Article

Odontocete bycatch and depredation in longline fisheries: A review of available literature and of potential solutions

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Abstract

Operational interactions between odontocetes (i.e., toothed whales) and longline gear are a global phenomenon that may threaten the conservation of odontocete populations and the economic viability of longline fisheries. This review attempts to define the issue, summarize the trends and geographical extent of its occurrence over the last half century, explore the potential impact on odontocetes and on fisheries, and describe potential acoustic and physical mitigation solutions.Reports of odontocete bycatch rates are highly variable (between 0.002 and 0.231 individuals killed per set) and at least 20 species may be involved. Information about marine mammal population size, migration patterns and life history characteristics are scarce, although at least one population may be in decline due to losses attributable to longline bycatch. Information about the financial impact of depredation on pelagic longline fisheries is also scarce, although estimates of daily fleet‐wide losses range between US$1,034 and US$8,495 (overall fleet income was not reported). Such biological and financial losses may be unsustainable.Recent developments in acoustic and physical mitigation technologies have yielded mixed results. Acoustic mitigation technologies have no moving parts, although require complex electronics. To date, they are insufficiently developed and their efficacy has been difficult to assess. Physical mitigation technologies generally require complex moving parts, although they are relatively simple to develop and assess. Further development and testing remains necessary before widespread implementation would be possible. Development of these approaches should be prioritized and a “toolbox” of various strategies and solutions should be compiled, because a single panacea to the problem is unlikely to emerge.

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... Additionally to these induced costs, fishermen increase their fishing effort to complete their quota or to avoid depredation, increasing expenses due to fuel consumption, extra food and crew salaries (Gilman et al. 2006, Peterson and Carothers 2013, Peterson et al. 2014, Tixier et al. 2015c, Werner et al. 2015. On the other hand, depredation for marine predators increases risks of mortality by the use of lethal retaliation by fishermen (Yano and Dahlheim 1995, Woodroffe et al. 2005, Treves et al. 2006, Read 2008, or by a greater risk of bycatch, especially in gillnets (Northridge 1991, Gilman et al. 2006, Read et al. 2006, Read 2008, Hamer et al. 2012, Reeves et al. 2013. For instance, it has been observed that at least 75% of odontocetes, 64% of mysticetes, 66% of pinnipeds, and all sirenians and marine mustelids species have been recorded as gillnet bycatch since the 1990's (Reeves et al. 2013). ...
... Depredation has been observed on all fisheries and by a broad range of large marine vertebrates (Northridge and Hofman 1999, Donoghue et al. 2002, Gilman et al. 2006, 2008, Read 2008, Hamer et al. 2012, Werner et al. 2015. However, most of these conflicts involved the longline fisheries, with a growing cases since the 1950s (Northridge and Hofman 1999, Donoghue et al. 2002, Gilman et al. 2006, Read 2008, Hamer et al. 2012, and have involved mainly odontocetes species (Northridge 1991, Northridge and Hofman 1999, Gilman et al. 2006, Read 2008, Reeves et al. 2013, Werner et al. 2015. ...
... Depredation has been observed on all fisheries and by a broad range of large marine vertebrates (Northridge and Hofman 1999, Donoghue et al. 2002, Gilman et al. 2006, 2008, Read 2008, Hamer et al. 2012, Werner et al. 2015. However, most of these conflicts involved the longline fisheries, with a growing cases since the 1950s (Northridge and Hofman 1999, Donoghue et al. 2002, Gilman et al. 2006, Read 2008, Hamer et al. 2012, and have involved mainly odontocetes species (Northridge 1991, Northridge and Hofman 1999, Gilman et al. 2006, Read 2008, Reeves et al. 2013, Werner et al. 2015. Indeed, at least 31 species of odontocetes have been reported to interact (either depredation or bycatch) with longline fisheries against 15 species of pinnipeds, 6 species of mysticetes, and 2 species of sirenians (Werner et al. 2015). ...
Thesis
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Many marine predator species feed on fish caught by fishers directly from the fishing gear. Known as depredation this interaction issue has substantial socio-economic consequences for fishermen and conservation implications for the wildlife. Costs for fishers include damages to the fishing gear and increased fishing effort to complete quotas. For marine predators, depredation increases risks of mortality (lethal retaliation from fishers or bycatch on the gear). Longline fisheries are the most impacted worldwide, primarily by odontocetes (toothed whales) depredation, urging the need for mitigation solutions to be developed. Most of studies assessing depredation have primarily relied on surface observation data, thus the way odontocetes interact with longlines underwater remains unclear. Besides, the way fishermen respond to depredation during fishing operations, or can influence their detectability to odontocetes, have been poorly investigated. This thesis therefore aimed at investigating these aspects through a passive acoustic monitoring, bio-logging and human ecology approaches, focusing on the French Patagonian toothfish (Dissostichus eleginoides) longline fisheries impacted by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus). Firstly, this thesis reveals that captains behave as optimal foragers but with different personal perception of competition and fishing fulfilment. Some captains would thus be more likely to stay within a patch or to haul closest longline even in presence of competition, suggesting these captains would show higher interaction rates. Additionally, the propagation of vessels’ acoustics varied depending on the type of manoeuvre (e.g. going backward vs. forward). The way captains use their vessels to navigate may therefore influence their detectability and so their depredation level. Secondly, loggers deployed on both the longlines (accelerometers) and odontocetes (GPS-TDR) revealed that killer whales and sperm whales are able to depredate on longlines while soaking on the seafloor. These observations suggest, therefore, that odontocetes can localise fishing activity before the hauling, which could be partially explained by specific acoustic signatures recorded during the setting process. Altogether, the results of the thesis suggest that depredation rates on demersal longlines are most likely underestimated. The thesis also brings some important insights for mitigation measures, suggesting that countermeasures should start from setting to hauling.
... The threat is different in pelagic waters, where one of the primary gear types implicated in direct interactions with cetaceans is the pelagic longline (Lewison et al., 2014). Whereas some bycatch problems are a function of cetaceans failing to perceive gear (e.g., gillnets) or being actively entrapped by fishermen (e.g., purse seines), interactions between cetaceans and hook and line gear, such as longlines, are often driven by attraction of the animal to feed on bait or fish secured on the gear, a behavior known as depredation (Gilman et al., 2007a;Read, 2008;Hamer et al., 2012). Many odontocete species are adept at depredation and can remove large quantities of catch, which can result in substantial economic costs to fishermen (Peterson et al., 2014;Tixier et al., 2020a). ...
... Numerous workshops involving fishermen, scientific experts, and fishery managers have assessed available mitigation strategies and considered approaches for research, testing, and implementation. These past efforts and general syntheses of odontocete-longline interactions and research have been summarized in several previous reviews (e.g., Gilman et al., 2007a;Hamer et al., 2012;Werner et al., 2015;FAO, 2018;Hamilton and Baker, 2019;Tixier et al., 2020b). ...
... Depredation and bycatch in pelagic longline fisheries are related, but separate and unique problems that have proven exceedingly difficult to solve. There has been little success in implementing effective strategies to protect target catch and reduce the economic costs of depredation to fishermen (Hamer et al., 2012;Werner et al., 2015;Tixier et al., 2020a). Likewise, it has been challenging to reduce injuries or mortalities due to hookings or entanglements of depredating cetaceans, even when mandated by legislation (e.g., Baird, 2019). ...
Article
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Direct interactions with fisheries are broadly recognized as the leading conservation threat to small cetaceans. In open-ocean environments, one of the primary gear types implicated in these interactions is the pelagic longline. Unlike accidental entanglement in driftnets or deliberate entrapment by purse-seines, interactions between cetaceans and longlines are often driven by attraction of the animals to feed on bait or fish secured on the gear, a behavior known as depredation. Many small and medium-sized delphinid species have learned to exploit such opportunities, leading to economic costs to fisheries and a risk of mortality to the animals from either retaliation by fishermen or hooking or entanglement in fishing gear. Two pelagic longline fisheries in the United States experience depredation and bycatch by odontocete depredators: the Hawai‘i deep-set longline fishery, which is depredated primarily by false killer whales (Pseudorca crassidens), and the Atlantic pelagic longline fishery depredated primarily by short-finned pilot whales (Globicephala macrorhynchus). These fisheries are among the most intensively documented and managed pelagic longline fisheries in the world, with high levels of observer coverage, and bycatch mitigation measures required to reduce the mortality of seabirds, sea turtles and cetaceans. Both fisheries have active, multi-stakeholder “Take Reduction Teams,” enacted under the U.S. Marine Mammal Protection Act (MMPA), that are tasked to develop measures to reduce the bycatch of cetaceans below statutory reference points. Consequently, these two Teams represent model processes within which to address depredation and bycatch, having access to detailed, high-quality data on the nature and frequency of interactions with cetaceans, meaningful stakeholder involvement, resources to test potential solutions, and the institutional will to improve outcomes. We review how mitigation strategies have been considered, developed, and implemented by both Teams and provide a critical analysis of their effectiveness in addressing these problems. Notably, in the absence of straightforward avoidance or deterrence strategies, both Teams have developed gear and handling strategies that depend critically on comprehensive observer coverage. Lessons offered from these Teams, which have implemented consensus-driven management measures under a statutory framework, provide important insights to managers and scientists addressing other depredation problems.
... Fisheries interactions with cetaceans have been well documented in almost all existing fishing gears (Northridge and Hofman, 1999;Dalla Rosa and Secchi, 2007;Forney et al., 2011;Guinet et al., 2015) with different targeted species (Hamer et al., 2012) and at different geographical areas (Lauriano, 2004;Dıáz Loṕez, 2006;Brotons et al., 2008;Maccarrone et al., 2014;Gonzalvo et al., 2015). These interactions are associated with negative economic and conservation consequences (Hall and Donovan, 2002;Lauriano, 2006;Zollet and Read, 2006;Brotons et al., 2008), which may lead to controversial practises like culling of cetaceans to avoid depredation (Bearzi et al., 2004). ...
... Many studies dealing with depredation and cetacean-fisheries interactions showed that this is a common strategy among cetaceans and that depredation on fishing gear is a practice that is taught within populations (Pennino et al., 2013). Consequently, the practise of depredation seems to be increasing compared to previous decades and is, therefore, more frequently reported in the literature (Hamer et al., 2012). ...
... Interactions with cetaceans and longlines have been reported since 1952 when the global pelagic tuna longline fishing began in the Indian, Atlantic and Pacific Oceans (Sivasubramaniam, 1964). Among other fishing methods, longline is the most impacted from depredation worldwide (Northridge and Hofman 1999;Gilman et al., 2006;Garrison, 2007;Hamer et al., 2012) with more than 31 odontocete species, six mysticete species, 15 pinniped species and two sirenian species been reported to interact with longline fisheries (Werner et al., 2015). From the fishermen perspective, depredation on longlines is known to cause significant damage on fishing gear and catch and is also related with increased fishing effort to avoid competition with cetaceans and reach quota levels and annual profits (Peterson et al., 2014;Tixier et al., 2015;Werner et al., 2015). ...
Article
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Depredation by cetaceans on fisheries is a major issue globally, both in terms of conservation and fisheries economics. The present study conducted in Cyprus, Eastern Mediterranean Sea, aimed to understand the extent, level, and type of cetacean depredation on the albacore tuna pelagic longline fishery, and in particular to quantify and evaluate the economic consequences of depredation and identify potential dolphin-longline conflict areas and mitigation practices for management. The data were obtained from fisher's logbooks, interviews and onboard observations between June and August 2018. A novel and simple approach was applied to estimate the depredation rate and economic loss by using simple calculations including the number and weight of depredated fish, landings and fishing effort. The results revealed that there is an estimated economic loss per fishing trip of 313.07± 486.19 EUR and an estimated annual economic loss for the entire fleet of 259,272 EUR from depredation caused by cetaceans. The study also estimated that 16,639 albacore tunas were depredated in 2018 and the depredation rate ranged between 0% to 100% with a mean depredation rate of 17% per fishing trip. Depredation by the common bottlenose dolphin and striped dolphin was reported in more than 50% of their fishing trips. Other species that were found to be involved in depredation were the neon flying squid, the shortfin mako shark and the Risso's dolphin. This is the first official record worldwide of depredation from the common bottlenose dolphin, the striped dolphin and the neon flying squid on the pelagic longline albacore tuna fishery. A total bycatch of 62 individuals of common bottlenose dolphins and one individual of stripped dolphin were reported in interviews as a result of depredation on bait and catch. The study also identified depredation hotspots and possible depredation mitigation measures. Such information could support the development of management action plans and measures to minimise interactions between cetaceans and pelagic longlines.
... This early knowledge may explain the greater number of publications applying modelling to terrestrial depredation. Marine depredation has emerged as problematic around 1970s, concomitantly with the global expansion of fisheries and the emergence of non-lethal mitigation in a conservation context (Hamer et al., 2012;Mitchell et al., 2018;Read, 2008;Tixier et al., 2021a). The study of depredation in the marine realm is therefore relatively recent, which implies limited availability of data. ...
... Des preuves circonstancielles de la transmission sociale du comportement de déprédation ont notamment été mises en évidence chez les cachalots dans le golfe d'Alaska (Schakner et al., 2014). De plus, malgré de nombreuses études focalisées sur des mesures de mitigation permettant d'atténuer la déprédation ainsi que les prises accessoires (Hamer et al., 2012(Hamer et al., , 2015Mandelman et al., 2008;Werner et al., 2015), cette capacité d'apprentissage s'est avérée le principal obstacle à l'élaboration de stratégie de mitigation efficace. En effet, bien que des modifications technologiques ou stratégiques permettent à court ou moyen terme de réduire la quantité de ressources déprédatée, les déprédateurs s'adaptent souvent sur le long terme en apprenant de nouvelles façon d'utiliser les engins de pêche (Varjopuro, 2011 (Fulton et al., 2003). ...
