Search

The impoundment of Aoos springs was created in 1990 to facilitate hydroelectric production, and fish fauna has been enriched through the years due to deliberate or accidental fish stockings, with certain invasive alien fish species arising (i.e., Lepomis gibbosus, Carassius gibelio), some of which are ranked among the most dangerous species for global biodiversity. A three-year monitoring survey was conducting to map the nesting areas of Pumpkinseed, L. gibbosus, to assess the effectiveness of electrofishing as an active method to reduce the spread of the corresponding species and to identify the impact of the L. gibbosus on native species. The largest percentage of nests was found in areas with silty-sand bottoms (53.4%) and low vegetation. The potential nesting area was estimated at 1.97 km2 and the area of confirmed nesting was 0.33 km2. The species appeared to nest in a small area, compared to the potential nesting area. The results also indicate that a significant percentage of the target species (71.6% of the total number of species) was removed, with an average time per sampling of 1.2 ± 1 h, whereas the impact on the other native species was minimal. These results are important for designing and implementing programs for the eradication or reduction of L. gibbosus in the impoundment of Aoos springs.

Objective: In West Alabama, catfish Ictalurus spp. producers routinely face the challenge of fish that exceed market size (aka "Big Fish") in their commercial ponds. These fish are skilled at evading seine nets during harvest and can increase in size significantly before subsequent harvests occur. This is problematic for catfish producers because processing plants prefer catfish within the 0.45–1.81‐kg range and farmers are paid a premium price for catfish of this size. Due to their larger size and growth potential, hybrid catfish (female Channel Catfish Ictalurus punctatus × male Blue Catfish I. furcatus) can become a more significant issue than Channel Catfish if they evade harvest. The objective of this study was to describe and quantify the age structure and growth rate of hybrid catfish that evade capture and remain in commercial ponds following harvest and grow beyond acceptable market size as defined by catfish processing plants (i.e., Big Fish). Methods: Hybrid catfish were collected from 12 recently harvested commercial ponds in West Alabama from December 2021 to August 2022 using an electroshocking boat. Total length (mm), body weight (kg), and sex of collected fish were recorded, and lapilli otoliths were removed to estimate fish age and determine total length and total body weight at estimated ages. Result: In this study, 1005 hybrid catfish were collected with the successful age estimation for 1001 catfish, ranging from 1 to 11 years. Results of this study indicate that hybrid catfish exceeded the premium size threshold in 2.72 years ± 8 months. Additionally, from age 2 to age 3, the average hybrid catfish gained 2.90 kg, growing from 0.40 to 3.30 kg. Growth rate was significantly affected by sex; males overall were predicted to weigh more than females based on the weight‐at‐age model. Conclusion: Hybrid catfish should be completely harvested from commercial ponds following 1 year of harvest to receive the premium price per kilogram of live fish. If a complete harvest is unsuccessful, farmers can receive a discounted price per kilogram of leftover hybrid catfish based on current market trends. Impact StatementCollecting age and growth statistics on leftover hybrid catfish allowed researchers to estimate at what age these catfish should be harvested based on the premium size category set by catfish processing plants. Researchers were also able to estimate hybrid catfish growth and that the average hybrid catfish will exceed the premium size category by age 3 and grow into a "Big Fish" by age 4. [ABSTRACT FROM AUTHOR]

Following the introduction of the 'Boolarra' strain to Australia in the mid 1960's, Common carp (Cyprinus carpio) rapidly spread in waterways across the Murray–Darling Basin (MDB) in southern-eastern Australia. A previous study of the population expansion based upon data up to the early 2000s suggested the carp population may have reached, and was fluctuating around, the ecosystem carrying capacity. It has been widely stated in the scientific literature and media that carp comprise up to 90% of fish biomass in MDB rivers; however, this figure is largely based on sparse data collected in the 1990s and the accuracy of this estimate is uncertain. Here, we analyse three decades (1994–2023) of electrofishing data to estimate the median proportion of total fish biomass contributed by carp across > 1,400 sites in lowland rivers (< 700 m elevation) of the New South Wales (NSW) portion of the MDB. The proportion of sites with fish biomass dominated (> 90%) by carp has declined from ≈ 33% of sites in the mid-1990s to ≈ 20% of sites. The proportion of biomass comprised by carp varied depending on the scale of analysis. Across the NSW MDB, carp accounted for a median of 57% (95% CI: 42.5–70.4) of fish biomass at the site level. At the river catchment scale estimates ranged from ≈ 45–66%. In contrast, the median proportion of carp within key rivers ranged from ≈ 46–80%, suggesting that carp can dominate total fish biomass in some rivers for short time-periods. The proportion of biomass contributed by carp at the NSW MDB scale was remarkably stable across decades, suggesting that the carrying capacity of carp may have been reached. Our revised estimates of the contribution of carp to overall fish biomass can facilitate informed debate around the dominance of carp in MDB rivers and provide important information for carp management in the future. [ABSTRACT FROM AUTHOR]

The impoundment of Aoos springs was created in 1990 to facilitate hydroelectric production, and fish fauna has been enriched through the years due to deliberate or accidental fish stockings, with certain invasive alien fish species arising (i.e., Lepomis gibbosus, Carassius gibelio), some of which are ranked among the most dangerous species for global biodiversity. A three-year monitoring survey was conducting to map the nesting areas of Pumpkinseed, L. gibbosus, to assess the effectiveness of electrofishing as an active method to reduce the spread of the corresponding species and to identify the impact of the L. gibbosus on native species. The largest percentage of nests was found in areas with silty-sand bottoms (53.4%) and low vegetation. The potential nesting area was estimated at 1.97 km2 and the area of confirmed nesting was 0.33 km2. The species appeared to nest in a small area, compared to the potential nesting area. The results also indicate that a significant percentage of the target species (71.6% of the total number of species) was removed, with an average time per sampling of 1.2 ± 1 h, whereas the impact on the other native species was minimal. These results are important for designing and implementing programs for the eradication or reduction of L. gibbosus in the impoundment of Aoos springs. [ABSTRACT FROM AUTHOR]

To enhance management of aquatic systems, long‐term monitoring programs are crucial. However, managers often lack sufficient guidance in decision‐making. In this study, we analyzed nearshore electrofishing data from Lake Ontario spanning 18 years and over 100,000 caught fish to assess sampling designs for various coastal habitats. Using simulation, we evaluated precision of catch per unit effort (CPUE) for all species, piscivores, and specialist species, at different levels of electrofishing sampling effort. For overall CPUE in any habitat type, increased precision declined with additional electrofishing runs, particularly after reaching 30–40 runs. Adjustments in sampling effort, such as adding 10 runs per year for open‐coast sites, increased precision of overall CPUE by 10%. Adding 8 runs per year for wetlands increased precision of specialist‐species CPUE by 10%. However, additional runs in embayments did not increase precision for all species, piscivores, or specialist species. Our findings underscore the importance of considering community composition and abundance when evaluating CPUE precision and illustrates a flexible approach to optimize sampling effort in aquatic monitoring programs. [ABSTRACT FROM AUTHOR]

