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Fisheries can adversely affect threatened bycatch species and vulnerable marine ecosystems (VMEs). Thresholds are unique amongst bycatch management methods in providing flexibility in individual participants' approaches to avoid exceeding limits, and particularly for individual vessel quotas, in incentivizing the innovation of effective and commercially viable solutions. This study assessed bycatch thresholds for sharks and relatives, air-breathing marine species and macroinvertebrate indicators for identifying benthic VMEs of 21 intergovernmental organizations and arrangements (IGOs). Seven IGOs lacking bycatch thresholds, who tended to have fewer members, might rely on bycatch management by national authorities. Sharks were the predominant focus. IGOs did not know if thresholds were reached for almost half of measures, likely due to compliance monitoring deficits. Individual vessel limits may be more equitable and prevent a race for fish. However, risk pools and fleetwide thresholds may be more effective when mitigation approaches for individual vessels are limited. No IGO uses individual transferable bycatch quotas or risk pools, which would be challenging to implement regionally. No thresholds were reference points of a harvest strategy. There were limited incidences of thresholds being reached. Thresholds might be set too high to meet objectives. When reached, there was high variability in management responses being systematically implemented. Addressing deficits of thresholds being set too low, inadequate compliance monitoring and inconsistent management response implementation could improve performance. Thresholds have the potential to be an effective component of regional bycatch management strategies, incentivizing fishers to minimize their individual and collective bycatch fishing mortality and adverse effects on VMEs. [ABSTRACT FROM AUTHOR]

There is growing concern over the conservation status of sharks and relatives exposed to fishing mortality. The Food and Agriculture Organization of the United Nations in 1999 adopted the International Plan of Action for the Conservation and Management of Sharks (IPOA), which provides nations with advice on adopting and implementing national plans. An assessment of global national and regional plans of action on sharks (NPOAs) found: most are out of date; limited use of specific, measurable and timebound objectives and activities; no outcome objectives; and few performance assessments. This makes most NPOAs inadequate for planning and assessing efficacy. Over 33% of the annual retained catch of sharks and relatives was from countries without NPOAs and less than 12% was from countries with current NPOAs. NPOAs identified fisheries management framework deficits, ecology knowledge gaps, institutional capacity and coordination shortfalls, and budget constraints as the largest obstacles to implementation and are improvement priorities. We recommend how to amend the IPOA to better support the adoption and effective design and implementation of NPOAs for evidence‐informed conservation and management. [ABSTRACT FROM AUTHOR]

Apex and mesopredators such as elasmobranchs are important for maintaining ocean health and are the focus of conservation efforts to mitigate exposure to fishing and other anthropogenic hazards. Quantifying fishing mortality components such as at-vessel mortality (AVM) is necessary for effective bycatch management. We assembled a database for 61 elasmobranch species and conducted a global meta-synthesis to estimate pelagic longline AVM rates. Evolutionary history was a significant predictor of AVM, accounting for up to 13% of variance in Bayesian phylogenetic meta-regression models for Lamniformes and Carcharhiniformes clades. Phylogenetically related species may have a high degree of shared traits that explain AVM. Model-estimated posterior mean AVM rates ranged from 5% (95% HDI 0.1%–16%) for pelagic stingrays and 76% (95% HDI 49%–90%) for salmon sharks. Measures that reduce catch, and hence AVM levels, such as input controls, bycatch quotas and gear technology to increase selectivity are appropriate for species with higher AVM rates. In addition to reducing catchability, handling-and-release practices and interventions such as retention bans in shark sanctuaries and bans on shark finning and trade hold promise for species with lower AVM rates. Robust, and where applicable, phylogenetically-adjusted elasmobranch AVM rates are essential for evidence-informed bycatch policy. [ABSTRACT FROM AUTHOR]

Participatory decision tools enable stakeholders to reconcile conflicting natural resources management objectives. Fisheries targeting highly productive species can have profound impacts on co-occurring bycatch species with low fecundity and other life history traits that make them vulnerable to anthropogenic sources of mortality. This study developed a decision tool for integrated bycatch management for data-limited to data-rich fisheries, improving upon current piecemeal approaches. First, through a systematic literature review, participants compile a comprehensive database of methods to mitigate the catch and fishing mortality of threatened bycatch species. These mitigation methods are then categorized into tiers of a sequential mitigation hierarchy, where interventions that avoid capture are considered before those that minimize catchability, followed by methods that minimize fishing mortality, before approaches that offset residual impacts. The methods are also assembled within an evidence hierarchy, where findings from meta-analytic modelling studies are more robust and generalizable than from individual studies. The decision tool enables stakeholders to evaluate alternative bycatch management strategies' efficacy at meeting specific and measurable objectives for mitigating the catch and mortality of bycatch and for costs from multispecies conflicts, economic viability, practicality and safety, while accounting for the fishery-specific feasibility of compliance monitoring of alternative bycatch management measures. Ongoing adaptation of the bycatch management framework addresses findings from performance assessments, updated evidence, new mitigation methods and changes to governance systems. The proposed decision tool therefore enables stakeholders to develop bycatch management frameworks that provide precautionary protection for the most vulnerable populations with acceptable tradeoffs. [ABSTRACT FROM AUTHOR]

• Drift speeds and trajectories were similar for shallow and standard depth DFADs. • Tuna aggregation times were similar for shallow and standard depth DFADs. • Purse-seine catch rates for tunas were similar for shallow and standard depth DFADs. An at-sea experiment was undertaken to evaluate the performance of 150 shallow depth (5 m) prototype drifting fish-aggregating devices (DFADs) with rope appendages, compared to 150 standard depth (∼ 40 m) traditional design DFADs with purse-seine net appendages, in the equatorial eastern Pacific Ocean tuna purse-seine fishery, seeking a solution to reduce purse-seine fishing mortality on undesirable sizes of bigeye tuna. Following concurrent deployments of the two DFAD types along transects, the average daily drift speeds were significantly different but similar as were the drift trajectories among the two DFAD types. Based on evaluations of the time-series of acoustic data from the echo-sounder buoys attached to the shallow and standard depth DFADs, the average time before aggregation by non-tuna species was 15.3 d (range: 3.2–65.5) and 18.2 d (range: 1.1–101.2), respectively, and the average time before aggregation by tuna species was 62.2 d (range: 3.3–248.3) and 70.2 d (range: 1.5–270.5), respectively. Analyses of the catch per set data for tunas and non-tuna species, using generalized additive mixed models with Bayesian inference, indicated no significant differences in catch rates from sets on shallow and standard depth DFADs. There was a similar proportion of bigeye tuna in the catch for purse-seine sets on the shallow and standard depth DFADs. [ABSTRACT FROM AUTHOR]