Search Results (67)

A small-sized shark was accidentally caught in the coastal waters of southeastern France and abandoned in the port of L’Estaque (Marseille) in May 2024. An autopsy revealed that it was a young female shortfin mako, Isurus oxyrinchus (Rafinesque, 1810). Numerous superficial wounds on the head, back, and flanks, in the form of parallel striations resulting from heavy friction, indicate meshing in a gillnet that provoked the animal’s death by asphyxiation. Its very small size (64.77 cm TL) suggests that this is a newborn individual, leading to the hypothesis that the waters off Marseille could be a nursery area for this species. This observation alone is not enough to prove this point, but it does suggest the need for closer monitoring to validate it. Should the area be proven to play this key role for this critically endangered species, measures to limit fishing pressure would be essential, particularly during the parturition period between February and May. Full article

The European Water Framework Directive (WFD) 2000/60/EC emphasizes the use of fish communities as key indicators for assessing the ecological quality of freshwater ecosystems. Despite over two decades of WFD implementation, many Balkan countries lack standardized ecological assessment indices, particularly for fish fauna. This situation complicates efforts to monitor and manage aquatic ecosystems, especially transboundary waters facing significant environmental pressures. In this context, our study assesses fish communities and ecological quality in Lake Dojran, a transboundary lake shared by Greece and North Macedonia. Fish sampling was independently conducted by each country (North Macedonia in 2021 and Greece in 2023), using benthic multi-mesh gillnets following standardized European methodologies (CEN 2005). A total of 12 out of 16 historically recorded fish species were confirmed. Higher catch per unit effort (CPUE) values were observed in 2021 (282.50 specimens/gillnet, biomass 6321.81 g/gillnet) compared to 2023 (207.83 specimens/gillnet, 2378.67 g/gillnet). Dominant species included Alburnus macedonicus and Perca fluviatilis. No significant differences were found in CPUE values based on either number of specimens (NPUE) or biomass (BPUE) across the different depth zones. Using the Greek Lake Fish Index (GLFI), ecological quality based on fish fauna was classified as “good” in 2021 and “high” in 2023, reflecting the low relative contribution of both introduced numerical abundance and omnivorous species biomass in total catches. This study contributes valuable baseline data for transboundary ecological management and conservation strategies, supporting efforts aligned with WFD objectives. Full article

This study aims to enhance our understanding of the marbled spinefoot (Siganus rivulatus) population along the Red Sea coast of Saudi Arabia. It investigates whether the stock is subject to overfishing and tests the hypothesis that current fishing mortality exceeds sustainable thresholds. A total of 6192 specimens were sampled during a comprehensive survey conducted from 2022 to 2024, utilizing a range of fishing methods, including handline, trap, gillnet, and demersal trawl fisheries. The sampled fish ranged in total length (TL) from 100 to 335 mm and in total weight (W) from 17 to 470 g. The length–weight relationship was W = 0.0175 × TL^2.92. Growth parameters derived from the von Bertalanffy model were TL_∞ = 43.5 cm, K = 1.12 year⁻¹, and t₀ = −0.18 year. The median size at first maturity was estimated at 14.83 cm TL for both sexes. Virtual Population Analysis revealed fishing mortality rates ranging from 0.01 year⁻¹ to 0.89 year⁻¹ across age classes 1 to 5 years, with exploitation levels of 0.6, 0.55, and 0.5 at ages 3, 4, and 5, respectively, indicating slight overfishing. The annual average catch of marbled spinefoot along the Saudi Arabian Red Sea coast was approximately 211 tonnes, contributing an estimated 1.8 million USD to the national economy. Maintaining the current fishing effort at sustainable levels is essential to ensure the long-term viability of this stock. Full article

Carassius auratus, a key invasive species in the high-altitude Lugu Lake (2690 m) in China, was studied to assess its length–weight relationship, age structure, and growth patterns using scale-based age determination. A total of 670 specimens were collected via systematic gillnet surveys conducted in May and October 2023. The population comprised five age groups (0+ to 4+), with 0+ and 1+ individuals dominating (69.40%). Body lengths ranged from 36 to 178 mm (mean: 93.73 mm), peaking at 60–70 mm (33.88%). Body weights varied from 1.3 to 175 g (mean: 33.60 g), with 1.3–10 g as the dominant range (26.27%). The length–weight relationship was modeled as W = 2 × 10⁻⁵L^3.026 (n = 670, R² = 0.985), indicating isometric growth. Von Bertalanffy growth parameters indicated an asymptotic length (L∞) of 401.57 mm, an asymptotic weight (W∞) of 484.38 g, a growth coefficient (k) of 0.0721, and a theoretical age at zero length (t₀) of −1.6174 years, with an inflection point at 6.66 years. The simplified age structure and dominance of young cohorts suggest rapid population expansion, highlighting the urgent need for management strategies to mitigate ecological impacts on this fragile plateau ecosystem. Full article