ABSTRACT Reunion Island is in the South‐West Indian Ocean (SWIO), where all freshwater fish species are diadromous. The ecological status assessments of freshwater in watersheds have revealed a continuing deterioration in these fish populations due to anthropic pressures. In this context, monitoring the fish's biological sustainability is crucial to ensure the health of these estuarine ecosystems. The aim of this study was to compare the efficacy of conventional electrofishing monitoring (EF) with the environmental DNA metabarcoding tool to evaluate fish biodiversity in the estuaries. We measured the diversity and structure of the fish community in three estuaries with various geographical, hydrological, and anthropogenic conditions over different seasons. To this end, fish were captured by EF, and we then isolated DNA from the water samples to perform bioinformatic analyses derived from eDNA, using the 12S marker. Statistical analyses were carried out to compare the results of these two methods. For all watersheds combined, a comparison of the results for measuring fish richness showed that eDNA performed significantly better than EF. Indeed, the eDNA detected 31 species, whereas the EF detected only 12 species. For both methods, we observed significant differences in community structure between watersheds, with a significant nestedness phenomenon where the fish assemblage obtained from EF captures is a sub‐assemblage of that obtained from eDNA. Moreover, compared to EF, eDNA enabled the detection of endemic to the Mascarene region species (e.g., Cotylopus acutipinnis), introduced exotic species (e.g., Oreochromis niloticus), and species difficult to capture and identify due to their juvenile life stage through EF (e.g., Anguilla sp.). Our data confirm the effectiveness of eDNA to detect fish species, both taxonomically and in terms of species richness and proves to be an effective tool for monitoring fish diversity of the islands of the SWIO.

This study compared electrofishing (ES) with conventional suffocation (AS) for harvesting fish, analyzing meat quality, biochemical, and microbiological indices. ES-caught fish show delayed rigor mortis, a milder pH decrease, and unaffected biochemical indicators. Although ES fish exhibited higher drip and cooking losses within the initial 24 hours, no significant differences emerged later. Free fatty acids and total volatile base nitrogen were higher in ES fish but remained within acceptable limits. Bacterial load was lower, indicating that electrofishing induces rapid unconsciousness with minimal impact on product quality. Further optimization of electrofishing devices is needed to address potential concerns like muscle bleeding. [ABSTRACT FROM AUTHOR]

Fish play an important role in river ecosystems, and the conservation of their diversity is a common goal worldwide. It is still unclear how fish monitoring programs should be developed in order to rationalize the monitoring of fish diversity in rivers. To help address this issue, we conducted a comparative study of fish species richness obtained through three site-interval monitoring programs (SS1: 3 km interval scheme; SS2: 6 km interval scheme; SS3: 9 km interval scheme) in wadeable rivers in northeastern China. Here, a total of 18 fish species and 4 rare species were collected from 3 rivers. The cumulative species-richness curves showed that SS1 had the highest species richness in a single river and in the whole region, and the species richness gradually decreased with increasing site intervals. The results of the cumulative percentage of species richness indicated that SS1 and SS2 could achieve a level of 80% of potential species richness, while only SS1 could achieve a level of 90% of potential species richness in the Lanhe River (where no rare species were present). However, the results of cumulative species richness per unit of effort indicated that SS2 and SS3 had higher input-output benefits. These results suggested that rare species were more susceptible to monitoring programs and that SS2 was more advantageous in terms of obtaining species richness and cost-effectiveness. This study provides a reliable reference for river fish-monitoring program development. [ABSTRACT FROM AUTHOR]

ABSTRACT There are numerous downsides and risks associated with electrofishing; hence, environmental DNA (eDNA) metabarcoding is becoming increasingly common in aquatic ecological studies. Generally, researchers agree that eDNA metabarcoding is more sensitive than electrofishing, and that eDNA metabarcoding is better at detecting rare species. As predatory species tend to be rarer than prey species, eDNA metabarcoding should hypothetically detect more predator species than electrofishing. Instead of supporting the notion that eDNA must replace electrofishing, or that eDNA and electrofishing must display the same results, the current study aims to establish the strengths and weaknesses of eDNA metabarcoding when compared to electrofishing. eDNA metabarcoding and electrofishing data were collected on three sampling dates at four experimental sites. A RV coefficient analysis confirmed that the eDNA metabarcoding data (RV = 0.395, p = 0.057) are statistically different from the electrofishing data. A paired Wilcoxon signed rank test revealed that eDNA data collection techniques detect more predatory species than electrofishing (p = 0.041). When the analysis was conducted for prey species a statistically significant difference did not occur (p = 0.661). Overall, the results of the study suggest that eDNA metabarcoding does not display the same results as electrofishing due to eDNA metabarcoding detecting predatory species at higher rates. The combined use of eDNA alongside electrofishing can help mitigate electrofishing's bias against predatory species, while electrofishing can address reliability concerns associated with eDNA. This collaborative approach ultimately enhances the accuracy of fish community assessments.

Freshwater fish are crucial components of aquatic ecosystems that are affected by a range of anthropogenic activities. Freshwater bodies in Nepal are under different threats affecting biodiversity. Inter-basin water transfer (IBWT) involving damming and diversion of water from one river basin to another is considered a major threat to aquatic biodiversity. Impact assessment of such projects include generation of baseline information on different biotic and abiotic variables. The aim of this study was to generate baseline information on fish diversity from the glacial-fed (Bheri) and the spring-fed (Babai) rivers and their selected tributaries from western Nepal in the wake of the first proposed inter-basin water transfer from the former to the latter. A total of 10 sampling sites, five each from Bheri and Babai River systems, were chosen strategically. Electrofishing was conducted encompassing different seasons in 2018 following the standard method. A total of 32 species with catch per unit effort (CPUE) of 47±24 from Bheri and 42 species with CPUE of 63±52 from Babai River were recorded. Cyprinidae, followed by Nemacheilidae, were the most dominant families in both river systems, and Barilius vagra and Schistura beavani were the most dominant species in both. Species richness and abundance showed a significant difference between rivers, and differences in fish assemblages reflects differences in ecological regimes. Failure to observe migratory species such as Anguilla bengalensis suggests that migratory routes may already have been affected. Of the total 52 species recorded, eight are in the threatened categories of the IUCN Red List and need active conservation measures. The findings provide a reference to assess the impacts of water transfers on fish assemblages in these river systems. [ABSTRACT FROM AUTHOR]

