Albacore Research Articles

Dynamic human, oceanographic, and ecological factors mediate transboundary fishery overlap across the Pacific high seas

AbstractThe management and conservation of tuna and other transboundary marine species have to date been limited by an incomplete understanding of the oceanographic, ecological and socioeconomic factors mediating fishery overlap and interactions, and how these factors vary across expansive, open ocean habitats. Despite advances in fisheries monitoring and biologging technology, few attempts have been made to conduct integrated ecological analyses at basin scales relevant to pelagic fisheries and the highly migratory species they target. Here, we use vessel tracking data, archival tags, observer records, and machine learning to examine inter‐ and intra‐annual variability in fisheries overlap (2013–2020) of five pelagic longline fishing fleets with North Pacific albacore tuna (Thunnus alalunga, Scombridae). Although progressive declines in catch and biomass have been observed over the past several decades, the North Pacific albacore is one of the only Pacific tuna stocks primarily targeted by pelagic longlines not currently listed as overfished or experiencing overfishing. We find that fishery overlap varies significantly across time and space as mediated by (1) differences in habitat preferences between juvenile and adult albacore; (2) variation of oceanographic features known to aggregate pelagic biomass; and (3) the different spatial niches targeted by shallow‐set and deep‐set longline fishing gear. These findings may have significant implications for stock assessment in this and other transboundary fishery systems, particularly the reliance on fishery‐dependent data to index abundance. Indeed, we argue that additional consideration of how overlap, catchability, and size selectivity parameters vary over time and space may be required to ensure the development of robust, equitable, and climate‐resilient harvest control rules.

Optimization of a method designed to extract and characterize microplastics in different packaged fish products

The study of the presence of microplastics (MPs) in seafood products is usually carried out by analyzing the gastrointestinal tract. However, this part is mostly removed during food processing. Moreover, few studies have produced results from processed fishery products. The primary objective of this study was to optimize methods for evaluating the presence of MPs in the edible portions of several products available in supermarkets. Seven seafood products, including smoked, canned, marinated, and those stored in polystyrene trays, were selected for analysis, with saithe fillets (Pollachius virens) and canned tuna (Thunnus alalunga) among them. To achieve optimal digestion of the samples, a 10% KOH solution at 40 °C was used. For the fattiest samples, such as marinated anchovies, hydrophobic filters were employed. Additionally, bleach was utilized to lighten dark filters obtained, ensuring readability under the microscope. These parameters were defined to obtain suitable methods for each product. The average concentrations in different seafood matrices ranged from 0.05 ± 0.04 to 0.33 ± 0.08 MP/g for saithe fillets and canned tuna, respectively. After extrapolation of these values to all the particles observed on each filter, the concentrations increased from 0.06 ± 0.05 MP/g to 2.17 ± 0.33 MP/g. Particles identification across all samples, using a microscope coupled with Fournier transform infrared spectroscopy (μ-FTIR), confirmed the presence of MPs, including PET, PP, and EVA.

Projected Changes in Spawning Ground Distribution of Mature Albacore Tuna in the Indian Ocean under Various Global Climate Change Scenarios

The present study utilised a geometric mean model in which sea surface temperature, oxygen, and sea surface salinity were used to predict the effects of climate change on the habitats of mature albacore tuna in the Indian Ocean under multiple representative concentration pathway (RCP) scenarios. Data pertaining to the albacore tuna fishing conducted by Taiwanese longline fisheries during the October–March period in 1998–2016 were analysed. The fishery data comprised fishing location (latitude and longitude), fishing effort (number of hooks used), number of catches, fishing time (month and year), and fish weight. Nominal catch per unit effort data were standardised to mitigate the potential effects of temporal and spatial factors in causing bias and overestimation. The Habitat Suitability Index (HSI) scores of potential habitats for mature albacore in the Indian Ocean are predicted to change considerably in response to varying levels of predicted climate change. Under projected warm climate conditions (RCP 8.5), the stratification of water is predicted to cause low HSI areas to expand and potential habitats for mature albacore to shift southward by 2100. The findings derived from these mature albacore habitat forecasts can contribute to the evaluation of potential hazards and feasible adaptation measures for albacore fishery resources in the context of climate change. The distribution trends pertaining to potential habitats for mature albacore should be used with caution and can provide resource stakeholders with guidance for decision-making.

