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 US1,034andUS1,034 and US8,495 (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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... Several species of odontocetes (Odontoceti, toothed whales), including the false killer whale (Pseudorca crassidens), short-finned pilot whale (Globicephala macrorhynchus) and killer whale (Orcinus orca), depredate catch and bait in pelagic longline fisheries, which can result in their bycatch by becoming hooked or entangled in line [20,21]. A U.S. central north Pacific Ocean tuna longline fishery with vessels based primarily from Hawaii experiences odontocete depredation and bycatch primarily by false killer whales [22]. ...
... • Acoustic masking, including quieter vessels; bubble screen to reduce the dissemination of vessel sounds; broadcast of sounds to conceal the sounds of the vessel gear, setting and hauling; not remaining near the gear after it is set; and minimizing shifting in and out of gear [20]; ...
... • Chemical deterrents [20,24,42]. ...
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Several odontocete species depredate catch and bait from fishing gear, resulting in their bycatch and causing substantial economic costs. There are no known mitigation methods for odontocete depredation in pelagic longline fisheries that are effective, do not harm odontocetes and are commercially viable. Understanding odontocetes’ depredation strategies can contribute to mitigating this human-wildlife conflict. Using observer data from the Hawaii-based tuna longline fishery, this study summarized teleost and elasmobranch species-specific mean posterior odontocete depredation rates using a simple Bayesian binomial likelihood estimator with a Bayes-Laplace prior. Depredation rates of species with sufficient sample sizes ranged from a high of 1.2% (1.1 to 1.3 95% highest posterior density interval or HDI) for shortbill spearfish to a low of 0.002% (0.001 to 0.003 95% HDI) for blue shark. Depredation of catch is a rare event in this fishery, occurring in about 6% of sets. When depredation did occur, most frequently odontocetes depredated a small proportion of the catch, however, there was large variability in depredation rates between teleost species. For example, bigeye tuna was two times more likely to be depredated than yellowfin tuna (odds ratio = 2.03, 95% CI: 1.8–2.3, P<0.0001). For sets with depredation, 10% and 2% of sets had depredation of over half of the captured bigeye tuna and combined teleosts, respectively. All elasmobranch species had relatively low depredation rates, where only 7 of almost 0.5M captured elasmobranchs were depredated. Odontocetes selectively depredate a subset of the teleost species captured within sets, possibly based on net energy value, chemical, visual, acoustic and textural characteristics and body size, but not median length, which was found to be unrelated to depredation rate (Pearson’s r = 0.14, 95% CI: -0.26 to 0.50, p = 0.49). Study findings provide evidence to support the identification and innovation of effective and commercially viable methods to mitigate odontocete depredation and bycatch.
... However, fisher-wildlife interactions have been recognised as a threat to the economic and ecological sustainability of fisheries globally (Carlucci et al., 2021;Cook et al., 2022;FAO, 2021;Garrison, 2007). For longline fishers, depredation by non-target marine predators is particularly problematic (Bayless et al., 2017;Casselberry et al., 2022;Donoghue et al., 2003;Hamer et al., 2012;Sivasubramaniam, 1964;Vardon et al., 2021;Werner et al., 2015). ...
... Depredation in longline fisheries occurs when marine predators, such as sharks, cetaceans, squid or seals, partially or completely remove bait or catch from hooks (Gilman et al., 2007;Rabearisoa et al., 2018). While competition between fishers and marine apex predators is a long-reported issue (Hamer et al., 2012;Sivasubramaniam, 1964), the number of peer-reviewed studies addressing depredation by toothed whales (odontocetes; paraorder Odontoceti) has increased steadily over the past 20 years (McPherson and Nishida, 2010;Sivasubramaniam, 1964;Tixier et al., 2020). It is unclear whether this is due to an increase in depredation events, or simply an increase in fishing and/or research effort (Tixier et al., 2019). ...
... Regardless, longline fishers have identified odontocetes as more problematic than other depredating species, due to their proficiency at removing substantial quantities of hooked fish (Chapman et al., 2006;Charles et al., 2020;Fader et al., 2021a). Short-finned pilot whales (Globicephala macrorhynchus) and false killer whales (Pseudorca crassidens), which are difficult to distinguish from one another at sea (Yahn et al., 2019), are identified as the main species responsible for depredation in subtropical and tropical pelagic longline fisheries (Fader et al., 2021b;Hamer et al., 2012). These species are blamed for annual losses of ~US$13 million in Hawai`i's longline tuna fishery (TECInc, 2009). ...
Article
Depredation is a threat to the socioeconomic and ecological sustainability of pelagic longline fisheries, globally. Toothed whales (odontocetes) are anecdotally reported as responsible for annual revenue losses of AU$10-12 million in Australia's Eastern Tuna and Billfish Fishery (ETBF), presenting a challenge for industry and management in developing avoidance and mitigation techniques. We trialled the use of electronic monitoring footage as a timely and cost-effective method for quantifying odontocete depredation interactions. Between March and July 2023, a mean of 5% of total catch of each set sampled (n = 27) was lost to odontocete depredation, but this was highly variable among sets (0-24% of catch). We used generalised additive models (GAMs) to explore the effects of operational, spatiotemporal and environmental factors on depredation rates. Our results reveal that odontocete depredation is more likely to occur when: (i) hauling process is initiated at night and completed after dawn, (ii) lines are set at shallower depths, (iii) light-sticks are used, (iv) sea-surface temperature is warmer, (v) lines are set and hauled between 24 • and 27 • S, and (vi) lines are set and hauled during Austral autumn. It remains difficult to disentangle the effects of spatial and temporal drivers due to our relatively small sample size, however, our work provides actionable information to guide fisher interaction-avoidance tactics and help promote fishery sustainability.
... The associated issue of depredation (herein referred to as 'foraging around fishing gear', as suggested in Bearzi and Reeves (2022)) occurs where animals feed on target catch already caught in gear. Foraging around fishing gear is a common recurring issue in some fisheries (Brill et al. 2009;Hamer et al. 2012;Guinet et al. 2015;Santana-Garcon et al. 2018;Lucchetti et al. 2019). Although this paper does not focus on foraging around fishing gear, the solutions are likely congruent with bycatch reduction. ...
... Jordan et al. 2013). Physical barriers either fit into visual deterrents (such as artificial kelp in physical models) or are primarily used to prevent foraging around fishing gear rather than bycatch reduction, as is the case for hook sleeves (Hamer et al. 2012). Escape options are excluded because, despite some excellent results and promise for reducing bycatch of turtles (Cox et al. 2007), they are not designed to avert contact with marine megafauna, but rather to reduce mortality Rev Fish Biol Fisheries after contact with gear is made. ...
... The increases in sea lion catch were attributed to behavioural changes during an El Niño year, reduction in fishing fleet size and a potential 'dinner-bell' effect. Hamer et al. (2012) suggested a toolbox of solutions may be needed to reduce bycatch, on a caseby-case basis for each fishery including technical mitigation options, fisher behaviour and management strategies, rather than a single technical gear modification, such as pingers, which may be ineffective at deterring some species. This approach was successful in the Gulf of Maine fishery, where a Take Reduction Plan paired time-area closures with pingers and caused drastic reductions of porpoise bycatch from 1990 to 1999, to below target levels . ...
