Aquatic Conservation-Marine and Freshwater Ecosystems最新文献

Green Island lies approximately 11 km off the north Queensland coast of Australia. The associated 710-ha reef flat supports a Chelonia mydas foraging population, which has been monitored by the Queensland Government's Threatened Species Program since 1988. Population census data for this area show a significant adult age-class-specific population decline for C. mydas. Preliminary evaluation indicates the decline in adult age-classed turtles is unlikely to be caused by incidental capture, habitat degradation, pollution, change of foraging sites or climate change. Traditional take (locally or during reproductive migrations) provides a plausible explanation. A continuation of this trend may threaten the existence of C. mydas in this part of the Great Barrier Reef World Heritage Area.

Totoaba macdonaldi is a large Sciaenid fish listed as a vulnerable species. The illegal commerce of its swimming bladder has caused severe overfishing, which has in turn been associated to the population decline of vaquita, a porpoise endemic to the Gulf of California. The present study had two objectives; the first was to use the natural carbon and nitrogen stable isotope values of wild and farmed totoaba as biomarkers to identify their origin. In the second part of the study, a group of juvenile totoabas was maintained under controlled feeding conditions to explore their rates of isotopic change and estimate the time required for the dietary isotopic values to be transferred into muscle tissue. Results from the feeding experiment indicated that muscle tissue of fish reached an isotopic equilibrium with the offered diet after 28 days for carbon and 43 days for nitrogen. Muscle samples collected from wild and farmed totoaba were analysed and data revealed that the isotopic values (carbon and nitrogen) were significantly different between both groups of organisms. A discriminant analysis using dual isotopic measurements showed a significant separation of classes, indicating that the isotopic values measured at natural abundance levels, can be effectively applied as biomarkers to support the traceability processes of farmed totoaba. The implications to promote a reduction of product mislabelling and to improve detection of illegally extracted fish are addressed.

Identifying biogeographical patterns and important biological (blue) corridors can greatly contribute to conservation planning. Yet, this is particularly challenging when addressing pelagic species. In this study, satellite telemetry and photographic-identification data of short-finned pilot whales (Globicephala macrorhynchus) were used to identify preferred areas and pathways in the Macaronesia biogeographical region, namely between Madeira and two regions in the Canary Islands, the Western (WCI, La Palma and El Hierro) and the Central (CCI, Tenerife and La Gomera). Home-range and time-varying move persistence analyses from tracking data of four whales that moved between both archipelagos over 578 days revealed preferred areas in Madeira and the WCI, new connectivity pathways and the importance of both regions for area-restricted behaviours. These findings were corroborated by a high number (n = 71) of photographic matches between Madeira (catalogue of 1276 individuals) and the WCI (456 individuals), compared to only four between Madeira and the CCI (717 individuals). The high linkage of the WCI with Madeira and the CCI (n = 48) suggests that the WCI constitute a key habitat for potential mixing of pilot whales from different groups. This study emphasizes that a combined methodological approach provides robust baseline information for pilot whales' conservation management, which could be valuable for other scenarios and species. Furthermore, shown connectivity patterns contribute to broadening our knowledge on potential blue corridors in the eastern North Atlantic and highlight the importance of considering wide and international geographic areas for conservation planning of highly mobile marine species.

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.