Objective: The removal of invasive Silver Carp Hypophthalmichthys molitrix is a primary control action in North America. Strong avoidance responses to underwater sound and electricity have been shown to facilitate herding and mass removal of these fish. We conducted a telemetry study on a closed population of Silver Carp (i.e., 10 telemetered fish) to assess fine‐scale movement responses to herding stimuli. Methods: Two herding boats traveled along bank‐to‐bank transects through the study area (longitudinal progression rate = 0.37 m/s) emitting sound and electricity ("combination technique") or no added stimuli ("control"). Result: The combination technique was most effective in terms of increasing fish presence (2.2 × the control) in the refuge zones when herding had concluded and effective range (i.e., fish reaction distance; 1.6 × the control) relative to the herding boats. The median (~1 m/s) and maximum (~2 m/s) swimming velocity was relatively stable across fixed effects, except for the negative influence of water depth on maximum velocity. Water depth also exhibited a negative effect on fish reaction distance. Conclusion: Our results suggest that the effective range of the combination technique was conservatively 200 m (~20 dB re 1 μPa > ambient level) when accounting for water depth in the study area. Herding deployments <1 m/s (longitudinal progression) could control fish passing and maintain fish movements toward an intended location. The information provided herein can serve to assist planning, designing, and applying herding efforts to manage, control, and remove these invasive fish. Impact statementInvasive Silver Carp are a nuisance to boat operators and a threat to native aquatic species. Harvest and/or removal is the fundamental control practice for addressing Silver Carp populations in North America. Herding stimuli is often used to aggregate fish into large schools to increase the efficiency of the capture process. However, little is known about the fine‐scale relationship between herding stimuli gradients and fish herding behavior. This study represents the first attempt to understanding this relationship using tagged fish and stationary receivers on a closed population. Results can provide insight into working towards understanding the effective spatial coverage of herding stimuli, standardizing the speed of herding deployments, and optimizing cost efficiency in terms of boats, nets, and personnel required to meet management goals. [ABSTRACT FROM AUTHOR]

Objective: Gill lice Salmincola spp. are among the most widely reported parasites of freshwater salmonids and have been associated with recent declines in native Brook Trout Salvelinus fontinalis populations. Effective gill lice surveillance is vital for salmonid conservation success, but current survey approaches are often inadequate or problematic. We developed an environmental DNA (eDNA)‐based approach to detect the gill louse Salmincola edwardsii and explored the viability of this approach as a management tool for rapid, large‐scale gill lice surveillance at Fort McCoy, Wisconsin, USA. Methods: Reference sequences were generated from gill lice specimens collected at Fort McCoy to confirm their identify as S. edwardsii and used to design a quantitative polymerase chain reaction (qPCR) assay that targets S. edwardsii mitochondrial cytochrome c oxidase I (COI). Assay validation included in silico and in vitro sensitivity and nontarget specificity testing, and assay performance was validated in situ by sampling eDNA at sites characterized via electrofishing. Result: Molecular analysis of reference sequences confirmed S. edwardsii identity while also providing the first multi‐population assessment of genetic variation for North American Salmincola and the most taxonomically comprehensive molecular phylogeny of Lernaeopodidae to date. Salmincola edwardsii eDNA was detected at 14 of 38 sites, including 12 of 14 sites with known active infestations, with no evidence that the odds of detecting gill lice via electrofishing was greater than the odds of detections from eDNA analysis. Brook Trout presence was highly predictive of gill lice eDNA site occupancy, concordant with S. edwardsii being an obligate parasite of Salvelinus fishes. However, by expanding survey coverage via eDNA analysis, we were able to identify an isolated drainage with Brook Trout where S. edwardsii is apparently absent, confirming electrofishing observations. Conclusion: These results suggest that eDNA analysis is equivalent to electrofishing for detecting gill lice in terms of performance yet offers substantial gains in survey efficiency. Further, this study demonstrates how eDNA analysis can provide valuable intel for directing management efforts, especially when used to expand survey coverage and prioritize follow‐up conventional surveys to assess host–parasite abundance, demographics, and status. Impact statementEnvironmental DNA analysis can accurately detect gill lice, providing fisheries managers with a rapid, cost‐effective, and non‐invasive survey tool to improve understanding and management of gill lice epizootics and their impacts on vulnerable freshwater salmonids. [ABSTRACT FROM AUTHOR]

Abstract The current knowledge about fish biodiversity and species distributions in Arctic freshwater systems is generally limited. This contrasts the clear urgency for more accurate biodiversity data to assess the effects of future ecosystem challenges such as climate change and other anthropogenic effects. Here we compare traditional electrofishing surveys with environmental DNA (eDNA) for monitoring species distribution of Atlantic salmon (Salmo salar) and Arctic char (Salvelinus alpinus) in the West Greenlandic sub‐Arctic river system of Kapisillit, which contains the only known population of Atlantic salmon in Greenland. Overall, electrofishing and eDNA surveys show high compatibility in regard to species detection and quantification, with Arctic char confirming a significant relationship between eDNA concentration and observed fish abundance. Both methods confirm a shift in species occurrence and relative species abundance through the river system. Specifically, salmon is restricted to the lower warmer sections of the river system while Arctic char is found throughout the system but dominates the upper parts. In total, the study supports eDNA as a promising tool for fish community assessment, which may serve a wide array of applications for Arctic freshwater monitoring. These applications include analyzing species occurrence and distribution of native and invasive species, as well as documenting potential shifts in relative species abundance as shown here. Given the ease of sampling and high sensitivity of the method, eDNA provides a powerful cost‐effective approach capable of detecting species in remote areas as well as corroborating fish community monitoring programs. This may especially be valuable for monitoring in the Arctic where logistic complications with sampling and high operational costs so far constrains routine monitoring.

Abstract Accurate data on the distribution and population status of threatened fish species are fundamental for effective conservation planning and management. In this work, in order to reassess the distribution of the globally threatened Evia barbel, Barbus euboicus, we undertook an environmental DNA (eDNA) survey coupled with conventional electrofishing, focusing on major river basins in Evia Island in proximity to its known occurrence in a single Evian basin (Manikiatiko stream). For comparison purposes, we conducted eDNA sampling in several locations in the geographically closest continental river basin, the Sperchios basin (Central Greece) which hosts the closely related Barbus sperchiensis. Our results expand the known range of the Evia barbel on Evia adding four new river basins, apart from its type locality (Manikiatiko stream (EV3)). In a single Evian River, where the species had never been located before, there was also a positive eDNA signal for Barbus sperchiensis within the same basin. The research confirms the occurrence of Evia barbel in a wider geographical area, highlighting however the sensitive conservation status of the species due to its still very narrow geographical distribution. The biogeographical implications of our study, as well as potential conservation interventions, are discussed.

The published database RivFishTIME (Comte et al. 2021, Global Ecology and Biogeography, doi: 10.1111/geb.13210) includes a large section of time-series data on fish abundance in Swedish rivers from the Swedish Electrofishing RegiSter, SERS. Knowledge about the limitations of the source data are important when extracting and analyzing data and with this brief note we provide some details that may be helpful for interpreting the Swedish time-series. The note highlights the importance of linking vital metadata to extracted focal data when constructing new databases, especially concerning time series data from monitoring programs conducted in non-randomly selected sites with human environmental impacts. Many of the SERS data come from rivers that have been affected by human impact, e.g. liming to mitigate environmental acidification and hydropower dams, since before monitoring was initiated. Data in SERS are also biased towards shallow salmonid habitats, due to the configuration of Swedish monitoring programs. Hence, data from many rivers are not representative of their fish biodiversity in general. This information is vital for appropriate interpretation of fish biodiversity trends. For RivFishTIME analyses considerations are important since Swedish data constitutes a large proportion of the database. We also provide background information about SERS and references to other Swedish databases containing complementary information. Finally, we provide contact information of the SERS database curators, who can assist prospective analysts with data extraction from SERS.

