Pelagic Trawl Research Articles

Biology of One of the Most Abundant Mesopelagic Fish in Icelandic and Surrounding Waters: The Krøyer's Lantern Fish Notoscopelus kroyeri (Malm, 1861)

ABSTRACTMyctophids play an essential role in the marine ecosystem, linking the surface to the mesopelagic layer through diel vertical migration, and contributing to carbon sequestration. However, basic knowledge of their biology and distribution is still limited. Here, we described the length and age distribution, growth and otolith morphometrics for one of the most abundant myctophid fish of the Northeast Atlantic, the Krøyer's lantern fish Notoscopelus kroyeri (Malm, 1861). Individuals were sampled opportunistically by pelagic trawls during the International Ecosystem Summer Survey in the Nordic Seas (IESSNS) conducted in July 2020 and 2021. We provide the length–weight and otolith–fish size relationships and the size distribution for 336 N. kroyeri individuals collected along Iceland's south and west shelf, the Iceland Basin, and the Irminger Sea. Fish were primarily distributed along the Reykjanes Ridge and the continental shelf at depths between 0 and 550 m. Three size groups, corresponding to three different age groups, with individuals from 2 to 9 years old, were detected across sampling areas. We found positive allometric growth during both sampling years. Linear regressions were significant between otolith length, width and area, and fish length and weight, with adjusted r2 values ranging between 0.93 and 0.94. This study provides new information on the biology and distribution of one of the most abundant mesopelagic species in south Icelandic and surrounding waters.

Prediction of the Relative Resource Abundance of the Argentine Shortfin Squid Illex argentinus in the High Sea in the Southwest Atlantic Based on a Deep Learning Model.

To analyze the impact of the marine environment on the relative abundance of Illex argentinus (high and low categories) in the southwest Atlantic, this study collected logbook data from Chinese pelagic trawlers from December 2014 to June 2024, including vessel position data and oceanographic variables such as sea surface temperature, 50 m and 100 m water temperature, sea surface salinity, sea surface height, chlorophyll-a concentration, and mixed layer depth. Vessel positions were used to enhance the logbook data quality, allowing an analysis of the annual trends in the resource center of this squid at a spatial resolution of 0.1° × 0.1° and a temporal resolution of ten days. The findings showed that the resource center is primarily located around 42° S in the north and between 45° S and 47° S in the south, with a trend of northward movement during the study period. Additionally, we constructed two ensemble learning models based on decision trees-AdaBoost and PSO-RF-aiming to identify the most critical environmental factors that affect its resource abundance; we found that the optimal model was the PSO-RF model with max_depth of 5 and n_estimators of 46. The importance analysis revealed that sea surface temperature, mixed layer depth, sea surface height, sea surface salinity, and 50 m water temperature are critical environmental factors affecting this species' resources. Given that deep learning models generally have shorter running times and higher accuracy than other models, we developed a CNN-Attention model based on the five most important input factors. This model achieved an accuracy of 73.6% in forecasting this squid for 2024, predicting that the population would first appear near the Argentine exclusive economic zone around mid-December 2023 and gradually move east and south thereafter. The predictions of the model, validated through log data, maintained over 70% accuracy during most periods at a time scale of ten days. The successful construction of the resource abundance forecasting model and its accuracy improvements can help enterprises save fuel and time costs associated with blind searches for target species. Moreover, this research contributes to improving resource utilization efficiency and reducing fishing duration, thereby aiding in lowering carbon emissions from pelagic trawling activities, offering valuable insights for the sustainable development of this species' resources.

Biological Characteristics of the Glacier Lantern Fish Benthosema glaciale (Myctophidae) in Icelandic Waters andthe Irminger Sea During Summer.

