Trawl Fishing Research Articles

Мегабентос западного прибрежья архипелага Новая Земля в приловах донного трала

As a part of a marine expedition on the R/V «Dalnye Zelentsy» along the western coast of the Novaya Zemlya archipelago, an assessment of megabenthic species diversity and biomass in bycatch of trawl was carried out in August 2023 specimens of 29 taxa belonging to 6 phyla were identified during the survey. The highest species diversity (20 species) was recorded in the northern coastal area of the Novaya Zemlya archipelago, where the dominant forms in terms of biomass were sea urchins Strongylocentrotus pallidus – 237.1 kg/km2. A tendency for a 5-fold decrease in megabenthos species diversity and a decrease in the average biomass of organisms – from 17.2 to 0.47 kg/km2 was detected with transition from north to south. The association of sea urchins S. pallidus and brittle stars Gorgonocephalus sp. (84 % biomass share of representatives in bycatch) is identified in the north of the study area, which is replaced by the association of sea urchins S. pallidus and crustaceans Chionoecetes opilio (74.6 %) when moving to the south. According to the results of the RDA analysis, the effects of trawl fishing and type of water mass have the greatest impact on species diversity and biomass of megabenthic organisms. Trawling intensity, type of water mass, and sediment characteristics explain 75 % of the observed variability in these biological parameters.

Biological characteristics of the Pacific halibut in the Bering Sea and off the eastern coast of Kamchatka in spring 2022

The purpose of the work: to give a biological characteristic of the Pacific halibut in different areas of the Bering Sea and off the eastern coast of Kamchatka and to analyze its size age composition in catches of trawl fishing. Methods used: the material was collected during the expedition research, a complete biological analysis of the Pacific halibut was carried out, the otoliths were selected to determine the age. The age was determined in accordance with the guidelines developed specifically for the Pacific halibut in the International Commission on Pacific Halibut (International Pacific Halibut Commission, IPHC).Novelty: the elements of novelty are generalized and analyzed data on Pacific halibut. The material collected in the waters of Eastern Kamchatka and the Bering Sea in 2022. Pacific halibut from trawl catches have been studied, its biological characteristics have been considered, the size-age composition and growth rate have been analyzed.Practical significance: the results of these studies can be used in forecasting the stocks of Pacific halibut in this area.Result: data on catches of Pacific halibut in different regions of the North West Pacific Ocean, the size and age composition, a comparative characteristic of males and females by growth rate, the age composition of fish by maturity stages.

Non‐extractive fish diversity assessment in Mediterranean rhodolith beds

Abstract Rhodolith beds, recognized as biodiversity hotspots with high ecological and conservation importance, face local anthropic pressures, including trawl fishing. However, monitoring the diversity associated with this sensitive biogenic habitat in the deep waters of the Mediterranean Sea is challenging. Traditional monitoring methods, such as experimental trawling and trammel nets, are extractive and have sampling limitations in providing comprehensive diversity inventories. In this work, we explore three alternative techniques (still video cameras, environmental DNA [eDNA] and bioacoustics) to monitor fish assemblages associated with rhodolith beds in the Menorca Channel at 45–80 m depth. Ten sites were surveyed with eDNA, and 66 fish taxa were identified, including endangered sharks and cryptic species. The molecular operational taxonomic units (MOTUs) richness varied significantly according to habitat heterogeneity, being higher in homogeneous bottoms, and to exposure to trawling, with higher richness in non‐exposed areas. Bioacoustics, though limited by a reduced library of fish sounds, detected differences in sound richness between habitat types, and the highest abundance of sounds was recorded in the areas with the greatest small‐scale habitat heterogeneity. Underwater video revealed limitations in species detection but proved effective for characterizing small‐scale habitat types and heterogeneity. In summary, each technique provides valuable information at different spatial scales and levels of detail. To assess the feasibility of these techniques for long‐term monitoring, we explored their capabilities and limitations in terms of costs, survey logistics and data output.

