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Knowing the distribution of fish larvae can inform fisheries science and resource management in several ways, by: 1) providing information on spawning areas; 2) identifying key areas to manage and conserve; and 3) helping to understand how fish populations are affected by anthropogenic pressures, such as overfishing and climate change. With the expansion of industrial fishing activity after 1945, there was increased sampling of fish larvae to help better understand variation in fish stocks. However, large-scale larval records are rare and often unavailable. Here we digitize data from Nishikawa et al. (1985), which were collected from 1956–1981 and are near-global (50°N–50°S), seasonal distribution maps of fish larvae of 18 mainly commercial pelagic taxa of the families Scombridae, Xiphiidae, Istiophoridae, Scombrolabracidae, and Scomberesocidae. Data were collected from the Pacific, Atlantic, and Indian Oceans. We present four seasonal 1° × 1° resolution maps per taxa representing larval abundance per grid cell and highlight some of the main patterns. Data are made available as delimited text, raster, and vector files. Measurement(s) larva abundance Technology Type(s) tows Factor Type(s) location of tows Sample Characteristic - Organism fish taxa Sample Characteristic - Environment open-ocean Sample Characteristic - Location near-global (Atlantic, Pacific, and Indian Oceans) [ABSTRACT FROM AUTHOR]

Priolepis (Gobiidae) is a genus of cryptobenthic fishes with a cosmopolitan distribution in tropical oceans. In the Atlantic, it is represented by P. ascensionis, P. dawsoni, P. hipoliti, and P. robinsi. With the exception of the latter, these species have their distribution limited by known biogeographic barriers signaling allopatric origins. In the present study, we used phylogenetic/phylogeographic approaches to uncover the evolutionary history of Priolepis in the Atlantic by testing three hypotheses: (i) The closure of the Tethyan Passage gave rise to a monophyletic Atlantic lineage; (ii) The formation of the Amazon Barrier divided the species into southwestern and northwestern Atlantic lineages; and (iii) Dispersal from Brazil across the Mid-Atlantic Barrier gave rise to the Santa Helena and Ascension Islands lineage. Neither hypothesis was refuted by our results. Phylogenies recovered the monophyly of the Atlantic Priolepis clade and its isolation from the Western Indian/Pacific Ocean ~ 16.9 million years ago. A few million years later (14-10 Mya), the emergence of the Amazon Barrier divided Priolepis into a southwestern and a northwestern ancestral. The closure of the Isthmus of Panama, as well as Pliocene and Pleistocene climatic variations, had an important influence on the formation of the different lineages within P. dawsoni, and P. hipoliti. During the Pleistocene, the occupation of the Vitoria-Trindade chain may have favored dispersal to the Mid-Atlantic islands, influencing the origin of P. ascensionis. Our results also highlight the great ability of P. dawsoni and P. hipoliti to maintain connectivity between remote areas and different habitats, a singular pattern among Brazilian cryptobenthic fishes. [ABSTRACT FROM AUTHOR]

The Marmarik River is the largest tributary of the Hrazdan River. However, it is heavily isolated from the main course of the river by the Aghbyurak dam. Considering low density of population and lack of pollution sources in the basin, the Marmarik River valley is a well-known biodiversity area within Armenia. As in many small tributaries, there is a limited knowledge about the ichthyofauna and its spatial distribution in the drainage basin. Thus, the aim of the study was to reveal the species structure and spatial distribution of fish in the Marmarik River. The results show five species of fish permanently dwelling the river where the most abundant one is the Kura chub and the rarest species is Khramicarp. Limited distribution was revealed also for Brown trout and Berg loach. [ABSTRACT FROM AUTHOR]

In this paper, we compile estimates of cod size distributions based on zooarchaeological data and contemporary lengthfrequency data to look at variability in size composition through time across the North Pacific, from the northern Kuril Islands through the Aleutian Islands to southeast Alaska. The results suggest that a strong longitudinal trend in cod size has remained consistent over time, with the largest cod found to the west. We find that five of nine sites show that overall cod length and distribution of the largest fish remain relatively unchanged. Two sites wherewe find truncation of the length distributions-or loss of the largest fish-are places where the modern fisheries have the longest history and have been most intense, suggesting a potential for anthropogenic impacts on these local populations. We acknowledge two limitations in these data: (1) there are differences in selectivity between the ancient and modern fisheries; and (2) seasonal variability in fish availability was observed to be an important explanatory variable in the modern data set, but the season of harvest is poorly understood for the ancient collections. Therefore, while differences observed between the two data sets suggest possible anthropogenic influence on the size structure of Pacific cod, they are not conclusive. [ABSTRACT FROM AUTHOR]

Pakistan managed extensive canal irrigation systems and has 19 Ramsar sites. Almost 27,977 fish species are present globally; there are 786 marine and 171 freshwater fishes in Pakistan. Fish diversity and distribution are closely related to various factors i.e. depth of water, availability of food, topography, breeding sites, and physicochemical features. Therefore, it is necessary to study the diversity of ichthyofauna in various regions and elevations. So, this study was planned to examine the fish diversity of Chashma Barrage to include more data related to fish diversity and distribution. Data were collected both by direct (physical count) and indirect methods (meeting with local people of Chashma Barrage) to find out fish diversity of Chashma Reservoir, Mianwali, from April 2016 to March 2017. In the current study, 1089 fish specimens of 21 species were documented from Chashma Barrage monthly. The Shannon-wiener Index (H') was recorded as 2.17, Simpson Index (S) was 0.16, Richness (R) was 20.67 and Evenness (E) was 0.712. It is concluded that study area has high diversity of fishes. Chashma Barrage is an important wetland for fishes, it should be declared as Ramsar site. [ABSTRACT FROM AUTHOR]

Fisheries and aquaculture are facing many challenges worldwide, especially adaptation to climate change. Investigating future distributional changes of largely harvested species has become an extensive research topic, aiming at providing realistic ecological scenarios on which to build management measures, to help fisheries and aquaculture adapt to future climate-driven changes. Here, we use an ensemble modelling approach to estimate the contemporary and future distributional range of eight demersal fish species of high economic value in the Mediterranean Sea. We identify a cardinal influence of (i) temperature on fish species distributions, all being shaped by yearly mean and seasonality in sea bottom temperature, and (ii) the primary production. By assessing the effects of changes in future climate conditions under three Representative Concentration Pathway (RCP2.6, RCP4.5 and RCP8.5) scenarios over three periods of the twenty-first century, we project a contraction of the distributional range of the eight species in the Mediterranean Sea, with a general biogeographical displacement towards the North European coasts. This will help anticipating changes in future catch potential in a warmer world, which is expected to have substantial economic consequences for Mediterranean fisheries. [ABSTRACT FROM AUTHOR]

Despite the large number of dams in most important rivers of Brazil, little is known about fish vertical distribution in neotropical reservoirs, especially deep ones. This study aims to understand how fish were vertically distributed in the deepest reservoir in Brazil, located in the Jequitinhonha River. Three areas of the reservoir were sampled quarterly using an echosounder. The deepest fish detected was at 115 m, but most were shallower than 25 m. Diel vertical migration of fish was detected, but not in all the sampling areas and campaigns. Fish distribution was determined by several limnological factors of the reservoir, but mainly by thermal variation in water column. These results can provide guidance for environmental and fisheries managers and ecologists to improve sampling techniques in deep reservoirs since vertical distribution and its relation with habitat use are determinant to propose management measures in similar ecosystems. [ABSTRACT FROM AUTHOR]

