Longline Fisheries Research Articles

Incidental Mortality of Black‐Browed Albatross and White‐Chinned Petrel in Argentine Longline Fisheries: A Comprehensive Estimation Addressing Spatial and Temporal Stratification and Cryptic Mortality

ABSTRACTThe continental shelf and shelf‐break of the Southwest Atlantic are among the most productive and biodiverse regions globally. Incidental mortality from fishing activities poses a significant threat to seabird populations in this area. The overlap between fishing operations and seabird distributions leads to bycatch, particularly in longline fisheries where seabirds get hooked during setting or hauling operations. This study is the first in Argentina to assess seabird incidental mortality considering cryptic mortality. We estimated potential annual mortalities between 2005 and 2009 for two keystone species that predominantly interact with fishing vessels. For black‐browed albatrosses, the estimated annual mortality was 686 individuals (95% CI: 582–800), whereas for white‐chinned petrels was 2278 individuals (95% CI: 1981–2606). We evaluated the differential impact of three longline fleets, distinguished by their operating areas, gear configurations and target species. For both seabird species, the estimated mortality levels in the fleet targeting kingklip were an order of magnitude higher than the fleets targeting skate and Patagonian toothfish. The highest incidental mortality levels were concentrated in the central continental shelf between 44° S and 49° S near the slope. Identifying bycatch patterns may inform and improve the spatial management of fisheries, which is crucial as their cumulative bycatch significantly impacts the sustainability of seabird populations. We emphasise the need to increase the observer coverage in fisheries and improve data quality. Future research should aim to evaluate the effects of incidental mortality on the sustainability of seabird populations across multiple fisheries.

A Crusade Throughout the World’s Oceans: Genetic Evidence of the Southern Bluefin Tuna Thunnus maccoyii and the Pacific Bluefin Tuna Thunnus orientalis in Brazilian Waters

The large pelagic species play an important role in transferring energy in vast distant marine ecoregions. Results obtained report on extraordinary findings of important commercial species in southeast–south Brazilian waters, including the Southern bluefin tuna Thunnus maccoyii and the Pacific bluefin tuna Thunnus orientalis, an endemic species from the Pacific Ocean. These specimens were identified within the genomic description of 10 individuals randomly selected from the catch to evaluate the catch composition of pelagic longline fisheries off Brazilian waters. Most of the records were from T. maccoyii (6), followed by the Bigeye tuna T. obesus (2), Yellowfin tuna T. albacares (1), and T. orientalis (1). Yellowfin and Bigeye tuna are expected to be captured in the vicinity of the longline fishing areas. However, the unlikely presence of the cold-water T. maccoyii and the warm-water T. orientalis suggests a long migration from common species ranges that could be influenced by climate change. These results imply a readjustment of spatial management structures for these species.

6. Vertical longline fisheries around FADs and behavior of the fishing gear

6. Vertical longline fisheries around FADs and behavior of the fishing gear

Historical changes in conservation measurements on target, predictable bycatch and bycatch species caught by pelagic longline fisheries in Southwest Atlantic Ocean

Historical changes in conservation measurements on target, predictable bycatch and bycatch species caught by pelagic longline fisheries in Southwest Atlantic Ocean

The Spatial Distribution Dynamics of Shark Bycatch by the Longline Fishery in the Western and Central Pacific Ocean

Shark bycatch represents a substantial issue in the management of oceanic fisheries. Utilizing data on shark bycatch from the longline fishery, as released by the Western and Central Pacific Fisheries Commission, this study applied the boosted regression tree model to examine the impact of environmental factors on the bycatch per unit effort (BPUE) of key bycatch species, as well as to predict the spatial distribution dynamics of both BPUE and bycatch risk (BR). The findings emphasize that the oxygen concentration, sea surface temperature, and chlorophyll-a concentration are paramount to sharks’ BPUE. Furthermore, the study compared the variations in environmental preferences across diverse shark species, pinpointing key environmental attributes defining the ecological niches of distinct shark populations. The spatial predictions identified the hotspots of BPUE and BR for the bigeye thresher shark (Alopias superciliosus), longfin mako (Isurus paucus), silky shark (Carcharhinus falciformis), and oceanic whitetip shark (Carcharhinus longimanus) in tropical latitudes (10° S to 15° N), and for the blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) in temperate zones (south of 30° S or north of 30° N). The geometric center analysis indicated that all shark species exhibited large annual fluctuations in BPUE and BR, and most populations displayed significant shifting trends. Several grids (5° × 5°) were identified as high-risk areas due to their considerable contribution to bycatch. Furthermore, the geometric centers of BR were observed to shift eastward towards equatorial waters, compared to the geometric centers of BPUE. This underscores the necessity of considering factors beyond BPUE when identifying critical areas for the implementation of area-specific bycatch mitigation measures. The insights derived from this study can enhance and support the development and enforcement of targeted area-based fishery management initiatives.

