Sharks and rays are often caught as bycatch by commercial fisheries, and high incidences of bycatch are partially to blame for the declines in many populations of elasmobranchs. In an effort to reduce rates of bycatch, researchers have tested various deterrents that could benefit fisheries. Permanent magnets are one promising form of bycatch reduction device, yet their efficacy has only been tested for hook-and-line fisheries with variable results. Here, we examined the potential benefits of permanent magnets on an ocean fish trap fishery targeting snapper (Pagrus auratus) where more than 10% of the total catch is comprised of unwanted elasmobranchs and the presence of elasmobranchs reduces the catch of target species. Over 1000 fish traps were deployed in a fishery-dependent survey in New South Wales, Australia. Standardised catch rates indicate that the incorporation of magnets into fish traps significantly reduced incidences of elasmobranch bycatch (mainly Brachaelurus waddi) by over a third, while increasing the amount of target fish caught by an equivalent amount. Together these results suggest that magnets can be used as an effective bycatch reduction device that reduces incidences of elasmobranch bycatch while increasing the profitability of fish traps for fishermen. Future studies should aim to replicate these results in areas where different species of elasmobranchs occur.
Incidental catch of nontarget species (bycatch) is a major barrier to ecological and economic sustainability in marine capture fisheries. Key to mitigating bycatch is an understanding of the habitat requirements of target and nontarget species and the influence of heterogeneity and variability in the dynamic marine environment. While patterns of overlap among marine capture fisheries and habitats of a taxonomically diverse range of marine vertebrates have been reported, a mechanistic understanding of the real-time physical drivers of bycatch events is lacking. Moving from describing patterns toward understanding processes, we apply a Lagrangian analysis to a high-resolution ocean model output to elucidate the fundamental mechanisms that drive fisheries interactions. We find that the likelihood of marine megafauna bycatch is intensified in attracting Lagrangian coherent structures associated with submesoscale and mesoscale filaments, fronts, and eddies. These results highlight how the real-time tracking of dynamic structures in the oceans can support fisheries sustainability and advance ecosystem-based management.
Bycatch of marine megafauna by small-scale fisheries is of growing global concern. The southeastern Pacific sustains extensive fisheries that are important sources of food and employment for millions of people. Mismanagement, however, jeopardizes the sustainability of ecosystems and vulnerable species. We used survey questionnaires to assess the impact of small-scale gillnet fisheries on sea turtles across 3 nations (Ecuador, Peru and Chile), designed to fill data gaps and identify priority areas for future conservation work. A total of 765 surveys from 43 small-scale fishing ports were obtained (Ecuador: n = 379 fishers, 7 ports; Peru: n = 342 fishers, 30 ports; Chile: n = 44 fishers, 6 ports). The survey coverage in study harbors was 28% for Ecuador, 37.0% for Peru, and 62.7% for Chile. When these survey data are scaled up across the fleets within surveyed ports, the resulting estimate of total annual bycatch across the study harbors is 46 478 turtles; where Ecuador is 40 480, Peru 5 828 and Chile 170 turtles. Estimated mortality rates vary markedly between countries (Ecuador: 32.5%; Peru 50.8%; Chile 3.2%), leading to estimated lethal takes of 13 225, 2 927, and 6 turtles for Ecuador, Peru, and Chile, respectively. These estimates are remarkably large given that the ports surveyed constitute only 16.4, 41, and 22% of the national gillnet fleets in Ecuador, Peru, and Chile, respectively. Limited data from observer-based surveys in Peru suggest that information from surveys are reliable and still informative. Information from surveys clearly highlight Ecuador and Peru as priority areas for future work to reduce turtle bycatch, particularly given the status of regional populations such as leatherback and hawksbill turtles.