Contribution of glass jar packaging to the environmental assessment of canned seafood products: Albacore tuna (Thunnus alalunga) and Atlantic chub mackerel (Scomber colias) as case studies

Canned seafood is a practical option for consumers with high nutritional value. However, packaging plays a key role in its environmental impacts due to the production of metal cans made by aluminium or tinplate and glass jars. The aim of this study was to perform a life cycle assessment of four seafood canned products in glass jars with Atlantic chub mackerel and albacore tuna. The contribution of end-of-life options for glass jar (reuse, recycle or landfill) was also evaluated, as well as environmental burden of storage at home scenarios of canned, chilled and frozen fish productspotential seafood waste in the different supply chains.Glass jar packaging contribution to environmental assessment of products was half compared with metal cans. The production of ingredients was the life cycle phase with highest contribution in all products followed by primary packaging for climate change impact category. Results pointed out the benefits of recycling glass jar with 8% GHG emissions reduction on average. Storage at the consumer stage represented less GHG emissions for canned products when compared to frozen when considering a period of more than one month.

Climate Change Potential Impacts on the Tuna Fisheries in the Exclusive Economic Zones of Tonga

The potential impacts of climate change on the distribution of tuna in Pacific Island countries’ exclusive economic zones have yet to be investigated rigorously and so their persistence and abundance in these areas remain uncertain. Here, we estimate optimal fisheries areas for four tuna species: albacore (Thunnus alalunga), bigeye (Thunnus obesus), skipjack (Katsuwonus pelamis), and yellowfin (Thunnus albacares). We consider different climate change scenarios, RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5, within a set of tuna catch records in the exclusive economic zone of Tonga. Using environmental and CPUE datasets, species distribution modelling estimated and predicted these fisheries areas in the current and future climatic scenarios. Our projections indicate an expansion in area and a shift of productive areas to the southern part of this exclusive economic zone of Tonga. This is an indication that future climatic scenarios might be suitable for the species under study; however, changes in trophic layers, ocean currents, and ocean chemistry might alter this finding. The information provided here will be relevant in planning future national actions towards the proper management of these species.

Role of environmental conditions in structuring the stock trajectory of Thunnus albacares, Th. alalunga and Th. obesus in the South Pacific Region

The lifestyle and culture of South Pacific Island countries have been long intertwined with oceanic resources. These countries are heavily dependent on tuna resources for their economies and socioeconomic livelihoods. Despite their importance, the mechanisms behind tuna stock trajectory patterns need to be better understood. With changing climatic and environmental conditions, it has become vital to understand the impact of these changes on tuna resources and if possible include them in long-term tuna harvest and management plans. A significant portion of the stock dynamics of yellowfin tuna (Thunnus albacares), albacore tuna (Th. alalunga) and bigeye tuna (Th. obesus) in the South Pacific Region may possibly be explained only by the environmental factors of sea surface temperature (SST) and Atlantic Multidecadal Oscillation AMO. The relationship of monthly SST and AMO was investigated with time series stock patterns of Th. albacares, Th. alalunga and Th. obesus in the Eastern and Western Pacific Ocean for the years 1972 to 2019. Monthly variables that exhibited significant correlation with CPUE variables were used in the Generalised Linear Model and Generalized Additive Model to reproduce the CPUE trajectory of the three tuna species from 1972 to 2019. Results showed that a significant portion of stock dynamics of Th. albacares, Th. alalunga and Th. obesus can be explained well by two environmental conditions of SST and AMO. This shows that a large portion of tuna variation in the Eastern and Southern Pacific is related to environmental conditions. Models with single variables are evidence of the significant individual effect of SST and AMO on stock time series of each tuna species. Models with two variables had a better fit in comparison to models with a single variable for all tuna stocks. Possibilities of two significantly different patterns in the trajectory of the three tuna species and environmental conditions used in the models were also observed. The trajectory patterns seemed to change around the 1990s and had significantly different means, indicating possible regime shifts. Environmental conditions play a highly significant role in structuring tuna stock trajectory in the South Pacific and need to be included in tuna management / harvest plans to ensure sustainability of this important resource. The importance of regime shifts should be recognised and further investigated for possible inclusion in tuna sustainability plans due to their influence on long-term tuna trajectory patterns.