... En effet, ces conflits d'usages partagent des caractéristiques communes et peuvent se produire en même temps que les évènements de déprédation. Comme précisé précédemment, les évènements de déprédation peuvent notamment mener à des prises accessoires de déprédateurs (Hamer et al., 2012). Un grand nombre de prises accessoires de phoque a été documenté dans les eaux Irlandaises, où les phoques sont également connus pour déprédater les captures de merlu commun (Merluccius merluccius), de la lotte (Lophius sp.) et du lieu jaune (Pollachius pollachius) (Cosgrove et al., 2013). ...
Thesis
Les espèces qui se nourrissent de plantes ou d’animaux élevés ou capturés par l’homme, un comportement appelé « déprédation », entraînent souvent de graves Conflits Homme-Faune sauvage (CHF). La déprédation a été signalée dans le monde entier et, dans les écosystèmes marins, elle a été développée par de nombreux grands prédateurs se nourrissant des prises de pêche, ce qui a un impact à la fois sur les activités de pêche et les interactions écologiques. Cependant, bien que les approches écosystémiques soient de plus en plus utilisées dans la gestion des pêches, les effets de la déprédation sur l’ensemble de l’écosystème sont encore rarement considérés de manière holistique. Par conséquent, cette thèse a (i) identifié les limites, manques et priorités pour le développement d’approches de modélisation intégrant la déprédation et (ii) évalué la capacité de deux approches de modélisation existantes pour caractériser les conséquences de la déprédation marine et, plus spécifiquement, comprendre les enjeux et conditions requises pour que les activités d’exploitation halieutique et les déprédateurs marins puissent co-exister. Cette thèse est composée de cinq chapitres. Le chapitre 1 présente le contexte dans lequel s’inscrit ces travaux. Le chapitre 2 identifie les principales lacunes dans les connaissances et met en évidence les principales orientations futures pour parvenir à une inclusion efficace de la déprédation dans les études de modélisation en réalisant une revue systématique. Le chapitre 3 utilise le cadre Ecopath pour évaluer les effets de la déprédation sur l'écosystème dans une étude de cas bien documentée impliquant des mammifères marins et une pêcherie commerciale. Le chapitre 4 s'appuie sur une modélisation qualitative pour évaluer les conditions de persistance d'une ressource exploitée, d'une pêcherie et d'une espèce déprédatrice dans les systèmes marins touchés par la déprédation, et la façon dont la déprédation marine affecte les réponses à long terme à des scénarios alternatifs. Enfin, la discussion générale présentée dans le chapitre 5, fournit des recommandations qui vise à mieux comprendre et prévoir les effets de la déprédation au niveau du socio-écosystème.
... Known as depredation, the behaviour where marine predators take food directly from commercial fishing operations may have substantial impacts on the depredating animal, the fish stock and the fishery itself (Hamer et al., 2012;FAO, 2018). The impact to marine predators can include injury from gear or fishers (Yano and Dahlheim, 1995;Poncelet et al., 2009) and modification of natural diet and energy balance (Tixier et al., 2017). ...
... Marine mammals are the most important group of marine predators that depredate fisheries both financially and spatially, with reports of depredation occurring across a broad range of fisheries and techniques (Garrison, 2007;Hamer et al., 2012;Ríos et al., 2017, Rabearisoa et al., 2018Rechimont et al., 2018). Demersal longline fishing, which submerges baited hooks at the sea floor for prolonged periods of time, is a primary target for depredating marine mammals, especially the killer whale (Orcinus orca) (Gilman et al., 2006). ...
... Killer whale depredation on demersal longlines is of significance globally (Hamer et al., 2012). In Alaskan sablefish fisheries, over US$ 8000 in daily losses has been reported due to animals taking sablefish (Anoplopoma fimbria) from hooks (Yano and Dahlheim, 1995). ...
Article
Removal of target catch from longlines by marine mammals, known as depredation, is a global issue creating animal welfare, socioeconomic and management concerns. The killer whale (Orcinus orca) is a key species of concern for longline depredation due to their global presence and ability to remove large quantities of caught fish. Currently, data on whale behaviours around fishing vessels, including timing of depredation and ability to follow vessels, is not completely understood. This lack of knowledge prevents a complete assessment of depre-dation both spatially and temporally, which is important to reduce the chance of underestimating depredation events. Our study utilised both photo-identification and acoustics as complementary approaches to investigate depredation on the blue-eye trevalla (Hyperoglyphe antarctica) demersal longline fishery in Australia. Of the 14 d when depredations were recorded acoustic detection of killer whales prior to visual confirmations occurred in 13 (93 %). Photo-identification revealed individuals repeatedly interacting with the vessel, sometimes over long distances (>1000 km), with increasing inter-depredation times as the vessel travelled further. These findings suggest that killer whales move to known fishing areas well before detection from surface monitoring occurs. While this study has revealed aspects of killer whale behaviours when encountering and interacting with longline fisheries, it has highlighted how traditional monitoring methods underestimate depredation and that this aspect needs to be further investigated.
... As a direct result, fishermen have a considerable interest in the issue of depredation, and there has been much research into the problem and its mitigation (indeed, much more than into any other cetacean-tuna fishery interaction in the WIO). Among the many reviews of the topic are those of Donoghue et al. (2003), Anon (2007) and Hamer et al. (2012). ...
... There is strong possibility that false killer whales, and possibly also other small cetacean species, are being shot by tuna longline fishermen within the Indian Ocean.Work to mitigate longline depredation has included studies on devices to provide a physical covering for any fish caught, on devices to acoustically deter cetaceans from approaching vessels or longlines, and on modifying fishing strategies to reduce interactions with cetaceans. These are well described in the literature and need not be repeated here (e.g.Anon, 2007;Mooney et al., 2009;Rabearisoa et al., 2010;Hamer et al., 2012; ...
Technical Report
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This report reviews information on interactions between cetaceans (whales and dolphins) and tuna fisheries in the western and central Indian Ocean.
... This interaction is harmful for both cetaceans and fishermen: fishermen lose the catch and fishing time and costs are increased, while cetaceans can become caught or tangled in the fishing gear (Read 2005(Read , 2008Goetz et al. 2011;Peterson et al. 2013;Belonovich et al. 2019a, b). At least 20 Odontoceti species are known to be involved in depredation (Hamer et al. 2012;Tixier et al. 2018). Killer whales (Orcinus orca) started to depredate the longline fisheries in the Pacific in the 1950s. ...
... Despite the fact that killer whale depredation has been known for a long time, and fishermen and experts from different countries have been trying to resolve this issue for many years, no effective method has been found. Killer whales actively interfere with fisheries in the Crozet Islands, Australia, New Zealand, Alaska, Pribilof Islands, the Atlantic Ocean, and other areas (Hamer et al. 2012;Peterson et al. 2013;Tixier et al. 2014Tixier et al. , 2018Passadore et al. 2015;Esteban et al. 2016). Recent research suggests that killer whales can take fish from the lines soaking on the ocean bottom, even before they have been pulled (Richard et al. 2019). ...
Article
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The killer whale (Orcinus orca) behavior termed “depredation” is a major issue negatively affecting fisheries worldwide. Information on killer whale depredation in the northwestern Pacific Ocean is limited. The goal of this work was to assess the extent of killer whale depredation on the groundfish fisheries in the western Bering Sea and the Sea of Okhotsk. Observations of killer whale depredation were conducted on 8 of the 42 (19%) longline fishing vessels between October 2018 and September 2019. Killer whales depredated during 2.0% of vessel days in the western Bering Sea and 18.6% of vessel days in the Sea of Okhotsk, taking exclusively Greenland turbot (Reinhardtius hippoglossoides). Seventy-one killer whales were identified depredating on longlines in the Sea of Okhotsk, with the best estimation for the total number of killer whales depredating about 139 individuals. Results suggest that killer whale depredation is an issue for Greenland turbot longline fisheries in the northwestern Pacific. There is a strong need for mitigation measures, as this has an economic impact on the fisheries and also affects the killer whale population and associated ecosystems.
... The emergence of longline fishing throughout the world's oceans is concomitant with increasing reports of depredation interactions by marine toppredators, primarily odontocetes (toothed whales), with fishing vessels (Northridge, 1991;Northridge and Hofman, 1999;DeMaster et al., 2001;Read, 2008;Hamer et al., 2012). Depredation occurs when odontocetes feed on fish caught by fishers on longline sets (Read et al., 2005, Hamer et al. 2012, Werner et al. 2015. ...
... The emergence of longline fishing throughout the world's oceans is concomitant with increasing reports of depredation interactions by marine toppredators, primarily odontocetes (toothed whales), with fishing vessels (Northridge, 1991;Northridge and Hofman, 1999;DeMaster et al., 2001;Read, 2008;Hamer et al., 2012). Depredation occurs when odontocetes feed on fish caught by fishers on longline sets (Read et al., 2005, Hamer et al. 2012, Werner et al. 2015. This depredation often results in socio-economic (financial losses for fishers), ecological (effects on depredating species) and conservation issues (impacts on depredated resources) (Gasco et al., 2015;Tixier et al., 2015Tixier et al., , 2017Werner et al., 2015;Esteban et al., 2016;Peterson and Hanselman, 2017;Hanselman et al., 2018). ...
Conference Paper
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The emergence of longline fishing for Patagonian toothfish (Dissostichus eleginoides) on the Kerguelen Plateau over the past two decades is concomitant with the development of depredation-type interactions by sperm whales (Physeter macrocephalus). Through a unique collaboration between the French and the Australian fisheries operating respectively around Kerguelen, and Heard Island and McDonald Islands (HIMI), this study preliminarily investigated the spatio–temporal variations of the rate of occurrence of sperm whale depredation on the Kerguelen Plateau. Between 2011 and 2016, sperm whales depredated toothfish on 29.1% of all longline sets and over 49.4% of the fished area. The probability of vessels to experience depredation decreased with the latitude and decreased in winter. Vessels operating in Kerguelen experienced significantly higher rates of occurrence of sperm whale depredation (33.2 ± 4.5% of sets; 48.2 ± 7.2% of the area) than vessels operating in HIMI (3.1 ± 1.2% of sets; 5.4 ± 2.0% of the area) over the 2011–2016 period, but also during any season of the year. The results suggested that heterogeneity in the distribution of sperm whales is likely a key driver of depredation. The Kerguelen Plateau fisheries represent a unique opportunity to investigate the spatial factors influencing this distribution, and therefore to predict the occurrence of depredation.
... This is the case for some fishing activities which produce acoustic cues that inform marine mammals about the ongoing fishing activity, and the easily available fish resource (Carretta and Barlow, 2011;Mul et al., 2020;Thode et al., 2015). Competition between fishermen and predators may result in depredation behaviour, i.e., predators removing fish from fishing gear (Hamer et al., 2012). This has been mainly reported for longlines, since this fishing gear is composed of a main line with baited hooks, making fish easily accessible for depredating animals (Hamer et al., 2012). ...
... Competition between fishermen and predators may result in depredation behaviour, i.e., predators removing fish from fishing gear (Hamer et al., 2012). This has been mainly reported for longlines, since this fishing gear is composed of a main line with baited hooks, making fish easily accessible for depredating animals (Hamer et al., 2012). Depredation behaviour has substantial socio-economic consequences (Peterson et al., 2014) as well as conservation issues either for the depredating species and for the fish resources (Hanselman et al., 2018). ...
Article
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Fishing boats produce acoustic cues while hauling longlines. These acoustic signals are known to be used by odontocetes to detect the fishing activity and to depredate. However, very little is known about potential interactions before hauling. This article describes the acoustic signature of the setting activity. Using passive acoustic recorders attached to the buoys of longlines, this work demonstrates an increase in the ambient sound of ~6dB re 1 µPa² /Hz within 2–7 kHz during the setting activity. This could also be used as an acoustic cue by depredating species, suggesting that predators can detect longlines as soon as they are set.
... This behaviour, termed depredation, has been reported in large proportions of the world's fisheries (commercial, artisanal and recreational) on most existing types of fishing gear and has multiple impacts on fishing activity, fish resources and marine predator populations (Gilman et al. 2007;Hamer et al. 2012;Trijoulet et al. 2018;Mitchell et al. 2018). For fishermen and fishing companies, depredation-type interactions (hereafter ''depredation'') can generate substantial socio-economic costs by decreasing catch rates, increasing fishing effort and/or causing damage to the fishing gear (Brotons et al. 2008;Gilman et al. 2008;Peterson et al. 2014). ...
... Commercial demersal longline fisheries operating in subantarctic waters targeting Patagonian toothfish (Dissostichus eleginoides) are among the fisheries most impacted by depredation, with two odontocete (toothed whales) species removing toothfish catches from hooks: killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) (Hamer et al. 2012). These fisheries, which operate primarily on shelf edges (500-2000 m deep) within Exclusive Economic Zones (EEZs) of southern Chile, southern Argentina, the Falkland Islands (hereafter ''Falklands''), South Georgia, Prince Edward and Marion Islands (hereafter ''PEMI''), Crozet Islands, Kerguelen Islands, and Heard Island and McDonald Islands (hereafter ''HIMI'') have all experienced depredation by either one or both of these species (Kock et al. 2006;Tixier et al. 2019a). ...