Article
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Marine megafauna are critical for marine ecosystem health and their removal can cause food webs to collapse. Methods to reduce marine megafauna mortality can result in conflict between scientists, conservationists, fishers and fisheries management due to real or perceived effects on target catch, income and food security. Sensory deterrents have been used in attempts to mitigate bycatch and retain target catch quantity and quality. Here, we completed a systematic review of 116 papers, plus 25 literature reviews published between 1991 and 2022, to investigate potential for sensory deterrents to mitigate bycatch across four marine megafauna taxonomic groups (marine mammals, sea turtles, seabirds and elasmobranchs). Lights on gillnets are the only technology so far to result in significant bycatch reductions across all four taxonomic groups. It is difficult to make generalisations about the efficacy of sensory deterrents and their ability to deliver consistent bycatch reductions. The efficacy of each method is context dependent, varying with species, fishery and environmental characteristics. Further research is recommended for field studies assessing bycatch mitigation in all sensory deterrents, including combinations of deterrents, to assess effects on target and non-target species. The associated issues of habituation, habitat exclusion and foraging around fishing gear are important, although reducing mortality of vulnerable species should remain the highest priority for conservation and preserving ecosystems that fishers depend on. Multiple complementary measures will be required to achieve consistent bycatch reduction targets in many fisheries, of which sensory deterrents could play some part if implemented appropriately.
... As fisheries expanded in coastal and pelagic habitats, large marine predators came into contact with fishing and aquaculture gear, where prey could be concentrated predictably and is easier to catch (Würsig and Gailey, 2002;Powell and Wells, 2011;Tixier et al., 2018Tixier et al., , 2021Bonizzoni et al., 2022). Some populations (primarily of odontocete cetaceans, pinnipeds, and sharks; Mitchell et al., 2018;Tixier et al., 2021) have responded by modifying their behaviour to take advantage of the new foraging opportunities provided by fishing (Northridge and Hofman, 1999;Whitehead et al., 2004;Read, 2008;Hamer et al., 2012;Bearzi et al., 2019;Tixier et al., 2021). These behavioural modifications have led to interactions that include forms of "depredation", a word commonly used by fishery scientists and managers to refer to the removal of, or damage to, marketable organisms caught in fishing gear or farmed (Würsig and Gailey, 2002;Read, 2005;Mitchell et al., 2018;Jog et al., 2022) as well as to the removal of bait from fishing lines (Zollett and Read, 2006;Powell and Wells, 2011;Weir and Nicolson, 2014;Kumar et al., 2016). ...
... In the scientific literature, the word depredation is sometimes used to encompass damage to and loss of fishing gear as well as loss of fishing time or opportunity (e.g. Zollett and Read, 2006;Brotons et al., 2007;Lauriano et al., 2009;Powell and Wells, 2011;Hamer et al., 2012). Also, depredation can be applied to situations that involve mortality or injury of marine predators resulting from interactions with fishing gear (bycatch), often including consideration of how to mitigate such mortality and injury, and to reduce the extent of catch removal and gear damage (Gilman et al., 2006;Hamer et al., 2012;Dawson et al., 2013;Götz and Janik, 2013;Werner et al., 2015;Mitchell et al., 2018;Dahlheim et al., 2022). ...
... Zollett and Read, 2006;Brotons et al., 2007;Lauriano et al., 2009;Powell and Wells, 2011;Hamer et al., 2012). Also, depredation can be applied to situations that involve mortality or injury of marine predators resulting from interactions with fishing gear (bycatch), often including consideration of how to mitigate such mortality and injury, and to reduce the extent of catch removal and gear damage (Gilman et al., 2006;Hamer et al., 2012;Dawson et al., 2013;Götz and Janik, 2013;Werner et al., 2015;Mitchell et al., 2018;Dahlheim et al., 2022). ...
Article
Some populations of marine mammals (particularly odontocete cetaceans, and pinnipeds) have responded to the expansion of fisheries by modifying their behaviour to take advantage of the foraging opportunities provided by fishing. This has led to interactions that include forms of “depredation”, referring to the removal of, or damage to, marketable organisms as well as bait from fishing gear. The current scientific and technical usage of depredate or depredation appears inconsistent with some of the meanings found in dictionaries, such as to plunder (typically using force), pillage, ravage, lay waste, despoil, destroy, commit waste, or ransack. We suggest that the use of “depredation” when referring to marine mammal behaviour could strengthen misperception and misunderstanding, hardening notions that they are unfairly taking or destroying what is ours. Though most contemporary researchers do not mean to imply that predators are “stealing our fish”, continued reference to the mammals’ behaviour as depredation may reinforce, at least in some minds, the belief that fish and other marine resources “belong” only to humans. Alternative wording would help to prevent ambiguity in communications, especially outside the scientific community, and preserve recognition of the ecological roles that large marine predators play. --- AVAILABLE AT: https://doi.org/10.1093/icesjms/fsac173
... 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.
... Isolated (e.g., island-associated) odontocete populations may be most at risk (Gilman, 2011). Several species of odontocetes depredate catch and bait in pelagic longline fisheries, which can result in their bycatch by becoming hooked or entangled in line, such as the false killer whale (Pseudorca crassidens), short-finned pilot whale (Globicephala macrorhynchus), and killer whale (Orcinus orca) (Hamer et al., 2012;Werner et al., 2015). ...
... However, the sink rate of baited hooks will be unaffected by the sink rate of the mainline until the hook has settled to the full length of the branchline, which in most fisheries is below the depth where seabirds susceptible to pelagic longline capture can dive (for details, see WPRFMC, 2019). Gearin et al., 1988;Gilman et al., 2006;Swimmer et al., 2007;Hamer et al., 2012;Garagouni et al., 2022 ...
Technical Report
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There has been growing concern over the sustainability of marine megafauna exposed to bycatch fishing mortality. This study assembled databases of mitigation methods for at-risk species exposed to pelagic longline, tuna purse seine and drift gillnet fisheries. The databases enable the discovery of bycatch mitigation methods and enable accounting for multispecies effects of alternative bycatch mitigation strategies across exposed populations and stocks of at-risk species. The study defines key inputs for comprehensive, multispecies bycatch management strategy evaluation of: the size of the effect of an intervention on catch and fishing mortality rates; multispecies conflicts and mutual benefits; strength of evidence, including in practice; commercial viability costs; compliance likelihood; and rates of components of fishing mortality. The robust evaluation of alternative bycatch management strategies against this suite of criteria enables simulating the outcomes of alternative strategies to determine which best meets objectives. The report includes a draft Decision or Resolution on holistic bycatch MSE to aid regional fisheries management organizations in identifying candidate elements for potential inclusion in measures.
... Direct interactions include intentional and accidental captures of by-catch species, entanglement of marine fauna in fishing gear, damage to fishing gear, and damage to captured fish due to interactions with nontarget predator species. The latter occurs when large marine predators, mainly sharks and toothed whales (odontocetes), feed directly on fish that are captured by fishers on fishing gear, a behaviour termed 'depredation' (Donoghue et al. 2003, Gilman et al. 2006, Hamer et al. 2012. ...