Inferring the ecology of north-Pacific albacore tuna from catch-and-effort data

Catch-and-effort data are among the primary sources of information for assessing the status of terrestrial wildlife and fish. In fishery science, elaborate stock-assessment models are fitted to such data in order to estimate fish-population sizes and guide management decisions. Given the importance of catch-and-effort data, we scoured a comprehensive dataset pertaining to albacore tuna (Thunnus alalunga) in the north Pacific Ocean for novel ecological information content about this commercially valuable species. Specifically, we used unsupervised learning based on finite mixture modelling to reveal that the north Pacific albacore-tuna stock can be divided into four pseudo-cohorts. We discovered that smaller body mass pseudo-cohorts inhabit relatively high—subtropical to temperate—latitudes, with hotspots off the coast of Japan. Larger body mass pseudo-cohorts inhabit lower—tropical to subtropical—latitudes, with hotspots in the western and central north Pacific. These results offer evidence that albacore tuna prefer different habitats depending on their body mass, and point to long-term migratory routes for the species that the current tagging technology is unlikely to capture in full. We discuss the implications of the results for data-driven modelling of albacore tuna in the north Pacific, as well as the management of the north Pacific albacore-tuna fishery.

Forecasting Albacore (Thunnus alalunga) Fishing Grounds in the South Pacific Based on Machine Learning Algorithms and Ensemble Learning Model

To achieve high-precision forecasting of different grades of albacore fishing grounds in the South Pacific Ocean, we used albacore fishing data and marine environmental factors data from 2009 to 2019 as data sources. An ensemble learning model (ELM) for albacore fishing grounds forecasting was constructed based on six machine learning algorithms. The overall accuracy (ACC), fishing ground forecast precision (P) and recall (R) were used as model accuracy evaluation metrics, to compare and analyze the accuracy of different machine learning algorithms for fishing grounds forecasting. We also explored the forecasting capability of the ELM for different grades of fishing grounds. A quantitative evaluation of the effects of different marine environmental factors on the forecast accuracy of albacore tuna fisheries was conducted. The results of this study showed the following: (1) The ELM achieved high accuracy forecasts of albacore fishing grounds (ACC = 86.92%), with an overall improvement of 4.39~19.48% over the machine learning models. (2) A better forecast accuracy (R2 of 81.82–98%) for high-yield albacore fishing grounds and a poorer forecast accuracy (R1 of 47.37–96.15%) for low-yield fishing grounds were obtained for different months based on the ELM; the high-yield fishing grounds were distributed in the sea south of 10° S. (3) A feature importance analysis based on RF found that latitude (Lat) had the greatest influence on the forecast accuracy of albacore tuna fishing grounds of different grades from February to December (0.377), and Chl-a had the greatest influence on the forecast accuracy of albacore tuna fishing grounds of different grades in January (0.295), while longitude (Lon) had the smallest effect on the forecast of different grades of fishing grounds (0.037).

High throughput identification of tuna (Thunnus spp.) larvae in the Gulf of Mexico using unlabeled-probe high-resolution melting analysis (UP-HRMA).