ANALISIS HASIL TANGKAPAN IKAN TONGKOL YANG DIDARATKAN DI PELABUHAN PERIKANAN NUSANTARA AMBON

This research aims to analyze the catches of tuna landed at the Ambon Nusantara Fisheries Port. The research was conducted for two months, from January to February 2023, using descriptive methods. Primary data was collected through direct observation and interviews with fishermen and port officers, while secondary data was obtained from PPN Ambon. The results of this research show that the catch was landed by four fishing fleets, namely purse seines, gill nets, fish trawls and lines fishing. The total catch landed during the 2012-2021 period was 510,203 tons, which was dominated by Auxis thazard. Purse seines are the most dominant fishing gear used, contributing 52.1% of the total catch with a total fishing effort of 597 trips. The productivity of the fishing fleet fluctuates from year to year, the lowest productivity for Euthynnus affinis occurred in 2018 and the highest in 2013, while the lowest productivity forl Auxis thazard occurred in 2017 and the highest in 2018. Fluctuating and low productivity indicates the existence of potential for overfishing. This research suggests the need for further analysis regarding the potential and level of utilization of the two species of frigate tuna landed in PPN Ambon

Innovative Cutting and Valorization of Waste Fishing Trawl and Waste Fishing Rope Fibers in Cementitious Materials

The valorization of waste fishing trawl (WFT) and waste fishing rope (WFR) fibers in cementitious materials (CMs) has gained attention in recent years; however, the lack of information on the cutting and cleaning techniques for these fibers hinders their widespread commercial utilization. Existing research primarily relies on manual cutting, which proves to be impractical for large-scale production due to its time-consuming nature and lack of industrial feasibility. This research is a component of the VALNET project and introduces an innovative technique that utilizes the cutting mill to convert WFT and WFR into fibers to effectively overcome the constraints of earlier methodologies. By employing a rotor with blades, this apparatus enables efficient and precise cutting of WFT and WFR, eliminating the need for labor-intensive manual cutting. The sustainable cleaning of WFT and WFR was carried out utilizing rain and wind by placing them outside for a certain period of time. The advancements presented in this study provide a pathway for an efficient and scalable valorization of WFT and WFR fibers in CM. The study focused on analyzing the impact of varying fiber sizes and percentages on the mechanical properties of CM. Different sizes obtained from the cutting machine and different fiber percentages were examined to gain a better understanding of their influence. The fibers obtained by the utilization of a 20 mm sieve yield optimal outcomes, while the incorporation of fibers at a volume fraction of 0.5% yields the most favorable results. Furthermore, the study presents evidence of a noticeable rise in porosity resulting from the incorporation of WFT and WFR fibers, regardless of their size and proportion. Porosity slightly increases as the fiber length increases, but the rise in fiber proportion leads to a significantly greater increase in porosity.

From caves to seamounts: the hidden diversity of tetractinellid sponges from the Balearic Islands, with the description of eight new species

The sponge fauna of the Western Mediterranean stands as one of the most studied in the world. Yet sampling new habitats and a poorly studied region like the Balearic Islands highlights once again our limited knowledge of this group of animals. This work focused on demosponges of the order Tetractinellida collected in several research surveys (2016–2021) on a variety of ecosystems of the Balearic Islands, including shallow caves, seamounts and trawl fishing grounds, in a broad depth range (0–725 m). Tetractinellid material from the North Atlantic and more than twenty type specimens were also examined and, for some, re-described in this work. All species were barcoded with the traditional molecular markers COI (Folmer fragment) and 28S (C1-C2 or C1-D2 fragment). A total of 36 species were identified, mostly belonging to the family Geodiidae (15 species), thereby bringing the number of tetractinellids recorded in the Balearic Islands from 15 to 39. Eight species from this study are new: Stelletta mortarium sp. nov., Penares cavernensis sp. nov., Penares isabellae sp. nov., Geodia bibilonae sp. nov., Geodia microsphaera sp. nov. and Geodia matrix sp. nov. from the Balearic Islands; Geodia phlegraeioides sp. nov. and Caminus xavierae sp. nov. from the North East Atlantic. Stelletta dichoclada and Erylus corsicus are reported for the first time since their description in Corsica in 1983. Pachastrella ovisternata is documented for the first time in the Mediterranean Sea. Finally, after comparisons of type material, we propose new synonymies: Geodia anceps as a junior synonym of Geodia geodina, Erylus cantabricus as a junior synonym of Erylus discophorus and Spongosorites maximus as a junior synonym of Characella pachastrelloides.