Article
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Marine predators feeding on fisheries catches directly on the fishing gear, a behaviour termed “depredation”, has emerged as a major human-wildlife conflict globally, often resulting in substantial socio-economic and ecological impacts. This study investigated the extent of this conflict in commercial Patagonian toothfish (Dissostichus eleginoides) fisheries across subantarctic waters where both killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) feed on toothfish caught on longline hooks. Using long-term datasets from six major fishing areas, from southern Chile to the Indian Ocean sector of the Southern Ocean, statistical models were developed to quantify the catch removals due to whale depredation interactions. The results indicated that these removals were large, totalling more than 6600 t of toothfish between 2009 and 2016 with an annual mean of 837 t [95% CI 480–1195 t], comprised of 317 t [232–403 t] and 518 t [247–790 t] removed by killer whales and sperm whales, respectively. Catch removals greatly varied between areas, with the largest estimates found at Crozet, where on average 279 t [179–379 t] of toothfish per year, equivalent to 30% [21–37%] of the total catches. Together, these findings provide metrics to assess the impacts of depredation interactions on the fishing industry, whale populations, fish stocks and associated ecosystems. With an estimated $15 M USD worth of fish depredated every year, this study highlights the large geographic scale and economic significance of the depredation issue and its potential to compromise the viability of some toothfish fisheries which are the primary socio-economic activity in subantarctic regions.
... This behavior, termed 'depredation,' has emerged as a worldwide issue in a broad range of fisheries using various fishing techniques (Reeves et al. 2001, Read 2008, Tixier et al. 2021. Longlining stands as the technique most affected by depredation because catches are fully exposed in the water column (Gilman et al. 2006, Read 2008, Hamer et al. 2012, Mitchell et al. 2018. ...
... While depredation has socio-economic impacts on fishing industries through reduced catch rates and damage to fishing gear, it also has effects on biodiversity and ecosystem functioning (Gilman et al. 2006, 2008, Hamer et al. 2012, Mitchell et al. 2018). Among these effects, bycatch and injuries to the predators from direct interactions with fishing gear have been documented in many fisheries (Werner et al. 2015). ...
Article
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Fisheries modify prey availability for marine predators by extracting resources but also by providing them with new feeding opportunities. Among these, depredation, which occurs when predators feed on fish caught on fishing gear, is a behavior developed by many species as a way to acquire food through limited foraging effort. However, the extent to which depredated resources from fisheries contribute to the energetic requirements and affect the demography of depredating individuals is unknown. We investigated the contribution of Patagonian toothfish Dissostichus eleginoides depredated on longlines to the energetic requirements of killer whales Orcinus orca around the Crozet Islands (southern Indian Ocean) over the period 2007−2018. Our results indicate that during days when depredation occurred, depredating individuals fulfilled on average 94.1% of their daily energetic requirements with depredated toothfish. However, the contribution varied from 1.2 to 13.3% of the monthly energetic requirements and from 2.4 to 8.8% of the yearly energetic requirements of the total population. Together, these findings suggest that intake of depredated toothfish can be substantial at a fine scale (daily and individually), potentially leading to temporary provisioning effects and changes in predation pressures. These effects become minor (<10%), however, when considering the full population over a whole year. The contribution of depredated fish to the annual energetic requirements of the population has increased in recent years, likely due to larger fishing quotas and greater opportunities for whales to depredate, which stresses the importance of accounting for depredation in ecosystem-based management of fishing activity.
... Therefore, longlining is a fishing technique that makes caught fish easily accessible for depredating animals. It has been reported to be the fishing technique most impacted by depredation, especially by toothed whales, i.e. odontocetes (Northridge and Hofman 1999;Donoghue et al. 2002;Gilman et al. 2006;Hamer et al. 2012). Indeed, at least 31 species of odontocetes have been reported to interact (either through depredation or bycatch) with longline fisheries worldwide (Werner et al. 2015). ...
... contains supplementary material, which is available to authorized users. with longlines may increase risks of mortality, either by entanglement in fishing gear, i.e. bycatch (Northridge 1991;Trites et al. 1997;Read et al. 2006;Hamer et al. 2012), or by the use of lethal methods by illegal fisheries to eliminate competitors (Poncelet et al. 2009;Guinet et al. 2015). Also, depredation often involves access to new and easy-to-catch prey resource for predators, which may modify both the energy balance of odontocetes and the natural predator-prey dynamics of local ecosystems (Trites et al. 1997;Northridge and Hofman 1999;Boyd 2002;Guénette et al. 2006;Morissette et al. 2012;Tixier et al. 2017). ...
Article
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Toothed whales (odontocetes) feeding on fish caught on hooks in longline fisheries is a growing issue worldwide. The substantial impacts that this behaviour, called depredation, can have on the fishing economy, fish stocks and odontocetes populations, raise a critical need for mitigation solutions to be developed. However, information on when, where and how odontocete depredation occurs underwater is still limited, especially in demersal longline fisheries (fishing gear set on the seafloor). In the present study, we investigated depredation by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) on demersal longlines in the French Patagonian toothfish fishery (Southern Ocean). Using a combination of animal-borne behavioural and longline-attached data loggers, we demonstrated that both species are able to depredate longlines on the seafloor. This study, therefore, suggests that odontocetes whales–longline interaction events at depth may be unrecorded when assessing depredation rates from surface observations during hauling phases only. This result has implications for the management of fisheries facing similar depredation issues as underestimated depredation rates may result in unaccounted fish mortality in fish-stock assessments. Therefore, while further research should be conducted to assess the extent of deep-sea whale–longline interaction events during soaking, the evidence that depredation can occur at any time during the whole fishing process as brought out by this study should be considered in future developments of mitigation solutions to the issue. (Free access here: https://rdcu.be/bAkAi )
... Conservation impacts for the depredated fish include inaccurate stock assessments due to difficulties in estimating the amount of fish taken by odontocetes. For the depredating species, conservation impacts include negative effects due to increased risks of injury caused by fishing gear or lethal responses from fishers, increased dependency to depredation and alteration of natural energy intake balances, and positive effects from artificial food provisioning 8,[10][11][12][13][14][15][16][17][18][19][20] . While odontocete interactions have been increasingly reported over the past decade, it is unclear whether the issue is actually increasing in frequency and intensity 10 . ...
... For the depredating species, conservation impacts include negative effects due to increased risks of injury caused by fishing gear or lethal responses from fishers, increased dependency to depredation and alteration of natural energy intake balances, and positive effects from artificial food provisioning 8,[10][11][12][13][14][15][16][17][18][19][20] . While odontocete interactions have been increasingly reported over the past decade, it is unclear whether the issue is actually increasing in frequency and intensity 10 . In addition, the mechanisms leading whales to change from natural foraging behaviours to depredation are poorly understood. ...
Article
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The emergence of longline fishing around the world has been concomitant with an increase in depredation-interactions by odontocete whales (removal of fish caught on hooks), resulting in substantial socio-economic and ecological impacts. The extent, trends and underlying mechanisms driving these interactions remain poorly known. Using long-term (2003–2017) datasets from seven major Patagonian toothfish (Dissostichus eleginoides) longline fisheries, this study assessed the levels and inter-annual trends of sperm whale (Physeter macrocephalus) and/or killer whale (Orcinus orca) interactions as proportions of fishing time (days) and fishing area (spatial cells). The role of fishing patterns in explaining between-fisheries variations of probabilities of odontocete interactions was investigated. While interaction levels remained globally stable since the early 2000s, they varied greatly between fisheries from 0 to >50% of the fishing days and area. Interaction probabilities were influenced by the seasonal concentration of fishing effort, size of fishing areas, density of vessels, their mobility and the depth at which they operated. The results suggest that between-fisheries variations of interaction probabilities are largely explained by the extent to which vessels provide whales with opportunities for interactions. Determining the natural distribution of whales will, therefore, allow fishers to implement better strategies of spatio-temporal avoidance of depredation.
... This study updates information provided in an earlier review of cetacean interactions with trawlers (Fertl and Leatherwood 1997), and is intended to complement previous work describing conflict and behavioral adaptation to fishing gear generally (e.g. Northridge and Hofman 1999;Plagányi and Butterworth 2005;Gilman et al. 2006a, b;Kock et al. 2006;Read 2008;Hamer et al. 2012;Werner et al. 2015;Northridge 2018;Bearzi et al. 2019;Tixier et al. 2021). We searched the literature for records of cetacean occurrence and behavior in the proximity of trawlers, worldwide. ...
... Finally, a "move-on" tactic (moving away from an area where interactions have occurred or are likely to occur) is sometimes used to "outrun" wouldbe depredating odontocetes and pinnipeds, particularly in longline fisheries. This tactic is costly and difficult to enforce, however, and its effectiveness seems questionable (Hamer et al. 2012;Werner et al. 2015;Fader et al. 2021) considering that some odontocetes (as well as pinnipeds; Tilzey et al. 2006) are able to follow and remain with a fast-moving trawler over long distances (Genov et al. 2008;Allen and Loneragan 2010;Allen et al. 2017), and to detect acoustic signatures from faraway fishing vessels (Fader et al. 2021). ...
Article
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Several populations of odontocete cetaceans, including at least 19 species, have modified their behavior and adapted to foraging in association with trawlers. We review information on odontocete interactions with different types of trawlers across 13 Food and Agriculture Organization fishing areas around the world. We also review knowledge gaps, the effects on odontocete ecology, distribution, behavior and social organization, the main mitigation options, and some management avenues that could help reduce incidental mortality. Trawlers involved in the interactions varied greatly in gear and target species, implying odontocetes have developed behavioral specializations to forage under a variety of conditions. Specialized behavior included venturing into a moving trawl net to feed on the organisms trapped in the net, feeding on fish stirred up by the net, extracting fish from the outer mesh, feeding on catch lost during hauling, and scavenging on discarded catch. Foraging behind trawlers facilitates access to prey, and in some instances may compensate for scarcity of natural prey within areas exposed to intensive fishing or environmental degradation. This opportunistic foraging strategy, however, exposes the animals to potential harm and mortality in trawl gear. The combined effect of facilitated foraging and bycatch on the status and trends of odontocete populations is unknown. The economic damage caused by odontocetes, e.g. in terms of loss of marketable catch and gear damage, remains largely conjectural. Attempts to reduce depredation and/or bycatch in trawl gear have included acoustic deterrents and exclusion devices installed in nets, although neither technique has proven to be consistently effective. --- https://doi.org/10.1007/s11160-022-09712-z
... To date, research has focused predominantly on the occurrence of shark depredation in large scale commercial longline fisheries in open ocean areas, where the rates of depredation have been quantified and the shark species responsible identified (Gilman et al., 2007b;IOTC, 2007;Mandelman et al., 2008;MacNeil et al., 2009;Mitchell et al., 2018b). There is also a large body of research focusing on depredation by cetaceans in these fisheries (Hamer et al., 2012;Tixier et al., 2020), where these predators are responsible for more substantial losses of catch than sharks in some cases (IOTC, 2007;Rabearisoa et al., 2007). Gilman et al. (2007b) quantified shark depredation in 12 commercial longline fisheries around the world, with the highest rate (20%) recorded in the Australian Eastern Tuna and Billfish Fishery. ...
... Sperm whales are responsible for depredation in commercial longline fisheries around the Australian Heard and McDonald Islands in the Southern Ocean (Tixier et al., 2019). These whales sometimes get hooked or entangled in the longlines, leading to mortality, and they may occasionally be deliberately injured or killed by frustrated fishers (Hamer et al., 2012). Certain localised populations of these whales have changed their behaviour to take advantage of this food resource (Gilman et al., 2007a), and their habituation to vessels may make them more vulnerable to ship strikes. ...
... Previous interviews with local artisanal fishermen in the study area did not report any interaction with franciscanas when using hooks (Weiskel et al., 2002). However, entanglement and death in unbaited and rolling hooks was documented for the Baiji (Lipotes vexillifer) (Zhou and Li, 1989;Zhou and Wang, 1994;Zhou et al., 1998;Reeves et al., 2000) and up to 15 odontocetes species have been recorded bycaught on pelagic longline hooks (Hamer et al., 2012). Therefore, the possibility of increased bycatch risk and/or depredation of bait by franciscana in this fishing gear should be monitored. ...
... The use of fishing lines, especially pelagic longlines, has been widely reported to result in the bycatch of seabirds, sea turtles (e.g., Cherel et al., 1996;Barnes et al., 1997;Lewison et al., 2004b) FIGURE 7 | Incremental Profitability Rate (IRP) profiles for BSB at 1-and 5-year scenarios. and marine mammals (Szteren and Páez, 2002;Donoghue et al., 2003;Hamer et al., 2012). However, no seabirds were caught in bottom longlines or even gillnets during this experiment, and have not previously been documented as bycatch in this artisanal fishery. ...
Article
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The franciscana dolphin (Pontoporia blainvillei) is considered the most threatened cetacean in the South Western Atlantic due to bycatch in gillnet fisheries of Argentina, Uruguay, and Brazil. As gillnet fisheries operate in the same areas inhabited by dolphins, methods and strategies to reduce bycatch require particular attention. This study investigated the potential of switching gillnets to bottom longlines to reduce franciscana bycatch rates while maintaining economic returns in a small-scale artisanal fishery in Argentina. Trials were conducted in Bahía Samborombón and Cabo San Antonio between October 2004 and January 2007, in cooperation with artisanal fishermen who simultaneously fished using bottom longlines and gillnets. Target and non-target catch composition, fishing yield, catch size distribution and quality of catch, as well as bycatch of dolphins, sea turtles, and interaction with sea lions were compared between the two fishing methods to assess the profitability of switching fishing gears. Hauls of both gear types deployed simultaneously in the same locations showed similar fish catch composition and catch size with both gears but reduced catch of juvenile fishes in longlines. Bycatch of franciscana in bottom longlines was limited to only one dolphin in three consecutive years of trials, and no direct interaction between turtles and hooks were recorded. The economic analysis showed financially acceptable perspectives under a 5-year scenario. Reducing gillnet effort by switching to bottom longlines appears a practical approach to creating a sustainable fishery that could result in significant mitigation of current bycatch of franciscana dolphins in Argentina. However, implementation requires acceptance and compliance by the artisanal gillnet fishery.
