Bottom Trawl Fishery Research Articles

Hermit crabs associated to the shrimp bottom-trawl fishery along the Pacific coast of Costa Rica, Central America

Hermit crabs associated to the shrimp bottom-trawl fishery along the Pacific coast of Costa Rica, Central America

Hermit crabs associated to the shrimp bottom-trawl fishery along the Pacific coast of Costa Rica, Central America

Studies of the bycatch associated to the shrimp trawling fishery in the Pacific coast of Costa Rica do not assess small organisms (< 10 cm TL) and non-dominant species (< 0.1% of total catch). There is a void in assessing the maintenance of the ecology and ecosystem on which the fishery depends. Furthermore, the Constitutional Court of Costa Rica prohibited the renewal of existing and the issuing of new shrimp bottom-trawl licenses, indicating the necessity of more scientific information on the impacts of this fishery. We present the results of a 23-month study of the shrimp bottom-trawl fishery performed between 50 and 350 m deep in the Pacific coast of Costa Rica. A total of 109 hermit crabs were collected (six species and two families). Paguristes cf. holmesi was the most common species. Zone II presented the highest species richness and abundance. Most specimens (81.8 %) were caught in shallower waters (50-149 m). More than 45% of the trawls presented hermit crabs. It is imperative to further assess the trawling effects on non-commercial benthic fauna and changes on predator-prey relationships before issuing new shrimp licenses

Population dynamics of threadfin porgy Evynnis cardinalis, an endangered species on the IUCN red list in the Beibu Gulf, South China Sea.

Threadfin porgy Evynnis cardinalis is both a dominant fish species and an important fishing target in bottom trawl fisheries in the Beibu Gulf, South China Sea. It was listed as endangered (EN) in a recent International Union for Conservation of Nature (IUCN) red list. Despite its economic importance and endangered status, limited research on its biological characteristics and spatial-temporal distribution has been undertaken this last decade, creating uncertainty in current conservation and management. We analyse this species' spatial distribution characteristics using data from four seasonal bottom trawl surveys in 2014-2015, and report average catch per unit effort to vary seasonally, from 49.1 to 594.5 ind h-1 . Growth, mortality and sexual maturity are reported for four time periods based on data from bottom trawl fishery surveys over 1961-1962, 1998-1999, 2006, and 2014-2015. Length frequency distributions changed from bimodal to unimodal, and the female-to-male ratio increased. Mean body length and length at first maturity decreased, whereas the growth coefficient increased, indicating miniaturization, early sexual maturity and accelerated growth, respectively. We report sparid catch to have first exceeded maximum sustainable yield in 2001, and to have remained overfished from 2010 to 2015. Since the 1980s, low-trophic-level fishes such as E. cardinalis have replaced high-trophic-level fishes such as Crimson snapper Lutjanus erythropterus to become dominant species. As catches have increased substantially, these species have been faced with overfishing, driving the ecosystem into an unstable state.

Strategies and trends of bottom trawl fisheries in the Mediterranean Sea

An effective management of trawl fishing should be based on the classification of strategies adopted by fishers in terms of fishing grounds selected and target species. In addition, the dynamics behind strategy selection should be investigated and understood, since they are likely to affect the status of the stocks. This study applies artificial neural networks to identify the main strategies characterizing the fishing activity of Italian trawlers operating in the Central Mediterranean during the period 2009–2016. Moreover, the rationale driving fishers' choice is modelled using General Additive Models (to investigate the role of external factors) and Conditional Logit (to investigate the interaction among fishers). Five strategies were identified together with the potential effects on some key stocks which, in turn, determine the fishers' preference towards alternative strategies. Results suggest that both external factors and interactions are relevant in driving fishers’ behavior, and provide some potentially useful insights for the set-up of management strategies in which the adaptation of fishers to biological and economic factors are explicitly considered.