An assessment of demersal fisheries by trawling in less than 50 m of water off Egypt’s Mediterranean coast

Trawl fishing is identified as one of the most significant factors that could affect the diversity of demersal fish groups but not for all depth strata. Since the increased exploitation of Non-Indigenous Species (NIS) has caused the trawl fishing grounds to shift towards shallower seas where their biomass density is maximum, this study aimed to assess demersal fisheries by bottom trawls in the Mediterranean water off Egypt at depths less than 50 m. In this study, data from eight bottom-trawl hauls were used to describe the diversity of the demersal fish catch. The hauls varied in their species composition and both in the number and the weight of individuals. The length frequency distribution of the most occurred species was studied. A total of 87 species were identified in the catch, out of which 32 were recognized as NIS. The percentages of most of the NIS decreased from the east to the west of the surveyed area. There are always changes in fish diversity because of increasing fishing efforts on demersal fish communities, but not for all depth strata, therefore, a monitoring program has to be designed for better assessment of fisheries resources in the Mediterranean water off Egypt.

No deleterious circumference effects for T90 codends in an Australian fish trawl targeting tiger flathead, Platycephalus richardsoni

In an attempt to improve the selectivity of Australian fish trawls targeting tiger flathead, Platycephalus richardsoni (≥28 cm total length), the utility of four-seam codends with shortened lastridge ropes and comprising 71-mm meshes turned 90° (T90) hung at the narrowest and widest coherent circumferences was compared against a traditional 91-mm diamond-mesh (T0) codend. Significant effects of codend configuration were limited to an increase in the catches of another commercially important species, latchet, Pterygotrigla polyommata, by both T90 codends, and greater escape of some small tiger flathead from the wide 71-mm T90 codend than from the 91-mm T0 codend. Notwithstanding a need to investigate slightly larger T90 mesh sizes for the fishery, the data imply that unlike most codend configurations, circumference does not negatively affect selection in the stated designs and might not require future regulation.

Pengaruh kemiringan pada bagian sayap terhadap kelajuan tenggelam tali pemberat alat tangkap pukat cincin

Purse seine is a tool (gear) used to catch pelagic fish that form a swarm. As with other fishing gear, a purse seine unit consists of a net, a boat, and auxiliary equipment (rollers, lights, echosounders, and so on). Purse seine is a fishing gear classified in the surrounding net group. Purse seine is also known as a ring trawl because it is equipped with a ring that is used as a place to attach the coloring rope which is very important during the operation of the net. Because the net that was originally bagless will form a pocket at the end of the capture operation. The ring trawl itself has a different name in each region in Indonesia, in North Sulawesi it is known as soma pajeko. There are three technical factors that need to be considered for the success of ring trawl fishing, namely: (1) circular speed, (2) speed and depth of sinking ballast rope, and (3) speed of pulling the choir ropeThe speed of sinking is largely determined by the ballast, the type of material, the size of the thread and the size of the net bit, as well as the ratio of the length of the float rope and the ballast rope. The sinking speed of the ballast rope is calculated based on the relationship between the depth and the sinking time of the ballast rope needed. The speed of the ballast can be increased by increasing the weight of the ballast, but it must be considered because it will increase the tension of the net. Ballast weight per meter ballast ropeBut it should be considered because it will add tension to the net. Greater ballast weight per meter ballast rope will add greater sinking speed. The method used in this study is an experimental method, which is a study that looks for the influence of certain variables on other variables under tightly controlled conditions. The analysis in this study consisted of 4 net models with different slope percentages, namely 57%, 75%, 100% and 125% slopes. The results of the analysis showed that the more tilted the wing with a slope of 57%, 75% and 100%, the more the sinking rate of the ballast rope but for a slope of 125% it does not contribute to the speed of sinking 57% slope at a depth of 5.5 meters the required time is 16.37 seconds, 75% slope at a depth of 5.5 meters is 15.16 seconds, 100% slope at a depth of 5.5 meters the time required is 19.84 seconds and 125% slope the time required at a depth of 5.5 meters is 19.88 seconds. The best sinking speed of the four net models that have been made based on existing data is at 75% slope.

