Trawl Fishery Research Articles

Artisanal trawl fisheries as a sentinel of marine litter pollution

Systematic seafloor surveys are a highly desirable method of marine litter monitoring, but the high costs involved in seafloor sampling are not a trivial handicap. In the present work, we explore the opportunity provided by the artisanal trawling fisheries to obtain systematic data on marine litter in the Gulf of Cadiz between 2019 and 2021. We find that plastic was the most frequent material, with a prevalence of single-use and fishing-related items. Litter densities decreased with increasing distance to shore with a seasonal migration of the main litter hotspots. During pre-lockdown and post-lockdown stages derived from COVID-19, marine litter density decreased by 65 %, likely related to the decline in tourism and outdoor recreational activities. A continuous collaboration of 33 % of the local fleet would imply a removal of hundreds of thousands of items each year. The artisanal trawl fishing sector can play a unique role of monitoring marine litter on the seabed.

Integrating research and fishing extension approaches to engage small-scale fishers in the participatory evaluation and voluntary use of bycatch reduction devices

The main strategy for reducing discards in shrimp trawl fisheries has been the development and use of bycatch reduction devices (BRDs). Research has focused on the performance of BRD in biological and technological terms, undermining the importance of the human dimensions, such as fishers’ perceptions. On the other hand, a better comprehension of which methodological approach enables fishers volunteer adoption of BRDs is required. This paper analyzed the performance of BRD through a combination of interaction activities and conventional scientific experiments. Four interaction activities were conducted with shrimp trawlers from 12 fishing sites at the coast of Paraná, South Brazil. Adapted from previous research and after fishers’ suggestion in the interaction activities, a Nordmore grid was tested against a control net to evaluate differences in shrimp (Xiphopenaeus kroyeri) and bycatch weight, and total length of X. Kroyeri. Interaction activities stressed the importance of dialogue and participation and showed that fishers perceived a high diversity of parameters, expanding the understanding of BRD performance. Also, the methodological approach provided room for collective learning and fishers’ engagement, with reports of voluntary initiatives to reduce bycatch. The results showed that the dialog is improved with diversification and integration of communication methods, as well as timing is crucial for fishers to process information and to build knowledge. An analysis of the methodological approach used in this paper provide insights on how to increase voluntary BRD adoption as well as to engage fishers more consistently in being stewards for the responsible fishing.

Vulnerability assessment of species caught by the shrimp trawl fishery in northeastern Brazil

In Brazil, there are no official fisheries statistics to quantitatively assess the status of target and bycatch species. Since food security is at stake, appropriate tools are needed to maintain fisheries sustainability. One widely used “data-poor” method, despite the critics of its subjectivity, is Productivity and Susceptibility Analysis (PSA). In this study, we use PSA to assess the impact of a northeastern Brazil shrimp fishery which is socioeconomically relevant for the local population but is known to have adverse ecological impacts. The vulnerability status (high, medium, or low) of 30 species were determined by the PSA and compared with two other semi-quantitative approaches that assess stock or extinction risk. The results obtained from the PSA and other methods were partially convergent, highlighting six bycatch and one target species for which management measures or data collection should be prioritised. This study showed that PSA, when compared with other semi-quantitative methods, can constitute a valuable preliminary assessment for assessing data-poor fisheries. The integrated use of various methods is advisable in diagnosing fishery resources. However, it is essential to understand the peculiarities of each technique to appreciate its applicability and feasibility.

Effects of Lunar Phases and Weather Conditions on Small-scale and Trawl Fishery Landings in Southern Aegean Sea, Türkiye

Effects of Lunar Phases and Weather Conditions on Small-scale and Trawl Fishery Landings in Southern Aegean Sea, Türkiye

Developing a subseasonal ecological forecast to reduce fisheries bycatch in the Northeast U.S.