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Ciguatoxins (CTXs) are naturally occurring neurotoxins that can accumulate in fish and cause Ciguatera Poisoning (CP) in seafood consumers. Ciguatoxic fish have been detected in tropical and subtropical regions of the world including the Pacific and Indian Oceans, the Caribbean Sea, and more recently in the northeast Atlantic Ocean. The biogeographic distribution of ciguatoxic fish appears to be expanding; however, the paucity of CTX standards and reference materials limits the ability of public health authorities to monitor for these toxins in seafood supply chains. Recent reports establish that Caribbean Ciguatoxin-1 (C-CTX1) is the principal toxin responsible for CP cases and outbreaks in the northeast Atlantic Ocean and that C-CTX congener profiles in contaminated fish samples match those from the Caribbean Sea. Therefore, in this work, C-CTX reference materials were prepared from fish obtained from the northeast Atlantic Ocean. The collection of fish specimens (e.g., amberjack, grouper, or snapper) was screened for CTX-like toxicity using the in vitro sodium channel mouse neuroblastoma cytotoxicity assay (N2a cell assay). Muscle and liver tissues from toxic specimens were pooled for extraction and purified products were ultimately profiled and quantified by comparison with authentic C-CTX1 using LC-MS/MS. This work presents a detailed protocol for the preparation of purified C-CTX reference materials to enable continued research and monitoring of the ciguatera public health hazard. To carry out this work, C-CTX1 was isolated and purified from fish muscle and liver tissues obtained from the Canary Islands (Spain) and Madeira archipelago (Portugal). [ABSTRACT FROM AUTHOR]

Rivulidae represents one of the most endangered taxa in Brazil. This family encompasses species known as annual or seasonal fish because they possess unique adaptations that enable their survival in seasonal ponds. Several Brazilian species of annual fish inhabit the Patos-Mirim Lagoon System (PMLS), which is considered a hotspot of these species. However, within this area, no strategic regions have yet been defined for in situ conservation of annual fish. Therefore, the aim of this study is to assist in the delimitation of micro-hotspots of endemism, sympatry and richness of annual fish along the PMLS, while assessing conservation priorities of evolutionary lineages and areas. For this purpose, distribution data were compiled for 42 species or evolutionary lineages that occur along 144 ponds located at the PMLS, which enabled to evaluate patterns of distribution of endemism, sympatry and richness. Moreover, measures of genetic diversity were obtained using sequences from one mitochondrial gene, and phylogenetic positioning was assessed using one mitochondrial and one nuclear marker. These values were considered in the context of the number of populations within and outside conservation units to evaluate conservation priority for 29 of these lineages (Wlineage) and 112 of these ponds (Wpond). Among the evaluated species and lineages, eight were detected as strictly endemic, and 55 of the evaluated ponds showed records of sympatry. The patterns of lineage richness showed a heterogeneous distribution of annual fish along the sampling area, with seven grids presenting records for four or more lineages. Interestingly, these are concentrated in four larger areas, located on the Southeast and on the Southwest margins of the Patos Lagoon and on the Southeast and Center-West Margins of the Mirim Lagoon, which present several ponds whose conservation is urging. [ABSTRACT FROM AUTHOR]

This study argued for the first time that 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) and perfluorooctanesulfonic acid (PFOS) might have different tissue distribution mechanisms in wild fish species. Nine emerging and legacy per- and polyfluoroalkyl substances (PFASs) were detected in the water and wild fish tissues samples collected from the Qiantang River. Perfluorooctanoic acid (213 ng/L) was the predominant PFAS contaminant, and the other contaminants included perfluorohexanoate (19 ng/L), perfluorobutanoate (199 ng/L) and hexafuoropropylene oxide dimer acid (55 ng/L), which are the main fluorinated alternatives used in various industries located along the Qiantang River. Furthermore, PFOS (742 ng/g) and 6:2 Cl-PFESA (9.0 ng/g) were the predominant PFAS contaminants detected in the fish tissue samples. The differences in the potential molecular mechanism of the tissue distribution of PFOS and 6:2 Cl-PFESA in wild fish species are discussed. Additionally, we hypothesize that phospholipid partitioning is the primary mechanism underlying the tissue distribution of PFOS, and that a specific protein-binding mechanism is involved in the tissue distribution of 6:2 Cl-PFESA. [Display omitted] • HFPO-DA and 6:2 Cl-PFESA are perfluorinated alternatives of concern in water samples and fish tissue samples, respectively. • Tissue distribution of individual PFASs shows structure-related. • Molecular mechanisms underlying the tissue distribution of PFOS and 6:2 Cl-PFESA differ. • The bioaccumulation potential of 6:2 Cl-PFESA in the heart, spleen, and liver of fish is higher than that of PFOS. [ABSTRACT FROM AUTHOR]

Mapping fishing effort and fish abundance across management areas is required to adjust and enforce time–area management measures. Seasonal closures are imposed in Thai waters to mitigate the overexploitation of short mackerel (Rastrelliger brachysoma), one of Southeast Asia's most economically important pelagic species. This study applied machine learning to fishing vessel surveillance data to estimate spatiotemporal distributions of fishing effort and fish abundance in the Gulf of Thailand (GOT) and the Andaman Sea (ADS) to provide reliable and near real-time information to support seasonal closures. Data collected between 2018 and 2020 from Thai purse seiners targeting short mackerel included VMS data, fishing trip records, and landing information. Spatiotemporal patterns in fishing effort and catch per unit effort (CPUE) were then visualized in relation to the closures in different statistical management zones. The results show that fishing effort in the ADS increased in 2020 from 2018 and 2019, and peaked in 2019 in the GOT. No significant spatiotemporal trend in the distribution of CPUE was identified over the 3 years. Notably, the results reveal spatiotemporal adjustments to fishing effort and CPUE following the implementation of seasonal closures. This study is the first to present a practical approach to using vessel surveillance data to examine seasonal patterns in fishing effort and estimated fish distribution in Thai waters. The findings improve our understanding of fishing effort in response to area closures. The information generated here supports the time–area management of an intensively exploited migratory fish species, given timely and accurate information. • Timely and accurate information is required to manage heavily exploited migratory fish species. • VMS and landing data can provide reliable information on fishing effort and fish abundance. • Spatiotemporal adjustments in fishing effort for short mackerel followed closures. • So-called derby fishing and 'fishing in line' by vessels were observed during seasonal closures. • Fishery closures should be revised in response to fish population fluctuations. [ABSTRACT FROM AUTHOR]

Pelagic fishes are a key trophic component of the Southern Ocean ecosystem. However, understanding the spatial and temporal changes in geographic distribution patterns of pelagic fishes in the context of climate change remains limited. This research applied the MaxEnt model to project the distributions of current and future (2100s) suitable habitats for ten major pelagic fish species in the Southern Ocean (two scenarios: RCP4.5 and RCP8.5). Results suggested that the current spatial distribution of pelagic fishes is significantly correlated with their realized niche and that global warming will lead to significant changes in the spatial distribution of pelagic fishes in the Southern Ocean. Model predictions showed that eight out of ten pelagic fish species are likely to face a significant reduction in their ranges of suitable habitats under the RCP8.5 scenario by the 2100s. Except for the Bathylagus antarcticus , all of the other nine species were predicted to migrate toward South Pole by the 2100s. In addition, the community composition of pelagic fishes also may change significantly, mostly because of species loss. The results of this study clarify the impact of climate change on pelagic fishes in the Southern Ocean, and provide theoretical support for sustainable management and conservation efforts of these pelagic fishes. • The study predicts current and future distribution of ten major pelagic fish species in the Southern Ocean. • The spatial distribution of pelagic fishes is significantly correlated with their realized niche. • Suitable habitats of eight pelagic fishes are at serious risk from climate change. • Species loss is a major factor causing future shifts in the community composition of pelagic fishes. [ABSTRACT FROM AUTHOR]