The San Francisco Estuary is an incredibly diverse ecosystem with a mosaic of aquatic habitats inhabited by a number of economically, culturally, and ecologically important fish species. To monitor the temporal and spatial trends of this rich fish community, long-term fish monitoring programs within the estuary use a variety of gear types to capture fish species across life stages and habitats. However, concerns have been raised that current sampling gears may fail to detect certain species—or life stages—that inhabit areas that are not accessible by current gear types (e.g., riprap banks, shallow vegetated areas). Boat electrofishing is one sampling method that has been proposed to supplement current long-term fish monitoring in the upper estuary. In this study, we used fish catch data from past boat electrofishing studies, a long-term beach seine survey, and a couple of long-running trawl surveys to compare the relative probability of detecting various fishes across these sampling gears. Overall, we found that boat electrofishing led to notable improvements in the detection rates for many native and non-native fishes we examined. Boat electrofishing gear was better at detecting the majority of species in the spring (20 out of 38 species, 53%) and fall-winter (24 out of 34 species, 70%) sampling periods. Based on these findings, we recommend that resource managers consider the implementation of a long-term boat electrofishing survey to help them in their long-term conservation planning for fishes within the upper estuary.

The Japanese eel (Anguilla japonica) is the most prevalent freshwater eel species in Taiwan. However, its population has undergone a significant decline in recent decades due to factors such as overfishing, habitat destruction, and the effects of climate change. Urgent action is needed to conserve this species. Before implementing conservation measures, it is imperative to ascertain the distribution of Japanese eels in Taiwan's rivers. This study's primary objective was to assess the effectiveness of eDNA analysis as a method for detecting Japanese eels. To achieve this goal, we compared eDNA analysis data with results obtained from electrofishing, with the Fengshan and Shimen Rivers serving as our designated test sites. Additionally, we collected water samples from 34 other rivers across Taiwan to comprehensively assess the species' wider distribution using eDNA analysis. Our findings demonstrated eDNA analysis's viability for detecting Japanese eels. Of the 36 rivers tested, Japanese eel DNA was detected in samples from 21 rivers, scattered across northern, eastern, southern, and western Taiwan, with no specific concentration in any region. We also noted reduced detectability of Japanese eel DNA in highly polluted rivers, indicating that river pollution may have a potential impact on their population. In the future, expanding eDNA analysis to more rivers could identify additional rivers that Japanese eels inhabit. Subsequently, resource management and conservation efforts can be focused on these identified habitats. Furthermore, developing advanced eDNA-based methods for estimating the abundance or biomass of Japanese eels could enhance the flexibility of management and conservation measures. [ABSTRACT FROM AUTHOR]

As conditions of Chicago's (Illinois, USA) waterways improved following implementation of the Clean Water Act, interest in recreational use of the waterways continued to grow, but the ability of this system to support quality recreational fishing opportunities remained unclear. We analyzed historical electrofishing data (1985–2020) to determine the status and trends in body‐size metrics of fish populations throughout Chicago's waterways. Many species exhibited increases in abundance, size, and diversity of lengths. Despite these increases, the number of quality‐sized or larger fish was sparse. While many species increased in abundance, Common Carp (Cyprinus carpio) and Gizzard Shad (Dorosoma cepedianum) declined in abundance during 2001–2020. Improvements to the availability and diversity of key habitats within Chicago's waterways would likely improve target fish demographics further and resultant recreational fishery opportunities. [ABSTRACT FROM AUTHOR]

The distribution, relative abundance, and rearing habitat of larvae of the Patagonian lamprey (Geotria macrostoma) were investigated in the Santa Cruz River basin, Patagonia, Argentina, using electrofishing and bile acid (petromyzonol sulfate) concentration. Both techniques revealed that larvae are widely distributed along the basin, aggregated at habitats of fine substrates and slow waters. Both, density and pheromone concentrations were consistent in detecting the presence of larvae and for gauging their abundance. Throughout the basin, length distribution of larvae ranged from 10 to 122 mm; larvae of the smaller length classes were present at both, upper sections and at the lower course of the main stem river, suggesting that these sites contained 0 + recruits from the previous spawning season. Currently construction of two hydroelectric dams in the main course of the Santa Cruz River will interrupt the migratory corridor of adult lamprey in search of their spawning grounds and will flood critical habitats for larvae rearing. The information generated in this study may be used as guidance for developing sampling surveys for the purpose of monitoring changes in populations trends for Patagonian lamprey in this river and other Patagonian drainages altered by human activities. [ABSTRACT FROM AUTHOR]

Copyright of Natura Sloveniae: Revija za Terensko Biologijo / Journal of Field Biology is the property of Natura Sloveniae and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Catches from standardized littoral electrofishing (EF) surveys (1990–2016) at various locales in Severn Sound, Georgian Bay, were analyzed. Catches were adjusted for size-selectivity using published results of laboratory immobilization experiments. Adjusted abundance-mean size relationships were consistent with the metabolic theory of ecology where body size has a central role in structuring community features. Relationships among species richness and areal estimates of biomass and annual production of the adjusted catches were assessed. Richness was the key variable driving other community metrics and was, in turn, largely driven by habitat fetch metrics and sampling time of day. Richness, biomass, and production decreased with increasing maximum effective fetch. Richness increased with time after sunset. Year and locale had smaller roles in variation of community metrics with more vegetated/ less urbanized areas having higher values. Higher fish production is expected in sheltered areas where the contributions of allochthonous and benthic primary production are expected to be greater. Further analyses using additional EF datasets from Great Lakes' littoral zones should increase understanding of the differences between littoral and offshore fish productivity and help guide management of littoral habitats to ensure healthy fish communities. [ABSTRACT FROM AUTHOR]

Context: Native fish populations in Australia's Murray–Darling Basin (MDB) have experienced severe declines since European settlement. Information on their status is needed to guide management and recovery. Aims: To quantify trends in MDB fish populations in New South Wales (NSW) from 1994 to 2022. Methods: Relative abundance, biomass, and size structure were examined using generalised additive mixed models at NSW MDB and river catchment (valley) scales for five native species (Murray cod, Maccullochella peelii ; golden perch, Macquaria ambigua ; silver perch, Bidyanus bidyanus ; Macquarie perch, Macquaria australasica ; freshwater catfish, Tandanus tandanus) and one alien species (common carp, Cyprinus carpio). Key results: There was strong inter-annual variation in relative abundance, biomass and population structure for all species. At the Basin scale, relative abundance of Murray cod, golden perch and common carp increased across the time series, with no clear trends for silver perch, Macquarie perch or freshwater catfish. Patterns in relative abundance, biomass, and population structure were variable among valleys for most species. Conclusions and implications: Although native fish populations in the MDB remain degraded and face escalating threats, recent increases in the abundance of some native species are an encouraging sign that integrated restoration efforts can improve the outlook for native fish. Native fish populations in Australia's Murray–Darling Basin have experienced severe declines since European settlement. We quantified trends in populations of six large-bodied fish species in New South Wales from 1994 to 2022. Results showed strong inter-annual variation in relative abundance, biomass and population structure for all species, with little evidence of continued decline of native species since the 1990s. [ABSTRACT FROM AUTHOR]