An Integrated Global‐To‐Regional Scale Workflow for Simulating Climate Change Impacts on Marine Ecosystems

AbstractAs the urgency to evaluate the impacts of climate change on marine ecosystems increases, there is a need to develop robust projections and improve the uptake of ecosystem model outputs in policy and planning. Standardizing input and output data is a crucial step in evaluating and communicating results, but can be challenging when using models with diverse structures, assumptions, and outputs that address region‐specific issues. We developed an implementation framework and workflow to standardize the climate and fishing forcings used by regional models contributing to the Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP) and to facilitate comparative analyses across models and a wide range of regions, in line with the FishMIP 3a protocol. We applied our workflow to three case study areas‐models: the Baltic Sea Mizer, Hawai'i‐based Longline fisheries therMizer, and the southern Benguela ecosystem Atlantis marine ecosystem models. We then selected the most challenging steps of the workflow and illustrated their implementation in different model types and regions. Our workflow is adaptable across a wide range of regional models, from non‐spatially explicit to spatially explicit and fully‐depth resolved models and models that include one or several fishing fleets. This workflow will facilitate the development of regional marine ecosystem model ensembles and enhance future research on marine ecosystem model development and applications, model evaluation and benchmarking, and global‐to‐regional model comparisons.

Composition of pelagic fish in commercial landings of the longline fishery in the Costa Rica Pacific during 2015-2021

Longline fishing in the Pacific of Costa Rica targets multiple species of large pelagic fishes and faces challenges in assessment due to lack of data. This study analyzes landing data of pelagic fish in this fishery using unconventional statistical methods, to better understand the dynamics and provide recommendations for improving data collection and analysis. Landing data reported during 2015-2021 were examined. A descriptive and comparative analysis of landings was conducted using Spearman correlation tests and Non-Metric Multidimensional Scaling (NMDS) to visualize patterns in catch composition. Permutational Multivariate Analysis of Variance (PERMANOVA) and Similarity Percentage Analysis (SIMPER) were employed to identify significant differences between fleet types, landing ports, months, and years, as well as species contribution to these differences. The annual mean total landing of large pelagic fish was 7531.01 tons, with 39.14% corresponding to sharks, 24.34% to billfish (Istiophoridae and Xiphiidae), 18.05% to mahi-mahi, and 14.94% to tuna. Statistically significant differences were found between fleet types, landing ports, months, and years. Shark landings were the least correlated (rho=0.36) and had the greatest influence on variation by fleet type. An increase in the similarity of catch composition by port since 2015 was observed. In addition, a shift towards increasingly less selective fishing over the study period was evident. Our findings highlight the urgent need for advanced research methodologies to address gaps in data collection for commercial fisheries in Costa Rica. Improving these methods is crucial to ensure that management policies are based on accurate and comprehensive information. Results highlight the need for a comprehensive strategy involving diverse stakeholders to improve our understanding and ensure the sustainability of fisheries and the preservation of marine ecosystems in Costa Rica.

Effects of hook size on the catch variation, size selectivity, and bycatch of the bottom set longline fisheries targeting nemipterid fishes in the Philippines

In the Philippines, nemipterid fishes hold substantial economic importance due to their high market value. However, the local longline fisheries lack specific regulations for managing the capture of these fishes. This study aimed to determine the optimum hook size for increasing catchability in nemipterid fishing while minimizing bycatch, thus promoting sustainable fisheries. We conducted experimental fishing at three depth ranges, using Mustad J-type hooks of 11 different sizes, ranging from #562, the largest, to #572, the smallest. All Mustad J-type hooks utilized medium-sundried Sardinella lemuru as bait. Seven Nemipteridae species and 31 other bycatch species were collected, with Nemipterus nematophorus emerging as the predominant species, constituting 61.96% and 56.99% of the catch by count and weight, respectively. The largest hook size (#562) demonstrated the lowest catch in both fish count and weight, revealing its inefficacy in capturing a wider size variation of fish. However, larger fish were collected with larger hooks, as suggested by the generalized additive model (GAM). In contrast, the generalized additive model suggested that middle-sized hooks (#566 to #568) yielded the highest catches but with an increased bycatch. Thus, these hook sizes, commonly used by many fishermen, were identified as the most exploitative and risky in terms of increasing bycatch. Using large hooks, preferably #562 to #565, would lead to an increase in the individual catch size for nemipterids, to reduce the small-size fish, and to minimize bycatch. These results suggest that regulating hook sizes is essential for sustainable fishing, which can result in a potential short-term reduction in catch rates but offer long-term benefits for nemipterid fisheries management.

