Beam Trawl Fishery Research Articles

Connecting catch profiles with efficiency: An application to the beam trawl fishery in the Northern Adriatic Sea

Estimation of technical efficiency in fisheries is most commonly finalized at comparing the conversion from inputs (e.g. time at sea, fuel consumption) to production (i.e. landed fish) among vessels or gears. In this paper we adopt a novel approach focusing on the efficiency of fishing trips characterized by different catch composition within the same fleet. In particular, the case study under analysis is represented by the beam trawl (“rapido”) fishery of Chioggia (Adriatic Sea, GSA 17), which has been subject to increasing technical and effort limitations in recent years due to its severe impacts on the marine ecosystem. The methodological strategy first involves a cluster analysis of catch profiles to identify homogeneous groups of fishing trips, which are subsequently compared in terms of economic performance based on the efficiency scores from stochastic frontier analysis. By including also an estimation of Greenhouse Gas emissions per trip, the results from our study can be used to inform future management interventions that aim at improving the overall efficiency of the fishery while reducing its carbon footprint and the pressure on the most relevant target species.

Effects of environmental conditions and catch processing on survival probability of plaice discards in the North Sea pulse trawl fishery.

Undersized European plaice dominate the discarded fraction of the catch of the beam trawl fisheries for sole in the Southern North Sea. Effects of environmental conditions at sea and of the use of a water-filled hopper on the survival of undersized European plaice discarded by pulse trawl fisheries were explored. During trips with commercial pulse-trawlers catches were discharged in either water-filled hoppers or conventional dry hoppers. For both hoppers, undersized plaice were sampled from the sorting belt. After assessment of vitality status, sampled fish were housed in dedicated survival monitoring tanks on board. Upon return in the harbour fish were transferred to the laboratory to monitor their survival for up to 18 days post-catch. Conditions at sea, such as wave height and water temperature, as prevailing during these trips were recorded or obtained from public data sources. The overall estimate for the survival probability for plaice discarded by pulse trawl fisheries is 12% (95% CI: 8% - 18%). Both water temperature and vitality status had strong effects on survival probabilities of discarded plaice. Increasing water temperature increased mortality. The vitality of the fish could be moderately increased by using a water-filled hopper to collect the fish on deck, but we found no significant direct effect of hopper type on plaice discard survival. It seems that to increase discards survival, fish need to be landed on deck in much better condition by a reduction of the impact of capture and hauling processes on fish condition.

An Assessment of Potential Beam Trawling Impact on North-Western Black Sea Benthic Habitats Aiming at a Sustainable Fisheries Management

The North-Western Black Sea shelf is extremely vulnerable to disturbances of its habitats and ecosystems. In the past 10 years, this area has become targeted by beam trawl fisheries for the invasive gastropod Rapana venosa (Valenciennes, 1846), with a potentially destructive impact on the area’s soft bottoms. Not many studies have been performed in the region, and most investigations have focused on gear selectivity and by-catch rates. In this context, our novel research aimed, on the one hand, to assess and quantify the actual impact of beam trawling and, on the other hand, to propose effective spatial/temporal management measures for a sustainable zonation of the North-Western Black Sea shelf (marine zone of the Danube Delta Biosphere Reserve). The methodology used integrated beam trawl catch dynamics information, VMS data, geophysical investigations, and macrozoobenthos sampling. Our findings show that beam trawling activities can cause changes in the benthic habitat structure (lower number of taxa, lower values of ecological indicators, and an overall non-GES status). Further in-depth investigations are needed to underpin the ecosystem-based management of this marine protected area (MPA), aiming to allow the recovery of the affected benthic habitats, by alternating defined areas undergoing fishing with biological recovery polygons.