... However, while the study provided initial insights on the potential drivers of depredation in the region, further research is needed to understand the aspects of the fishers' behaviour and/or the marine predators' ecology that can be used to better predict, avoid, and reduce depredation through adjustments in fishing practices. The effectiveness of practices to reduce depredation relies on the characteristics of the species and the habitats involved, the behaviour of the fishers, individually and collectively, as well as their perceptions and attitudes towards sharks and odontocetes (Nishida and Tanio 2001, Gilman 2007, Dickman 2010, Hamer et al. 2012, Pardalou and Tsikliras 2018. These aspects have yet to be understood for shark and odontocete depredation in New Caledonia and adjacent waters of the South Pacific Ocean. ...
Article
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Large marine predators feeding on fish caught on fishing gear, referred to as ‘depredation’, occur in a wide range of fisheries worldwide. Depredation can result in negative ecological and socio-economic impacts, leading to conflict between fishers and depredating species. However, depredation remains understudied in many fisheries, and this hampers the development of effective mitigation solutions. In this study, 21 years of fishing data (2002–2022) were used to assess shark and odontocete depredation in the pelagic tuna longline fishery of New Caledonia. Using generalized linear models, the year, season, effort, soaking time, and vessel were identified as variables significantly influencing the probability of depredation to occur. Results showed that while shark depredation occurred more frequently than odontocete depredation (58.5% vs. 9.2% of the longline sets), they damaged a lower proportion of fish (3.9% vs. 12.3%) over the study period. Unlike sharks, odontocetes selectively depredate tuna, with their highest occurrence during periods of high tuna catch rates, suggesting a co-occurrence with fishing activities. Together, these results indicate that depredation in the New Caledonian fishery is high compared to other regions and provide essential information on the dynamics and impacts of the issue as a basis for considering management and mitigation options.
... It primarily involves both sharks (Gilman et al., 2008;Mitchell et al., 2018) and toothed whales (Clarke et al., 2014;Gilman et al., 2006;Lewison et al., 2014;Werner et al., 2015). Depredation is often a causal factor of bycatch, i.e., predators become hooked or entangled when attempting to feed on catch or bait, potentially leading to death or injury of depredating individuals (Gilman and Clarke, 2007;Hamer et al., 2012). The life history traits of sharks and odontocetes (slow growing, late maturing and long-lived) can make Abbreviations: CPUE, Catch per unit of effort; GDR, Gross depredation rate, DPUE, Depredation per unit of effort; IR, interaction rate; BPUE, Bycatch per unit of effort. ...
... Indeed, the data included species such as spectacled and Dall's porpoises, and Pacific white-sided dolphins that were never (and unlikely to be) documented in French Polynesia given their ecology and distribution (Perrin et al., 2009;Shirihai and Jarret, 2007). Difficulties to identify odontocete species was made even more apparent from the results of the questionnaire, with most captains indicating that they did not know about false killer whales, one of the species likely involved in depredation in the region (Carzon and Portal, 2012;Hamer et al., 2012;Laran et al., 2012). The monitoring can be easily improved by offering species identification tools and training, and by adding new fields in logbooks for captains to record the bycatch of odontocetes, the occurrence of depredation and the number of fish depredated, as we showed captains would be willing to participate in such monitoring. ...
Article
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Marine megafauna feeding on fishery catches (depredation) or being incidentally caught on fishing gear (bycatch) have become important issues. Their socioeconomic and conservation stakes have been increasingly studied across the world fisheries. They remain understudied in the Pacific Ocean, where longline tuna fisheries reported such interactions. In this study, we provide the first assessment of bycatch and depredation by sharks and odontocetes on longlines in French Polynesia between 2000 and 2018, using data from observers reporting, captains’ logbooks, questionnaires and additional monitoring by authors during three fishing trip. We found that less than 2% of the catch had been depredated, and that shark depredation was more common than odontocete depredation. Shark bycatch was important (20,000 sharks annually, 0.5 shark every 1000 hooks) and odontocete bycatch seemed low (13 occurrences in 18 years), though we identified clear reporting flaws. We discuss the range of uncertainty associated with our assessment, based on the current reporting systems, and the potential consequences of depredation and bycatch on tuna fisheries, as well as on shark and odontocete populations in French Polynesia.
... 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.
... 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. ...
... 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
... 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.
... Marine mammals-fisheries interactions have been well documented across the world with different fishing gears and targeted species [1][2][3][4][5][6][7][8][9]. From the mutually beneficial, like cooperative fishing between fishers and marine mammals [10][11][12], to the most detrimental, like direct killing as a retaliatory measure [13,14], these interactions can take different forms. ...
Article
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The study explores the interactions between dolphins and Cypriot fisheries, emphasizing the economic impact and fisher perceptions through data collected from structured interviews with small-scale and large pelagic fishers. The research documents frequent dolphin interactions, impacting catch and gear in both fishing sectors. Reported financial losses and gear damage highlight a significant economic burden, with annual losses averaging EUR 6144 for small-scale and EUR 29,882 for large pelagic fishers. Efforts to mitigate these interactions, such as using acoustic deterrents, have shown mixed results, reflecting dolphins' adaptability to human activity. While some fishers use deterrents, others remain hesitant due to cost and inconsistent efficacy. The study underscores the need for improved, sustainable solutions that integrate fisher input to enhance acceptance and effectiveness. Findings suggest that dolphins are increasingly relying on fishing activities as a foraging strategy, aligning with broader trends in the Mediterranean. In the context of EU Directive 2014/89/EU, the study integrates ecological considerations and socioeconomic impacts to ensure balanced marine management strategies. This work emphasizes the complexity of human-wildlife conflicts in marine environments, suggesting that further research and collaboration with fishers are essential to developing adaptive strategies that balance conservation with the economic needs of local fishing communities.
... Read et al., 2006;Reeves et al., 2013;Brownell et al., 2019). However, depending on geographical area and species, trawls, encircling nets, long lines and traps, have also been identified for their significant contribution to marine mammal bycatch (Smith, 1983;Read et al., 2006;Campbell et al., 2008;Fernańdez-Contreras et al., 2010;Hamer et al., 2012;Brownell et al., 2019). ...
Article
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Bycatch is the most significant threat to marine mammals globally. There are increasing requirements for national governments to fulfil their obligations to international agreements and treaties to assess fisheries catch and bycatch of non-target species. Questionnaire surveys represent one low-cost method to collect data to estimate fisheries catch and bycatch of vulnerable species including marine mammals. Questionnaire surveys can be particularly advantageous when bycatch is being investigated on large spatial and temporal scales, or in data-poor areas. This review aims to provide the necessary guidance required to design and conduct questionnaire studies investigating marine mammal bycatch. To do so, a systematic review was conducted of the methods used in 91 peer-reviewed or grey literature questionnaire studies from 1990 to 2023 investigating marine mammal bycatch. Literature was searched, screened, and analysed following the RepOrting standards for Systematic Evidence Syntheses (ROSES) protocols. A narrative synthesis and critical evaluation of the methods used were conducted and best practice recommendations are proposed. The recommendations include suggestions for how to generate representative samples, the steps that should be followed when designing a questionnaire instrument, how to collect reliable data, how to reduce under-reporting and interviewer bias, and how weighting or model-based bycatch estimation techniques can be used to reduce sampling bias. The review’s guidance and best practice recommendations provide much-needed resources to develop and employ questionnaire studies that produce robust bycatch estimates for marine mammal populations where they are currently missing. Recommendations can be used by scientists and decision-makers across the globe. Whilst the focus of this review is on using questionnaires to investigate marine mammal bycatch, the information and recommendations will also be useful for those investigating bycatch of any other non-target species.