Myctophids are one of the most diverse and abundant fish families in the mesopelagic zone, making them a key component in the marine pelagic community. In the North Atlantic, Benthosema glaciale (glacier lantern fish) is considered the most abundant myctophid north of 35° N, yet some regions within its extensive range lack information on its basic biological parameters. We investigated the growth and described the distribution of B. glaciale in Icelandic waters, including the southern continental shelf, Iceland Basin, and Irminger Sea. Length distribution, growth, relative body condition, age, and otolith-fish size relationships were analyzed from samples collected opportunistically with pelagic trawls during the International Ecosystem Summer Survey in the Nordic Seas (IESSNS) in July 2020. In total, 1374 individuals were caught, and only a subset of 225 were measured fresh at sea and 89 were frozen and dissected on land. Total lengths of fresh fish ranged from 38 to 85 mm, while dissected individuals ranged from 40 to 74 mm and were 2 to 6 years old. Located over the Reykjanes Ridge in the Iceland Basin region, individuals had a significantly higher mean standard length and mean age, and a lower mean body condition. We reported length-weight relationships for both fresh and frozen samples, indicating evidence that preserving of the specimens through freezing affected relationships. The von Bertalanffy growth curve was calculated along with significant otolith-fish size relationships where r 2 values ranged between 0.87 and 0.92. Our research highlights the importance of cross-regional studies and provides baseline biology for B. glaciale in Icelandic waters, specifically in the southern continental slope and Reykjanes Ridge.

Length-based assessment of penaeid shrimp fishery stocks along the north-eastern Arabian Sea

Penaeid shrimps are a key resource in marine fisheries and are of great ecological and economic importance. The north-west (NW) coast of India contributes significantly (~30%) to the penaeid shrimp landings in India. Four species of penaeid shrimps, namelyParapenaeopsis stylifera, Solenocera crassicornis, Metapenaeus affinis, and M. monoceros, were assessed using Length-based spawning potential ratio (SPR) based on the length frequency data collected during 2017-21, from commercial trawlers operating in the depth range of 20-100 m along the north-west coast of India bordering the north-eastern Arabian Sea. The current status (2021) of P. stylifera, S. crassicornis and M. affinis was found to be healthy, with a spawning potential ratio of ≥ 0.40. For M. monoceros, the SPR was slightly below 0.40 (0.34-35), however, considering the fast growth and short generation time for the resources, the stock status can be considered fair. Significant reduction in fishing pressure (F/M < 1.0) and increase in SPR (>0.40) during COVID-19 affected years (2020-21) were evident. The reduction in fishing hours during the pandemic has allowed the resource to regain the target reference point (TRP) for SPR. Declining catches over the past decade for the group are not due to resource depletion but for the shift in species preference and the diversification of trawls in the region, with bottom trawling giving way to pelagic trawling. Keywords: Sustainability, Spawning potential ratio, COVID-19, Penaeid shrimps

Extensive avoidance behaviour of krill from predators and nets

Abstract We used echosounders to assess krill (Meganyctiphanes norvegica) responses to sampling gear and predators. Towing pelagic trawls above autonomous submerged, upward-looking echosounders revealed instantaneous diving by the krill during daytime but not at night. The krill dived at 10–30 cm s−1 with a near-simultaneous response throughout the krill layer below the gear (>10 m). Traversing the paths of the previous sampling revealed long-lasting voids in the krill distribution during the daytime. Such voids were less apparent at night. Backscatter increased in the wake of the gear during nocturnal sampling, possibly due to changes in individual backscatter related to variation in swimming behaviour. During daytime, krill responded to fish schools with instantaneous coherent diving, spanning tens of meters at speeds of 10–27 cm s−1. Coordinated and far-ranging responses indicate that even loose krill aggregations may facilitate predator avoidance by enabling efficient signal transmission between individuals. The krill antipredator behaviour instigated marked daytime krill patchiness. Krill patchiness will vary relative to the predator regime and reflect recent encounters.

Under the Sea: Investigation of Telson Morphology and Cryptic Diversity within Eucopia sculpticauda, a Deep-Sea Lophogastrid from the Gulf of Mexico (Peracarida: Lophogastrida).