... Such species are often inherently vulnerable, having low reproductive rates, and reduced and declining population trends (e.g. [8] [9] [10] [11] [12] ). Some ETP species have important ecological value as top predators, and also have high cultural value to many people around the world. ...
Technical Report
Full-text available
Remote Electronic Monitoring with cameras (REM) of fisheries is a powerful tool to underpin sustainable fisheries management. This report explores how REM can be used to address the particular issue of unintentional capture of Endangered, Threatened and Protected (ETP) species in commercial fishing.
... While livestock depredation is a long established HWC, large marine predators feeding on fisheries catches has emerged as another form of depredation, concomitantly with the global expansion of fisheries (Hamer, Childerhouse, & Gales, 2012;Northridge, 1984Northridge, , 1991Read, 2008;Wickens, 1995). By reducing catches for fishers, causing damage to fishing gear, increasing risks of by-catch or lethal retaliation and provisioning predators with easy-to-capture and sometimes new prey resources, the depredation conflict affects marine socio-ecological systems at all levels (Bearzi, Piwetz, & Reeves, 2019;Gilman, Laporta, Martinez Portela, Santos, & Pierce, 2008;Werner, Northridge, Press, & Young, 2015). ...
Article
The sustainable mitigation of human–wildlife conflicts has become a major societal and environmental challenge globally. Among these conflicts, large marine predators feeding on fisheries catches, a behaviour termed “depredation,” has emerged concomitantly with the expansion of the world’s fisheries. Depredation poses threats to both the socio‐economic viability of fisheries and species conservation, stressing the need for mitigation. This review synthesizes the extent and socio‐ecological impacts of depredation by sharks and marine mammals across the world, and the various approaches used to minimize it. Depredation was reported in 214 fisheries between 1979 and 2019 (70% post‐2000) and affected fleets from 44 countries, in all sectors (commercial, artisanal and recreational), and in all major fishing techniques (nets, traps and hook‐and‐lines). A total of 68 predator species were involved in depredation (20 odontocetes, 21 pinnipeds and 27 sharks), and most (73%) were subject to either by‐catch and/or retaliatory killing from fishers when interacting with gear. Impacts on fishers were primarily associated with catch losses and gear damage but often lacked assessments. Deterrence was a major mitigation approach but also the least effective. Gear modifications or behavioural adaptation by fishers were more promising. This review highlights the need for improved monitoring, and interdisciplinary and integrated research to quantify the determinants and impacts of depredation in the socio‐ecological dimension. More importantly, as the conflict is likely to escalate, efforts directed towards changing perceptions and integrating knowledge through adaptive co‐management are raised as key directions towards coexistence between fisheries and large marine predators.
... In Table 10.1 we provide examples of published cases of behavioral adaptation or changed behavior in response to human encroachment. Recognizing that many reviews of odontocete "interactions" with human activities have already been published, including those involving opportunistic depredation of fishing gear, scavenging, and facilitated predation (Fertl and Leatherwood 1997;Northridge and Hofman 1999;Plagányi and Butterworth 2005;Gilman et al. 2006;Kock et al. 2006;Read 2008;Hamer et al. 2012;Werner et al. 2015;Northridge 2018), we have sought to offer a quick overview rather than a comprehensive literature survey. The examples included in Table 10.1 encompass cases of adaptation of odontocete species to fisheries and aquaculture, as well as occurrence in human-made channels and canals, near dams, near oil and gas platforms, or close to urbanized areas. ...
Chapter
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Some mammalian species that have not succumbed to pervasive human impacts and encroachments have managed to adapt to certain types of human activities. Several odontocetes have modified their behavior to persist, and in some cases even prosper, in human-altered riverine, coastal, and oceanic habitat. Examples include cooperation with fishers to catch fish, depredation on fishing gear, scavenging, and other kinds of opportunistic foraging (e.g., behind trawlers, around fish farms, or near built structures such as dams and offshore platforms). Some populations have adapted to life in human-made channels and waterways. We review information on the variety of odontocete adaptations to human encroachment, highlight some of the risks and benefits, and try to single out factors that may trigger or contribute to adaptation. Adaptation often brings wildlife into close contact with humans, which leads to conflict. We discuss the challenges of coexistence and contend that we humans, too, need to adjust our behavior and change how we perceive and value wildlife for coexistence to be possible. In addition to good management and conservation action, tolerance on our part will be key for allowing wildlife—odontocetes included—to persist. We advocate cultural and even spiritual shifts that can foster tolerance, nurture the social change that leads to appreciation for wildlife, and create more opportunities to preserve nature.
... Killer whales often forage in groups, and in some populations, group size was shown to determine the success of prey capture and the size of the prey (11,16,49). The killer whale is also one of the species most involved in depredation interactions with fisheries worldwide (50). At the Crozet Islands, early studies initiated in the 1970s and 1980s showed that killer whales associated in stable social groups with limited dispersal from these units. ...
Article
In highly social top predators, group living is an ecological strategy that enhances individual fitness, primarily through increased foraging success. Additive mortality events across multiple social groups in populations may affect the social structure, and therefore the fitness, of surviving individuals. This hypothesis was examined in a killer whale ( Orcinus orca ) population that experienced a 7-y period of severe additive mortality due to lethal interactions with illegal fishing vessels. Using both social and demographic analyses conducted on a unique long-term dataset encompassing periods before, during, and after this event, results indicated a decrease in both the number and the mean strength of associations of surviving individuals during the additive mortality period. A positive significant correlation between association strength and apparent survival suggested that the fitness of surviving individuals was impacted by the additive mortality event. After this event, individuals responded to the loss of relatives in their social groups by associating with a greater number of other social groups, likely to maintain a functional group size that maximized their foraging success. However, these associations were loose; individuals did not reassociate in highly stable social groups, and their survival remained low years after the mortality event. These findings demonstrate how the disruption of social structure in killer whales may lead to prolonged negative effects of demographic stress beyond an additive mortality event. More importantly, this study shows that sociality has a key role in the resilience of populations to human-induced mortality; this has major implications for the conservation of highly social and long-lived species.
... If rates of bait depredation vary by bait type, then this could reduce the accuracy of estimates of the effect of bait type on species-specific catch risk. Cetaceans, sharks, seabirds and some teleosts are the main species that remove baits from pelagic longline gear, while squids and crustaceans can partially depredate pelagic longline baits (Brothers 1991;Gilman et al. 2006Gilman et al. , 2008Hamer et al. 2012). For example, if blue sharks have a higher depredation rate of squid bait relative to forage fish bait, then this would result in overestimating other species' relative risk of capture on fish relative to squid bait due to squiddepredated baitless hooks being counted as available squid-baited hooks. ...
Article
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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 trade-offs when multispecies conflicts are unavoidable, and highlight research priorities for global pelagic longline fisheries.
... Swordfish diet composition studies have been conducted in the East Atlantic (Moreira, 1990;Clarke et al. 1995;Hernández-García, 1995), North Atlantic (Scott & Tibbo, 1968;Stillwell & Kohler 1985;Guerra et al. 1993;Chancollon et al, 2006;), Mediterranean Sea (Bello 1991), and Pacific (Markaida & Sosa-Nishizaki 1998). The species changes its eating habits at a very early age, moving from a diet based on copepods to one based almost entirely on fish (Vedel Tanning 1955). ...
Technical Report
This Public Comment Draft Report provides details to the stakeholders and general public on the MSC assessment for the North and South Swordfish fishery prepared by the team. CLIENTS: Organización de Palangreros Guardeses (ORPAGU) & the fishing Spanish Confederation, Confederación Española de Pesca (CEPESCA)
... Depredation occurs when hooked fish are removed or killed from fishing lines and/or gear by predators prior to landing (Raby et al., 2014). Though depredation has been studied in other taxa (Knowlton et al., 1999;Naughton-Treves et al., 2003), with several examples coming from the marine environment (Garrison, 2007;Powell and Wells, 2011;Hamer et al., 2012;Mitchell et al., 2018a), little is known about its impact with respect to recreational C&R angling. Depredation is not unique to the Florida Keys (O'Toole et al., 2010;Mitchell et al., 2018aMitchell et al., , 2018b, however, the incidence of permit depredation on offshore structures represents a potential threat to their conservation. ...
... In anticipation of, or in response to, these impacts, fishers generally implement fishing behaviours (i.e. a set of decisions and strategies related to fishing) aimed to maximise fishing success and minimise depredation-type interactions (hereafter referred to as "interactions"). This is achieved by spatial and temporal avoidance of depredating species and/or by operational changes in the way they use the fishing equipment (Hamer et al., 2012;Werner et al., 2015). For example, avoidance behaviours include the selection of areas and/or time of the year during which the risks of interactions are low, and, when an interaction occurs, the displacement of fishing operations to new fishing grounds located large distances away (Janc et al., 2018;Straley et al., 2015;Tixier et al., 2016). ...
Article
Full-text available
Fishers aim to optimise cost-benefit ratios of their behaviour when exploiting resources. Avoidance of interactions with marine predators (i.e. their feeding on catches in fishing gear, known as depredation), has recently become an important component of their decisions. How fishers minimise these interactions whilst maximising fishing success is poorly understood. This issue is addressed in a sub-Antarctic, long-line fishery confronted with extensive depredation by sperm whales Physeter macrocephalus and killer whales Orcinus orca by examining a 15-year dataset. Whereas a broad range of behaviours was identified from spatio-temporal and operational descriptors, none combined high fishing success with low frequency of interactions. With experience, fishers favoured exploitation of productive patches with high frequencies of interactions over avoidance behaviours. Such decisions, although potentially optimal in the short-term, are likely to intensify pressures on fish stocks and impact depredating whales. Therefore, the present study provides additional evidence to inform management decisions pertaining to the coexistence between fisheries and marine predators.
... Solutions to mitigate cetacean bycatch have targeted specific fisheries and gears (e.g., longline [Hamer et al. 2012]; gill net [Trippel et al. 1999], trawl [Hamer et al. 2008], trap [How et al. 2015]) or individual species (e.g., Hamer et al. 2008;Leaper 2016). Such targeted management can be effective if interactions only occur between a particular population and gear type or fishery. ...
Article
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Globally, fisheries bycatch threatens the survival of many whale and dolphin species. Strategies for reducing bycatch can be expensive. Management is inclined to prioritize investment in actions that are inexpensive, but these may not be the most effective. We used an economic tool, return-on-investment, to identify cost-effective measures to reduce cetacean bycatch in the trawl, net, and line fisheries of Australia. We examined 3 management actions: spatial closures, acoustic deterrents, and gear modifications. We compared an approach for which the primary goal was to reduce the cost of bycatch reduction to fisheries with an approach that aims solely to protect whale and dolphin species. Based on cost-effectiveness and at a fine spatial resolution, we identified the management strategies across Australia that most effectively abated dolphin and whale bycatch. Although trawl-net modifications were the cheapest strategy overall, there were many locations where spatial closures were the most cost-effective solution, despite their high costs to fisheries, due to their effectiveness in reducing all fisheries interactions. Our method can be used to delineate strategies to reduce bycatch threats to mobile marine species across diverse fisheries at relevant spatial scales to improve conservation outcomes. © 2019 Society for Conservation Biology.
... Our study brings new, objective (quantified from scientific data) information about marine mammal and fisheries interactions in the Northwestern Mediterranean Sea. These interactions usually occur because of competition for a similar resource, and has become a worldwide concern (Morissette et al. 2012, Snape et al. 2018) -both in terms of conservation, as they result in dolphin mortality due to by-catch (Hall et al. 2000, Bearzi 2002) and in terms of economic losses due to depredation or damage to fishing gear (Bearzi 2002, Hamer et al. 2012, even if they could be overvalued in some cases (Trites et al. 1997, Gazo et al. 2008. This is true in several parts of the Mediterranean Sea (e.g. ...
Thesis
The Gulf of Lions has faced a sharp drop in the catches of its two main small pelagic exploited species, the sardine Sardina pilchardus and the anchovy Engraulis encrasicolus since the mid-2000s, despite both population abundances remaining high. This situation has been due to a severe decrease in individual body condition and size as a result of both lower growth and the disappearance of the oldest and largest individuals. While overfishing, predation or disease outbreaks have been refuted to explain this situation, one major hypothesis remained to be investigated. A potential shift in sardine and anchovy diet towards smaller planktonic prey indeed suggested bottom-up control as the main driver of these populations in the Gulf of Lions. The first aim of this thesis was to investigate whether bottom-up processes could explain the changes in sardine growth and condition through changes in both food size and/or quantity and to understand the behavioral and physiological mechanisms involved in this control. The second objective of this PhD thesis was to identify the potential underlying drivers leading to adult overmortality. To do so, we combined an experimental approach on wild sardines maintained in captivity with a modeling approach. Experimentations showed that body condition, growth and storage lipids were significantly impacted by both food size and quantity. Thus, sardines fed on small particles needed to consume twice as much as those feeding on large particles to achieve the same condition and growth. Such results seemed to be linked to higher energy expenditures of sardines while filtering small prey compared to particulate feeding on large prey (sardines being able to shift between two feeding modes according to the prey size). Moreover, our results suggested several adaptations to cope with small food and caloric restriction. The study of the gill raker apparatus involved in the filtration of small prey suggested an increase of the filtration capacity for a given length between 2007-2009 and 2016. Then, sardines fed on small particles exhibited higher mitochondria efficiency and abundance suggesting energy-saving adaptation. Finally, sardines accustomed to feed on small pellets showed lower activity to limit energy expenditure. Nevertheless, all these strategies might incur other costs or may not be enough to compensate the high energy demands of filtration on small prey, as growth and condition remained lower for sardines filtering small prey in all our experiments. Further, sardines fed on large pellets exhibited higher spawning frequency than sardines fed with the same quantity of small ones. The low egg production of these sardines might be explained by a too high body condition of these individuals to observe a change in energy trade-off towards reproduction. For the same reasons, small particle meals did not seem to impact their immunity and stress, leucocyte and cortisol concentrations being similar whatever the feeding treatment. Furthermore, to investigate the hypothesis of adult overmortality, we first studied whether individual could die from starvation and low body reserves. The survival probability sharply decreased when the body condition index became lower than 0.75 and the threshold of 0.72 was identified as the entry in phase III of fasting. While the proportion of sardines reaching such thresholds in the wild remains low, it still increased two-fold in the recent period, reaching about 10% in winter months. A DEB model parameterized using a combination of in-situ and experimental data suggested a lower survival probability for larger fish. Individuals larger than 14 cm, i.e. older than 2-3 years, had a lower than 50 % probability to survive 1 month after the reproduction period. In conclusion, these previous results comforted the two hypotheses of a bottom-up control and an overmortality of adult sardines after reproduction to explain the dynamic and demographic truncation of the sardine population.