First data on the occurence and ecology of Giant hookear sculpin <i>Artediellus ingens</i> (Cottidae) off the Kuril Islands

Based on materials collected during monitoring of bottom trawl fishing, the occurrence, some aspects of ecology and size composition of giant hookear sculpin Artediellus ingens were examined for the first time off the Middle Kuril Islands. It has been established that this species is a regular bycatch at the depths 250–488 m at the temperature of the near-bottom water layer of 1.8–3.9 °C. Most likely A. ingens belongs to mesobenthal ichthyocene. In the trawl catches, this species is represented by individuals of 10–19 cm TL. Comparison of the maximum body length with that of the other species of the genera Artediellus indicated this species is one of the largest.

Semi-pelagic self-adjusting otter boards: effects on the catching performance of a demersal trawl

In this study, we investigate whether replacing conventional seabed-contacting otter boards with semi-pelagic self-adjusting otter (SAO) boards, which have the ability to maintain a given height above the seabed, affects the catch efficiency of a demersal fish trawl. Experimental fishing trials, using the alternate haul method, were conducted in the Kattegat and Skagerrak with three otter board configurations using conventional seabed-contacting otter boards; the SAO set to maintain a target height over the seabed of 1 m; and the SAO set to maintain a target height of 5 m. Replacing conventional otter boards with SAO resulted in a loss of catch efficiency for haddock ( Melanogrammus aeglefinus), whiting ( Merlangius merlangus), and plaice ( Hippoglossoides platessoides), while no significant difference was found for cod ( Gadus morhua), common dab ( Limanda limanda), and lemon sole ( Microstomus kitt). When comparing the SAO-1 m and SAO-5 m, it was observed that SAO-5 m resulted in a loss of catch efficiency for haddock and plaice, a minimal reduction for cod, and no significant difference for whiting, common dab, and lemon sole.

УСОВЕРШЕНСТВОВАНИЕ ТРАЛОВОГО ПРОМЫСЛА ТЮЛЬКИ В АЗОВСКОМ МОРЕ В СОВРЕМЕННЫХ УСЛОВИЯХ ВОССТАНОВЛЕНИЯ ПОПУЛЯЦИЙ ОСЕТРОВЫХ РЫБ

Background. At present, the Black and Caspian Sea sprat (tyulka) is the least exploited species of the aquatic biological resources in the Azov and Black Sea Fishery Basin, although it has always been a valuable fishing target and a possible reserve pool for the increase of fish catches in the Basin. In the recent years, with the increasing number of midwater trawls allowed for using in the Black and Caspian Sea sprat (tyulka) fishery, all vessels transitioned to its trawl fishing; however, its total catch is decreasing, and the fishing results of these vessels are on the decline. Relevance. Taking into consideration the stock restoration occurring to the sturgeon fish species in the Azov Sea Basin in the recent years, it is necessary to take measures for maintaining this trend, as the Black and Caspian Sea sprat trawl fishing can result in increased mortality or injury of sturgeon fish and considerably damage their population. With a substantial decrease in the Black and Caspian Sea sprat fishing stock, the matter of stock restoration of the sturgeon fish species in the Azov Sea can induce the prohibition of the trawl operations in this water body, including the complete ban of the insufficiently profitable trawl fishing of the Black and Caspian Sea sprat in its current form. The aim of this article is to examine the design of the midwater trawls used in the Black and Caspian Sea sprat fishing in the Azov Sea, to investigate the global best practices in the trawl selectivity improvement, and to substantiate the main design characteristics for the specialized tyulka midwater trawls and means of their selectivity improvement. Methods. The standard methods of sample collection and data processing that could characterize fishing methods, gears and techniques for harvesting aquatic bioresources have been used. Results. The designs for the specialized trawls for the Black and Caspian Sea sprat fishing (exploitation) and methods for their selectivity improvement have been developed. Conclusion. These specialized trawls with the sorting units and a new principle of using otter boards (trawl doors) can increase fishing selectivity and mitigate possible damage inflicted by trawling to the populations of sturgeon fish species in the Azov Sea.

