Fish Density Research Articles

Fish dispersal from a sabotage-mediated massive escape event

Farm sabotage can cause massive fish escape events with significant ecological and socio-economic risks. This study examined the fate of Mediterranean seabass Dicentrarchus labrax escapees following a large-scale escape event caused by sabotage in the Western Mediterranean Sea. We monitored the escapee density and size structure over 3 mo after the escape at increasing distances from the escape point, up to 45 km away. Fish density adjacent to the escape location 5 d after the sabotage was, on average, 114 ± 44.7 (SE) fish per 100 m2. Our analyses showed that fish density decreased by 17% for every km away from the location, dropping to 2 and 1% after 1 and 2 mo, respectively, following the escape event. As escapee density declined throughout time and space, the size distribution of seabass shifted towards larger sizes. The rapid decrease in fish densities highlights the need for contingency plans focusing on fishing efforts in the coastal areas near the escape location (<20 km) within the first 24 h. These results are paramount to mitigating the risks associated with escape events cost-effectively. We emphasise the importance of sabotage prevention measures, such as security systems that can quickly detect intruders and trigger an immediate response to deter them. Additionally, enforcing appropriate sanctions based on the severity of the damage caused could help to discourage future sabotage attempts.

Structured neural networks for CPUE standardization: A case study of the blue endeavour prawn in Australia's Northern Prawn Fishery

We performed a study on standardizing the catch per unit effort (CPUE) for blue endeavour prawns (Metapenaeus endeavouri) caught in the Northern Prawn Fishery (NPF), one of Australia’s largest and most valuable prawn fisheries. Blue endeavour prawns constitute a significant proportion of the total NPF catches. However, there have been very limited studies on their population dynamics. This study assessed the effectiveness of Artificial Neural Networks (ANNs) for CPUE standardization, with a focus on blue endeavour prawns as a case study. Our approach involved developing new ANN models for CPUE standardization with two key ideas: using an architecture inspired by the catch equation to mitigate overfitting; and using the Tweedie distribution to manage uncertainties and zero counts in the catch data. Specifically, we grouped variables into three distinct modules based on the catch equation, with each representing catchability, fishing effort, and fish density, respectively. Parameter estimation for our ANNs was achieved by maximizing the likelihood using a coordinate descent approach, which alternates between optimizing the Tweedie distribution parameters (power and dispersion) and the standard neural net parameters. We conducted a comprehensive comparison among ANNs, generalized linear models, and generalized additive models. The findings suggest that customizing ANN structure improves model fitting and effectively mitigates the risk of overfitting. It also reveals a promising path for the application of neural networks in CPUE standardization.

Effects of Stocking Density of Filter-Feeding Fishes on Water Quality and Bacterial Community in Rice–Crayfish Polyculture System

To evaluate the effects of filter-feeding fishes on water quality and bacterial community in the rice–crayfish coculture system, four different stocking densities of bighead carp (0, 500, 1000, 1500 ind./200 m2) were set up in rice–crayfish coculture systems. Water samples in the systems were collected biweekly to detect dissolved oxygen (DO), temperature (T), potential of Hydrogen (pH), ammonia nitrogen (NH4+-N), nitrite nitrogen (NO2−-N), nitrate nitrogen (NO3−-N), total nitrogen (TN), total phosphorus (TP), and Chlorophyll-a (Chl-a); the bacterial community in the water was analyzed simultaneously, then the correlation between water quality and microorganisms were studied. The results showed that concentrations of TN, TP, NO2−-N, and NH4+-N decreased while DO and NO3−-N increased along with the breeding process. NO2−-N, NO3−-N, TN, and NH4+-N were important environmental factors affecting the bacterial community structure in water (p < 0.05). Bighead carp stocking had an impact on the diversity, richness, and evenness of the bacterial communities in the systems. The dominant bacteria in the four different carp density groups were Proteobacteria, Actinomycetes, Bacteroidetes, and Cyanobacteria. Bighead carp increased the abundance of Bacteroidea but reduced that of Actinomycetes, Cyanobacteria, and Proteobacteria. The introduction of bighead carp promoted the conversion of nitrogen and phosphorus, reducing the risk of cyanobacterial blooms. Group 1000 ind./200 m2 exhibited the best effect on the removal of nitrogen and phosphorus from the water body.

