Pair Trawl Research Articles

An evaluation of the cetacean bycatch monitoring programme on board the Spanish set gillnet and bottom pair trawl fleets in the Bay of Biscay

Abstract Bycatch of cetaceans by European Union (EU) fleets is mostly monitored by onboard observers under the EU Data Collection Framework (DCF) programme. There is concern that the resulting estimates of cetacean bycatch mortality are biased and imprecise, because bycatch events are rare, sampling coverage is limited, and DCF observers prioritize the sampling of the discard of commercial species. Here, we explore the utility of the recently established Spanish cetacean bycatch monitoring programme to estimate cetacean bycatch mortality and compare it to the EU DCF programme. Data from October 2020 to September 2021 from this new Spanish programme were analysed to explore the following issues: (i) representativeness of the sampling frame; (ii) estimation of bycatch per unit of effort (BPUE); and (iii) sampling coverage. The probabilistic sampling design of the programme, with a record of refusals, has allowed identification and correction of biases in BPUE estimation. BPUE estimates for the bottom pair trawl fleet were recalculated to account for the fact that although boats work in pairs, each pair is monitored by a single observer located in a single boat. In relation to the sampling coverage, our results point to a need for levels up to 31% to achieve statistically robust bycatch rates. The current Spanish EU DCF at-sea sampling programme (which includes the sampling of bycatch of non-target protected species) and the Spanish (dedicated) cetacean bycatch monitoring programme provided similar results on cetacean bycatch for some of the ICES Divisions and Metiers monitored but sampling coverage of both is insufficient to obtain robust estimates.

At sea mortality estimates of loggerhead turtle (Caretta caretta) in Southwestern Atlantic Ocean

Sea turtles are vulnerable to various threats, with incidental capture in fisheries being a main concern. Limited knowledge exists regarding sea turtle mortality at sea, and stranding events serve as an indicator of such mortality. However, stranding data only represent a fraction of the turtles killed in the ocean. The southern coast of Brazil is an important foraging area for loggerhead turtles. This study aimed to estimate loggerhead turtle mortality at sea in southern Brazil using stranding data. Between 2012 and 2016, a total of 70 incidentally caught and dead turtles in pair trawl fisheries were tagged and released back into the sea, with the recording of date and geographic position. Biweekly beach surveys were conducted in an effort to retrieve these carcasses. Bayesian logistic regression models were employed to assess the influence of meteoceanographic and geographic variables on the stranding probabilities of tagged turtles. Considering the total number of stranded loggerhead turtles in the study area and the predicted stranding probabilities, the annual mortality of the species at sea was estimated. Season, distance from the shore, and currents were identified as variables influencing the stranding probability. The stranding probability was 19.72 % for the warm period and 12.96 % for the cold period. A total of 1897 loggerhead turtles stranded between 2012 and 2016. The estimated mortality during this period was 14,377 loggerhead turtles killed. This high mortality can have a substantial impact on the population, thus conservation measures that effectively protect sea turtles are in urgent need.

Cumulative ecosystem pressures exerted by demersal fisheries in the Brazilian Meridional Margin: Hotspots and refuges

Demersal fishing operations exert, cumulatively, at least three forms of pressures over the benthic environment: mortality of megafauna (landed and discarded), discards of carrion back to the marine environment (also referred to as Predictable Anthropogenic Food Subsidies - PAFS) and disturbance of the seabed, by contact with bottom gear. This study presents a spatial synthesis of these forms of pressure on the Brazilian Meridional Margin (BMM, SW Atlantic) and their accumulated effect, in contribution to the development of effective space-based fishing management strategies. We analyzed landed catch, discards and effort of 2,125 fishing trips of industrial vessels operating double-rig trawlers, pair trawlers, stern trawlers, bottom longline and gillnets, monitored during 2018 in the main fishing harbors of Southern and Southeastern Brazil. All forms of pressure and the Accumulated Pressure Index (API) were represented spatially in a 20 × 20 nautical mile quads mesh grid. We demonstrated that nearly half of the BMM area was under high pressure. We also delimited fishing pressure hotspots in coastal and shelf areas mostly within the ‘Brazilian Bight’ region, between São Paulo and Santa Catarina states (24–29°S). Conversely, slope regions were found to be less demanded by demersal fishing, with both benthic ecosystems and demersal populations being barely disturbed. These were regarded as the main refuge areas for benthic and benthopelagic megafauna. Double-rig trawling was a major driver of pressure accumulating over half of total number of demersal fishing trips in 2018. Individual double-rig trawling operations also disturbed a seabed area far greater than the areas disturbed by the other fishing gear, and discarded the largest fraction (∼48%) of the produced mortality. Reducing the demersal fishing pressure on the BMM seems to be primarily concerned with abating the intensity of double-rig trawling, and/or diluting their effect through spatial management measures.

