Catch Composition Research Articles

Intense pressure on small and juvenile coral reef fishes threatens fishery production in Madagascar

AbstractSize‐based indicators are appropriate for monitoring status and guiding management of multi‐species, multi‐gear fisheries, such as coral reef fisheries. From May 2018 to April 2019, size distribution and composition of coral reef fish catches were monitored through a participatory landing survey in southwestern Madagascar. Fishers targeted a large diversity of fish taxa (75 families) and range of sizes (1.6–86 cm). Five predominant gears accounted for most of the catch (1360 [±39] t), including mosquito net trawl (27.7%), beach seine (26.8%), speargun (7.2%), gillnet (30.6%), and handline (7.1%). Due to widespread use of gears made from mosquito nets, 75% of fishes smaller than 9 cm and 47% of juvenile fishes were represented in the total catch number. Large‐size taxa (Scaridae, Lethrinidae, Siganidae, Acanthuridae, Synodontidae, Mullidae, and Labridae) were mostly harvested as juveniles. Catches varied by 8%–70% throughout the year. Size of coral reef fish, annual catches, and catch rates all declined since the 1990s.

Insights from catch composition and historical records of elasmobranchs in the Malvan fishery on the central west coast of India.

Although elasmobranchs (sharks and rays) are highly threatened by fisheries, there are few studies that examine gear and fishery effects on catch composition and abundance across India, one of the top elasmobranch fishing nations globally. We assessed elasmobranch diversity, abundance, catch rates and fishery characteristics using landing surveys in Malvan on the central-western coast of India, a major multi-gear, multi-species fishing centre, over three sampling periods from February 2018 to March 2020. We sampled 3145 fishing trips and recorded 27 elasmobranch species, of which nearly half are categorised as "Threatened" by the IUCN. In addition, we documented historical records by compiling information from identification guides, research papers, articles and reports. During the study period, the catch was dominated by small-sized coastal species like the spadenose shark (Scoliodon laticaudus) and the scaly whipray (Brevitrygon walga). Trawlers accounted for 64.9% of the catch, highest by number, and captured smaller-sized individuals. Nonetheless, artisanal and gillnet fisheries had higher catch per unit effort (CPUE) for rays (5.1 ± 1.0) and sharks (10 ± 1.0), respectively, and captured significantly larger-sized individuals. Through generalised linear models, we found seasonal, gear and fishery effects on the abundance and size of commonly caught species. The presence of neonates and gravid females of multiple species also suggests nursery grounds in this region. Historically, 141 species have been recorded in this region, and a comparison with current catch suggests a shift in elasmobranch community structure and potential mesopredator release. This study emphasises the importance of gear and species-specific research for conservation planning at the local level and suggests the need for management strategies with fisher cooperation.

Handling and Composition of Purse Seine Catches at Fishing Port, Batam City

Handling fish on board must be carried out properly to maintain the quality of the fish obtained. This study analyzed the handling process and composition of catches on purse seine vessels unloaded at the Fishing Port, Batam City. Handling of catches on purse seine vessels is carried out in the following stages, namely loading fish onto the ship, washing fish, sorting fish, washing fish before entering the Air Blasting Freezer (ABF) room, freezing using Air Blasting Freezer (ABF), packaging, and storage in cold storage rooms. The catch on trip 1st, with fishing operations from March 21st to April 15th 2022, resulted in a catch of 36,308 kg, with the following percentage of dominant catch composition, namely Indian scad of 78.61%, Bigeye scad of 7 .52%, Shrimp scad of 3.41%, Yellowtail scad of 3.05%, and Indian mackerel of 2.63%. The catch on trip 2nd, during the fishing operation period, from April 21st to May 13th, 2022, is presented in Table 2. The catch consisted of target and non-target species, with a total weight of 21,386 kg. The catch was dominated by Indian scad of 80.47%, Bigeye scad of 5.81%, Goldstripe sardinella of 5.29%, Bullet tuna of 2.63%, and Squid of 2.14%. Indian scad is the dominant species caught in the purse seine operation.

