Aquatic Conservation-Marine and Freshwater Ecosystems最新文献

Estimating population parameters is crucial for understanding species dynamics and assessing anthropogenic impacts, thereby supporting conservation efforts. We evaluate key population parameters—group structure, abundance and capture–recapture probabilities—of the Guiana dolphin in the Paranaguá Estuarine Complex and adjacent coastal waters, southern Brazil. During 2021, we conducted 40 boat surveys to collect group structure and photo-identification data for mark–recapture modelling. We sighted 317 dolphin groups, with calves present in 56% of them. Group sizes ranged from 1 to 50 individuals, including aggregations of ~100–150 dolphins in Paranaguá Bay. We identified a total of 518 individuals and estimated the abundance of Guiana dolphins using two different programs, given the sparse nature of our dataset. The programme CAPTURE estimated N = 3770 (95% CI = 2591–5483; CV = 0.19), and Program MARK estimated N = 3087 (95% CI = 2072–4599; CV = 0.21) individuals, representing the largest Guiana dolphin population reported along the species' range. Capture probabilities varied seasonally, being lower during the wet season and higher during the dry season, consistent with greater numbers of identified individuals, larger group sizes and higher calf presence during the dry season. These results highlight the influence of environmental variability on habitat use and population dynamics and underscore the importance of long-term monitoring to understand population structure, movement patterns and anthropogenic impacts. Our findings emphasize that both biological and methodological factors must be considered when interpreting abundance estimates and that standardized approaches are essential for reliable comparisons across populations.

In this study, we explored the population genetic structure and its relation to environmental adaptations of the dolphinfish (Coryphaena hippurus) in the western Atlantic Ocean and Mediterranean Sea. Although previously two populations within the Mediterranean Sea were identified, recent evidence suggests more complex structuring. We employed 3RAD sequencing on 138 samples from the Atlantic and Mediterranean, obtaining a total of 20,072 SNPs of which 24 SNPs were strongly associated with temperature and salinity variables (putative adaptive outlier loci). Results revealed a clear genetic differentiation between the Atlantic and Mediterranean basins, with practically no connectivity between them, confirming the Mediterranean basin's long-term isolation. Within the Mediterranean basin, subtle genetic differences were detected between eastern and western Mediterranean sub-basins based on neutral loci with an increased signal of differences in the outlier loci associated with temperature and salinity that identified further differences into three genetically distinct groups, despite an overall high genetic connectivity. Environmental–genetic association analyses identified salinity, temperature and nitrate as major drivers of genetic variation. The most informative dataset (outlier SNPs related to temperature and salinity) explained over 80% of the genetic variation through a model incorporating multiple oceanographic variables. Overall, this research underscores how high-resolution genomic tools can detect hidden genetic structure and adaptation, even in highly dispersive marine species. These findings are essential for fisheries management, particularly in the Mediterranean Sea, where distinct local adaptations may be at risk from global environmental change. Recognizing and preserving this genetic diversity is crucial for the long-term sustainability of dolphinfish populations under climate and anthropogenic pressures.

The European eel (Anguilla anguilla) faces significant challenges during its migratory lifecycle due to anthropogenic habitat fragmentation. Fish passage solutions, such as eel ramps, aim to mitigate such barriers, but their effectiveness varies and may impose selective pressures on eel phenotypes. This study evaluates the impact of ramp design and water flow on the climbing success of juvenile eels, with particular focus on effects of individual eel exploratory phenotypes. Choice between two ramp designs—laterally flat and V-shaped—was evaluated under low (3 L min⁻¹) and high (9 L min⁻¹) flow conditions. The proportion of eels climbing the flat and V-shaped ramps was similar at low flows (36% and 32%, respectively), while a V-shaped ramp led to a higher proportion of climbs than a flat ramp at high flows (30% and 2%, respectively). Additionally, individuals with lower activity scores had a higher probability of climbing. These findings suggest that ramp design influences eel passage efficiency and highlight the potential for unintended selective pressures against high-activity phenotypes. Optimizing eel passage design is crucial to allow upstream and downstream migration and maintaining population diversity. Further studies are needed to assess if upstream migration over multiple eel ramps can affect the migration or phenotypic selection to ensure that passage design does not inadvertently disadvantage climbing success for certain phenotypes within the already threatened eel population.