... Marine predator bycatch and depredation in commercial and recreational fisheries is a global issue, with consequences for both conservation and fisheries economics (Read 2008, Hamer et al. 2012, Lewison et al. 2014, Mitchell et al. 2018, Jog et al. 2022. Species with slow life histories (i.e. ...
Article
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Monitoring bycatch in fisheries is essential for effective conservation and fisheries sustainability. False killer whales Pseudorca crassidens in Hawaiian waters are known to interact with both commercial and recreational fisheries, but limited observer coverage across Hawaiian fisheries obscures the ability to assess bycatch. We build upon previous work and assess occurrence of fisheries interactions through photographic evidence of dorsal fin and mouthline injuries for 3 false killer whale populations in Hawai‘i. Photographs of injuries on dorsal fins and mouthlines collected between 1999-2021 were scored for consistency with fishery interactions (‘not consistent’, ‘possibly consistent’, ‘consistent’). For individuals with both dorsal fin and mouthline photos available, the endangered main Hawaiian Islands (MHI) population had the highest rates of injuries consistent with fisheries interactions (28.7% of individuals), followed by the pelagic stock (11.7%), while no individuals from the Northwestern Hawaiian Islands population with both types of photos had fisheries-related injuries. Some individuals from the MHI population were documented with multiple fisheries-related injuries acquired on different occasions, indicating repeated interactions with fisheries. Individuals first began acquiring injuries consistent with fishery interactions at an estimated age of 2 yr. Females were more likely to have fisheries-related dorsal fin injuries than males, but rates of fisheries-related mouthline injuries were similar between the sexes. Injuries consistent with fisheries interactions were acquired throughout the study period, indicating that this is an ongoing issue, not a legacy of past fishery interactions. Our results suggest that efforts to reduce bycatch and begin monitoring of fisheries that overlap the range of the endangered MHI population are needed.
... Whaling data from the northeastern Pacific from 1948 to 1967 also supports this seasonal pattern with an increased mean length of male sperm whales starting between May and June and sustained through September, attributed to the sexual maturity of the animals [3]. Male sperm whales in the GOA are also notorious for longline depredation [70] particularly from the sablefish fishery which has its season from mid-March to mid-November [71], aligning with the peak in presence of Adult Males. ...
Article
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Sperm whales exhibit sexual dimorphism and sex-specific latitudinal segregation. Females and their young form social groups and are usually found in temperate and tropical latitudes, while males forage at higher latitudes. Historical whaling data and rare sightings of social groups in high latitude regions of the North Pacific, such as the Gulf of Alaska (GOA) and Bering Sea/Aleutian Islands (BSAI), suggest a more complex distribution than previously understood. Sperm whales are the most sighted and recorded cetacean in marine mammal surveys in these regions but capturing their demographic composition and habitat use has proven challenging. This study detects sperm whale presence using passive acoustic data from seven sites in the GOA and BSAI from 2010 to 2019. Differences in click characteristics between males and females (i.e., inter-click and inter-pulse interval) was used as a proxy for animal size/sex to derive time series of animal detections. Generalized additive models with generalized estimation equations demonstrate how spatiotemporal patterns differ between the sexes. Social groups were present at all recording sites with the largest relative proportion at two seamount sites in the GOA and an island site in the BSAI. We found that the seasonal patterns of presence varied for the sexes and between the sites. Male presence was highest in the summer and lowest in the winter, conversely, social group peak presence was in the winter for the BSAI and in the spring for the GOA region, with the lowest presence in the summer months. This study demonstrates that social groups are not restricted to lower latitudes and capture their present-day habitat use in the North Pacific. It highlights that sperm whale distribution is more complex than accounted for in management protocol and underscores the need for improved understanding of sperm whale demographic composition to better understand the impacts of increasing anthropogenic threats, particularly climate change.
... The killer whale Orcinus orca is one of the marine top predator species most frequently reported feeding on fisheries catches on fishing gear . This behaviour, termed "depredation," has been documented in many killer whale populations around the world, especially in fisheries using longlines (lines bearing series of baited hooks; Bearzi et al., 2019;Hamer et al., 2012). As a highly social species, killer whales generally depredate in groups of closely related individuals (hereafter "social units" -in which stability varies across populations; Baird & Dill, 1996;Ford, 2019). ...
Article
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Intra‐population heterogeneity in the behavioural response of predators to changes in prey availability caused by human activities can have major evolutionary implications. Among these activities, fisheries, while extracting resources, also provide new feeding opportunities for marine top predators. However, heterogeneity in the extent to which individuals have responded to these opportunities within populations is poorly understood. Here, we used 18 years of photo‐identification data paired with statistical models to assess variation in the way killer whale social units within a subantarctic population (Crozet Islands) interact with fisheries to feed on fish caught on fishing gear (i.e., depredation behaviour). Our results indicate large heterogeneity in both the spatial and temporal extents of depredation across social units. While some frequently depredated on fishery catches over large areas, others sporadically did so and in small areas consistently over the years. These findings suggest that killer whale social units are exposed to varying levels of impacts of depredation, both negative (potential retaliation from fishers) and positive (food provisioning), on their life history traits, and may explain the contrasted demographic patterns observed within the declining population at Crozet but also potentially within the many other killer whale populations documented depredating on fisheries catches worldwide.
... Depredation occurs when whales learn to remove fish from fishing gear or feed on escapees and discards from fisheries [109,124]. Cetaceans engaging in depredation behaviour may face an increased risk of injury or mortality due to close associations with vessels and gear, or deterrent methods that can be employed by fishers [110]. Depredation behaviour has been documented in at least 19 species of odontocetes across the globe, and commonly occurs with long-line fishing activities (e.g. ...
Article
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This review comprehensively evaluates the impacts of anthropogenic threats on beaked whales (Ziphiidae)—a taxonomic group characterized by cryptic biology, deep dives and remote offshore habitat, which have challenged direct scientific observation. By synthesizing information published in peer-reviewed studies and grey literature, we identified available evidence of impacts across 14 threats for each Ziphiidae species. Threats were assessed based on their pathways of effects on individuals, revealing many gaps in scientific understanding of the risks faced by beaked whales. By applying a comprehensive taxon-level analysis, we found evidence that all beaked whale species are affected by multiple stressors, with climate change, entanglement and plastic pollution being the most common threats documented across beaked whale species. Threats assessed as having a serious impact on individuals included whaling, military sonar, entanglement, depredation, vessel strikes, plastics and oil spills. This review emphasizes the urgent need for targeted research to address a range of uncertainties, including cumulative and population-level impacts. Understanding the evidence and pathways of the effects of stressors on individuals can support future assessments, guide practical mitigation strategies and advance current understanding of anthropogenic impacts on rare and elusive marine species.