Effect of Natural Feeding Capacity of Dengue Mosquito (Aedes aegypti) Larvae and Different Stocking Densities of Gold Molly Panda Fish (Poecilia spp) on the Feeding Speed and Function of Natural Predators in Gold Molly Panda Fish (Poecilia spp)

Effect of Natural Feeding Capacity of Dengue Mosquito (Aedes aegypti) Larvae and Different Stocking Densities of Gold Molly Panda Fish (Poecilia spp) on the Feeding Speed and Function of Natural Predators in Gold Molly Panda Fish (Poecilia spp)

Habitat-specific response of fish assemblages in a small fully protected urban MPA

Abstract This study aims at assessing the reserve effect on fish assemblage in a small urban fully protected and highly enforced Marine Protected Area (MPA), Larvotto MPA (Monaco, Mediterranean Sea). The data about fish density, size, and biomass was collected by underwater visual census in the MPA and unprotected areas in two habitats, artificial rocky substrates and Posidonia oceanica meadows. On artificial rocky substrates, we recorded significantly higher fish biomass within the MPA compared to unprotected areas, while no significant difference was detected on Posidonia, with this suggesting the habitat-specific responses of fish assemblages to protection. Here we highlight the potential effectiveness of highly enforced small-sized urban MPAs, such as the Larvotto MPA, in generating ecological benefits, and speculate about their potential role in supporting networks of MPAs. This study supports increased attention to urban MPAs in conservation efforts, emphasizing the need for efficient management strategies in the face of ongoing coastal expansion.

Both rapid hyperplasia and hypertrophy promoted skeletal muscle growth in mandarin fish Siniperca chuatsi, compared to big-eye mandarin fish Siniperca kneri

As important cultured fishes in China, mandarin fish, Siniperca chuatsi and big-eye mandarin fish, Siniperca kneri share similar external morphology and genomes, but have significant differences in growth rates. In this study, we used 6 mph (month post hatching) mandarin fish and big-eye mandarin fish to compare differences in skeletal muscle growth over a one-month period, and use transcriptomes to explore the reasons for the growth differences. The results showed that the different value in number of muscle fibers (2.72 times), density (2.56 times), area (1.95 times) and diameter (2.73 times) of mandarin fish are significantly higher than that of big-eye mandarin fish (P<0.05). Hypertrophy (Contribution rate: 97.9%) is the dominant factor in big-eye mandarin fish, and both hypertrophy and hyperplasia (Contribution rate: 2.1%) were significantly different from mandarin fish (P<0.05). Transcriptome results showed that differential genes were enriched in proliferation of satellite cells, protein synthesis and degradation. Further analysis of the transcriptome results showed that the number of Pax7-positive cells per unit area of mandarin fish was 2.3 fold higher that of big-eye mandarin fish (P<0.05). Myod, pax3, pax7, and myf5 mRNA expression of mandarin fish were significantly higher than those of big-eye mandarin fish(P<0.05). In muscle fiber fusion, mef2, myog, and myomaker mRNA expression of mandarin fish were significantly higher than that of big-eye mandarin fish (P < 0.05). In protein deposits, the results showed that the muscle fiber area of mandarin fish was 2.85 times larger than that of big-eye mandarin fish by comparing the muscle fiber area with the same number of nuclei. Polr2a, mtorc1, 4e-bp1, s6, e1, murf, foxo3, atg5, beclin, and atg14 mRNA expression of mandarin fish were significantly higher than that of big-eye mandarin fish (P < 0.05), while eef2, eif2α, gcn2, eif2b, capn and cast of mandarin fish was significantly lower than that of big-eye mandarin fish (P < 0.05). This work verified that the skeletal muscle growth rate of mandarin fish is faster than that of big-eye mandarin fish. The greater number and higher activity of satellite cells of mandarin fish increased hyperplasia efficiency, and the faster fusion rate and protein precipitation rate increased hypertrophy efficiency. Both hyperplasia and hypertrophy contribute to faster skeletal muscle growth of mandarin fish than that of big-eye mandarin fish.