Over the past decade, substantial progress has been made in projecting and predicting the spatial distribution of many marine species at seasonal to multidecadal time scales. However, managers and fishers often need to make decisions at much shorter time scales. Subseasonal environmental forecasts, which generate predictions over one to several weeks, can now be combined with species-specific habitat preference data to create ecological forecasts that could facilitate dynamic spatial management. The development of such predictive tools could aid in identifying optimal times and areas for fishers to maximize target catch and avoid nontarget catch. Nontarget catch, or bycatch, can have numerous and potentially severe economic and ecological consequences. Here, we focus on a population of anadromous fish known collectively as river herring (alewife and blueback herring), as they are species of concern and are heavily impacted by bycatch. Using bottom trawl survey data from the Northeast US and subseasonal forecasts of sea surface temperature, we constructed a bycatch risk model to generate probabilistic predictions of river herring distributions in regions frequented by the US mid-water trawl fishery. Assessments of model skill showed that our ecological model performed well in predicting the distribution of river herring and that subseasonal forecasts were effective at 1-week timeframes. There was a clear seasonal effect on forecasted bycatch risk throughout the Northeast US, with particularly high risk in winter and spring months. Importantly, variability in risk was detectable at the weekly timescale and our model identified specific areas and times that fishers should avoid in order to decrease their likelihood of bycatch. The bycatch risk forecast developed in this study is a significant advance from near-real time forecasts and the foundation to build forecast systems by combining species co-occurrence models with subseasonal forecasts. As these subseasonal forecasts are available globally, this approach could be adapted to facilitate the management of other natural resource conflicts around the world.

Trawl Fisheries in the Gulf of Thailand: Vulnerability Assessment and Trend Analysis of the Fish Landings

Vulnerability of each stock in the catches from trawl fisheries in the Gulf of Thailand was assessed by productivity susceptibility analysis. Separate assessments were made based on type of trawler (otter-board, pair and beam) and vessel size (SS, S, M, L and XL, according to gross tonnage). Catches were distinctly different among trawler types and were dominated by demersal fishes, pelagic fishes and shrimps in the otter-board, pair and beam trawlers, respectively. The stocks of over 200 taxa were included in the study; high-vulnerability taxa were found for all trawl types and sizes, except the beam trawler size S. Only seven (7) taxa were classified as high vulnerability, including four (4) teleost taxa, namely Saurida elongata, Plotosus spp., Gymnothorax spp. and Sphyraena spp., and three (3) elasmobranch taxa, namely Carcharhinus spp., Brevitrygon heterura and Neotrygon kuhlii. Meanwhile, as many as 26 high-medium vulnerability taxa were found in catches by otter-board trawler size L, which included not only fishes but also cephalopods. Trends and variation in fish landings of 20 high and high-medium vulnerability taxa were analyzed. Eighteen (18) taxa showed monotonic trends, both continuous and discontinuous, in their time series of annual landings, but not Muraenesox spp. nor Uroteuthis spp. The long-term variations in fish landings ranged mostly between 40% and 50%. The short-term variations showed positive absolute and relative skewness, i.e., mostly between 10% and 20%. Results of this study highlight the taxa that require a precautionary approach for fishery management and warrant comprehensive fish stock assessment. Such data will allow more accurate determination of their status compared to the reference points and facilitate better management of trawl fisheries in the Gulf of Thailand.

Redistribution of fisheries catch potential in Mediterranean and North European waters under climate change scenarios