Catostomidae (catostomids) are suckers of the order Cypriniformes, and the majority of species are native to North America; however, species in this group are understudied and rarely managed. The popularity in bowfishing and gigging for suckers in the United States has increased concerns related to overfishing. Little information exists about the relative gear effectiveness for sampling catostomids. We sought to evaluate the relative effectiveness of boat electrofishing for sampling Black Redhorse Moxostoma duquesnei, Golden Redhorse M. erythrurum, Northern Hogsucker Hypentelium nigricans, White Sucker Catostomus commersonii, and Spotted Sucker Minytrema melanops populations in Lake Eucha, Oklahoma. We used an information theoretic approach to determine the abiotic variables related to sucker catch per effort (C/f). Our analysis indicated that sucker C/f was highest during the night and decreased with increasing water temperature. Sucker size structure was significantly different between daytime and nighttime samples; however, effect size estimates for size structure comparisons indicated that size distributions exhibited moderate overlap. Distributional comparisons indicated that daytime and nighttime samples were similar for fish greater than 180 mm in total length. Effect size estimates also indicated little association between the proportion of each species captured and time of day or water temperature. Night electrofishing in reservoirs at water temperatures from 16 to 25°C yielded the most precise C/f estimates, with the highest numbers of suckers collected at water temperatures from 6 to 15°C. Further study of the relationship between abiotic variables and catostomid catchability using various gears will be beneficial to agencies interested in these populations. [ABSTRACT FROM AUTHOR]

Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtaining a representative sample of fish community composition is fundamental to fishery management, research and nature conservation. Estimates of the size distribution, density and biomass of the topmouth gudgeon (Pseudorasbora parva) model species of invasive fish in three ponds were compared among three sampling methods: electrofishing, fish‐trapping and throw‐netting. The study illustrates that the invasive fish, P. parva, can be detected by all tested fishing methods, yet our results clearly showed that there are pronounced differences among methods in population characteristic estimates. Electrofishing and throw‐netting gave biased information on the size distribution of P. parva. Fish‐trapping and throw‐netting gave reasonable P. parva density and biomass estimates, while electrofishing clearly underestimated it. All tested methods showed a body size increment of P. parva between summer and autumn sampling sessions, yet neither throw‐netting nor electrofishing recorded an increment in its density. Our study showed that fish‐trapping is the most reliable and affordable method to estimate invasive P. parva population characteristics in ponds despite more time‐demanding sampling. The success depends on the mesh size of sampling gear, operator skill and habitat structure. The cost‐effectiveness of the selected methods and the importance of invasive fish monitoring in ponds is discussed. The sampling gear must be considered carefully according to the aim of the monitoring. [ABSTRACT FROM AUTHOR]

RNA sequencing (RNA‐Seq) is popular for measuring gene expression in non‐model organisms, including wild populations. While RNA‐Seq can detect gene expression variation among wild‐caught individuals and yield important insights into biological function, sampling methods can also affect gene expression estimates. We examined the influence of multiple technical variables on estimated gene expression in a non‐model fish, the westslope cutthroat trout (Oncorhynchus clarkii lewisi), using two RNA‐Seq library types: 3′ RNA‐Seq (QuantSeq) and whole mRNA‐Seq (NEB). We evaluated effects of dip netting versus electrofishing, and of harvesting tissue immediately versus 5 min after euthanasia on estimated gene expression in blood, gill, and muscle. We found no significant differences in gene expression between sampling methods or tissue collection times with either library type. When library types were compared using the same blood samples, 58% of genes detected by both NEB and QuantSeq showed significantly different expression between library types, and NEB detected 31% more genes than QuantSeq. Although the two library types recovered different numbers of genes and expression levels, results with NEB and QuantSeq were consistent in that neither library type showed differences in gene expression between sampling methods and tissue harvesting times. Our study suggests that researchers can safely rely on different fish sampling strategies in the field. In addition, while QuantSeq is more cost effective, NEB detects more expressed genes. Therefore, when it is crucial to detect as many genes as possible (especially low expressed genes), when alternative splicing is of interest, or when working with an organism lacking good genomic resources, whole mRNA‐Seq is more powerful. [ABSTRACT FROM AUTHOR]

Objective: Atlantic Salmon Salmo salar in the United States have been the focus of recovery efforts for over 150 years, but long‐term analyses of juvenile demographics are limited. We examined how parr size (fork length [FL]) varied across three Maine drainages (East Machias, Narraguagus, and Sheepscot rivers) during 1980–2014 and was affected by habitat and biological variables using a long‐term electrofishing data set. Methods: We fitted generalized additive mixed models (GAMMs) to determine how parr FL varied with explanatory variables, including mean summer air temperature, elevation, mean channel width, juvenile salmon density, age‐0 parr stocked, a metric for the number of effective fry stocked, and year. When examining model‐averaged GAMM results, we found that parr size varied throughout the 34‐year time period across the three drainages. Result: Between 1980 and 2014, parr FL in the Sheepscot River drainage (mean = 143.9 mm) steadily increased (~5‐mm increase). Parr FL in the Narraguagus River drainage (mean = 124.4 mm) declined from 1980 to about 2005 and then increased from 2006 to 2014. Parr FL in the East Machias River drainage (mean = 127.7 mm) experienced a decrease of approximately 10 mm during the study period. Density dependence was evident across drainages, suggesting that habitats were at capacity or that parr were experiencing competition. Given that the production of parr in Maine is highly reliant on stock enhancement, localized high stocking densities may limit parr growth without further restoration or habitat improvements. Stocking intensities generally decreased in all three drainages after 2000, possibly relaxing density dependence and partially explaining the plateau or increase in FL during recent years in the Sheepscot and Narraguagus rivers. Relationships between FL and summer air temperature were drainage specific, while wide channels and lower elevations were consistently associated with larger parr. Conclusion: Given our results, management should continue to prioritize habitat improvements to improve local carrying capacity and potentially reduce density‐dependent growth so as to increase stock enhancement efficacy within an adaptive management framework at the southern edge of the Atlantic Salmon's range. Impact statement:We examined trends in juvenile Atlantic Salmon size in three Maine, USA, watersheds from 1980 through 2014. Higher densities of juvenile salmon or higher stocking efforts were generally associated with smaller juvenile salmon sizes. Management should continue to prioritize habitat improvements and consider local stocking densities to increase effectiveness of hatchery programs. [ABSTRACT FROM AUTHOR]