The fish biodiversity of the Beagle Channel is insufficiently assessed, poorly managed, and threatened by exotic species. Novel, rapid, and cost-effective DNA-based approaches are valuable for understanding fish communities and biomonitoring in remote areas. Here, we evaluate the potential of environmental DNA (eDNA) metabarcoding for assessing fish species composition by analyzing water samples from three sites along the Beagle Channel in the extreme south of Argentina. Fish biodiversity was estimated using high-throughput sequencing of 12S rRNA amplicons. First, a local reference database was generated, including 12S sequences of 48 spp. In total, 31 environmental sequences were recovered, belonging to 11 families, 15 genera, and 22 species. Six eDNA sequences did not match any species in our database. Multivariate analyses indicated that the relative species composition differed significantly among the sampled sites. However, the most abundant species detected were consistent with historical data on fish species recorded in the sites sampled. In conclusion, eDNA metabarcoding is sensitive, reliable, and suitable for studies on the presence and distribution of fish species in the area. We further strengthen the potential of eDNA metabarcoding as a biomonitoring tool. • EDNA metabarcoding method detects abundant and rare species of the Beagle Channel. • The list of species reported for the Beagle Channel has been updated. • Information for the 12S rRNA gene was enriched with Southern-Hemisphere fish species. [ABSTRACT FROM AUTHOR]

The environment in large aquaculture sea cages is never uniform. Abiotic factors such as oxygen level, water temperature, and ambient light, as well as farm operations such as feed distribution variate within a cage. Fish in cages look for the optimal conditions they can find, which results in higher stocking densities at specific areas. Understanding their spatial distribution patterns may help farmers to improve fish welfare, because unnormal distribution may imply sub-optimal living conditions, and the farmers can act for improvement. Good knowledge of fish distribution patterns in cages may also enable more efficient farm operations such as behaviour-based feeding. In the salmon farming sector, there has been a tremendous effort to understand fish behaviour by using diverse approaches. Much of the work was conducted in experimental cages which were smaller than the industrial scale sea cages commonly used nowadays, by using underwater cameras or single-beam echosounders. Every approach has its own pros and cons. Valuable knowledge about fish behaviour was brought by previous studies, but they had a disadvantage of seeing only a small proportion of fish in the entire cage. Consequently, their findings might be inapplicable to the industrial scale farming. Thus, there is a need for more representative information of fish behaviour in large cages, but we lack monitoring methods which can provide such information. The presented study aimed at filling this gap. The multi-beam sonar Wide Angle Sonar Seafloor Profiler , henceforth WASSP was used for the first time to understand fish distribution patterns in industrial aquaculture cages. The sonar had a 120° fan-shaped coverage, and it was rotated by the side wall of the cage to scan about 80% of the cage volume. The sonar data collected under three different farming conditions were used for 2D and 3D data visualization to test whether WASSP was able to capture changes in fish distribution patterns. The 3D distribution patterns captured by the sonar was validated by the optical data obtained by underwater cameras, which highlighted the suitability of the multi-beam sonar to monitor fish distribution patterns over the entire cage. Although the tested method exhibited some challenges such as noisy data near the water surface, it expanded our "vision" for the fish distribution in aquaculture cages. This innovative pilot study opened the possibility for continuous monitoring of 3D fish distribution in commercial scale cages, which will be focused in our future studies. • We visualized the 3D fish distribution in sea cages using a multi-beam sonar. • We can see the 3D fish distribution in good resolution. • The presented method can assist behaviour-based fish welfare assessment. [ABSTRACT FROM AUTHOR]

Seafood is an essential protein source for coastal communities. However, they can accumulate heavy metals from human activities which could pose a potential health risk to consumers. In this study, we investigated the distribution, bioaccumulation, trophic transfer and potential human health risk of heavy metals in sediments, shell and fin fish collected from the Escravos Estuary in southern Nigeria. Heavy metals (Ni, Cd, V, Pb and Cu) in sediments, periwinkles and tongue soles from the two study sites were lower than the permissible limits for fishery products. The metal distribution in fish tissues was in the decreasing order of liver > gills > muscles > gonads > rest of the fish. Moderate to high BSAF (>1) was reported for Cd, Pb and Cu. All the studied metals, except Pb, showed evidence of biomagnification from periwinkle to tongue sole. The estimated daily intake (EDI) and hazard ratio (HR) for metals in periwinkles from both study sites were lower or within the USEPA reference doses (RfD) for the respective daily intake and HR value < 1, except for Cd, V and Pb for children. In contrast, EDI values in the muscle of tongue soles were higher than the RfD values for heavy metals except for Ni and Pb, whereas HR values > 1 except for Ni, Cd and V. In the whole fish, EDI and HR values were disproportionately high in both study sites with higher values reported for children. This study provides the first insights on the trophic transfer and risk assessment of heavy metals from petroleum and gas operations impacting the Escravos Estuary and the implications to public health. [Display omitted] • Heavy metals in periwinkles and tongue sole were lower than the permissible limits. • Metal in fish decrease from liver > gills > muscles > gonads > rest of the fish. • Moderate to high BSAFs (>1) was reported for Cd, Pb and Cu. • EDI and HR were disproportionately high in muscle and whole fish. • Higher values were reported for children compared to adults. [ABSTRACT FROM AUTHOR]

Syngnathus lowiskmae (Chain Pipefish) is a species of fish belonging to the Syngnathidae family. Syngnathus louisianae can be observed throughout the lagoon, but there is little research that addresses the densities of these fish's distribution in the estuary, and their habitat associations. This study aims to identify the population density of these fish throughout the Indian River Lagoon, and the habitats they associate themselves with. The Florida Fish and Wildlife Commission (FWC), Fisheries Independent Monitoring (FIM) data was used to analyze the presence of Syngnathus louisianae in ArcGIS Pro through point density and pair-wise buffer analyses. [ABSTRACT FROM AUTHOR]

Fluctuations in reef fish settlement and recruitment significantly impact local population dynamics and adult population size. We use light traps to evaluate reef fish settlement in inshore and offshore reefs in the Abrolhos Bank, in addition to the spatio-temporal distribution patterns, and environmental variables' influence. Data were collected from inshore and offshore reefs, and statistical analyses, including GLMs, PERMANOVA and nMDS, aimed to understand spatial-temporal species distribution patterns and the relationship between environmental variables. Results indicate greater species abundance and diversity offshore, influenced by winds, tides, and distance from shore, explaining 50% of larval patterns and highlighting the importance of spatial-temporal variations in early-life reef fish assemblages. However, several factors, including habitat type, quality, complexity, seascape configuration, and MPA location, may influence these patterns. Additionally, we provide evidence that commercially important species like Lutjanids use Abrolhos reef areas as nursery grounds. • This is the first study on the postlarval reef fish assemblage in the Abrolhos Bank. • Spatial-temporal variations driven the early-life reef fish distribution patterns. • Winds, tides, and coastal distance explain 50% of postlarval distribution. • The importance of larval behavior in small-scale settlement variation. • Commercially important species use Abrolhos reef areas as nursery grounds. [ABSTRACT FROM AUTHOR]

A well-developed lateral line system enables fish to perceive their surroundings and make appropriate movements. Inspired by such a biological characteristic, an artificial lateral line system (ALLs) is proposed to differentiate the shape and dimensions of dynamic targets. A total of 25 distinct perception models approaching the carrier are studied to analyze the perceptual characteristics of the ALLs. The pressure distribution on the fish body surface is calculated and extracted using the computational fluid dynamics (CFD) method, and is verified by experimental tests. An artificial neural network (ANN) model is then constructed for building the relationship between the ALLs and the perceived target features. The implementation of a suitable network architecture results in the achievement of a more precise categorization outcome. The findings indicate that the artificial lateral line system, as described, demonstrates exceptional proficiency in perceiving underwater targets. • An artificial lateral-line system is built to collect real-time hydro-static pressure caused by moving objects approaching a carrier. • Simulations and experiments are carried out on 25 moving targets of various shapes and dimensions, and the change trend of both are consistent. • A neural network model is developed to effectively recognise the dimension and shape characteristics of a moving target object. [ABSTRACT FROM AUTHOR]

