Aquatic Conservation-Marine and Freshwater Ecosystems最新文献

Brown trout (Salmo trutta L.) is a widely distributed fish species native to Europe, with high phenotypic plasticity, including resident and anadromous (sea trout) forms. Many populations are in decline, especially the anadromous ecotype towards the southern edge of their range. Evidence-based management is dependent on reliable assessment methods to characterise underperforming populations and identify mitigation actions. Assessment methods based on juvenile data are useful for trout given the species' plasticity. These typically involve comparisons between observed and expected juvenile densities, which vary geographically and with habitat quality. These estimates are mostly obtained through wading electrofishing and field-based habitat surveys. Although some national and regional trout assessment methods have been developed, efforts to develop range-wide evaluations have been constrained by a lack of common protocols. This paper summarises the national methods used to characterise juvenile trout and associated habitat based on information compiled by national representatives of the ICES WGTRUTTA. It then considers opportunities for harmonising data with the aim of developing a range-wide assessment. Survey methods varied substantially within and between countries but showed no clear spatial patterns of coherence. Development of a single set of survey and data collection methods appears highly unlikely. A more pragmatic approach could involve harmonising existing data to make them broadly comparable. This could involve selective use of fish survey data, integration of range-wide macro-scale spatial and habitat data obtained from spatial datasets and use of appropriate modelling frameworks. We also emphasise the critical importance of population data from index rivers to validate and scale juvenile assessments and to compare sampling methods.

Squatina californica is a near-threatened angel shark distributed in coastal areas of eastern Pacific. Despite its wide distribution and the conservation threats, basic knowledge of the species populations, evolutionary history and genetic diversity is scarce. In this study, we use two mitochondrial genetic markers (Control Region of mtDNA and Cytochrome C Oxidase subunit I) to explore the species' phylogeography. We included samples from locations in the Southern Californian Pacific (SCP), the Gulf of California (GC) and the Southeast Pacific (SEP). We identified three populations of the Pacific Angel Shark, corresponding to the regions SCP, GC and SEP. These results show an antitropical distribution for the species, which may be a consequence of the climatic instability of Central America during the Pliocene. Additionally, we infer that the divergence of the SCP populations from those of the GC coincided closely with the formation of the Baja California Peninsula, without current migration through the southern end of the peninsula. Finally, we detected a signal of population expansion and substructure within the GC, probably promoted by environmental heterogeneity in this area. Our results indicate that the three populations identified herein should be considered separate management units, because they exhibited independent evolutionary histories that may influence their levels of resilience to fishing pressure.

Knowledge about the reproductive success of sea turtles is essential for their conservation. These nest preferentially on the beaches where they were born and may nest more than once during each nesting season, with a variable number of nests per female. Several factors can lead to variations in reproductive output. This study estimated the clutch frequency and internesting period of the threatened subpopulation of the loggerhead turtle (Caretta caretta) from the island of Boa Vista, Cabo Verde. This archipelago hosts the second-largest (or perhaps largest) population of C. caretta globally, with Boa Vista being the most important nesting island. Female distinctions were made on their previous experience (neophytes and remigrants) and their body size. Data were collected between 2013 and 2020 through marking and recapture, on João Barrosa beach, in the Reserva Natural das Tartarugas. In years with more females nesting on beaches, a smaller percentage of nests are studied because of the difficulty in reporting them all. As such, only the first 25% of the nests were analysed. Minimum clutch frequency ranged between 3.8 and 4.1. Remigrants had a larger body size and higher clutch frequency than neophytes, without differences in the internesting period. This study also showed differences between neophyte and remigrant females, specifically only in their measured clutch frequency. However, neophytes likely switch between nesting grounds more often, evading monitoring, and highlighting their potential to move to other islands or to breed out of the main season. These findings enhance our understanding of reproductive strategies, enabling the application of distinct conservation strategies tailored to each group. Satellite telemetry could address study limitations regarding clutch frequency values and provide a better understanding of nesting patterns and the impact of environmental factors on reproduction. This could improve conservation strategies by identifying critical habitats and guiding targeted protective measures, supporting population recovery.

