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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)

A structured literature review of 103 papers was conducted to characterize trends in shark bycatch research.  Gear modifications, such as hook size/type and net size, were the most commonly evaluated technique to reduce shark bycatch.  Early studies tended to focus on trawl fisheries while more current studies focus on longline fisheries, particularly tuna fisheries. Overall, longline fishery studies made up the majority (44.6%) of published papers and typically were aimed at reducing bycatch.  Later studies also tended to explore potential solutions to bycatch issues.

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.

During the period 1998-2001, a survey to study the incidence of the drifting longline fishery on shark populations was carried out in the eastern Mediterranean Sea. A total of 8 different pelagic shark species were recorded in the catches of the Greek swordfish and albacore longline fisheries. Among them, the blue shark, Prionace glauca, was the most common species in the catches while the bigeyed sixgill shark, Hexanchus nakamurai, was reported for the first time in the area.

Large pelagic sharks are caught incidentally in the swordfish and tuna fisheries of the Mediterranean Sea. In our study, twelve shark species were documented as bycatch over three years from 1998 to 2000. Blue shark (Prionace glauca) was the predominant species in all gears and areas examined. Shortfin mako (Isurus oxyrinchus), common thresher shark (Alopias vulpinus), and tope shark (Galeorhinus galeus) were the next most abundant shark species found in more than half of the areas sampled. Catch composition varied both in the areas and gears investigated.

A study was conducted from 1998 to 2001 on blue shark (Prionace glauca) by-catch of the Italian and Greek surface drifting swordfish long-line fisheries in the Mediterranean Sea. The focus was on examining whether catches are related to some environmental, spatial, temporal or operational parameters and to what extent, applying generalized linear model (GLM) approaches. Spatial and temporal factors were the most influential regarding blue shark distribution and abundance, with a considerable interaction between them; the modeled environmental factors were of minor importance.

Blue sharks (Prionace glauca) and oilfish (Ruvettus pretiosus) are frequently caught incidentally in the swordfish surface drifting longline fishery of the eastern Mediterranean Sea. An information theoretic generalized additive model approach, modelling separately: (1) the probability of making a catch; and (2) the positive catch rates, suggested the presence of intra-annual variations in their abundance and revealed interesting associations with some environmental features. Blue sharks were more frequently encountered during late summer in cool water masses.

A ten year study in the Aegean Sea, divided into two sub-periods (1995-2000; 2003-2006) examined bottom trawl fishery data for chondrichthyan fishes. A total of 30 different species were caught making up 14.3% of the total catch in weight and 2.2% by number. A significant decrease in the chondrichthan species richness  and abundance was observed. More than 90% (by number) of individuals were discarded at sea. 

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.

Three modified hoop-net designs were tested in the Gasconade and Osage Rivers of Missouri to determine their ability to reduce turtle bycatch without reducing the capture of targeted catfish.  The three designs included an excluder net with tightly spread mesh and a sewn in ring, a chimney-set design and a loose-weave design.  The chimney-net design was the only one that significantly reduced turtle bycatch (84%), while not decreasing the number of average size of flathead catfish.

Wisconsin-type fyke nets were modified in an effort to reduce the incidental bycatch of turtles, without significantly reducing the catch of targeted fish species.  The tests were conducted in three rivers (Missouri, Mississippi and Gasconade) in Missouri.  The net was modified by adding four lines in the vertical gap of the net and this modification was successful at significantly reducing turtle bycatch with no significant decrease in the quantity of fish caught.

An experimental leader design was tested on pound nets in the Chesapeake Bay in 2004 and 2005 to determine their effectiveness in reducing the incidental catches of sea turtles.  The experimental design consisted of replacing the top two thirds of the traditional mesh panel leader with vertical ropes spaced 61 cm apart. During the study, 21 sea turtles interacted with the control net, while only 1 interaction with the experimental net occurred, which was a significant difference.

An experimental release panel was installed in purse seine nets to determine their ability to release both silky sharks and non-target finfish.  The release panels (5.5 m wide, extending down from the corkline for 11 m) were installed in a portion of the net that forms a "pocket" toward the end of net retrieval.  Dive surveys previously reported that silky sharks tend to segregate and collect in this section of the net.  The release panel was tested during seven purse seine sets, but only two silky sharks (out of 105) exited through this panel.

Pelagic stingrays (Pteroplatytrygon violacea) are a common bycatch species in the Mediterranean pelagic longline swordfish fishery. Experimental trials took place in the central Mediterranean Sea from 2005 to 2007 to investigate the importance of bait size, presence and type of light attractors, and hook size and shape on pelagic stingrays. Bait size and light attractants did not have a significant effect on stingray catch rate. Larger J-hooks reduced the stingray capture rate. 16/0 circle hooks had a significantly lower number of stingrays captured than J-hooks, up to 80%

The biting behaviour of the loggerhead sea turtle, Caretta caretta, a high bycatch species by longling fishing gear, was studied on 30 wild specimens held temporarily at rescue centers. Chemicals from squid baits elicited significantly more biting behaviour than those from mackerel baits. 

The proven effectiveness of a bycatch reduction technology (BRT) does not guarantee its adoption by fishermen. This case study evaluated the willingness of Sicilian longline fishermen to use relatively large circle hooks (16/0) as a BRT for loggerhead sea turtles (Caretta caretta). Fishermen tested circle hooks with their fishing vessels and their own commercial fishing gear, and their opinnions before and after trials at sea were recorded.

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.

Modified trap openings were developed to reduce juvenile rockfish bycatch in British Columbia spot prawn traps. Smaller trap openings had no impact on rockfish or other non-target species bycatch. A novel bent tunnel opening resulted in no rockfish bycatch and the exclusion of other fish species. However, all trap modifications resulted in reductions in prawn catch rates. Large prawns were also excluded more than small prawns.  

Two types of depredation mitigation devices (DMD) were designed and tested aboard pelagic longline fishing vessels targeting tunas and swordfish off the Seychelles.  The DMD's were designed to reduce the damage and removal of fish from the fishing gear by predators such as toothed whales and sharks. The first DMD was termed "spider" and was made up of a 100 mm diameter plastic disc with sixteen holes in its outer range and a 37 mm diameter central hole.

Fisheries observers and skippers tested the effectiveness of the Dolphin Dissuasive Device (DDD) as a bycatch mitigation tool for porpoises and dolphins. This study was conducted aboard fishing vessels in the Cornish over-12m static net sector fishery in the waters of Southwest England. DDD's were placed at the end nets. The DDD's caught significantly fewer porpoises but no significant difference in dolphin bycatch was observed.