Composition of The Catch of Mini Purse Seine in The Java Sea

Pelagic fish are a type of fish that live in groups, with their habitat in shallow waters or sea level. Groups of small pelagic fish living in coastal waters and juveniles (kids) are known to be more abundant on the north coast of Java, which is a traditional mini purse seine fishing area. This study aims to analyze the catch composition of the mini purse seine fishing unit, which is operated in the Java Sea. The composition of the catch obtained using the mini purse seine fishing gear operating in the northern part of the Java Sea is dominated by small pelagic fish, which are the main catches mackerel (Rastrelliger sp.) 76%, white sardinella (Sardinella sp.) 18 %, and Splendid ponyfish (Eubleekeria splendens) by 4%, as for the bycatch obtained in the form of Largehead hairtail (Trichiurus lepturus), squid (Loligo sp.), Kawakawa (Euthynnus affinis), and other fish.

Participatory-based bio-economic activity mapping of small-scale fisheries: towards holistic management in the Bay of Biscay

Abstract The main goal of this paper is to improve the understanding of the spatial distribution of small-scale inshore fisheries (SSF) in coastal waters of the Bay of Biscay. The study used a participatory process, in which fishers, regional administration, and researchers were involved in supplying the data. Displayed on a 1-km2 grid, the data for effort and catch composition, variable costs, revenue, and profits at each site show the spatial patterns of the main SSF metier activities. This information indicates the economic value of the fishing grounds and the cost of reaching those areas, which can reveal possible trade-offs for more distant fishing grounds. Trammelnet vessels are widely dispersed, following economic incentives, while longliners also demonstrate high mobility, using many fishing sites, though the economic incentive does not always lead to high benefits. A narrow expansion range with activity close to the coastal area (trap, gillnet, and trammelnet users) suggests that the target-species stocks maintain their economic profitability even though it is lower than that in other coastal fleets. Such information helps develop a holistic approach to SSF management in this multi-use region by increasing the availability of high-quality multidisciplinary geospatial data, currently in short supply for this fleet.

Integrating fishers’ knowledge with oceanographic observations to understand changing ocean conditions in the Northeast United States

Recent warming in the Northeast United States continental shelf ecosystem has raised several concerns about the impacts on the ecosystem and commercial fisheries. In 2014, researchers from the Commercial Fisheries Research Foundation and Woods Hole Oceanographic Institution founded the Shelf Research Fleet to involve fishers in monitoring the rapidly changing ocean environment and encourage sharing of ecological knowledge. The Shelf Research Fleet is a transdisciplinary, cooperative program that trains commercial fishers to collect oceanographic information by deploying conductivity, temperature, and depth (CTD) instruments while commercially fishing. A total of 806 CTD profiles have been collected by the Shelf Research Fleet through December 2022. Participating vessels can view the conductivity and temperature water column profiles they collect in real-time. These profiles help inform their fishing practices and give insights when unexpected species appear in their gear or if their catch composition changes from previous years. The data collected by the Shelf Research Fleet are shared with and processed by researchers from numerous partnering institutions. The Shelf Research Fleet data have been used by researchers to better understand oceanographic phenomena including marine heatwaves, shelf-break exchange processes, warm core rings, and salinity maximum intrusions onto the continental shelf. The scope of the Shelf Research Fleet has grown over time to include efforts to more directly link oceanographic results with biological observations to better understand how changing ocean conditions are affecting commercially important species. This article describes the approach, successes, challenges, and future directions of the Shelf Research Fleet and aims to outline a framework for a cost-effective research program that engages fishers in the collection of oceanographic data, strengthening partnerships between fishing industry members and the scientific community.

Socioeconomic impacts of Australian redclaw crayfish Cherax quadricarinatus in Lake Kariba