The Mediterranean Sea is a hotspot of global warming where key commercial species, such as demersal and pelagic fishes, and cephalopods, could experience abrupt distribution shifts in the near future. However, the extent to which these range shifts may impact fisheries catch potential remains poorly understood at the scale of Exclusive Economic Zones (EEZs). Here, we evaluated the projected changes in Mediterranean fisheries catches potential, by target fishing gears, under different climate scenarios throughout the 21st century. We show that the future Mediterranean maximum catch potential may decrease considerably by the end of the century under high emission scenarios in South Eastern Mediterranean countries. These projected decreases range between −20 to −75 % for catch by pelagic trawl and seine, −50 to −75 % for fixed nets and traps and exceed −75 % for benthic trawl. In contrast, fixed nets and traps, and benthic trawl fisheries may experience an increase in their catch potential in the North and Celtic seas, while future catches by pelagic trawl and seine may decrease in the same areas. We show that a high emission scenario may considerably amplify the future redistribution of fisheries catch potential across European Seas, thus highlighting the need to limit global warming. Our projections at the manageable scale of EEZ and the quantification of climate-induced impacts on a large part of the Mediterranean and European fisheries is therefore a first, and considerable step toward the development of climate mitigation and adaptations strategies for the fisheries sector.

Atlantic cod (Gadus morhua) assessment approaches in the North and Baltic Sea: A comparison of environmental DNA analysis versus bottom trawl sampling

The assessment of fish stocks is often dependent on scientific trawl fisheries surveys, which are both invasive and costly. The analysis of environmental DNA (eDNA) from water samples is regarded as a non-invasive and cost-effective alternative, but meaningful performance evaluations are required for a wider application. The goal of this study was to comparatively analyze a newly developed, more sensitive real-time PCR based eDNA approach with bottom trawl fisheries catches to locally detect and quantify Atlantic cod (Gadus morhua) in the North and Baltic Seas. With a species-specificity of the qPCR assay of 100%, a minimal limit of 15 Cytochrome b eDNA copies was determined for the detection of cod. In addition, a Gaussian processing regression proved a significant correlation (95%) between eDNA (copies per L of water) and cod biomass (CPUE/Ha) found by bottom trawling. The results presented here prove the potential of eDNA analyses for quantitative assessments of commercial fish stocks in the open ocean, although additional comparative analyses are needed to demonstrate its performance under different oceanographic conditions.

Every animal matters! Evaluating the selectivity of a Mediterranean bottom trawl fishery from a species community perspective.

Bottom trawl fisheries often catch several species simultaneously. However, most studies addressing the catch performance and selectivity of a specific trawl focus on a few commercially important or most vulnerable species requiring management measures. By contrast, the present study considers the multispecies nature of Mediterranean bottom trawl fisheries through a holistic approach that accounts for the full species community in the catches. Specifically, we evaluated and compared the catch performance of the two codends allowed for this fishery, made of 40 mm square (SM40) and 50 mm diamond (DM50) meshes. Results showed that 50 and 80% of the catch in weight and count numbers, respectively, consisted of species without commercial value, demonstrating that large proportions of the catch are not considered when using the existing approach to evaluate the ecological impact of the fishing activity. Significant differences in catch profiles between the two codends were observed, especially for two commercial flatfish species, Arnoglossus laterna and Citharus linguatula, with larger contributions in the SM40. Further, the SM40 codend had a significantly higher retention, compared to DM50 codend, for specific sizes of Merluccius merluccius and Mullus barbatus. The outcomes of the study can be useful for the Mediterranean bottom trawl fisheries management.

Sea lion and fur seal interactions with fisheries and aquaculture in South American waters: threats and management perspectives