Internal injuries in marine fishes caught in beam trawls using electrical versus mechanical stimulations

Abstract To improve the ecological and economic sustainability in the Dutch beam trawl fishery, tickler chains were replaced by electrical pulse stimulation to drive common sole (Solea solea) out of the seabed. Because electrical stimulation may cause internal injuries, we quantified this risk by sampling fish species from commercial beam trawlers and recording spinal injuries and haemorrhages from X-radiographs and autopsy. To distinguish mechanically-induced and electrical-pulse-induced injuries, we compared injuries in ten species sampled from pulse (PUL) and tickler-chain (TCK) trawlers and four species sampled from PUL trawlers with the stimulus switched on or off. Co-occurrence of a major spinal injury and major haemorrhage at the same location was only observed in PUL samples, and were frequently (40%) observed in Atlantic cod (Gadus morhua) and in low numbers (0–2%) in whiting (Merlangius merlangus), grey gurnard (Eutrigla gurnardus), and greater sandeel (Hyperoplus lanceolatus), but not in flatfishes and other species. In cod, injury occurrence correlated with fish length, with lower probabilities for small fish. Major spinal injury or major haemorrhage occurrence in PUL (range: <1–16%) was lower than in TCK (range: <1–42%) in eight of the ten species studied. Population level consequences of pulse-induced injuries are considered negligible.

Changes in catch efficiency and selectivity in the beam trawl fishery for sole when mechanical stimulation is replaced by electrical stimulation

Beam trawl fisheries for sole are characterised by large amounts of unwanted bycatch (i.e. discards) consisting of fish below the Minimum Conservation Reference Size, unwanted fish due to low commercial value or lack of quota, and benthic invertebrates. In order to reduce the quantity of discards, a substantial part of the Dutch beam trawl fleet was allowed to replace the conventional tickler chain beam trawl (BT) with the pulse trawl (PT) on an experimental basis. The PT used electrical stimulation to immobilise and capture fish. Here we study whether pulse trawling reduced the amount of discards by comparing catch rates of landings and discards of BT and PT in the period 2009–2018 for a wide range of species. The PT caught (kg.km-2) significantly more marketable sized sole (Solea solea, 48 %), turbot (Psetta maxima, 8 %), brill (Scophthalmus rhombus, 28 %) and whiting (Merlangius merlangus, 95 %), and significantly less marketable sized plaice (Pleuronectes platessa, −16 %), cod (Gadus morhua, −32 %) and gurnards (−12 %). No significant difference was found for dab (Limanda limanda), gadoids, or rays and sharks. Among discards, the PT caught more undersized sole (27 %) and whiting (42 %) but less undersized plaice (−21 %), dab (−19 %) and grey gurnard (Eutrigla gurnardus, −31 %). The observed differences in species selectivity are discussed in relation to the response of fish to bottom trawl gear and the effects of pulse stimulation. For the benthic invertebrates Ophiuroidae, bivalves and crabs the PT caught fewer individuals (between −38 % and −57 %). No significant difference was observed in sea urchins and sea stars. Overall, this study shows that the transition from the BT to PT resulted in a 36 % decrease (95 % prediction interval: 31–42 %) in discards (kg.hour-1).

Selectivity Characteristics of the Sorting Grid in Shrimp Beam Trawls used to Reduce Bycatch in the Sea of Marmara

Considerable by-catch problems have occurred in the commercial beam trawl fishery targeted at deep water pink shrimp in the Sea of Marmara. In this study, the grid systems were used to reduce the untargeted catch and improve the species' selectivity. By-catch reduction ratios of the beam trawls deployed with and without the grid were compared by the parallel hauling method. Selectivity values of 20 mm bar spacing grid and 24 mm mesh size cod-end were also analyzed by SELNET program. In general, by-catch reduction ratios of the grid beam trawl were determined as 50.6% and 56.9% in terms of number and weight, respectively. The reduction of target catch (Parapenaus longirostris) in the same gear was found to 23.1% in terms of number and 23.2% in terms of weight. In the model for rose shrimp, obtained according to the lowest AIC value, the selectivity parameters of the grid for L50 were 13.51 cm and for SR 4.76 cm. Selectivity parameters of the same species for 24 mm mesh size cod-end were; L50 = 8.99 cm and SR = 5.56 cm. These results indicated that grid usage benefits and contribute to sustainable fishery in the target catch-oriented fishing applications.