The field of phylogenetics employs a variety of methods and techniques to study the evolution of life across the planet. Understanding evolutionary relationships is crucial to enriching our understanding of how genes and organisms have evolved throughout time and how they could possibly evolve in the future. Eucopia sculpticauda Faxon, 1893 is a deep-water peracarid in the order Lophogastrida Boas, 1883, which can often be found in high abundances in pelagic trawls. The species can be found along the Mariana Trench, in the Mid-Atlantic Ridge, west Atlantic and east Pacific Oceans, and in the Gulf of Mexico and as deep as 7526 m. Recent collections of E. sculpticauda in the Gulf of Mexico have revealed putative cryptic diversity within the species based on both molecular and morphological evidence. Previous studies have documented two different morphotypes of the telson: the terminal part of the pleon (abdomen) and part of the tail fan. In adults, the morphotypes can be distinguished by lateral constrictions in the telson. This evidence, combined with a previous barcoding study, led to the speculation that telson morphology may be a distinguishing character useful to define cryptic diversity within E. sculpticauda. This study presents additional molecular data from the mitochondrial genes cytochrome c oxidase subunit I, and the large ribosomal subunit (16S), and the nuclear histone 3 gene (H3) to investigate telson morphotypes in relation to evolutionary history within this species. Molecular data identified two strongly supported clades, lending support for potential cryptic diversification within the Gulf of Mexico. Investigations into telson morphology suggest that this character may be informative, but the morphotypes were sometimes ambiguous and additional characters could not be found that discriminate clades. At present, our data suggest early evidence for cryptic diversification within Gulf of Mexico populations, but additional morphological characters and geographic sampling are needed before a new species can be described.

Climate damage from fishing the mesopelagic zone exceeds its economic benefits

Abstract Mesopelagic fish represent an opportunity for fishing companies and food production, but their exploitation carries substantial environmental risks related to these populations’ role in the oceanic carbon pump. We assess the economic viability of mesopelagic fishing from a private economic perspective, focusing on costs and revenues accruing to the fishing industry, and a public economic perspective, considering impacts on society at large, notably climate change. We develop a stylized model, which we apply to four pelagic trawling fleets in the European Union. We find that a mesopelagic fishery operated with current excess capacity in the four fleets considered is profitable from a private perspective, but the climate impacts potentially outweigh the private economic benefits. This implies that strict governance arrangements are needed to safeguard the sustainability of the mesopelagic zone. Considering long-term dynamics, we explore potential natural limits to an expanding mesopelagic fishery. First, a growing fishery will reduce biomass level, affecting profitability. Second, an increase in mesopelagic production may lower the price, also limiting potential for expansion. For the time being, however, it is unlikely that the fishery will reach a scale level where such feedbacks can be expected, making effective governance arrangements even more crucial.

Evaluating Pacific salmon swimming behavior in the aft end of a pelagic trawl to inform bycatch reduction device design and use

