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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.

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。

Vasanth, K.; Muthupandi, K.; Naganandhini, V.; Radhakrishnan, K., and Narayanan, M., 2025. Length-weight relationships of eight pelagic fish species caught by drift longlines in the Gulf of Mannar, India. Journal of Coastal Research, 41(3), 510–515. Charlotte (North Carolina), ISSN 0749-0208. The length-weight relationships were estimated for eight pelagic species caught in the Gulf of Mannar, India, using experimental longlines. The experimental study was conducted from January to October 2022 in fortnightly intervals using longlines (3000 m for needlefish and 11,250 m for carangids), each equipped with 600 “J”-type fishing hooks of various types (straight, reversed, kirbed). The hook numbers used were standard sizes that ranged from 8 to 11 for both groups (needlefish and carangids). The longlines were fabricated with polyamide monofilament and operated from 1 to 2 m depth for needlefish and 20 to 25 m depth for carangids for 3 to 5 hours for both longline units. Overall, 21,150 hooks were deployed in 24 fishing trials for each experimental longline. A maximum total length was recorded for four needlefish species, Strongylura strongylura (80), Tylosurus choram (91), Tylosurus crocodilus (97), and Ablennes hians (96), and four carangids species, Caranx bajad (60.5), Alectis indicus (62), Caranx ignoblis (69), and Scomberomorus commerson (74). In terms of growth, the length-weight relationships revealed positive allometric growth (b >3) for three species of carangids, C. bajad, S. commerson, and A. indicus (p < 0.05) and negative allometric growth (b <3) for four species of needlefishes, T. choram, S. strongylura, T. crocodilus, and A. hians, and one species of carangid, C. ignoblis.

Pelagic fisheries can have profound effects on ecosystem structure and functioning, affecting ecosystem services, including fisheries production, and threaten vulnerable bycatch species. Controlling hook size could manage the species- and size-selectivity and survival of target and incidental catch. To test this hypothesis, we conducted experimental pelagic longline fishing in the western tropical Pacific testing a control hook and two hooks with wider minimum widths. Data such as catch, length and condition were fit to response-specific Bayesian geo-additive generalized additive and linear mixed regression models. Model fits were assessed using posterior predictive check tests. Catch rates of both retained and discarded species were significantly higher on medium hooks. Target tuna species were significantly larger and had significantly higher at-vessel survival rates on wider hooks. Significantly larger billfishes, also market species, were caught on narrowest hooks. These effects of hook width on length and survival, however, are a much smaller determinant of economic value of the catch than effects on catch rates. If input controls are limiting, then, relative to medium hooks, continued use of narrowest hooks would maintain current economic viability without causing a significant increase in discard catch levels, including of vulnerable sharks. If market species output controls are limiting, because the ratio of retained to discarded catch on medium hooks was greater than on narrowest hooks, medium hooks would generate lower discard levels. Further research assessing single-factor effects of longline hook width is needed to support robust meta-analyses that account for fishery-specific effects.

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.

Objective The Gulf of Mexico (GOM) reef bottom longline fishery typically not only targets groupers and snappers but also interacts with 27 species of sharks, which are primarily discarded as bycatch. Slow growth, late maturity, and low fecundity in a landscape of increasing fishing pressure make sharks comparatively more susceptible to overfishing and endangered status than other fishes. The purpose of this study was to determine which gear and/or environmental variables best predict the shark catch per set for commonly caught shark species in the GOM reef bottom longline fishery. Methods We considered 12 commonly caught shark species that vary from the abundant Atlantic Sharpnose Shark Rhizoprionodon terraenovae to the critically endangered Scalloped Hammerhead Sphyrna lewini. Catch per set, effort, gear, and environmental data were taken from the National Oceanic and Atmospheric Administration National Marine Fisheries Service observer dataset for the GOM reef bottom longline fishery (2009–2017) and were used to fit generalized additive models. The Bayesian information criterion and 10‐fold cross‐validation were used to select the best set of variables that predicted catch per set to determine gear configurations, fisher activities, and environmental conditions contributing to higher shark catch per unit effort. We modeled each species individually, all species combined, and species grouped by similar ecology. Result Gear and fishing method variables were consistently included in the best predictive models across species and were the only potential basis for a single strategy that could decrease bycatch across all 12 species. Patterns of environmental variables were only consistent across species with similar ecology and habitat. Conclusion Sharks as a group should not be lumped together, as the effects of mitigation measures become confounded and directly managing trade‐offs between species when minimizing bycatch becomes impossible. Focusing on gear rather than environmental variables is the best apparent option to potentially reduce shark catch per set across commonly caught species while minimizing trade‐offs. Impact statement Sharks are slow‐growing species that give birth to very few offspring late in life, making them highly susceptible to overfishing. We used catch data from the Gulf of Mexico to determine gear and environmental conditions that contribute to high shark catch in an attempt to minimize incidental shark catch and prevent overfishing. Focusing on gear configurations is the best apparent option to potentially reduce shark incidental catch across commonly caught species.