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Fisheries bycatch is one of the biggest threats to marine mammal populations. A literature review was undertaken to provide a comprehensive assessment and synopsis of gear modifications and technical devices to reduce marine mammal bycatch in commercial trawl, purse seine, longline, gillnet and pot/trap fisheries. Successfully implemented mitigation measures include acoustic deterrent devices (pingers) which reduced the bycatch of some small cetacean species in gillnets, appropriately designed exclusion devices which reduced pinniped bycatch in some trawl fisheries, and various pot/trap guard designs that reduced marine mammal entrapment. However, substantial development and research of mitigation options is required to address the bycatch of a range of species in many fisheries. No reliably effective technical solutions to reduce small cetacean bycatch in trawl nets are available, although loud pingers have shown potential. There are currently no technical options that effectively reduce marine mammal interactions in longline fisheries, although development of catch and hook protection devices is promising. Solutions are also needed for species, particularly pinnipeds and small cetaceans, that are not deterred by pingers and continue to be caught in static gillnets. Large whale entanglements in static gear, particularly buoy lines for pots/traps, needs urgent attention although there is encouraging research on rope-less pot/trap systems and identification of rope colours that are more detectable to whale species. Future mitigation development and deployment requires rigorous scientific testing to determine if significant bycatch reduction has been achieved, as well as consideration of potentially conflicting mitigation outcomes if multiple species are impacted by a fishery.

Over the last three decades, the advent and the continuous sophistication of telemetry devices have revolutionized our understanding of how pelagic sharks move and exploit their three-dimensional underwater habitat, with implications for management and conservation. In this study, conventional (4,648) and electronic (18) tags were used to assess the horizontal and vertical movements of blue sharks, Prionace glauca , and their vertical overlap with shallow and deep-set longline fishing gears in the southwestern Atlantic Ocean. Results revealed prolonged permanence in the area, large-scale displacements, including trans-equatorial, trans-Atlantic and Indian–Atlantic movements, and high daily displacement rates. Blue sharks showed an extensive use of the water column and considerable variability among and within individuals in vertical behavior, involving normal and reverse diel vertical migrations, surface-oriented behavior, extended use of mesopelagic waters, and occasional extreme dives into bathypelagic waters. Depth distribution appeared unrelated to size or sex but was influenced by the time of day and temperature, with deeper and colder temperatures consistently found during the day. The moon cycle affected the vertical distribution of some sharks but not others. Temperature-depth recorders deployed on hooks, combined with depth distribution from electronic tags, provided insightful information on the species’ vertical overlap with shallow- and deep-set longline configurations. Encounterability values were higher during nighttime and lower during daytime for both longline configurations, but were largely affected by the individuals’ vertical behavior, highlighting the importance of accounting for environmental conditions besides fishing gear configuration and métiers. This novel information on blue sharks’ movements and fishery interactions in the South Atlantic Ocean can inform future management and conservation strategies.

Vasanth, K.; Muthupandi, K.; Naganandhini, V.; Kumar, M.; Krishnan, A.; Patolla, H., and Radhakrishnan, K., 2023. Effect of J-hook shapes on catch rate, efficiency, and hooking position of Needlefish: Evidence from Palk Bay, India. Journal of Coastal Research, 39(5), 933–939. Charlotte (North Carolina), ISSN 0749-0208. The efficiency of different shapes of J hooks No. 11 (nonoffset straight hook, 10° offset kirbed hook, and 10° offset reversed hook) in needlefish longline fishing gears was studied in 24 fishing grounds in Palk Bay, India, from, February to July 2022. A total of 24 fishing trips were conducted for each experimental gear for the comparative study, with 14,400 hooks, with a total catch of 582 fish during the study. The result was that the kirbed hook had the highest percentage composition of the needlefish (37.36%), followed by the reversed hook (31.79%) and the straight hook (30.75%). Further, the overall hooking rate was higher for the kirbed hook than for the straight hook (13.43% vs. 8.60%). Considering the catch rate, the overall catch per unit effort (CPUE; individual/200 hooks) of the kirbed hook was higher (9.08 vs. 7.45) than that of the straight hook, whereas for the straight hook, the CPUE of nontarget species (0.29) was much higher than that of the kirbed hook (0.12). In terms of the targeted species, the Ablennes hians showed the highest CPUE of 3.78 individuals/200 hooks followed by Tylosurus crocodilus crocodilus (1.78), Strongylura strongylura (1.38); the least dominant CPUE was T. choram (0.94). The percentage of hooking position in the jaw was higher in the kirbed hook than that of the straight hook (64.7% vs. 39.1%) and was found lower in the gut system (11.5% vs. 28.5%). Among the three hook shapes tested, the overall performance of the 10° offset kirbed hook was found to be better than the other 10° offset reversed and nonoffset J hook in terms of a higher catch efficiency, hooking rate, CPUE, and hooking position for needlefish (<0.05).

