Aquatic Conservation-Marine and Freshwater Ecosystems最新文献

Illegal, unreported and unregulated (IUU) fishing is one of the major anthropogenic impacts threatening aquatic ecosystem functioning. In the middle and lower reaches of the Yangtze River (MLYR), effective mitigation measures for IUU fishing are still absent, primarily due to gaps in prioritizing conservation actions and limited enforcement capabilities. In the present study, keywords associated with public concern, resource endowments and conservation efforts on online platforms were searched and analysed using the entropy-weighting method to identify major areas in the MLYR requiring immediate mitigation measures against IUU fishing. Key factors associated with the variation in public concern in these major areas were examined to discuss the feasibility of guiding actions against IUU fishing. From 2011 to 2023, public concern on IUU fishing were increasing, though the trend for recreational angling was not statistically significant. Following the implementation of the ‘Ten-Year Fishing Ban’ policy in Yangtze River, public concern on IUU fishing significantly increased. Changes in public concern were correlated with domestic human population, GDP, water area and the number of fishers. The results of entropy-weighting analysis highlighted the catchments of Dongting Lake and Poyang Lake as the major areas for reinforcing IUU fishing mitigation. In Poyang Lake, the areas requiring reinforced patrols and enforcement against IUU fishing include habitats around the river mouth of the Ganjiang River and central-eastern part of the lake during the flood season and the southern and eastern tributaries of the lake during the dry season. We recommend advancing the application of web-based data in biodiversity conservation and encouraging policy interventions to engage anglers as advocates for aquatic conservation, fostering a sound patrol network through social engagement.

Although sharks are important for marine ecosystems, they still suffer culling campaigns after human fatalities. A case study from the Caribbean shows how the rapid use of several complementary and reproducible forensic techniques not only allowed the confirmation of the species implicated in the bite but also the accurate assessment of the size of the animal. Six non-lethal fishing sessions led to the capture of several shark individuals that were released after either being eliminated due to their unsuitable size or the absence of human remains in their stomach. Such an ecologically responsible risk management can contribute to shark conservation.

The Atlantic salmon (Salmo salar) has suffered significant population declines worldwide, prompting urgent conservation efforts, especially in its southern distribution area. This study is aimed at characterising the population dynamics of Atlantic salmon in the Bidasoa River (Spain), by focusing on fluctuations and long-term trends in salmon returns, population characteristics and effects of angling and stocking activities. For this, monitoring data spanning three decades (1993–2023) from a salmon monitoring station and anglers' captures were used together with data on stocking activities provided by the Fish Management Section of the Navarre Government. Results reveal cyclical patterns driven by three distinctive wavelengths linked to the salmon life cycle, climatic variations and local habitat and connectivity improvements. The Bidasoa population was primarily dominated by one-sea-winter males returning during the autumn–winter season. Over the study period, a significant reduction in body size was observed, likely reflecting challenging marine conditions. Angling pressure was notably skewed towards multi-sea-winter females, which could influence natural recruitment dynamics. Despite the low mean stocking return rate of stocked salmon (0.13%), they contributed to one-third of the annual returns, underscoring their potential role in supporting population persistence albeit at the expense of reducing natural spawning, amid broader ecological challenges. This study provides valuable insights into the complex interplay of ecological and anthropogenic factors affecting Atlantic salmon populations in southern European rivers. These insights are crucial for developing and implementing effective conservation strategies aimed at preserving the Atlantic salmon, a species of significant cultural and ecological importance.

The northern form (often called Tappanaga type) population of short-finned pilot whales (T-SPW) is a local population that inhabits the Kuroshio-Oyashio mixed water regions off northern Japan. The population has been severely depleted by past whaling. Rigorous management was first introduced in the 1980s, and whalers have voluntarily refrained from taking T-SPW since 2007. Our primary goal is to investigate whether the T-SPW population has recovered. We estimated recent abundances based on data from the line-transect sighting surveys dedicated to T-SPW. Simple population dynamics models were fitted to these and previously published estimates for 1985–2006. When a detection probability on the track line was assumed to be 1 (g(0) = 1), the estimated abundances in 2007, 2021 and 2022 were 1659 (coefficient of variation, CV = 0.79), 2634 (0.93) and 759 (0.64), respectively. The population dynamics model showed that past whaling substantially reduced abundance, and no clear tendency for population recovery was seen even after the voluntary suspension of whaling. Compared with the estimated carrying capacity, the current population size was still considered to be nearly depleted. To improve the conservation and management measures, we need more efforts to identify the causes of nonrecovery of the T-SPW population.