The field of environmental DNA (eDNA) is rapidly expanding with established applications in biodiversity monitoring, rare species detection and ecological assessment. However, its potential to evaluate species connectivity in fragmented aquatic systems remains underexplored. This study addresses this gap by applying eDNA metabarcoding to assess community connectivity in a dam-fragmented river network, combining a multispecies framework with haplotype-level analyses to investigate both community composition and within-species variability. Community changes associated with reservoirs included biodiversity losses in the dammed area and have been found, as well as dams acting as barriers to the upstream advance of the invasive acute bladder snail Physella acuta. Haplotype analysis of the fish Phoxinus bigerri and Salmo trutta, the red alga Sheathia arcuata and the amoeba Koretnevella stella showed different levels of connectivity according to species biology, with genetic barriers associated with dams for the three species and diversity losses in the dammed area for the native S. trutta. Despite methodological limitations such as the non-met premise of one haplotype one individual, the results suggest that metabarcoding on eDNA extracted from water samples can provide valuable insights into genetic diversity and connectivity across multiple taxa, offering new opportunities in conservation biology.

The European eel (Anguilla anguilla) faces significant challenges during its migratory lifecycle due to anthropogenic habitat fragmentation. Fish passage solutions, such as eel ramps, aim to mitigate such barriers, but their effectiveness varies and may impose selective pressures on eel phenotypes. This study evaluates the impact of ramp design and water flow on the climbing success of juvenile eels, with particular focus on effects of individual eel exploratory phenotypes. Choice between two ramp designs—laterally flat and V-shaped—was evaluated under low (3 L min⁻¹) and high (9 L min⁻¹) flow conditions. The proportion of eels climbing the flat and V-shaped ramps was similar at low flows (36% and 32%, respectively), while a V-shaped ramp led to a higher proportion of climbs than a flat ramp at high flows (30% and 2%, respectively). Additionally, individuals with lower activity scores had a higher probability of climbing. These findings suggest that ramp design influences eel passage efficiency and highlight the potential for unintended selective pressures against high-activity phenotypes. Optimizing eel passage design is crucial to allow upstream and downstream migration and maintaining population diversity. Further studies are needed to assess if upstream migration over multiple eel ramps can affect the migration or phenotypic selection to ensure that passage design does not inadvertently disadvantage climbing success for certain phenotypes within the already threatened eel population.

This study aimed to investigate the trophic ecology of loggerhead turtles recorded stranded along the Paraná coast in southern Brazil. Carbon and nitrogen stable isotopes were analysed in muscle tissues from 20 loggerhead turtles and in 69 specimens representing 12 prey species (molluscs, crustaceans and teleost fishes). The δ¹³C values for turtles ranged from −19.5‰ to −16.0‰ (mean ± SD: −17.7‰ ± 1.2‰) and δ¹⁵N values ranged from 9.9‰ to 18.3‰ (mean ± SD: 14.2‰ ± 2.6‰). Juveniles (curved carapace length [CCL] < 83 cm) had lower mean values of δ¹³C (−18.4‰ ± 1.1‰) and δ¹⁵N (12.9‰ ± 2.4‰) than adults (−16.8‰ ± 0.7‰; 16.2‰ ± 1.3‰, respectively). Both isotopes were positively correlated with CCL. Bayesian mixing model analysis indicated that adults and juveniles mainly forage on fishes and crustaceans, although the most important prey species likely differ between age classes. This pattern is supported by the isotopic niche analysis, which showed little overlap. The results suggest that juveniles forage across different regions, including the oceanic zone, or have recently settled in the neritic zone while retaining the isotopic composition of the oceanic habitats. Loggerhead turtles displayed a varied diet, including several prey species that are bycaught by local fisheries, and they occupied different trophic levels depending on age class. These interactions between loggerhead turtles and fisheries present significant conservation implications for both the turtles and their prey.

Commercial fishing is often assumed to have greater impacts than recreational fishing, and many fisheries assessments overlook the latter. Yet, numerous coastal and freshwater fish populations are subject to both fishing types and environmental pressures, all influencing biomass, body size and community structure and making management outcomes difficult to predict. In this study, we reconstruct 70 years of fish size and 30 years of biomass trends and explore environmental and harvesting impacts in two productive water bodies with contrasting management regimes: Kaunas Reservoir and the Curonian Lagoon (Lithuania). Commercial fishing has been banned in Kaunas Reservoir since 2013 but continues in the Curonian Lagoon, whereas recreational fishing occurs in both. Fish biomasses in the lagoon generally declined, while in the Reservoir biomasses of commercial target species increased up to fourfold since the fishery ban. Yet, recovery of popular angling species, including main predators, remains slow. Across species, body sizes were stable in the Curonian Lagoon and increased significantly in Kaunas Reservoir. Such positive size trends were partly explained by positive temperature impacts, although fishing had a larger effect on body sizes than temperature. Our findings indicate that rapid population recovery of temperate fish populations could be expected within a decade if all types of fishing mortality are removed, and that effective no-take reserves could see a several-fold increase in fish biomasses. Notably, due to often positive effects of warming on average fish sizes, body size trends may suggest a more optimistic population status than biomass data, and both should be studied simultaneously.