Different bottom trawl fisheries have a differential impact on the status of the North Sea seafloor habitats

AbstractFisheries using bottom trawls are the most widespread source of anthropogenic physical disturbance to seafloor habitats. To mitigate such disturbances, the development of fisheries-, conservation-, and ecosystem-based management strategies requires the assessment of the impact of bottom trawling on the state of benthic biota. We explore a quantitative and mechanistic framework to assess trawling impact. Pressure and impact indicators that provide a continuous pressure–response curve are estimated at a spatial resolution of 1 × 1 min latitude and longitude (∼2 km2) using three methods: L1 estimates the proportion of the community with a life span exceeding the time interval between trawling events; L2 estimates the decrease in median longevity in response to trawling; and population dynamic (PD) estimates the decrease in biomass in response to trawling and the recovery time. Although impact scores are correlated, PD has the best performance over a broad range of trawling intensities. Using the framework in a trawling impact assessment of ten métiers in the North Sea shows that muddy habitats are impacted the most and coarse habitats are impacted the least. Otter trawling for crustaceans has the highest impact, followed by otter trawling for demersal fish and beam trawling for flatfish and flyshooting. Beam trawling for brown shrimps, otter trawling for industrial fish, and dredging for molluscs have the lowest impact. Trawling is highly aggregated in core fishing grounds where the status of the seafloor is low but the catch per unit of effort (CPUE) per unit of impact is high, in contrast to peripheral grounds, where CPUE per unit of impact is low.

Effect of a lateral square-mesh panel on the catch pattern and catch efficiency in a Mediterranean bottom trawl fishery

The current legal codends used in Mediterranean bottom trawl fisheries are at high risk of retaining undersized individuals of several commercial fish species. This entails that codends alone are unable to provide the desired exploitation pattern. A simple technological measure that potentially can provide higher release efficiency of undersized fish are Square-Mesh Panels (SMPs). SMPs are often applied in the upper section of the trawl belly, just ahead the codend. However, recent studies in the Mediterranean have demonstrated that SMPs mounted in this position provided limited release efficiency, because very few fish came into contact with their meshes. In attempt to improve SMPs efficiency in the Mediterranean bottom trawl fisheries, we applied them on the lateral sides of the last tapered section of the trawl belly, just ahead of the codend, and fitted two guiding panels in the trawl belly to enhance fish-SMP contact. We compared the catch performance of a standard commercial trawl with a 52 mm diamond-mesh codend and of a similar trawl fitted with lateral SMPs (70 mm mesh size) in the belly using a twin trawl. The study focused on red mullet (Mullus barbatus), a commercially important species, but data for gurnard (Chelidonichthys lucerna and Chelidonichthys cuculus) were also obtained and analysed. In contrast to previous research on SMPs mounted in the top panel of the trawl, in this study SMPs induced a significant effect on catch performance for red mullet, demonstrating that their lateral position involved greater fish-SMP contact. However, since the test trawl lost a significant amount of legal-sized red mullet compared with the standard trawl, the effect was not wholly positive, possibly due to an excessively large mesh size. Therefore, future studies should be encouraged to test lateral SMPs with smaller mesh sizes.

On-board study of gas embolism in marine turtles caught in bottom trawl fisheries in the Atlantic Ocean

Decompression sickness (DCS) was first diagnosed in marine turtles in 2014. After capture in net fisheries, animals typically start showing clinical evidence of DCS hours after being hauled on-board, often dying if untreated. These turtles are normally immediately released without any understanding of subsequent clinical problems or outcome. The objectives of this study were to describe early occurrence and severity of gaseous embolism (GE) and DCS in marine turtles after incidental capture in trawl gear, and to provide estimates of on-board and post-release mortality. Twenty-eight marine turtles were examined on-board fishing vessels. All 20 turtles assessed by ultrasound and/or post-mortem examination developed GE, independent of season, depth and duration of trawl and ascent speed. Gas emboli were obvious by ultrasound within 15 minutes after surfacing and worsened over the course of 2 hours. Blood data were consistent with extreme lactic acidosis, reduced glomerular filtration, and stress. Twelve of 28 (43%) animals died on-board, and 3 of 15 (20%) active turtles released with satellite tags died within 6 days. This is the first empirically-based estimate of on-board and post-release mortality of bycaught marine turtles that has until now been unaccounted for in trawl fisheries not equipped with turtle excluder devices.