The quest to understand species' distribution patterns and delineate their limits has led to the establishment of the world's ecoregions, large units of land containing a distinct assemblage of species, both for terrestrial and marine ecosystems. However, freshwaters constitute their own special case within terrestrial ecosystems, and have only recently been divided into freshwater ecoregions, primarily based on watershed limits. Freshwater ecoregions used by the European Water Frame Directive (WFD), which guides freshwater management policies in the European Union, have been criticized for not adequately representing freshwater fish biogeography. This study compares the geographic agreement between WFD ecoregions and freshwater fish distribution at the European scale. Using IUCN Red List distribution maps, we determined the composition of freshwater fish communities in major European basins. Then, we calculated a similarity matrix in order to cluster freshwater basins with more related fish assemblages. We compare our findings with WFD ecoregions and global ecoregions from the Freshwater Ecoregions of the World (FEOW) database. Our results reveal that WFD ecoregions do not sufficiently capture freshwater fish assemblage differences across Europe. Mediterranean basins exhibit high freshwater fish endemism and greater species variation, whereas central European basins harbor more similar fauna. Overall, our results align more with those of FEOW. To enhance the relevance of freshwater ecoregions in Europe for management and conservation, we propose several measures to ensure a comprehensive study involving all stakeholders in the process of defining these ecoregions accurately. • European Water Frame Directive ecoregions have been previously questioned. • Freshwater fish biodiversity patterns in Europe do not agree with WFD ecoregions. • Endemic species shape the communities' delineation in Mediterranean basins. • Central European basins show higher clustering patterns than established in WFD. • There is a need for a better approach to delineate European freshwater biogeography. [ABSTRACT FROM AUTHOR]

Accurate assessment of high-density underwater fish resources is vital to the aquaculture industry. It is directly related to the formulation of fishery insurance strategies and the implementation of breeding plans. However, accurately counting fish in high-density environments becomes challenging due to the uneven distribution of fish density and individual fish's different sizes and postures. To break through this technical bottleneck, we developed an advanced adaptive density-guided high-density fish counting network. In detail, first of all, the network adopts a multi-layer feature fusion structure similar to UNet, which significantly enhances the matching between fish targets of different scales and feature pyramid levels, effectively alleviating the problems caused by scale changes and morphological deformations. Secondly, the network also introduces a density-guided adaptive selection module, which can intelligently judge the applicability of Convolutional Neural Network and Transformer blocks in different density areas, thereby achieving robust information transfer and interaction between blocks. Finally, to verify the effectiveness of this method, we also specially constructed two high-density data sets: a simulated high-density underwater fish image data set (SHUFD) and a real high-density underwater fish image data set (RHUFD). The proposed method has significant improvements over the state-of-the-art method (CUT) on SHUFD and RHUFD datasets, with the mean absolute error, mean square error, background region bias, foreground region bias and density map bias indicators improving by 3.44% and 6.47%, 11.43% and 4.41%, 23.91% and 29.48%, 4.43% and 10.33%, 8.3% and 13.14%, respectively. • Introduction of a UNet-like multi-level feature fusion structure for improved alignment of fish targets across different scales and feature pyramid levels, addressing scale and deformation challenges. • Implemented density-guided adaptive selection with CNN-Transformer hybrid for improved information exchange in varying fish densities, handling uneven distribution. • Created SHUFD and RHUFD datasets with 500 and 1750 images and point labels for validating high-density fish counting methods. • Our counting network achieves optimal performance with 9.1M parameters, 6x fewer than the previous CUT method. [ABSTRACT FROM AUTHOR]

Understanding biota distribution patterns is essential for ecosystem conservation and restoration. In addition to biogeography, the distribution patterns of aquatic organisms that inhabit rivers vary longitudinally along river networks. Although longitudinal changes in distribution patterns in aquatic organisms along river networks have been studied in single river basins, it is crucial to understand these patterns at a regional ecological scale for broad-scale ecosystem conservation. This study aimed to elucidate the longitudinal distribution patterns of fish fauna and their correlation with environmental factors in several watersheds within the East Setouchi Ecological Region, renowned for its rich freshwater fish diversity in the Japanese archipelago. Data were obtained for 118 species across 10 watersheds and 85 sites, and the surveyed sites were classified into four longitudinal groups based on the similarity of the fish fauna. The lowest group comprised river estuaries, abundant in brackish-water fish, comprising primarily Gobiidae species. In lower watershed areas with low agricultural land and forest cover but high urbanization, all fish species selected as indicators were non-native. Upstream areas with a high percentage of agricultural land featured a mix of native Cyprinidae and non-native species such as Micropterus salmoides and Rhodeus ocellatus ocellatus. The most upstream groups, marked by significantly greater elevations and bed slopes, exclusively comprised native species as indicator species. Analyzing the longitudinal distribution patterns of fish fauna at multiple sites within the same ecological region enabled us to choose endemic fish species as indicators and identify important species for conservation. Additionally, the selection of sites characterized by significant urbanization and strong anthropogenic influences, along with the selection of non-native species as indicators, underscores the urgency of conserving native organisms in these areas, calling for continuous monitoring. [ABSTRACT FROM AUTHOR]

• A high-resolution (1 km) model study of Red Snapper larvae dispersal. • Buoyancy and ontogenetic vertical migration are pivotal behaviors. • Ocean advection can shape larvae dispersal. • Limited connectivity between areas west and east of the Mississippi Delta. Advancements in computing power and improved biophysical dispersal models, have enhanced our ability to realistically simulate distributions and behaviors of fish larvae. In this study, a 1 km high-resolution ocean model capable of capturing the ocean's mesoscale and sub-mesoscale motions is integrated with a biophysical dispersal model that considers a range of larval behaviors. Together they are used to investigate the dispersal and connectivity of Red Snapper (Lutjanus campechanus) larvae, a key species for both commercial and recreational fisheries in the northern Gulf of Mexico (GOM). We quantify how various larval behaviors influence the spatiotemporal dispersal, connectivity and settling of Red Snapper larvae focusing on egg buoyancy, larvae swimming capability, and ontogenetic vertical migration. Alongside habitat preferences, the ocean advection of Red Snapper larvae is crucial in shaping their dispersal patterns. Moreover, our simulations suggest different settling and connectivity characteristics between the eastern and western GOM. These results, indicate the need to divide these regions into distinct entities for stock management, rather than treating them as a unified stock as conventionally done. [ABSTRACT FROM AUTHOR]

In the Southwest Atlantic, fisheries and in situ observations suggest that mesophotic reefs occur further south than has been reported in the literature, and a description of these subtropical regions is still lacking. We used Baited Remote Underwater stereo-Videos to explore unrevealed patterns in the vertical structure of fish assemblages on subtropical Atlantic reefs, contrasting shallow and mesophotic habitats. Our data on species turnover and light penetration reveal that in the subtropical Atlantic, the boundaries between shallow and mesophotic habitats occur at depths of 18 m, which is shallower than most previous studies have shown. Generalized additive mixed models identified different environmental and management factors as important predictor variables that explain distribution of fish assemblages' attributes. Besides adding new evidence about mesophotic limits, we described variations in the vertical structure of fish assemblages, providing important information for the description and conservation of mesophotic environments in subtropical regions. [Display omitted] • Light penetration and species turnover determine boundaries of mesophotic ecosystems. • Shallow and mesophotic zones shelter different species richness and abundance. • Subtropical mesophotic zones do not provide refuge for fishery target species. • Environmental and management factors act in synergy shaping fish assemblages. [ABSTRACT FROM AUTHOR]