Quillworts are highly threatened worldwide and many Isoëtes species have been suffering population decreases. Isoëtes cangae is a lycophyte endemic from a single Amazon lake that has been challenging due to climate change and deforestation of the Amazon rainforest. The development of strategies for ex situ conservation of lycophyte germplasm is urgent to prevent biodiversity losses. Spores of I. cangae were obtained from specimens collected in situ. Samples were submitted to three different moisture conditions: hydrated, air-dry desiccation and drying in silica gel. Desiccated samples were stored in an ultrafreezer (−80°C) or liquid nitrogen (−196°C) and the hydrated spores at room temperature. The spore viability was evaluated through spore germination (G) and sporeling emergence (SE) indices after 30, 90, 180 and 275 days of storage. The growth of emerged sporophytes was evaluated after 3 months. Desiccated–cryopreserved spores had high G% and SE%, even after 275 days of storage, and did not differ from hydrated spores. Hydrated spores had higher daily emergence and a longer time to maximum sporophyte emergence than desiccated spores, but not in all storage periods. Sporophytes that emerged from hydrated and desiccated spores had a similar development. Both desiccated methods and temperatures of storage maintained spore viability high. The methodologies tested in this study are novel for the genus and represent a significant step towards the ex situ conservation of quillworts.

Mesophotic rhodolith beds are free-living nongeniculate coralline algae (NGCA) bioconstructions with slow growth rates and massive associated diversity, distributed worldwide along continental shelves. They are subjected to deleterious impacts of sedimentation from natural and anthropogenic sources, which can bury the thalli, causing photosynthetic reduction and impaired gas exchange, among other effects. There have been only a few studies exploring the consequences of smothering and burial, which limit our knowledge of these type of impact. In this study, we evaluated the photosynthetic response and recovery of NGCA under different sedimentation conditions in the laboratory. Experiments were performed considering different loads of natural sediment (medium sand) during continuous burial periods. The Potential (Fv/Fm) and Effective Quantum Yield (ΔF/Fm′) of photosystem II (PSII) and the relative Electron Transport Rate (rETR) were determined using pulse-amplitude modulated fluorometry as indicators of PSII integrity and photosynthetic activity. PSII functionality (Fv/Fm) was impaired over time under the highest sediment load tested (burial under 100 g of sediment per thallus). However, only 2 days was necessary to recover at least half of the photosynthetic capacity observed in the control samples. This recovery pattern was also supported by ΔF/Fm′ and rETR. Our results illuminated the limits of the resilient behaviour of NGCA to sediment smothering and burial, where long burial periods (2 months) associated with heavy sediment load could cause heavy damage to the photosynthetic apparatus, which can lead to death. However, these organisms could recover after sediment removal. These results provide important information for setting up management strategies to assess the smothering and burial impacts of sediments on rhodoliths.

The global problem of ocean acidification and localised decline in water quality are major threats to coral reefs worldwide. This study examined the individual and interactive impacts of global and local stressors by investigating the effects of increased seawater pCO₂, elevated nutrient concentrations and reduced light levels on linear growth and metabolic rates of the common branching crustose coralline alga Lithophyllum cf. pygmaeum. We found complex interactions between factors on algal growth and photosynthetic rates, but overall, growth was significantly enhanced by pCO₂ enrichment under all light and nutrient combinations. This is the first study to report a positive growth response in coralline algae to elevated pCO₂ using linear extension methods. In contrast, the combination of reduced light levels and high nutrient concentrations simulating poor water quality conditions reduced algal growth rates by up to 67% (compared to individuals exposed to high light, low nutrients and elevated pCO₂). Decreased light levels reduced linear growth, P_gross and P_net rates by 33%, 18% and 24%, respectively, highlighting the critical role of light in coralline algal physiology. We suggest that poor water quality may counteract any CO₂ fertilisation effect under ocean acidification conditions on the growth of coralline algae, and this has implications for coral reef conservation as it emphasises the importance of improving water quality to maintaining coral reef functions. These results further highlight the need for multifactorial experiments to better understand the interplay between global and local processes on coralline algae growth.

Standard tools for detection and identification of invasive macrophytes have limitations that may result in failure to detect patches of invasive vegetation. These undetected growths can spread rapidly, leading to significant disruption of invasive macrophyte control programs. The ability to accurately identify and map invasive submerged aquatic vegetation (SAV) over large transects in a cost-efficient manner has been identified by water resource managers as a pressing issue that requires an immediate solution. To help with this challenge, we have developed an artificial intelligence/machine learning (AI/ML)–based image analysis program to automatically detect a priority invasive macrophyte, hydrilla (Hydrilla verticillata), in real time. The AI/ML model, based on the existing AI model EfficientDet, was trained and tested on nearly 12,000 images of H. verticillata captured underwater using remotely operated vehicles (ROVs) and handheld cameras. Accuracy of the object detection model was evaluated based on the Microsoft Common Objects in Context (MS COCO) metric of mean average precision (mAP). Our model had a peak mAP@[0.5:0.05:0.95] of 58.2% and a mAP@[0.5] of 81.2% (with inference latencies between 50 and 100 ms). These results suggest that real-time underwater identification of H. verticillata with our detection model is achievable at high accuracy, with further enhancement possible through integration with multiple commercially available underwater ROV platforms and continued training in environments with various combinations of invasive and native SAV assemblages.