The rapidly spreading Australian red claw crayfish Cherax quadricarinatus in the Zambezi Basin is a cause for concern considering its potential impacts. The assessment of the impacts of C. quadricarinatus is critical for the prioritisation of policy and management actions in Africa where literature on impacts of C. quadricarinatus is generally scant. We quantified the socioeconomic impacts conferred by C. quadricarinatus on artisanal gillnetting fishery in Lake Kariba to validate anecdotal fisher reports regarding crayfish damage to fish catch on static gillnets. From the catch assessments with registered fishers, fish catch composition, catch per unit effort (CPUE), crayfish entangled on gillnets CPUE, damaged fish CPUE, and damaged areas of the fish were recorded. Basin 2 had significantly higher CPUE with respect to fish catch and crayfish, as well as catch damage, compared to other basins. Damage by crayfish on fish was recorded in all the basins except in Basin 5. There was no correlation between number of crayfish bycatch and fish catch damage. The most frequently affected species was Oreochromis niloticus. On all fish species, eyes, guts and the tail were the frequently damaged parts. Due to C. quadricarinatus damage, fishers are losing 212 tonnes per year which translates to US$ 512 352.92 in Lake Kariba. Damage losses are particularly high when the total income per household in the region, which is mainly contributed by fishing, is considered. The lack of damage in Basin 5 is likely due to fishers developing adaptive new techniques which are less likely to be affected by crayfish. This study is the first in Africa to quantify the socio-economic losses due to crayfish in the field, and the first globally to derive observed costs for C. quadricarinatus. Data from this study have huge conservation and management implications, as crayfish threaten food security as well as incur personal losses to fishers via damage-related costs.

Simple pot modification improves catch efficiency and species composition in a tropical estuary mud crab (Scylla serrata) fishery

Pots are widely used fishing gear type for targeting different crustacean and fish species. Pot entrance size and design are among the most important technical parameters that influence the catch efficiency of certain species. An optimal pot entrance design should allow an efficient entry for the target species while preventing subsequent escape. The tropical estuary pot fishery targeting mud crab (Scylla serrata) in Vembanad Lake, India, employs rectangular pots with rectangular-shaped entrances. Low catch rates for target species and high bycatch rates are observed in this fishery. This study was carried out to investigate if a simple pot modification by extending the entrance of the traditional pots, can improve the catch efficiency of mud crab. Further, we estimated and compared the catch composition in this small-scale fishery using the traditional and modified entrance pots. The results showed that the catch efficiency for all sizes of mud crab is on average more than six times higher with the modified entrance pots compared to the traditional pots (622% (CI: 344–1867%)). However, significant quantities of juvenile crabs are caught in modified pots. Further, the bycatch ratio was significantly reduced for modified compared to the standard entrance pots in this fishery. These results show that such pot modifications have potential to significantly improve the catches in mud crab pot fisheries without increase in capture of bycatch species. However, additional mechanisms for excluding undersized crabs from pot catches should be investigated.

The Portuguese industrial pelagic longline fishery in the Northeast Atlantic: Catch composition, spatio-temporal dynamics of fishing effort, and target species catch rates

The multispecific and highly dynamic nature of pelagic longline fisheries demands a holistic view that will likely benefit the development of effective management strategies. This study aims to provide an integrated perspective of the Portuguese longline fishery targeting swordfish Xiphias gladius and blue shark Prionace glauca in the Northeast Atlantic, regarding fishing dynamics, target species catches and associated bycatch. Data from 896 observed fishing sets (887,641 hooks) collected between 2015 and 2020 were used in a cluster analysis to group sets according to the target species. These sets were investigated for spatio-temporal patterns, and the relationship between target species catches and environmental and operational characteristics were examined using generalized additive mixed models (GAMM). A total of 46,306 individuals from 54 species (30 fish, 11 sharks, 2 manta rays, 6 cetaceans, 2 sea turtles and 2 seabirds) were recorded. Swordfish and blue shark comprised over 88.3% of the total catch in numbers (33.6% and 54.7%, respectively). Overall, most of the fishing effort occurred west off mainland Portugal, congregated during autumn when vessels targeted mostly swordfish, and dispersed over the region during spring and summer, when vessels targeted mostly blue shark. The bycatch of sea turtles and a relatively higher diversity of bony fish species, yet low catch in terms of abundance, appeared more associated with sets identified as targeting swordfish. Recorded catch of tunas Thunnus spp. and pelagic sharks, such as the shortfin mako Isurus oxyrinchus and the porbeagle Lamna nasus, were more associated with blue shark sets. Bigeye thresher Alopias superciliosus, thresher Alopias vulpinus, pelagic stingray Pteroplatytrygon violacea and lancetfish Alepisauros ferox were found equally associated with both targeted species. Management strategies for the region are discussed in light of these new findings.