Avalanche dynamics of zebrafish schools: Unveiling self-organization and phase transitions

Collective behavior in animal groups exhibits intriguing dynamics that can be analyzed through the lens of self-organized criticality. In this context, we analyze behavioral cascades in zebrafish (Danio rerio) groups of varying sizes within controlled tank environments. Through experimental observations and data analysis, we unveil scale-free signatures reminiscent of self-organized critical processes in the collective movement of zebrafish. Notably, as fish density varies, we observe a dynamic phase transition: at low densities, coordinated and highly polarized movement dominates, while at high densities, the group fractures into uncorrelated domains. These findings shed light on the complex dynamics of collective behavior in fish groups and provide valuable insights into the responses of individuals to environmental stimuli. Moreover, the observed phase transition highlights the sensitivity of zebrafish behavior to changes in population density, which has implications for understanding collective behavior in various contexts, from ecological systems to preclinical studies. Finally, we compare our findings with the known results of avalanche analyses of collective motion and neuronal activity. All follow the same power law, indicating a possible universality in one parameter of avalanche processes.

Combination of herbal extracts regulates growth performance, liver and intestinal morphology, antioxidant capacity, and intestinal microbiota in Acrossocheilus fasciatus

In the present study, the herbal extracts (RPTS) composed of Rheum palmatum: Schisandra sphenanthera: Terminalia chebula: Punica granatum with a weight ratio of 1.07: 3.00: 1.18: 1.38, was evaluated through a bacteriostatic assay in vitro. Afterwards, a 56-day feeding trial was operated to assess the impact of dietary RPTS at the dose of 0, 1.0, 2.5, 5.0, and 10 g·Kg−1 feed (entitled as Con, RPTS010, RPTS025, RPTS050, RPTS100 group, respectively) on the performance of Acrossocheilus fasciatus fingerlings. The results revealed that dietary RPTS at the dose of 2.5 g·Kg−1 feed remarkably improved the specific growth rate (SGR), and the gastrointestinal trypsin activity, as well as the catalase (CAT) activities, while slightly increased the alanine aminotransferase (ALT) activity and aspartate aminotransferase (AST) activity in the fish liver. Histological examination indicated that dietary high dose of RPTS (5.0 and 10.0 g·Kg−1 feed) could induce hepatic cell vacuolization and reduce the intestinal villi density of fish. Furthermore, the analysis of intestinal microbiota showed that Bacteroidota, Firmicutes and Proteobacteria were the three dominant phylum in all experimental groups, while the Firmicutes/Bacteroidota ratio exhibited a trend of initially decreasing followed by rising, with the supplementation level of RPTS increase. Additionally, the LEfSe analysis revealed that Cetobacterium was the most impacted species, which notably increased in RPTS025 group. Collectively, this study unveiled that the impact of dietary RPTS on fish performance was in a dose-dependent manner, and dietary RPTS at the dose of 2.5 g·Kg−1 feed could potentially enhance growth performance, digestive and antioxidant capacity, and positively modulate the intestinal microflora, without significantly impact liver health of A. fasciatus.

Fine-scale spatial distribution of a fish community in artificial reefs investigated using an underwater drone and environmental DNA analysis

Although artificial reef (AR) effect evaluation is useful for planning the installation of high-rise ARs and their management, few studies have investigated them quantitatively. The fine-scale 2-dimensional fish distribution in ARs was estimated regarding current fields and vertical structures of 2 high-rise ARs (20 and 30 m high at 62 and 72 m depths, respectively) in Tateyama Bay, central Japan, using underwater drone recordings with vertical line transects and environmental DNA (eDNA) metabarcoding. The species detected by video surveys (21 taxa were identified to species, and 1 to genus) were fewer than by eDNA analysis (103 species and 6 genera), especially for pelagic, small-sized, and cryptic fish. Video surveys revealed that demersal fish increased with decreasing horizontal distance from the AR surface within 20 m, and the richness and total fish density were significantly higher upstream of the ARs. Conversely, the fish eDNA concentration showed different patterns, with significantly higher concentrations downstream of the ARs. The richness peaked at horizontal AR surfaces (e.g. reef top), but density of the dominant species peaked near the bottom by video survey. In comparison, eDNA analysis indicated lower richness and higher eDNA concentration of the dominant species at the reef top. Such discrepancies may be explained by the influence of eDNA transport or its specific behavior or buoyancy. Video surveys revealed the growth stage and sex information of 4 species from their morphology, which is not possible using eDNA analysis. This study shows that the advantages of each evaluation method can complement each other.