Grid-net design that successfully reduces discarded catch and damage to benthic species in the veined rapa whelk beam trawl fishery

ABSTRACT In this study, a grid-net design (GND) with three different bar spacings was compared with the commercial beam trawl used in the veined rapa whelk fishery to minimize the discarded catch amount and the loss of commercial product. In addition, the damage and mortality rates of the species that entered the tested fishing gear were determined to understand whether the tested fishing gear has a possible negative effect on benthic species. In the grid-net design, a rectangular metallic grid positioned 6 cm off the ground substituted half of the codend to allow the escape of discard species. Sea trials were carried out in the south-eastern Black Sea between 13 and 24 October 2021. Results showed that the discarded catch amount was significantly reduced by each GND (P < 0.05). Compared with the commercial fishing gear, the reductions in the discarded catch amounts (in terms of number) were 91.6%, 92.2%, and 95.0% for 22, 25, and 28 mm GNDs, respectively. The minimum commercial product loss was determined at 22 mm GND. In addition, it was seen that each GND compared to commercial gear caused statistically significantly less damage and mortality on the discarded species. In conclusion, 22 mm GND was the most successful design among the tested gears in minimizing commercial product loss and reducing the discarded catch amount. Recommendations are given for this design to be adopted by the commercial fleet.

Effect of electrical stimulation used in the pulse trawl fishery for common sole on internal injuries in sandeels

Abstract Electric stimulation was used in the North Sea beam trawl fishery for common sole to reduce its environmental impact. Because electrical stimulation may cause internal injuries in fish, a laboratory experiment was conducted to study the effect of pulse exposure on lesser sandeel (Ammodytes tobianus) and greater sandeel (Hyperoplus lanceolatus), important mid-trophic species in the North Sea ecosystem. We exposed 244 sandeels between two electrodes to a pulsed bipolar current for 2 s in an experimental cage with 5 cm sediment; 221 control fish were handled similarly but not exposed. The occurrence of spinal injuries and internal haemorrhages were scored using X-radiography and dissection. None of the sandeels exposed to a field strength of up to 600 V m–1 showed spinal injury or haemorrhage. Equal numbers of minor spinal abnormalities were found in exposed and control fish. In the absence of spinal injuries, we estimated by bootstrapping the field strength below which spinal injuries are unlikely to occur, i.e. the lower limit threshold, and the corresponding limit dose–response relationship between field strength and injury probability. We conclude that it is unlikely that pulse trawl fishery will have an ecologically significant adverse effect on the population abundance of sandeels, because of the low probabilities of exposure and injury.

The effect of electrical stimulation on the footrope and cod-end selection of a flatfish bottom trawl

The beam trawl fishery targeting sole is known for their substantial bycatch of flatfish below the minimum landing size. Pulse trawls were developed to improve the selectivity by replacing mechanical stimulation with electrical stimulation which immobilises fish in front of the footrope. Results are presented of an experiment on board of a commercial pulse trawler studying the effect of electrical stimulation on footrope and cod-end selectivity for three flatfish species - sole (Solea solea), plaice (Pleuronectes platessa) and dab (Limanda limanda) - in 29 paired hauls with electrical stimulation alternating between the starboard and portside gear. It was shown that electrical stimulation increased the footrope selection by a factor 2 in plaice and dab and a factor 7 in sole. The effect on sole is related to the specific response of sole which cramps into a U-shape. Footrope selection showed a small diurnal pattern with the highest selectivity of the pulse trawl during the day. Electrical stimulation and catch weight were shown to have a small effect on the cod-end selectivity retaining slightly more marketable sole. Cod-end mesh selection factors (SF) were estimated at 3.00 (se = 0.02), 2.11 (se = 0.02), and 2.3 (se = 0.1) for sole, plaice and dab, respectively. Selection ratio (SFA = selection range/mesh size) was estimated at 0.45 (se = 0.03), 0.23 (se = 0.02), and 0.41 (se = 0.04) for sole, plaice and dab, respectively. The SF and SFA of the pulse trawl is comparable to values reported for conventional beam or otter trawls.