... Identifying sharks involved in depredation events is important for fisheries management and for designing effective deterrent measures, which can be species-specific (Brill et al. 2009, Hart & Collin 2015. However, depredation by sharks remains relatively understudied (compared to cetacean depredation) (IOTC 2007, Hamer et al. 2012, Mitchell et al. 2018b due to difficulties observing depredation events not occurring close to fishing vessels. Previous studies identified depredating shark species through observation of surface depredation events (Backus et al. 1956) or through the analysis of stomach contents (Celona et al. 2005, Romanov et al. 2007), but this may not be possible for a large proportion of depredation events. ...
Article
Shark depredation, whereby a shark consumes an animal caught by fishing gear, can cause higher mortality for target species, injury to sharks and the loss of catch and fishing gear. A critical first step towards potential mitigation is understanding this behaviour and the shark species involved, because the identity of depredating shark species is unknown in many fisheries, and behavioural dynamics of shark interactions with fishing gear are not well understood. We used line-mounted video cameras in a recreational fishery in the Ningaloo region of Western Australia to: (1) identify shark species responsible for depredation, (2) investigate behavioural interactions with fishing gear, (3) identify the prevalence of retained fishing gear in sharks and (4) quantify the influence of environmental variables and fishing methods on shark abundance during demersal fishing at 92 locations. The shark depredation rate was 9.1%, and sicklefin lemon Negaprion acutidens, blacktip/Australian blacktip Carcharhinus limbatus/tilstoni, grey reef C. amblyrhynchos and spottail C. sorrah sharks were observed depredating lethrinid and epinephelid fishes. Five additional shark species from 4 families were recorded but were not responsible for depredation. Sharks frequently investigated baited hooks and other fishing gear components and were observed following the fishing gear as it was retrieved. The relative abundance of sharks at each fishing location was influenced by longitude, sea surface temperature and total number of fish hooked. By identifying the shark species responsible for depredation, and investigating their behavioural interactions with fishing gear, this study provides important insights that have broader significance to other fisheries, particularly for understanding impacts on sharks and for developing effective deterrents to mitigate shark depredation.
... For common bottlenose dolphins in Ecuador, the prevalence of anthropogenic scarring in the population was ∼44% (Felix et al., 2018), in the Mayotte archipelago 15% of Indo-Pacific bottlenose dolphins (Tursiops aduncus) had anthropogenic scars (Kiszka et al., 2008), while 7.5% of false killer whales off Hawaii were found to have anthropogenic scarring (Baird et al., 2014). Entanglement rates have also been found to increase due to particular kinds of cetacean social or foraging behavior, such as depredation in sperm whales (Physeter macrocephalus, Hamer et al., 2012) and open mouth filter feeding in North Atlantic right whales, where 85% of individuals bear entanglement scars (Moore, 2019). While we have observed and are aware of other accounts of northern bottlenose approaching fishing vessels, being hand fed by fishers and depredating trawl and longline fisheries in Newfoundland, Labrador and Baffin Bay (Oyarbide Cuervas-Mons, 2008;Fisheries and Oceans Canada, 2009;Johnson et al., 2020; Wayne Ledwell pers. ...
Article
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Photo-identification methods depend on markings that are stable over time. Using a large dataset of photographs taken over a 31-year period, we evaluate the reliability, rate of change and demographic trends in different mark types on northern bottlenose whales (Hyperoodon ampullatus) in the Endangered Scotian Shelf population, and assess the prevalence and severity of anthropogenically caused markings. Only fin notches and back indentations were stable over long timescales, leading to 48% of the overall population being assessed as reliably marked. Males and mature males were found to have higher incidence of most mark types compared to females and juveniles. The proportion of reliably marked individuals increased over time, a trend that should be accounted for in any temporal analysis of population size using mark-recapture methods. An overall increase in marked individuals may reflect the accumulation of scars on an aging population post whaling. Anthropogenic markings, including probable entanglement and propeller-vessel strike scars, occurred at a steady rate over the study period and were observed on 6.6% of the population. The annual gain rate for all injuries associated with anthropogenic interactions was over 5 times the annual potential biological removal (PBR) calculated for the endangered population. As entanglement incidents and propeller-vessel strike injuries are typically undetected in offshore areas, we provide the first minimum estimate of harmful human interactions for northern bottlenose whales. With low observer effort for fisheries across the Canadian Atlantic, photo-identification offers an important line of evidence of the risks faced by this Endangered whale population.
... Within the last decade, humpback whales have been reported for the first time feeding on juvenile Pacific salmon (Oncorhynchus spp.) at hatchery release sites in Southeast Alaska (Chenoweth et al., 2017) with documented economic impacts (Chenoweth & Criddle, 2019). Depredation, including by marine mammals, is commonly associated with energetic benefits partially offsetting risks of close human contact (Hamer et al., 2012;Mathias et al., 2012;Tixier et al., 2015). In this situation, differences in marginal potential energetic benefit (PEB) between hatchery salmon and typical wild prey, like krill and small schooling fishes (Nemoto, 1957(Nemoto, , 1973Straley et al., 2017), may determine whether whale predation of juvenile hatchery salmon is likely to increase in the future. ...
Article
The relative energetic benefits of foraging on one type of prey rather than another are not easily measured, particularly for large free‐ranging predators. Nonetheless, assumptions about preferred and alternative prey are frequently made when predicting how a predator may impact its environment, adapt to environmental change, or interact with human activities. We developed and implemented a process‐based model to investigate the potential energetic benefit (PEB) of in situ foraging opportunities in rorqual whales. The model integrates and evaluates the energetic importance of measured prey patch characteristics (prey distribution, energy content and predator avoidance) and predator characteristics (morphometrics, foraging tactics and feeding rates). We applied the model to test the assumption that hatchery‐released juvenile salmon are an “easy meal” for humpback whales compared to more common prey, herring and krill. In eleven out of the thirteen foraging situations considered, whales were found to be feeding in a manner where net energy gain was greater than the energetic costs of non‐foraging swimming. Humpback whale PEB for hatchery‐released juvenile salmon fell within the range of the PEB for krill and herring but varied by species, from relatively high PEB for chum salmon to relatively low for coho salmon. Our model provides behavioral insight as well, indicating that shallow feeding may be more important for reducing energy expenditure through slower lunge speeds than for increasing prey capture. The model also provides a means of identifying prey patch characteristics, with prey aggregation playing the largest role in determining PEB despite being a poor overall proxy for PEB, supporting the use of the complex model framework. Modeling approaches are especially valuable where they can use reasonable assumptions to substitute for lack of reliable observations, thereby integrating a range of interacting factors into a single framework. Additionally, because process‐based models can make predictions outside the range of previously observed conditions, they will be increasingly useful in a changing climate.
... Many marine predators engage in depredation by consuming bait or fish secured on fishing gear. This behavior is very common and costly in longline fisheries worldwide (Read 2008, Hamer et al. 2012. Odontocetes, or toothed whales, are particularly adept at depredation and can remove large quantities of catch, often with substantial economic impacts ). ...
Article
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False killer whales (Pseudorca crassidens) depredate bait and catch in the Hawai‘i‐based deep‐set longline fishery, and as a result, this species is hooked or entangled more than any other cetacean in this fishery. We analyzed data collected by fisheries observers and from satellite‐linked transmitters deployed on false killer whales to identify patterns of odontocete depredation that could help fishermen avoid overlap with whales. Odontocete depredation was observed on ˜6% of deep‐set hauls across the fleet from 2004 to 2018. Model outcomes from binomial GAMMs suggested coarse patterns, for example, higher rates of depredation in winter, at lower latitudes, and with higher fishing effort. However, explanatory power was low, and no covariates were identified that could be used in a predictive context. The best indicator of depredation was the occurrence of depredation on a previous set of the same vessel. We identified spatiotemporal scales of this repeat depredation to provide guidance to fishermen on how far to move or how long to wait to reduce the probability of repeated interactions. The risk of depredation decreased with both space and time from a previous occurrence, with the greatest benefits achieved by moving ˜400 km or waiting ˜9 d, which reduced the occurrence of depredation from 18% to 9% (a 50% reduction). Fishermen moved a median 46 km and waited 4.7 h following an observed depredation interaction, which our analysis suggests is unlikely to lead to large reductions in risk. Satellite‐tagged pelagic false killer whales moved up to 75 km in 4 h and 335 km in 24 h, suggesting that they can likely keep pace with longline vessels for at least four hours and likely longer. We recommend fishermen avoid areas of known depredation or bycatch by moving as far and as quickly as practical, especially within a day or two of the depredation or bycatch event. We also encourage captains to communicate depredation and bycatch occurrence to enable other vessels to similarly avoid high‐risk areas.
... This behavior, known as depredation, leads to substantial impacts on fishing productivity, the depredating species, and fish stocks (Donoghue et al., 2002;Gilman et al., 2006;Read, 2008). Depredation behavior has been reported for most fisheries and involves a broad range of large marine vertebrates (Donoghue et al., 2002;Gilman et al., 2006Gilman et al., , 2008Hamer et al., 2012;Northridge & Hofman, 1999;Read, 2008;Werner et al., 2015). Most research efforts have focused on interactions between odontocetes and both pelagic and demersal longlines over the last 15 years (Donoghue et al., 2002;Gilman et al., 2006;Northridge, 1991;Northridge & Hofman, 1999;Read, 2008;Reeves et al., 2013;Werner et al., 2015). ...
Article
Odontocetes depredating fish caught on longlines is a serious socio‐economic and conservation issue. A good understanding of the underwater depredation behavior by odontocetes is therefore required. Historically, depredation on demersal longlines has always been assumed to occur during the hauling phase. In this study, we have focused on the depredation behavior of two ecotypes of killer whales, Orcinus orca, (Crozet and Type D) from demersal longlines around the Crozet Archipelago (Southern Indian Ocean) using passive acoustic monitoring. We assessed 74 hr of killer whale acoustic presence out of 1,233 hr of recordings. Data were obtained from 29 hydrophone deployments from five fishing vessels between February and March 2018. We monitored killer whale buzzing activity (i.e., echolocation signals) as a proxy for feeding attempts around soaking longlines. These recordings revealed that the two ecotypes were feeding at close range from soaking longlines, even when fishing vessels were not present. Our results suggest that both killer whale ecotypes are likely to depredate soaking longlines, which would imply an underestimation of their depredation rates. The implication of underestimating depredation rates is inaccurate accounting for fish mortality in fisheries' stock assessments.
... Depredation occurs when fisheries catch is partially or completely consumed by a predator before it can be retrieved (Gilman et al. 2006, Mitchell et al. 2018a. Depredation behaviour has been observed for several taxa including sharks (Mandelman et al. 2008, Mitchell et al. 2018a, teleosts (Shideler et al. 2015), cetaceans (Gilman et al. 2006, Ramos-Cartelle & Mejuto 2008, Hamer et al. 2012) and pinnipeds (Cook et al. 2015, van den Hoff et al. 2017). Depredation by sharks can have economic implications for commercial and recreational fisheries, potentially reaching losses of several hundred dollars per set in ABSTRACT: Shark depredation, whereby hooked fish are partially or completely consumed before they can be retrieved, occurs globally in commercial and recreational fisheries. ...
Article
Shark depredation, whereby hooked fish are partially or completely consumed before they can be retrieved, occurs globally in commercial and recreational fisheries. Depredation can damage fishing gear, injure sharks, cause additional mortality to targeted fish species and result in economic losses to fishers. Knowledge of the mechanisms behind depredation is limited. We used a 13 yr dataset of fishery-dependent commercial daily logbook data for the Mackerel Managed Fishery in Western Australia, which covers 15° of latitude and 10000 km of coastline, to quantify how fishing effort and environmental variables influence depredation. We found that shark depredation rates were relatively low in comparison with previous studies and varied across the 3 management zones of the fishery, with 1.7% of hooked fish being depredated in the northern Zone 1, 2.5% in the central Zone 2 and 5.7% in the southern Zone 3. Generalized additive mixed models found that measures of commercial fishing activity and a proxy for recreational fishing effort (distance from town centre) were positively correlated with shark depredation across Zones 1 and 2. Depredation rates increased during the 13 yr period in Zones 2 and 3, and were higher at dawn and dusk, suggesting crepuscular feeding in Zone 1. This study provides one of the first quantitative assessments of shark depredation in a commercial fishery in Western Australia, and for a trolling fishery globally. The results demonstrate a correlation between fishing effort and depredation, suggesting greater fishing effort in a concentrated area may change shark behaviour, leading to high rates of depredation.
... Other gear types can pose a medium to high risk to marine mammals depending upon their configuration and operation. Longline fisheries can have substantial bycatch of marine mammals, especially odontocetes (toothed whales) known to take bait or target fish from fishing gear (Hamer et al., 2012). Many hooked and/or entangled marine mammals are able to reach the surface to breathe, but even those that are released alive or self-release with some gear remaining attached (e.g., a hook and some amount of line) may have suffered serious injuries that are likely to lead to death. ...