Impacts of estuarine habitat degradation on the modeled life history of marine estuarine-dependent and resident fish species.

Shallow coastal and estuarine habitats play an essential role in the life cycles of many fish species, providing spawning, nursery, feeding, and migration areas. However, these ecologically valuable habitats are increasingly threatened by anthropogenic activities, causing substantial changes in both habitat availability and quality. Fish species use these shallow coastal habitats and estuaries during various life stages, leading to their categorization into guilds based on how and when they rely on these areas. This differential functional use of estuaries means that changes to these habitats may affect each guild differently. To understand the impact of estuarine habitat degradation on fish populations, it is therefore necessary to consider the full life cycle of fish and when they rely on these coastal habitats. Here, we use conceptual size-structured population models to study how estuarine habitat degradation affects two functionally different guilds. We use these models to predict how reduced food productivity in the estuary affects the demographic rates and population dynamics of these groups. Specifically, we model estuarine residents, which complete their entire life cycle in estuaries, and marine estuarine-dependent species, which inhabit estuaries during early life before transitioning offshore. We find that total fish biomass for both guilds decreases with decreasing food productivity. However, the density of juveniles of the marine estuarine-dependent guild can, under certain conditions, increase in the estuary. This occurs due to a shift in the population biomass distribution over different life stages and a simultaneous shift in which life stage is most limited by food. At the individual level, somatic growth of juveniles belonging to the estuarine-dependent guild decreased with lower food supply in the estuary, due to increased competition for food. The somatic growth rates of fish belonging to the resident guild were largely unaffected by low food supply, as the total fish density decreased at the same time and therefore the per-capita food availability was similar. These outcomes challenge the assumption that responses to habitat degradation are similar between fish guilds. Our study highlights the need to assess not only fish biomass but also size distributions, survival, and somatic growth rates for a comprehensive understanding of the effects of habitat degradation on fish populations. This understanding is crucial not only for estuary fish communities but also for successful conservation and management of commercially harvested offshore population components.

A Web-Based Interactive Application to Simulate and Correct Distortion in Multibeam Sonars

Multibeam sonars are advanced scientific tools for estimating fish school volume and density, using multiple beams to provide comprehensive size measurements of detected targets. However, challenges remain in accurately estimating target dimensions due to beam geometric expansion and overlap, particularly in athwart-beam measurements, which tend to be overestimated with increasing distance from the transducer. We present an interactive web application that simulates distortion caused by beam overlap and expansion in multibeam sonars using simple geometric equations. Users can define sonar characteristics, such as the number of beams, swath opening, or degree of overlap, as well as specify an elliptical target’s dimensions, orientation, and distance from the transducer. The application estimates and visualises the true and distorted shapes of the target, calculating the level of distortion. It can run simulations in both forward and inverse directions, either simulating the distortion of a true school or correcting the shape of a distorted school. This tool aims to enhance the interpretation of multibeam sonar signals and improve the accuracy of target dimension estimates, facilitating more effective use of these sonars in scientific research.

Spatial ecology and population dynamics of brown trout Salmo trutta L. in reservoirs and headwater tributaries.