STATE OF STOCKS AND MODERN FISHERY OF ATKA MACKEREL PLEUROGRAMMUS MONOPTERYGIUS (PALLAS, 1810) IN THE OLYUTORSKY-NAVARINSKY AREA OF THE BERING SEA

Atka mackerel Pleurogrammus monopterygius is one of the mass species of fam. Hexagrammidae that inhabits the boreal and subarctic waters of the North Pacific and forms two large populations in its western and eastern parts. Reproductive range of the eastern, Aleutian population extends from the Gulf of Alaska, along Aleutian Islands to Commander Islands, with the main spawning grounds at the Aleutians and in the southeastern Bering Sea. From these areas, the fish at early stages of ontogenesis spread widely in system of the Bering Sea currents to the western-southwestern Bering Sea, where the atka mackerel aggregations are formed on the external shelf at prominent capes, as Cape Olyutorsky. Dynamics of the atka mackerel stock in the Olyutorsky-Navarinsky area in 1994–2019 is presented on the base of bottom trawl surveys, fishery statistics, and open NOAA data. After the period of low stock in the middle 1990s, the atka mackerel abundance increased sharply to the maximum in 2006–2008, when the spawning stock in this area was about 9.5 . 103 t and the commercial stock about 14.0 . 103t. Since that time, trend to decreasing is observed, with the spawning stock 3.6 . 103t and the commercial stock 5.6 . 103t in 2013, and recent stabilization at the low level with slight decline continuing. A possible reason of the sharp increase in 2000s could be the intensive transport of the atka mackerel juveniles from the main spawning grounds at Aleutian Islands to the area at Cape Olyutorsky. The catches of atka mackerel in the Olyutorsky-Navarinsky area in 1994–2018 corresponded well with its stock dynamics.

Combining selection models and population structures to inform fisheries management: a case study on hake in the Mediterranean bottom trawl fishery

The reduction of juvenile catch and discards are important targets in fisheries policy. This work examines how selection models can predict the size structure (LFD) of discards and landings considering the effects of area, time period, gear and fisher behaviour. Additional exploitation indicators related to the gear used, fisher's selection pattern, and discards were also estimated. The approach is demonstrated in a study concerning hake in the Mediterranean trawl fishery, focusing on high (HRA) and low (LRA) recruitment areas in the Saronikos Gulf (Eastern Mediterranean) during two periods (June, September) using two codends (40 mm square-40S, 50 mm diamond-50D mesh). The predicted discards LFDs revealed generally higher percentages in the HRA in June when using the 50D. The predicted landings LFDs showed higher percentages in the LRA in September for both codends, but undersized hake were always included. LFDs and exploitation indicators indicated that both codends were inappropriate for sustainable fishing of hake in the HRA, where 50D performed worse than the 40S. Fishing with both codends in the LRA in September revealed the lowest discards rates and minimum sizes of landings close to MCRS (minimum conservation reference size). These results can provide information to fisheries management aiming to protect juveniles and reduce discards through spatio-temporal fishing closures.

Survival rates for Nephrops norvegicus discarded from Northern European trawl fisheries

Abstract When discarded from bottom trawl fisheries, survival of Nephrops norvegicus may be sufficiently high that this species can be exempted from the EU Landing Obligation. In three studies, Nephrops were sampled from trawlers in northern European waters, and the fate of individuals monitored for a minimum of 13 days in onshore tanks. Winter estimates of captive survival (means ± 95% confidence intervals), including immediate mortality during catch sorting, were 62 ± 2.8% for the West of Scotland, 57 ± 1.8% for the Farne Deeps (North Sea), and 67 ± 5.4% for the Skagerrak. The Farne Deeps fishery is not active in summer, but captive survival rates in summer in the other two areas were reduced to 47 ± 3.4% for West of Scotland and 40 ± 4.8% for the Skagerrak. Linear modelling of the West of Scotland and Skagerrak data suggested that higher survivals in winter were related to colder water or air temperatures, although temperatures during captive observation may also have had an impact. Net modifications in the Skagerrak study had an effect on survival, which was higher for Nephrops sampled from nets equipped with the more selective Swedish sorting grid compared to Seltra trawls.

Release efficiency and selectivity of four different square mesh panel configurations in the Basque mixed bottom trawl fishery

Reduction of discards from the Basque mixed bottom trawl fishery is a challenge. To improve the selective properties of the gear used by the fleet and supplement codend size selection, a square mesh panel (SMP) installed in the upper panel of the trawl was introduced in 2006. However, recent studies have shown that the release efficiency of this SMP is low due to lack of contact between the fish and the SMP. In this study, we tested the release efficiency of the SMP for four different gear configurations. We tested the effect of adding LED lights at two different positions and altering panel size and panel position in the trawl. The analyses were focused on two species: hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou). The results showed that the position of LED lights did not significantly affect the SMP’s release efficiency for any species. However, increasing panel size had a significant positive effect on the release efficiency of blue whiting, and placing the SMP in the lower panel improved the release efficiency of hake. These results highlight the challenge of simultaneously improving the selective properties of gear for species with different behaviour, especially in mixed demersal fisheries.