Article
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Bycatch in marine fisheries is the leading source of human-caused mortality for marine mammals, has contributed to substantial declines of many marine mammal populations and species, and the extinction of at least one. Schemes for evaluating marine mammal bycatch largely rely on estimates of abundance and bycatch, which are needed for calculating biological reference points and for determining conservation status. However, obtaining these estimates is resource intensive and takes careful long-term planning. The need for assessments of marine mammal bycatch in fisheries is expected to increase worldwide due to the recently implemented Import Provisions of the United States Marine Mammal Protection Act. Managers and other stakeholders need reliable, standardized methods for collecting data to estimate abundance and bycatch rates. In some cases, managers will be starting with little or no data and no system in place to collect data. We outline a comprehensive framework for managing bycatch of marine mammals. We describe and provide guidance on (1) planning for an assessment of bycatch, (2) collecting appropriate data (e.g., abundance and bycatch estimates), (3) assessing bycatch and calculating reference points, and (4) using the results of the assessment to guide marine mammal bycatch reduction. We also provide a brief overview of available mitigation techniques to reduce marine mammal bycatch in various fisheries. This paper provides information for scientists and resource managers in the hope that it will lead to new or improved programs for assessing marine mammal bycatch, establishing best practices, and enhancing marine mammal conservation globally.
... Seabirds and marine mammals are also commonly caught in longline fisheries worldwide while attempting to feed on the bait or caught fish (Anderson et al., 2011;Hammer et al., 2012;Lewison et al., 2004). The halibut survey bycatch included seven seabird species, such as Northern gannets (Morus bassanus), but in low numbers as in the commercial halibut longline fishery (Mateo et al., 2018). ...
Article
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The Atlantic halibut (Hippoglossus hippoglossus) longline fishery is the second most valuable groundfish fishery in Atlantic Canada and received Marine Stewardship Council certification in 2013. The bottom longline fishery accounts for most halibut landings but incidentally catches nontargeted species (bycatch). Since 1998, Fisheries and Oceans Canada and the halibut fishing industry performed annual longline surveys across the Scotian Shelf and Southern Grand Banks stock management area to monitor halibut abundance, and at‐sea observers also recorded bycatch information. We examined the species composition and proportion of the survey bycatch and analyzed temporal and spatial trends in standardized weight of (a) halibut catch, (b) total bycatch, and (c) bycatch of species of conservation concern. From 1998 to 2016, 70% of the total catch by weight and 85% by number of individuals were bycatch. Over 100 identified species of finfish, sharks, skates, benthic invertebrates, marine mammals, and seabirds were caught as bycatch in the survey. This included four species listed under the Species at Risk Act (Northern wolffish, Anarhichas denticulatus; spotted wolffish, A. minor; Atlantic wolffish, A. lupus; Atlantic cod, Gadus morhua), and another 14 species awaiting a listing decision based on assessments by the Committee on the Status of Endangered Wildlife in Canada. Generally, the standardized weight of halibut and barndoor skate (Dipturus laevis) increased over time, while Atlantic cod, spiny dogfish (Squalus acanthias), white hake (Urophycis tenuis), and thorny skate (Amblyraja radiata) decreased. Spatial patterns indicated high bycatch levels on the southern Scotian Shelf and southern edge of the Southern Grand Banks, with hotspots for certain species of conservation concern. Our results identify temporal trends in threatened species and areas where they are susceptible to the Atlantic halibut longline fishery which can inform recovery strategies, bycatch levels and spatial zoning in fisheries management and marine conservation.
... Surveys of Alaskan longline fishermen suggest that 10-25% of sets may be affected by killer whales Orcinus orca (Peterson and Carothers 2013), and sperm whales Physeter macrocephalus also affect longline fisheries in the Gulf of Alaska (Hanselman et al. 2018). However, published research has focused on removal of fish directly from longlines during soak and retrieval (Hamer et al. 2012), which would not be considered discard mortality in the context of the current study. We observed no marine mammals during tag release, and the cause of the inferred postrelease mortalities could not be identified. ...
Article
Pacific Halibut Hippoglossus stenolepis captured in directed commercial longline fisheries in Canada and the USA that are below the legal minimum size for retention must be returned to the sea without incurring additional injury. Estimates of mortality caused by discarding sublegal‐sized fish are included in annual estimates of total mortality from all sources and affect the results of stock assessment and the yield available to fisheries. Currently, an average discard mortality rate (DMR) of 16% is applied to all sublegal‐sized longline discards. These discards consist of fish that suffer injuries ranging from minor to severe. The 16% DMR that is currently applied was derived by averaging injury‐specific DMRs that in turn assume 3.5% mortality of Pacific Halibut that are released to the sea with only minor injuries. The latter has been derived experimentally but only in captivity. Here, we used acceleration‐logging pop‐up archival transmitting tags to infer individual survival outcomes for Pacific Halibut that were released in situ following capture on longline gear. Postrelease behavioral data were evaluated for 75 fish that were at liberty for 2–96 d. Three fish were confidently inferred to have died after periods at liberty of 41–80 d, and another three fish may have died 96 d after release, resulting in minimum and maximum estimated 96‐d postrelease DMRs of 4.2% (range = 0.0–8.7%) and 8.4% (range = 1.7–14.6%), respectively. These ranges are consistent with the currently applied value of 3.5%. However, the observation that no mortalities occurred until after 40 d postrelease departs from the findings of captive studies, in which the majority of capture‐induced mortality occurred within 20 d of release.
... Bycatch in longlines is reported in other regions but mainly for medium-size odontocetes such as Risso's dolphin (Grampus griseus) and pilot whales (Globicephala spp.) (e.g. Gilman et al., 2006;Hamer et al., 2012;Werner et al., 2015). Seals are often reported to depredate and cause damage to longlines in the ASCOBANS region (Königson et al., 2015b). ...
Technical Report
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Bycatch is a major conservation and welfare issue for cetaceans in European waters. Harbour porpoises and common dolphins are frequently reported to be bycaught in static nets (gillnets and entangling nets) and trawls. Despite European legislation to monitor and mitigate cetacean bycatch in fisheries where it has a negative impact on the conservation status of a species, bycatch still occurs at high rates in several fisheries in the ASCOBANS Agreement Area. The lack of compliance by some countries has resulted in legal challenges from the European Commission for implementation of the required measures. There are two main parts covered in this report. The first part reviews different mitigation measures (acoustic deterrent devices, porpoise alerting devices, reflective nets, acrylic echo enhancers, lights and various technical modifications and changes to fishing practices) that have been trialed in the ASCOBANS region. The cost of implementation and pros and cons of each method are discussed in detail in the relevant sections. The second part of the report reviews alternative fishing methods to replace static nets (i.e. gillnets and entangling nets). The cost of implementation, and pros and cons of the different gears, are discussed in depth in the relevant sections.
... In many regions, spatial, temporal, and oceanographic factors a ect bycatch. For example, management area and season were not associated with bycatch in Australian trawl fisheries (Hamer et al., 2012;Allen et al., 2014), whereas, in the gillnet fisheries of Peru, bycatch was higher in certain geographic locations, but was not associated with seasons (Majluf et al., 2002;Mangel et al., 2010;Ayala et al., 2019). Bycatch estimates also vary across di erent gear types. ...
Article
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Marine mammal interactions with fisheries, such as bycatch and depredation, are a common occurrence across commercial and small-scale fisheries. We conducted a systematic review to assess the management responses to marine mammal interactions with fisheries. We analyzed literature between 1995 and 2021 to measure research trends in studies on direct and indirect interactions for: (i) high and low to middle-income countries, (ii) fishery operations (commercial and small-scale), and (iii) taxonomic groups. Management responses were categorized using the framework described previously in peer-reviewed studies. Marine mammal bycatch remains a major conservation concern, followed by marine mammal depredation of fishing gear. A high proportion of studies concentrated on commercial fisheries in high-income countries, with an increase in small-scale fisheries in low to middle-income countries between 1999 and 2020. The insufficient understanding of the social dimensions of interactions and the inevitable uncertainties concerning animal and human behaviors are major challenges to effective management. Despite the key role of human behavior and socioeconomics, we found only eight articles that incorporate human dimensions in the management context. Integrating social dimensions of marine mammal interactions with fisheries could help in setting pragmatic conservation priorities based on enhanced understanding of critical knowledge gaps. An area-specific adaptive management framework could be an effective tool in reducing the risk to marine mammals from fisheries by coupling technical solutions with socio-economic and political interventions. We conclude that despite the vast body of literature on this subject, a “silver bullet” management solution to marine mammal interactions with fisheries does not yet exist.
... This is paradoxically the case for odontocetes (toothed whales) for which there is a simultaneous need for studies of foraging ecology to inform conservation efforts, and an immense challenge to acquire such data from these species that capture prey out of view, underwater. Many odontocetes are threatened by anthropogenic activities that impair foraging behavior, including acoustic masking of communication or echolocation signals from manmade sound (Nowacek et al., 2007;Weilgart, 2007), bycatch from fishing (Hamer et al., 2012) and disturbance from whale-watching vessels (Lusseau and Bejder, 2007;Senigaglia et al., 2016). Studies that reveal how odontocetes capture prey below the surface are critical for predicting anthropogenic impacts and ultimately informing conservation and management activities. ...
Article
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Studies of odontocete foraging ecology have been limited by the challenges of observing prey capture events and outcomes underwater. We sought to determine whether subsurface movement behavior recorded from archival tags could accurately identify foraging events by fish-eating killer whales. We used multisensor bio-logging tags attached by suction cups to Southern Resident killer whales (Orcinus orca) to: (1) identify a stereotyped movement signature that co-occurred with visually confirmed prey capture dives; (2) construct a prey capture dive detector and validate it against acoustically confirmed prey capture dives; and (3) demonstrate the utility of the detector by testing hypotheses about foraging ecology. Predation events were significantly predicted by peaks in the rate of change of acceleration ('jerk peak'), roll angle and heading variance. Detection of prey capture dives by movement signatures enabled substantially more dives to be included in subsequent analyses compared with previous surface or acoustic detection methods. Males made significantly more prey capture dives than females and more dives to the depth of their preferred prey, Chinook salmon. Additionally, only half of the tag deployments on females (5 out of 10) included a prey capture dive, whereas all tag deployments on males exhibited at least one prey capture dive (12 out of 12). This dual approach of kinematic detection of prey capture coupled with hypothesis testing can be applied across odontocetes and other marine predators to investigate the impacts of social, environmental and anthropogenic factors on foraging ecology.
... More recently, the diversity of animal culture in cetaceans and its importance in conservation has gained greater attention [14,15]. The last few decades have seen increasing awareness of the need to reduce or prevent cetacean bycatch, and for the implementation of mitigation and other measures across fishery types (see, for example, reviews of all fisheries: [8,[16][17][18][19][20]; and, more specifically, gillnets: [21]; trawls: [22,23]; tuna fisheries: [24]; longlines: [25]; pot/trap fisheries: [26]; and purse-seines: [27]). ...
Article
The prevalence of small cetacean (including dolphins, porpoises and small odontocete whales) bycatch in fisheries worldwide remains an ongoing conservation and welfare challenge. Various mitigation methods have been implemented in attempts to reduce bycatch. Two such methods involve gear modification: placement of Bycatch Reduction Devices (BRDs) within trawl nets, usually involving a physical barrier and an escape hatch; and, deployment of Acoustic Deterrent Devices (ADDs, ‘pingers’), typically placed on static nets and some trawl nets, to alert cetaceans to their presence and deter them from interacting with the gear. Despite their efficacy in reducing bycatch under certain circumstances, negative welfare impacts remain for individuals interacting with both BRDs and ADDs. Post-mortem analyses of small cetaceans caught in trawl gear, for example, illustrate the potential long-term effects of capture myopathies and cardiac damage sustained during the acute stress of entanglement, prior to and during escape through the BRD. Further, animals may become entangled in the bars, ropes or mesh of the BRD or escape hatch itself, and little is known of their post-release survival. ADD efficacy is typically fishery- and cetacean species-specific and, even where deemed a success at reducing bycatch, displacing animals from their optimal foraging habitat could negatively impact individual survival. Some species display equivocal responses to ADDs, while others may habituate to or be attracted to the sounds produced as they learn to associate it with food rewards, as they do in trawl fisheries, thereby reducing ADD efficacy and increasing the likelihood of entanglement. Here, we provide a synthesis of existing studies of these mitigation methods and discuss the associated welfare issues, where poor welfare negatively impacts an individual’s physical or mental state. We conclude that cetacean welfare considerations should become an integral part of decision-making in relation to bycatch globally.
Article
Analysis of published sources and own data on the intensity of fisheries and records of cetaceans in the Western Bering Sea and Eastern Kamchatka from 2003 to 2017 was conducted. Cetaceans were observed throughout the aquatic area mentioned, and the highest number of records were made between the coast of Kamchatka and the Commander Islands and around the islands. The most intensive fisheries operated on the shelf off Cape Navarin. In view of cancellation of the drift nets fishing, overlapping between the areas of intense fishing by all fishing gear and the sites of associated records of cetaceans does not exist for major part of the area considered.