This investigation compared the spatial ecology and population dynamics of brown trout Salmo trutta L. between reservoirs with (impact; Langsett Reservoir) and without (control; Grimwith Reservoir) barriers to fish movements into headwater tributaries, and the effectiveness of a fish pass intended to remediate connectivity. Passive integrated transponder (PIT) telemetry revealed that fish that emigrated from Langsett and Grimwith tributaries were 1-3 and 0-2 years old, respectively, and predominantly did so in spring and autumn-early winterin both systems. Weirs at Langsett Reservoir appeared to thwart emigration rate (26%) relative to Grimwith Reservoir (85%). Acoustic telemetry (two-dimensional positions) in the impacted reservoir revealed thatthe largest home range was in October-December (95% monthly activity space S.D. up to 26.9 ± 6.69 ha in November), activity was influenced by both month and time of day, and fish occupied shallow water depths (relative to reservoir depth), especially at night. Brown trout tagged in Grimwith and Langsett Reservoirs (42.9% and 64.1%, respectively) and fish tagged in the tributariesthat emigrated (37.2% and 27.7%, respectively) were detected immigrating into tributaries throughout the year. At both reservoirs, peak immigration for ≥3-year-old trout occurred primarily in autumn-early winter. Overall passage efficiency went from 3% prior to remediation to 14% after and there was no significant increase in fish densities following the construction of the fish pass. Fish were attracted towards and entered the fish pass under a wide range of river levels, but only succeeded in passing upstream during low levels, which are uncommon druing the main migration period. Overall, this investigation significantly furthers our understanding of brown trout spatial ecology and population dynamics in reservoirs and headwater tributaries.

Saprolegniosis in aquaculture and how to control it?

AbstractSaprolegniosis, also called water mould, induces a cotton or wool‐like white growth on fish skin. It can kill fish at all stages of life, from eggs to adults. It is caused by oomycetes from the genus Saprolegnia and causes fish mortality and huge financial losses to fish farms and hatcheries. Saprolegnia species are endemic and ubiquitous in all freshwater habitats around the world. The exposing factors for saprolegniosis are still largely unknown, but stressors such as temperature shocks, poor water quality, handling and high fish density have been associated with outbreaks. For decades, malachite green was the most effective treatment against Saprolegnia infection, but it has been banned due to its carcinogenic and toxic effects. This has forced farmers to use alternative disinfection methods against Saprolegnia infection, such as hydrogen peroxide, formalin, Bronopol, NaCl, acetic acid and ozone, although many may have safety concerns or are impractical to use. This has led to the investigation of plant‐based compounds with antifungal and antibacterial properties against saprolegniosis. These include extracts of certain herbs, onion, garlic, extracts of the plant Chrysanthemum, essential oils of Eryngium campestre, Mentha piperita, Cuminum cyminum and Thymus linearis, which include a variety of phenolic compounds and fatty acids with antifungal properties. This review combines the current knowledge regarding the predisposing factors to Saprolegnia infections and current methods to prevent and treat them, including those under further research. Thus far, many compounds have been tested and studied, but an effective, suitable and safe compound to treat Saprolegnia infection remains to be found.

Coral reef fish density at a tourist destination responded rapidly to COVID-19 restrictions.

Throughout the world, anthropogenic pressure on natural ecosystems is intensifying, notably through urbanisation, economic development, and tourism. Coral reefs have become exposed to stressors related to tourism. To reveal the impact of human activities on fish communities, we used COVID-19-related social restrictions in 2021. In French Polynesia, from February to December 2021, there was a series of restrictions on local activities and international tourism. We assessed the response of fish populations in terms of changes in the species richness and density of fish in the lagoon of Bora-Bora (French Polynesia). We selected sites with varying human pressures-some dedicated to tourism activities, others affected by boat traffic, and control sites with little human presence. Underwater visual surveys demonstrated that fish density and richness differed spatially and temporally. They were lowest on sites affected by boat traffic regardless of pandemic-related restrictions, and when activities were authorised; they were highest during lockdowns. Adult fish density increased threefold on sites usually affected by boat traffic during lockdowns and increased 2.7-fold on eco-tourism sites during international travel bans. Human activities are major drivers of fish density and species richness spatially across the lagoon of Bora-Bora but also temporally across pandemic-related restrictions, with dynamic responses to different restrictions. These results highlight the opportunity provided by pauses in human activities to assess their impact on the environment and confirm the need for sustainable lagoon management in Bora-Bora and similar coral reef settings affected by tourism and boat traffic.