Impact of ports construction activities on structure, composition and diversity of fish population: case study of Tema, Ghana

Ports offer economic progress to many coastal developing countries. In view of the economic importance, the rising demand for maritime benefits requires the expansion of existing ports. However, marine ecosystems may become vulnerable to negative impact from the construction of these maritime structures. Therefore, the aim of the study was to establish the impact of Tema port expansion on the diversity and population structure of fish species. Data were collected quarterly from June 2018 to November 2021 through trawling fishing activities off the coast of Greater Accra, Ghana, and subsequently analysed using Primer 6 software. Sampling locations along the coast of Greater Accra included Vernon Bank (VNB), Disposal area (DSA) and Offshore Sakumono (OSK). The increased and reduced number of species at VNB and DSA, respectively, could be alluded to dredging and disposal of dredged spoils. Diversity indices at OSK site was higher than those observed in disturbed areas due to the absence of impact in this control area. Thus, it is recommended to conduct further studies on the assemblage of invasive species that migrated to the VNB during dredging activities, since these species can have severe economic impact on fishing activities of artisanal fishermen, especially at the local level.

OCCURRENCE OF Bregmaceros nectabanus (WHITLEY, 1941) IN THE GULF OF ANTALYA

With the opening of the Suez Canal in 1869, a connection was established between the Red Sea and the Mediterranean. Because of this connection, many organisms of Red Sea origin migrated to the Mediterranean. These migratory organisms also include fish. For this reason, we monitor and determine the number of fish originating from the Red Sea in the Gulf of Antalya. One of the fishing methods in the Gulf of Antalya is trawler fishing. One of the fish species caught during commercial trawling is horse mackerel. A small and different type of fish was found in the stomach of horse mackerel caught during trawling on October 26, 2021 in the Gulf of Antalya. During the species identification of these fish samples, which were intact in the stomach content of horse mackerel and preserved their integrity, it was determined that these fish were Bregmaceros nectabanus, which is included in the Bregmacerotidae family. With this study, the presence of B. nectabanus identified in the Gulf of Antalya was one more addition to the number of Red Sea origin fish species in the Gulf.

Vulnerability of six cold-water corals to sediment resuspension from bottom trawling fishing

Bottom trawling can significantly affect benthic communities, directly through immediate removal of sessile organisms and indirectly through sediment resuspension. Submarine canyons, often surrounded by fishing grounds, are important habitats for cold-water corals (CWC). Vulnerability of CWCs to increased suspended sediment concentration (SSC) is key to understanding the severity of bottom trawling effects on those communities. Here we show survival, growth, and physiological response of six CWCs from a Mediterranean submarine canyon (Dendrophyllia cornigera, Desmophyllum dianthus, Desmophyllum pertusum, Madrepora oculata, Leiopathes glaberrima and Muriceides lepida), exposed to a long-term, aquarium-based sedimentary disturbance experiment. Compared to cup coral and octocoral, which did not exhibit symptoms of distress, our data indicate that colonial scleractinian corals and black coral, which experienced substantial polyp mortality in enhanced SSC treatments, are more vulnerable. Indirect impact of bottom trawling could thus contribute to structural simplification of CWC communities posing an additional stressor alongside with global climate change.