... This is an issue that has been commonly reported in the literature (Brown et al. 2013, Roberson et al. 2022. For example, most baleen whale species included in the PSA and for which vulnerability scores were high, are unlikely to be at significant risk in pelagic longline fisheries, as indicated by rare bycatch and mortality events documented (Gilman et al. 2006, Hamer et al. 2012, Passadore et al. 2015. Similarly, large toothed whales and large oceanic delphinids (e.g., pilot whales, false killer whales) are unlikely to be vulnerable to purse seine fisheries, particularly in the Indian Ocean where no such occurrences have been previously reported (Romanov 2002, Escalle et al. 2015. ...
Technical Report
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Bycatch, or the incidental capture in fishing gears, is the most significant threat to marine megafauna in the world's oceans. It is currently the main driver of the decline and extirpation of cetaceans (whales, dolphins and porpoises) in many regions around the globe, both in coastal and open-ocean ecosystems. However, the magnitude of bycatch remains poorly quantified in many regions and fisheries. Over the past decade, there has been increasing concerns about the extent of cetacean bycatch in the Indian Ocean, particularly in expanding drift gillnet fisheries. Here, an ecological risk assessment including a productivity-susceptibility analysis (PSA) designed for data-poor situations was adapted to investigate the vulnerability of cetaceans to bycatch in tuna fisheries, particularly in drift gillnets, pelagic longlines, and purse seines within the IOTC (Indian Ocean Tuna Commission) Area Of Competence. The PSA revealed that risk varies greatly between gears and species. Overall, risk is higher and for more species in drift gillnets than in pelagic longlines and purse seines. Species at higher risk include oceanic small delphinids, medium-sized delphinids, and, to a much lesser extent, baleen whales. For pelagic longline fisheries, risk was also relatively high for several large oceanic delphinids. Risk for purse seine fisheries was lower than for other gears, but was relatively high for some baleen whales (particularly B. edeni). Most species with high susceptibility to capture also had high vulnerability scores based on their life history traits. Overall, the highest vulnerability scores were for gillnets across all species, but particularly small oceanic dolphins. An assessment of the spatial overlap between cetacean occurrence generated by AquaMaps (https://www.aquamaps.org) and tuna fishing effort also allowed assessment of vulnerability of species groups for each gear. The spatial overlap between gillnet fisheries and baleen whales is limited to the northern portion of the Indian Ocean. Small and large oceanic dolphins exhibit similar patterns of overlap for all three gears, with high overlap in the northern Indian Ocean with gillnets, and with pelagic longlines and purse seines in the western tropical Indian Ocean. Large toothed whale distribution overlaps extensively with the three gears, including gillnets in the northern Indian Ocean and pelagic longlines in the southern and southwestern parts of the IOTC area. Overall, this study highlights the need to better quantify cetacean bycatch in Indian Ocean tuna fisheries, particularly in gillnet fisheries.
... In recent years, several studies have investigated pinger effectiveness in reducing dolphin bycatch in trawl fisheries (van Marlen, 2007;Morizur et al., 2008;Northridge et al., 2011;Rimaud et al., 2019). However, the low rates of bycatch and subsequent lack of statistical significance make it challenging to assess the effectiveness of pingers in commercial fisheries (Hamer et al., 2012). Furthermore, comparative studies that collect catch or behavioural data from experiments with and without pingers in trawl gears often rely on grey literature, and the lack of systematic experimental designs (e.g., lack of control experiments or low number of replicas) results in statistically non-significant results. ...
Article
Bycatch of common dolphin (Delphinus delphis) in commercial trawl fisheries in the Bay of Biscay (NE Atlantic) is of concern and its mitigation a priority. Active acoustic deterrent devices (pingers) attached to fishing gear seem to be promising for bycatch mitigation, as they have demonstrated to effectively reduce cetacean bycatch in some set-net fisheries. However, the low occurrence of common dolphin bycatch in many trawl fisheries, coupled with the extensive amount of time needed to monitor them, makes it difficult to prove the effectiveness of pingers. Remote electronic monitoring (REM) systems in fisheries can substantially increase onboard observation, providing access to extensive databases to comprehensively address bycatch mitigation studies. In this study, the effectiveness of DDD®03H Dolphin Dissuasive Device (hereinafter DDD pingers) to reduce common dolphin bycatch was evaluated in a demersal pair trawler in FAO Division 27.8.c. In 195 fishing days, one of the vessels in the pair operated with a set of DDD pingers whereas the other operated without them, and the bycatch of common dolphin was monitored through the REM system. In total, 660 fishing hauls were conducted of which 223 hauls had the DDDs attached. The results showed that the DDDs reduced common dolphin bycatch by more than 90%, with both bycatch frequency and the number of individuals bycaught per haul being significantly lower. The results also showed that common dolphin bycatch in this fishery is related to factors such as the fishing zone and depth, whereas the type of net deployed, time of day and haul duration were found to not significantly affect the bycatch of this species.
... Crop raiding is a prominent example. Wildlife that consumes harvest or livestock are direct competitors of human workers, and in retaliation, community members will kill individuals of that species often without knowing which individuals were the culprits (Hamer et al. 2012, McManus et al. 2015, Moreto 2019. ...
Thesis
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Human-wildlife conflict is present across the world. In areas where human settlements overlap with elephant habitats, human-elephant conflict can result from crop raiding events, compromising farmers’ food and economic security, and putting humans and elephants in danger through farmer retaliation. Elephants raid crops primarily at night, when detection by humans is lowest, and during the dry season, as crops are developing towards harvest and natural forage quality drops. People living in these areas facing HEC have developed mitigation strategies to lessen the impacts and move towards coexistence. As a team member on the Elephants and Sustainable Agriculture in Kenya project, I conducted my research in the Kasigau Wildlife Corridor of southeastern Kenya. Over the past five years (2017-2022), our international team tested the effectiveness of eight deterrent fence designs, including four modern single deterrents (one line of deterrent strung between fence posts), three modern double deterrents (two strands of single deterrents), and one traditional deterrent (acacia branches). Each fence consisted of one or more negative stimuli to deter elephants, and any deterrent was hypothesized to perform better than the grand control of just fence posts alone. Compared to single deterrents, double deterrent fences were hypothesized to deter elephants better because they stimulate more sensory modalities. We also examined timing within the crop season and moon phase as potential predictors of crop raiding events. Elephant presence around experimental fields was hypothesized to be higher during the end of the crop season and inversely related with lunar light levels. To test these four hypotheses, eight blocks of land were leased from farmers along the boundary between Sasenyi Village and Rukinga Wildlife Sanctuary. Four of the eight blocks were divided into eight fields each around which four experimental deterrent fences and their matching four controls were erected. The other four blocks were each divided in half with one half encompassed by a beehive fence and the other by fake hives. Moon phase and timing within the crop season were determined using a lunar calendar, camera trap evidence, and crop data. During each of the two growing seasons per year, all elephants within 12 m of the deterrent fences were categorized as approaching; an instance of entering a field was termed a breach and not entering a deterrence. Analyses consisted of generalized linear mixed models, Linear Regression, and mixed effect logistic regression models. In support of my first hypothesis, the modern experimental deterrents performed better than the grand control, which had a successful deterrent rate of 27%. The traditional acacia fence (19%), and the cloth fence (66.6%) were the only deterrents tested that did not perform significantly better than the grand control. In contrast to the second hypothesis, the double deterrent fences (68%) did not perform significantly better than single deterrent (62.3%) fence designs. The third hypothesis on elephant presence being positively correlated with progression of the crop season was supported and aligned with past findings in other study sites. However, the fourth hypothesis that presence was inversely correlated with lunar light levels was not upheld, though was impacted by the direction of lunar light level, as more elephants were present during the waning moon phases, as light levels were decreasing. Using these results, we can advise farmers on which deterrents to use, and at what times to be more vigilant due to changes in the probability of crop raiding events. The results of this study are being shared with the farmers living in the KWC and may be useful to others living in high HEC areas by providing additional crop raiding mitigation strategies. Our methods of analysis can be expanded past HEC and applied to areas facing other forms of HWC to promote coexistence.
