Abundance Of Fish Species Research Articles

Relative Abundance and Size Composition of Tuna Caught by Major Fishing Gears Landed in the General Santos Fish Port Complex, Philippines

Tunas (family Scombridae) are the most abundant fish species caught by purse seine, ring net, and handline landed in the fish port markets of General Santos City. In this study, an assessment of tuna fisheries was conducted from January 2013 to December 2017. A total of six fish classifications, seven families, four genera, and seven species were observed from Market 1, Market 2, and Market 3 landing sites in the General Santos Fish Port Complex. On average, tuna catches contributed about 89% of the annual catch production and showed an increasing trend throughout the five years. The four genera of tunas were Katsuwonus (53.7%), Thunnus (25.9%), Auxis (8.4%), and Euthynnus (0.5%). The composition of tuna species comprised of oceanic tunas (Katsuwonus pelamis, Thunnus albacares, Thunnus obesus) and neritic tunas (Auxis rochei, Auxis thazard, Euthynnus affinis). Katsuwonus pelamis was the most dominant among the scombrid species with 53.66% relative abundance, followed by Thunnus albacares with 24.03%. Mainly, mature tuna sizes were observed using handline, which caught oceanic tunas ranging from 105 cm to 170 cm. Other gears, purse seine and ring net, caught immature sizes of most neritic tunas. Thus, tunas were caught throughout the year, and two peak seasons were observed from May to June and October to December during the five-year study period. The study's results on relative abundance, size composition, seasonality, and length-frequency distribution provide analysis and information that help implement fisheries management of tuna stocks in Region 12 and high seas pocket. Thus, this paper needs further investigations on catch per unit effort (CPUE), reproductive biology, and the value chain of the landed tuna catches to determine their significance to the economy of General Santos City.

Monitoring fish using imaging sonar: Capacity, challenges and future perspective

AbstractThe demand for fish products, which provide crucial protein for humans, is rising as the global population grows. In contrast, fish stock is declining due to human activity, environmental changes and overfishing. Fish monitoring provides valuable support data for effective fishery management and ecosystem conservation. The common monitoring methods are based on manual sampling, which is time‐consuming, laborious and intrusive. Imaging sonar is a hydroacoustic system that produces acoustic images similar to optical images by transmitting and receiving sound waves, allowing for in situ monitoring of fish non‐intrusively in the dark and turbid water environments where optical cameras are limited. In the last decade, imaging sonar, especially high frequency multibeam forward‐looking sonar and side‐scan sonar, has been widely used in fish monitoring. We reviewed the literature from the previous decade on the use of these two types of imaging sonar in fish species identification, abundance estimation, length measurement and behaviour analysis, as well as the sonar imagery processing concerning fish. The review results show that these imaging sonars are efficient and effective tools for fish monitoring in complex environments. The challenges include (1) the recognition of small fish forming dense aggregations; (2) species identification, which limits their use in species‐specific studies; (3) time‐consuming massive data processing. Therefore, advanced algorithms for sonar imagery processing and integrations with other sampling technologies are needed for future development.

Fish stock mass reduction is indicated in standard abundance and biomass estimates from gillnets and hydroacoustics

Gillnetting is a technique commonly used in relative abundance and biomass estimates of fish. However, due to its passive nature, the direct recalculation of the catch to reservoir volume or area is not trivial. This issue is often solved by using hydroacoustics, which provides information about fish density, though without the ability to distinguish species. However, the precision of such density estimates are also questionable. In this study, we estimated the abundance and biomass of dominant fish species before and after a biomanipulation program (fish removal) in 2020 using gillnetting and hydroacoustic surveys in a temperate reservoir. Between the two sampling periods, nearly 27,000 individuals (9000 kg) older than 0 + of bleak (Alburnus alburnus) and bream (Abramis brama) were removed during the biomanipulation program. Decreases in abundance and biomass estimates were expected for both techniques and both species. The gillnet decrease was 68% in CPUE (catch per unit of effort) and 48% in BPUE (biomass per unit of effort) for both species and all gillnets grouped together. Hydroacoustic observations showed a decrease of approximately 79% in abundance and 74% in biomass after fish reduction. Considering the numbers and biomass of fish removed, the absolute hydroacoustic estimates were underestimated for fish abundance but credibly estimated for biomass. The average weight of the fish taken was between the values of the fish caught with gillnets and the weights determined by hydroacoustics. In terms of results, both methods appear to be a suitable tool for estimating fish abundance and biomass in large inland waters, although the spatial and temporal distribution of fish of different sizes should be considered when using different sampling methods for fish monitoring.

