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Static and dynamic area‐based management tools hold substantial potential to balance socioeconomic benefits derived from fisheries and costs from bycatch mortality of at‐risk species. Palau longline fisheries have high bycatch of at‐risk species including the olive ridley marine turtle and silky and blue sharks. This study analyzed a two decades‐long time series of observer and electronic monitoring datasets from the Palau distant‐water and locally‐based pelagic longline fisheries. An interpretable or explainable machine learning‐based modeling approach was used to derive spatially resolved species‐specific catch rate predictions. These models were conditioned on a suite of potentially informative environmental, bathymetric, ocean‐climate metric, vessel, monitoring system, and set‐specific operational predictors. Overall, there would be limited ecological tradeoffs from focusing fishing effort within primary catch rate hotspots for target bigeye and yellowfin tunas. Mean field prediction surfaces also defined catch rate hotspots for at‐risk species of silky and blue sharks, olive ridley turtle, and pelagic stingray, which did not overlap the hotspots for target species. The predicted target species hotspots, however, overlap olive ridley and pelagic stingray warmspots. Results also identify opportunities for temporally dynamic spatial management to control catch rates of target and bycatch species. Management of fishery operational predictors of fishing depth and soak duration present additional opportunities to balance catch rates of at‐risk bycatch and target species. A transition to employing fleetwide or vessel‐based output controls that effectively constrain the fishery would alter the spatial management strategy to focus on zones with the lowest ratio of at‐risk bycatch to commercial catch. Our findings support evidence‐informed evaluation of spatial management strategies and complementary measures to meet objectives for balancing socioeconomic benefits derived from target species catch with costs to threatened species. [ABSTRACT FROM AUTHOR]

Marine megafauna exposed to fisheries bycatch belong to some of the most threatened taxonomic groups and include apex and mesopredators that contribute to ecosystem regulation. Fisheries bycatch is a major threat to the conservation of albatrosses, large petrels and other pelagic seabirds. Using data sourced from a fisheries electronic monitoring system, we assessed the effects of the time-of-day and relative depth of fishing on seabird and target species catch rates for a Pacific Ocean pelagic longline fishery that targets albacore tuna with an apparently high albatross bycatch rate. Using a Bayesian inference workflow with a spatially-explicit generalized additive mixed model for albacore tuna and generalized linear mixed regression models both for combined albatrosses and combined seabirds, we found that time-of-day and fishing depth did not significantly affect the target species catch rate while night-time deep setting had > 99% lower albatross and total seabird catch rates compared to both deep and shallow partial day-time sets. This provides the first evidence that night-time setting in combination with fishing deep reduces seabird catch risk and may be commercially viable in this and similar albacore tuna longline fisheries. Findings support evidence-informed interventions to reduce the mortality of threatened seabird bycatch species in pelagic longline fisheries. [ABSTRACT FROM AUTHOR]

Fisheries bycatch threatens the viability of some seabird populations and reduces fishing efficiency. Albatross bycatch in a US North Pacific tuna longline fishery has increased over the past decade and now exceeds 1000 annual captures. Seabirds interacting with this fishery reach hooks at depths up to 1 m. A branchline weight's mass and distance from the hook affect seabird catch rates. We conducted experimental fishing to compare the commercial viability of a weighted hook relative to conventional gear with weights attached 0.75 m from the hook. We used a Bayesian random effects meta-analytic regression modelling approach to estimate pooled expected species-specific log relative risk of capture on conventional versus experimental gear. There was a significant 53% (95% HDI: − 75 to − 25%) decrease in retained species' catch rates on experimental hooks, indicating an unacceptable economic cost, and no significant effect for discarded species. Using a Bayesian general linear mixed regression modelling approach, experimental hooks sank to 85 cm ca. 1.4 times (95% HDI: 1.37–1.48) faster than control hooks. Given their potential to reduce seabird catch rates, eliminate safety risks from bite-offs and facilitate robust compliance monitoring, it is a priority to find a weighted hook design with acceptable catch rates. [ABSTRACT FROM AUTHOR]