The The Effect of Using Led Lights (Light Emitting Diode) in the Operation of Bottom Gillnets on Catches In Pangandaran Waters, West Java

The objectives of the study were to analyse the response of dominant fish to different light colours that reflect the wavelength of light and to analyse the species composition of the gillnet catch to determine the fish that are positively phototaxis to LED light. Data collection was conducted using the experimental method. The experimental design used 1 unit of bottom gillnet gear with a mesh size of 4 inches, and used LED (Light Emitting Diode) lights. Trials using green LED lights and white LED lights were operated simultaneously between the control gillnet (without LED lights) and the experimental gillnet (with LED lights). The results of statistical analysis of gillnet catches with green LED light aids with white LED light aids and control nets have a significant effect on the number of gillnet catches. The results were: (1) The number of fish caught at a distance of < 1 m and at a distance of 1-2 m, this proves that many fish are attracted to light (positive phototaxis); (2) Proven by gill net fishing gear using green LED light aids obtained fish weighing up to 77.7 kg. (3) It is proven that the distance of the lamp with the position of the fish caught on the net sheet can produce the highest weight of fish caught, on green LED lights at a distance of <1 m the weight of the fish reached 30.89 kg.

PENGARUH WAKTU PENANGKAPAN PADA SIANG DAN MALAM HARI MENGGUNAKAN ALAT TANGKAP MINI PURSE SEINE TERHADAP HASIL TANGKAPAN IKAN YANG DI DARATKAN DI LINGKUNGAN PONDOK PRASI

The purpose of this study was to determine the number of catches obtained when caught during the day and caught at night, to determine the most effective composition of catches during the day and at night from the Mini Purse Seine Fishing Gear. This research was conducted in Pondok Prasi Environment, Ampenan District, Mataram City for 1 (month) starting from October 1 to November 1, 2013. The method used in this research is the Experimental Method, namely conducting experiments to see a result that leads to affirmation of the position cause and effect between the variables to be observed. Based on statistical analysis using the Ttest test at the 5% level (0.05) it can be seen that the total weight of the catch (kg) in treatment X1 (during the day) and treatment X2 (at night) showed a significant difference, where Thit (2, 93) > Ttab (2.048) this means fishing using a mini purse seine fishing gear which is operated during the day and at night gives different catches but has no effect on the type of fish caught

Brief results of research on scallops off the northern Kuril Islands in autumn 2022

The purpose of the work: to collect materials for assessing the state and dynamics of scallop stocks in the North Kuril zone, to study the spatial structure of settlements, to monitor the dynamics, distribution and composition of commercial catches in 2022.Materials and Methods: The work was carried out on a specialized rowing vessel “Vladimir Nikora” performed 210 dredging in the area limited by coordinates 49°20'N 49°30'N. and 154°57'E154°53'E at depths of 79-170 meters. The data collection tool is an industrial scallop dredge with a working width of 3.7 m (scallop dredge 1.04 / 3.74 m). The material type of the scallop dredge bag is kapron. The length of the dredging was 0.4-0.5 miles. The research covered the water area of 23 square meters. miles. Biological analysis was carried out for 5 thousand specimens of chlamy scallops. The biological state of hydrobionts was studied according to the methods generally accepted in fisheries research. For comparability of data on the distribution of hydrobionts, the catchability coefficient of the scallop dredge was used equal to 1. The linear dimensions of the scallops were measured with an accuracy of 1 mm.The practical significance of the research: to provide commercial and biological information materials on the total allowable catches of scallops in the North Kuril.

Entrapment of harbour porpoises (Phocoena phocoena) in herring weirs in the Bay of Fundy, Canada