Thesis
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La surexploitation des ressources halieutiques entraîne une compétition croissante entre les pêcheries et la biodiversité marine. Cette compétition donne lieu à des interactions de type déprédation (consommation des poissons directement sur le matériel de pêche par les prédateurs marins). La déprédation engendre des conséquences i) socio-économiques pour les pêcheries (diminution des rendements) ; ii) écologiques pour les prédateurs marins (risques accrus de capture accidentelle ou d’exposition à une réponse létale) et iii) écosystémiques (impacts sur les ressources cibles et auxiliaires). Cette thèse propose d’étudier, sur une des pêcheries des plus lucratives, des plus sélectives mais également des plus exposées à la déprédation, les mécanismes décisionnels (capitaines) et comportementaux (prédateurs marins) impliqués dans la déprédation exercée par les orques (Orcinus orca) et les cachalots (Physeter macrocephalus) sur la pêcherie à la palangre démersale ciblant la légine australe (Dissostichus eleginoides) dans les Zones Économiques Exclusives françaises des îles Crozet et Kerguelen, océan Indien. Par une approche originale combinant éthologie humaine et animale sur fond de théorie de l’approvisionnement optimal à deux échelles spatio-temporelles, nous montrons que i) cette déprédation est marquée avec une compétition d’autant plus importante que les capitaines sont expérimentés ; ii) les odontocètes ajustent leur comportement naturel pour bénéficier de l’apport de nourriture issue des pêcheries ; iii) aucune prise de décision ne permet simultanément un haut rendement de pêche et une déprédation réduite. Ces résultats soulignent l’importance de la pression exercée par les pêcheries sur les ressources naturelles et la pertinence de futures évaluations bioéconomiques et socio-écosystémiques pour assurer la viabilité économique des pêcheries et la durabilité des ressources naturelles exploitées et auxiliaires. Overexploitation of fisheries resources leads to increasing competition between fisheries and marine biodiversity. This competition gives rise to depredation-type interactions (consumption of fish directly on the fishing gears by marine predators). Depredation has i) socio-economic consequences for fisheries (reduced yields); ii) ecological for marine predators (increased risk of bycatch or exposure to a lethal response) and iii) ecosystems (impacts on target and auxiliary resources). This thesis proposes to study, on one of the most lucrative fisheries, the most selective but also the most exposed to depredation, the decisional mechanisms (captains) and behavioural (marine predators) involved in the depredation exerted by the orcas (Orcinus orca) and sperm whales (Physeter macrocephalus) on the demersal longline fishery targeting Patagonian toothfish (Dissostichus eleginoides) in the French Exclusive Economic Zones of the Crozet and Kerguelen, Indian Ocean. By an original approach combining human and animal ethology against the backdrop of optimal foraging theory at two spatio-temporal scales, we show that i) this depredation is marked with a competition all the more important as the captains are experienced; (ii) odontocetes adjust their natural behaviour to benefit from the supply of food from the fisheries; (iii) no decision-making simultaneously allows high fishing yield and reduced depredation. These results highlight the importance of fisheries pressure on natural resources and the relevance of future bio economic and socio-ecosystem assessments to ensure the economic viability of fisheries and the sustainability of exploited and ancillary natural resources.
Article
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Killer whale populations throughout the world tend to exhibit dietary specialization, feeding selectively upon only a very small subset of prey species from the 200 species that they are known to predate. Here, we present details of a single observation of killer whales feeding upon a blue shark captured in a pelagic longline fishery in the northeastern Atlantic Ocean. The fact that these killer whales targeted the liver, which is a highly selective feeding behavior that is likely learned, suggests that these individuals have fed upon sharks before. As this is the first report of shark depredation by killer whales in the North Atlantic, further studies are needed to determine if killer whales prey frequently on sharks in the North Atlantic Ocean. https://youtu.be/Wi0M0570aEw
Technical Report
Final report/relatório final do Projeto iNOVPESCA - Redução de capturas acidentais de espécies marinhas protegidas em pescarias costeiras algarvias: inovação de procedimentos e técnicas de mitigação. Contextualização, metodologia, resultados e proposta de boas práticas para encontrar reduzir conflitos entre pescas e espécies marinhas protegidas na costa Algarvia.
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Fisheries can generate feeding opportunities for large marine predators in the form of discards or accessible catch. How the use of this anthropogenic food may spread as a new behaviour, across individuals within populations over time, is poorly understood. This study used a 16-year (2003–2018) monitoring of two killer whale Orcinus orca subantarctic populations (regular and Type-D at Crozet), and Bayesian multistate capture–mark–recapture models, to assess temporal changes in the number of individuals feeding on fish caught on hooks (‘depredation’ behaviour) of a fishery started in 1996. For both populations, the number of depredating individuals increased during the study period (34 to 94 for regular; 17 to 43 for Type-D). Increasing abundance is unlikely to account for this and, rather, the results suggest depredation was acquired by increasing numbers of existing individuals. For regular killer whales, a plateau reached from 2014 suggests that it took 18 years for the behaviour to spread across the whole population. A more recent plateau was apparent for Type-Ds but additional years are needed to confirm this. These findings show how changes in prey availability caused by human activities lead to rapid, yet progressive, innovations in killer whales, likely altering the ecological role of this top-predator.
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Large marine predators feeding on fish caught on fishing gear, a behaviour termed as depredation, can incur socio-economic costs for fisheries and have serious implications on the depredating species, fish stocks and associated ecosystems. The quantity of depredated fish as well as the quantity of depredated fish relative to the retained catch dictates the severity of these impacts, yet these depredated quantities are often unknown due to the complexity of assessing depredation. This is the case for many demersal longline fisheries experiencing depredation by killer whales (Orcinus orca), which remove entire fish from hooks when interacting with the fishing gear. In the present study, we used Generalized Linear Models fitted to the Catch per Unit Effort (CPUE) to quantify killer whale depredation in the blue-eye trevalla (Hyperoglyphe antarctica) commercial longline fishery of south-east Australia. Our results showed that during days when killer whales were present around fishing vessels (7.3% of total fishing days), blue-eye trevalla CPUE decreased by 45.6%. Killer whales were estimated to have removed a total of 63.9 t (95% CI: 45.3–82.7 t) of blue-eye trevalla from the hooks between 2006 and 2017, with a mean removal of 5.3 t (3.8–6.9 t) per year. The mean rate of killer whale depredation in south-east Australia was estimated to be 5.2% (4.0–6.4%) for the entire study period. We estimated that the current depredation rate equates to an additional 27 fishing days per year across the fishery. This figure grows to 354 additional fishing days if depredation was assumed to occur during every fishing operation. Considering that killer whale observations are voluntarily reported in logbooks, this likely underestimates the depredation in our study. Together, these findings suggest that the impacts of killer whale depredation in the blue-eye trevalla fishery of south-east Australia are not negligible given the small scale of the fishery and the historical decline of its catches in this region. We recommend estimates provided in this study to be used as baselines for the future assessment and management of the blue-eye trevalla stocks and for assessing the socio-economic and ecological implications of this issue. In addition, regardless of the limitations associated with assessing depredation, our study also highlights the importance of cross-sectoral and interdisciplinary collaborations between scientists, fishers and fishery managers for effectively improving the management of commercially important fisheries globally.
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Pelagic fishes support a vital part of the local and export production and trade at global, regional, and local levels. In the Western Indian Ocean, pelagic fishes are mainly exploited by purse-seiners and long-line fishing vessels operating in national exclusive economic zones and international waters. Catch data from these vessels is often not adequately evaluated to determine the variation of catches and the state of the exploited stocks. This study evaluates the Kenya long line fishery between 2016 and 2020 to determine catch rates, temporal variation over time, and the key species’ maximum sustainable yield (MSY). The catches were dominated by Xiphias gladius (44.7%), Thunnus albacares (24.4%), Thunnus obesus (10.9%), and Prionace glauca (7.7%). Catch rates were significantly different among years, months, vessels, and depths for all species except for X. gladius and P. glauca, whose catch rates did not significantly differ at different depths. The catch rates for X. gladius, T. obesus, and T. albacares were higher during the northeast monsoon season, while P. glauca had higher catch rates during the southeast monsoon season. The maximum sustainable yield (MSY) was higher than the annual catches for the four species. We recommend catch rates be monitored over a more extended period for trend comparison and future work to consider discards encountered during fishing. We recommend seasonal closures for management, especially for the vessels targeting tunas and swordfish to conduct fishing during the NEM season when the catch rates are higher. There is a need for future work to focus on hook selectivity for the long-line fisheries along the Kenya EEZ.
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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.
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On the basis of information provided by the fleet and by scientific observers during the 1992-2006 period, it was possible to identify the areas of interaction between the surface longline fishery and Pseudorca crassidens, the level of sporadic incidental by-catches of this cetacean and its depredation level carried out on the swordfish individuals caught by this fleet. In roughly 98% of the sets sampled by scientific observers, no depredation was detected on the swordfish longline catches and in only 2% there were signs evidencing this depredation. According to on-board scientific observations, the incidental catch rate of the false killer whale was estimated to be 1.464, 1.685 and 0.797 individuals per million hooks for the Atlantic, Indian and Pacific Oceans, respectively. The incidental mortality rate of the false killer whale was estimated 0.36 individuals per million hooks in the Atlantic and zero in the two other oceans. The intertropical band of the three oceans presented the greatest interaction with the swordfish fishery, reaching in some of the areas a mean impact affecting over 10% of the swordfish catch in number. On the basis of mean predation rates by region and quarter, the average number of swordfish estimated to have been depredated by the false killer whale in 2005 would range from 2999-4804, 509-2706, 114-348 specimens, in the Atlantic, Indian and Pacific Oceans, respectively. These modest overall incidences compared with other fleets are probably due to fishing areas selected as well as the fleet’s effective practice of avoiding areas of interaction with the false killer whale. However, when attacks do occur, they can be devastating to the fishery interests of the vessel and may ruin their yields. Data from sets with HPUE>0 indicate that predation usually amounts to less than 5 swordfish per thousand hooks, although, it may sporadically reach or exceed 20 fish. Sets having HPR>0 indicate that, when attacks occur, depredation may affect a number of swordfish equivalent to 50% or more of the catch held on board and may even damage the catch in a proportion that is several times greater than the number of swordfish retained on board. For general purposes it was estimated that in 2005 Pseudorca crassidens carried out a mean overall depredation in the Spanish surface longline fleet of around 1.1-1.8%, 0.5-2.6%, 0.1-0.3% on the total number of swordfish caught in the Atlantic, Indian and Pacific Oceans, respectively.
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The U.S. East Coast pelagic longline fishery has a history of interactions with marine mammals, where animals are hooked and entangled in longline gear. Pilot whales (Globicephala spp.) and Risso's dolphin (Grampus griseus) are the primary species that interact with longline gear. Logistic regression was used to assess the environmental and gear characteristics that influence interaction rates. Pilot whale interactions were correlated with warm water temperatures, proximity to the shelf break, mainline lengths greater than 20 nautical miles, and damage to swordfish catch. Similarly, Risso's dolphin interactions were correlated with geographic location, proximity the shelf break, the length of the mainline, and bait type. The incidental bycatch of marine mammals is likely associated with depredation of the commercial catch and is increased by the overlap between marine mammal and target species habitats. Altering gear characteristics and fishery practices may mitigate incidental bycatch and reduce economic losses due to depredation.
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The Endangered Australian sea lion Neophoca cinerea occurs in low numbers, exhibits low fecundity, extreme philopatry and substantial population genetic structure at the breeding colony level. These traits may increase susceptibility to population decline, with additional mortality as bycatch in shark gillnets being a possible threat. The Great Australian Bight Marine Park (GABMP) was established, in part, to protect the small and remote Bunda Cliffs population from anthropogenic impacts such as commercial fishing. This study investigated the effectiveness of the GABMP in reducing spatial overlap between Australian sea lions and gillnets and in preventing bycatch. An independent fishery observer program reported a mortality rate of 0.0206 individuals (ind.) km-1 of gillnet set within the GABMP, amounting to between 4 and 15 (confidence bounds of standard error of the estimate) ind. killed there during the most recent breeding cycle. A mortality rate of 0.0093 ind. km-1 of gillnet set was recorded across the broader GAB region, amounting to between 14 and 33 ind. killed each breeding cycle during recent times, and between 128 and 177 over the 10 yr since the GABMP was established in the mid-1990s. These reported bycatch levels are unlikely to be sustainable and may represent minimum estimates, because drowned individuals may drop out of the gillnet and go unobserved. A tracking program involving 9 females (5.6% of the estimated female population) demonstrated that they spent only 27.7% of their time inside the GABMP. Four of them regularly travelled more than 180 km from home, or 9 times further than the southern boundary of the GABMP. These results indicate that the level of protection afforded by the GABMP to Australian sea lions residing at Bunda Cliffs is unlikely to reduce bycatch to below the levels that would reduce the risk of decline in this small population. Suggested improvements to the GABMP include a year-round closure to gillnetting, low bycatch limits and extension of the southern boundary further south. Additional regulatory mechanisms may be needed in the gillnet fishery to minimise its impact on this and other small Australian sea lion populations.
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Interactions between killer whales (Orcinus orca), sperm whales (Physeter macrocephalus), fur seals (Arctocephalus spp.) and longline fishing operations were reported by observers on board fishing vessels targeting Patagonian toothfish (Dissostichus eleginoides) in the Crozet and Kerguelen Islands Exclusive Economic Zones (EEZs) between 2003 and 2005. In the Crozet EEZ, the reported interactions involved killer whales and sperm whales. These two species, alone or in co-occurrence with each other, were observed in 71% of the 1 308 longlines set. In the Kerguelen EEZ, the reported interactions involved sperm whales and fur seals. These two species, alone or in co-occurrence with each other, were observed in 54% of the 6 262 longlines monitored. Interactions were observed in all fishing areas. The effect of depredation was assessed by comparing catch-per-unit-effort (CPUE) (fish weight/hook) of each longline set in the absence/presence of marine mammal species alone or in co-occurrence. In the Crozet EEZ, CPUE was found to be reduced by 22.5% in the presence of killer whales, 12.1% by sperm whales, and 42.5% when both species were present together. An extensive photo-identification effort, primarily focussing on killer whales, allowed a total of 103 individual whales to be identified. The analysis of photo-identification indicated that a small number of individual killer whales were responsible for most of the interactions with the fishery. In the Kerguelen EEZ only sperm whales, alone or in co-occurrence with fur seals, were found to impact negatively on CPUE.