Insights into the connection between pathogen water eDNA and disease progression in zebrafish infected with Vibrio anguillarum

The host-pathogen interactions are tripartite and include the host, the pathogen, and the environment. For a long time, attention has mainly been addressed to the host's immune mechanisms and the pathogen's virulence factors while the environmental factor has received less interest. About a decade ago, studies on environmental DNA (eDNA) started to emerge as this approach is versatile for numerous research fields and interest is persistently growing. In the present study, the relationship between disease progression and pathogen water environmental DNA level was investigated. To perform this investigation, an infection model was setup using zebrafish and the gram-negative bacteria Vibrio anguillarum. Two different fish densities and bacterial concentrations were used to determine different patterns of pathogen eDNA in the fish tanks. Water sampling to collect eDNA was conducted alongside with observation of the fish Clinical Signs, mortalities, and immune responses. Water eDNA relative abundance of the pathogen could be determined directly after fish challenge, when Clinical Signs occurred, and when mortality started. Moreover, immune-relevant gene expression in zebrafish gills showed that il-1β, il-8, il-10, nf-κb and saa correlated to the pathogen eDNA signal, depending on fish density and bacterial concentration. In conclusion, this study demonstrated that water eDNA is a promising non-invasive tool to state disease progression and immune response in zebrafish infected with V. anguillarum.

Investigating the nursery function of the Alboran MPA on the Mediterranean coast of Morocco

Coastal habitats provide shelter and food for juvenile fish, ensuring their survival and supporting a range of species that are both commercially and ecologically important. The Alboran Marine Protected Area (MPA) off the Mediterranean coast of Morocco has been identified as a nursery area, although this role has never been the subject of characterisation. This study investigates the nursery function of habitats at six sites, two of which have seasonally flooded rivers with small persistent lagoons (transition systems) actively connected to the sea. Mixed sand-and-gravel beaches and transition systems were surveyed using a beach seine (four hauls) during two consecutive summer periods (June 2019 and July 2020), and a beam trawl was used in July 2020 in order to survey shallow waters at three depths: 3, 5 and 7 m. The use of both fishing methods provided a comprehensive assessment of juvenile fish communities. Different habitats in these coastal areas supported juvenile fish of 31 different species, with higher species richness and densities of young-of-the-year (YOY; first year of life) fish in transition systems despite their limited surface area and depth. Shallow marine waters supported fish species with specific microhabitat requirements despite lower overall YOY fish densities. The Alboran MPA coast has a nursery function, with different habitats acting as nurseries for juveniles of different fish species, creating a seascape of interconnected nursery habitats. As low densities of juvenile fish were a common concern across species and habitats, protecting these nursery habitats through enforcement of their protection regime appears to be a priority.

Investigation of the pangas (Pangasianodon hypophthalmus) cultivation sustainability in cages at the Ratargul Freshwater Swamp Forest of Bangladesh

AbstractDetermining the most appropriate stocking density for a specific fish species in an ambient condition is essential for successful cage aquaculture in terms of profitability which is mainly governed by growth. The current study was conducted to ascertain which stocking density gives the best result of widely cultured species in cage aquaculture, pangas (Pangasianodon hypophthalmus), at swamp forest environment of Ratargul Freshwater Swamp Forest, Bangladesh in terms of growth, production and economic return. Fish were reared for 93 days at three stocking densities, namely 30, 40 and 50 fish/m3 which were denoted as FSD30, FSD40 and FSD50, respectively, containing three replications of each. Growth and yield comparisons indicated that the stocking density of fish had significant (p &lt; 0.05) effects on growth rate and productivity. Fish cultivated at the maximum density (FSD50) had lower mean weights than fish reared at lower densities. The significantly highest mean weights (376.58 ± 14.65 g) and benefit–cost ratio (BCR) (1.617 ± 0.035) obtained from FSD30 show the suitability of this density in terms of fish growth and profitability of pangas in swamp forest environment.