The genus Thunnus (family Scombridae) comprises eight species of tunas of which all but one are targeted by industrialized fisheries. While intact individuals of these species can be distinguished by morphological characteristics, researchers and managers often rely on dressed, frozen, juvenile, or larval fish samples which often necessitates molecular species identification. Here we investigate short amplicon (SA) and unlabeled probe (UP) high-resolution melting analysis (HRMA) as a low-cost, high-throughput molecular genotyping assay capable of distinguishing between albacore tuna (T. alalunga), blackfin tuna (T. atlanticus), bigeye tuna (T. obesus), Atlantic bluefin tuna (T. thynnus), and yellowfin tuna (T. albacares) in the Gulf of Mexico. While SA-HRMA of variable regions in the NADH dehydrogenase subunit 4 (ND4) and subunit 5 (ND5), and subunit 6 (ND6) of the mitochondrial DNA (mtDNA) genome did yield some species-specific diagnostic melting curves (ex. ND4 assay can reliably distinguish Atlantic bluefin tuna) genotype masking produced excessive variation in melting curves for reliable multi-species identification. To minimize the genotyping masking of SA-HRMA a 26 base pair long UP containing four SNPs was developed within a 133 bp segment of ND4. The UP-HRMA is able to reliably distinguish Gulf of Mexico species T. thynnus, T. obesus, T. albacares, and T. atlanticus by UP melting temperature at 67°C, 62°C, 59°C, and 57°C respectively. The developed UP-HRMA assay is a lower-cost, higher-throughput, alternative to previously published molecular assays for tuna identification that can be easily automated for large data sets including ichthyological larval surveys, fisheries specimens lacking distinguishing morphological characteristics, or detection of fraudulent trading of tuna species.

Scalar politics in transboundary fisheries management: The Western and Central Pacific Fisheries Commission as an eco-scalar fix for South Pacific albacore tuna management

Scholars and policymakers have debated the correct scales for managing and conserving ocean resources for decades. To address the conservation and management of highly migratory fish species, like tuna, countries have established regional fisheries management organisations (RFMOs) to regulate transboundary fisheries at the scale of oceanic regions. However, in the Western and Central Pacific Ocean region, countries have expanded their tuna management efforts to encompass multiple and overlapping intergovernmental institutions operating at regional and subregional scales. Scholars have argued that this proliferation of institutions across scales—including the development of the region’s RFMO, the Western and Central Pacific Fisheries Commission (WCPFC)—has strengthened transboundary tuna management. However, while scholars focus on the successes of scalar dynamics in the tropical purse seine fishery, less attention has been devoted to the smaller and less valuable southern longline fishery, where management progress has stalled. Management inaction at multiple scales has impacted the status of the fishery’s target stock, South Pacific albacore, and domestic fishing and processing industries in Pacific Island countries and territories. This article employs a scalar politics lens to consider why multi-scalar efforts to improve southern longline fishery management have produced no decisive change in management outcomes. Analysing over a decade of management debate and subregional institutional development, the article argues that the WCPFC has operated as an ‘eco-scalar fix’ in managing the southern longline fishery. Through a combination of ecological and political factors unique to the fishery, this eco-scalar fix has enabled distant water fishing countries to locate political authority with the WCPFC while shifting the responsibility for management reform onto the subregional efforts of Pacific Island countries. This case complicates and contributes to debates concerning scale in transboundary fisheries management by concluding that the effects of scalar politics on management outcomes are uneven and the product of asymmetrical, interest-driven dynamics among countries seeking to advance their interests in industrial fisheries.

Blue Shark (Prionace glauca) Distribution in the Pacific Ocean: A Look at Continuity and Size Differences

Blue shark (Prionace glauca) is a major bycatch species in the long-line and gill-net Pacific Ocean tuna fisheries, and the population structure is critical for fishery management. We employed generalized additive models to analyze the fork lengths of blue sharks and biological data (i.e., feeding level, sex, and genetic data), as well as environmental and spatial variables (i.e., sea surface temperature, month, longitude, and latitude) collected from 2011 to 2014 by the Chinese Thunnus alalunga long-line tuna fishery observer program. Fork length was significantly affected (p < 0.05) with location (latitude and longitude) and sex, and positively effected with sea surface temperature. No relationships were found between fork length and feeding level, month, and genetic data. We detected fork length differences among blue sharks over the range of the observed data, but the genetic data implied a panmictic population. Thus, we hypothesize that the genetic similarity was so close that it could not be well separated. Based on the precautionary principle, we recommend that the blue shark in the Pacific Ocean should be managed as two independent populations to ensure its sustainable use.