Abstract The main issue affecting the conservation of most pinniped species has been identified as interactions with fisheries and aquaculture. In South American waters in particular, this problem has not been well evaluated. Consequently, there is an urgent need for research and conservation measures to address the problem, particularly for species of conservation concern. In this study, we reviewed published and unpublished research and observations from the last 25 years on operational and biological interactions between pinnipeds and fisheries and salmonid aquaculture activities in South American waters, and the conservation and management implications of these interactions in the near future. Two species of pinnipeds are primarily involved in biological and operational interactions with fisheries and aquaculture in South America: the South American sea lion Otaria flavescens and the South American fur seal Arctocephalus australis. Although phocids are present in South American waters, there is no published research on conflicts between phocids and human activities. Interactions between fisheries and pinnipeds have been reported by many countries. In South American waters, interactions mostly involve male and subadult male South American sea lions. However, despite the high frequency of interactions, the estimated economic losses to fisheries and aquaculture related to sea lion depredation are generally low. Incidental capture and mortality of pinnipeds has been reported, especially in artisanal gillnet fisheries and in industrial purse seine and trawl fisheries. Mortality of sea lions in salmonid aquaculture has been reported, but the magnitude of the problem is unknown. In South America, limited progress has been made to incorporate mitigation measures, such as time‐area closures, acoustic deterrent devices, and modifications to fishing gear, into fisheries and aquaculture. This is likely to be due to our limited understanding of ecosystem complexity, the costs of modifying fishing gear or incorporating acoustic deterrent devices, and the scarcity of fishing controls. We suggest that strategies for effectively reducing conflicts between pinnipeds, fisheries, and aquaculture should involve all stakeholders in participative research to facilitate co‐management.

Smaller bar spacings in a Nordmøre grid reduces the bycatch of redfish (Sebastes spp.) in the offshore Northern shrimp (Pandalus borealis) fishery of eastern Canada

The offshore Northern shrimp (Pandalus borealis) bottom trawl fishery in eastern Canada currently uses 22 and 28 mm bar spacing Nordmøre grids to limit bycatch from using small mesh codends. However, a recent rebound of juvenile redfish (Sebastes spp.), that can pass through the grids, has greatly increased bycatch. To address this concern, this study investigated the effectiveness of 17 and 15 mm bar spacing Nordmøre grids in a twin-trawl (paired) configuration against the traditional 22 mm bar spacing grid. Size selectivity analyses showed that the 17 and 15 mm grids resulted in no significant reduction in shrimp catch across all length classes. The 17 mm grid significantly reduced redfish bycatch for all length classes and the 15 mm grid significantly reduced redfish bycatch for individuals larger than 95 mm total length. Less redfish entered the codend with the experimental grids, however, the overlap in width between redfish and Northern shrimp limits the overall sorting efficiency of the grids, leaving some redfish still vulnerable to capture.

Variations in fish community composition and trophic structure under multiple drivers in the Beibu Gulf

IntroductionBeibu Gulf is a semi-enclosed bay with important ecological and economic value of the northwestern South China Sea (SCS). It proved to be a stressed ecosystem and therefore clearly vulnerable to further external disturbances.MethodsData from 26 fishery bottom trawl surveys in the Beibu Gulf from 2006 to 2018 are analyzed to reveal changes in the fish abundance, dominant species composition, diversity, mean trophic level (MTL), and fishing-in-balance (FiB) index.ResultsFish abundance decreased significantly (p< 0.05) with increased anthropogenic disturbance (e.g., fishing intensity and land-derived pollutants), with catch per unit effort (CPUE) decreasing from 40.69 kg·h−1 in 2006 to 15.84 kg·h−1 in 2018. Dominant species composition has changed dramatically from 2006 to 2018, with fish communities shifting from demersal to pelagic species, and from large and high-trophic-level species to small and low-trophic-level species. Meanwhile, Margalef’s richness and Shannon–Wiener diversity indexes trend downward. The MTL declines from 3.82 in 2006 to 3.71 in 2018 (at 0.08 trophic level per decade), and decreasing with the decrease of the proportion of high-trophic fish and demersal fish in total catch (p< 0.05). A FiB index tends to be less than 0, this index declines with decreasing MTL and fish abundance (p< 0.05).DiscussionOverall, fish stocks in the Beibu Gulf continue to decline and are currently overexploited. Multiple external disturbances, such as fishing (including overfishing, dominance of trawl fishery, and ‘skipper effect’), habitat disturbance, pollution, and temperature changes, may have contributed to significant changes in fish communities and trophic structure in the Beibu Gulf.