Implementation of exclusion devices to mitigate seal (Arctocephalus australis, Otaria flavescens) incidental mortalities during bottom-trawling in the Falkland Islands (Southwest Atlantic)

In the Falkland Islands, the South American fur seal and South American sea lion spatially overlap and interact with bottom-trawling fisheries. Until 2015, interactions of these species with the Patagonian bottom trawl squid fishery were uncommon. During the second fishing season 2017 a dramatic increase in seal interactions was observed, with a corresponding increase in incidental mortalities. Various mitigation measures were applied, seal exclusion devices (SEDs) fitted inside a net extension inserted between the trawl net and cod-end being the most efficient. The SEDs became mandatory in the fishery in September 2017. Since then, the number of seal mortalities remains negligible. SED efficiency is monitored by 100 % observer coverage. To the best of our knowledge, the Falkland Islands Patagonian squid fishery is currently the only trawl fishery in the Southwest Atlantic with full observer coverage and SED usage. It is hoped in the near future similar mitigation measures extend to other coastal countries whose fisheries also interact with these otariids.

Comparative study on the full-scale prediction performance of four trawl nets used in the coastal bottom trawl fishery by flume tank experimental investigation

Energy efficiency, catchability, and ecological sustainability have become important issues for coastal bottom trawl fisheries. Thus, fishing gear has been modified to increase the swept area and decrease the drag and bycatch. To evaluate the effect of twine thickness, twine material, and mesh size on the drag (bridle tension) and geometrical shape of trawl nets, this study focused on the full-scale prediction performance (geometry and resistance) of bottom trawl nets used in the coastal fishery. Four 1/18-scale bottom trawl models with different twine diameters, different mesh sizes, and even the Geometrical shape of wing-end were designed and tested in a flume tank at Tokyo University of Marine Sciences and Technology (TUMST). The flume tank experimental data were evaluated to predict full-scale performance at sea and to compare the performance of trawl nets built with traditional materials (polyethylene), namely, trawl nets 1 and 4, with those built with innovative materials (Dyneema and nylon monofilament), namely, trawl nets 2 and 3, respectively. The geometrical shape of bottom trawl net was determined from the nonlinear equation constructed and solved using the experimental data with various door spreads and towing speeds. The results show that an increase in mesh size using Dyneema (trawl net 2) systematically leads to a decrease in bridle tension ~ 34.55%, a decrease of twine diameter using nylon monofilament (trawl net 3) lead to a decrease in bridle tension ~ 35.4%, and an increase in mesh size using triangular shape in the wing-end (trawl net 4) lead to a decrease in bridle tension ~ 19.92%. The net mouth area of trawl net 1 is 4.36%, 10.88%, and 6.47% greater than those of trawl nets 2, 3, and 4, respectively. The filtered volume of trawl net 3 is 1.29%, 7.48%, and 4.13% greater than those of trawl nets 1, 2, and 4, respectively, indicating that trawl net 3 has better catch performance than other trawl nets. The shapes of floating rope of all the four trawl nets are very close with a gap of less than 1.5%, indicating that the increase in mesh size and decrease in twine diameter do not affect the geometrical shape significantly as the drag force. The results also show that the ratio between bridle tension and net mouth area of trawl net 1 is 31.57 %, 27.61%, and 14.37% greater than those of trawl nets 2, 3, and 4, respectively.

Incidental capture and mortality of sea turtles in the industrial double‐rig‐bottom trawl fishery in south‐eastern Brazil