Juvenile Albacore tuna (Thunnus alalunga) foraging ecology varies with environmental conditions in the California Current Large Marine Ecosystem

AbstractJuvenile North Pacific Albacore tuna (Thunnus alalunga) support commercial and recreational fisheries in the California Current Large Marine Ecosystem (CCLME), where they forage during summer and fall. The distributions of the commercial and recreational fisheries and estimates of forage availability have varied substantially over the past century. Time‐series quantifying Albacore diet can help link forage composition to variability in Albacore abundance and distribution and, consequently, their availability to fishers. Previous diet studies in the CCLME are of relatively short duration, and long‐term variability in Albacore diet remains poorly understood. We describe the diets of juvenile Albacore from three regions in the CCLME from 2007 to 2019 and use classification and regression tree analysis to explore environmental drivers of variability. Important prey include Northern Anchovy (Engraulis mordax), rockfishes (Sebastes spp.), Boreal Clubhook Squid (Onychoteuthis borealijaponica), euphausiids (Order: Euphausiidae), and amphipods (Order: Amphipoda), each contributing >5% mean proportional abundance. Most prey items were short lived species or young‐of‐the‐year smaller than 10 cm. Diet variability was related to environmental conditions over the first 6 months of the year (PDO, sea surface temperature, and NPGO) and conditions concurrent with Albacore capture (region and surface nitrate flux). We describe foraging flexibility over regional and annual scales associated with these environmental influences. Continuous, long‐term studies offer the opportunity to identify flexibility in Albacore foraging behavior and begin to make a predictive link between environmental conditions early in the year and Albacore foraging during summer and fall.

Adjusting time-of-day and depth of fishing provides an economically viable solution to seabird bycatch in an albacore tuna longline fishery

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.

An optimized acidic digestion for the isolation of microplastics from biota-rich samples and cellulose acetate matrices

Plastic pollution is a growing concern. To analyze plastics in environmental samples, plastics need to be isolated. We present an acidic/oxidative method optimized to preserve plastics while digesting synthetic cellulose acetate and a range of organics encountered in environmental samples. Cellulose acetate was chosen for optimization as it can be purchased as a reference material, can co-occur with plastics in environmental samples and, if it can be completely digested, is a potential filter material for the collection of nano- and micro-plastics from natural waters. Other forms of particulate organic matter (POM) were chosen to provide a range of chemistries that might alter digestion efficiency and due to the interest in the community of isolating plastics from samples where these organics occur. For instance, microalgal POM occurs in lake and ocean waters, riverine POM in rivers, and inclusion of tuna provides a test for the suitability of the method for isolating plastics from animal tissues. The method is a one-pot overnight (16–18 h) digestion in 5 M nitric acid with 0.3 M sodium persulfate heated to 80 °C. The method provides quantitative removal of cellulose acetate (exceeding detection limits), near quantitative removal of microalgal POM and Albacore tuna tissue (>99%), but only 86% of urban river POM, all while retaining >99% by mass of C–C bonded polymers polyethylene, polypropylene, and polystyrene and >96% by mass of polyethylene terephthalate. Fourier transform infrared spectroscopy (FT-IR) and %-C content analysis confirmed plastic polymer stability during digestion. However, some additives in appear susceptible to digestion with FT-IR results indicating the loss of N,N′-ethylenebis(stearamide) from polyethylene. This method provides a simpler and more effective method than many in the literature. We present recommendations for the application of this method, as well as limitations and areas for future improvement.

Projecting climate change impacts from physics to fisheries: A view from three California Current fisheries

Motivated by a need for climate-informed living marine resource management, increased emphasis has been placed on regional end-to-end modeling frameworks designed to project climate impacts on marine ecosystems and evaluate the efficacy of potential management strategies under changing conditions. The ‘Future Seas’ project was initiated with a focus on three fisheries (Pacific sardine, swordfish, and albacore tuna) in the California Current System (CCS). This work leverages a suite of climate, ocean, ecosystem, and economic models to project physical, ecological, and socio-economic change, evaluate management strategies, and quantify uncertainty in model projections. Here we describe the components of the modeling framework, considerations underlying choices made in model development, engagement with stakeholders, and key physical, ecological, and socio-economic results to date, including projections to 2100. Our broad aims are to (i) synthesize a large body of climate and fisheries research that has been conducted, and continues, under the Future Seas umbrella, and (ii) provide insight and recommendations to those pursuing similar efforts for other applications and in other regions. In general, our results indicate that all three species will likely shift their distributions (predominantly poleward) in the future, which impacts accessibility to fishing fleets, spatial management, and quota allocation. For similar integrative climate-to-fisheries projections, we recommend attention is given to: recognizing potential biases arising from differences between the climate products used for ecological model fitting and those used for model projection; how sources of projection uncertainty are prioritized, incorporated, and communicated; and quantitatively linking scenarios – especially socio-economic scenarios – with climate and ecological projections.