Species composition and abundance of fishes in seagrass meadow ecosystem in tontayuo village and lamu village, batudaa pantai subdistrict, gorontalo regency, tomini bay area.

The objective of this research was to determine the species composition and abundance of fishes in the waters of Tontayuo Village and Lamu Village, Batudaa Pantai Subdistrict, Gorontalo Regency. This research was conducted from April to May 2022. The data collection of this research was carried out using a net with a length of 50 m, a widh of 2 m, and a mesh size of 1.5 cm drawn in the seagrass meadow, and it was replicated three times at each station, namely station I (Tontayuo Village) and station 2 (Lamu Village). The findings denoted that the highest species composition was found at station I with 34 species, while at station 2, there ware only 11 species. At the same time, the highest abundance value found at station 1 was Piotosus lineatus species, and the highest abudance at station II was Caranx melampyus species. Overall, the finding signified that the composition and abundance of fishes at station I and station II ware highly different due to the different water condition and fishing times.

Change in cephalopod species composition in the overexploited coastal China seas with a closer look on Haizhou Bay, Yellow Sea

Climate change and intensive fishing have affected not only population abundance, but also species composition. Cephalopods have been increasing in abundance in the world ocean under climate change due to their flexible life-history traits, including the over-exploited China Seas. Despite the increasing importance of coastal cephalopods in the China Seas, there have been no reports of changes in either species composition, nor the ecological roles of species with different life-history traits. Thus, this study first presents the changes in species composition of coastal cephalopods throughout the China Seas as summarized from fishery-independent survey reports over the last six decades. This is followed by an investigation of species composition of cephalopods in Haizhou Bay in the Yellow Sea. The ecological roles of two currently targeted cephalopods, Amphioctopus fangsiao and Loliolus spp. (Loliolus beka and Loliolus japonicus), are evaluated using an ecosystem model. The species composition of coastal cephalopods in the China Seas has changed since the 1960s, from species of large size and high value to small-size, low-value species. Cephalopod species composition in Haizhou Bay shows great seasonality, which is probably due largely to the characteristics of their life cycle. The population abundance of A. fangsiao and Loliolus spp. appear to be affected by ambient water temperature, and population distribution of Loliolus spp. seems to correlate with water depth. Occupying the highest trophic level in this ecosystem, A. fangsiao potentially displays strong top-down control over other organisms. Loliolus spp. are keystone species showing higher keystoneness in the autumn, owing to a low abundance of fish species which normally prey on them. The species-specific life-history traits and ecological roles of cephalopods are therefore important factors to consider in order to manage them effectively.

Multivariate analysis of abundance and distribution of fish species in coast of Ghana, West Africa

Marine fishes are currently experiencing population decline which has severe repercussions on food security, especially in fishing households. However, without assessing the distribution and abundance of these marine fishes, ensuring sustainable management will become impossible. Therefore, the study aimed at applying multivariate techniques to determine the biodiversity of fishes along the coast of Ahanta West, Ghana. Fish samples were collected daily through experimental fishing from November-December, 2011. Data obtained from the study were analyzed for ecological indices, species diversity, and community structure using PAST and PRIMER v6 software. From the results, Pteroscion peli (19.2%), Galeoides decadactylus (11.7%), and Brachydeuterus auritus (9.0%) were the dominant fishes. Multivariate analysis identified three main assemblages of fishes, at 18%. For the ecological indices, the species dominance index (SDI) ranged from 0.89 to 0.93, which indicated that the fish species were highly dominated by a few species. The Shannon Weiner index (SWI) and Species Richness index (SRI) spanned between 2.64 – 2.92 and 4.43 – 648 respectively, showing high diversity of fish species. It is concluded that the marine environment along the Ahanta West, Ghana is rich in fish species diversity, and hence, there is the need to regulate existing fishing operations for sustainable utilization and conservation of these commercially important fish species.
 Res. Agric., Livest. Fish.9(1): 57-59, April 2022

