks or a control net. There was a significant difference in hook location between the two types of hooks, with more fish being hooked in the lip with the circle hooks. The majority of mortality occured in fish with hook damage to the esophagus but equal numbers of these fish were caught on the two hook types.
Tests were conducted in the Gulf of Maine to determine the effectivenss of a new Rope Grid in reducing the bycatch of small finfish in the pink shrimp (Pandalus borealis) trawl fishery. The new Rope Grid was constructed by removing two-thrids of the netting surrounding the traditional Nordmore Grid and replacing it with four ropes. This new Rope Grid was tested against the traditional Nordmore Grid during sea trials.
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.
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.
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.
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.