Search Results (285)

The sustainable management of water bodies with hydropower plants (HPPs) and protected rheophilic fish species is challenging. The key question is whether impounded rivers can still provide habitat for protected rheophilic fish species, including Natura 2000 species. We investigated hydro-morphological conditions and fish communities, focusing on the bottom-dwelling Danube longbarbel gudgeon (Romanogobio uranoscopus) and the medium-distance migrating cactus roach (Rutilus virgo) in the Brežice HPP system on the Sava River in Slovenia. Fish sampling using an electric bottom trawl in the HPP impoundment, electrofishing in the nearshore, and video surveillance in the fish pass revealed a diverse and distinctive fish community. This community reflected rheophilic conditions in the upper impoundment and fish pass, and lentic conditions in the lower impoundment. These findings provide evidence that impounded rivers, when complemented by well-designed mitigation measures, can sustain rheophilic fish species, including the Danube longbarbel gudgeon and cactus roach. Maintaining rheophilic habitat within the impoundment, combined with a functioning river-like side channel, is crucial. However, at Brežice HPP, changes in the management of the fish pass water inflow are necessary to ensure adequate and consistent hydraulic conditions and water temperatures. Applying a knowledge co-creation approach, which requires productive interaction among scientists, managers and policy makers, could help to find the best solutions for sustainable water ecosystem management. Full article

Understanding the seasonal dynamics of the fisheries and crustacean communities are of crucial ecological significance. To investigate the structural characteristics of these communities and their seasonal dynamics in the offshore of the Zhoushan Archipelago Seas, China, this study conducted a four seasons’ trawl survey to collect fisheries data in spring, summer, autumn, and winter of 2022. A normalized abundance size spectrum approach was applied to investigate the seasonal variation in regressed parameters (slope and intercept) for fish-only and fish-plus-crustacean communities. Our study found that average values of the slope of the size spectrum for fish and fish-plus-crustacean were −1.36 and −1.53, respectively; the overall adding effect with crustaceans in all seasons was more negative (a steeper slope). The results also showed that the adding effect of crustaceans in the fisheries communities were season-specific and region-specific. Temporally, adding crustaceans into fisheries communities contributed to more/less negative slopes in temperate/warm seasons, respectively. Regionally, the inclusion of crustaceans induced a reverse distribution pattern (nearshore–offshore) for fish abundance, as well as the re-scaled intercept, which could indicate the abundance in all seasons except in summer. It was assumed that although fish dominated the overall community structure, crustaceans contributed a compensatory effect by regulating the size distribution across trophic levels. This study provides valuable insights for the dynamic assessment and scientific management of fisheries and crustacean resources in the whole ecosystem. Full article

The genus Pasiphaea Savigny, 1816, comprises a diverse assemblage of meso- to bathypelagic shrimps, currently including 69 valid species. Taxonomic investigations have long been hampered by numerous synonymies and by species known only from their original, overly brief descriptions. Here, we address these deficiencies by examining Pasiphaea specimens collected in the Western and Central Pacific during multiple research cruises using mid-water trawls. Integrating traditional morphological characters (carapace carination, pleonal relief, telson end morphology, and pereopodal dentition) with a novel morphometric framework, we standardized terminology and defined a suite of quantitative measurements across the carapace, pleon, telson, and chelae. In order to corroborate species boundaries, we sequenced three mitochondrial gene markers (COI, 16S rDNA, and 12S rDNA) and calculated genetic distances under the Kimura two-parameter model. This combined approach extended or confirmed the geographic ranges of five described taxa, facilitated the formal description of eight new species, and demonstrated the synonymy of P. gracilis Hayashi, 1999, and P. fragilis Hayashi, 1999. Phylogenetic reconstructions further highlighted cases of pseudocryptic speciation in neighboring bathyal habitats. Our results expose substantial lacunae in the Southwest Pacific Pasiphaea fauna and substantiate the necessity for a comprehensive, genus-level revision. This study thereby contributes to both refining species diagnoses and advancing our understanding of deep-sea crustacean biodiversity. Full article