Distribution of rhodolith beds and their functional biodiversity characterisation using ROV images in the western Mediterranean Sea

Underwater biogenic habitats composed of unattached calcified red algae, named as rhodolith or maërl beds, may extant either alive or dead, over the seabed. The accumulation of rhodoliths constitute three-dimensional structured biogenic habitats that harbour high diversity of benthic organisms. In the Mediterranean Sea, rhodolith beds can be found between ca. 50 and 100 m, increasing diversity of the continental shelf habitats and their conservation value. Despite the remarkable relevance of these habitats, information regarding their spatial distribution in the western Mediterranean is scarce. In addition, these habitats are threatened by a range of anthropogenic activities and by climate-driven changes. In this study, we explored areas with rhodoliths' occurrence from the north to the south of the east coast of Spain. By feeding video recording data into a spatial distribution model, we assessed which biophysical drivers: (i) shape the spatial variation in the abundance of rhodoliths and (ii) define the assemblages of the biological traits and functional richness of the associated epibenthic fauna recorded by video. In addition, we examined the impact of fishing activities on these habitats. Our results evidenced that ‘Depth’ and ‘Temperature’ were important environmental factors explaining rhodoliths variation, and we defined their optimal distribution range in the western Mediterranean. The biological traits approach showed significant effects of the geographical location of rhodolith beds and their small-scale spatial heterogeneity on the functional richness index. Indeed, the lowest functional richness value was observed in the area closer to trawl fishing which could be related to habitat degradation due to trawling. This study contributes to the knowledge of deep-water rhodolith beds in the western Mediterranean and reinforce the importance of rhodolith beds in continental shelves as these constitute heterogeneous seabed habitats that harbour a high species and functional diversity.

Modeling the Distribution of Atlantic Croaker and Spot in a Dynamic Seascape Using Metabolic Scope

In estuarine and coastal systems, anthropogenic activities and directional changes in global air temperatures have led to increased water temperatures, as well as increased frequency and severity of episodic hypoxia. These alterations have had population-level effects on aquatic organisms, including changes in species-specific distributions. Because physiology is the transfer function connecting environmental conditions to individual behaviors and eventually to population-level effects, we used individual-based models (IBMs) that incorporate changes in metabolic scope as motivation for movement. Our objective was to investigate the effects of temperature and hypoxia on the distribution of Atlantic croaker and spot in Chesapeake Bay. We compared the predicted monthly fish distributions from the IBMs with apparent fish distributions recorded by the VIMS Juvenile Fish Trawl Survey during 1988–2014. IBMs failed to reproduce accurately the apparent spatial distributions of Atlantic croaker and spot. More specifically, compared with the trawl survey, IBMs predicted larger proportions of these two species would be captured in the lower regions of Chesapeake Bay and smaller proportions in the York and Rappahannock rivers. We postulate that, because similar thermal and oxygen conditions were occupied by fish in the IBMs and in the wild, temperature may not be the most important factor motivating the movement of Atlantic croaker and spot in Chesapeake Bay, and other spatial factors (e.g., prey availability) act in concert with temperature and hypoxia to determine the spatial distributions of Atlantic croaker and spot in Chesapeake Bay. Alternatively, surveys used to estimate species occurrences could be biased if gear vulnerability is affected by temperature or oxygen conditions (or both). Additional research is needed to clarify which condition is true or if a combination of these factors (and others) led to discrepancies between predicted and apparent fish distributions based on trawl survey data.

Marine fisheries management in the Eastern Central Atlantic Ocean

Marine fishing is crucial to the socio-economy of West Africa fishery. However, the sector has many challenges, which have increased the call for an integrated approach that provides links among human needs, activities, changes in the state of the environment, and the resultant effect on ecosystem services for sustainable management in fulfilment of the Conservation on Biological Diversity and the Sustainable Development Goals. This study uses a socio-ecological framework (Drivers (D), Activities (A), Pressure (P), State (S), Impact (I) on welfare (W), and Response (R) as a Measure (M); DAPSI(W)R(M)) to assess the marine fishery sector of Ghana. Data were systematically sampled and analysed from vessel logbooks, fish manifests, observer reports, and relevant publications.Results show that Drivers, including livelihoods and revenue, food, and social status, contribute to industrial tuna and trawl fishing, and marine artisanal fishing activities. Where illegal fishing methods such as small mesh-size nets (less than 25 mm), lights, poisonous substances, among others, are used. These activities have contributed to the pressures of selective fishing of juvenile and adult pelagic and demersal fish species. This has contributed to (changes in the State) the decline and vulnerability of Sardinella spp., and Engraulis encrasicolus, among others. The Impact on welfare includes Ghana becoming a net importer of marine species with increasing idleness of fishers due to reduced catch. Several management measures, including the Fisheries Act 625 of 2002 and Fisheries (Amendment) Regulations L.I. 2217 of 2015, and quotas in the tuna sector, among others, have been instituted to curb the effect of anthropogenic activities. Management measures, including influencing consumer behaviour for a sustainable fishery, enforcement, and data-driven management, have been recommended, in response to the targets of the Sustainable Development Goals, the United Nations Decade of Ocean and the Convention on Biological Diversity.