Analysis of Demersal Fish Fauna off the Sea of Marmara, Turkey

Demersal fish fauna of the Sea of Marmara, Turkey was determined by bottom trawl surveys between March 2017-December 2018 at 34 stations with the monthly samplings. During the study, a total of 61 teleost and 12 cartilaginous fish species belonging to 42 families were sampled. The target, bycatch and discard rates of CPUE were determined as 13.40%, 69.64% and 16.95%, respectively. In total, 53.9% of the CPUE was stemmed from Trachurus trachurus. Mustelus mustelus, Raja clavata, Merluccius merluccius and Merlangius merlangius had the highest CPUE with a mean of 77.63, 71.86, 71.72 and 72.68 kg/km2, respectively. The highest biodiversity was observed in the southwestern part of the Marmara Sea. With increasing depth, the species number of the teleost fish decreased, whereas the species number of the cartilaginous fish increased. The mean CPUE values of the economical demersal fish species were lower in comparison to those reported from other regions in Turkey. Evidence suggests fish stocks with shallower distribution is under heavier threat against fishing pressure. Since commercial trawling is banned in the Sea of Marmara, beam trawl fishery can be considered as the major threat to demersal fish stocks in the region.

Reducing catch efficiency of rabbitfish (Siganus oramin) in a shrimp beam trawl fishery of the South China Sea

The bycatch of unwanted fish species is a main concern in shrimp beam trawl fishery of the South China Sea. This study evaluated the effect of using combined square-mesh and diamond-mesh codends (CSDM codends) on catch efficiency of a shrimp trawl fishery with the catch comparison and catch ratio approach. The trouser trawl method was applied using the commercial 22-mm diamond mesh codend (D22) as the baseline. The target species, greasyback shrimp (Metapenaeus ensis), and main fish bycatch rabbitfish (Siganus oramin) were chosen as the referred species. The results demonstrated that there was no significant change for the target species but a significant reduction on the unwanted fish bycatch when the CSDM codends were used. Compared with the D22 codend, the CSDM codends would reduce the catch efficiency of greasyback shrimp by less than 18% on average, and the reduction was not statistically significant; whereas catch efficiency of rabbitfish would be significantly reduced by more than 45% and the reduction was length-dependent. The results also showed that the catch efficiency of fish bycatch would reduce as the mesh sizes of the diamond-section of the tested codends increased. These promising results demonstrate that the CSDM codends have a potential to be applied to fishery management for mitigating fish bycatch in the shrimp fishery of the studied area.

Flatfish survivors have tales to tell: Cold seawater and reduced deployment duration contribute to the survival of European plaice (Pleuronectes platessa) discarded by Belgian beam trawlers

The ‘high survival’ exemption to the European Landing Obligation regulation intensified the relevance of quantifying the survival of commonly discarded European plaice (Pleuronectes platessa) within the discard-intensive Belgian beam-trawl fishery, together with the search for ways to maximize discard survival. In this study we worked together with vessel owners and the crews of three Belgian beam trawlers representing the small (≤221 kW) engine power, coastal (n = 1 vessel), ‘Eurocutter’ (1), and large (>221 kW) (1) fleet segments. During 12 commercial trips which included 99 beam-trawl deployments in 2014 and 2015, three scientific observers assessed the survival of 3849 plaice aboard the vessel (by checking for the presence of reflex responses and bleeding injury; on-board survival assessment) and counted how many survived among a sub-sample (n = 489 plaice) monitored for at least 9 days in captivity (post-release survival). These fish were monitored alongside 160 captive controls. Only three control fish died (<2%) during daily monitoring. Survival of plaice discarded from conventional trawls of Belgian beam-trawl vessels representing the three fleet segments was estimated to range between 41–58 %, 11–28 %, 2–4 % (95 % confidence interval; Kaplan-Meier models) for trips of the coastal (≤221 kW), Eurocutter (≤221 kW) and >221 kW vessel, respectively. More challenging operational fishing conditions of >221 kW compared to ≤221 kW vessels such as ∼150 min gear deployment and ∼37 min sorting durations meant that down to only 20 % of undersized plaice were still alive when landed on deck. Such immediate mortality was hardly observed among ≤221 kW vessels. These effects were cumulative to the effect of elevated seawater temperatures of >14 °C during summer, because despite warm waters, immediate mortality among ≤221 kW vessels was low compared to >221 kW vessel-trips. Out of those fish that were still alive after sorting at the point of discarding and monitored for 9 days, on average 23 % (0%–100 %, 95 % CI) survived. Post-release survival was associated with stress and injury sustained during the capture and sorting process (proxied by the reflex impairment and injury index) and seawater temperature. Survival rates can be improved by choosing when to fish, and restricting gear deployments to practicable minimum durations. Without further adaptations to current fishing practices, justifying a high survival exemption for discarded plaice in the Belgian beam-trawl fishery will remain a challenge in compliance with the Landing Obligation.