In terrestrial and coastal systems, the mitigation hierarchy is widely and increasingly used to guide actions to ensure that no net loss of biodiversity ensues from development. We develop a conceptual model which applies this approach to the mitigation of marine megafauna by‐catch in fisheries, going from defining an overarching goal with an associated quantitative target, through avoidance, minimization, remediation to offsetting. We demonstrate the framework's utility as a tool for structuring thinking and exposing uncertainties. We draw comparisons between debates ongoing in terrestrial situations and in by‐catch mitigation, to show how insights from each could inform the other; these are the hierarchical nature of mitigation, out‐of‐kind offsets, research as an offset, incentivizing implementation of mitigation measures, societal limits and uncertainty. We explore how economic incentives could be used throughout the hierarchy to improve the achievement of by‐catch goals. We conclude by highlighting the importance of clear agreed goals, of thinking beyond single species and individual jurisdictions to account for complex interactions and policy leakage, of taking uncertainty explicitly into account and of thinking creatively about approaches to by‐catch mitigation in order to improve outcomes for conservation and fishers. We suggest that the framework set out here could be helpful in supporting efforts to improve by‐catch mitigation efforts and highlight the need for a full empirical application to substantiate this.
Bycatch interactions with deep-sea elasmobranchs are increasingly common and can lead to dramatic declines in abundance over short time scales. Sharks hooked in the deep sea could face a higher likelihood of severe physiological disturbance, at-vessel mortality, and post-release mortality (PRM) than their shallower counterparts. Unfortunately, robust PRM rates have not yet been estimated for longline-caught deep-sea sharks, and as such are not currently incorporated into total fishery mortality estimates or bycatch assessments, limiting the effectiveness of current conservation or management initiatives. We empirically estimated PRM for 2 focal taxa of deep-sea shark, the Cuban dogfish Squalus cubensis and the gulper shark Centrophorus sp., using post-release enclosures deployed at-depth. We calculated 24 h PRM rates of 49.7 ± 8.5% (mean ± SE) for S. cubensis and 83 ± 16% for Centrophorus sp. and identified blood lactate, total length, glucose, and vitality scores as predictors of PRM in S. cubensis. We also observed all 24 h PRM within 11 h post-capture and demonstrated the effects of recovery depth and at-vessel blood chemistry metrics on post-release behavior. Our results suggest that PRM rates of deep-sea sharks are high and highlight the need for filling in this gap in fishery mortality estimates for other common discards in the future.
The European Union banned fishing operations with trammel, entangling and gillnets in Portuguese continental waters at depths >200 m in consideration of the potential impact of fisheries on deep-sea sharks. Derogation could be considered if Member States demonstrate that by-catch mortality does not adversely affect this group of species. This regulation has had an impact on the trammel net fishery for anglerfish (Lophius piscatoriusand Lophius budegassa), one of the most important Portuguese multi-species fisheries. This study evaluates the impact of this fishery on deep-water shark populations by looking at onboard observations of by-catch in the commercial fishery and by analysing survey catch composition. Results suggest that this fishery has a very low impact on deep-water shark populations: by-catch was <5% by weight of the total catch in 98% of the hauls conducted in the depth range allowed for this fishery (<600 m). Frequency of occurrence of deep-water sharks was also low. Etmopterus spinax and Etmopterus pusillus were the only species found to overlap with this fishery to any great extent; all the others largely distribute at depths greater than 600 m. A higher overlap is expected in hauls catching L. piscatorius, which seems to distribute at greater depths, but more information is needed to clarify the distribution pattern of this species. Scientific data supports the proposed change to the EU regulation. If necessary, future management measures may rely on spatial closures, but would require enhanced knowledge on species’ spatial distributions and also on social and economic aspects of this fishery.
This paper considers fisheries bycatch reduction within the least-cost biodiversity impact mitigation hierarchy. It introduces conservatory offsets that are implemented earlier in the biodiversity impact mitigation hierarchy than conventional compensatory offsets used as instruments of last resort. The paper illustrates implementation in an on-going sea turtle conservation programme by the International Seafood Sustainability Foundation.