Traditional single-species fisheries management has proven inadequate for capturing ecosystem interactions, leading to a shift toward ecosystem-based approaches. In Korea, diverse small- and medium-scale with varying gear types, production volumes, and practices require management tools that address both ecological and industrial needs. This study developed a Gear-based Fisheries Management Index (GFMI) for 24 coastal and offshore fisheries in Korea. The framework, based on the “ideal gear attributes” defined by ICES, is structured around three objectives: gear controllability, environmental sustainability, and operational functionality. Sub-indicators and weights were derived through expert consultation using the Analytic Hierarchy Process and standardized with Z-scores from national statistics, including production volume, license numbers, and accident rates. Results show that in coastal fisheries, coastal gillnets (61.7) and coastal improved stow nets (60.7) recorded the highest scores, largely due to negative impacts such as bycatch, reproductive capacity, and gear loss. Coastal purse seines (40.9) received the lowest score, reflecting species selectivity advantages. In offshore fisheries, large bottom pair trawls (71.8) and Southwestern medium-size bottom pair trawl (69.3) ranked highest, indicating strong habitat impacts. While coastal improved stow nets, large purse seines, and large trawls performed well in operational functionality, high costs and efficiency constraints remain key vulnerabilities. Full article

The waters surrounding the Five West Sea Islands of South Korea are ecologically important but challenging to survey due to their location within a strategic military zone, strong tidal currents, and significant tidal variation. To assess the fish community in this region, we conducted Korea’s first parallel investigation combining traditional bottom trawl surveys with environmental DNA (eDNA) metabarcoding. Sampling was performed at 10 stations in March, May, and August 2023, and the relationship between fish species occurrence and environmental variables (water temperature, salinity, and depth) was examined. Dominant trawl-caught species included Engraulis japonicus, Johnius grypotus, Coilia nasus, and Okamejei kenojei, each showing seasonal migration and spawning patterns associated with temperature changes. eDNA analysis detected nine additional species absent from trawl catches, such as Ilisha elongata and Thamnaconus modestus, demonstrating its sensitivity in identifying both migratory and sedentary taxa. Our findings confirm that eDNA surveys can complement traditional sampling, improving biodiversity assessment in regions with limited accessibility and complex oceanographic conditions. Full article

The Indian Ocean is globally significant in terms of capture fisheries, and understanding the species composition of fish in the Indian Ocean is of great importance for the protection and development of its fishery resources. While coastal fish communities in the Indian Ocean are relatively well-documented, studies on pelagic zones remain sparse, especially for non-target species constituting fishery bycatch. Traditional biodiversity surveys rely on labor-intensive, inefficient trawling methods. To address these limitations, this study aims to apply environmental DNA (eDNA) metabarcoding for a species diversity survey in the Western Indian Ocean, offering a more reliable, efficient, and non-invasive alternative to traditional methods. The results will provide important insights into the region’s fish biodiversity, supporting sustainable management and conservation of fisheries resources in the area. Samples were collected from 130 stations in different water layers in the Western Indian Ocean, and species diversity was analyzed through 12S rRNA gene amplicon sequencing. The results showed that 98 fish species were detected from 176 seawater eDNA samples, belonging to two classes (Actinopteri and Chondrichthyes), 20 orders, 35 families, and 60 genera. Within a depth range of 300 m, there were no significant differences in species diversity parameters among samples from different depths. The orders with the highest relative abundance detected include Scombriformes, Aulopiformes, and Myctophiformes. The species with the highest relative abundance include Thunnus albacares, Alepisaurus ferox, Xiphias gladius, Diaphus fragilis, Decapterus macarellus, Thunnus maccoyii, and Platycephalus cultellatus. The species composition and relative abundance of economic species observed in this study showed, as expected, differences from fishery catch statistics. These results suggest that eDNA technology can not only monitor marine fish diversity more efficiently but also complement the lack of fisheries data. Integrating eDNA technology into routine monitoring in the Western Indian Ocean in the future could promote sustainable management of fisheries resources in the region. Full article

This study develops integrated bioeconomic management strategies for the common squid (Todarodes pacificus) fishery in Korea’s coastal waters, addressing both biological conservation and economic sustainability amid severe stock depletion and declining fishery profitability. Drawing on recent catch data and cost structures for six Total allowable Catch (TAC)-managed fishery types, common squid-specific economic indicators were estimated using a stepwise cost allocation method. Based on previous research using the Catch—Maximum Sustainable Yield (CMSY) model with limited Catch Per Unit Effort (CPUE) data, the biomass in 2020 was estimated at approximately 56% of Biomass at Maximum Sustainable Yield (BMSY), indicating an overfished state. Scenario-based simulations identified TAC allocation thresholds at which net profits reach zero, providing a benchmark for adaptive quota redistribution. Results show variation in economic sensitivity and common squid dependency among fishery types: common squid-dependent gears such as offshore jigging and East Sea trawl exhibit high vulnerability, while multi-species fisheries such as purse seine remain resilient. These results provide a basis for developing tailored management strategies for each fishery, thereby enhancing the effectiveness of interventions. Accordingly, policy recommendations include dynamic TAC adjustments, expanded monitoring, introduction of an Individual Transferable Quota system, and coordinated stock assessments with China and Japan. These findings contribute to refining Korea’s TAC system by aligning stock recovery goals with the economic viability of fishing operations. Full article