SFA를 이용한 근해어업의 온실가스 배출 효율성 및 감축잠재량 추정

The purpose of this study is to estimate greenhouse gas(GHG) emission efficiency(GEE) and GHG mitigation potential(GMP) of offshore fisheries in preparation for carbon neutral and negative promotion in the ocean and fisheries sector, and to suggest policy improvements related to GHG mitigation. To this end, this study used stochastic frontier analysis(SFA) considering exogenous determinants of GHG emission inefficiency. As a result, the GEE of fleet and drag net fisheries with high fuel cost and vessel age was lower than other fisheries. In addition, the GMP and mitigation ratio of large purse seine, large pair trawl, large otter trawl, and anchovy drag net were higher than those of other fisheries. Lastly, as policy improvements to reduce GHG emission from offshore fisheries, fleet size reduction, development of low-energy used fishing gear, easing of conditions for participation in fishing vessel modernization projects, revising laws to supply eco-friendly fishing vessel, and improvement of the tax-free petroleum supply system were proposed.

Comparative trophic ecology of two sympatric guitarfishes Pseudobatos (Chondrichthyes, Rhinobatidae) from Southeast Brazil, southwestern Atlantic.

The present study compares the trophic ecology of two guitarfishes (Pseudobatos percellens and Pseudobatos horkelii) from the continental shelf of the São Paulo State, Brazil, caught by the bottom pair trawls between 2007 and 2009. These two sympatric species are under different threat categories, "Vulnerable" and "Critically Endangered," respectively, according to Brazilian agencies. Thus, any study considering trophic ecology parameters is pivotal in understanding the trophic ecology role of such species in the ecosystem. The authors analysed 500 stomachs of P. percellens and 108 of P. horkelii, quantifying with dietary indexes: numerical (%N), gravimetric (%W), frequency of occurrence (%FO) and the prey-specific index of relative importance (%PSIRI). For P. percellens and P. horkelii, 26 and 14 different prey items were found, respectively. Crustacea and Teleostei were the most important prey items for both species, indicating a specialist feeding behaviour due to their low niche amplitude. The results provide evidence related to ontogenetic dietary shift in P. percellens and individual-level diet specialization in both species. These two benthic-demersal elasmobranchs are important mesopredators (3,7 for P. percellens, and 3,5 for P. horkelii) in the study area, with high trophic-level values.

Energy audit and carbon footprint in trawl fisheries

The combustion of fossil fuels is considered a major cause of climate change, which is why the reduction of emissions has become a key goal of the Paris climate agreement. Coherent monitoring of the energy profile of fishing vessels through an energy audit can effectively identify sources of inefficiency, allowing for the deployment of well-informed and cost-efficient remedial interventions. We applied energy audits to a test fleet of ten vessels, representing three typical Mediterranean trawl fisheries: midwater pair trawl, bottom otter trawl, and Rapido beam trawl. Overall, these fisheries use approximately 2.9 litres of fuel per kilogram of landed fish, but the fuel consumption rate varies widely according to gear type and vessel size. This amount of fuel burned from capture to landing generates approximately 7.6 kg∙CO2/kg fish on average. Minimising impacts and energy consumption throughout the product chain may be another essential element needed to reduce the environmental costs of fishing. Our results provided a set of recognised benchmarks that can be used for monitoring progress in this field.

A 14-year time series of marine megafauna bycatch in the Italian midwater pair trawl fishery

Fisheries bycatch is recognised as a global threat to vulnerable marine megafauna and historical data can contribute to quantify the magnitude of the impact. Here, we present a collection of three datasets generated between 2006 and 2019 by a monitoring programme on marine megafauna bycatch in one of the main Italian fisheries, the northern central Adriatic midwater pair trawl fishery. The three datasets consist of: (i) monitored fishing effort; (ii) bycatch and biological data of dolphins, sea turtles and elasmobranchs; (iii) and dolphin sightings. Some information included in these datasets has already proved to provide a unique opportunity to estimate total incidental capture of species of conservation concern and trends of their relative abundance over time in the northern - central Adriatic Sea. These datasets are expected to be considered by different end users to improve the conservation of species and fishery management approaches to assess the impact of a fishery on species of conservation concern.