In social species, social relationships of an individual play a crucial role in its fitness, and the social structure of a population can be vital to its viability. This study investigated the social network of the critically endangered Taiwanese humpback dolphin (Sousa chinensis taiwanensis) population during the periods 2017–2020 and 2021–2023. We observed a reduction in the strength and reach of the social network compared with a decade ago. The population could be divided into three clusters, each characterized by distinct age compositions and network metrics, with limited intercluster associations and minimal overlap in core areas. The decline and ageing of the northern cluster suggested the need for further research into its habitat quality. In the central cluster, which previously had high calf sighting rates, low intracluster association and a limited number of young individuals raised concerns about reproductive constraints. The southern cluster, although most socially vigorous, partly occupied areas outside the protected zone. Our findings emphasized the need for cluster-specific management strategies to enhance conservation efforts.

The stable isotopes δ¹³C and δ¹⁵N are widely recognized and utilized as biomarkers for analysing trophic links, paleoenvironmental reconstruction, biogeography and nutrient sources. However, it is essential to further develop their applications, as their use in marine environmental monitoring is not as prominent. ¹³C and ¹⁵N have distinct signatures in organic compounds, which can be utilized to identify potential carbon and nitrogen sources. Marine bivalves are often employed in environmental studies as efficient bioindicators because sessile filter feeders tend to bioaccumulate pollutants. The present study analysed δ¹³C and δ¹⁵N in seston and oysters inhabiting two areas with different environmental conditions in a marine extractive reserve. The isotopic values were compared for two trophic levels and three oyster tissues, resulting in a broad view of local dynamics. Seston samples from Forno Beach (FB) exhibited depleted δ¹³C values, possibly reflecting a terrigenous carbon contribution in this area. Considering oyster tissues, δ¹³C and δ¹⁵N values in the hepatopancreas were similar to seston, possibly due to oysters' role as filter feeders, supporting the use of digestive tissues for assessing short-term changes of environmental conditions. Moreover, isotope values for oyster gills and muscles suggest long-term homogeneous conditions for Anjos Beach (AB) and FB, with a predominance of marine carbon and nitrogen sources. Our results underline the relevance of analysing bivalve tissues separately because they display different turnover rates and depict variable time frames of environmental conditions. This article provides valuable information on the variables that must be considered when applying stable isotope analysis in coastal environmental monitoring, highlights knowledge gaps and recommends best practices for future work in this area.

Estimates of apparent survival and abundance are crucial for understanding the population dynamics of sentinel species. To achieve this, it is necessary to establish a baseline of these parameters for effective management planning in areas strongly impacted. This is the case of the dusky dolphin (Lagenorhynchus obscurus), a species inhabiting the Argentine coasts. In Golfo Nuevo, information on the demographic parameters of this species, which coexists with tourism activities, remains insufficient. In this study, the abundance of dusky dolphins in Golfo Nuevo, Patagonia, Argentina, was estimated through long-term monitoring using the mark-recapture model for open populations (POPAN model). Moreover, the apparent survival rate of this species was estimated for the first time through live recaptures using the Cormack–Jolly–Seber (CJS) model. Photo-identification surveys were conducted from 2004 to 2022, and models were built using the MARK program, selecting the best models based on the lowest AIC. Our results suggest that in Golfo Nuevo, the apparent survival rate is high, around 0.95 ± 0.01, whereas the local abundance reached 2862.81 individuals throughout the entire sampling period. The number of individuals showed an increase with an average annual change rate of 4.65%. These findings represent a baseline estimate of abundance, apparent survival and population trend for dusky dolphins. However, future studies should prioritize estimates of site fidelity and emigration to achieve accurate estimations of true survival rates for the species. Our results contribute to the understanding of dusky dolphin population dynamics and can be considered in management and conservation projects at the local level.

Urchin barrens (‘blanquizales’) are habitats dominated by encrusting non-geniculate coralline algae and maintained by urchin grazing. Taxonomic information of coralline communities in Mediterranean blanquizales is limited. Lumpy to fruticose coralline algal specimens, unusual in blanquizales, were found along the southern Spanish coast. Sequences from these specimens resolved with foliose samples morpho-anatomically identified as Lithophyllum dentatum. Initial observations suggested that this protuberant Lithophyllum species increases diversity in the otherwise species-poor exposed blanquizales. When present, higher macroalgal cover was observed with algae and microfauna frequently observed as epibiotic among the coralline's protuberances.