... A wide range of marine predators are known to engage in depredation with a diverse array of fishing gear (Tixier et al. 2020b). The impacts of depredation extend to fishermen, predators, and ecosystem structure and function (Gilman et al. 2007(Gilman et al. , 2008Hamer et al. 2012;Mitchell et al. 2018). ...
Article
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Depredation by marine predators causes economic losses and impacts depredating species and fish stocks. To understand these impacts, it is important to accurately estimate catch losses from depredation. Pelagic longline fisheries are susceptible to depredation, and depredation is difficult to quantify, because gear is suspended in the water column away from the vessel for extended periods. In the present study, we used fisheries data and a novel modeling approach to estimate catch removal by odontocetes in the Hawai‘i deep-set longline fishery. We estimated annual biomass and economic value lost to depredation of three of the most commonly landed species as approximately 100 t and 1 million USD, respectively, during 2012–2018. The median cost on sets when depredation occurred was 600USD,withtheworst10600 USD, with the worst 10% of sets experiencing losses exceeding 2300 USD. We also identified broad-scale spatiotemporal patterns and hotspots of depredation across the range of the fishery. Our findings quantify the ecological and economic implications of this interaction, and our methods can be applied in similar fisheries elsewhere to assess the impacts of depredation.
... ➔ Catch Protecting Gear, Net sleeves: A variety of triggered devices have been developed that encapsulates catch to deter depredation (Hamer and Childerhouse, 2012). A buoyant net or "umbrella" is attached to the vertical line above baited hooks. ...
Technical Report
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Depredation (raiding of fish from fishing gear) by toothed whales is an acute and widespread problem in many oceans around the world that has caused substantial economic losses to fishers, increased pressure on fish stocks, and inflicted injury or mortality to whales. On February 7th and 8th, 2018 the Whale Depredation Workshop was hosted at the Vancouver Aquarium by Ocean Wise, the first workshop to be held on this issue in B.C. since the 2006 Depredation Symposium. This workshop brought together fisheries representatives, managers, and scientists to tackle this complex issue, and discuss next steps. Gear modifications and deterrent devices have had limited or temporary success, so it is vital to not only work to mitigate this problem, but also to track the onset and spread of depredation in B.C. Once depredation behavior is established, there is no quick solution.
... The energetic benefit of depredation (Tixier et al., 2015) comes with an increased risk of injury for individuals, incidental capture (bycatch), and/or mortality during the interaction with the fishing gear, leading to a risk-reward trade-off that can modify individual behavior and social dynamics (Santana-Garcon et al., 2018;Buscaino et al., 2021). Several common bottlenose dolphin populations are known to interact with different fishing gears (e.g., Blasi and Boitani, 2014;Pennino et al., 2015;Buscaino et al., 2021), and a number of reports are related to trawling boats (e.g., Pace et al., 2012;Genov et al., 2019;Bonizzoni et al., 2021;Bonizzoni et al., 2022), with individuals intentionally entering the nets and actively take advantage of fisheries through depredation (i.e., injuries or removal of captured fish from a fishing gear; Chilvers and Corkeron, 2001;Hamer et al., 2012). ...
Article
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Sociality and ecological drivers that can influence individual association patterns are infrequently considered in wildlife management, although they are essential aspects affecting animals’ responses to both human-related pressures and conservation strategies. In common bottlenose dolphins (Tursiops truncatus), sex-specific social dynamics and interactions with anthropogenic activities may affect grouping and induce changes in relationships between individuals. Out of a total of 347 individuals, we assessed the level of association among 68 bottlenose dolphins that have been sighted more than five times near the Roman coast (central Mediterranean Sea, Italy). The half-weight index (HWI) of dyadic associations, their network relations, and stability over time were investigated by using the SOCPROG software. Outcomes showed that females were more strongly associated than other individuals, with both preferred constant short-term associations and random long-term associations, possibly resulting in greater success in rearing young. Individuals interacting with the bottom trawl fishery showed weaker and short-term associations. Temporary disruption of individual associations during interaction with fishery and the relatively low number of females with calves participating in depredation seem to denote both the opportunistic nature of interactions with fishing vessels and the offspring-related protection strategy. The results show that the dolphins in this region maintain a complex but flexible social structure that varies with local biological requirements and is resilient to anthropogenic pressures.
... 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.
... In many regions, spatial, temporal, and oceanographic factors affect 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 different 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.
... The killer whale, Orcinus orca, (hereafter 'KW') is one of the marine top-predator species most frequently reported depredating on fisheries catches [7]. This behaviour has been developed by different forms and populations of KW worldwide and primarily occurs in longline fisheries [8][9][10][11][12][13][14][15]. ...
Article
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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.
... Ils se traduisent par un ensemble d'interactions directes ou opérationnelles, notamment les captures accidentelles d'espèces a priori non-pêchées et la déprédation (c.-à-d., prise alimentaire directe sur le matériel de pêche par les espèces animales), et indirectes, telles qu'une compétition pour la ressource et autres effets écosystémiques associés à l'exploitation, entre pêcheries et mégafaune marine (Lewison et al., 2004(Lewison et al., , 2014Read, 2008 ;Tixier et al. 2021). Ces interactions, souvent interconnectées par des liens de causalité, peuvent menacer la survie des populations, voire des espèces, de la mégafaune marine (diminution de la disponibilité des proies, mortalité directe sur les engins de pêche ou par l'action létale des pêcheurs), et/ou induire des coûts socio-économiques substantiels pour les communautés dépendantes de la pêche (diminution du succès de pêche, dommages matériels, effort de pêche et charge de travail supplémentaires) (Gilman et al., 2008;Hamer et al., 2012;Hall et al., 2017). ...