Recovery of the river connectivity relies on the application of structural and non-structural solutions. Within the structural solutions, vertical slot fishways (VSF) are most popular, but achieving the desired efficiency remains a challenge. To this end, evaluation of both biological and hydraulic efficiency is imperative. A Eulerian Lagrangian Agent Based Model (ELAM) of fish upstream migration through VSFs is presented in this work that considers one passive and three active behaviors affecting fish swimming pathlines of bighead carps (Hypophthalmichthys nobilis) and silver carps (Hypophthalmichthys molitrix). The passive behavior consists in a 2-D random walk where no external stimuli are detected. The first active behavior represents fish attraction to a nearby flow region as a Gaussian distribution function of turbulent kinetic energy, velocity magnitude and velocity strain rate. The second active behavior represents wall collision avoidance, whereas the third considers the tendency of the fish to escape from high velocity zones. Stochasticity is considered in the model to represent the dispersion in the experimental pathlines. The ELAM is tested for two different VSF configurations and is found to well reproduce the experimental pathlines, particularly when the escaping response to high velocity zones is considered. Results show that the ELAM model can be used as an appropriate tool for modelers and designers to evaluate fish passage efficiency. • A model is presented for fish upstream migration in vertical slot fishways. • Eulearian flow simulations are used to drive an individual-based fish model. • The model considers the stochasticity of fish migration pathlines. • Good agreement is found between simulated fish pathlines and experimental data. • Results show a tendency of the fish to escape from high-velocity zones. [ABSTRACT FROM AUTHOR]

The intensification of aquaculture practices in the last decade can compromise the welfare of farmed fish. However, one strategy to be considered to improve the welfare of captive fish is the implementation of structural enrichment in the rearing environment. The behavioural and physiological effects of suspended ropes inside rearing tanks were experimentally assessed on gilthead seabream (Sparus aurata) breeders, evaluating the potential use of such structures in production units. Over the course of six months, 60 adult gilthead seabreams, were reared in cylindrical tanks with and without structural enrichment. Fish were video recorded regularly before, during and after feeding. Biometry and blood samples for biochemical analyses of plasma (cortisol, glucose and lactate) were taken throughout the experiment. Suspended ropes modified the horizontal distribution of fish after feeding, influencing the swimming activity and social interactions throughout the experimental period. In addition, structural enrichment promoted foraging and anticipatory behaviour of gilthead seabream. No effects of structural enrichment were detected on gilthead seabream condition or growth, although there was an apparent positive yet fading effect of enrichment on plasma cortisol and glucose. In general, structural enrichment had diverse positive effects on the behaviour diversity and natural repertoire of captive gilthead seabream, and therefore, on fish welfare. This type of structural environmental enrichment can be easily incorporated into land-based flow-through and recirculating aquaculture systems, both for experimentation and commercial purposes. • Behaviour of gilthead seabream broodstock under structural enrichment vs stand rearing environment was recorded for 6 months. • Enrichment evoked positive changes in spatial distribution, swimming activity, social interactions and feeding behaviour. • Fish broodstocks spend long lives in captivity and can greatly benefit from simple enrichment strategies. [ABSTRACT FROM AUTHOR]

Invertebrate drift is a key process in riverine ecosystems controlling aquatic invertebrate distribution and availability to fish as prey. However, accurately quantifying drifting invertebrates of all sizes is difficult because the fine-mesh nets required to capture the smallest specimens clog easily, which reduces filtration efficiency and measurement accuracy. To address this problem, we developed a gas-powered pump system that delivers 20 m3/hour of river water through nested 80- and 750-μm-mesh nets suspended in the air. We compared 17 pumped samples with those obtained by adjacent, conventional deployment of a 250-μm drift net in a clear-water Alaskan river during both low and high flows. Our drift pump system sampled a geometric mean drift concentration of 467 invertebrates m−3 (maximum 5637 m−3) – eleven times the mean concentration of 42 m−3 estimated using the drift net. Invertebrates ≤ 3 mm long, primarily chironomids, comprised the entire difference between methods. Investigators for whom the drift of 0.5–3 mm invertebrates might be relevant (e.g., those applying foraging models for juvenile drift-feeding fishes) should consider using a pump or similar aerial filtration method to quantify small invertebrate drift, lest they underestimate it by an order of magnitude. [ABSTRACT FROM AUTHOR]

The existing fish counting methods count the number of fish through target detection or regression, and these methods are difficult to process the image of fish with serious occlusion and small target. In response to this problem, using the idea of density regression, this paper proposes a fish counting method based on a multi-scale dense residual network, and designs a multi-scale attention mechanism to improve the network's ability to extract features of fish of different sizes. The weight is used to discriminate the size of the fish scale, which solves the problem of large changes in the fish scale. In order to generate a higher definition fish density map, a dense residual module is constructed to fuse the shallow and deep features of the image, which ensures that the density map generated by this method can truly reflect the distribution of fish. Experimental results show that the peak signal to noise ratio (PSNR) and structural similarity of the density map generated by the proposed method are within a reasonable range. Compared with the existing methods, our method improves the mean absolute error by 21.8% and the mean square error by 22.8% under high density, and our method also achieves good results in real scenes. [ABSTRACT FROM AUTHOR]

Many fish and marine organisms are responding to our planet's changing climate by shifting their distribution. Such shifts can drive international conflicts and are highly problematic for the communities and businesses that depend on these living marine resources. Advances in climate prediction mean that in some regions the drivers of these shifts can be forecast up to a decade ahead, although forecasts of distribution shifts on this critical time-scale, while highly sought after by stakeholders, have yet to materialise. Here, we demonstrate the application of decadal-scale climate predictions to the habitat and distribution of marine fish species. We show statistically significant forecast skill of individual years that outperform baseline forecasts 3–10 years ahead; forecasts of multi-year averages perform even better, yielding correlation coefficients in excess of 0.90 in some cases. We also demonstrate that the habitat shifts underlying conflicts over Atlantic mackerel fishing rights could have been foreseen. Our results show that climate predictions can provide information of direct relevance to stakeholders on the decadal-scale. This tool will be critical in foreseeing, adapting to and coping with the challenges of a changing future climate, particularly in the most ocean-dependent nations and communities. Advances in climate prediction mean that the state of the ocean and the drivers of shifts can be skilfully forecast up to a decade ahead. This study applies decadal-scale climate predictions to forecast shifts in the habitat and distribution of marine fish species, providing information relevant to stakeholders and a tool to foresee and adapt to the challenges of a changing climate. [ABSTRACT FROM AUTHOR]

Developing Species Distribution Models (SDM) for marine exploited species is a major challenge in fisheries ecology. Classical modelling approaches typically rely on fish research survey data. They benefit from a standardized sampling design and a controlled catchability, but they usually occur once or twice a year and they may sample a relatively small number of spatial locations. Spatial monitoring of commercial data (based on logbooks crossed with Vessel Monitoring Systems) can provide an additional extensive data source to inform fish spatial distribution. We propose a spatial hierarchical framework integrating both data sources while accounting for preferential sampling (PS) of commercial data. From simulations, we demonstrate that PS should be accounted for in estimation when PS is actually strong. When commercial data far exceed scientific data, the later bring little information to spatial predictions in the areas sampled by commercial data, but bring information in areas with low fishing intensity and provide a validation dataset to assess the integrated model consistency. We applied the framework to three demersal species (hake, sole, and squids) in the Bay of Biscay that emphasize contrasted PS intensity and we demonstrate that the framework can account for several fleets with varying catchabilities and PS behaviours. [ABSTRACT FROM AUTHOR]