Length–weight relationships for six elasmobranch species from the Adriatic Sea

Length–weight relationships were observed for six elasmobranch species from the Adriatic Sea. Between 2006 and 2019, data on weight and total length were collected for three shark species Alopias vulpinus, Mustelus mustelus, Mustelus punctulatus; and data on weight and disk width were collected for three batoid species Aetomylaeus bovinus, Myliobatis aquila, Pteroplatytrygon violacea. Data collection comes from monthly observations as part of a monitoring program targeting specifically bycatch on pelagic pair trawlers involved in anchovy and sardine fishing. This fishery operates using pelagic trawls with a minimum mesh size opening of 20 mm. All elasmobranchs were measured to the nearest cm using a measuring board and weighed to the nearest gram using an electronic scale or a dynamometer for the largest specimens. A linear regression analysis performed on log-transformed data was used to estimate intercept and slope, and to describe the length–weight relationship for each species.

Estimating Bycatch From Non-representative Samples (II): A Case Study of Pair Trawlers and Common Dolphins in the Bay of Biscay

Marine megafauna plays an important functional role in marine ecosystems as top predators but are threatened by a wide range of anthropogenic activities. Bycatch, the incidental capture of non-targeted species in commercial and recreational fisheries, is of particular concern for small cetacean species, such as dolphins and porpoises. In the North-East Atlantic, common dolphin (Delphinus delphis, Linné 1758) bycatch has been increasing and associated with large numbers of animals stranding during winter on the French Atlantic seashore since at least 2017. However, uncertainties around the true magnitude of common dolphin bycatch and the fisheries involved have led to delays in the implementation of mitigation measures. Current data collection on dolphin bycatch in France is with non-dedicated observers deployed on vessels for the purpose of national fisheries sampling programmes. These data cannot be assumed representative of the whole fisheries' bycatch events. This feature makes it difficult to use classic ratio estimators since they require a truly randomised sample of the fishery by dedicated observers. We applied a newly developed approach, regularised multilevel regression with post-stratification, to estimate total bycatch from unrepresentative samples and total fishing effort. The latter is needed for post-stratification and the former is analysed in a Bayesian framework with multilevel regression to regularise and better predict bycatch risk. We estimated the number of bycaught dolphins for each week and 10 International Council for the Exploration of the Sea (ICES) divisions from 2004 to 2020 by estimating jointly bycatch risk, haul duration, and the number of hauls per days at sea (DaS). Bycatch risk in pair trawlers flying the French flag was the highest in winter 2017 and 2019 and was associated with the longest haul durations. ICES divisions 8.a and 8.b (shelf part of the Bay of Biscay) were estimated to have the highest common dolphin bycatch. Our results were consistent with independent estimates of common dolphin bycatch from strandings. Our method show cases how non-representative observer data can nevertheless be analysed to estimate fishing duration, bycatch risk and, ultimately, the number of bycaught dolphins. These weekly-estimates improve upon current knowledge of the nature of common dolphin bycatch and can be used to inform management and policy decisions at a finer spatio-temporal scale than has been possible to date. Our results suggest that limiting haul duration, especially in winter, could serve as an effective mitigation strategy.

An assessment of discarded catches from the bottom pair trawling fishery in southern Brazil

Onboard discards of a fraction of the catch can be considered one of the main issues related to bottom trawling fisheries. The magnitude and composition of the discards still need to be better understood. We assessed the industrial bottom pair trawling fishery’s discards from southern Brazil by monitoring 159 fishing hauls during four fishing trips. From the 318.9 mt captured, 77.7 t were discarded (24%). The discards per haul were highly variable, on average 488.9 kg (95% CI: 433.6-544.2 kg) and 31% (95% CI 28-34%) of the total. The rejected catch comprised 64 species, 37 teleosts (78.4% in weight) and 13 elasmobranchs (21.3% in weight), besides crustaceans, mollusks, cnidarians, and echinoderms. The three most commercially important species in the region (Umbrina canosai, Cynoscion guatucupa, and Micropogonias furnieri) accounted for 13% of the discarded biomass, and most of them were individuals under 20-25 cm. The discard rates and species composition did not change over the last 40 years; however, the discarded biomass for both teleost fishes and elasmobranchs decreased sharply, reflecting the abundance decrease of these groups in the region. This work highlights the need for management measures to reduce the bottom pair trawling fishery discards in southern Brazil.