Amphibians are facing large population declines as a result of both natural and anthropogenic threats. Reconstructing and understanding the composition and structure of amphibian communities is essential for developing effective monitoring and conservation strategies. In this study, we compared environmental DNA metabarcoding (eDNA-MB) data with a comprehensive dataset obtained from acoustic and visual encounter surveys (AVES) in a set of Mediterranean ponds. Additionally, we designed and validated a quantitative PCR (qPCR) assay for the Iberian ribbed newt (Pleurodeles waltl) and tested its ability with eDNA-MB and AVES in assessing the presence and population densities of this species. Our findings provide evidence that eDNA-MB can be a valuable method for reconstructing the composition and structure of amphibian communities. eDNA-MB identified all expected amphibian species from the regional species pool, including some that were missed in traditional surveys. Although eDNA-MB abundance estimations for P. waltl seemed virtually independent of population densities obtained through field surveys, we found a significant association between eDNA concentration (qPCR) and AVES abundance estimates. Our findings suggest that effective strategies for amphibian biomonitoring need the combination of community data obtained from both traditional and eDNA surveys, especially in the Mediterranean region where strong environmental constraints can affect the detection and persistence of eDNA in freshwater ecosystems.

We used imaging sonar to continuously monitor wildlife at an operational tidal turbine in the Pentland Firth, Scotland, between May 2022 and June 2023. Of 704 detected seal tracks, 347 occurred during turbine operation and 122 of these were detected directly upstream of the rotating blades in the horizontal plane. Using a series of repeatable and objective questions in a semi-automatic assessment, we characterised factors that were associated with a higher likelihood of collision and assessed the associated risk of collision between each seal track and the rotating blades. Thirty-five tracks (10% of tracks during operation) approached the rotor swept area within 10 m and 16 of these passed through the rotor swept area in the horizontal plane. There is strong evidence to suggest that most of these high-risk tracks passed above, around or possibly through, the turbine without collision. As well as providing useful data to assist in the prediction of collision risk, this approach provides a standardised method to evaluate similar data from other tidal energy sites or species. These outcomes can help inform the consenting process and support the sustainable development of the tidal energy industry.

Inland fisheries in South Africa are crucial for the livelihoods of local communities, but they face pressures that threaten the sustainability of small-scale and recreational fishers livelihoods, the latter making the dominant economic contribution. However, distinctions between small-scale and recreational fishing rights are unclear. We aimed to address the knowledge gap regarding economically significant fish species, their contribution to fishers, and how they are spatial distributed across the uMngeni and uThukela Catchment Management Areas in KwaZulu-Natal, South Africa. Additionally, we addressed the fisher perceptions and use of targetted fish species. A questionnaire-based interview was conducted with fishers between 2021 and 2023 across rivers and impoundments. Our findings highlight several key challenges for inland fisheries management. We found that there are difficulties in categorising fishers, particularly in distinguishing small-scale from recreational fishers, an ambiguity reflected in fishers’ self-identifications and practices, with ‘subsistence’ as a self-identifier. This complexity was further highlighted by the ecological and economic significance of key species, with the invasive Cyprinus carpio having the greatest market value and being the most economically important species. Fishers largely viewed these invasive species through an economic lens, perceiving them as valuable resources and adapting their practices to target their harvest. Regarding fishing behaviours, subsistence fishers were a significant group, reporting weekly or monthly fish consumption and exhibiting a clear preference for river fishing over other waterbody types. Finally, gender significantly influenced participation, with males exhibiting higher fishing frequencies. We conclude that the definitions of inland fisheries in South Africa do not align with the realities on the ground, and the fuzzy boundary between defined small-scale, recreational fisheries and undefined subsistence fishers will likely negatively influence policy implementation. In addition, it highlighted the need for integrated management of South African inland fisheries and economics to sustain inland fisheries that support livelihoods and fish conservation.