Age and Growth of the Threatened Smalleye Round Ray, Urotrygon microphthalmum, Delsman, 1941, from Northeastern Brazil

The age and growth of Urotrygon microphthalmum were studied using specimens captured between March 2010 and March 2012 as by-catch in the shrimp trawl fishery off the coast of the state of Pernambuco, Brazil. A total of 347 vertebrae were read, 161 from males (81.6–249.55 mm) and 186 from females (86.15–298.1 mm). The estimated average percentage index (IAPE) ranged from 0.71% to 4.33% (mean = 2.5%) in vertebrae from specimens with 1 and 6 band pairs, respectively. In the present study, the different approaches to validation produced variable results (partially valid growth zones). We then decided to discuss the growth of the species considering the formation of an annual ring. There were statistically significant differences in growth between the sexes. The best model to describe male growth was the von Bertalanffy growth model for two phases (VBGM TP) with growth parameters L∞ (maximum theoretical length) = 230.35 mm, k (growth constant) = 1.00, t0 (theoretical age of size zero) = −0.76 years and for females it was the von Bertalanffy with birth size (VBGM L0) model with parameters L∞ = 282.55 mm, k = 0.37. The age of maturity for males and females was 1.52 and 2.02 years, respectively, and the maximum age observed was 5.5 and 8.5 years, respectively. Despite being a fast-growing species, Urotrygon microphthalmum is threatened, probably due to the high mortality levels from shrimp trawling in a very narrow range of the shelf where all the life stages are captured.

Come, tell me how you live: Habitat suitability analysis for Ostrea edulis restoration

Abstract Against the background of the UN decade on ecosystem restoration and the new EU Biodiversity Strategy for 2030, and in the context of marine spatial planning and complex maritime user conflicts, reliable information on habitat suitability for large‐scale restoration is an important prerequisite for implementing conservation management and for supporting successful, sustainable, and ecologically efficient restoration measures. In this study, habitat suitability was assessed using multicriteria decision analysis (MCDA) for the restoration of the European oyster, Ostrea edulis, in marine protected areas (MPAs) of the German Bight in the North Sea: Borkum Reef Ground (Borkum Riffgrund, BRG) and Sylt Outer Reef – Eastern German Bight (Sylter Außenriff, SAR). Based on site selection criteria, exclusion and suitability factors for the MCDA were defined. Results were integrated with the available geodata to produce habitat suitability maps for oyster restoration in the area of interest. Suitable as well as unsuitable habitats have been successfully identified for both MPAs: several hundred square kilometres (≥97.2% of BRG) or several thousand square kilometres (≥74.5% of SAR) were classified as ecologically and logistically suitable for oyster restoration measures in the respective MPAs. As oyster restoration is significantly limited by human activities (e.g. bottom trawl fisheries), the management of fisheries is an important prerequisite for successful oyster restoration in both MPAs. Results show that designated fishery management measures will increase the possibilities for oyster restoration. In BRG, our results correspond to the known historical distribution. In SAR, our results significantly exceed the historically known distribution. The habitat suitability analysis will facilitate decision‐making regarding ocean use, and will reduce restoration costs through targeted management activities in areas of high suitability and expand species recovery by improving the survival of reintroduced individuals. The habitat suitability analysis procedure is easily adaptable for application to other areas, other species, or other habitat restoration projects, or to other conservation management settings. The software applied is open source and the suitability calculation is described in detail to inform wider applications.