Fisheries can profoundly affect bycatch species with ‘slow’ life history traits. Managing bait type offers one tool to control species selectivity. Different species and sizes of marine predators have different prey, and hence bait, preferences. This preference is a function of a bait’s chemical, visual, acoustic and textural characteristics and size, and for seabirds the effect on hook sink rate is also important. We conducted a global meta-analysis of existing estimates of the relative risk of capture on different pelagic longline baits. We applied a Bayesian random effects meta-analytic regression modelling approach to estimate overall expected bait-specific catch rates. For blue shark and marine turtles, there were 34% (95% HDI: 4–59%) and 60% (95% HDI: 44–76%) significantly lower relative risks of capture on forage fish bait than squid bait, respectively. Overall estimates of bait-specific relative risk were not significantly different for seven other assessed taxa. The lack of a significant overall estimate of relative capture risk for pelagic shark species combined but significant effect for blue sharks suggests there is species-specific variability in bait-specific catch risk within this group. A qualitative literature review suggests that tunas and istiophorid billfishes may have higher catch rates on squid than fish bait, which conflicts with reducing marine turtle and blue shark catch rates. The findings from this synthesis of quantitative and qualitative evidence support identifying economically viable bycatch management measures with acceptable tradeoffs when multispecies conflicts are unavoidable, and highlight research priorities for global pelagic longline fisheries.

Although bycatch of seabirds and other long-lived species is a critical conservation issue in world fisheries, case studies documenting significant reductions in the mortality of these low-productivity species in a fishery are rare. We studied progress toward seabird conservation in the Alaskan longline fisheries, one of the largest and most diverse demersal fisheries. We generated annual seabird bycatch rates in 4 target fisheries and all fisheries combined from 23 years of fisheries observer data. We used 0-inflated negative binomial models to evaluate variables influencing seabird bycatch per unit effort (BPUE) in 2 target fisheries. Following adoption of streamer lines, at first voluntarily and then mandatorily, seabird BPUE was reduced by 77–90%, preventing mortality of thousands of birds per year. Despite this, BPUE increased significantly in 2 of 4 target fisheries since streamer lines were adopted. Although night setting yielded significant reductions (74–97%) in seabird BPUE and significant increases (7–11%) in fish catch per unit effort over daytime setting, nighttime setting increased the BPUE of Northern Fulmar (Fulmarus glacialis) by 40% and nontarget fish species by 5–17%. Thus, best practices to prevent seabird mortalities in longline fisheries varied by species assemblage and fishery. Our results inform global efforts toward fisheries bycatch reduction by illustrating that successful conservation requires fishery-specific solutions, strong industry support, constant vigilance in analysis and reporting observer data, and ongoing outreach to fleets, especially to vessels with anomalously high BPUE. Aunque la captura accesoria de aves marinas y otras especies con ciclos de vida largos es un asunto de importancia para la conservación en las pesquerías a nivel global, son raros los estudios de caso que documentan las reducciones significativas de la mortalidad de estas especies de baja productividad en las pesquerías. Estudiamos el progreso hacia la conservación de aves marinas en las pesquerías con palangre en Alaska, una de las pesquerías demersales más grandes y con mayor diversidad. Generamos tasas anuales de capturas accesorias de aves marinas para cuatro pesquerías y todas las pesquerías combinadas a partir de 23 años de datos de observación de pesquerías. Usamos modelos binomiales negativos con inflación 0 para evaluar las variables que influyen sobre la captura accesoria de aves marinas por unidad de esfuerzo (BPUE, en tnglés) en dos pesquerías. Después de la adopción de la caña de pescar, al principio voluntariamente y después de manera obligatoria, el BPUE de aves marinas se redujo entre un 77 y 90%, lo que previno la mortalidad de miles de aves por año. A pesar de esto, el BPUE incrementó significativamente en dos de las cuatro pesquerías diana desde que se adoptaron las cañas de pescar. Aunque las puestas nocturnas resultaron en reducciones significativas (74-97%) en el BPUE de aves marinas e incrementos significativos (7-11%) en la captura de peces por unidad de esfuerzo comparadas con las puestas diurnas, las puestas nocturnas incrementaron el BPUE del fulmar boreal (Fulmarus glacialis) en un 40% y entre un 5 y 17% el de las especies de peces cuya captura no es relevante para las pesquerías. Por lo tanto, las mejores prácticas para prevenir la mortalidad de las aves marinas en las pesquerías con palangre variaron dependiendo del grupo de especies y de la pesquería. Nuestros resultados informan a los esfuerzos globales hacia la reducción de la captura accesoria de las pesquerías al ilustrar que la conservación exitosa requiere de soluciones específicas por pesquería, un fuerte apoyo por parte de la industria, una vigilancia constante del análisis y el reporte de los datos de observación, y una participación continua de las flotas, especialmente en el caso de navíos con un BPUE anormalmente alto. 尽管全世界的渔场都面临着海鸟和其它寿命长的物种遭到兼捕这样ー个重要保护向题，但关于渔场中这 些低繁殖率物种的死亡率显著下降的案例分析仍然狼少。本研究分析了規模最大、种类最多的底层渔场之一 的阿拉斯加延绳钓渔场在海鸟保护方面的进展。我们根据 23 年间渔场的观察数据，获得了四个目标渔场和所 有渔场整体上毎年海鸟兼捕率的数据，并用零膨张负ニ项模型估计了两个目标渔场中影响每单位工作量的海鸟 兼捕量(bycatch per unit effort, BPUE)的因素。在从自愿到强制性地采用了飞绳钓方法之后，海鸟BPUE減 少了77-90%，毎年防止了数千只鸟的死亡。尽管如此，采用飞绳钓后，四个目标渔场中还是有两个渔场BPUE 显著增加。虽然夜间放钓竿相比于日间放钓竿，海鸟BPUE显著减少(74-97%),且每单位工作量的渔获量显著 増加77-11%),担夜间放钓竿导致暴雪鹱(Fulmarus glacialis；的BPUE増加了40%，非目标鱼种的BPUE也增加 T5-17%o因此，防止延绳钓渔场中海鸟死亡的最佳实践取决于物种群落和渔场的具体情况。我们的结果阐明 了成功的保护需要针对各个渔场_ 定解决方案、有强有力的产业支持、对观察数据的分析和报告保持谨慎，以 及要注意不断扩大的船队，特别是引起异常高BPUE的船只。这些结果为全球渔场减少兼捕的努力提供了重要 信息。