AbstractObjectiveAlthough the bycatch of Pacific salmon Oncorhynchus spp. is relatively low in the Walleye Pollock Gadus chalcogrammus and Pacific Hake Merluccius productus pelagic trawl fisheries, different efforts are employed to reduce it, including the use of bycatch reduction devices (BRDs) that retain the targeted species and provide Pacific salmon a pathway to escape. The objective of this study was to evaluate Pacific salmon behavior inside a pelagic trawl and to determine what conditions favor the probability of a salmon moving forward in the trawl and increase their probability of escapement.MethodsWe placed a video camera at the entrance of the cod end and recorded the behaviors of Pacific salmon as they passed by. The timing of the forward movement Pacific salmon in relation to fishing operations and the correlations between forward movement of Pacific salmon and vessel speed over ground, water flow rate, ambient light levels, and abundance of Walleye Pollock were examined.ResultOf the 2969 Pacific salmon observed, 71% were moving aft toward the cod end, 24% were observed moving forward, and 5% were moving aft then forward or forward then aft. The percentage (77%) and rate (0.86 fish per minute) of forward‐moving Pacific salmon was greatest once the trawl doors were back on the vessel and water flow within the trawl was reduced. Speed over ground and Walleye Pollock abundance were negatively correlated with forward movement of Pacific salmon. Only 6.5% of Pacific salmon that were in the cod end when fishing ended were able to move forward before the cod end was on the vessel.ConclusionPacific salmon can move forward in the trawl throughout fishing operations and haulback, but the percentage increases as the speed over ground and water flow inside the trawl is reduced. The low percentage of Pacific salmon that move forward after fishing has ended suggests that Pacific salmon escapement at the end of a tow is relatively low and suggests that BRD design should focus on stimulating escapement at the first BRD encounter.

Investigating the effects of pelagic trawling on the welfare of Atlantic herring (Clupea harengus)

The effects of pelagic trawling on the health and welfare of Atlantic herring (Clupea harengus L.) were investigated on a refrigerated seawater vessel operating in the North Sea. A total of 495 Atlantic herring (Clupea harengus L.) were sampled during five hauls from two fishing trips in September 2021 and 2022. For assessments of consciousness and mortality, a Reflex Action Mortality Predictor test (i.e. RAMP-test) was used on herring collected following trawling and pumping. Inspections for external and internal damage or wounds were performed via morphological welfare indicators and analyses of photos and radiographs. In addition, blood samples were taken and analysed for haematological indicators of stress. Following trawling and pumping, only 5% of the investigated herring showed signs of external wounds associated with the morphological indicators of welfare, and no internal damage was observed in the radiographic inspections. However, 96% of the assessed herring scored 0 on all three reflexes included in the RAMP-test and were therefore judged dead. On average, herring lost 95% of their scales, while 95% of herring had a very high degree of ruptured red blood cells (i.e. haemolysis). Extensive scale loss results in a deterioration of the skin's protective barrier function, which in turn impairs the osmoregulatory capacity of the herring. This was evident by elevated levels of plasma osmolality and circulating chloride concentrations, which could also likely explain the high occurrence of haemolysis in captured herring. Extended trawling time and larger catch size proved to be two important factors to consider, as the former led to increased plasma levels of osmolality, whereas the latter was associated with elevated plasma levels of lactate and cortisol. In conclusion, the high mortality appears to be influenced by a combination of factors such as severe stress, loss of osmoregulatory ability, crowding density within the trawl, and extended trawling times. This study provides important information on the welfare of wild Atlantic herring caught using pelagic trawls and highlights areas where improvements can be made to safeguard the welfare of fish captured in pelagic fisheries in the future.

Feeding Habits and Prey Composition of Six Mesopelagic Fish Species from an Isolated Central Mediterranean Basin

Mesopelagic fishes hold an important position in marine food webs, serving as a link between lower trophic levels and top predators and transferring energy from their deep mesopelagic habitat to shallower oceanic layers. Despite their ecological importance, research on mesopelagic fishes’ diet and feeding habits in the Mediterranean Sea is far from thorough. The present work attempts to assess the preying patterns and diet composition of four myctophid (Benthosema glaciale, Ceratoscopelus maderensis, Myctophum punctatum, Notoscopelus elongatus) and two sternoptychid (Argyropelecus hemigymnus, Maurolicus muelleri) species from the Corinthian Gulf (Ionian Sea, Greece), sampled during pelagic trawl surveys in 2018 and 2019. Stomach vacuity was high for myctophids caught during daytime, a pattern which sternoptychids did not follow. Estimated trophic indices revealed high dietary diversity (Shannon’s H’ index) for most investigated species, but a narrow trophic niche breadth (Levins’ normalized Bn index). Copepods and various marine crustaceans were dominant in all diets, classifying them under the zooplanktivorous trophic guild, while A. hemigymnus exhibited high concentrations of particulate organic matter in their stomachs and N. elongatus exhibited consumption of fish. Diet overlap was significant among most studied mesopelagic species, as indicated by Shoener’s S index and confirmed by both the multidimensional scaling ordination and a hierarchical cluster analysis. Information on mesopelagic fishes’ diet composition in this poorly studied part of the Mediterranean is useful in further assessing and parameterizing marine food webs and midwater trophic interactions, as well as in quantifying the ensued energy transfer to top predators of commercial interest or conservation concerns.