This article presents a personal account of the important contribution a publication from David Noakes' lab (Pot, Noakes, Ferguson and Coker 1984, Quantitative sampling of fishes in a simple system: failure of conventional methods. Hydrobiologia 114:249–254) made to freshwater fish science in general and to the successful public defence of a doctoral thesis in particular. Pot et al. (1984) tested the accuracy of two conventional sampling approaches in their estimation of numbers of fish in a small pond (capture-mark-recapture and total sampling, following rotenone treatment). Their results demonstrated that even in a small and relatively uniform freshwater system (a pond of 0.1 ha), the so-called total sampling approach failed to provide the true number of any species of fish in the pond. The outcome of the study provided the evidence to debunk the assumption that absolute numbers of fishes can be obtained using rotenone treatment. This article therefore allowed me to defend my doctoral dissertation in the face of critical comments from a principal jury member, and firm proponent of 'absolute sampling', and it provided fish biologists with justification to focus on the development and application of sampling approaches, such as relative densities, which do not require futile attempts to obtain total fish numbers. [ABSTRACT FROM AUTHOR]

The possible recovery of a white-spotted charr population in a small tributary of a river to Lake Biwa, following removal of previously stocked red-spotted masu salmon, was investigated by electrofishing. We captured 30 red-spotted masu salmon and two hybrids of these two species in 2014. Prior to the stocking of red-spotted masu salmon, the estimated number of white-spotted charr ≥ 100 mm standard length (SL) in the tributary was more than 200 individuals in 2005, which had reduced to fewer than 30 individuals by 2014 when 30 red-spotted masu salmon plus two charr/masu salmon hybrids were captured. However, no red-spotted masu salmon were captured from 2015 to 2017, indicating the success of a red-spotted masu salmon removal program. The estimated number of white-spotted charr ≥ 100 mm SL ranged from 25 to 91 individuals between 2015 and 2017, implying a great reduction of red-spotted masu. The estimated population size of the former increased further to 171–221 individuals in 2021, comparable to 2005. These results suggest that the white-spotted charr population declined due to stocking of red-spotted masu salmon, and recovered following removal of the latter. [ABSTRACT FROM AUTHOR]

During spawning activity, fish release large amounts of sperm and eggs into the water, which has been assumed to cause an increase in environmental DNA (eDNA) levels and nuclear DNA/mitochondrial DNA ratios. To test whether these assumptions are valid and whether nuclear and mitochondrial eDNA analysis can be used to monitor the spawning activity of freshwater fish, we conducted field eDNA surveys and traditional surveys using common carp (Cyprinus carpio), largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) as model species.Fish spawning periods were estimated based on age, as estimated using the body lengths of juveniles collected in the Miharu reservoir in Fukushima, Japan. The results showed that the main spawning periods of largemouth bass and bluegill sunfish were from April to July and from July to August, respectively.Field eDNA surveys were conducted in the Hebisawagawa front reservoir, which is connected to the Miharu reservoir. From March to August 2019 and 2020, weekly eDNA sampling was conducted at three sites, and daily sampling was conducted at six sites from 23 June to 3 July 2020. The eDNA concentrations of the nuclear internal transcribed spacer 1 (ITS1) and mitochondrial cytochrome B (CytB), as well as the ITS1/CytB ratio, were measured for each of the three fish in each water sample. Water temperature had a statistically significant effect on eDNA concentration, probably reflecting the relationship between water temperature and spawning.We created generalised additive mixed models to estimate spawning activity periods based on weekly eDNA data. The estimated periods of spawning activity for common carp, largemouth bass and bluegill sunfish were March to May, May to July, and May to August, respectively. The estimated spawning periods coincided with known fish ecology or the results of traditional methods. This method also has been applied to daily eDNA samples, showing the feasibility of high‐resolution estimation of spawning activity.For common carp and bluegill sunfish, we were able to estimate the spawning period using this method. Although the method is affected by biomass and the diffusion and degradation of eDNA, it has the potential to accurately estimating spawning activities. These then can be estimated without conducting laborious traditional surveys, facilitating the monitoring of reproduction by rare, invasive or important fishery species. Further research on the diffusion distance and degradation time of the eDNA concentration peak caused by fish spawning activity may improve the accuracy of monitoring. [ABSTRACT FROM AUTHOR]

Assessment of fish assemblage structure depends on representative sampling. In contrast to lotic water bodies, recommendations for a general study design are sparse for lentic water bodies. Therefore, we evaluated the fish assemblages in different littoral structure types (e.g. macrophytes and riprap stone) and the impact of these structure types on the minimum distance required to obtain samples representative of fish species number in oxbow lakes. Boat‐based electrofishing was used at 88 sections, each 200‐m long within five oxbow lakes connected to the Upper River Rhine in southwest Germany. Submerged macrophytes and riprap stones were important littoral structures for determining fish community structure. Littoral structure was related to species accumulation, which illustrates the importance of littoral structure to define the minimum length of sampling. Our findings suggest that at least 200‐m stretches should be sampled to describe fish assemblages in oxbow lakes. [ABSTRACT FROM AUTHOR]

Biological indicators are important quality elements for classification of ecological status of water bodies according to the European Water Framework Directive. Multimetric indices are commonly regarded as robust and reliable indicators of human impact and are often used as quality elements. In fish-based indices, species are often grouped into guilds based on general tolerance to common anthropogenic pressures, with higher proportion of tolerant species being indicative of degraded systems. Within the Swedish electrofishing index VIX, the critically endangered European eel Anguilla anguilla (L.) is classified as a tolerant indicator species, and it therefore has a negative effect on classified ecological status. The scientific literature, however, suggests that eels are not generally tolerant and they benefit from similar environmental conditions as many insensitive species. VIX has been criticized for being too sensitive to the presence of eel in catch data, leading to low status classifications when eels are caught in the monitoring surveys. In a case study using manipulations of historical electrofishing data, we assessed the influence of eel presence and abundance on the ecological status classification as determined by VIX. We demonstrate that reduction of eels in survey data have positive effects on the classified status, in many cases substantial effects. An increase of eels in the data had the reverse effect. Mere presence of eel had a strong negative effect, which is problematic if the aim is to increase the endangered eel population. Given the Swedish classification system where the quality element indicating the worst status is decisive, the classified ecological status of Swedish rivers can theoretically be improved by management actions disfavouring eel, unless the results from VIX are carefully evaluated by experts. Along the same lines, measures implemented with an aim to increase the endangered eel population will lead to a decrease in assessed ecological status of Swedish rivers. Our conclusion is that the usage of VIX within Swedish water management is problematic and needs revision. From a broader perspective, the classification of species as generally tolerant need to be approached with great caution when developing new indices for assessing ecological status and integrity.

