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Abstract

By-catch is one of the most significant issues affecting fisheries management today. Incidental mortality of species which are long-lived and have low reproductive rates is a conservation problem affecting marine mammals, sea birds, sea turtles, sharks and other groups. By-catches can affect biodiversity through impacts on top predators, the removal of individuals from many species, or by elimination of prey. The by-catch issue is also one of waste; the millions of tons of protein dumped in the ocean, and the waste of animal lives is often condemned on moral grounds. For the economist, it generates additional costs without affecting the revenues, and may hinder profitability. For the fishers, it causes conflicts among fisheries, it gives fishers a bad public image, generates regulations and limitations on the use of resources, and frequently has negative effects on the resources harvested through the mortality of juvenile and undersized individuals of the target species before they reach their optimal size from the point of view of future yield.Several examples of major by-catch issues are described, focusing also on the solutions to the problems which have been developed by scientists, fisheries managers and members of the fishing industry itself. By-catch is an extremely complex set of scientific issues, not only an economic, political, or moral one. Although only a few fisheries include by-catches of the target species in their stock assessment (e.g. Pacific halibut), it is clear that by-catch management will be an integral part of most future ecosystem management schemes. These considerations, together with the introduction of environmental variability and a better handling of scientific uncertainty, should lead to more intelligent ways to harvest our resources.
... Overfishing is the most significant threat to marine living resources and in particular for this region fishing pressure, caused by beam trawling. Among the actual topics in the field of fisheries are studies on the effects of bycatch (part of the catch, unintentionally captured during a fishing operation as an addition to the target species) on marine species and habitats (Hall et al., 2000;Tudela, 2004;Sewell & Hiscock, 2005;Peres et al., 2019;Pitcher et al., 2021). Bycatch observations can contribute to a better understanding of the local biodiversity status and abundance trends and play a role in the development of indicators within the Marine Strategy Directive of the European Union (2008/56/EC, MSFD). ...
... Overall, bycatch levels have been shown to be fishery-specific, and display strong variations in space and time, and can be explained by compound factors, including technical, economic, environmental, and management measures (Hall et al., 2000;Kelleher, 2005;Rochet and Trenkel, 2005;Amande et al., 2012;Lezama-Ochoa et al, 2017). The present study provides baseline information on the abundance and diversity of decapod and mollusc bycatch by beam trawl fishery for Rapa whelk in the Bulgarian Black Sea region and presents the specificity of their spatial distribution. ...
... The 2017 catch data in these lakes showed that these species were the main targets of catches, accounting for 10-30% of the total annual catch. In addition, there were many discarded and uncounted catch yields for those low economic value species through bycatch, so fishing mortality in these lakes could be much higher than reported (Hall et al., 2000;Lescrauwaet et al., 2013). ...
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Unselective fishing involves activities that target the entire assemblage rather than specific fish species, size classes, or trophic levels. This common fishing approach has been in practice for decades in inland waters in China but its implications for biodiversity remain unclear. We addressed this issue by studying fish assemblages in freshwater lakes (five fishing lakes, one reference lake, and a total of 51 sampling sites) between pre- and post-fishing time-periods in Eastern China during 2017–2019. The effects of lake, fishing period, and their interactions on fish abundance, biomass, and diversity indices were assessed. Multivariate analysis was conducted to test for differences in fish assemblages among lakes and between fishing periods. After the implementation of fishing activities, significant reductions in fish species richness, abundance, biomass, and all three life-history strategies (opportunistic, equilibrium, and periodic) were observed in fishing lakes, whereas opposite trends were observed in the reference lake. Compositional similarity of fish assemblages among fishing lakes increased over the three-year monitoring period. Our results suggest that unselective fishing reduces fish diversity and homogenizes fish assemblage structure in lakes. These findings have important implications for protecting both biodiversity and fisheries in inland waters in China and are applicable to other countries or regions that rely on fish as a major food source.