Estimation of Albacore Tuna Potential Fishing Grounds in the Southeastern Indian Ocean

To maintain sustainable fisheries, albacore tuna is one of the commercial fish species whose management is regulated globally by the Regional Fisheries Management Organizations. Generally, sea surface temperature (SST) and chlorophyll-a (SSC) are used to determine fish suitability based on the catch data. In this research, we attempt to identify optimal habitats for albacore tuna in the southeastern Indian Ocean by analyzing in situ data based on onboard observers on tuna long line vessels from 2006–2019 and optimum interpolation sea surface temperature from NOAA-Advanced Very High-Resolution Radiometer and sea surface chlorophyll-a from Aqua MODIS satellites. The albacore tuna’s habitat suitability index was examined using the generalized additive model. The results suggested that albacore tuna inhabited waters with an SST range of 15–26 °C and SSC concentration of 0.075–0.125 mg/m3. In the Indian Ocean, most albacore tunas were captured at higher latitudes of 20°-30° S.

Relationship Between Musculoskeletal Load and Weight of Manual Fish Handling Via 2D Simulation

Fisherman experienced work-related musculoskeletal disorders (WMSDs) due to manual handling. Especially, manual handling for heavy fish makes physical load for fisherman. To prevent these WMSDs, fisherman should know the limit of weight in manual fish handling. Thus, the objective of this study was to find the relationship between the musculoskeletal load and weight of manual fish handling. This investigation was performed by the 2D musculoskeletal simulation. Posture of fishermen during manual fish handling on the commercial fishing boat was obtained from the Fishnet Open Images Database. Compression force of L5-S1 and joint torque of elbow, shoulder, knee, and ankle as musculoskeletal load were calculated by BlessPro2 software. The weight values of bigeye tuna, yellowfin tuna, and albacore tuna were used for this simulation. The results showed that compression force of L5-S1 and joint torque were increased with fish weight. In addition, the compression forces of L5-S1 during manual handling for bigeye tuna and yellowfin tuna were much larger than 3400 N as injury threshold of the National Institute of Occupational Safety and Health (NIOSH). These results indicate that fishermen should avoid heavy fish such as bigeye tuna and yellowfin tuna in manual fish handling for preventing WMSDs.

Ensemble Three-Dimensional Habitat Modeling of Indian Ocean Immature Albacore Tuna (Thunnus alalunga) Using Remote Sensing Data

This study evaluated the vertical distribution of immature albacore tuna (Thunnus alalunga) in the Indian Ocean as a function of various environmental parameters. Albacore tuna fishing data were gathered from the logbooks of large-sized Taiwanese longline vessels. Fishery and environmental data for the period from 1998 to 2016 were collected. In addition to the surface variable, the most influential vertical temperature, dissolved oxygen (OXY), chlorophyll, and salinity layers were found at various depths (i.e., 5, 26, and 53 m for SST; 200, 244, and 147 m for OXY; 508, 628, and 411 for SSCI; and 411, 508, and 773 m for SSS) among 20 vertical layers based on Akaike criterion information value of generalized linear model. Relative to the 20 vertical layers base models, these layers had the lowest Akaike information criteria. For the correlation between the standardized and predicted catch per unit effort (CPUE), the correlation values for the generalized linear model (GLM), generalized additive model (GAM), boosted regression tree (BRT), and random forest (RF) model were 0.798, 0.832, 0.841, and 0.856, respectively. The GAM-, BRT-, and RF-derived full models were selected, whereas the GLM-derived full model was excluded because its correlation value was the lowest among the four models. From March to September, a higher immature albacore standardized CPUE was mainly observed from 30°S to 40°S. A northward shift was observed after September, and the standardized CPUE was mainly concentrated at the south coast of Madagascar from November to January.