The Atlantic seabob (Xiphopenaeus kroyeri) trawl fishery is very important to Guyana, with 88 licensed industrial vessels harvesting about 15,000 mt annually, representing Guyana’s most valuable seafood export. All vessels are already using both teleost by—catch reduction devices (BRDs) and turtle excluder devices (TEDs) to satisfy international market standards. However, the key stakeholder, the Guyana Association of Private Trawler Owners and Seafood Processors, is now seeking to access sustainable seafood markets through pursuing Marine Stewardship Council (MSC) certification. To this end, this study documents elasmobranch by—catch in the current fishery and examines the effectiveness of a modified TED (with a reduced bar spacing and the addition of a brace bar) in reducing elasmobranch by—catch. From July—August 2014, 131 tows were made, 80 of which represented simultaneous hauls with control and modified TEDs. One shark and 8 ray species were recorded. A statistically significant 40% decline in the elasmobranch catch rate was observed when using modified TEDs compared with control TEDs (mean by—catch rate dropped from 2.3 to 1.4 individuals per twin—trawl/h). Furthermore, modified TEDs significantly reduced the mean size of rays caught by 6.3%. This also resulted in a virtual elimination of 3 IUCN—designated 'Near Threatened' ray species in the by—catch, although having little effect on the capture of small—sized elasmobranch species, including the 'Critically Endangered' Caribbean Electric Ray (Narcine bancroftii). We conclude that the modified TED was successful in reducing the by—catch of vulnerable elasmobranch species and should advance progress towards attaining by—catch standards required for MSC certification.
A principal role of marine protected areas (MPAs) is to mitigate the decline of biodiversity. A key part of this role is to reduce the effects of fisheries on bycatch of vulnerable species. Bycatch can have an impact on species by reducing population sizes, and an ecosystem-level impact through the significant removal of biomass and subsequent trophic changes. In this regard, it is crucial to refine methods for quantifying interactions between fisheries and bycatch species, and to manage these interactions spatially. A new method is presented for quantifying interactions between fisheries and bycatch species at high spatial and temporal resolutions. Temporally explicit species distribution models are used to examine temporal dynamics of fisheries and bycatch. This method is applied to Australia’s Eastern Tuna and Billfish Fishery to estimate interactions with seven principal bycatch species. The ability of MPAs to reduce bycatch is evaluated, and considerations are outlined for the spatial management of fishery-bycatch species interactions. Australia’s Commonwealth Marine Reserve Network had a minimal impact on bycatch reduction under both the 2012 proclaimed and the 2015 panel-recommended zonings. These results highlight the need for threats to marine biodiversity to be incorporated directly into design of MPAs, and for close scrutiny of assumptions that threats will be incidentally abated after MPAs have been proclaimed, or that off-reserve mechanisms will compensate for inadequacies of MPAs.
By-catch is considered a significant problem in large-scale fisheries yet in small-scale fisheries (SSF), employing >99% of the world's fishers, there is limited quantitative understanding of by-catch, and catches in general. We provide an assessment of by-catch from fishing gears (fyke, trawl, set trammel, and drift trammel nets) commonly used in small-scale fisheries across the globe, using a representative Sri Lankan case study and placing this in the context of local resource use patterns. We reveal evidence of how SSF generate significant finfish by-catch with potentially significant ecological impacts. Fishers targeting shrimp (fyke, trawl, and drift trammel nets) caught more non-target species than global averages (44, 44, and 67% by weight, respectively). Fishers targeting finfish (set trammel nets) caught fewer non-target species. We found that by-catch depends more on target species and gear type, supporting suggestions that SSF are not “inherently more sustainable” than their large-scale counterparts and a collective effort is required for an improved understanding of the impacts of SSF. This study highlights an additional issue of valuable food fish discards, raising questions about fisheries exploitation in the context of food security in areas where poverty and food insecurity are prevalent.