Article
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Human-Wildlife coexistence, crystalizing trade-offs between socio-economic viability, food security of human populations and species conservation, has become a major societal and environmental challenge. This challenge represents an experimental framework for putting the principle of ecological solidarity to the test in the field. In the oceans, the global conflict between fisheries and megafauna has recently intensified but its mitigation is hampered by complex stakes in local socio-ecosystems and a lack of cross-sectorial expertise and management. Using the longline fishery operating off Crozet and Kerguelen (French subantarctic islands) as a case study, and to propose social-ecological systems models that can be implemented in other similar situations, we examined how players have mobilized and reorganized in response to two severe conflicts: seabird bycatch and depredation by cetaceans (species feeding on fishery catches).
... 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.
... 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
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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.
... 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.
... 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.
... 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
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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.
... 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.
Chapter
This chapter describes the current threats to dolphins and how these are linked to physiology
Preprint
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Several odontocete species depredate catch and bait from fishing gear, which can lead to bycatch and substantial economic costs. There are no known odontocete depredation mitigation methods for pelagic longline fisheries that are effective, do not harm odontocetes and are economically viable. Using observer data from the Hawaii-based tuna longline fishery, this study summarized teleost and elasmobranch species-specific mean posterior odontocete depredation rates using a simple Bayesian binomial likelihood estimator with a Bayes-Laplace prior. Depredation rates of species with sufficient sample sizes ranged from a high of ca. 1.2% (1.1 to 1.3 95% highest posterior density interval or HDI) for shortbill spearfish to a low of 0.002% (0.001 to 0.003 95% HDI) for blue shark. Depredation of catch is a rare event in this fishery, occurring in about 6% of sets. When depredation did occur, most frequently a small proportion of the total catch was depredated, however, there was large variability in depredation rates between teleost species. For example, bigeye tuna was two times more likely to be depredated than yellowfin tuna (odds ratio=2.03, 95% CI: 1.8-2.3, P<0.0001). For sets with depredation of one or more fish of any species, 10% and 2% of sets had depredation of over half of the captured bigeye tuna and combined teleosts, respectively. All elasmobranch species had relatively low depredation rates, where only 7 of almost 0.5M captured elasmobranchs were depredated. Odontocetes selectively depredate a subset of the teleost species captured within sets, possibly based on net energy value, chemical, visual, acoustic and textural characteristics and body size, but not median length, which was found to be unrelated to depredation rate (Pearson’s r= 0.14, 95% CI: -0.26 to 0.50, p=0.49). Study findings provide evidence to support the identification and innovation of effective and commercially viable methods to mitigate odontocete depredation and bycatch.
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Cetacean and shark depredations in a small-scale longline fishery in the southeastern Taiwan waters were estimated based on interviews of 21 fishermen and logbooks of 12 sampling vessels, including 649 operations (681,310 hooks) from October 2009 to December 2010. Cetacean depredations were more serious than shark depredations, with damage rates of 19.26% and 11.56%, respectively. The depredation rates in number and weight from cetaceans were estimated to be 2.21% and 3.23%, respectively, and were significantly higher than those from sharks, which were estimated to be 0.51% and 0.47%, respectively. The depredation indices from cetacean and shark were estimated to be 0.93 and 0.22 per 1000 hooks, respectively. The dolphinfish and yellowfin tuna were the top two species depredated by cetaceans and sharks. The annual economic loss of the small-scale longline fishery due to cetacean and shark depredations was estimated to be USD 441.9 thousand and USD 58.8 thousand, respectively, which corresponded to 4.5% and 0.6% of the total sales of the longline fishery at Hsinkang fishing port, southeastern Taiwan. The catch in number of dolphinfish and the operation depth were significant factors that affected cetacean depredations.
Technical Report
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El proyecto Interespecies ha realizado una caracterización del escenario de interacciones entre la pesca artesanal y cetáceos, elasmobranquios, tortugas y aves a nivel archipelágico. Se han detectado interacciones de colaboración, depredación/rotura y captura accidental de cetáceos, elasmobranquios, tortugas y aves. La frecuencia e intensidad de las distintas interacciones varía según la técnica de pesca y el puerto/refugio. Las interacciones de depredación/rotura están causando pérdidas económicas de diversa magnitud en las diferentes pesquerías, con las mayores pérdidas por interacción en las pesquerías de atún, en interacciones con cetáceos y tiburones. Entre las especies reportadas en interacciones de captura accidental se incluyen varias especies protegidas y amenazadas. Se han identificado diferentes medidas de mitigación empleadas actualmente por los pescadores, algunas de las cuales pueden entrañar un riesgo para los animales. Se han detectado interacciones de alta incidencia dónde se recomienda hacer estudios específicos para comprender la naturaleza de las interacciones y poder encontrar soluciones adecuadas. La correcta gestión de las interacciones entre fauna marina y pesca artesanal permite asegurar la conservación de especies protegidas y el desarrollo de un sector pesquero sostenible.
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Sperm whales exhibit sexual dimorphism and sex-specific latitudinal segregation. Females and their young form social groups and are usually found in temperate and tropical latitudes, while males forage at higher latitudes. Historical whaling data and rare sightings of social groups in high latitude regions of the North Pacific, such as the Gulf of Alaska (GOA) and Bering Sea/Aleutian Islands (BSAI), suggest a more nuanced distribution than previously understood. Sperm whales are the most sighted and recorded cetacean in marine mammal surveys in these regions but capturing their demographic composition and habitat use has proven challenging. This study detects sperm whale presence using passive acoustic data from seven sites in the GOA and BSAI from 2010 to 2019. Differences in click characteristics between males and females (i.e., inter-click and inter-pulse interval) was used as a proxy for animal size/sex to derive time series of animal detections. Generalized additive models with generalized estimation equations demonstrate how spatiotemporal patterns differ between the sexes. Social groups were present at all recording sites with the largest relative proportion at two seamount sites in the GOA and an island site in the BSAI. We found that the seasonal patterns of presence varied for the sexes and between the sites. Male presence was highest in the summer and lowest in the winter, conversely, social group peak presence was in the winter for the BSAI and in the spring for the GOA region, with the lowest presence in the summer months. This study demonstrates that social groups are not restricted to lower latitudes and capture their present-day habitat use in the North Pacific. It highlights that sperm whale distribution is more complex than accounted for in management protocol and underscores the need for improved understanding of sperm whale demographic composition to better understand the impacts of increasing anthropogenic threats, particularly climate change.
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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.
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Predators adapt their foraging behavior to exploit a variety of prey in a range of environments. Short-finned pilot whales are wide-ranging predators in tropical and sub-tropical oceans, but most previous studies of their foraging ecology have been conducted near oceanic islands. We deployed sound- and movement-recording tags on 43 short-finned pilot whales off Cape Hatteras, North Carolina, USA, to measure their foraging behavior in a continental shelf-break ecosystem and investigate how variation in the environment shapes their behavior. Overall, the foraging behavior of pilot whales off Cape Hatteras was similar to that of their counterparts from island-associated habitats. Off Cape Hatteras, pilot whales made foraging dives as deep as 1077 m (mean: 445 m), lasting up to 23 min (mean: 12.8 min), with sprints (pursuit at speeds over 3 m s ⁻¹ and up to 6.9 m s ⁻¹ ) in more than half of foraging dives. However, tagged whales off Cape Hatteras produced higher buzz rates (11.3 buzzes dive ⁻¹ ), foraged more extensively in daytime hours, and engaged in more frequent benthic foraging than island-associated ecotypes. By parsing the echoic scene generated by the animal’s own echolocation clicks, we show that pilot whales off Cape Hatteras frequently exploit bathymetric features for foraging, with benthic dives resulting in higher prey capture attempts than pelagic dives. The ability of these predators to strategically adapt foraging strategies to local habitat features likely contributes to their ecological success and may allow them to adjust to shifts in prey distributions in a rapidly changing Anthropocene ocean.