BAWAL FISH GROWTH PATTERN CAUGHT BY FISHERMEN IN TPI KUALA LANGSA LANGSA LANGSA CITY

The waters of the East Coast sea of Aceh have promising fishery potential with an abundance of fish species. a fish with a high selling value is the bawal fish species. Sea bawal fish in TPI Kuala Langsa is an important fishery commodity that has a high protein content and its marketing includes domestic and exports, especially in Asia, thus encouraging fishermen to make over fihing. The study was conducted from December to January 2022. The methods in this study are descriptive methods and observation techniques. The results showed that the bawal species caught by fishermen at TPI Kuala Langsa Kota langsa as many as 2 species, namely white bawal (Pampus argentus) and black bawal (Parastromateus niger). The long frequency distribution on white carries ranges from 156-307 mm class and black bawal in class 154-378 mm. The growth pattern of white bawal in December with a value of b is 1.143 while in January with a value of b is 1.4569 and black bawal in December with a value of b of 1.5484 while in January with a value of b of 1.8233.

Potential Efficiency of Earth Observation for Optimum Fishing Zone Detection of the Pelagic Sardinella aurita Species along the Mediterranean Coast of Egypt

This research utilizes the efficiency of remotely sensed data and advanced digital image processing techniques to assist in monitoring for the management of marine fisheries in Egypt (south Mediterranean Sea region). A newly developed model is applied to the Sardinella aurita fisheries to determine optimal fishing zones, and is then applied to monitor and detect the potentially optimal fishing zones for other locally important and economic fish species. This approach depends on chlorophyll-a (Chl-a) and sea-surface temperature (SST) characteristics that are that known to control this species communities. The ranges and distribution of SST and Chl-a were obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) aqua as well as Sentinel-3 satellites during the period from 2018 to 2020. The results revealed that there is a strong link between Sardinella abundance and both the SST and the Chl-a concentration. The suitable months for the abundance of this pelagic fish species were defined to be from May to November, producing 75% of the catch (nearly 42 K tons). Low abundances were recorded during the months from December to April, below the suitable harvest levels for this species. This research highlighted the importance of using satellite data as a tool to help scientists to develop appropriate management strategies for the sustainable management of fisheries resources worldwide.

Importance of pneumatophore fringe-mudflat continuum for an estuary-dependent fish species

ABSTRACT Shallow estuarine habitats are well recognized for providing a positive correlation to the abundance and diversity of juvenile fish species. This has been associated with the hypotheses of refuge from predators and the availability of food. Therefore, this study aimed to evaluate the importance of two adjacent habitats to mangrove fringes (area adjacent to pneumatophore zone and mudflat) as an ecological habitat for Diapterus auratus juveniles. Sampling was carried out in the rainy (January–July 2016) and dry (August–December 2016) periods. This study indicated that D. auratus juveniles did not show significant differences in abundance and biomass between adjacent habitats. However, univariate analyses found there was a significant increase in fish abundance in the dry season, due to influx of young-of-the-year. Further, the size-frequency of D. auratus showed a recruitment pattern recorded between August and January, suggesting a broad spawning period between the end of the rainy season and a recovery period between March and May. There were distinct changes in the diet between seasons for D. auratus, according to the dendrogram of the food eaten by the fish. The combined results from the distribution and feeding ecology suggest a connectivity among adjacent areas, and indicate that both habitats provide critical foraging and refuge habitat for D. auratus in this tropical estuary.