Harbour porpoises (Phocoena phocoena) are small coastal cetaceans vulnerable to mortality in fishing operations. Not all interactions are fatal, however, and each year many porpoises swim into and are subsequently released from herring weirs in the Bay of Fundy, Canada through a targeted release programme. This study examines catch composition, body condition, characteristics associated with mortality and factors affecting entrapment of porpoises in weirs between 1992-2001. A total of 886 porpoises were recorded in weirs during this period. A total of 657 animals were involved in attempted releases: 588 were released alive and 69 were incidentally killed during release. The remainder of the animals swam out on their own or their fates were unknown. Estimated annual mortality represents less than 0.01% of the Bay of Fundy/Gulf of Maine population and only 1.03% of its annual potential biological removal level. The number of porpoises caught in weirs varied from eight in 1996 to 312 in 2001. Of the 390 animals released with a numbered identification tag, 25 were recaptured in weirs and 4 of those porpoises entered a weir a third time. Males comprised 63.5% of entrapments. Weirs and demersal gillnets captured animals from the same population, but the weir bycatch was biased towards younger, smaller animals. Porpoises that became trapped in weirs exhibited measures of body condition similar to those killed in gillnets and by gunshot wounds in the same waters. None were considered emaciated. Mortality in weirs appeared to be random; porpoises that died during release attempts were of the same age and sex composition and body condition as the individuals that survived. The use of a specialised large-mesh seine significantly increased the probability of successful release. Observations of the stomach contents data of porpoises killed in weirs indicate that porpoises feed while trapped in weirs, but perhaps not at the same rate as animals killed in gillnets. Entrapments peaked in August, concurrent with the highest landings of Atlantic herring, the target species of the weir fishery. Based on a logistical regression model, porpoises are 3.3 times more likely to swim into a weir on a night in which high tide falls during darkness. Weir entrapments do not have a significant effect on this population, largely because of on-going efforts to release porpoises from weirs.

The dominance of non-indigenous species in the catch composition of small-scale fisheries: A case study from the Kaş–Kekova Special Environmental Protection Area, Türkiye, Eastern Mediterranean

This study aimed to determine the catch composition and compare the catch per unit effort (CPUE) of indigenous and non-indigenous species in longline and trammel net fisheries in the Mediterranean coasts of Türkiye. The data were collected weekly from May 2020 to September 2021 by commercial fishing vessels (n = 62 days for trammel nets, n = 75 days for longlines). The results of the study indicated that more than 90% of the catch composition consisted of non-indigenous species in trammel net fishery and Pterois miles (Bennett, 1828), Siganus rivulatus Forsskål et Niebuhr, 1775, Siganus luridus (Rüppell, 1829), and Scarus ghobban Forsskål, 1775 were the most commonly caught species. Although indigenous species were more common in longlines compared with trammel nets, non-indigenous species Lagocephalus sceleratus (Gmelin, 1789) and Lagocephalus suezensis Clark et Gohar, 1953 were represented by relatively high catch ratios. The results also revealed that the CPUE of non-indigenous species exhibited seasonal differences. Although some non-indigenous species caught within this study have a market value, some other highly invasive species do not. Therefore, it is critically important to develop effective management tools to control bio-invasion. This study provides the first comprehensive research by utilizing basic data with relatively long-term surveys in the small-scale fishery on the Mediterranean coasts of Türkiye. The outcomes of this study can provide guidance to decision-makers.

Identifikasi dan Komposisi Hasil Tangkapan Ikan dengan Alat Tangkap Mini Purse Seine di Pesisir Kubutambahan, Bali

Kubutambahan Village is one of the villages in Kubutambahan Subdistrict, Buleleng Regency with the main catch fishery potential of Mackerel scad and several other species of fish. The fishing gear used by fishermen is dominated by mini purse seine. The purpose of this research was to determine the types of fish caught and the composition of fish catches. This research was conducted from September 2021 until October 2021. The data were obtained by direct observation in the field. Fish samples were taken using simple random sampling. The results showed that there were 20 species of fish, grouped into 5 orders, 9 families and 16 genera. The composition of the catches of fishermen using mini purse seine is dominated by Mackerel scad at 48.4% and the lowest is Hound Needlefish at 0.001% of overall catch.

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

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

Characterizing gear-based exploitation patterns of artisanal tuna fisheries in the western Indian Ocean: A snapshot from Kenya

