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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.  

The study compared the catch efficiency and impacts on chondrichthyan bycatch between monofilament and multifilament trammel nets in small-scale fisheries along the coast of Çanakkale, Türkiye. Multifilament trammel nets caught 1.22 times more target species (species with economic value) than monofilament trammel nets. Monofilament nets also had a higher catch rate of non-target (discard) species, including higher catch of species listed on the IUCN Red List as vulnerable, endangered, or data-deficient. 

Between 2019 and 2022, trials using three different pinger models (Future Oceans 10 kHz, Future Oceans 70 kHz, and PAL Wideband) were conducted in Bulgaria during standard turbot fishing operations. Marine mammal bycatch was observed in  61% of all hauls. No significant difference in bycatch rates between active and control nets was observed in trials involving Future Oceans 10 kHz (17 trials) and 70 kHz (6 trials) pingers. However, a significant reduction (74%) in cetacean bycatch was recorded during the trials conducted with PAL Wideband pingers. 

Most bycatch studies focus on technical changes and compare a modified gear or fishing method to the traditional gear and method under experimental conditions. Relatively few studies have been able to track the actual reduction achieved if there is fleetwide implementation of the change.  Modifications to fishing gear and methods emerges as by far the most effective for ETP species, with observed reductions from 40% to nearly 100% in actual fishery case studies. However, with some exceptions, gear modification has not been widely implemented in fishing fleets and evaluated estimates of their effectiveness are based on what is not caught, usually without accounting for post-release mortality resulting from gear-related injuries. In addition, to evaluate fleetwide effectiveness, a very high rate of observer or electronic monitoring would be required and there are relatively few fisheries in the world where such conditions are met. 

Gear and fishing method changes, followed by dynamic area management, are the most effective approaches for bycatch reduction and probably the most well accepted by fishers. They are already implemented in many parts of the world and managers can learn from those case studies on how to implement and enforce these mitigation measures. Permanently closed areas appear to be less effective than closed areas that move with changing fish distribution but do require either intensive real-time monitoring or reliable predictive monitoring. However, if the dominant bycatch concern is a single species, then closed areas targeting the areas of high bycatch can be effective. 

Time-depth recorders paired with geolocation sensors or GPS loggers in Aotearoa, New Zealand were used to quantify the diving ecology of three Procellaria petrel species. All three species dove faster than the current best-practice longline sink rate of 0.5 meters/second, highlighting that the risk of interaction with these species is still present. There were also significant differences in diving behavior among and within species, including diurnal trends, sex-specific differences, and for black (P. parkinsoni) and Westland petrels (P. westlandica), changes in diving behavior across the breeding period. These results highlight the necessity of ensuring that bycatch mitigation methods take the strong diving capabilities of these three species into account. This includes night setting when many seabirds are less active and when dives are shallower, use of tori lines for smaller vessels, and a 20m threshold for hook-shielding or bait-setting devices (or combining these devices with bird-scaring devices and/or additional weighted branch lines to protect hooks to 20m). Furthermore, it can be beneficial for custom/target-specific bycatch mitigation methods being developed to take into account the necessary ecological context.