The impact of oceanographic factors on the composition and abundance of mesopelagic fish communities in the central and equatorial Atlantic

This paper presents an overview of the composition and abundance of pelagic fish communities collected during the 43rd cruise of the R/V ′Akademik Sergey Vavilov' on the transect in the central Atlantic, from the Azores to the Equator, in autumn 2016. Samples were taken only at night with a Samyshev-Aseev modified Isaacs-Kidd non-closing midwater pelagic trawl (SAMT) at 18 stations from two depth of 0–200 and 0–700 m. The study recorded 112 species of juvenile and adult mesopelagic fishes belonging to 20 families at the sampled stations. The statistical analysis indicated notable disparities in the fish communities that were caught at depths of 0–200 and 0–700 m. Our study suggests that there are notable differences in pelagic fish associations between the North Atlantic anticyclonic gyre zone and the equatorial jets region, at both depths analyzed. These differences are most likely the result of variations in hydro-physical and other environmental parameters. It has been observed that deep-sea fish communities in the equatorial and central North Atlantic are capable of inhabiting at the same time multiple habitats that exhibit varying physical and chemical structures of water masses. This phenomenon highlights the remarkable ecological adaptability of the species that make up mesopelagic deep-sea communities, as well as their wide geographical distribution. The higher abundance and diversity of mesopelagic fishes observed at stations located above the Mid-Atlantic Ridge may be due to a general decrease in depth over the ridge compared to the surrounding regions and/or local circulations occurring over its crests. Thus, the tops and slopes of seamounts may become unique concentrations of mesopelagic fishes for a limited time due to their topography.

Using low volume eDNA methods to sample pelagic marine animal assemblages.

Environmental DNA (eDNA) is an increasingly useful method for detecting pelagic animals in the ocean but typically requires large water volumes to sample diverse assemblages. Ship-based pelagic sampling programs that could implement eDNA methods generally have restrictive water budgets. Studies that quantify how eDNA methods perform on low water volumes in the ocean are limited, especially in deep-sea habitats with low animal biomass and poorly described species assemblages. Using 12S rRNA and COI gene primers, we quantified assemblages comprised of micronekton, coastal forage fishes, and zooplankton from low volume eDNA seawater samples (n = 436, 380-1800 mL) collected at depths of 0-2200 m in the southern California Current. We compared diversity in eDNA samples to concurrently collected pelagic trawl samples (n = 27), detecting a higher diversity of vertebrate and invertebrate groups in the eDNA samples. Differences in assemblage composition could be explained by variability in size-selectivity among methods and DNA primer suitability across taxonomic groups. The number of reads and amplicon sequences variants (ASVs) did not vary substantially among shallow (<200 m) and deep samples (>600 m), but the proportion of invertebrate ASVs that could be assigned a species-level identification decreased with sampling depth. Using hierarchical clustering, we resolved horizontal and vertical variability in marine animal assemblages from samples characterized by a relatively low diversity of ecologically important species. Low volume eDNA samples will quantify greater taxonomic diversity as reference libraries, especially for deep-dwelling invertebrate species, continue to expand.