Incidental mortality (bycatch) in fisheries represents a threat to marine vertebrates. Research has predominantly focussed on bycatch in longline fisheries, but bycatch from gillnet fisheries is of increasing concern. To address this concern, we combined comprehensive biologging data sets and multiple sources of fishing effort data to assess the spatial overlap of 3 diving seabird species during the breeding season (common guillemot Uria aalge, razorbill Alca torda and European shag Phalacrocorax aristotelis) with UK gillnet fisheries. Species distribution models based on birds’ diving behaviour identified areas of elevated bycatch risk where high levels of diving activity and fishing effort coincided. In addition, we identified times of day and water depths where diving activity, and hence bycatch risk, may be concentrated. Bycatch risk hotspots for all 3 species were identified along the north-east coast of England. Risk hotspots were also identified along the Pembrokeshire coast for both auk species and along the Cornish coast for shag. Lack of fishing effort data for smaller vessels made it difficult to assess seabird−fishery overlap in Scottish waters. Across species, diving activity was lower at night. For razorbill and guillemot, dive depth tended to increase at sunrise and decrease after sunset. For shag, dive depth showed no diel pattern but was associated with water depth. Our findings should assist in targeting spatio-temporal measures and designing deterrent devices to reduce bycatch. However, scarcity of data on the behaviour of gillnet fishers at comparable spatio-temporal resolution as seabird movement data remains a constraint to fully understanding seabird−fisheries interactions.

In the Mediterranean Sea, pelagic longline fisheries, targeting tuna and swordfish, have contributed significantly to the bycatch of threatened chondrichthyan species, such as blue shark (Prionace glauca). The Mediterranean blue shark population is assessed as critically endangered, making a timely implementation of mitigation measures crucial. A comprehensive understanding of blue shark habitat use dynamics is essential for deriving appropriate mitigation measures. This study aimed at evaluating vertical movement behaviour and investigating factors potentially influencing the movements of blue sharks in the Mediterranean Sea. Twenty-six blue sharks, bycaught in a longline fishery in the southern Adriatic, were tagged with pop-up satellite archival tags. Analysis of data from thirteen recovered tags revealed a distinctive diel movement pattern. Blue sharks used shallower waters during the night and deeper waters during the day, characterised by steep ascents and descents during sunset and sunrise, respectively. In addition, lunar phases were also influencing the depth of blue shark movements, with sharks using deeper waters right before and during full-moon. Shark size, salinity, currents, spatial location and time of the year were additional factors influencing blue shark depth use. The observed tendency of blue sharks to use deeper areas at daytime and prior and during the full moon period offers possibilities to develop and test bycatch mitigation strategies. Aligning longline fishing schedules and fishing depths with blue shark behaviour during the fishing seasons could hold promise to effectively reduce spatio-temporal overlap between fishing and blue shark distribution and may ultimately decrease the bycatch impact of the fishery.