Stress physiology of scalloped and great hammerhead sharks from a bottom longline fishery

Abstract The scalloped hammerhead Sphyrna lewini and the great hammerhead S. mokarran are large, coastal to semi-oceanic shark species common to waters of the US east coast where they are regularly taken in commercial and recreational fisheries, particularly the bottom longline fishery. High rates of hooking mortality and low rates of population growth are believed to have caused severe declines in the US Atlantic populations of these species. The objective of this study was to determine the physiological stress induced by bottom longline capture in both S. lewini and S. mokarran. Physiological stress was quantified using the blood biochemical indicators glucose, lactate, pH, haematocrit, sodium, potassium, calcium, chloride and magnesium, which have been demonstrated to indicate physiological stress in elasmobranchs. Each shark captured was assigned a condition factor, which was compared with the stress parameters and time on hook to quantify stress induced by different longline hook times. In S. lewini, the physiological stress parameters lactate, pH, sodium and chloride scaled with hook time, whereas in S. mokarran, only lactate was affected by hook time. In both species, water temperature affected lactate and glucose levels, as well as sodium and pH levels in S. lewini and magnesium levels in S. mokarran. These data will be useful for estimating post-release mortality of S. lewini and S. mokarran from measurements taken at the time of capture, and quantifying the physiological stress response to longline capture in both species to the Atlantic bottom longline fishery.

Opportunity to Leverage Tactics Used by Skilled Fishers to Address Persistent Bycatch Challenges

ABSTRACTEffective management of shark bycatch is urgently needed to reverse widespread population declines, especially in longline fisheries that are estimated to be responsible for half of global shark catch. Management of shark catch typically focuses on the safe release of landed sharks, with limited attention to reducing the initial catch. Where controls on fishing effort or catch do exist, management frameworks tend to treat fishing fleets as homogeneous units. The underlying assumption is that fishers have similar abilities to catch target species and avoid bycatch. We test this assumption by analysing variability in shark bycatch rates among individual vessels in an industrial tuna longline fleet operating in the Western Pacific. Controlling for factors such as geographic location, time of day and gear depth, we find that individual vessels drive highly variable bycatch rates of blue (Prionace glauca) and silky sharks (Carcharhinus falciformis) – two shark species with the highest global catch volumes. Additionally, we found that the operating company can influence fisher performance. As countries and regional organisations increasingly adopt shark conservation plans and make international conservation commitments, it is crucial to identify viable new strategies that do not unduly burden the industry or penalise good actors. Tailoring management actions to individual fishers and companies – holding high‐bycatch fishers accountable and incentivising low‐bycatch fishers to continuously improve – presents a crucial opportunity to address the overfishing of sharks and other global bycatch challenges.

Increased longline bait predation by northern fulmars (Fulmarus glacialis) around the Faroe Islands during the breeding season

Abstract Seabird bycatch is common in longline fisheries and detrimental to some seabird populations. Simultaneously, the loss of longline bait to seabirds may pose a considerable economic loss to fishermen. Here, we study northern fulmars (Fulmarus glacialis), bycaught in longline fisheries close to the Faroe Islands between 2004 and 2021. Biological data on age and sex and the quantity of bait in the stomachs was assessed. Males were over-represented in the bycatch sample, as were adult birds, likely caused by sex- and age-specific foraging segregation. Overall, 71% of 820 fulmars contained bait, on average 2 items per bird (range: 0–17 items). No difference in the average number of bait items was detected between males and females or between adult and non-adult birds. During the breeding season, however, adults contained significantly more bait in their stomach than outside the breeding season. No such effect was found for non-adult birds. Together with a lower body condition during the breeding season, this may indicate higher food requirements by breeding birds, potentially increasing entanglement risks. Regular loss of bait reduces fishing efficiency, likely resulting in economic loss. Reducing seabird bycatch may therefore benefit fishermen as well as seabird populations.

Unraveling migratory corridors of loggerhead and green turtles from the Yucatán Peninsula and its overlap with bycatch zones of the Northwest Atlantic.