Situation of Offenses Observed in Maritime Fishing and Proposal for Measures to Improve the Surveillance System: Case of the National Fisheries Surveillance and Police Center (CNSP) in Guinea

Research work on the theme “Situation of offenses observed in maritime fishing and proposal for measures to improve the surveillance system: case of the National Fisheries Surveillance and Police Center (CNSP) in Guinea » Conakry took place in the period from September 14 to December 14, 2022 inclusive. The objective of this work was to take stock of the offenses recorded in fishing with a view to proposing solutions for improving the surveillance system. To achieve this objective, the following methodology was adopted: consultation of executives and exploitation of archives; survey of surveillance agents; identification and descriptions of the surveillance system; identification of the offenses and fleet involved in the Guinean EEZ in recent years; determination and classification of the causes of offenses; evaluation of the surveillance system; proposal for improved measures of the surveillance system. Monitoring of this approach revealed that: the offenses committed in the Guinean EEZ are related to the fishing gear used; administrative documents and fishing operation zones. According to records, for the period from 2006 to 2021, there were 308 boardings. The rate of infringements in IP is 59%, 25% in PAM and 16% in PSI. The flags which have committed more IP infringements are Chinese 86 and Korean 60; in PSI the Chinese 17 and the Senegalese 16 and in PAM the Guineans 33, Senegalese 23 and the Leonese 18. The stakeholder survey revealed that the number of vessels monitored by VMS in 2021 was 79 in PI and 49 in PSI. The main documents inspected at sea are generally: registration certificates, crew, rescue equipment, gross tonnage, coastal state fishing authorization, maritime radio license. The fleets involved in the infringements in the Guinean EEZ from 2006 to 2022 numbered 135 including 80 demersal trawlers, 7 cephalopod boats, 21 shrimp boats, 22 pelagic trawlers and 5 cargo ships. The improvement of the surveillance system in Guinea may be more efficient, incombining the AIS and VMS system in fisheries surveillance, by creating a marking system for fishing gear, by purchasing very powerful launches and maintaining the confidentiality of patrol operations.

Biodiversity of Gelatinous Organisms in the Western Adriatic Sea and Identification of Their Echo Traces in Acoustic Data

The abundance of gelatinous organisms, such as salps and jellyfish, in the Adriatic Sea has significantly increased over the past decade. Environmental factors play a key role in driving this shift in abundance through rising temperatures and a consequent decrease in oxygen levels in the water, for which jellyfish have higher tolerance levels. Additionally, fisheries may contribute to the proliferation of jellyfish by diminishing their natural predators and food competitors. Pelagic trawl catch data from 2015 to 2023 acquired during MEDIAS acoustic surveys in the western Adriatic Sea were reviewed to extract information concerning the abundance and distribution of salps and jellyfish. These data were subsequently analyzed and compared with satellite environmental information to identify potential correlations. When considering environmental information related to the month of the survey, the results show two significant relationships: one between the abundance of Aequorea aequorea and average salinity and another one between the abundance of Rhizostoma pulmo and bottom temperature. Furthermore, when considering environmental data from the month preceding the survey, a relationship between the overall abundance of gelatinous organisms, salps and jellyfish together, and surface temperature was identified. Additionally, an analysis was conducted on specific hauls that almost exclusively yielded jellyfish, with the aim of identifying their echo traces. Although it was not possible to allocate one jellyfish species to a specific echo trace due to the frequent co-occurrence of more than one species, a general indication of typical backscatter for these species, with a higher response at 70 kHz, was consistently observed in all cases examined.