Abstract Incidental capture by fisheries is one of the principal threats to sea turtles. This study analysed spatial and temporal patterns of sea turtle bycatch, and estimated the direct initial mortality rate of these animals, in the industrial double‐rig‐bottom trawl fishery in south‐eastern Brazil. This is also the first attempt to relate bycatch/at‐sea mortality in bottom trawling to stranded turtles found along the adjacent coast. The fishery was monitored from October 2015 to April 2018 through data collected voluntarily by the captains of eight industrial double‐rig trawlers. Two hundred and one sea turtles were captured during 9362 tows (43,657.52 trawling hours), resulting in a catch per unit effort (CPUE) of 0.0025 ± 0.0032 turtles h−1 with a standard net of 30.5 m headrope, with no significant difference between the estimated CPUEs for licensed shrimp and demersal fish trawlers. Caretta caretta (52.24%) and Lepidochelys olivacea (38.81%) were the most frequently captured species. According to Generalized Linear Models, C. caretta bycatch was significantly higher during winter, at lower latitudes (−24° to −23°) and higher longitudes (−42° to −40°), while the L. olivacea bycatch was significantly higher at higher latitudes (−23° to −21°). The direct initial mortality rate of sea turtles in the shrimp trawlers was 7.65 ± 3.85%. However, none of the dead individuals subsequently released with plastic tags (n = 10) were found stranded on the coast. Mortality was not significantly related to the depth or duration of the trawling. The results of this study suggest the need for improvements to the current management of the bottom trawl fishery in Brazil, moving from a species‐based to a spatial and seasonal‐based approach. There is also a need to develop turtle excluder devices adapted to local fishing conditions.

The importance of alien species to the food web and bottom trawl fisheries of the Northeastern Mediterranean, a modelling approach

Abstract Alien species and bottom trawl fisheries are of significant concern in the Eastern Mediterranean as both can put pressure on coastal systems whilst some alien species also constitute an important component of the trawl catches. Using an Ecopath model representing the Gulf of Mersin (Northeastern Mediterranean) for the period September 2009 to September 2013, this study describes the impacts of alien species and bottom trawl fisheries on the structure and functioning of this Northeastern Mediterranean food web. Our results show that the increase in alien species has had an important ecological impact on ecosystem structure and function. The alien species have had mostly negative impacts on native taxa, and trawl fisheries may have helped some alien species gain an advantage over native species, particularly at lower trophic levels. The Mixed Trophic Impact analysis showed that trawling and trawl discards had a noticeable direct and indirect impact on the food web, to the extent that trawling now affects the ecological role of the alien species. The cumulative overall impact of alien demersal functional groups on the pelagic domain, and vice versa suggest that alien species now play a role in benthic-pelagic coupling, and that this role is mediated by the fisheries. These results support the idea that alien species and trawling are now both important factors in structuring the Northeastern Mediterranean food web. It will thus be critical to consider both factors, as well as their interactions, when developing ecosystem-based management approaches for the region.

Utilization of pop-up satellite archival transmitting tags to evaluate thorny skate (Amblyraja radiata) discard mortality in the Gulf of Maine groundfish bottom trawl fishery

Abstract Thorny skate (Amblyraja radiata) remain one of the most overfished species in the Gulf of Maine (GOM) despite being designated as a prohibited (zero-possession, mandatory release) species by the New England Fishery Management Council in 2003. To better understand the extent to which discard mortality (DM) occurring after incidental capture in the GOM groundfish bottom trawl fishery may be impeding recovery, 75 individuals (55–94 cm total length, TL) were tagged with pop-up satellite archival transmitting (PSAT) tags and monitored for up to 28 days following capture under representative commercial trawl fishing practices. Data recovered from 61 PSAT-tagged skate were analysed with a longitudinal survival analysis to estimate DM and identify influential capture-related variables. DM rate was a function of TL, with larger skates (>70 cm; DM = 16.5%) experiencing lower mortality than smaller conspecifics (55–70 cm; DM = 24.5%). From our results, we estimate annual thorny skate DM in the GOM groundfish bottom trawl fishery to be 79.2 ± 0.2 mt, which accounts for <1% of the existing stock biomass in the GOM (8400 mt). This study confirms that thorny skate are relatively resilient to bottom trawl fishing practices in the GOM, and suggests that other sources of mortality may be impeding population recovery.

CPUE standardization for the Pacific saury (Cololabis saira) fishery in the Northwest Pacific