Greater resilience of reef fish assemblages in a no-take reserve compared to multi-use areas of the Gulf of California

Conservation strategies, such as the establishment of Marine Protected Areas (MPAs), aim to safeguard biodiversity and to promote resilience of ecosystems by increasing their capacity to maintain key functions and processes following disturbance. However, the extent to which ecosystems in MPAs exhibit resilience remains debated. To address this question, we evaluated changes in reef fish species and functional diversity over time in relation to environmental and anthropogenic disturbances at multiple locations in the Gulf of California, Mexico. From 2005 to 2017, we assessed reef fish species richness and abundance in three MPAs: one no-take marine reserve (Cabo Pulmo) and two multi-use marine protected areas (MUMPAs: Espíritu Santo and Loreto). To examine change in functional diversity and composition, we calculated three functional diversity indices – functional richness, functional dispersion and functional originality – using six biological traits (size, mobility, period of activity, gregariousness, water column position, and diet). Species richness, density and functional diversity were maintained over time (resilience) in the no-take marine reserve. In contrast, MUMPAs showed temporal decline in species richness, which translated into decreases in functional richness and increases in functional dispersion. These differences were also observed at the species level: in Cabo Pulmo, only two ‘loser’ species declined in density, while Espíritu Santo and Loreto showed declines of 12 and 17 species, respectively. The two MUMPAs also shared 9 of the total 22 ‘loser’ species, which are generally abundant and common in the Gulf of California. Density declines were attributed to the combined effect of environmental (sea surface temperature and Chlorophyll-a anomalies) and anthropogenic (fishing, tourism and coastal population density) disturbances. Given the regional decline and the ecological importance of dominant species, long-term decreases in their populations can profoundly modify processes and reef ecosystem services in this region. Thus, local management strategies should be implemented to try to reverse the observed recent decline in fish diversity in MUMPAs.

The functional ecology of mangrove fishes across the Isthmus of Panama

AbstractAimBiogeographic history and variation in modern environmental conditions can greatly influence local and regional community structure and, more generally, ecosystem functioning. This is clearly exemplified at the Isthmus of Panama where marine communities and environments from the Caribbean Sea and the Tropical Eastern Pacific Ocean differ despite ancient connections during the Miocene and Pleistocene. Here, we compare the functional (implied from traits) and isotopic structure of mangrove fish communities from those two biogeographic regions, which have been separated by the Isthmus of Panama for ~3 my.LocationCaribbean and Pacific coasts of Panama (Eastern Pacific and Caribbean Sea).MethodsWe gathered data on five functional traits (salinity preference, body mass, diet, position in the water column and lifespan) of mangrove fishes from the sampled regions. We also analysed δ13C and δ15C isotopic values and calculated functional isotopic metrics of the most abundant fish species inhabiting mangroves of these two regions.ResultsThe taxonomic composition and functional and trophic diversity differed between the mangrove fish communities of the Caribbean and the Eastern Pacific. Although the species richness of both assemblages was similar, there was very little taxonomic overlap between them: Snooks (Centropomidae) numerically dominated in the Eastern Pacific, whereas grunts (Haemulidae) and snappers (Lutjanidae) dominated in the Caribbean Sea. Functional divergence (FDiv) and isotopic richness (IRic) were higher in the Caribbean than in the Eastern Pacific, indicating differences in the way fishes use mangroves in these areas.Main conclusionsTaxonomic and functional characteristics of mangrove fish assemblages across biogeographic realms can be strongly influenced by local environmental factors (e.g. tidal regimes, the presence of adjacent coastal ecosystems and productivity), and these can override similarities that recent historical connections of faunas might be expected to produce. All such aspects need to be considered when seeking generalizations about ecosystem functioning.