An investigation was conducted during 2018-19 after a time span of 13 years in the Senkhi stream, an important hill stream that flows through western corner of the capital city, Itanagar. The present study aims to compare decadal changes in ichthyofaunal diversity, status, and abundance with reference to the impact of increasing urbanization in the capital city. The ichthyofaunal diversity assessed presently is restricted to 37 species spreading over 30 genera under 13 families which include four species more, not reported in the past. Thus, of the 37 species recorded, 33 species only could be compared, and noticeably resulted ultimate reduction of 14 species belonging to 11 genera under 10 families from the study area. It indicated that nearly 64% decline in fish abundance within stream zone under urban area and about 46% reduction in undisturbed area. The present study hitherto revealed the alarming rate of decline in fish diversity and also unfolded key factors responsible for crucial decline of fish diversity along with the possible mitigation measures. [ABSTRACT FROM AUTHOR]

Although bull trout (Salvelinus confluentus) and tailed frogs (Ascaphus montanus) have co-existed in forested Pacific Northwest streams for millennia, these iconic cold-water specialists are experiencing rapid environmental change caused by a warming climate and enhanced wildfire activity. Our goal was to inform future conservation by examining the habitat associations of each species and conditions that facilitate co-occupancy. We repurposed data from previous studies in the northern Rocky Mountains to assess the efficacy of bull trout electrofishing surveys for determining the occurrence of tailed frogs and the predictive capacity of habitat covariates derived from in-stream measurements and geospatial sources to model distributions of both species. Electrofishing reliably detected frog presence (89.2% rate). Both species were strongly associated with stream temperature and flow regime characteristics, and less responsive to riparian canopy cover, slope, and other salmonids. Tailed frogs were also sensitive to wildfire, with occupancy probability peaking around 80 years after a fire. Co-occupancy was most probable in locations with low-to-moderate frequencies of high winter flow events, few other salmonids, a low base-flow index, and intermediate years since fire. The distributions of these species appear to be sensitive to environmental conditions that are changing this century in forests of the northern Rocky Mountains. The amplification of climate-driven effects after wildfire may prove to be particularly problematic in the future. Habitat differences between these two species, considered to be headwater specialists, suggest that conservation measures designed for one may not fully protect the other. Additional studies involving future climate and wildfire scenarios are needed to assess broader conservation strategies and the potential to identify refuge streams where both species are likely to persist, or complementary streams where each could exist separately into the future. [ABSTRACT FROM AUTHOR]

In areas where commercial fishing is prohibited, demographic metrics obtained from recreational fisheries and fishery‐independent methods can be integral to population ecology and management. For Australian bass Percalates novemaculeata (Steindachner) and Murray cod Maccullochella peelii peelii (Mitchell), two key finfish species native to the recreational‐only fresh waters of New South Wales (NSW), Australia, recreational fishing surveys were combined with electrofishing methods to capture information on spatial patterns of exploitation and variation in size. The species' catch across NSW fresh waters (2013–2014) was estimated using a telephone‐diary longitudinal panel survey and examined for spatial effects using generalised linear mixed effects models. Length data, collected through electrofishing (2013–2015), were compared among geographic zones using Kolmogorov–Smirnov tests and kernel density estimate tests. Catch patterns for each species were mainly spatially static, but significant regional differences in the size composition of both species were detected. The findings are discussed in the context of current catch‐and‐release practices for Australian bass and the application of size limits for Murray cod to illustrate the value of quantitative spatial information from recreational surveys and fishery‐independent methods in developing evidence‐based management and conservation initiatives. [ABSTRACT FROM AUTHOR]

This study is the first reference regarding the length-weight relationships of freshwater fishes inhabiting one of the most important spawning waters of the endemic endangered Danube salmon (Hucho hucho). Fulton condition factor (K) was calculated for 1366 individuals belonging to 16 species from Ruscova River, north of Romania. Length-weight relationships were determined for 1362 specimens from 14 species. The smallest slope value (b) was determined for Romanogobio uranoscopus (b=2.2437) and the highest value for Telestes souffia (b=3.6058). The Danube salmon (Hucho hucho) showed positive allometric growth, having the calculated value of the slope of 3.3879. The mean values of Fulton condition factor (K) for the captured specimens were: Cottus gobio (1.161), Alburnus alburnus (0.3726), Alburnoides bipunctatus (0.8142), Barbus barbus (0.9434), Barbus carpathicus (0.9202), Chondrostoma nasus (0.8867), Romanogobio uranoscopus (0.8196), Phoxinus phoxinus (0.9888), Squalius cephalus (1.137), Telestes souffia (0.898), Barbatula barbatula (0.6693), Eudontomyzon danfordi (0.1293), Hucho hucho (0.8454) and Thymallus thymallus (0.9522). [ABSTRACT FROM AUTHOR]

The data presented here cover ∼4 decades of electrofishing surveys in mainland France rivers. Despite some changes in field protocols and sampling site locations over time, the ASPE database offers a unique set of 47,869 georeferenced and standardised sampling surveys. Fish individuals are identified to species, measured and weighted. Additional information encompasses habitat features as well as "river health" assessment by two fish-based indices. Though preferentially focused on fishes, the surveys also report crayfish data. Numerous studies have been already published using these data, mainly on the fields of macroecology, community and/or population ecology and bioassessment. However, we believe much more knowledge can be gained from the database in fields such as population dynamics or conservation practices in the context of global change. [ABSTRACT FROM AUTHOR]

Abstract Electrofishing is a well‐established and widely used method for surveying fish populations. Nonetheless, its effectiveness is impacted by numerous factors, including water chemistry, habitat type and fish species. Both physiological and behavioural responses make bottom‐dwelling ‘benthic’ fish which lack swim bladders (e.g. European bullhead Cottus gobio) particularly difficult to survey by electrofishing. We compare the performance and practicalities of electrofishing for benthic fish at a rocky northern English headwater stream with two sampling methods originally designed for crayfish surveys; the triple drawdown method which involves repeated dewatering of a site, and the Pritchard Trap method which involves sunken traps filled with natural substrate that samples a small, fixed (0.25 m2) area of river bed. Both the Pritchard trapping and triple drawdown methods provided similar high‐density population density estimates for bullhead which were at least 2.5–5 times higher than predicted from electrofishing derived sweep depletion curves. Electrofishing and the triple drawdown method are both resource‐intensive, requiring expensive equipment and a team of trained operatives. These approaches also pose a risk to fish and non‐target organisms. In contrast, Pritchard Traps provide a cost‐effective passive, low risk survey method requiring minimal training and only one operative. Pritchard traps, therefore, show particular promise for benthic fish surveying and monitoring.

