Search The Database

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.

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.

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.

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 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. Fishermen said that they would be willing to use circle hooks in months with a high probability of bycatch if an economic incentive was provided and there was also public acknowledgement of their efforts. 

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.

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.  Eight 1200 mm long hanging legs were created by placing four polyester strands into the outer holes and the entire system is triggered by a biting fish.  The second DMD, "sock", was designed to cover the fish to hide it from predators through either a net made up of fiberglass mosquito netting or of propylene fiber net.  Shark depredation was significantly higher throughout the surveys than toothed whale depredation, but toothed whales caused more damaged to fish through depredation events. The sock DMD did not affect the catch rates of targeted species or depredation events by either sharks or toothed whales.  These results for the spider DMD were not presented. Trigger rates for the two DMD's were up to 87.3% for the spider and 69.2% for the sock.  The protection rate was as high as 80% for spider but only 15.5% for the sock. Entanglement rates of the DMD's with the fishing gear were low for the spider (3.6%) and higher for the sock (17.8%).  In addition, the use of these DMD's signficantly slowed down the fishing process, and therefore additional work into the design and application of DMD's needs to be explored.

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. When bycatch rates were separated between short (up to 4 km) fleets and long (larger than 4 km) fleets, there was no significant difference in porpoise bycatch in the long fleet but there was in the short fleet. 

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.