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Killer whales (Orcinus orca) interact with longline fisheries around the world, however they have not previously been reported taking fish off longlines in New Zealand waters. Two new killer whale prey species (school shark, Galeorhinus galeus and blue-nose, Hyperoglyphe antarchia) have been recorded. A great deal of effort has been applied, world wide, to reduce killer whale-fishery interactions, but few methods are successful. Fishers in New Zealand have used 'tuna bombs' and shooting.
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Within the Crozet Islands Exclusive Economic Zone (EEZ), the Patagonian toothfish (Dissostichus eleginoides) longline fishery is exposed to high levels of depredation by killer (Orcinus orca) and sperm whales (Physeter macrocephalus). From 2003 to 2008, sperm whales alone, killer whales alone, and the two species co-occurring were observed on 32.6%, 18.6% and 23.4% respectively of the 4 289 hauled lines. It was estimated that a total of 571 tonnes (€4.8 million) of Patagonian toothfish were lost due to depredation by killer whales and both killer and sperm whales. Killer whales were found to be responsible for the largest part of this loss (>75%), while sperm whales had a lower impact (>25%). Photo-identification data revealed 35 killer whales belonging to four different pods were involved in 81.3% of the interactions. Significant variations of interaction rates with killer whales were detected between vessels suggesting the influence of operational factors on depredation. When killer whales were absent at the beginning of the line hauling process, short lines (<5 000 m) provided higher yield and were significantly less impacted by depredation than longer lines. Also, when facing depredation, it is recommended that vessels leave their fishing area and travel distances >40 n miles to prevent killer whales from finding them within a few hours. Although more data are still needed to better understand the way killer whales search and detect vessels, this study gives preliminary insights into possible mitigation solutions to the widespread depredation issue.
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Observers from the Australian Fisheries Management Authority worked on randomly chosen Japanese long-line vessels in the Australian Fishing Zone (AFZ) between 1980 and 1997. Observer reports (n = 451) were inspected for interactions or sightings of marine mammals. An operational interaction was defined as an activity or behaviour that involved direct contact between a marine mammal and fishing gear, bait, target fish or bycatch, or indications that the marine mammal was feeding. A sighting was defined as the recording of marine mammals that passed the vessel without changing course and/or did not appear to interact with the vessel or its gear. Observers witnessed 23 interactions and made another 44 sightings of marine mammals. A further 24 interactions and sightings were relayed by crew members. Killer whales were reported most frequently; most incidences of fish being damaged, taken or frightened away were attributed to them. Eleven marine mammals were caught: two died, seven were released, and the fate of two others was not recorded. Between 1991 and 1996, when observer coverage was 11.5% overall in the AFZ, the incidence of interactions was 1.71 per million hooks set. The estimated number of interactions in that seven-year period was 157 in the AFZ. Since 1997, the long-line fishery has been conducted by Australian vessels, primarily off the east coast of mainland Australia in warm-temperate waters. A higher proportion of interactions can be expected with killer whales and short-finned pilot whales in these waters, and fewer with seals.
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Recent case studies have highlighted high bycatch mortality of sea turtles and marine mammals in arti-sanal fisheries, but in most countries there are few data on artisanal fishing effort, catch, or bycatch. With artisanal fisheries comprising >95% of the world's fishermen, this knowledge gap presents a major chal-lenge to threatened species conservation and sustainable fisheries initiatives. We report on results from an intensive pilot study to evaluate whether interview surveys can be effective in assessing fishing effort and threatened species bycatch. Fisheries and bycatch data from interviews with >6100 fishermen in seven developing countries were collected in <1 year for approximately USD $47,000, indicating that this approach may rapidly yield coarse-level information over large areas at low cost. This effort provided the first fisheries characterizations for many areas and revealed the widespread nature of high bycatch in artisanal fisheries. Challenges to study design and implementation prevented quantitative estimation or spatial comparisons of bycatch during this pilot research phase, but results suggested that annual sea turtle bycatch may number at least in the low thousands of individuals per country. Annual odontoc-ete bycatch may number at least in the low hundreds per country. Sirenian bycatch occurred in all study areas but was frequent only in West Africa. We discuss lessons learned from this survey effort and pres-ent a revised protocol for future interview-based bycatch assessments.
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Killer whale (Orcinus orca) and sperm whale (Physeter macrocephalus) interactions with longline fi shing operations were recorded by CCAMLR observers between 2000 and 2002 at South Georgia (Subarea 48.3). Demersal longlines, targeting Patagonian toothfi sh (Dissostichus eleginoides), were deployed in depths of 169 to 2 150 m. Most effort was concentrated along the 1 000 m depth contour. Sperm whales were the most abundant marine mammal observed in the vicinity of vessels when lines were being hauled, being present during 24% of hauling observations. Killer whales, the second most frequently sighted cetacean, were present during 5% of haul observations. A high inter-vessel variation was noted for interactions with both species. A comparison of geographic plots of cetacean sightings during hauls to fi shing positions showed that interactions occurred over a wide geographic range. These were mostly correlated to the fi shing effort on the different grounds, although some 'hotspots' for interactions were noted. Killer whale pods were generally small (2-8 animals), while solitary animals and larger pods (>15 animals) occurred less frequently. Sperm whales were most often solitary when interacting with fi shing vessels, although smaller groups (2-3 animals) were also relatively common. Interactions with killer whales were most often observed in the day, generally in the afternoon, while night-time interactions were relatively few and usually occurred before midnight. Interactions with sperm whales followed a similar pattern, occurring most often in the afternoon, while very few interactions were observed at night. Catch rates were signifi cantly lower when killer whales were present when compared to hauls during which no cetaceans were present. Catch rates were slightly higher in the presence of sperm whales and it is possible that sperm whales were attracted to some areas because of abundant prey (toothfi sh). However, in areas with lower catch rates, indications are that depredation by sperm whales can lead to a decrease in catches. Some mitigation measures have been tried by vessels to reduce interactions with cetaceans, although no quantitative studies have been carried out to measure their effectiveness. Apart from the obvious economic implications of fi sh loss due to depredation, ecological implications such as the effect of unrecorded fi sh removals on stock assessment models, modifi cations in the behaviour of marine mammals and entanglements with fi shing gear are also important considerations. Further investigations are needed to determine the extent and effects of
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Bakun, A., Babcock, E. A., and Santora, C. 2009. Regulating a complex adaptive system via its wasp-waist: grappling with ecosystem-based management of the New England herring fishery. – ICES Journal of Marine Science, 66: 1768–1775. We use the New England herring fishery as an example of the unresolved scientific issues pertinent to ecosystem-based management of forage-fish fisheries. The biomass of herring off New England is currently well above maximum sustainable yield (BMSY), leading to pressure for expanded harvests. Associated concerns include: the maintenance of sufficiently abundant forage to meet the current needs of marine mammals and seabirds while supporting the rebuilding of overfished groundfish resources; the preservation of the service functions of a healthy population of pelagic zooplanktivorous fish to prevent possible outbreaks of pests, or hypoxia events; and the limitation of unintended bycatch of marine mammals, seabirds, and juvenile stages of groundfish. Perhaps a self-enhancing feedback loop, involving predation by herring on the early life stages of their groundfish predators, might result in regime shifts that could not be easily reversed. A plausible outcome of these ideas is a dichotomy in management choice between (i) promoting an ecosystem dominated by valuable groundfish resources and (ii) promoting the current ecosystem that features a large herring resource associated with abundant and energy-rich forage for marine mammals, seabirds, and continued high productivity of valuable shellfish resources.
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Demersal gill nets equipped with acoustic alarms reduced harbour porpoise (Phocoena phocoena) by-catch rates by 77% over those without alarms in the Swallowtail area of the lower Bay of Fundy during field testing in August 1996 (68% reduction) and 1997 (85% reduction) (both years combined, three harbour porpoises in 249 alarmed nets versus 14 harbour porpoises in 267 nonalarmed nets). The alarms spaced 100 m apart along the net floatline produced a 0.3-s pulse at 10-12 kHz ever y4sa t al evel of 133-145 dB re 1 μPa at 1 m. In conditions of no rain and low wind (Sea State 0-2) the alarms were presumed to be clearly audible to harbour porpoises at ranges of 0.1- 0.6 km. Catch rates of Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), and pollock (Pollachius virens) were not significantly different in alarmed and nonalarmed nets (except in one season when pollock were caught in lower numbers in alarmed nets). Harbour porpoise by-catch and herring movements may be linked. During years of low herring abundance, we also observed low harbour porpoise entanglement rates.
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Field tests were conducted on the effectiveness of acoustic alarms (pingers) in reducing the incidental catch of harbour porpoise (Phocoena phocoena) in a salmon gillnet fishery in northern Washington in July and August of 1995-1997. The alarms produced a broadband signal with peaks at 3 and 20kHz, with mean source levels between 121.7-124.7dB re 1 mu Pa at 1m. For 1995 and 1996 combined, 47 harbour porpoise were taken in control nets and only two were taken in alarmed nets. The alarms significantly reduced the bycatch of harbour porpoise for both seasons (1995: chi super(2) = 5.28, df = 1, p = 0.02; 1996: chi super(2) = 11.2, df = 1, p = 0.001). In 1997, all nets were alarmed and 12 porpoise were taken; however, the expected catch without alarms would have been 79. There were no significant differences in catch rates of chinook salmon (Oncorhynchus tshawytscha) ( chi super(2) = 0.31. df = 1, p = 0.58), or sturgeon (Acipenser sp.) ( chi super(2) = 1.44, df = 1, p = 0.23) in control or alarmed nets. There were also no significant differences in the bycatch of harbour seals (Phoca vitulina) ( chi super(2) = 0.09, df = 1, p = 0.76) or depredation of salmon by seals in nets with and without alarms ( chi super(2) = 0.07, df = 1, p = 0.79). The results of these studies indicate that acoustic alarms significantly reduce the probability of harbour porpoise entanglement in bottom-set gillnets in the fishery without reducing the catch of target fish species.
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A new fishing technique, adapted from the artisanal trotline fishery for Patagonian toothfish ( Dissostichus eleginoides) in Chile is described. The modified artisanal system, which includes a net sleeve that is placed on secondary vertical lines, has practically eliminated depredation of fish by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus). The performance of this fishing technique with regard to seabird mortality . The performance of this fishing technique with regard to seabird mortality and depredation by sperm and killer whales on fish catch rate was assessed during September-December 2006. The results were then compared with similar data obtained in 2002 in the same fleet in the same fishing grounds prior to the implementation of the modification. The number of seabirds killed in 2002 was 1 542 compared to zero in 2006; there was also a reduction in depredation of the catch from a maximum of 5% in 2002 to a maximum of 0.36% of the total catch in 2006. The fishers who developed the net sleeve modification called it 'cachalotera' (from 'cachalote' meaning sperm whale in Spanish). The term 'Chilean longline' is preferred in this paper because it was developed in 2005 in the Chilean toothfish fishery in the Magellan region.
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Recent evidence indicates that there is a small, demographically iso- lated, island-associated population of false killer whales (Pseudorca crassidens) around the main Hawaiian Islands. Although it is known that false killer whales in Hawai'i are sometimes killed or seriously injured in the Hawai'i-based long- line fishery, it is not known whether such interactions have resulted in a reduc- tion in population size or whether other factors have been negatively influencing population size. We report the results of an aerial survey in June and July 1989, the purpose of which was to obtain a minimum count of the number of false killer whales around the main Hawaiian Islands. The false killer whale was the third most commonly seen species of odontocete off the island of Hawai'i dur- ing the survey, representing 17% of sightings. Groups of more than 300 indi- viduals were seen on three different days, with minimum counts of 380, 460, and 470 individuals in these groups. The encounter rate, relative species rank- ing, and average group size from the 1989 survey were all substantially greater than those from more recent aerial and ship-based surveys. The largest group observed in 1989 (470) contained almost four times as many whales as estimated for the entire main Hawaiian Islands from recent aerial surveys (121 individuals, CV ¼ 0.47) or mark-recapture analyses (123 individuals, CV ¼ 0.72). There- fore, the population of false killer whales around the main Hawaiian Islands may have declined substantially since 1989. The cause or causes of such a de- cline are uncertain.
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False killer whales (Pseudorca crassidens (Owen, 1846)) are incidentally taken in the North Pacific pelagic long-line fishery, but little is known about their population structure to assess the impact of these takes. Using mitochondrial DNA (mtDNA) control region sequence data, we quantified genetic variation for the species and tested for genetic differentiation among geographic strata. Our data set of 124 samples included 115 skin-biopsy samples collected from false killer whales inhabiting the eastern North Pacific Ocean (ENP), and nine samples collected from animals sampled at sea or on the beach in the western North Pacific, Indian, and Atlantic oceans. Twenty-four (24). haplotypes were identified, and nucleotide diversity was low (pi = 0.37%) but comparable with that of closely related species. Phylogeographic concordance in the distribution of haplotypes was revealed and a demographically isolated population of false killer whales associated with the main Hawaiian islands was identified (Phi(ST) = 0.47, p < 0.0001). This result supports recognition of the existing management unit, which has geo-political boundaries corresponding to the USA's exclusive economic zone (EEZ) of Hawai'i. However, a small number of animals sampled within the EEZ but away from the near-shore island area, which is defined as <25 nautical miles (1 nautical mile = 1.852 km) from shore, had haplotypes that were the same or closely related to those found elsewhere in the ENP, which suggests that there may be a second management unit within the Hawaiian EEZ. Biologically meaningful boundaries for the population(s) cannot be identified until we better understand the distribution and ecology of false killer whales.