CPUE standardization for southern bluefin tuna (Thunnus maccoyii) in the Korean tuna longline fishery, accounting for spatiotemporal variation in targeting through data exploration and clustering.

Accounting for spatial and temporal variation in targeting is a concern in many catch per unit effort (CPUE) standardization exercises. In this study we standardized southern bluefin tuna (Thunnus maccoyii, SBT) CPUE from the Korean tuna longline fishery (1996–2018) using generalized linear models (GLMs) with operational set by set data. Data were first explored to investigate the operational characteristics of Korean tuna longline vessels fishing for SBT, such as the spatial and temporal distributions of effort, and changes in the nominal catch rates among major species and species composition. Then we estimated SBT CPUE by area used for the stock assessment in the CCSBT (Commission for the Conservation of Southern Bluefin Tuna) and identified two separate areas in which Korean tuna longline vessels have targeted SBT and albacore tuna (T. alalunga), with targeting patterns varying spatially, seasonally and longer term. We applied two approaches, data selection and cluster analysis of species composition, and compared their ability to address concerns about the changing patterns of targeting through time. Explanatory variables for the GLM analyses were year, month, vessel identifier, fishing location (5° cell), number of hooks, moon phase, and cluster. GLM results for each area suggested that location, year, targeting, and month effects were the principal factors affecting the nominal CPUE. The standardized CPUEs for both areas decreased until the mid-2000s and have shown an increasing trend since that time.

Assessment of the Impact on 20 Pelagic Fish Species by the Taiwanese Small-Scale Longline Fishery in the Western North Pacific Using Ecological Risk Assessment.

Simple SummaryIn this study, a semi-quantitative ecological risk assessment (ERA) was used to evaluate the ecological risks of fishing impact on 20 pelagic fish species by the small-scale longline fisheries in the western North Pacific Ocean. More than 2.38 million individual landing records at Nangfangao and Hsinkang fishing ports, eastern Taiwan from 2001–2021 were used in this study. The productivity was estimated based on the mean ranking (high, median, and low) of seven life history parameters and the susceptibility was calculated by the multiplication of the catchability, selectivity and post-capture mortality. The ERA results indicated sharks have higher ecological risk than those of tunas and billfishes, except yellowfin tuna (Thunnus albacares). The shortfin mako shark (Isurus oxyrinchus) and dusky shark (Carcharhinus obscurus) have the highest risk. Yellowfin tuna, other shark species, and sailfish (Istiophorus platypterus) have medium risk. While the striped marlin (Kajikia audax), and albacore tuna (T. alalunga) have the lowest risk. Although ERA cannot replace the conventional stock assessment methods that can produce solid management information on catch and effort, yet it can provide useful information for precautionary management measures.Ecological risk assessment (ERA) has been applied on assessing the relative risk of bycatch species in recent years. ERA index is calculated by productivity of species and susceptibility of fisheries on fish species. In this study, a semi-quantitative method was used to evaluate the risks of exploitation for 20 pelagic fish species by the small-scale longline fisheries in the western North Pacific Ocean. The productivity was estimated based on the ranking (high, median, and low) of seven life history parameters. The susceptibility was calculated by the multiplication of the catchability, selectivity and post-capture mortality. The ERA results indicated the risks of sharks are higher than those of tunas and billfishes, except yellowfin tuna (Thunnus albacares). The shortfin mako shark (Isurus oxyrinchus) and dusky shark (Carcharhinus obscurus) have the highest risk. Other shark species, yellowfin tuna, and sailfish (Istiophorus platypterus) have medium risk. While the striped marlin (Kajikia audax), and albacore tuna (T. alalunga) have the lowest risk. Stock assessment and rigorous management measures such as catch quota and size limit are recommended for the species in high or medium ecological risk and a consistent monitoring management scheme is suggested for those in low ecological risk.