Identifying partners at sea from joint movement metrics of pelagic pair trawlers

Abstract Here, we present an approach to identify partners at sea based on fishing track analysis, and describe this behaviour in several fleets: pelagic pair trawlers, large and small bottom otter trawlers, mid-water otter trawlers, all in the North-East Atlantic Ocean, anchovy purse-seiners in the South-East Pacific Ocean, and tuna purse-seiners in the western Indian Ocean. This type of behaviour is known to exist within pair trawlers, since these vessels are in pairs at least during their fishing operations. To identify partners at sea, we used a heuristic approach based on joint-movement metrics computed from vessel monitoring system data and Gaussian mixture models. The models were fitted to joint-movement metrics of the pelagic pair trawlers, and subsequently used to identify partners at sea in other fleets. We found partners at sea in all of the fleets except for the tuna purse-seiners. We then analysed the connections between vessels and identified exclusive partners. Exclusiveness was more common in pelagic pair trawlers and small bottom otter trawlers, with 82% and 74% of the vessels involved in partnerships having exclusive partners. This work shows that there are collective tactics at least at a pairwise level in diverse fisheries in the world.

Flume tank testing, computer simulation and full-scale sea trials of a modified bottom trawl made of ultra-high-molecular-weight polyethylene twine for pair trawl fishery off Shimane Prefecture

島根県沖合底びき網漁業を対象として，現用網の袖網および身網の一部に超高分子量ポリエチレン繊維製網地を導入して網糸直径を細くした改良網1，さらに天井部の目合を拡大した改良網2について，模型実験と数値解析によって抵抗削減効果を推定した。現用網から改良網2に変更することで網抵抗は29.6％，網抵抗と海底との摩擦抵抗の合計は9.9％減少し，網形状はほとんど変化しないと考えられた。実物網を用いた海上実験では，通常の曳網速力3ノットで改良網2では現用網と比べてハンドロープ張力が19.3％減少した。

In the Wrong Place at the Wrong Time: Identifying Spatiotemporal Co-occurrence of Bycaught Common Dolphins and Fisheries in the Bay of Biscay (NE Atlantic) From 2010 to 2019

The first Unusual Mortality Event (UME) related to fishing activity along the Atlantic coast recorded by the French Stranding Network was in 1989: 697 small delphinids, mostly common dolphins, washed ashore, most of them with evidence of having been bycaught. Since then, UMEs of common dolphins have been observed nearly every year in the Bay of Biscay; unprecedented records were broken every year since 2016. The low and unequally distributed observation efforts aboard fishing vessels in the Bay of Biscay, as well as the lack of data on foreign fisheries necessitated the use of complementary data (such as stranding data) to elucidate the involvement of fisheries in dolphin bycatch. The aim of this work was to identify positive spatial and temporal correlations between the likely origins of bycaught stranded common dolphins (estimated from a mechanistic drift model) and fishing effort statistics inferred from Vessel Monitoring System (VMS) data on vessels >12 m long. Fisheries whose effort correlated positively with dolphin mortality areas after 2016 included French midwater trawlers, French Danish seiners, French gillnetters, French trammel netters, Spanish bottom trawlers, and Spanish gillnetters. For the French fleet only, logbook declarations, sales, and surveys carried out by Ifremer were integrated into fishing effort data. Six fleets were active in common dolphin bycatch areas at least twice between 2016 and 2019: gillnetters fishing hake, trammel netters fishing anglerfish, bottom pair trawlers fishing hake, midwater pair trawlers fishing sea bass and hake, and Danish seiners fishing whiting. Except for changes in hake landings in some fisheries, there were no notable changes in total fishing effort practice (gear or target species) based on the data required by the ICES and Council of the European Union that could explain the large increase in stranded common dolphins recorded along the French Atlantic coast after 2016. Small scale or unrecorded changes could have modified interactions between common dolphins and fisheries, but could not be detected through mandatory data-calls. The recent increase in strandings of bycaught common dolphins could have been caused by changes in their distribution and/or ecology, or changes in fishery practices that were undetectable through available data.

Обоснование основных параметров близнецовой траловой системы для судов малого и среднего классов

Materials are presented on the comparative effectiveness of fishing gear used to catch the Pacific sardine and mackerel in the northwestern part of the Pacific Ocean. It has been shown that the efficiency of catch of Pacific sardine by the pair trawl is 3.5–4.8 times higher than fishing by pelagic trawls. When catch mackerel, the picture is the opposite: pair trawl fishing efficiency is 3.0–8.9 times lower than fishing indices with pelagic trawls. This state of affairs indicates the need to improve the technique and tactics of catch of moving fish with pair trawls, which involves substantiating the operating parameters of the pair trawl system in accordance with the energy capabilities of fishing vessels of various tonnage and developing proposals for improving the equipping of the pair trawl system for fishing vessels of small and middle classes. The parameters of pair trawls are theoretically substantiated and a technical proposal has been developed for equipping a pelagic trawl with a net insert, which reduces the likelihood of fish leaving the catch zone under the footrope of pelagic trawl.