This study explores gear-based patterns in catch rates and catch composition of landings by artisanal tuna fishers along the Kenya coast based on data collected at eight landing sites from March 2014 to March 2020, representing 1960 fishing trips and 192 mt of fish. Tuna and tuna-like species constituted 55% and 38% respectively of the sampled catch by weight. Troll lines, ringnets and handlines were the most commonly used representing 52%, 18% and 12% of the sampled fishing trips. Ringnets were the most productive catching an average of 547 ± 99.3 kg of tuna per trip, while handlines caught the lowest (12.6 ± 1.4 kg trip −1). Longlines and drift gillnets caught the highest proportion of tuna representing 95% and 89% respectively of landings, while reef seines and monofilament gillnets caught the lowest. The mean catch per unit effort for tuna was 78.5 ± 7.7 (SE) kg trip −1, while that for tuna-like species was 35.2 ± 1.9 (SE) kg trip −1. Kawakawa (Euthynnus affinis), bigeye (Thunnus obesus), and yellowfin (Thunnus albacares) were the most common and most abundant representing 31.5%, 21.2%, and 20% of the tuna landings, respectively; while skipjack (Katsuwonus pelamis) constituted the lowest at 4%. Although tuna was landed year-round, species-specific variations in catch rates and size distribution were observed among the gear types and between seasons. Cluster analysis and non-metric ordination based on combinations of gear type and season defined four groupings with two gear types (ringnets and set gillnets) showing seasonal differentiation in the composition of tuna and tuna-like species. Majority of tuna were above the reported size at first maturity (L50) except for yellowfin and bigeye tuna. Overall, the findings provide new insights on Kenya’s artisanal tuna fishery addressing important information gaps on exploitation patterns of artisanal tuna fleets of the western Indian Ocean region.

The wedge clam (Donax trunculus) hand-operated fishery in the NW Mediterranean Sea: Landings, catch composition, damage rates and impact of fishing activity

The bivalve wedge clam Donax trunculus is a highly valued species in Spain, but wild stocks have decreased in the Mediterranean region in recent decades. Internal demand exceeds the existing supply derived from local production. Hand-operated dredge fishery is still important in some coastal areas of Spain, such as the Ebro Delta (NE Spain). However, scientific information is lacking on most aspects of this fishery which is essential for its sustainable management. In this context, this study aimed to provide the first characterization of the hand-operated dredges fishery; evaluate the damage of this fishery on the megabenthic fauna; and analyze the impact of the fishing activity on the wedge clam. Our results indicate that landings declined dramatically since the mid-1990s and the main causes for this decline are postulated. Fishing effort was highly seasonal, being more intense from March to September. The discard fraction was very small (5.74% in abundance and the 3.74% in biomass) and 61.93% of the discards did not suffer damage. Clam fishing activity had an impact on recruit density in the short term (3 months), but not on recruit size and commercial fraction density, biomass and size. Our results provide tools for a better management of this type of fisheries.

Length–length relationships for the main shark species caught in the commercial shark fisheries of Western Australia

AbstractLength–length relationships are presented for 19 shark species caught in the commercial shark fisheries of Western Australia. A robust linear regression model was used to estimate the relationship between interdorsal, total and fork lengths. Sharks are typically landed as trunks, so information generated in our study is essential for converting partial lengths to total lengths for reconstructing catch composition, an essential step for assessing the status of shark populations.

Net gain: Low‐cost, trawl‐associated eDNA samplers upscale ecological assessment of marine demersal communities

AbstractMarine biodiversity stewardship requires costly and time‐consuming capture‐based monitoring techniques, which limit our understanding of the distribution and status of marine populations. Here, we reconstruct catch and demersal community composition in a set of 24 fishing sites in the central Tyrrhenian Sea by gathering environmental DNA (eDNA) aboard commercial bottom‐trawl fishing vessels. We collected genetic material from two sources: the water draining from the net after the end of hauling operations (“slush”), and custom‐made rolls of gauze tied to a hollow perforated sphere placed inside the fishing net (“metaprobe”). Species inventories were generated using a combination of fish‐specific (Tele02 12S) and universal metazoan (COI) molecular markers. DNA metabarcoding data recovered over 90% of the caught taxa and accurately reconstructed the overall structure of the assemblages of the examined sites, reflecting expected differences linked to major drivers of community structure in Mediterranean demersal ecosystems, such as depth, distance from the coast, and fishing effort. eDNA also returned a “biodiversity bonus” mostly consisting of pelagic species not catchable by bottom trawl but present in the surrounding environment. Overall, the “metaprobe” gauzes showed a greater biodiversity detection power as compared to “slush” water, both qualitatively and quantitatively, strengthening the idea that these low‐cost sampling devices can play a major role in upscaling the gathering of data on both catch composition and the broader ecological characteristics of marine communities sustaining trawling activities. This approach has the potential to drastically expand the reach of ecological monitoring, whereby fishing vessels operating across the oceans may serve as opportunistic scientific platforms to increase the strength and granularity of marine biodiversity data.