Length weight relationships of fish species collected after impoundment of the Three Gorges Reservoir (TGR) in China; a study carried out in the upper Yangtze River

The Three Gorges Dam in the upper Yangtze River in China is the largest hydropower project in the world. Length- weight relationships (LWRs) are reported for fish species collected from three locations of the reservoir from November 2010 to October 2011. Fish were collected from the local fishing boats using 1.5 cm nylon mesh trap nets or 4, 5 and 6 cm nylon mesh gillnets (100- 120 m long × 1.4-1.5 m high). A total of 7,311 fish representing 49 species of 11 families were collected during the study period. There were 2,680 fish belonging to 32 species of 8 families sampled in Zigui (near the dam) reach, 2,845 fish representing 46 species of 8 families in Wanzhou (middle of the reservoir) reach and 1,786 fishes representing 38 species of 8 families in Fuling (upper reservoir) reach. The family with the highest number of species was Xenocyprididae. The intercept (a) and slope (b) of LWRs are useful in fisheries science in many ways. Therefore, the present study provides baseline data on LWRs of the economically valuable and most abundant fish species in the recently commissioned Three Gorges Reservoir.

Statistical methods for predicting the spatial abundance of reef fish species

Understanding the spatial distribution of organism abundance is fundamental to assessing and managing ecological populations. Marine species can be difficult and logistically challenging and expensive to observe. This often results in spatial data containing low detection rates when sampling underwater, biasing spatial predictions from many modeling approaches. We propose a multistage statistical workflow that can use zero inflated sampling data to develop non-linear predictive spatial distributions of reef fish abundance. The workflow includes: (1) an individual-based discrete event simulation which generates simulated survey data under different abundance settings; (2) empirical maximum likelihood analysis to establish the relationship between survey data and abundance from the simulation; (3) a two-step random smoothing method to estimate reliable block spatial abundance around each survey station; (4) an ensemble of different machine learning models which use the estimated abundance from step three as input to compute a stable non-linear prediction of abundance across the entire study area (Gulf of Mexico). Applying our workflow greatly improved the ability to forecast abundance at small spatial scales. The ability to forecast at fine spatial scales is critical when working with species that are patchily distributed. This workflow can apply to many ecological populations to develop abundance maps even if sample data is not well distributed across the study area or is zero inflated.

Temporal and spatial patterns in the shifting of otter diet to invasive prey after river damming

AbstractRiver damming promotes profound changes in aquatic biodiversity, including the facilitation of biological invasions, with subsequent impacts on native communities. The Eurasian otter (Lutra lutra) is a generalist aquatic predator that often incorporates new prey types when they become available. We studied the short‐ and long‐term effects of river damming on the trophic ecology of the otter across a riverine landscape gradient, from the flooded area to upstream tributaries, focusing on the largest artificial lake of Western Europe. Through the analysis of otter feces (spraints), we describe otter diet composition in 14 sites at different distances from the impounded area in three periods: (i) the pre‐filling phase (i.e., lotic conditions); (ii) the immediate filling phase; and (iii) 16 years after the dam closure. The diet of the otter drastically shifted in the short term, from being dominated by native cyprinids to being mainly composed of invasive species of fish and crayfish. In the long term, the number of invasive species consumed by the otter continued to increase while native fish completely disappeared as prey near the reservoir. Presumably, the construction of the dam generated clear spatial gradients of abundances of native and invasive fish species. These patterns arose in the short term but became accentuated in the long term and were mirrored in otter diet composition. Our results demonstrate the potential of otter diet analyses as a surrogate for the impacts of human alterations on aquatic ecosystems, including those of river damming and the associated facilitation of biological invasions.

