Shark depredation in commercial and recreational fisheries

Mitchell, J. D.; McLean, Dianne L.; Collin, Shaun P.; Langlois, Tim

doi:10.1007/s11160-018-9528-z

Cited by 65 publications

(55 citation statements)

References 201 publications

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“…For instance, if the depredated resource is fully artificial for the predator, depredation may lead to decreased availability of that resource for other functional groups in the ecosystem, subsequently affecting these groups through trophic effects (Woodroffe et al 2005). Also, by feeding on fish caught in fishing gear, marine predators may cause increased and difficult-to-quantify mortality for fish stocks, thereby increasing the catches needed for fisheries to reach their quotas (Gilman et al 2013, Mitchell et al 2018.…”

Section: Introductionmentioning

confidence: 99%

Importance of toothfish in the diet of generalist subantarctic killer whales: implications for fisheries interactions

Tixier¹,

Giménez²,

Reisinger³

et al. 2019

Mar. Ecol. Prog. Ser.

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Fisheries may generate new feeding opportunities for marine predators, which switch foraging behaviour to depredation when they feed on fish directly from fishing gear. However, the role of diet in the propensity of individuals to depredate and whether the depredated resource is artificial or part of the natural diet of individuals is often unclear. Using stable isotopes, this study investigated the importance of the commercially exploited Patagonian toothfish Dissostichus eleginoides in the diet of generalist subantarctic killer whales Orcinus orca depredating this fish at Crozet (45°S, 50°E). The isotopic niche of these killer whales was large and overlapped with that of sperm whales Physeter macrocephalus from the same region, which feed on toothfish both naturally and through depredation. There was no isotopic difference between killer whales that depredated toothfish and those that did not. Isotopic mixing models indicated that prey groups including large/medium sized toothfish and elephant seal Mirounga leonina pups represented ~60% of the diet relative to prey groups including penguins, baleen whales and coastal fish. These results indicate that toothfish are an important natural prey item of Crozet killer whales and that switching to depredation primarily occurs when fisheries facilitate access to that resource. This study suggests that toothfish, as a commercial species, may also have a key role as prey for top predators in subantarctic ecosystems. Therefore, assessing the extent to which predators use that resource naturally or from fisheries is now needed to improve both fish stock management and species conservation strategies.

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Section: Introductionmentioning

confidence: 99%

Importance of toothfish in the diet of generalist subantarctic killer whales: implications for fisheries interactions

Tixier¹,

Giménez²,

Reisinger³

et al. 2019

Mar. Ecol. Prog. Ser.

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“…The third form of human-wildlife conflict is increased depredation in fisheries (i.e., sharks taking fish caught on or in fishing gear). A review of studies that quantified shark depredation in commercial and recreational fisheries shows increasing levels across some studies (Mitchell et al 2018a). These increases in depredation rates, despite potential declines in many pelagic shark populations (Dulvy et al 2008), suggest changing behaviour patterns in sharks that may intensify conflict with humans and hamper conservation efforts.…”

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confidence: 99%

“…Some anglers perceive sharks as increasing in abundance and therefore posing a threat to their catch (Drymon & Scyphers 2017). Whether increased shark depredation is due to a learned behaviour, decreased prey abundance, increased shark abundance, or all three factors, it has substantial economic and sociocultural impacts in commercial, recreational and subsistence fisheries (Mitchell et al 2018a) and so must be considered as a source of conflict that may affect conservation efforts, especially where it leads to fishers killing sharks and/or lobbying against management measures. Increased stakeholder engagement, quantifying depredation rates and understanding socioeconomic drivers of when and where fishers choose to engage in retaliatory killing of sharks may help mitigate depredation.…”

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confidence: 99%

Are we ready for elasmobranch conservation success?

et al. 2019

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“…; Favaro and Cote ), and further field‐based work is needed to verify these approaches (Molina and Cooke ; Mitchell et al. ).…”

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confidence: 99%

“…Similarly, the unique electrosensory system in sharks has prompted researchers to investigate the use of electropositive metals (Brill et al 2009;Tallack and Mandelman 2009;Hutchinson et al 2012), permanent magnets (Rigg et al 2009;O'Connell et al 2011), and rare earth magnets (Robbins et al 2011) as mechanisms to reduce shark bycatch and depredation. While promising, results to date are mixed (Godin et al 2013;Favaro and Cote 2015), and further field-based work is needed to verify these approaches (Molina and Cooke 2012;Mitchell et al 2018).…”

mentioning

confidence: 99%

Genetic Identification of Species Responsible for Depredation in Commercial and Recreational Fisheries

Drymon

Cooper

Powers

et al. 2019

N American J Fish Manag

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Depredation, the partial or complete removal of hooked fish (prey) by a nontarget predator species, is a cryptic interaction that negatively affects predators, prey, and fishing industries. However, these interactions are rarely observed, rendering positive identification of the predator nearly impossible. We therefore tested a genetic method for predator identification. Depredated remains from sharks and bony fish were sampled with buccal swabs. Genetic material was isolated from the swabs, which we hypothesized contained oral cells from the predator. A portion of the cytochrome‐c oxidase subunit I locus was amplified using prey‐specific blocking primers and sequenced in high depth using a metagenetics approach. We sequenced haplotypes from the remains of four sharks, where the predator was visually confirmed, and four bony fish, where the predator was unknown. For all interactions with known predators, our technique suggested the correct predator species. For all interactions where the predators were unknown, our technique suggested species previously confirmed as perpetrators in depredation events. Our findings provide a basis for the development of a genetic technique for predator identification, while highlighting challenges to be overcome before predator identification can be applied to large‐scale fisheries.

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Shark depredation in commercial and recreational fisheries

Cited by 65 publications

References 201 publications

Importance of toothfish in the diet of generalist subantarctic killer whales: implications for fisheries interactions

Importance of toothfish in the diet of generalist subantarctic killer whales: implications for fisheries interactions

Are we ready for elasmobranch conservation success?

Genetic Identification of Species Responsible for Depredation in Commercial and Recreational Fisheries

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