Cold-water lakes in high-latitude regions are experiencing rapid changes in community structure and functioning associated with local and global stressors (e.g., climate change, hydropower and invasive species). However, the long-term ecological responses of cold-adapted top predators are relatively poorly monitored despite their high importance for structuring ecological communities and for the provisioning of ecosystem services. We studied long-term changes (2010–2021) in the population structure and trophic niche of two cold-adapted coregonid fishes in oligotrophic Lake Osensjøen, southeastern Norway. Our gillnet surveys indicated that the whitefish (Coregonus lavaretus) population declines simultaneously with the increasing population density of roach (Rutilus rutilus), whereas vendace (Coregonus albula) showed more stable densities. Both whitefish and vendace became increasingly dominated by small-sized individuals following the increase in coexisting roach and perch (Perca fluviatilis) populations. Our stomach content and stable isotope data indicated a marked overlap in the trophic niches of whitefish and roach, with both species showing high among-individual variation in δ¹³C and δ¹⁵N values as compared to the more specialized zooplanktivorous vendace. Our study provides further evidence that the ongoing environmental changes in high-latitude lakes may induce rapid changes in community structures and lead to the population declines of cold-adapted fishes, likely associated with strong resource competition with warm-adapted cyprinid and percid fishes. Such shifts in fish community structure may, in turn, affect the benthic and pelagic food-web compartments and reduce valuable ecosystem services such as local fisheries targeting salmonids. Full article

Walleye Sander vitreus is a valued sportfish in eastern North America, including the upper New River of Virginia, where individuals can grow to a large size (>7 kg). After construction of dams, especially Claytor Dam in 1939, the population declined and non-native walleye were stocked. Stocking of non-native walleye was stopped in 1997, and molecular marker data showed that the presumptive native population had persisted. To restore the native stock, selection of broodstock candidates bearing native marker alleles and hatchery-based augmentation have been practiced over a 20-year period. We evaluated the success of the marker-assisted selection and hatchery-based augmentation program. Marker-assisted selection of native New River walleye began with mean frequencies of marker alleles at microsatellite loci Svi17 and Svi33 of ~30%, and continuing selection has driven marker allele frequencies to ~65–70%. Numbers of walleye collected in fall gillnet and spring electrofishing surveys were responsive to augmentations with hatchery fish 2–3 years earlier. Stocking was not practiced in 2012–2013, and a decrease in walleye catch rates was noted in 2016, suggesting that the native New River walleye population still depends upon hatchery-based augmentation. We recommend the development of a small panel of single nucleotide polymorphism markers for more rigorous selection of broodstock representative of the native walleye population. Full article

Spotted stone loach (Triplophysa strauchii), a common fish species in Xinjiang, China, is ecologically pivotal within the local ecosystem; regrettably, human-induced factors like habitat destruction, pollution, and overfishing have gravely imperiled its survival, and compounding this is the dearth of research on the morphological disparities among its geographically diverse populations. Thus, between April and October 2024, 198 specimens were procured from Sayram Lake, Khamusigou Reservoir, and Chaiwopu Lake using cage traps and gillnets; post-collection, an array of morphological metrics were meticulously measured, and then statistical methods such as one-way analysis of variance (ANOVA), principal component analysis (PCA), stepwise discriminant analysis, and cluster analysis were employed for comprehensive data interrogation. Findings show that, across all sampled populations, the mean values of the total length (X1), body length (X2), body height (X3), and body width (X4) of the Chaiwopu Lake population are significantly lower than those of the Sayram Lake population and the Khamusigou Reservoir population; except for head length, the Khamusigou Reservoir population has lower variability in other morphological traits compared to the others. Moreover, significant divergences were detected in multiple trait ratios among the populations; PCA yielded five principal components, cumulatively accounting for 77.45% of the total variance, spotlighting the key ratios; discriminant analysis further validated highly significant morphological distinctions (p < 0.01), with the Khamusigou Reservoir population having the highest discriminant accuracy; cluster analysis graphically showed the Sayram Lake and Chaiwopu Lake populations clustering together while the Khamusigou Reservoir population formed a separate cluster; and the Chaiwopu Lake population had the most pronounced divergence in morphological traits. This research not only provides novel perspectives on the adaptive evolutionary mechanisms of T. strauchii but also serves as a cornerstone for formulating evidence-based conservation and management strategies for this species. Full article