Spatial distribution of the demersal chondrichthyan community from the western Mediterranean trawl bycatch

IntroductionChondrichthyans (sharks, batoids and chimaeras) play key roles in the regulation of marine food webs dynamics. However, more than half of the assessed species in the Mediterranean are threatened, primarily by fishing pressure and compounded by habitat degradation and climate change. Nevertheless, there is an important knowledge gap in identifying the underlying drivers of their community structure and spatial distribution.Methods and ResultsWe provide insights into the current bycatch rates of chondrichthyans in the western Mediterranean commercial bottom trawling fishery by accurately depicting the unaltered practices of the local fleet. A total of 17 species were recorded in the studied fishing grounds (ranging from 50 to 800 m deep), including 7 sharks, 9 batoids, and 1 chimaera, although the total catch was dominated by few species. Furthermore, we tested the effect of environmental and fishing-related factors on multiple community descriptors by using analysis of community structure (multidimensional scaling and analysis of similitude) and generalized linear mixed models to further understand the drivers of the chondrichthyan community distribution and structure. This study revealed the importance of combining environmental and anthropogenic drivers to further understand the spatial distribution patterns of chondrichthyan communities. Our results indicate that depth was the main driver of the community structure, with deeper areas within the fishing grounds hosting a higher diversity. Sea bottom temperature and substrate type also influenced the distribution of the community, with substrate effects changing depending on the intensity of fishing pressure. In all cases, density, biomass, and diversity of chondrichthyans were negatively impacted by increasing fishing effort. DiscussionUnderstanding the drivers of the structure and distribution of the chondrichthyan community is crucial to understand the potential impacts that increased fishing pressure, habitat loss and global change may entail. The ongoing challenges that the Mediterranean chondrichthyans and their ecosystems are facing highlights the need for continued monitoring and improved chondrichthyan-focused fisheries management.

Improving seabed substrate mapping with high-resolution bottom trawl data

Accurate seabed substrate maps are essential for marine management, as substrate is an important component of the habitat type and used as a proxy for the prevailing benthic community. The provision of substrate maps, however, is hampered by the excessive costs of at-sea observations and, consequently, the uncertainty associated with spatial models used to interpolate these observations to full-coverage maps. Here, we tested whether high-resolution distributions of bottom trawling activity, readily collected under EU law, could improve the accuracy of substrate interpolations. Fishing distributions contain indirect information of the substrate type, as targeted species often show habitat preferences and gear types are designed for particular substrates. For two study areas in the Danish North Sea, we demonstrate that including spatial distributions of bottom trawl fisheries in substrate interpolation models results in more accurate substrate predictions. This potentially opens a novel source of previously unused information for improved seabed substrate interpolation.

Investigating an Unknown Biodiversity: Evidence of Distinct Lineages of the Endemic Chola Guitarfish Pseudobatos percellens Walbaum, 1792 in the Western Atlantic Ocean

Anthropogenic actions have affected marine species for a long time, through overexploitation of natural stocks and habitat degradation, influencing the life strategies of several taxa, especially rays and sharks, which have suffered significant population declines in recent years. Therefore, conservation actions and stock management have become paramount. In this regard, chola guitarfish, Pseudobatos percellens, distributed throughout the Brazilian coast, is often commercially fished by local artisanal fleets or as by-catch in shrimp trawl fisheries. Therefore, this study aimed to understand the genetic diversity of P. percellens throughout the Brazilian coast, using single nucleotide polymorphisms (SNPs). Genetic analyses employing 3329 SNPs revealed a hidden biodiversity within P. percellens, with at least one lineage occurring in the Northern and Northeastern regions and another distributed in the Southeastern/Southern Brazilian coast, with high genetic differentiation between them. However, the Discriminant Analysis of Principal Components (DAPC) indicated the presence of in fact three lineages distributed in these regions that must still be better investigated. Therefore, to ensure adequate conservation of chola guitarfish biodiversity, populations must be managed separately along the Brazilian coast. Furthermore, the need for a taxonomic review for this group is noted.