... Discard rates by species were also calculated and compared between fleets. The discard rate refers to the percentage of discarded catch to the total catch of the species (Hall et al., 2000). The annual discard rates of common species caught by both fleets were calculated. ...
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Catch, bycatch and discard information is important for the assessment and management of fisheries. Using Chinese pelagic tuna longline observer data from 2010 to 2018, we studied the catch composition in the Chinese pelagic tuna longline fisheries in Atlantic targeting bigeye tuna (Thunnus obesus) and bluefin tuna (Thunnus thynnus), and analyzed the survival status and discard rates of common bycatch species. A total of 55 species, including tunas, billfishes, sharks, sea turtles, cetaceans, seabirds, and other pelagic species, were observed. The results indicated that the catch composition of the Chinese pelagic tuna longline fishery targeting bigeye tuna was significantly different from that targeting bluefin tuna. The annual discard rates of common species decreased over this period. Discard rate by length and discard mortality for common species were varied among species. This is the first study to estimate catch, bycatch, and discard using Chinese pelagic tuna longline observer data in the Atlantic Ocean, which is important for the management of Chinese tuna longline fisheries in Atlantic Ocean.
... Pelagic longline fishing practices result in negative bycatch interactions with sharks, sea turtles, seabirds, and marine mammals, which has emerged as an international priority (Hall et al., 2000;Lewison et al., 2004;Gilman et al., 2008;Petersen et al., 2009;Clarke et al., 2014;Sacchi, 2021). The impacts of these bycatch interactions may include economic loss of fishing resources and equipment (Secchi and Vaske Jr, 1998;Dalla-Rosa and Secchi, 2007;Passadore et al., 2015a;Richardson et al., 2019), as well as ecological impacts given the increased mortality of k-strategy species, which are longlived, show late sexual maturity, and have low reproductive rates (Lewison and Crowder, 2007;Bugoni et al., 2008Bugoni et al., , 2009Gallagher et al., 2014;Passadore et al., 2015b). ...
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Sustainable fisheries' managers increasingly seek to implement measures that reduce the mortality of threatened species while maintaining or increasing catch of target species. Our study proposed a simple management option for optimizing fishing over daily and seasonal scales to maximize catch success while protecting non-target species in pelagic longline fisheries. We used Bayesian beta mixed regression models to describe the effects of setting times and seasonality on catches in a pelagic longline fishery in the southwest South Atlantic Ocean (SWAO). Targeted species (swordfish, blue shark, and albacore tuna) are typically captured in fully nocturnal sets (started between 16 and 00 h), whereas shortfin mako shark and loggerhead turtles are typically captured during partially nocturnal sets (started between 00 and 04 h); probably a response to hook depth and circadian behaviours. The results suggest that it is feasible to use only fully nocturnal sets to target preferred species while reducing incidental catch of non-target species. The catch of target species was higher in austral winter, explained by the northward displacement of the subtropical convergence in the SWAO during this season. These results provide a baseline for bycatch mitigation strategies in pelagic longline fisheries at regional and global scales.
... La surexploitation est responsable de 29% de l'impact global des activités humaines sur les écosystèmes marins (IPBES, 2019a) et a causé le déclin des abondances d'une multitude d'espèces (Christensen et al., 2003 ;Pauly et al., 2005). La surexploitation touche principalement les ressources halieutiques bien que les prises accessoires par la pêche puisent aussi constituer une menace pour les espèces non ciblées (Hall et al., 2000). Outre l'effet de la surexploitation, de nombreuses études scientifiques ont mis en évidence la pression sélective exercée par les pêcheries qui privilégient le prélèvement d'individus de grande taille (Fenberg & Roy, 2008 ;Saura et al., 2010). ...