Latitudinal variation in diversity and abundance of mesopelagic fishes associated with change in oceanographic variables along 110°E, south-east Indian Ocean

As part of the second International Indian Ocean Expedition, an oceanic transect from 39.5°S to 11.5°S along 110°E in the south-eastern Indian Ocean enabled concurrent oceanographic measurements and sampling of early stages of mesopelagic fishes within the upper 500 m of the water column. Notable oceanographic features along the generally oligotrophic transect included an increase in surface water temperature from 12 to 28 °C from south to north and low salinities at both ends of the transect. High salinity Subtropical Surface Water was evident over the central part of the transect and low dissolved oxygen occurred at depth at the northern end where tropical waters were influenced by the Indonesian Throughflow. Throughout the study region larval fish stages were generally concentrated in the epipelagic zone. Species richness, abundance and diversity of fishes (n = 166 species) increased towards the tropical waters. The families Myctophidae (lanternfishes; 60 species), Phosichthyidae (lightfishes; 2 species) and Gonostomatidae (bristlemouths; 5 species) were numerically dominant. Clustering of integrated abundance data (0–500 m depth) revealed four major fish assemblages along the transect. When linked to oceanographic variables, multivariate multiple regression indicated that surface temperature, surface salinity and dissolved oxygen at 400 m depth provided the best fitting model explaining fish distribution patterns. Where possible, comparisons have been made with early data collected along this 110° E line in the 1960s during the first International Indian Ocean Expedition.

Initial biological development of a newly established side channel at the Lower Rhine

AbstractWithin the EU LIFE‐Nature project ‘River and floodplain revitalisation Emmericher Ward’, three small temporary waters and a former gravel pit were connected by a side channel running parallel to the river Rhine through former groyne fields. The initial status of macrozoobenthos, fish, avifauna, flora, vegetation, and habitats before and their development after implementation of the project's measures were recorded and compared. The monitoring years 2018 and 2019 were exceptionally dry and accompanied by an extremely low runoff in the Rhine and the side channel. These conditions likely affected the development of habitats and species populations in the new side channel. The new side channel showed intensive morphodynamic development and differentiation of its structures. While the more complex vegetation and habitat types appeared as mostly species‐poor initial stages, short‐lived species‐rich pioneer habitats such as annual mud banks in the water exchange area were already established. Two years after the implementation, the benthic invertebrate fauna was still predominantly species‐poor and dominated by neozoans. Occasionally, representatives of the more sensitive EPT fauna (Ephemeroptera, Plecoptera, Trichoptera) were already detected but were, in general, strongly underrepresented in the main stream. Low colonisation potential, nonpermanent flow, and lack of river wood limit the development of the macrozoobenthos community. The relative abundance of rheophilic fish species increased in the project area and high juvenile fish densities proved the function as a nursery habitat. As pioneer species of riverine landscapes, sand martins and little ringed plovers colonised the new structures already in the first year. The initial state of the side channel represented a typical dynamic pioneer habitat pattern of a sandy lowland river, which was almost absent in the Lower Rhine area. The new habitats were quickly colonised by pioneer flora and fauna, but the potential for more demanding and complex communities was restricted by the poor structural and biological states of the Lower Rhine.

Recreational angling and spearfishing on social media: insights on harvesting patterns, social engagement and sentiments related to the distributional range shift of a marine invasive species

Fisheries are among the human activities that are most strongly affected by ongoing climate-related changes in the presence and abundance of fish species across the globe. The ecological and social repercussions of such changes for recreational fisheries are however still poorly understood. Here, we compare selected ecological and social dimensions of both recreational angling and spearfishing targeting the bluefish (Pomatomus saltatrix) in Italy. The bluefish has undergone a northward expansion in the region over the last 20–30 years, during which it reached new areas and increased in abundance. Using digital videos and their associated data published by both recreational anglers and spearfishers on YouTube we characterized ecological and social dimensions using a culturomics approach. Specifically, we focused on harvesting patterns, social engagement and sentiments related to the bluefish. Our study revealed four major results: (1) similar harvesting patterns (i.e., declared mass and seasonal upload patterns) related to videos by both recreational anglers and spearfishers; (2) higher social engagement (i.e., number of views and likes) for videos by recreational anglers than spearfishers; (3) differences in themes of discussion, with anglers being mainly interested in fishing strategy and gears and spearfishers being more interested in fishing actions shown on the videos; (4) positive and negative sentiments of both recreational anglers and spearfishers towards the invasiveness and aggressiveness of the species. The latter represents an interesting trade-off associated with recreational fishing of the bluefish: it is perceived as an invasive species, but it is also a valued target fish because its voracity contributes to the quality of the recreational fishing experience. Our study showcases the value of exploring social media and associated data to better understand the ecological and human dimensions of marine recreational fisheries in relation to distributional range shifts of species associated with climate change.