Fish in the Yong River basin have been significantly impacted by pollution, habitat modification and overfishing. In order to facilitate the recovery of freshwater biodiversity, a fishing ban has been implemented in the Yong River basin since 2022. However, the high level of human activity along the waterways of the Yong River basin poses a significant challenge to the monitoring of fish biodiversity using established methods. It is essential, therefore, to have effective monitoring tools to assess the effectiveness of the fishing ban policy. In this study, environmental DNA (eDNA) metabarcoding was employed to assess fish species biodiversity across five river sections of the Yong River basin in October 2022. Additionally, we checked the results against fishing gear (drift gillnets and ground cages) surveys and historical records. A total of twenty-two fish species were found from eDNA metabarcoding, fourteen species were found via fishing, and only two species were found from both methods. The most dominant fish species identified by eDNA was Alburnus mossulensis, present in all river sections. However, a decline in species biodiversity was observed in the whole Yong River basin, with a significant difference in community composition across the Upper Yao River (UYAR) and Yong River (YOR). Moreover, eDNA detected fish and potentially invasive species consistent with their geographic distribution. Overall, the results of this study provide a snapshot of the current fish biodiversity in the Yong River basin, offering baseline data for future evaluations of fishing ban policies in this ecosystem. Full article

The franciscana dolphin (Pontoporia blainvillei) is a small cetacean endemic to the coastal waters of the southwestern Atlantic Ocean. Due to its restricted distribution, it is subject to high bycatch mortality in the gillnets used for commercial and artisanal fishing. The rehabilitation of the franciscana is still a major challenge, as most attempts to rehabilitate stranded animals have failed. This study aims to present the case of the rehabilitation of a franciscana dolphin calf, stranded in San Clemente del Tuyú, Argentina, at the beginning of the predation period. The feeding strategy and nutritional profile at different stages during the 88 days of rehabilitation are meticulously detailed. Its diet was prepared by hand based on studies of milk composition, the feeding ecology of franciscana in Argentinean waters, and previous records of the Fundación Mundo Marino Rehabilitation Center. The diets were designed to meet the nutritional needs of franciscana dolphins. In addition, the hematological, cytological, and fecal analyses recorded during the rehabilitation are presented. Although the animal could not be released, due to its death, this report provides baseline information that can improve the ability of veterinarians to care for debilitated, live-stranded dolphins. This information may also be useful in the implementation and development of healthcare protocols for this species. Full article

Coral reef fish are important groups of coral reefs, which have great economic and ecological value. Meiji Reef is a representative tropical semi-enclosed atoll in the South China Sea, with rich fish resources. Based on the data from hand-fishing, line-fishing, and gillnet surveys of fish in Meiji Reef from 1998 to 2018, this study summarized the fish species list of Meiji Reef and analyzed the species composition, inclusion index at the taxonomic level (TINCL), genus–family diversity index (G–F index), average taxonomic distinctness index (Δ⁺), and variation in taxonomic distinctness (Λ⁺) and their changes. The results revealed that from 1998 to 2018, there were 166 reef-dwelling fish species on Meiji Reef, belonging to 69 genera, 33 families, and 11 orders, of which 128 species were from 20 families of Perciformes, accounting for 77.10% of the total cataloged species. Regarding the dependence of fish on coral reefs, there were 155 reef-dependent species or resident species (accounting for 93.37%) and 11 reef-independent species or wandering species (accounting for 6.63%). The TINCL of the order, families, and genus of fish in Meiji Reef were very high. The genus diversity index (G index), family diversity index (F index), and G–F index of fish in Meiji Reef were very high, and the G index of fish in Meiji Reef in 1998–1999 was higher than that in 2016–2018. The Δ⁺ and Λ⁺ values of fish in Meiji Reef from 1998 to 2018 were 56.1 and 148.5, respectively. Compared with 1998–1999, Δ⁺ and Λ⁺ of fish increased during 2016–2018, reflecting that the relatives of fish in Meiji Reef became further distant, and the uniformity of taxonomic relationships among species decreased. The research findings indicated that fish exhibited a high taxonomic diversity in Meiji Reef; however, it also revealed significant fluctuations in the fish diversity of Meiji Reef over an extended period, emphasizing the urgent need for timely protection measures. This investigation significantly contributes to our comprehension of the intricate dynamics governing fish species within Meiji Reef and holds broader implications for biodiversity conservation in tropical marine ecosystems. Full article

Gillnets are widely used in research and commercial fishery activities. As passive gear, gillnets can be selective and dependent on the diel migration of fish. In areas with limited littoral extent, inshore–offshore migration may cause bias in the gillnet catch. Our hypothesis was that some factors, such as gillnet saturation, fish depletion, or chemical cues, could be the cause of the bias. We used a total of 66 CEN gillnets deployed at Římov Reservoir parallel to the shore at different positions of littoral-pelagic gradient. Individual fish direction was recorded from inshore, offshore, or unknown direction (i.e., entangled fish). A total of 5791 fishes from nine different species were caught. For most fish, it was possible to determine their directivity, and most fish were captured in littoral or first pelagic gillnets. Shallower and deeper benthic gillnets differed in their bleak (Alburnus alburnus) catch. No significant differences were found between fish directions. At the species level, only asp (Leuciscus aspius) and ruffe (Gymnocephalus cernua) showed differences between the captured directions in one case. The results support the assumption that gillnet capture is a random process that to a great extent is connected to random local movements. This is good news for fish monitoring projects. Sampling catch is likely to reflect true changes in the fish community, and not the effects of the deployment of the sampling gear. The experiment also showed that fish directivity statistics can be used for investigation of fish behavior and gear performance. Full article