Aim: The roles of physical barriers to dispersal and species' abilities to cross barriers have in shaping freshwater fish distributions has been little explored at the macroscale. This study investigates how topography and species migratory behaviours and salinity tolerances (vagility) affect catchment isolation, species richness, large‐scale distribution patterns and turnover across latitudes and coasts. Location: North (NAm), Middle (MAm) and South (SAm) America. Taxon: Fish. Methods: From a large, published, dataset Pacific and Atlantic coast catchments in NAm, MAm and SAm were allocated to six georegions and species richness and composition correlated with information on catchment size, channel gradient and discharge. Catchment species richnesses, species–area relations (SAR), endemicity and turnover relationships were examined across coasts and latitude for species with different migratory behaviours and salinity tolerances. Results: Pacific coast rivers are smaller, steeper, hydrologically more variable and have narrower marine shelves than Atlantic ones, except in MAm. Catchment isolation is greater in Pacific drainages but the barriers to species exchange differ across georegions. Species richnesses are greater in Atlantic drainages but the proportion of vagile species is smaller. SAR slopes are flatter in vagile species and endemicity less. Turnover varies with catchment topography, the relative contribution of vagile species and, in MAm, on evolutionary history. Main conclusions: Tectonic and geomorphic processes influence catchment size and topography, and along with species differences in dispersal potential, affect how isolated catchments are, with consequences for species richness and composition. [ABSTRACT FROM AUTHOR]

The fishing grounds of the Pacific saury began shifting eastward after 2013 and deviated further east in 2019 and 2020. Consequently, the migration pattern from the pre‐fishing distribution to fishing grounds may be changing. This study investigated inter‐annual variations in westward spawning migration parameters using a migration model. Case studies were conducted to estimate optimal values for the initiation date of spawning migration and migration speed during spawning migration. The estimated optimal initiation date of spawning migration from 2003 to 2018 was July 13 to August 8, with an average of July 31. However, in 2019 and 2020, the initiation date of spawning migration was August 22 and September 5, respectively, significantly later than that in 2003–2018 (p <.01). The estimated optimal swimming speed during spawning migration in 2019 and 2020 was not significantly different from that in 2003–2018 (p >.7). These results indicate that delays in the initiation of spawning migration occurred in 2019 and 2020, leading to an eastward shift of fishing grounds. The mean body weight of the age‐1 Pacific saury in the pre‐fishing season had a significant negative correlation (p <.01) with the initiation date of spawning migration. This result suggests that Pacific saury with low body weight continues to feed for growth instead of initiating spawning migration. However, body weight at initiation of spawning migration had a significant decreasing trend (p <.01), indicating that the Pacific saury had to start spawning migration despite low body weight in recent years. [ABSTRACT FROM AUTHOR]

Spatial patterns in fish distribution determine most fishing opportunities and tactics learned by fishers. To determine fishing opportunities and recurrent fishing grounds of deepwater fish such as the cardinalfish (Epigonus crassicaudus) in the south‐central zone of Chile, we analyzed records of fishing logs covering the period 1999–2007. Fishing trawls covered from Topocalma (34º06'S) to northwest Corral (39º52'S), and we compared the position of individual fishing hauls (Euclidean distance) applying a hierarchical agglomerative clustering technique. The clusters obtained represented spatially distributed fishing opportunities (n = 28), which were visited occasionally (<10 fishing hauls) or regularly (>50 fishing hauls) to fishing for cardinalfish. The recurrent fishing opportunities (n = 7) were distributed discretely, from Constitución (35°19'S) to northwest Mocha Island (38°23'S) along the continental shelf slope and between 313 and 333 m depth. The species composition in the bycatch and the catch per unit effort trends allow us to identify secondary species and locally depleted fishing opportunities, the last occurring close to main fishing ports. [ABSTRACT FROM AUTHOR]

The distribution of river fishes, including invasive species, is influenced by their abilities and tendencies to pass regulatory structures, which in the Upper Mississippi River (UMR) are locks and dams (LDs). However, how and why fish approach and then pass through individual LDs and their structural components is presently unknown. In this study, groups of 25 common carp, a well‐understood model species, were acoustically tagged, transplanted, and released every other week for two summers below a generic UMR LD which has both tainter and roller spillway gates as well as a lock. Common carp distribution, passage routes, and rates were then monitored and analyzed with respect to discharge and gate settings. Although nearly all carp were detected below this LD, weekly passage rates through its spillway gates were negligible until discharge exceeded 85,000 cfs when the gates were ~2/3 open and weekly passage rates increased to ~50% for its tainter gates and ~8% for its rollers. In contrast, carp passed through its lock at a relatively constant and modest rate (~6%), seemingly uninfluenced by discharge. This increase in spillway gate passage, which occurred at discharges shy of open‐river, was predicted by a fish passage model which estimated spillway passage using swimming performance and estimated water velocity (flow‐fields). When observed passage routes were incorporated into another discharge‐based fish passage model, it accurately predicted total seasonal passage. These models could be improved and applied to determine which fish species will pass particular LDs and guide efforts to increase or decrease these rates. [ABSTRACT FROM AUTHOR]

Studying the impact of bycatch on marine megafauna, including sea turtles, is challenging for a variety of technical and biological reasons. The Mediterranean Sea has among the highest levels of turtle bycatch globally, notably of the loggerhead sea turtle (Caretta caretta), and bottom trawling represents a particularly relevant threat.Bottom trawlers from a recently discovered neritic foraging area, the Gulf of Manfredonia, reported 1,152 loggerhead turtles incidentally caught in the period 2015–2020. Capture locations were available for 497 turtles. These data were complemented by the distribution of fishing effort obtained by the vessel monitoring system.High bycatch rates were observed, leading to more than an estimated 5,600 annual captures and to the death of a minimum of 560 large individuals with high reproductive value. These findings are extremely concerning for the affected population and require immediate action. A strong seasonality of turtle bycatch was observed, with most captures occurring in November–March when fishing effort occurs in shallow waters where turtles concentrate all year round.Therefore, a seasonal approach (e.g. adopting measures only in the high‐turtle bycatch season) can be pursued as long as the spatial distribution of fishing effort varies among seasons. However, such a spatio‐temporal pattern should be monitored; then, in the case of change, although more difficult to implement, an area‐based conservation approach should be pursued. Several recommendations are provided, including the urgent implementation of turtle excluder devices, at least on a seasonal basis.This case shows that identifying the best conservation approaches requires information on the actual spatio‐temporal pattern of turtle occurrence and bycatch. Such information can only be derived from spatial distribution of bycatch and fishing effort obtained through a voluntary collaboration of fishers. [ABSTRACT FROM AUTHOR]

The fishing cat Prionailurus viverrinus is a wetland specialist species endemic to South and Southeast Asia. Nepal represents the northern limit of its biogeographic range, but comprehensive information on fishing cat distribution in Nepal is lacking. To assess their distribution, we compiled fishing cat occurrence records (n = 154) from Nepal, available in published literature and unpublished data (2009–2020). Bioclimatic and environmental variables associated with their occurrence were used to predict the fishing cat habitat suitability using MaxEnt modeling. Fishing cat habitat suitability was associated with elevation (152–302 m), precipitation of the warmest quarter, i.e., April–June (668–1014 mm), precipitation of the driest month (4–7 mm), and land cover (forest/grassland and wetland). The model predicted an area of 4.4% (6679 km2) of Nepal as potential habitat for the fishing cat. About two‐thirds of the predicted potentially suitable habitat lies outside protected areas; however, a large part of the highly suitable habitat (67%) falls within protected areas. The predicted habitat suitability map serves as a reference for future investigation into fishing cat distribution as well as formulating and implementing effective conservation programs in Nepal. Fishing cat conservation initiatives should include habitats inside and outside the protected areas to ensure long‐term survival. We recommend conservation of wetland sites, surveys of fishing cats in the identified potential habitats, and studying their genetic connectivity and population status. [ABSTRACT FROM AUTHOR]