The impact of a Reno mattress installation on an adjacent seagrass meadow and its macrofauna in a South African estuary

Armouring of coastlines and the banks of estuaries to protect property against erosion can have a negative impact on natural habitats and their communities. Within estuaries, one of the most threatened habitats is seagrass meadows. The impact of newly installed Reno mattresses on an adjacent Zostera capensis meadow and associated fauna was investigated in the Keurbooms Estuary, South Africa. The impact on Z. capensis was studied by determining percentage cover and the length of blades before and after placement of Reno mattresses. At the impact site, percentage cover and blade length decreased during the installation phase, however, recovered shortly after installation was completed. At the control site no changes in eelgrass percentage cover were noted. Invertebrate and fish species richness, diversity and abundance were compared in the eelgrass meadows before and after the installation. Whilst invertebrate species richness increased significantly after the installation at the Impacted site, there was no significant difference at the Control site. There was also no significant difference in invertebrate diversity and fish species richness and diversity at the Control and Impacted sites before and after installation. This suggests that the installation had no net negative impact at the Impacted site. Within a month of installation, the Reno mattresses were colonised by two invertebrate species (Amphibalanus amphitrite and Littoraria sp.). Although the introduction of Reno mattresses at the study site created a hybrid habitat that continued to provide a habitat for fish and invertebrates, we suggest that the use of these artificial structures should be in combination with natural vegetation (e.g. as a hybrid habitat) and not one that replaces natural habitat. There is limited information regarding the ecological impacts of using Reno mattresses in estuaries and this study provides new information on their ecological efficacy thus providing valuable insights in future coastal erosion control practices.

Environmental DNA detection and abundance estimates comparable to conventional methods for three freshwater larval species at a power plant discharge

AbstractEarly life stage (ELS) fishes provide a valuable metric for species, population, and ecosystem monitoring. Industrial, manufacturing, and power generating facilities in the United States can be required to monitor ELS fishes to assess impacts of facility intake waters. Traditional methods for collecting, identifying, and enumerating ELS fishes include ichthyoplankton netting and pumping from intake and discharge waters. However, sampling at these sites can prove challenging from logistical and safety standpoints, with added challenges of identifying and post‐processing of ELS fishes to quantify facility impacts on waterbodies for regulatory purposes. Methods utilizing environmental DNA (eDNA) may offer improvements in these areas. This study assessed the utility of novel, species‐specific qPCR assays to detect eDNA from three differentially abundant fish species (alewife (Alosa pseudoharengus; Wilson, 1811), gizzard shad (Dorosoma cepedianum; Lesueur, 1818), and yellow perch (Perca flavescens; Mitchill, 1814)) at the outflow of an industrial site. eDNA concentrations were compared with abundance estimates derived from two conventional collection methods to explore the potential utility of eDNA‐based methods in future monitoring. The likelihood of detecting gizzard shad, yellow perch, and alewife in the discharge waters of the power generation station was not significantly different among eDNA, plankton netting, or pump sampling. Results suggest successful detections differ by species and time of year for each method. Gizzard shad eDNA relative abundance correlated strongly with total larval abundances captured by the pumping but not the netting methods, whereas yellow perch eDNA abundance was found to correlate with both conventional methods. Alewife was not detected by any method, consistent with documentation of the decline in this species within the lake. Overall, our study found a positive relationship between eDNA abundance and larval fish abundance in both daily and seasonal sampling, suggesting that fluctuations in eDNA concentration may be linked to larval abundance.

Fish distribution and behaviour with regard to the time of day and the anthropogenic structural modification of the shallow littoral.

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.