Bycatch represents a conservation problem when endangered species are affected. Sea turtles are highly vulnerable to this threat as their critical habitats overlap with fishing zones in all regions of the world. We used sequences of the mitochondrial DNA control region obtained from loggerhead (Caretta caretta) and green (Chelonia mydas) turtles to determine the migratory routes between nesting habitats in the Yucatán Peninsula and their critical marine habitats in the Northwest Atlantic. Mixed Stock Analysis revealed that loggerheads from Quintana Roo migrated to foraging areas in the northwestern Atlantic. Migratory routes used by green turtles are determined by their natal nesting colony: (1) green turtles from the Gulf of Mexico migrate to foraging aggregations in Texas and the northern Gulf of Mexico, (2) Mexican Caribbean turtles travel to foraging grounds in Florida, and (3) a smaller proportion of individuals born in the Yucatán Peninsula display a local connectivity pattern. Our results suggest that the migratory corridors used by Mexican loggerheads overlap with longline fisheries in the mid-Atlantic where sea turtle bycatch is comprised predominantly of immature individuals. Green turtles from the Yucatán Peninsula migrate to critical habitats that overlap with shrimp trawl fisheries within the Gulf of Mexico. Bycatch data and the identification of migratory corridors used by loggerheads and green turtles suggests that shrimp trawl fisheries on the east coast of the U.S. and the Gulf of Mexico pose a serious threat to the conservation and recovery of Mexican sea turtle populations.

Bycatch of northern fulmar (Fulmarus glacialis) in Norwegian longline fisheries: Assessing spatiotemporal variations in scale and risk to improve management

Bycatch of northern fulmar (Fulmarus glacialis) in Norwegian longline fisheries: Assessing spatiotemporal variations in scale and risk to improve management

The Development of DNA Markers to Resolve Uncertainties of Seabird Bycatch Identification From Longline Fisheries in Australian Waters.

Incidental mortality in fisheries is a major driver of population declines for albatrosses and petrels globally. However, accurate identification of species can be difficult due to the poor condition of bycaught birds and/or visual similarities between closely related species. We assessed three genetic markers for their ability to distinguish the 36 albatross and petrel species listed in Annex 1 to the Agreement on the Conservation of Albatrosses and Petrels (ACAP) and in Australia's Threat Abatement Plan (TAP) for the bycatch of seabirds during oceanic longline fishing operations. We generated 275 new sequences, from 29 species, to improve the coverage of reference databases for these listed species. The combined use of the selected Cytochrome b and Control Region markers enabled the identification of 31 of 36 listed seabirds to species level and four to sister species. One petrel species could not be evaluated as no reference sequences were available. We tested these markers on 59 feathers from bycaught seabirds and compared these to onboard visual identification. We successfully assigned all procellariiforms to species (n = 58), whereas only two seabirds were correctly identified to species visually onboard, highlighting the difficulty of visual species assignment and the need for alternative methods. We assessed the utility of our two chosen markers for the assignment of all procellariiform species, with 74% of species with reference sequences identified to species or sister species level. However, a precautionary approach is needed for application beyond our listed species due to unvalidated reference sequences. The approach described here provides a streamlined framework for the molecular identification of seabird bycatch. This approach is recommended for use in fisheries within and outside Australian waters to improve the resolution of bycatch reporting and to corroborate logbook entries, observer reports and audits of images captured by electronic monitoring systems as well as help inform conservation efforts.

Vulnerability assessment of elasmobranch species to fisheries in coastal Kenya: Implications for conservation and management policies

Vulnerability assessment of elasmobranch species to fisheries in coastal Kenya: Implications for conservation and management policies

A Meta‐Analysis of Bycatch Mitigation Methods for Sea Turtles Vulnerable to Swordfish and Tuna Longline Fisheries

ABSTRACTFisheries bycatch poses one of the most significant threats to sea turtles. Although various methodologies have been developed to mitigate sea turtle bycatch in swordfish and tuna longline fisheries, the effectiveness and interactions remain uncertain. In this study, we conducted a comprehensive meta‐analysis, encompassing 41 studies focused on sea turtles and 36 studies on tunas, swordfish and sharks, all derived from well‐controlled experimental research in swordfish and tuna longline fisheries. The objective was to systematically evaluate the relative effectiveness of species‐specific mitigation strategies for sea turtles, particularly examining the impact of circle hooks and fish bait as alternatives to conventional longline fishing practices. While a nuanced hierarchy, characterised by species‐specific patterns, was observed among the mitigation measures, circle hooks demonstrated great promise in reducing bycatch of loggerhead, olive ridley and leatherback turtles, with minimal impact on the catch rates of tuna, swordfish and sharks. We highlighted the broader applicability of fish bait in minimising sea turtle bycatch, noting that the effectiveness of bait may overlap with that of hooks, potentially making the additional benefits of the hooks less evident. The study also revealed regional variations in the effectiveness of these methods, emphasising the need for more detailed data collection. Given current data limitations that restrict extensive meta‐analyses, a series of small‐sample studies with promising innovations, exemplified by circle hooks with a wire appendage and blue‐white lights, necessitates in‐depth investigation and field tests.