Summer Biomass Variability and Spatial Interactions between European Sprat (Sprattus sprattus) and Moon Jellyfish (Aurelia aurita) in the Western Part of the Black Sea

Over the past few decades, various causal connections between commercial small pelagic fish species and gelatinous zooplankton have been reported in the Black Sea, which affect the pelagic ecosystem. Recently, moon jellyfish regained dominance among gelatinous plankton; however, biomass fluctuations and interactions with small pelagic fish remain poorly understood. During the summers of 2019–2022, scientific pelagic trawl surveys in the Western Black Sea enabled simultaneous monitoring of small pelagic fish biomass, with sprat as the key species and moon jellyfish as an incidental catch. In total, 153 trawl hauls were conducted across four depth strata from 15 to 100 m, and a “swept area” method was used for biomass estimation. The sprat stock biomass ranged from 10,698 to 29,177 t, with an average value of 19,432 ± 4834 t. The total biomass of moon jellyfish was 2002 ± 868.73 t, and dense aggregations were observed in the coastal waters during certain years. Two scenarios of spatial interactions between planktivorous species were identified and linked to the formation of A. aurita aggregations. We found that changes in jellyfish density were associated with weak-to-moderate effects on the spatial distribution of sprat assemblages in coastal areas.

Biological information on a rare pelagic fish, black ruff Centrolophus niger, caught in Icelandic waters: Distribution, feeding, and otoliths.

Black ruff (Centrolophus niger) is a rare and poorly studied species found in both the Atlantic and Pacific Oceans and also in the Mediterranean Sea. It is sporadically caught south of Iceland during the annual International Ecosystem Summer Survey of the Nordic Seas. In total, 43 specimens were caught from 2009 to 2021, of which 41 specimens were caught during 2017-2021. All specimens, except one, were caught using a pelagic trawl (cod-end mesh-size: 50 mm) close to the surface (trawl depth: 0-35 m) with in situ temperature ranging from 9 to 13°C. The area south of Iceland is characterized by having warmer temperatures than other areas around the island, which might be indicative of a northern limit for the distribution of black ruff. The fish were primarily in the range of 29-46 cm with a few larger individuals up to 71 cm. Fourteen fish, caught in 2017 and 2021, were dissected to gather biological information on this species. These fish were all juveniles with no obvious sign of gonad development. Correlations between total length, fork length, and standard length are presented. Otoliths were thin and delicate with a length of ~13-16 mm, and otolith size (length, width, and area) was correlated with fish size. Much of the stomach content was at an advanced stage of digestion, but some contents could be identified and consisted of invertebrates, primarily of the orders Amphipoda and Calanoida with some unidentified fish also present.

Development of approaches to regulation of flatfish fishery in the West Bering Sea zone

It is demonstrated based on results of bottom trawl surveys, that basis of flatfish resource in the West Bering Sea zone is formed by flathead sole, Alaska plaice and northern rock sole, respectively 40.3, 35.1 and 19.6% in the total flatfish biomass averaged for the period 2000–2021. Almost three quarters of the estimated flatfish stock of the zone are within the Anadyr Gulf. In 2001–2021 the stock was relatively stable and demonstrated a slight trend to growth. Estimates of the total biomass increased from 153 thous. t in 2001 to 230–305 thous. t in 2020–2021. The analysis of the current flatfish fishery showed that the major contribution to annual catches is made by the specialized fishery by bottom trawls – 39.4% and by Danish seines – 25.4%, and about 12.8% is taken as by-catch in the walleye pollock fishery by pelagic trawls. About 77.1% of the annual catches of flatfish reported in the West Bering Sea zone are taken from 169°E in Olutor Based on the analysis of the annual flatfish catch by different types of fishery, species composition of the catches and seasonal catch dynamics, the average proportion of northern rock sole in the total annual catches was about 53.1%. It is shown, that stocks of northern rock sole in this area bear the main fishing load, and Alaska plaice and flathead sole are not developed in full. Optimal scheme of the flatfish TAC assessment for the West Bering Sea zone is developed. It includes calculation of commercial biomass of northern rock sole by cohort methods, development of its fishery regulation rule, the TAC assessment based on this rule and assessment of possible by-catch of “minor” flatfish species based on their long-term proportional contribution into the catches.