Using a baited imaging sonar (BISON) to quantify the density, size, and detection range of fishes in a shallow, nearshore habitat

AbstractMethods that supplement optical instruments with bait, such as baited remote underwater video (BRUV), are used worldwide to detect and quantify marine life. Optical instruments only detect targets within visible range, such that BRUVs may underestimate fishes in light‐limited habitats, especially fishes that respond to the bait at ranges beyond visibility. Alternatively, light‐independent instruments (e.g., imaging sonars) can detect and quantify fishes regardless of visibility. This study presents the first application of a baited imaging sonar (BISON), deployed to survey fishes around a small, shallow artificial habitat in a turbid embayment in southern Florida. To establish the influence of bait on fish detection, BISON trials were alternately conducted alongside deployments of an unbaited control, with a high‐definition camera integrated to ascertain visibility and inform species composition. For fishes of two size classes, larger (&gt; 30 cm) and smaller (10–30 cm), maximum density (MaxD) and range of detection were quantified. Although the densities of larger and smaller fishes quantified by the BISON and unbaited control did not differ, over 55% of larger fishes were detected at ranges beyond maximum visibility, with asymptotes in fish density on the BISON identified at 15–20 min and 5–10 min for larger and smaller fishes, respectively. Overall, this study demonstrates the potential of BISONs as both a complementary and alternative method to BRUVs for quantifying fishes, especially in habitats of limited visibility. Future applications of BISONs in other habitats will further demonstrate its value as a tool to detect and enumerate aquatic assemblages.

Wood you believe it? Experimental addition of nonnative wood enhances instream habitat for native dryland fishes

AbstractFlow alteration and riparian vegetation encroachment are causing habitat simplification with severe consequences for native fishes. To assess the effectiveness of enhancing simplified habitat in a large dryland river, we experimentally added invasive wood at 19 paired treatment and reference (no wood added) subreaches (50–100 m) within the main channel of the San Juan River. Using a before‐after‐control‐impact design, we sampled fishes and macroinvertebrates, and quantified habitat complexity. After wood addition, total native fish densities were 2.2× higher in treatments compared with references, whereas total nonnative fish densities exhibited no response. Macroinvertebrate densities were 6.8× higher, and habitat complexity increased in treatments. Counts of geomorphic features in treatments increased from 1 to a maximum of 11 following wood addition, while the number of features in references remained unchanged. Wood addition has potential to instigate natural riverine processes, ultimately enhancing native fish habitat by increasing macroinvertebrate densities and habitat complexity in dryland rivers. Water overallocation and increasing aridity will continue to challenge efforts to improve habitat conditions with environmental flows alone, and managers might consider integrating non‐flow alternatives like addition of abundant, invasive wood to reduce habitat simplification.

Machine learning for cyanobacteria inversion via remote sensing and AlgaeTorch in the Třeboň fishponds, Czech Republic

Cyanobacteria blooms in fishponds, driven by climate change and anthropogenic activities, have become a critical concern for aquatic ecosystems worldwide. The diversity in fishpond sizes and fish densities further complicates their monitoring. This study addresses the challenge of accurately predicting cyanobacteria concentrations in turbid waters via remote sensing, hindered by optical complexities and diminished light signals. A comprehensive dataset of 740 sampling points was compiled, encompassing water quality metrics (cyanobacteria levels, total chlorophyll, turbidity, total cell count) and spectral data obtained through AlgaeTorch, alongside Sentinel-2 reflectance data from three Třeboň fishponds (UNESCO Man and Biosphere Reserve) in the Czech Republic over 2022–2023. Partial Least Squares Regression (PLSR) and three machine learning algorithms, Random Forest (RF), Support Vector Machine (SVM), and Extreme Gradient Boosting (XGBoost), were developed based on seasonal and annual data volumes. The SVM algorithm demonstrated commendable performance on the one-year data validation dataset from the Svět fishpond for the prediction of cyanobacteria, reflected by the key performance indicators: R2 = 0.88, RMSE = 15.07 μg Chl-a/L, and RPD = 2.82. Meanwhile, SVM displayed steady results in the unified one-year validation dataset from Naděje, Svět, and Vizír fishponds, with metrics showing R2 = 0.56, RMSE = 39.03 μg Chl-a/L, RPD = 1.50. Thus, Sentinel data proved viable for seasonal cyanobacteria monitoring across different fishponds. Overall, this study presents a novel approach for enhancing the precision of cyanobacteria predictions and long-term ecological monitoring in fishponds, contributing significantly to the water quality management strategies in the Třeboň region.