Synthesising a network of evidence on a seabird bycatch mitigation measure

AbstractRobust estimates of the relative efficacies of alternative management interventions are essential for developing evidence‐informed fisheries bycatch policy. Bycatch is a major threat to the conservation of albatrosses and other pelagic seabirds. Branchline weighting is one approach prescribed by regional fisheries management organisations and the Agreement on the Conservation of Albatrosses and Petrels to reduce seabird bycatch in pelagic longline fisheries. We used a Bayesian multilevel network meta‐regression modelling approach to conduct the first synthesis of available evidence to assess the relative efficacies at mitigating seabird bycatch of alternative pelagic longline weighting designs. Unlike conventional pairwise meta‐analysis, network meta‐analysis enables the simultaneous comparison of multiple interventions within a coherent modelling framework. There was a > 97% probability that all weighting designs significantly reduced seabird bycatch compared to a reference design with no weight within 5 m of the hook. Nonetheless, some weighting designs were significantly more effective at reducing seabird bycatch than others—for instance, the 2 designs with weights >60 g and >1 m from the hook performed the best with >93% probability that those 2 designs performed significantly better than 2 more commonly used designs with less weight but attached closer to the hook. These two best performing designs reduced seabird bycatch by ca 89% relative to the reference design. These relative efficacies and rankings, when combined with other performance criteria such as costs to commercial viability and crew safety, support robust evaluations of alternative bycatch management strategies.

Post-release survival of loggerhead sea turtles (Caretta caretta) incidentally hooked in a North Atlantic pelagic longline fishery

Estimating mortality of sea turtles incidentally captured in fishing gear is essential to understanding fishery impacts on sea turtle populations. Loggerhead turtles (Caretta caretta) are a component of bycatch in pelagic longline fisheries, including those operating in Atlantic Canada. In this study, we used pop-up satellite archival tags (PSATs) attached to 62 loggerhead turtles incidentally hooked in Atlantic Canadian shallow-set pelagic longline gear (2012–2018) to estimate associated post-release survival. Consistent with conventional fishing practices, hooks were not removed from turtles prior to release. Analysis of diving behaviour, ocean temperature, and ambient light level was used to assign fates to turtles. Post-release survival was calculated using the Kaplan-Meier estimator with right censoring. Based on this method, the annual survival probability of an individual loggerhead post-release is 0.877 ± SE 0.052. While it is commonly assumed that hook location is an important variable in predicting fates of turtles after release, there was no difference in survival of deep-hooked (swallowed hook) versus shallow-hooked turtles. These results indicate higher survivorship among hooked loggerheads captured in shallow-set pelagic longline gear than prevailing wisdom and suggest that at least some of the population impacts on loggerhead turtles conventionally attributed to pelagic longline interactions may be linked to other threats.

Large pelagic fish exploitation by longliners in the Atlantic Ocean and Mediterranean Sea: A contribution to spatial planning and sustainable fisheries

Large pelagic fish exploitation by longliners in the Atlantic Ocean and Mediterranean Sea: A contribution to spatial planning and sustainable fisheries

A roadmap for generating annual bycatch estimates from sparse at-sea observer data

Abstract To support ecosystem-based fisheries management, monitoring data from at-sea observer (ASO) programs should be leveraged to understand the impact of fisheries on discarded species (bycatch). Available techniques to estimate fishery-scale quantities from observations range from simple mean estimators to more complex spatiotemporal models, each making assumptions with differing degrees of support. However, the resulting implementation and analytical trade-offs are rarely discussed when applying these techniques in practice. Using blue shark (Prionace glauca) bycatch in the Canadian pelagic longline fishery as a case study, we evaluated the performance of seven contrasting approaches to estimating total annual discard amounts and assessed their trade-offs in application. Results demonstrated that simple approaches such as mean estimator and nearest neighbors are feasible to implement and can be as efficient for prediction as complex models such as random forest and mixed-effects models. The traditionally used catch-ratio estimator consistently underperformed among all tested models, likely due to misspecified correlative relationships between target and bycatch species. Overall, efforts in model-based approaches were rewarded with very small gains in predictive ability, suggesting that such models relying on environmental, biological, spatial, and/or temporal patterns to improve prediction of bycatch may lack sufficient foundation in data-limited contexts.