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Descender devices are increasingly recognized as a leading means of barotrauma mitigation for released reef fishes. Yet, some resource users oppose regulations requiring or encouraging descender device use, arguing that predators frequently eat fish during release (depredation), sometimes causing device loss. We synthesized data for over 1,200 descended releases (both videoed and non‐videoed) of 16 species of reef fish off North Carolina, USA. Of 114 videos, we observed possible predators on seven, none of which showed actual depredation. Of 1,176 non‐videoed releases, we lost zero descender devices, indicating that, although cryptic depredation may have occurred, equipment loss was nonexistent. The lack of any evidence of depredation in ocean waters off North Carolina provides information to managers that they can use to reinforce education and outreach to encourage descender use.
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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.
Article
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.
Article
Shark depredation, the full or partial removal of a hooked fish by a shark before it is landed, is anecdotally increasing in the United States. Perceptions of depredation by anglers and fishing guides may influence their behavior and have cascading effects on sharks and recreational fisheries. However, to date, these perceptions have not been broadly quantified. To better understand how anglers and guides respond to shark depredation in recreational fisheries, we used an online survey open to saltwater anglers in North America, distributed electronically via social media and online platforms. Of the 541 respondents, 77% had experienced depredation in nearshore and pelagic fisheries in the last five years, with depredation more commonly reported in the southeastern United States. Emotional responses to depredation were significantly different between anglers and guides, with the latter feeling more intense negative emotions. Behavioral changes in response to depredation, such as targeting and harvesting sharks, were driven largely by negative emotional responses and perceptions of sharks as threats to target species, while changes to protect target species varied with positive emotional responses and angler demographics. Guides were predominantly concerned about increased mortality to their target species and loss of trophy fish from the population. In fact, 87% of guides experienced depredation when fishing with clients and overwhelmingly reported that depredation has a negative effect on their livelihood. Overall, these results can be used to help inform strategies to reduce depredation while accounting for the values of stakeholder groups, particularly anglers and those advocating for shark conservation.
Article
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Проведен анализ опубликованных источников и собственных данных об интенсивности рыбного промысла и встречах китообразных в акватории Восточной Камчатки и западной части Берингова моря в период 2003–2017 гг. Китообразные встречались на всей рассматриваемой акватории, наибольшее количество встреч зарегистрировано между побережьем Камчатки и Командорскими островами. Наиболее интенсивный рыбный промысел проводится на шельфе в районе мыса Наварин.С учетом отмены дрифтерного промысла, районы интенсивного рыбного промысла всеми орудиями лова и места попутных летних встреч китообразных на большей части рассматриваемой акватории не пересекаются. 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 the 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 a major part of the area considered.
Technical Report
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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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Fishery-cetacean interactions, including those with longline gear, give rise to economic, ecological and social concerns. This paper reviews problems resulting from cetacean-longline interactions, considers potential strategies to reduce interactions and identifies research priorities and approaches. Depredation by cetaceans (removal and damage of hooked fish and bait from fishing gear) and damage and loss of fishing gear create economic problems; however, the magnitude of this problem is poorly understood. There is also insufficient information to determine whether there are population-level effects resulting from injury and mortality of cetaceans (from incidental entanglement and hooking and from deliberate actions to discourage depredation). Fishery-cetacean interactions may also: change cetacean foraging behaviour and distribution; increase fishing effort to make up for fish taken from gear by cetaceans; and create errors in fish stock assessments that do not account for cetacean depredation. Negative public perceptions of longline fishing can result from news of incidental and deliberate injury and mortality of cetaceans associated with longlining. Information on how to reduce cetacean interactions with longline gear is also limited, as is the understanding of the mechanisms responsible for them. Strategies already employed in some fleets include refraining from setting or cutting sets short when problematic species of cetaceans are observed and fleet coordination of daily fishing times and positions. Many fishermen perceive depredation as an inevitable part of fishing. This paper discusses a number of other possible cetacean avoidance strategies that warrant consideration, including: (1) fleet communication to enable vessels to avoid temporally and spatially unpredictable and sporadic hotspots of aggregations of cetaceans; (2) underwater acoustic masking devices to conceal the sound of the vessel, gear, and setting and hauling activities; (3) quieter vessels to reduce cetaceans’ ability to target longline vessels; (4) encasement of caught fish to reduce cetacean access to or interest in the catch; (5) use of bait or gear with an unpleasant smell or taste to reduce the attractiveness of gear, bait and catch to cetaceans; (6) use of pre-recorded fishing vessel sounds played from stations throughout a fleet’s fishing grounds to distract cetaceans from actual fishing vessels; (7) use of acoustic devices to mask returning cetacean echolocation signals; and (8) use of tethered sonobuoys to track cetaceans and enable fleet avoidance. Vessels with relatively low cetacean interaction rates should be examined for design and operational differences from vessels with high interaction rates, possibly allowing identification of effective avoidance methods. There is a need for experimentation in individual longline fisheries over several seasons to assess fisheryspecific efficacy and commercial viability of cetacean avoidance strategies. This is necessary as different cetacean species likely respond differently to an avoidance method and cetaceans may habituate to an avoidance strategy, especially in fisheries interacting with resident cetaceans.
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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 (= 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 (ST = 0.47, p< 0.0001). This result supports recognition of the existing management unit, which has geo-political boundaries corresponding to the USAs exclusive economic zone (EEZ) of Hawaii. However, a small number of animals sampled within the EEZ but away from the near-shore island area, which is defined as<25nautical 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.
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Pelagic longline gear had several independent evolutions, but the most widespread form appears to have been originally developed by the Japanese as early as the mid-19th century. Technological developments such as polyamide monofilament line and modern fishing vessel construction have resulted in the evolution and expansion of this gear type as the primary worldwide method of commercially harvesting large pelagic fishes such as broadbill swordfish and tunas. Although the adaptability of the gear through changes in materials, lengths, and deployment strategies has resulted in generally high selectivity for many target species, the bycatch of protected species by pelagic longlines is considered a global problem in the conservation effort to sustain populations of sea turtles, sea birds, and some istiophorid billfishes (sailfishes; spearfishes; marlins). Recent research on the modification of pelagic longline fishing strategies uses this inherent adaptability of the gear to avoid or reduce the mortality of bycatch species. This is an alternative to the traditional management strategy of closed areas, which fishermen view as less effective and generally more restrictive (limiting) with respect to target catches. This work with academic partners and commercial fishermen has resulted in the development of bycatch reduction strategies which include safe handling and release gear and protocols, use of circle hooks in place of traditional J-style hooks, restrictions on gangion and mainline lengths, and corrodible hooks.