This study assessed the effects of tidal stages and habitat conditions on nekton assemblage and distribution in the Kakum River estuarine mangrove system in the Central Region of Ghana. Teleosts and crustaceans were sampled using pole seine and cast net from a tidal mangrove pond and a channel, and characterised using morphometry and ecological guilds concept. In total, 1 146 specimens were collected, with 35 species from 19 families represented. The most abundant species encountered were Liza spp. (Mugilidae; 36%), Sarotherodon melanotheron (Cichlidae; 16%), Elops lacerta (Elopidae; 6%) and Sardinella aurita (Clupeidae; 5%), which exhibited pronounced spatial distribution. Sarotherodon melanotheron showed preference for ponds with minimal water flow and depth, Sardinella aurita occurred only in deeper sections of the mangrove channel with significant flow velocity, and Elops lacerta in the pond and all channel stations. Mugilids were found exclusively in the channel, whereas Palaemonidae (Macrobrachium macrobrachion and M. vollenhoveni) occurred in specific locations in the channel, with species- specific preferences for tidal stages. Most species encountered were identified to be predominantly marine migrants with bentophagous feeding habit. Site selection and tidal stages were found to affect the occurrence and distribution of fishes over a tidal cycle and interactively influence species diversity. [ABSTRACT FROM AUTHOR]

A myriad of factors affect stream fish assemblages, and most of them are intimately regulated by surrounding land uses. One of the most pernicious impacts on streams is the release of urban effluents. Accordingly, understanding the fish assemblage patterns as well as the environmental drivers that modulate them in the context of urban streams which also are exposed to other land uses is mandatory. We evaluated the longitudinal patterns of fish assemblages in an urbanised Neotropical prairie stream exposed to downstream patches of different surrounding land uses. Several variables of water quality, in‐stream habitat and riparian corridors were measured, and their relationships with fish metrics were explored. A fish metric selection protocol was implemented, and several multivariate analyses were used. Three main patterns of fish response were observed. Assemblage‐level attributes as diversity, richness, biomass, number of families and trophic guilds and proportion of Characiformes and intolerant species were responsive to the natural gradient in habitat (pools) and riparian (riparian width) conditions expected in non‐impacted lotic ecosystems. Conversely, a downstream continuum of recovery in water quality (dissolved oxygen, conductivity, NO3:NH4 and bacteriological loads) and habitat structure (sediment depth) would influence the distribution of fish species regarding their environmental tolerance and habitat preferences. Finally, local habitat aspects (nitrites, submerged macrophytes, bare soil cover and bank incisions by livestock) seemed relevant for the trophic structure (omnivorous species) of fish assemblages. A complex natural and anthropic longitudinal scenario together with local disruptions imposed by surrounding land uses were directive for fish. [ABSTRACT FROM AUTHOR]

Climate change is shifting the distribution of shared fish stocks between neighboring countries' Exclusive Economic Zones (EEZs) and the high seas. The timescale of these transboundary shifts determines how climate change will affect international fisheries governance. Here, we explore this timescale by coupling a large ensemble simulation of an Earth system model under a high emission climate change scenario to a dynamic population model. We show that by 2030, 23% of transboundary stocks will have shifted and 78% of the world's EEZs will have experienced at least one shifting stock. By the end of this century, projections show a total of 45% of stocks shifting globally and 81% of EEZs waters with at least one shifting stock. The magnitude of such shifts is reflected in changes in catch proportion between EEZs sharing a transboundary stock. By 2030, global EEZs are projected to experience an average change of 59% in catch proportion of transboundary stocks. Many countries that are highly dependent on fisheries for livelihood and food security emerge as hotspots for transboundary shifts. These hotspots are characterized by early shifts in the distribution of an important number of transboundary stocks. Existing international fisheries agreements need to be assessed for their capacity to address the social–ecological implications of climate‐change‐driven transboundary shifts. Some of these agreements will need to be adjusted to limit potential conflict between the parties of interest. Meanwhile, new agreements will need to be anticipatory and consider these concerns and their associated uncertainties to be resilient to global change. [ABSTRACT FROM AUTHOR]

Historical hydrological changes and the environmental characteristics of northern Middle America have promoted diversification and determined the distribution of fishes in the Grijalva and Usumacinta river basins of Mexico. In several taxa with wide distributions, cryptic diversity has been identified through molecular and morphological analyses. This study evaluated the intraspecific morphological variation of Dorosoma anale Meek, 1904 and Dorosoma petenense (Günther, 1867) along the Grijalva and Usumacinta river basins through geometric morphometric and linear biometric analyses. Little intraspecific differentiation was detected for either species. However, differences were identified between populations in the Grijalva basin and those from the upper Usumacinta River basins with respect to body height, head size, pelvic fin position, and anal fin size. The phenotypic expression of these attributes appears to be closely related to habitat type and geographic isolation. The morphological differences within D. petenense support the molecular hypothesis of two lineages existing in the Usumacinta River basin. [ABSTRACT FROM AUTHOR]

Swimming behavior of Chinook Salmon (Oncorhynchus tshawytscha) smolts affects transit time, route selection and survival in complex aquatic ecosystems. Behavior quantified at the river reach and junction scale is of particular importance for route selection and predator avoidance, though few studies have developed field-based approaches for quantifying swimming behavior of juvenile migratory fishes at this fine spatial scale. Two-dimensional acoustic fish telemetry at a river junction was combined with a three-dimensional hydrodynamic model to estimate in situ emigration swimming behavior of federally-threatened juvenile Chinook salmon smolts. Fish velocity over ground was estimated from telemetry, while the hydrodynamic model supplied simultaneous, colocated water velocities, with swimming velocity defined by the vector difference of the two velocities. Resulting swimming speeds were centered around 2 body lengths/second, and included distinct behaviors of positive rheotaxis, negative rheotaxis, lateral swimming, and passive transport. Lateral movement increased during the day, and positive rheotaxis increased in response to local hydrodynamic velocities. Swim velocity estimates were sensitive to the combination of vertical shear in water velocities and vertical distribution of fish. [ABSTRACT FROM AUTHOR]

Fish larvae supply in nearshore vegetated habitats, such as seagrass meadows and mangroves, contributes significantly to sustainable fish stocks. Yet, little information is available on distribution patterns of fish larvae in mangrove and seagrass habitats of the western Indian Ocean. The present study investigated the abundance, diversity and assemblage composition of fish larvae in mangrove creeks, inshore seagrass meadows (located adjacent to mangroves) and nearshore seagrass meadows (located in-between mangroves and coral reefs) in two coastal seascapes of Zanzibar (Tanzania) across seasons for 1 year. The highest mean abundances of fish larvae were recorded in mangrove creeks, while nearshore- and inshore seagrass meadows showed similar mean abundance levels. Generally, fish larvae representing 42 families were identified, with the fourteen most abundant families comprising 83% of all specimens. Fish larvae communities were dominated by specimens of the postflexion growth stage in all habitats, except in mangrove creeks in one of the two seascapes (i.e. Chwaka Bay) from April through June when abundances of the preflexion and very small-sized individuals were exceptionally high. Slightly higher fish larvae abundances were observed in mangroves during the southeast monsoon compared to the northeast monsoon, and there were also differences across months within monsoon periods for all three habitats studied. Assemblage composition of larvae did, however, not vary significantly in time or space. Our findings suggest that mangroves and seagrass meadows are highly linked shallow-water habitats with high retention of fish larvae contributing to similarity in assemblage compositions across shallow coastal seascapes. Conservation and management efforts should prioritize connected shallow-water seascapes for protection of fish larvae and to uphold sustainable coastal fisheries. [ABSTRACT FROM AUTHOR]