Bottlenose dolphins (Tursiops truncatus) in the north‐western Adriatic Sea: Spatial distribution and effects of trawling

Abstract Many species and populations of odontocetes have modified their behaviour to take advantage of feeding opportunities provided by fishing activities, with depredation of fishing gear being the most common type of adaptation. The northern Adriatic Sea has been identified as an important marine mammal area because of a regular occurrence of common bottlenose dolphins. Boat surveys were conducted within a 3,000 km2 sector of the Adriatic Sea off the coast of Veneto, Italy, between April and October 2018–2019. Based on 76 days at sea, 10,711 km of navigation, and 81 h 26 min of dolphin tracking, this study contributes novel quantitative information on dolphin spatial distribution, and on their occurrence in the wake of beam trawlers, otter trawlers, and midwater pair trawlers. A combined generalized additive model and generalized estimation equation framework indicated that trawling—along with other physiographic, biological and anthropogenic variables—influenced dolphin distribution. In days of trawling, the chance of encountering dolphins increased by ~4.5 times (95% confidence interval 1.8–11.0) near active beam trawlers, by ~16.0 times (7.1–36.0) near otter trawlers, and by ~28.9 times (12.0–69.6) near midwater pair trawlers. Spatial modelling was used to create maps of predicted distribution, suggesting differences in habitat use between trawling and no‐trawling days. Spatial modelling for all days identified a dolphin distribution hotspot of 832 km2, situated off the Po river delta. Evidence contributed by this study can be used to inform management action within one of the world's areas most heavily impacted by fishing and other human encroachment. Such management action would help enforce the European Union's Habitats Directive and Marine Strategy Framework Directive, while also informing EU's Maritime Spatial Planning.

Temporal and spatial patterns of trawl fishing activities in the Adriatic Sea (Central Mediterranean Sea, GSA17)

Trawl fishing activities have occurred for centuries on large spatial scale in the entire Mediterranean Sea, and today they are considered as one of the main and widespread causes of anthropogenic disturbance and habitat alteration in the marine environment. In order to delineate when, where and how marine ecosystems have been perturbed and to implement ecosystem-based management strategies, the identification and investigation of the spatial and temporal distribution of fishing effort and the fleet dynamics play a key role. In this context, Geospatial Technologies such as the Automatic Identification System (AIS) could represent a useful tool. The aim of the present work is to reconstruct spatial and temporal patterns of the trawl fishing activities in the Northern and Central Adriatic Sea (GSA17), by using AIS data. High-resolution maps of fishing effort per fishing gear allowed us to identify the main fishing grounds and seasonal variations, for the small and large trawlers, but also for the Rapido and mid-water pair trawlers, during the period 2015–2016. Moreover, the effects of the closure of the Pomo Pit in terms of fishing effort redistribution and possible effects of the enlargement of the ban for trawling to the 3–6 nm area have been explored. Obtained results highlighted the importance to take into account the spatial and temporal dynamics of the fishing effort within the context of the implementation of an ecosystem approach management in the study area.

Trophic overlap between marine mammals and fisheries in subtropical waters in the western South Atlantic

Marine mammals and humans are apex predators and both may compete for fish in ecosystems under continuous fishing pressure. We assessed the degree of trophic overlap between prey species found in the diet of 5 marine mammals (39 specimens of sea lion Otaria flavescens, 61 fur seals Arctocephalus australis, 76 franciscana dolphins Pontoporia blainvillei, 25 bottlenose dolphins Tursiops truncatus and 28 Lahille’s bottlenose dolphins T. gephyreus) and the catches of the 6 main commercial fishing gears used in southern Brazil (coastal gillnets, oceanic gillnets, purse seine, demersal pair trawling, bottom [single] trawl and double-rig trawling) between 1993 and 2016. An adjusted general overlap index indicated an overall moderate to high overlap. Specific overlap analysis showed that O. flavescens and T. truncatus presented high trophic relationships with fisheries, followed by T. gephyreus. Smaller interactions were observed for A. australis and P. blainvillei, even though they also exploit commercial fishing resources. Coastal gillnet and pair bottom trawling are the fisheries that most target the fish species favoured by O. flavescens, T. gephyreus and T. truncatus. The information presented in this study on trophic interactions may assist decision making for both fishery management and conservation measures for these apex predators. Commercial fishing activities are a major threat to marine mammals both regionally and globally. Current levels of fishing or its intensification may lead to dramatic changes in the coastal marine food web, including additional threats to coastal marine mammal populations in southern Brazil.