Multi-branch towed array systems are an important component of subsea information collection, which is increasingly required for subsea pipeline laying and offshore platform construction as ocean energy is exploited. However, the complexity of underwater conditions poses challenges for marine towing systems when collecting information, including the possibility of towing cable collisions with protruding seabed or submerged organisms during towing system travel, or towing cable interactions during torsion. These collisions can affect and interfere with the collection of information by the towing system, and can cause damage to the towing system or even cause the towing cable to break. After the failure and detachment of the outboard guide cable of a multi-branch towing cable array, the formation of the towing system changes, and these changes are complex and related to the prevailing sea state. To study the important condition of the damaged towing system, this paper draws an analogy between the towing system and the trawl net, and speculates the formation change and mechanical response of the multi-branch towed array system after damage by combining the influencing factors of the deployment of the towing system. Full article

The red mullet (Mullus barbatus, Linnaeus 1758) is a commercially vital demersal species in the Eastern Aegean Sea, yet it is subjected to high fishing pressure. This study assesses the population dynamics, growth, and exploitation status of M. barbatus based on 64 commercial trawl surveys conducted between 2022 and 2024 in the Lesvos–Ayvalik region. Length-frequency data identified eight age classes, with dominant cohorts at ages 3 (26.4%) and 5 (25%). The von Bertalanffy growth model estimated an asymptotic length (L∞) of 27.9 cm and growth coefficient (k = 0.21 year⁻¹), indicating a slow growth rate. The estimated fishing mortality (F = 0.74) exceeded natural mortality (M = 0.44), producing an exploitation rate (E = 0.63) that indicates overfishing. The length at 50% capture (LC₅₀ = 10.92 cm) was substantially below the optimal biomass length (Le = 16.6 cm), highlighting gear selectivity issues. Net benefit analysis revealed optimal fishing at 50–85 m depth and during December. These findings underscore the urgent need for improved management, including gear modifications, seasonal closures, and reduced effort, to restore sustainability and protect juvenile fish in the Eastern Aegean trawl fishery. Full article

Palaemon gravieri is an ecologically important shrimp species that plays a vital role in depressing jellyfish blooms in the southern Yellow and East China Seas of China. However, information on its distribution pattern and migration route related to environmental variables is fragmented. We conducted independent trawling surveys of P. gravieri between 2018 and 2019. Its sea surface temperature and sea surface salinity lower limits were 8 °C and 30‰, respectively. It showed the highest abundance at sea bottom temperatures and salinities of 12–14 °C and 32–33‰, respectively, in spring; 11–12 °C and 32.5‰ in autumn; and 10.5–14 °C and 31–33‰ in winter. Mean biomass, abundance, and size were ranked seasonally as follows: autumn > winter > spring > summer; autumn > winter and spring; and summer > spring > autumn > winter, respectively. Under the current climate scenario, P. gravieri is mainly concentrated in the inshore areas of the southern Yellow and northern East China Seas. Under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios in 2100, P. gravieri was mainly concentrated in the southern Yellow and northern East China Seas, and in inshore areas of the East China Sea. This species is therefore expected to benefit from climate warming. The findings of this study can facilitate the development of climate-induced fishery strategies and management schemes. Full article

Assessing fishery resources is crucial for sustainable marine ecosystem management and the operation of fisheries. This study integrates trawl surveys, environmental DNA (eDNA) analysis, and scientific echo sounder techniques to analyze the fishery resource distribution of and seasonal variations in the East China Sea. Surveys were conducted in April, July, August, and November 2022, utilizing bottom trawl sampling, eDNA metabarcoding, and acoustic data collection. The results revealed temporal differences in species composition, with crustaceans dominating in terms of abundance and fish species in biomass. The integration of eDNA analysis provided broader species detection, including cryptic and pelagic species, while acoustic techniques enabled large-scale resource assessment. However, discrepancies between methods highlighted the need for methodological refinement. Dominant species exhibited seasonal variation, with Portunus trituberculatus prevailing in spring (April), Trachurus japonicus and Scomber japonicus in summer (July–August), and Pampus argenteus in late autumn (November). A comparative analysis revealed that eDNA is sensitive to pelagic and cryptic species, trawl surveys effectively detect demersal fish, and acoustics allow for broad-scale biomass estimation, highlighting the complementary value of method integration. Full article