Estimating catch rates in real time: Development of a deep learning based Nephrops (Nephrops norvegicus) counter for demersal trawl fisheries

Demersal trawling is largely a blind process where information on catch rates and compositions is only available once the catch is taken onboard the vessel. Obtaining quantitative information on catch rates of target species while fishing can improve a fisheries economic and environmental performance as fishers would be able to use this information to make informed decisions during fishing. Despite there are real-time underwater monitoring systems developed for this purpose, the video data produced by these systems is not analyzed in near real-time. In other words, the user is expected to watch the video feed continuously to evaluate catch rates and composition. This is obviously a demanding process in which quantification of the fish counts will be of a qualitative nature. In this study, underwater footages collected using an in-trawl video recording system were processed to detect, track, and count the number of individuals of the target species, Nephrops norvegicus, entering the trawl in real-time. The detection was accomplished using a You Only Look Once v4 (YOLOv4) algorithm. Two other variants of the YOLOv4 algorithm (tiny and scaled) were included in the study to compare their effects on the accuracy of the subsequent steps and overall speed of the processing. SORT algorithm was used as the tracker and any Nephrops that cross the horizontal level at 4/5 of the frame height were counted as catch. The detection performance of the YOLOv4 model provided a mean average precision (mAP@50) value of 97.82%, which is higher than the other two variants. However, the average processing speed of the tiny model is the highest with 253.51 frames per second. A correct count rate of 80.73% was achieved by YOLOv4 when the total number of Nephrops are considered in all the test videos. In conclusion, this approach was successful in processing underwater images in real time to determine the catch rates of the target species. The approach has great potential to process multiple species simultaneously in order to provide quantitative information not only on the target species but also bycatch and unwanted species to provide a comprehensive picture of the catch composition.

Gradients of Variation in the At-Vessel Mortality Rate between Twelve Species of Sharks and Skates Sampled through a Fishery-Independent Trawl Survey in the Asinara Gulf (NW Mediterranean Sea)

Elasmobranchs are priority species for conservation due to their rapid decline determined by the unbalanced struggle between a fragile bio-ecology and strong anthropogenic impacts, such as bycatch from professional fishing. In this context, measuring species resistance to catch of poorly selective gear is of paramount importance. During June-October 2022, five experimental fishing campaigns were carried out in the Asinara Gulf (northern Sardinia) through 35 geographically and bathymetrically representative hauls of an area between 30 and 600 m in depth. Skates prevailed over sharks in the number of species, with seven and five species, respectively. We first evaluated the status of each individual with respect to stress due to the trawl's catch using a three-graded scale. We also recorded individual biometrics (total and disk length, weight and sex, and maturity for males) on board by implementing the best practices in manipulating individuals for physiological recovery and release at sea. After capture, skates resulted in generally better conditions than sharks, although deepwater species of both groups exhibited a worse state than coastal species. The estimated vitality rates also depended on the size of the individuals. This work provides standardized data on the intermingled effect of size, species type, and inhabited depth on the resistance response of some elasmobranch species against capture by trawl fishery activities.

Multi-decadal distribution changes of commercially important demersal species in the central-western Sea of Japan based on a multi-species spatiotemporal model

Understanding long-term changes in the distribution of commercially important species is a key first step for developing appropriate management plans. We estimated multi-decadal changes in the distributions of seven demersal fish species in the central-western Sea of Japan by fitting a multi-species spatiotemporal model to catch and effort data from a Japanese offshore trawl fishery from 1982 to 2020. We then identified any spatiotemporal patterns and discussed their relationship to oceanographic factors. Large distribution expansions were detected for Pacific cod (Gadus macrocephalus) and blackthroat seaperch (Doederleinia berycoides) in the southwestern region of the study area in the 2000s and 2010s. Combined with previous findings and an interannual trend of water temperature, it is thought that these changes could have been caused by expansions in the distribution of optimal thermal condition for stock-recruitment relationships. Species that did not experience large changes in distribution, such as cold-water flounders [the flathead flounder (Hippoglossoides dubius) and Korean flounder (Glyptocephalus stelleri)], mainly inhabit deep waters that are thought to be dominated by a colder and homogeneous water mass, meaning that their habitats were more likely to remain stable over time. Our results will contribute to improvement of adaptive stock managements for commercially important demersal species.