Sharks and batoids (Subclass Elasmobranchii) caught in the industrial fisheries off the Brazilian North coast

The Brazilian North coastline comprises a total area of approximately 223,000 km2, representing one of the world’s most essential fishing grounds. Availability of data on the diversity of fishes caught in the industrial fishery trawlers in the region are usually limited to the commercially important and targeted species. Knowledge gaps on the related marine fish fauna are eminent, which hamper both fisheries and conservation efforts of the local biodiversity. A comprehensive taxonomic list of elasmobranch species captured off the North coast from Brazil through industrial trawl fishery is provided. Trawling operations acting regionally included pink-shrimp and several fish (outrigger trawling) and piramutaba catfish (pair trawlers). Sixty-eigth elasmobranch species belonging to 20 families and nine orders were recorded for this region, according to fish collection, fishery observer and literature data. Thirty-two are by-catch species caught in the local trawl operations, including endemic and rare species as well as four new records and one possible undescribed species of electric ray.

Can modelling the drift of bycaught dolphin stranded carcasses help identify involved fisheries? An exploratory study

Between the 1st of February and the March 31, 2017, 793 stranded cetaceans were found along the French Atlantic coasts. Common dolphins made up 84% of these strandings, and most of these presented evidence of death in fishing gear. The aim of this work is to test an approach that could help identify the fisheries potentially involved in a given stranding event. To do this we examined how the distributions of likely areas of mortality of bycaught dolphins, inferred from carcass drift modelling, coincide with fishing effort statistics of various fleets, generated from the Vessel Monitoring System, in the area over the same dates. Using reverse drift modelling, two main mortality areas were identified. A total of 3690 common dolphins (IC95% [2230; 6900]) were estimated to have died in fishing gear within the Bay of Biscay during this unusual stranding event. There was a positive correlation between the origin of stranded bycaught dolphins and the fishing effort distribution of French midwater pair trawlers, Spanish otter bottom trawlers and French Danish seiners. This co-occurrence highlights a risk and identifies fisheries that require further investigation (through observers or e-monitoring). These fisheries differed in their fishing gear, but two characteristics appear to be shared: they targeted predatory fishes (sea bass and hake) in winter and used high vertical opening gear.

Trawling in the Mediterranean: An Exploration of Empirical Relations Connecting Fishing Gears, Otterboards and Propulsive Characteristics of Fishing Vessels

Fishing pressure is often expressed in terms of vessel’s physical attributes, like tonnage and engine power, while a common definition of fishing capacity identifies vessel size as a convenient proxy for the size of gear used. Nevertheless, these definitions remain arguable, and the refinement of these fishing descriptors is increasingly receiving growing consideration. A stronger understanding of the relationship between the standard measures of effort and capacity and fishing mortality remains a primary objective, followed by the need to overcome a traditional approach that simply describes effort, capacity and mortality as linearly related, conferring to larger vessels a greater fishing power. In this perspective, the analysis of trawls’ technical features in relation with the size and power of the vessel might constitute an essential step. This study specifically investigated a collection of trawl gears technical specifications collected by CNR-IRBIM, Ancona. The dataset used includes records from several Mediterranean fisheries, and involves three trawling techniques, including single trawl, twin trawl and pair trawling, and diverse trawling gear categories, comprising demersal/bottom 2-panel trawls (OTB2), demersal/bottom 4-panel trawls (OTB4), pelagic 4-panel trawls (PTM4), semi-pelagic 2-panel trawls (OTM2), semi-pelagic 4-panel trawls (OTM4), and Mediterranean bottom beam trawl (TBB). We analyzed and described the relationships between vessels’ technical features (LOA, towing force, engine power), some among the main trawl-metrics (headline length, footrope length, trawl length, square width; fishing circle) and otterboard’s technical features (height, width, projected area) in the attempt to enhance fishing capacity definition through the inclusion of the fishing gear deployed. Self-Organizing maps were used to explore the empirical relationships among different parts of the fishing trawl gears, as well as between some of these parts and the otterboard size and the engine power of the vessel.