Sediment mobilization by bottom trawls: a model approach applied to the Dutch North Sea beam trawl fishery

Abstract Bottom trawls impact the seafloor and benthic ecosystem. One of the direct physical impacts is the mobilization of sediment in the wake of trawl gear components that are in contact with or are close to the seabed. The quantity of sediment mobilized is related to the hydrodynamic drag of the gear components and the type of sediment over which they are trawled. Here we present a methodology to estimate the sediment mobilization from hydrodynamic drag. The hydrodynamic drag of individual gear components is estimated using empirical measurements of similarly shaped objects, including cylinders, cubes, and nets. The method is applied to beam trawls used in the Dutch North Sea flatfish fishery and validated using measurements of beam trawl drag from the literature. Netting contributes most to the hydrodynamic drag of pulse trawls, while the tickler chains and chain mat comprise most of the hydrodynamic drag of conventional beam trawls. Taking account of the silt content of the areas trawled and the number of different beam trawl types used by the fleet, sediment mobilization is estimated as 9.2 and 5.3 kg m−2 for conventional 12 m beam and pulse trawls, respectively, and 4.2 and 4.3 kg m−2 for conventional 4.5 m beam and pulse trawls.

Comparison of beam trawl catch, by-catch and discard in fishing and non-fishing areas – a case study from the northern Adriatic Sea

Beam trawl fishery is highly important in the Croatian part of the northern Adriatic wherein 116 vessels have a licence for this type of fishing gear. A sharp decrease in the beam trawl catch observed since 2015 has raised concern about not only socio-economic issues but also ecological issues and the effect that beam trawl fisheries have had on exploited stocks. Besides the effect that beam trawl fisheries can have on targeted economically important species, intensive dredging can cause long-term changes in the benthic community. Therefore, this study aimed to detect the effect that this type of fishing gear has on target and by-catch species. Furthermore, survey data were compared with the official beam trawl fishery data gathered through Vessel Monitoring System data together with fishermen’s logbooks. Our research targeted two adjacent areas: an area where beam trawl fishing is allowed and an area where it is forbidden. The results demonstrate that the commercially important catch represented a minor share of the total beam trawl catch in both survey areas, while discard made up more than 93% of the total catch. The main beam trawl commercially important species in the Croatian part of the northern Adriatic Sea was Pecten jacobaeus, followed by Solea solea and Ostrea edulis. Our results suggest that beam trawl fisheries mostly affect target bivalve species and some non-commercial benthic species (e.g. sponges). The differences recorded between areas could suggest that beam trawl fisheries cause changes mostly in the P. jacobaeus population.

Mitigating seafloor disturbance of bottom trawl fisheries for North Sea sole Solea solea by replacing mechanical with electrical stimulation.

Ecosystem effects of bottom trawl fisheries are of major concern. Although it is prohibited to catch fish using electricity in European Union waters, a number of beam trawlers obtained a derogation and switched to pulse trawling to explore the potential to reduce impacts. Here we analyse whether using electrical rather than mechanical stimulation results in an overall reduction in physical disturbance of the seafloor in the beam-trawl fishery for sole Solea solea. We extend and apply a recently developed assessment framework to the Dutch beam-trawl fleet and show that the switch to pulse trawling substantially reduced benthic impacts when exploiting the total allowable catch of sole in the North Sea. Using Vessel Monitoring by Satellite and logbook data from 2009 to 2017, we estimate that the trawling footprint decreased by 23%, the precautionary impact indicator of the benthic community decreased by 39%, the impact on median longevity of the benthic community decreased by 20%, the impact on benthic biomass decreased by 61%, and the amount of sediment mobilised decreased by 39%. The decrease in impact is due to the replacement of tickler chains by electrode arrays, a lower towing speed and higher catch efficiency for sole. The effort and benthic physical disturbance of the beam-trawl fishery targeting plaice Pleuronectes platessa in the central North Sea increased with the recovery of the plaice stock. Our study illustrates the utility of a standardized methodological framework to assess the differences in time trends and physical disturbance between gears.