The slender snipe eel Nemichthys scolopaceus Richardson, 1848 is cosmopolitan in tropical and temperate seas, inhabiting the mesopelagic and bathypelagic zone between 200 and 1000 m depth. It is known to be an active predator in the DSL (Deep Scattering Layer) and the NBA (Near Bottom Aggregation), feeding mostly on decapod and euphausiid crustaceans, and playing a central role in carbon fluxes through meso- and bathypelagic ecosystems. Despite its potential importance in the deep trophic web ecosystem, the trophic ecology of Nemichthys scolopaceus is not well known. The aim of this study was to start to fill this knowledge gap. A total of 35 specimens of N. scolopaceus caught through bottom trawling in the Mediterranean Sea were analyzed in the laboratory for stomach content composition. As expected, mainly decapod crustaceans were found, in particular Plesionika martia, Pasiphaea multidentata, Funchalia woodwardi, and Robustosergia robusta species. The degree of digestion of prey in the stomachs was high in all cases. Our findings seem to confirm the specialist diet of Nemichthys scolopaceus based on shrimp-like crustaceans. Full article

Posidonia oceanica seagrass, endemic to the Mediterranean Sea, provides ecological goods and ecosystem services of paramount importance. In shallow and sheltered bays, P. oceanica meadows can reach the sea surface, with leaf tips slightly emerging, forming fringing and barrier reefs. During the 20th century, P. oceanica declined conspicuously in the vicinity of large ports and urbanized areas, particularly in the north-western Mediterranean. The main causes of decline are land reclamation, anchoring, bottom trawling, turbidity and pollution. Artificial sand nourishment of beaches has also been called into question, with sand flowing into the sea, burying and destroying neighbouring meadows. A fringing reef of P. oceanica, located at Saint-Mandrier-sur-Mer, near the port of Toulon (Provence, France), is severely degraded. Analysis of aerial photos shows that, since the beginning of the 2000s, it has remained stable in some parts or continued to decline in others. This contrasts with the trend towards recovery, observed in France, thanks to e.g., the legally protected status of P. oceanica, and the reduction of pollution and coastal developments. The sand nourishment of the study beach, renewed every year, with the sand being washed or blown very quickly (within a few months) from the beach into the sea, burying the P. oceanica meadow, seems the most likely explanation. Other factors, such as pollution, trampling by beachgoers and overgrazing, may also play a role in the decline. Full article

Overfishing represents one of the most alarming threats to marine conservation in the Mediterranean Sea. In particular, deep-sea trawl fishing can severely damage marine habitats that may take decades to recover due to their slow growth rates. Hence, monitoring the health and subsistence of deep-sea ecosystems in fishing hotspots is vital to understand the impacts of deep-sea fishing. This paper presents a methodological study to prepare an expedition in Sardinian (Italy) deep waters. The methodology is composed of three sections: first, it offers a comparative analysis of the proper technological mix to identify fishing hotspots pre-expedition; second, it simulates an in situ expedition to monitor the state of deep-sea ecosystems in proximity of the fishing hotspots identified; and third, it offers recommendations for data analysis and management post-expedition. This study offers a replicable methodology for advancing knowledge on the state of deep-sea ecosystems affected by trawl fishing. Full article

Dense aggregations of species in the family Pinnidae give soft substrata a specific characterization. They may influence the biological and physical properties of the surrounding sediments. Bottom-trawl samplings performed in the Sea of Marmara revealed populations of a large pinnid species, particularly at depths of 40–45 m in soft substrata. Both morphological and DNA analyses confirmed the species’ taxonomic identity as Atrina fragilis. This species had a population density ranging from 31 to 469 ind.km⁻², and the shell lengths ranged from 21.3 to 31 cm. A total of 47 macrozoobenthic species belonging to eight taxonomic groups were found on the shells of ten live and nine dead A. fragilis individuals. Polychaeta accounted for 53% of the total number of species and 75% of the total number of individuals. Among these species, Protula tubularia and Serpula concharum comprised almost 30% of all epifaunal populations. Community parameters changed according to the shell length and width. Different faunal assemblages were encountered on the shells. Given the ecological significance of A. fragilis as both a habitat-forming and sensitive benthic species, conservation measures should prioritize the protection of known habitats and the regulation of activities that lead to seabed disturbance. Full article