Hydrozoans (Cnidaria) from the estuarine zone of the International Minho River, NW Iberian Peninsula, Atlantic Europe

In environmental impact studies conducted in coastal regions, the survey of biodiversity is crucial in areas that are subject to interventions. As the characterization of aquatic invertebrates may indicate important issues that need to be addressed. In this regard, hydrozoans (Class Hydrozoa, Phylum Cnidaria) are recognised as important bioindicators. These organisms are characterized by biradial, tetramerous, or polymerous symmetry, a simple gastrovascular system, and non-cellular mesoglea. The aim of the present study was to perform the first descriptive survey of hydrozoan species found in the estuary of the International Minho River (shared by Portugal and Spain), which is classified as an Important Bird Area and is a site of the Natura 2000 network. Specimens were collected from the tidal marine, brackish and tidal freshwater wetland zones through 1) glass eel fishing bycatch using stow nets at flood tides around the new moon (length of float lines: 10 m; bottom anchored lead line: 15 m; height: 8 m; mesh size: 1–2 mm); 2) beam trawl fishing (bottom trawling for 10 min), including species associated with bivalves; 3) Van Veen grab sampler for sediment sampling; 4) on wood fragments in the saltmarsh of the Coura River (tributary of the Minho River); and 5) individuals on the leaves of aquatic plants. A total of 19 species were identified, four of which were first occurrences for Portugal, six for the mainland coast of the country, and one for Southern Europe [Diphasia fallax (Johnston, 1847)]. Three neotypes are also proposed for the species Hydra viridissima, Hydra oligactis and Gymnangium montagui based on the criteria of the International Commission on Zoological Nomenclature. As these organisms are considered bioindicators, the diversity of the hydrozoan community in the Minho River may indicate good water quality.

Modelling the current status of Lake Malawi fish stocks, an inland lake in East Africa

Abstract Inland rift valley lake systems have been sustaining humanity for a long time. Only recently have commercial fisheries entered these systems and for Lake Malawi, this occurred in the mid-1970s upon successful experimental trawl fishing. Lake Malawi with the highest diversity of freshwater fishes in the world has had fisheries for centuries. Previous assessment of the impact of commercial trawl fisheries revealed significant changes in stock composition and overall biomass. The study evaluates the state of fisheries resources using novel techniques developed using integrated assessment methods amenable to data poor fisheries. Data from biomass assessment surveys and landed catch from 2016 to 2019 were examined to determine the status of selected fish stocks over time. Stock Synthesis for Data Limited tools in R environment were used to run the models. The Surplus Production Models and Statistical catch-at-age models that were used to examine alternative hypotheses on life history parameters on the key stocks exploited primarily by the commercial trawl fishery and evaluate long-term trends on these populations. The study results revealed that Mcheni (Rhamphochromis spp.), Ndunduma (Diplotaxodon limnothrissa) and Utaka (Copadichromis virginalis) stocks are within the sustainable limits, while Chambo (Oreochromis karongae), Chisawasawa (Lethrinops gossei), Mlamba (Bathyclarias nyasensis) and Kampango (Bagrus meridionalis) appear to be overfished in recent years, though Kampango may have recovered recently. Given, the large uncertainties with productivity of most tropical fishes with climate change, as well as large uncertainties due to inaccurate and untimely data submissions, it is recommended that a systematic monitoring and evaluation program, like the one being conducted in Lake Malawi should be developed for other inland lake systems. If stocks are facing overfishing by both the small-scale and commercial trawl fisheries, limits to overall catch and size should be implemented possibly through output controls such that the fisheries remain sustainable for the long term.