The shallow littoral zone is under a variety of environmental drivers and anthropogenic pressures. As these factors are highly dynamic, they may affect the distribution and behaviour of littoral fish. The present study investigates the effect of the time of day and the benthic habitat type on the shallow littoral fish community. Diel variations in total fish abundance, community composition, species abundance and behaviour were studied in two neighbouring stations in the Patraikos Gulf (Greece): one with cobble seabed cover and another with anthropogenic habitat structural modifications, like large artificial blocks, rocks and other objects. Visual census revealed that community composition differed depending on both the time of day and the habitat type. Total abundance was highest in the morning, whereas both diel abundance and habitat use were found to be taxon specific, with most species showing a preference for the artificial rocky habitat. Diel differences in species behavioural patterns were also observed, with a greater percentage of fish being active during the day (morning and noon) rather than in the afternoon. Although the fish community does not change entirely within a day or between adjacent locations, it is significantly variable in even small spatial and temporal scales. Consequently, there are implications for the design and implementation of sampling designs and monitoring plans that should be consistent in time of day throughout the sampling period and include locations structurally modified by humans. Furthermore, the management of the shallow littoral zone should consider the small‐scale variability and alternate anthropogenic habitat with natural unaltered patches. [ABSTRACT FROM AUTHOR]

A new approach for visual fish survey in reservoirs using underwater drones (remotely operated vehicle- ROV) is presented. The ROV was applied to identify abiotic gradients and to compare fish assemblages on the steep slopes in a tropical reservoir. The tested hypothesis is that fish are concentrated in the littoral zone due to the better physicochemical and habitat conditions, compared to deep and hypoxic layers. Twelve species were recorded (seven native, five exotic), with all species occurring in the littoral zone, seven species in the transition, and four in the profundal zone. A greater fish abundance and richness was found in the littoral zone corroborating the main hypothesis. The littoral zone was dominated by exotic cichlids (Cichla spp., Coptodon rendalli), while native catfish (Loricariichthys castaneus, Pimelodella lateristriga) occupied deeper areas. The fish distribution seems to be driven by local factors, such as oxygen availability and habitat structure. The preference for the littoral zone by alien cichlids may have led to the extirpation/decrease of native characids and induced catfishes to occupy deep habitats. Underwater drones can be a valuable tool for the simultaneous collection of abiotic/biotic data, especially in deep reservoirs with complex habitats, resulting in advances in the environmental monitoring. [ABSTRACT FROM AUTHOR]

Positive biotic interactions are recognized as important factors determining species distributions. Although effects of positive interactions have often been observed at local scales, much less is known about consequences at larger spatial scales. Here, we study nest associations of stream fishes – widespread reproductive facilitation between host (nest‐builder) and beneficiary (nest associate) species in North America – as a model system to examine the role of positive interactions in determining the metapopulation‐level relationship between host and beneficiary species. Using regional data of fish distribution in the Midwestern US, we found that watershed‐level occupancy of host species (i.e. metapopulation occupancy) remarkably increased that of nest associates. Our results illustrated that the effects of positive biotic interactions at the metapopulation level were comparable or even stronger than environmental drivers, i.e. factors that have been studied most extensively in metapopulation studies. Further, our model supported the hypothesis that the metapopulation‐level relationship between hosts and nest associates was mediated by a gradient of environmental conditions: strong associations occurred under stressful habitats. This study provides insightful evidence that positive biotic interactions have larger scale consequences for distributions of organisms than previously thought. Successful biodiversity conservation may need a broader framework that appreciates the role of positive biotic interactions at larger spatial scales. [ABSTRACT FROM AUTHOR]

Aim: Mesopelagic fishes have a near‐global distribution in the upper 1,000 m from tropical to sub‐Arctic oceans across temperature regimes. Yet, their abundance decreases poleward and viable populations seem excluded from high latitudes. Why? Location: North Atlantic between 50–85°N, with implications for high‐latitude oceans globally. Time period: Present‐day. Major taxa studied: Diel vertically migrating (DVM) mesopelagic fishes. Methods: We use a mechanistic, state‐dependent life‐history model to characterize DVM mesopelagic fishes. This model links light‐dependent encounters and temperature‐dependent physiology, allowing optimal DVM strategies to emerge. We run the model along a latitudinal gradient with increasing seasonality in light and track individual fitness‐related measures, that is, survival and surplus energy, through the annual cycle to make predictions about population consequences. Results: Mesopelagic fishes thrive in the oceans' twilight zone, and many are dependent on periods of darkness for safe foraging near the surface, before migrating back to depth during daytime. When daylight lasts for 24 hr during the Arctic summer, these fish are trapped in deep waters void of prey because it is never safe to forage in the shallow waters where zooplankton prey are found. Hence, they are left with two poor options, starvation at depth or depredation while foraging. Our model predicts surplus energy, vital for reproduction and growth, to halve from 50–85°N and annual survival to drop by two‐thirds over a narrow range of 10° of latitude around the Arctic Circle. Thus, low recruitment and high predation mortality during summer make polar waters population sinks for mesopelagic fishes because of the extreme seasonality in light. Main conclusions: At high latitudes, foraging mesopelagic fishes are exposed to sunlight in upper waters also at night. This makes them easy prey for visual predators, which limits their poleward distribution. Our findings highlight the importance to think beyond temperature to explain high‐latitude range limits. [ABSTRACT FROM AUTHOR]

Summary: Lake Balkhash is one of the largest lakes of Asia and belongs to the Republic of Kazakhstan. The lake has suffered from alien fish introduction, water pollution and overfishing during last decades. The goal of this study was to investigate contemporary fish diversity in shallow waters in western part of the Lake Balkhash. Fish samples were collected there 2018 and 2019. The data obtained showed changes in fish species diversity and significant decrease in the proportion of juvenile commercial fish in shallow sites of western part of the lake. The distribution of species seems random and needs further study to elucidate key factors. Thus, our data indicated deterioration of shallow waters in the western Balkhash as "nursery" for commercial fish species. [ABSTRACT FROM AUTHOR]

Flow structures at a river diversion juncture are complex and have been studied extensively. Their impact on the juvenile salmon entrainment into the side channel, however, is less investigated, and based mostly on empiricism. In this study, a Eulerian fish tracking model is developed and used in conjunction with a 3D flow solver to quantitatively evaluate the implications of complex flow characteristics at typical junctures on fish entrainment. First, the flow model is validated with the available experimental data, key flow structures are examined using the results, and their implications for fish entrainment are discussed. Next, the numerical fish tracking model is used to show that the cross-sectional fish distribution immediately upstream of a juncture is an important factor that controls fish entrainment efficiency. Fish entrainment efficiency curves are developed for different flow diversion ratios and fish distribution patterns and used to shed light on the reasons behind some field-observed fish entrainment patterns. Further, the model is used to show that the secondary flow in a river bend may have a significant impact on fish entrainment at flow junctures, in agreement with field observations. Finally, a submerged vane is demonstrated to be a potential management option to locally generate secondary flows upstream of a juncture to achieve the desired fish entrainment property. [ABSTRACT FROM AUTHOR]

Despite rapidly increasing demand for fishing, there is a lack of studies and information related to fishing, and there is a limit to obtaining the data on the global distribution of fish resources. Since the existing method of investigating fish resource distribution is designed to collect the fish resource information by visiting the investigation area using a throwing net, it is almost impossible to collect nation-wide data, such as streams, rivers, and seas. In addition, the existing method of measuring the length of fish used a tape measure, but in this study, a FishingTAG's smart measure was developed. When recording a picture using a FishingTAG's smart measure, the length of the fish and the environmental data when the fish was caught are automatically collected, and there is no need to carry a tape measure, so the user's convenience can be increased. With the development of a global fishing application using a FishingTAG’s smart measure, first, it is possible to collect fish resource samples in a wide area around the world continuously on a real time basis. Second, it is possible to reduce the enormous cost for collecting fish resource data and to monitor the distribution and expansion of the alien fish species disturbing the ecosystem. Third, by visualizing global fish resource information through the Google Maps, users can obtain the information on fish resources according to their location. Since it provides the fish resource data collected on a real time basis, it is expected to of great help to various studies and the establishment of policies. [ABSTRACT FROM AUTHOR]