Capture in global pelagic longline fisheries threatens the viability of some seabird populations. The Hawaii longline tuna fishery annually catches hundreds of seabirds, primarily Laysan (Phoebastria immutabilis) and black-footed (P. nigripes) albatrosses. Since seabird regulations were introduced in 2001, the seabird catch rate has declined 74%. However, over the past decade, seabird catch levels significantly increased due to significant increasing trends in both effort and nominal seabird catch rates. We modelled observer data using a spatio-temporal generalized additive mixed model with zero-inflated Poisson likelihood to determine the significance of the effect of various risk factors on the seabird catch rate. The seabird catch rate significantly increased as annual mean multivariate ENSO index values increased, suggesting that decreasing ocean productivity observed in recent years in the central north Pacific may have contributed to the increasing trend in nominal seabird catch rate. A significant increasing trend in number of albatrosses attending vessels, possibly linked to declining regional ocean productivity and increasing absolute abundance of black-footed albatrosses, may also have contributed to the increasing nominal seabird catch rate. Largest opportunities for reductions are through augmented efficacy of seabird bycatch mitigation north of 23° N where mitigation methods are required and during setting instead of during hauling. Both side vs. stern setting, and blue-dyed vs. untreated bait significantly reduced the seabird catch rate. Of two options for meeting regulatory requirements, side setting had a significantly lower seabird catch rate than blue-dyed bait. There was significant spatio-temporal and seasonal variation in the risk of seabird capture with highest catch rates in April and May and to the northwest of the main Hawaiian Islands. [ABSTRACT FROM AUTHOR]

Overexploitation is currently the main cause of marine defaunation. Vulnerability to overexploitation varies across populations. Determining which populations are of highest ecological risk from fishing mortality guides management. Because no single approach is optimal across taxonomic groups, a multi-model ensemble of relative risk estimates for a data-poor Pacific Ocean tuna longline fishery was obtained from two semi-quantitative Productivity-Susceptibility Analyses (PSAs) and from a quantitative approach that estimates instantaneous fishing mortality to compare to reference points of yield-per-recruit models. Individual estimates were combined to produce a pooled mean relative risk rank order. The study identified stocks below biological limits for which the contribution from this fishery to cumulative anthropogenic mortality may warrant intervention. Relative risks in descending order were for populations of albatrosses, cetaceans, mesopelagic sharks, rays, marine turtles, epipelagic sharks and teleosts. The fishery's contribution to cumulative fishing mortality of western central north Pacific Ocean striped marlin warrants a more rigorous assessment to determine absolute risks. The study identified the disparate factors explaining relative risk from an individual fishery versus absolute risk from cumulative anthropogenic mortality sources. Improved risk assessments are possible by addressing identified deficits with PSAs, obtaining information on variables that explain catch and post-capture survival risks that was unavailable for this assessment, improving electronic monitoring data quality and filling gaps in life history traits. Findings support stakeholders to design integrated bycatch management frameworks that mitigate fishing mortality of the most vulnerable taxa and account for multispecies conflicts that result from some bycatch mitigation methods. • A risk assessment identified most vulnerable taxa caught in a tuna longline fishery. • An ensemble of assessment approaches accounted for differences between taxa. • Relative risks were highest for albatrosses, mesopelagic sharks and cetaceans. • Mortality of a striped marlin stock warrants determining absolute risks. • Addressing assessment method deficits and filling information gaps are priorities. [ABSTRACT FROM AUTHOR]

Fisheries electronic monitoring (EM) is increasingly being used to augment human observer programs and provide coverage where none previously existed. This study identified observer data fields prioritized for research and compliance monitoring that were not collected by a pilot EM system and compared estimates made by the EM system and observer program. EM did not collect 64 of 101 prioritized fields. Repositioning existing or adding new cameras, integrating sensors and obtaining crew cooperation would enable the collection of most of the 64 missing fields. Almost half of missing fields could be collected dockside. The existing EM system could collect over a third of missing fields. Both the EM analyst and observer recorded the species, length and at-vessel condition of almost all retained catch, with only small differences in mean catch rates estimated by the EM analyst and observer for tunas, billfishes and other teleosts. EM performed poorly in recording species (43%), length (1%), at-vessel condition (57%) and release condition (48%) of discards. Improved views of areas where crew handle and release catch could be achieved by adding a camera to the outboard side of the rail near the hauling station, adjusting deck lighting at night and having crew bring catch that they will release in the water within the camera field of view. Accurate EM length estimates may only be possible for catch landed on deck. EM systems have the capacity to collect most fields of conventional observer programs with high precision while avoiding main sources of statistical sampling bias. • Fisheries electronic monitoring (EM) is increasingly being used. • Data collected by a pilot EM system for a pelagic longline fishery were assessed. • Collection of additional priority fields and improved discards data are needed. • Repositioned cameras, crew cooperation, and dockside monitoring are solutions. • EM has the capacity to collect most observer program fields with high precision. [ABSTRACT FROM AUTHOR]