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40 trial tows investigated the potential of excluder grids in mitigating bycatch in trawl fisheries in the Northern Levant Sea. Tested gear configurations included a flexible grid with 50mm bar spacing and a rigid grid with 95mm spacing within the trawl extension. The excluder grids significantly reduced bycatch of several elasmobranch species including the velvet-belly lanternshark (Etmopterus spinax) and the blackmouth catshark (Galeus melastomus), as well as some species of bony fish. Sea turtle bycatch also appeared to be reduced although in general, sea turtle bycatch during the trials was low (two individuals in the control gear). However, catch performance of target shrimp species (Aristaeomorpha foliacea and Aristeus antennatus) were also reduced in the gear equipped with BRDs, indicating a trade-off. 

Guarding nets may potentially help mitigate bycatch in trammel net fisheries through the attachment of a supplementary netting panel, typically 10–30 cm high and made of materials that resist entanglement, between the footrope and the main trammel net. Acting as a physical barrier, the panel prevents benthic organisms from becoming trapped. In a small-scale prawn trammel net fishery in Thailand, biomass of non-target organisms was significantly reduced while maintaining target species volume compared with conventional nets. However, the volume of commercial bycatch species was also significantly reduced, which may create a barrier to adoption in small-scale fisheries.  

Study authors conducted a comprehensive review of technical bycatch mitigation measures for sharks for all major commercial fishing gears. Only one technique (changing fishing gear), received a “beneficial” Conservation Evidence (CE) rating (indicating a high level of certainty and effectiveness, and low probability of harm), demonstrating that no single bycatch reduction measure can be applied to all species, fishing gear, and regions. However, many different types of BRTs were rated as “likely to be beneficial”, although additional testing or information is needed. Furthermore, fishery-specific characteristics may mean that BRTs reported as effective in one area or fishery may not be as effective elsewhere. Even when a measure has been rated as being potentially beneficial, implementation in commercial fisheries may still not be feasible due to technical complexities, cost, safety issues, pollution issues, a negative impact on target catch (e.g., electropositive metals), or animal harm/welfare issues. Future research priorities should include development and incorporation of necromones (natural compounds released by decomposing organisms) into commercially viable artificial baits, production of active electrical repellents at scale to encourage uptake, investigating the impact of removal of light-sticks from longlines on shark catch rates, and refinement of circle hook design to reduce shark catch rates. 

Elasmobranch bycatch significantly decreased in bottom-set gillnets in the Gulf of California using orange LEDs, ultraviolet LEDs, green LEDs, and green glow sticks, with orange LEDs being the most effective at reducing bycatch. As a whole, catch of bony fish was not affected by illumination, although responses were taxonomic-specific.  

Three types of acoustic deterrent devices were tested in the Icelandic cod gillnet fishery:  Fishtek Banana pingers, Porpoise ALert devices (PAL), and wideband PAL (wPAL) with a modified pinger signal (PAL device emitting a wideband pinger signal with a frequency range of 20 – 160 kHz and signal duration of 0.3 s (every 4–30 s) with the same source level at 145 db and maximum depth (320 m)). Banana pingers and PALs did not demonstrate any reduction of bycatch of marine mammals, while the wPAL-equipped nets had no bycatch during the trial. Fish catch and overall commercial value was significantly reduced in gillnets equipped with banana pingers and PALs.  

Hook appendages (16/0 size circle hooks modified with stiff wire extending from their shank at either a 22° or 45° angle in relation to the hooks’ offset and non-offset sides) have the potential to reduce yelloweye rockfish and Pacific spiny dogfish bycatch in the U.S. West Coast Pacific halibut longline fishery. Hooks with a 45° appendage on the non-offset side caught significantly fewer rockfish, Pacific spiny dogfish, and smaller Pacific halibut without impacting legal-sized halibut catch. The appendages change the shape of the hook and greatly reduce the available opening for a fish’s mouth to engage with the hook, which may make it more difficult for fishes with vertical mouths (e.g., dogfish and rockfishes) than fish with horizontal mouths (e.g., halibut) to be caught using this method.  

The study examined individual and cumulative bycatch during the first five years of a fisher engagement program in the tuna drift gillnet fishery in Pakistan, where fishers co-developed a sub-surface net setting strategy while also receiving bycatch awareness and safe release training. Captain identity and year were the strongest predictors of sea turtle and dolphin bycatch rates.  

The study investigated methods to decrease glass eel bycatch in spieringkamers (“smelt chamber”) gear. Several gear designs were tested - “ring with covering net”, “U-shaped PVC pipe”, and “slit design.” All three designs led to high levels of eel escapement, ranging from 70.1% in the ring design to 84.3% in the U-shaped PVC design. However, larger eels did not seem to be able to escape the PVC gear.  

The PearlNet aims to mitigate odontocete bycatch in bottom-set gillnets by enhancing the acoustic visibility of nets through the incorporation of small, acrylic glass spheres. This study found that PearlNet performed similarly to standard nets in terms of catch efficiency and handling time of gear. Performance of the gear in reducing marine mammal bycatch was not assessed during this study, however, no mammal bycatch was reported. 

This study tested the behavioral responses of little penguins (Eudyptula minor) to green LED lights in a non-fishing setting as a precursor to operational fishing trials. A grid fitted with commercially available green FishTek Marine NetLights was deployed across a known transit corridor, with trials alternating between illuminated and non-illuminated conditions. 

Penguins swam through the grid on five occasions when no green LED lights were illuminated, while no penguins passed through the grid when the LEDs were illuminated. Two observations involved penguins altering swimming behavior when the grid was illuminated, and there was no evidence of attraction to the green LED lights.