In stock assessment and fisheries management, the standardization of catch per unit effort (CPUE) is critical to derive an effective index of the abundance of exploited fish stocks. In addition to developing various statistical models, a method including the relative fishing power (RFP) of individual vessels has been developed from an intuition concept and applied to bottom trawl fisheries using logbook-based data. This is a convenient and straightforward approach for standardizing the catch-effort data of a fishery. The Pacific saury is a pelagic fish species, and its stock in the Northwest Pacific has been targeted by international fleets since the early 1980s; annual production ranged from 328,000 to 630,000 tons during 2001- 2016. The Pacific saury stock has been one of the resources managed by the North Pacific Fisheries Commission (NPFC) since 2015. In this study, the RFP method in CPUE standardization was applied to the Taiwanese Pacific saury fishery in the Northwest Pacific, and the effects of varying the parameters of the model were analyzed. The results indicate that more than 98.8% of the fishing effort can be standardized according to the estimated RFP, with 20 being the minimum number of required comparisons in each of the 4-year periods during 2001-2016. The RFP values of the model generally correlate with the length and gross tonnage of fishing vessels in the saury fishery. The result of the model, applied to the Pacific saury fishery, is robust when the model considers the effects of varying the model parameters (the minimum number of comparisons and standard vessel). This study suggests that first, the RFP method is appropriate for the CPUE standardization of the Pacific saury fishery, and that second, the resulting CPUE can be an effective index of abundance that reflects the annual variability of the Pacific saury stock in the Northwest Pacific.

The effect of bottom trawl fishery on biomass variations of demersal chondrichthyes in the eastern Mediterranean

Chondrichthyan species are considered highly susceptible to fishing activities and as “indicator species” for overfishing and ecosystem stability. In European waters, chondrichthyes have become a focus of conservation actions due to the abundance declines of several species.In the present study, fishery independent data obtained from the Mediterranean International Trawl Surveys (MEDITS) in the Aegean and E. Ionian Seas (eastern Mediterranean) were coupled with bottom trawl fishing effort data obtained from vessel monitoring systems (VMS) in order to evaluate the effect of fishing on biomass variations of demersal chondrichthyan species. The study focused on commonly captured species such as Raja clavata, Galeus melastomus, Scyliorhinus canicula and Squalus spp, as well as to the total chondrichthyan biomass. The effect of fishing effort on biomass indices, expressed in terms of kg per square km of swept area, was examined by means of Generalized Additive Model techniques, using also the sampling position, year and depth as co-variates.Overall findings suggested a biomass decline of chondrichthyan species with increasing fishing effort. Nevertheless, it was also found that certain species (e.g G. melastomus in both areas and S. canicula in the Aegean Sea) can withstand fishing pressure and it is likely that discard survival rates, depth preferences and fisheries exploitation patterns, are the main drivers explaining variations regarding the impact of fishing on the different stocks.

Population Composition, Growth and Fisheries of Nemipterus randalli Russell, 1986 in Antalya Gulf, Mediterranean Sea, Turkey

Most of the species migrating to the Mediterranean Sea as a result of the Lessepsian migration have been forming a sustainable population. In this study, population composition, growth, and fisheries of Nemipterus randalli Russell, 1986, an Indo-Pacific fish and live in Antalya Gulf, North-East Mediterranean Sea, were analyzed. The monthly samples were collected (N = 1715) by using experimental bottom trawl. The fish size ranges between 3.9 and 23.8 cm in total length, 0.73 and 171.78 g in weight, males are larger than females, and the length-weight relation was estimated as W = 0.0173 × TL 2.8584. The male and female ratio was calculated as 1:1.402, females are predominant in the population. The average condition factor fluctuated seasonally and ranged between 1.089 and 1.346. Five age groups were identified in the population; Von Bertalanffy Growth Equation was estimated as Lt = 32.56 [1-e -0.20 (t+1.75)]. The size, sex, and age composition show that it established a sustainable population in Antalya Gulf, grows well, reproduce and to be an item of bottom trawl fisheries, and sold in small percentages.

Using a trait-based approach to understand the efficiency of a selective device in a multispecific fishery

Improving the selectivity of a fishing gear is one technical management measure to significantly reduce by-catch of non-commercial species or undersized individuals. The efficiency of selective device is mainly estimated by comparing species composition, the biomass and length spectrum of caught individuals and escapees while the functional traits of species are rarely accounted for. Using an innovative technical device to reduce catches of undersized individuals in a multispecific bottom trawl fishery in the Bay of Biscay, namely a T90 mesh cylinder, we measured functional traits on both caught and escaped individuals of 18 species. Using a Principal Component Analysis and K-means partitioning, we clustered species into 6 groups illustrating 6 different locomotion strategies. We identified functional traits related to body size, visual ability and locomotion, differing between caught individuals and escapees using Linear Mixed-effects Models. As expected, escapees were smaller on average but also tended to be more streamlined, with a high position of the eyes and fin features characteristic of manoeuvrability and propulsion. Here, we present how a trait-based approach can shed light on the biological characteristics influencing the efficiency of selective devices.