The franciscana dolphin is a small, vulnerable species often caught in artisanal gillnets. This study aims to provide a comprehensive assessment of their acoustic capabilities by using advanced equipment to collect a large dataset of wideband, continuous recordings. We examined the detailed acoustic signals of franciscana dolphins, comparing the sounds from rehabilitated dolphins in captivity with those of wild dolphins near fishing nets. Significant differences in acoustic characteristics were found between neonates and older dolphins, with juvenile and wild dolphins showing similar features. For the first time, repetition patterns in click production were identified, highlighting the importance of understanding the context of these sounds in regards to feeding and communication. This study emphasizes the need for detecting neonates for species protection and suggests the potential for developing acoustic classifiers specific to different age groups. Our findings offer valuable insights for conservation efforts and the development of protection strategies for franciscana dolphins. Full article

The rapid spread of non-native species (NNS) poses a significant threat to biodiversity globally, with the Mediterranean region being particularly susceptible due to increased human activities and its status as a marine biodiversity hotspot. In this study, we focus on the introduction and distribution of Fistularia petimba, a member of the Fistulariidae family, in the eastern Mediterranean Sea and a record from the coasts of Amorgos Island, Greece. Through a baseline fishery study conducted over 12 months, utilizing experimental sampling with gillnets, trammel nets, and longlines, one individual of F. petimba was captured off the coast of Katapola Bay. Morphological examination confirmed its identity, with measurements on meristic characteristics obtained and the stomach content analysed. This finding represents a significant addition to the documented distribution of F. petimba in the Mediterranean Sea, particularly in the Aegean Sea, underscoring the importance of ongoing research in uncovering new occurrences and expanding our understanding of marine biodiversity and ecosystem changes. Further investigation into the ecological preferences and population dynamics of F. petimba in the Aegean Sea is crucial for informed conservation and management efforts if this species is considered to be established. Full article

The Tietê River receives most of the effluents and diffuse wastes from the São Paulo metropolis (21.9 million inhabitants). The study aimed to assess the extent to which environmental changes affected the fish fauna. We compared, in rainy and dry seasons, three sites in Tietê and three in tributaries with much better water quality conditions. No physical barriers exist between the sites. Fish were sampled with gillnets (exposed overnight) and the assemblage’s ecological attributes calculated. Water depth, transparency, temperature, electrical conductivity, dissolved oxygen, turbidity, total dissolved solids, pH, redox potential, total phosphorus, total nitrogen, and chlorophyll were simultaneously determined. Low oxygen concentrations (near zero in the rainy period), and the opposite for nutrients and total solids, separated the predominantly hypereutrophic Tietê from the tributaries (PCA). Differences in the fish assemblages were also evidenced (nMDS), including a higher richness per sample in tributaries (11 to 14 spp.) compared to Tietê (3 to 4 spp.). Siluriformes with accessory breathing dominated in Tietê and the highly tolerant detritivorous Prochilodus lineatus (the main commercial fish) was the only species found in all sites. The species correlated positively with oxygen in the tributaries and with turbidity, redox potential, and nutrients in Tietê (DistLM) (rainy season). Recovery measures are urgently required. Full article

Fishery bycatch poses a significant threat to sea turtles. This study provides an updated assessment of Loggerhead turtle (Caretta caretta) bycatch in the Gulf of Gabès, focusing on the impact of the Garrasia gillnets. Through 61 onboard observations conducted alongside fishermen in Zarzis deploying a bottom-set gillnet, called “Garrasia”, and targeting elasmobranch species, comprehensive data were collected, including the number of sea turtles captured, soak time, length of gillnets, location, and biometric data of sea turtles. Analysis revealed a catch per unit effort (CPUE) for sea turtles of 0.63 (95% CI [0.355–0.893]) turtles per kilometer per 24 h with a notably high mortality rate of 92.06% (95% CI [87.3–96.8]). In the Gulf of Gabès, 23 vessels are reported to use Garrasia, resulting in an estimated annual total capture of 3756.53 turtles with a 95% CI [1907.81–5902.30]. These findings underscore the significant impact of Garrasia on sea turtle populations in the Gulf of Gabès. The study calls for immediate collaborative efforts among researchers, local stakeholders, authorities and fishermen to elaborate balanced conservation strategies that consider both ecological sustainability and socio-economic factors, aiming to achieve a sustainable marine ecosystem. Full article