Relative survival scenarios: an application to undersized common sole (Solea solea L.) in a beam trawl fishery in the Mediterranean Sea

Abstract Fishery discard survival depends on multiple conditions; caution is essential when survival study outputs are employed to support management decisions. The study presents a stepwise procedure, devised to estimate discard survival, that accounts for the variability characterizing commercial fishing practices. The procedure was applied to the first survival study performed onboard rapido trawlers targeting Solea solea in the Mediterranean Sea. Undersized specimens collected during sorting were assessed for vitality; some were retained for captive observation. The main drivers affecting discard survival at the time of catch sorting (immediate survival) were identified and used to outline four different operational conditions set (scenarios). Immediate survival in each scenario was subsequently modified by applying a hazard coefficient of survival after 5 days of captive observation in relation to each vitality class, thus obtaining relative survival estimates following discarding. Temperature and air exposure duration were found to exert a major effect on survival, with catch weight and seabed type being additional important factors. The relative survival rate showed an aggregate value of 22.9% (10.5–33.4%). Scenario approach can enhance our understanding of the stressors influencing discard survival. The outcomes are discussed to explore the potential applications of the procedure to the identification of mitigation strategies.

Understanding the hydrodynamics of a size sorting grid in a crustacean fishery

A size-sorting grid with a 6 mm bar spacing was proposed for a brown shrimp (Crangon crangon) beam trawl fishery. Considering the bar spacing, concerns regarding the hydrodynamics of such grid were raised. Here we experimentally investigated the hydrodynamics of four grid designs in a wind tunnel to identify which parameters mostly affected flow. By observing the Reynolds similarity criteria, we ensured that the measurement results in the wind tunnel are applicable in water. The four grids were tested at different angles of attack and wind velocities. Porosity and the inclination of the grid were found to be the main factors affecting the flow. The shape of the bars was also found to affect the flow, although to a lesser extent than porosity and angle, indicating that grid effectiveness is a function of how they are designed and installed in the fishing gear.

전남 진도연안에서 조망어구에 채집된 어류 종조성과 계절변동

전남 진도연안에서 조망어구에 채집된 어류 종조성과 계절변동

Biomass Estimation with a Hydroacoustic Survey and the Shrimp Beam Trawl Fishery in Gwangyanh Bay in Summer

Biomass Estimation with a Hydroacoustic Survey and the Shrimp Beam Trawl Fishery in Gwangyanh Bay in Summer

Size selectivity of combined square and diamond mesh codends of shrimp beam trawl for banded scad Caranx ( Atule ) kalla in the northern South China Sea

The shrimp beam trawl fishery in the northern South China Sea is characterized by high by-catch and poor selectivity problems. Among by-catch species, banded scad ( Caranx ( Atule ) kalla ) is economically the most important one. The aim of this study is to improve the selective properties of codends for banded scad. Size selectivity of 2 traditional diamond mesh codends, with mesh size 25 and 30 mm (defined as D25 and D30, respectively), and 4 new combined square and diamond mesh codends, with 25 mm square-mesh and 25 mm diamond-mesh (S25+D25), 30 mm square-mesh and 25 mm diamondmesh (S30+D25), 35 mm square-mesh and 25 mm diamond-mesh (S35+D25), and 35 mm square-mesh and 18 mm diamond-mesh (S35+D18), were tested for banded scad in shrimp beam trawl fishery of the South China Sea. A total of 54 valid hauls were finished using the covered codend method, and 5750 banded scad were caught. Selective parameters were obtained using the logistic equation with the maximum likelihood method, by incorporating the between-haul variation. The results show that the present minimum mesh size for shrimp beam trawl in the South China Sea, 25-mm diamond mesh size, is insufficient to release immature banded scad. The S35+D25 codend is proved to be the most effective codend to release immature banded scad, and its 50% retention length ( L50 ) is larger than the minimum landing size (MLS=63.5 mm) of banded scad. However, the 95% confidence intervals of L50 overlap among the three combined mesh codends, the S25+D25, S30+D25 and S35+D25 codend. For a sustainable exploitation of banded scad, larger mesh sizes are suggested to be investigated for the combined mesh codends.