Thesis
Le déclin généralisé des ressources halieutiques à partir du début des années 80 a incité les scientifiques et les gestionnaires des pêcheries à développer des méthodes quantitatives d’évaluation pour améliorer leur gestion. Ces méthodes ont permis de justifier des politiques de diminution drastique de la pression de pêche qui ont été bénéfiques à beaucoup de ressources. Le développement et l’utilisation de ces méthodes ont été amorcés par les grandes pêcheries commerciales océaniques. Elles reposent sur des suivis à long terme, des procédures analytiques complexes et nécessite des mises à jour fréquentes pour ajuster les mesures de régulation en fonction de l’état de la ressource. Ces méthodes sont rarement appliquées aux petites pêcheries continentales qui sont par nature très différentes de leurs pendants océaniques. La diversité et la complexité de ces pêcheries, dominées par des pratiques artisanales ou récréatives, rend l’application de telles méthodes plus délicates.L’objectif de ce projet de thèse est d’élaborer une méthode d’évaluation quantitative des performances de différents scénarios de régulation des pêcheries récréatives bretonnes de saumon atlantique. La démarche de modélisation statistique entreprise valorise l’ensemble de données très diverses collectées depuis la fin des années 80 sur chacune des 18 populations de saumon ciblées par ces pêcheries afin de simuler leur dynamique spécifique sous différents scénarios de régulation. Le cadre statistique bayésien utilisé a facilité l’intégration des principales sources d’incertitudes relatives à ces simulations. Les performances en matière de conservation ont été évaluées à partir d’une nouvelle définition simple et claire de la conservation proposée dans le cadre de cette thèse et adoptée par les gestionnaires bretons. La méthode d’évaluation élaborée vise à faciliter et alimenter le dialogue avec et entre les acteurs de la gestion pour éclairer leur prise de décision. Dans cette optique, la méthode choisie se base sur des règles de décision aisément compréhensibles et elle permet d’obtenir un sous-ensemble de scénarios « les plus performants », qui laisse une latitude aux acteurs de la gestion dans le choix final qu’ils auront à opérer. Les résultats obtenus montre que la conservation n’est pas respectée, même en l’absence de prélèvement par la pêche sur au moins une rivière. Néanmoins dans la majorité des cas, le système de régulation actuel est compatible avec la conservation. Ce travail de thèse, mené à l’échelle d’un ensemble régional tel que la Bretagne, constitue une première pour le saumon atlantique au travers de son aire de répartition. Il pourrait être étendu à d’autres entités spatiales car la méthodologie peut s’appliquer et s’ajuster facilement à différents contextes. Ce travail a permis de mettre en évidence que l’intensité d’exploitation actuelle des pêcheries récréatives ne constituait pas une menace substantielle pour le saumon en Bretagne. Pour mieux comprendre les différentes menaces et leurs impacts sur les populations bretonnes, il faudrait s’orienter vers une gestion plus écosystémique de la ressource.
... The efforts promoted by the Earth Institute had a double effect for conservation purposes. On one hand, the tuna industry from the Eastern Pacific quickly and effectively reduced dolphin mortality from 133,000 caught in 1986 to just 1877 caught in 1998 [32] by applying simple fishing maneuvers, such as 'the going backwards technique' which forced tuna to the bottom and dolphins to the surface, and the latter were assisted by divers to jump out of the net. On the other hand, it forced the fleet to fish over floating logs (natural or man-made), associated with larger impacts on other vulnerable species [33]. ...
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The increasing speed of the establishment of large-scale marine protected areas (LSMPA) on a global scale has generated intense debate among the scientific community. In this paper, we revise the declaration of the Revillagigedo Marine Park, the largest marine reserve in North America, and propose a framework to assess the potential costs and benefits of having a competitive or a cooperative strategy between the tuna fishing industry and the conservation sector. By framing scenarios in a simple model of the prisoner dilemma and using multicriteria analysis with Delphos—an open-source multicriteria program developed by NGOs for this purpose—we show how conservationists and fishers might have a potential benefit of competing for marine spaces, but not as much as they could gain if they collaborate. Our ultimate goal with this paper is to retrieve the lessons learned in this process to propose a step-by-step process that helps to improve the creation of LSMPAs in the future, thus helping improve the outcome of marine conservation on a global scale.
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