Определение промысловой годности траулеров по тяговым характеристикам

The article considers the problems of the Russian fishing fleet. The trawlers whose age exceeds thirty years are actively operating along with commissioning of the new fishing vessels. Over such a long service life, they lose the necessary traction force due to the increased resistance of the hull and wear of the propulsion system. The possibility of rapid assessment of the traction characteristics of the vessel has been illustrated on the example of a large trawler-freezer type “Pulkovo meridian” project 1288, which has been in use since 1982. The dependence of the ship loss of traction on the voyage time was derived as well. Moreover, there is proposed a method for reducing the hydrodynamic resistance of the trawl system by replacing nylon mesh panels of a trawl’s net part with mesh panels of a smaller tie diameter made of modern high-strength materials. In preparation for the fishing voyage, it is necessary to store up consumables for trawl repairing, so if the fishing vessel-trawl is properly operated, such net sheets should be included in the consolidated list of materials. Numerical examples of the method are given here as well. As a result of applying this method, substituting the panels of the net part with a mesh pitch of 1 200 and 800 mm of the pelagic trawl P-K-120/1120 for the mesh panels made of high-strength Dyneema material can reduce the hydrodynamic resistance of the trawl by 1.3 times. The proposed methodology for determining a trawler’s commercial viability and correcting the hydrodynamically heavy fishing gear should solve the problem of the optimal correlation between the propulsion of a vessel and the hydrodynamic resistance of a trawl quickly, in the process of fishing by a crew of a vessel. The proposed methodologies would help avoid high main engine maintenance costs, operating a trawl that is not in line with the technical condition of the trawler or reduce fishing shortfalls of a smaller trawl.

The nocturnal distribution of deep-pelagic fish on the continental slope of the Bay of Biscay

The biomass of deep-sea pelagic fishes could represent more than 90% of the total fish biomass on earth, which represents an important potential for exploitation. However, this community plays multiple key ecological roles in biogeochemical cycles and food webs. Information on their ecology and function is needed to plan effective sustainable conservation measures. In particular, the distribution of deep-sea pelagic fish biomass and the environmental factors that control it remain poorly understood on slope areas at the interface of coastal and oceanic habitats. The combined use of biological data collected by pelagic trawling between 20 and 2000 m depth at night and 16 environmental variables allowed us to study the distribution of this community on the continental slope of the Bay of Biscay, NE Atlantic. Multivariate regression tree analysis suggested that immersion depth was the most important variable structuring this community by night, defining four depth assemblages with different indicator species (i.e. organisms whose presence, absence, or biomass reflects specific environmental conditions): the epipelagic (20–175 m), the upper mesopelagic (175–700 m), the lower mesopelagic (700–1000 m) and the bathypelagic assemblage (1000–2000 m). The use of generalized additive models indicated a positive relationship between bottom proximity and biomass for three of the four assemblages. This contrasts with the paradigm in open ocean areas where the biomass of meso- and bathypelagic fishes decreases with depth. The echograms also showed low acoustic detection at the surface at night, which differs from the open ocean models where nocturnal migration results in a high density of mesopelagic organisms in the epipelagic layer. Different mechanisms could explain this relationship, such as the concentration of food resources in the benthic boundary layer, an ontogenetic change of some species, active horizontal migration, or a demersal spawning behavior. This specific distribution on the continental slope may influence the transition of carbon and energy flows within this ecosystem located in a Special Area of Conservation (SAC).

First descriptions of diurnal pelagic aggregations of the Argentine red shrimp (Pleoticus muelleri) using a broadband echosounder operating at multiple frequencies

This is the first description of diurnal pelagic aggregations of the bottom-dwelling Argentine red shrimp (Pleoticus muelleri) registered with a broadband scientific echosounder. A pelagic trawl net and an underwater video camera were used to validate all the information presented in this paper. Shrimp aggregations were characterized by increasing frequency response, more evident at frequencies greater than 120 kHz. Identification of the acoustic signature of this resource is of particular interest for the development of new methodologies to complement the traditional swept area method of estimation.