Neglect of imperfect capture efficiency leads to biased inferences on population abundance, and correspondingly, seriously affects ecological research, bioassessment, conservation, and fisheries management. To date, many research studies have studied capture efficiency of salmonid fishes, but the catchability of fishes living in non‐salmonid streams has received much less attention. This paper estimates capture probability for seven fish species in densely vegetated lowland streams by using double‐pass electrofishing data and an N‐mixture removal model. Results show that capture probability can vary among species, and between‐stream differences have a stronger influence on the abundance and the catchability than within‐stream variability. Estimation uncertainty decreases with observed abundance, and the mean catchability tends to be the highest for the medium abundant species. These findings suggest that relative abundances from single‐pass data are biased to a species‐ and habitat‐specific degree. Therefore, plausible estimation of capture probability from double‐pass electrofishing requires data collected from numerous sites that cover a wide range of the environmental gradient in lowland streams. [ABSTRACT FROM AUTHOR]

There is increasing interest in the health of waterways in Aotearoa New Zealand. The National Policy Statement for Freshwater Management 2020 (NPS-FM) places a greater onus on resource managers to report on the state of freshwater ecosystem health, including fish. Routine fish monitoring is time intensive and is principally conducted in 'wadeable' stream reaches. In comparison, environmental DNA (eDNA) sampling is a relatively recent and rapid technique that likely detects fish and other vertebrate and invertebrate taxa over a broader spatial scale. In this study, we present data for five wadeable streams comparing diversity derived from multi-year standardised electrofishing with eDNA samples collected from the same reaches. Further, we explore whether the number of eDNA monitoring 'reads' for species at a site may provide an approximate (semi-quantitative) indication of their 'near field' relative abundance based on one-pass electrofishing captures. Results indicated that while some aspects of the methodology require fine-tuning, eDNA sampling shows substantial promise for complimenting state of the environment (SOE) reporting for describing fish diversity in wadeable streams. The use of aquatic eDNA monitoring to provide a cost-effective indication of broader catchment scale biodiversity (e.g. birds and exotic pests) in wadeable and non-wadeable streams is also discussed. [ABSTRACT FROM AUTHOR]

Despite aquatic invasive species (AIS) being a widely recognized threat to native biodiversity in streams on subtropical and tropical oceanic islands across the Pacific, AIS management has been constrained by concerns that methods of removal could result in more harm than good. In this study, we assessed the effectiveness and outcomes of combining hand-netting and streamside sequestration of native species with AIS removal via three-pass electrofishing tailored for Hawaiian Island watersheds. Removals were conducted in 13 watersheds on the island of O'ahu following a before-after, control-impact design to assess how AIS removal and post-removal community reassembly varied by surface flow and target species of interest. We found that removals resulted in a sharp reduction in AIS densities without altering native species densities. Removal efficacy was greatest in streams with intermediate mean discharge irrespective of target group or pre-removal AIS densities. Long-term monitoring demonstrated that removals led to persistent shifts in community composition reflecting sustained reductions in AIS densities. These findings indicate that electrofishing can be a valuable tool for AIS management in Hawaiian and other subtropical Pacific island streams, so long as steps are taken to minimize potential harm to at-risk and culturally important native species. [ABSTRACT FROM AUTHOR]

We compared the effectiveness of three sampling methods (kick seining, electrofishing, and nest trapping) to collect crayfishes and fishes, simultaneously, in southern Appalachian Mountain streams (Alabama, USA). For crayfishes, kick seining collected the highest species richness and most individuals. However, by combining kick seining and electrofishing collections, we decreased the number of sites needed to accurately assess crayfish richness relative to using one method. For 9 of the 13 species collected, no differences in crayfish sizes or sex ratios were detected between electrofishing and kick seining. In the remaining four species, electrofishing collected larger crayfishes and more females than kick seining. For fishes, electrofishing was most effective at assessing fish species richness. Sampled fish richness was higher when electrofishing in streams with higher water temperatures and width-to-depth ratios, as well as lower conductivities and smaller substrates. Electrofishing was the most effective sampling method for collecting Centrarchids, whereas kick seining was most effective at collecting Cyprinids. Nest traps were the least effective sampling method. We conclude that using a combination of kick seining and electrofishing is best for assessing stream fish and crayfish assemblages, simultaneously, which can improve management, biomonitoring, and understanding of the complex relationships between these faunal groups. [ABSTRACT FROM AUTHOR]

How fish assemblages change over time in highly-modified urban rivers, where physical and chemical properties rarely mimic non-urban systems, has sparsely been documented. Data have been collected on fishes within the boundaries of the Chicago Metropolitan area routinely since the mid-1980's. Representing fish assemblages in one of the largest cities of America, this dataset offers the ability to investigate and track changes in assemblage composition in an urbanized river. To this end, multivariate modelling, as well as various visualization techniques, were used to assess and describe compositional changes in the fish assemblage of Chicago's waterways. In general, there were gradual enhancements in the fish assemblages of Chicago's waterways throughout the years studied, which are characterized by more fish, of which more are native species. Small-bodied native fishes (Cyprinidae), game fishes (Centrarchidae), as well as catfish (Ictaluridae) have increased in relative abundance, whereas several invasive fish species exhibited declines. Exponential growth of Banded Killifish (Fundulus diaphanous) relative abundance appears to continue from previously noted range expansions. As Chicago and other cities move towards supporting fishable waterways, interest may lay in investigating population vital rates and habitat or water quality factors affecting them in heavily urbanized settings. [ABSTRACT FROM AUTHOR]

Electric fields (EFs) are widely used in human activities, and all organisms are potentially affected by EFs. The effects of an EF on terrestrial plants, seeds and water animals are well documented, whereas the effects of an EF on aquatic macrophytes remain unknown. We wanted to determine the effects of an EF, generated by backpack electrofishing equipment, on the growth and metabolism of three submerged plants (Vallisneria natans , Myriophyllum spicatum and Potamogeton maackianus). The results showed that the shoot heights, shoot dry weights, root dry weights, root : shoot ratios and contents of soluble proteins and soluble carbohydrates of the three tested submerged plants were influenced by the EF, and these effects were significantly different among the study plants. Thus, our results indicated that submerged macrophytes might be suppressed by EFs released by electrofishing. Accordingly, we highlight that the growth, development and metabolism of submerged macrophytes might be inhibited by EFs, although the results were obtained from a simulated experiment, and more extensive field experiments are needed. The effects of electric field (EF) on terrestrial plans, seeds and water animals are well documented, whereas the effects of EF on aquatic macrophytes remain unknown. Our results found that the growth, development and metabolism of submerged macrophytes might be inhibited by EF. More extensive field experiments deserve further attention to prove the negative effects because the results were obtained from a simulated experiment. [ABSTRACT FROM AUTHOR]

Abstract Freshwater shrimp can reach high biomasses, affecting ecosystem processes. It is important to define the most accurate methodology to estimate their densities and biomass. We studied two species of different sizes, Potimirim brasiliana Villalobos F., 1960 and Macrobrachium olfersii (Wiegmann, 1836), in three sites of a coastal stream in Ilha Grande, Rio de Janeiro, Brazil. We evaluated the efficiency of two infrequently used sampling methods: a depletion method using electrofishing, and a substrate method using benthic samplers. The methodologies provided different estimates, especially for M. olfersii, of density (electrofishing 1.27 ± 6.3 ind/m²; substrate sampling 0.1 ± 5.05 ind/m²) and biomass (electrofishing 1.66 ± 8.5 g/m²; substrate sampling 0.11 ± 1.16 g/m²). The median size of M. olfersii was higher for electrofishing, while the median size of P. brasiliana was higher for substrate sampling. Electrofishing is good at collecting bigger individuals that are not possible to catch with the substrate method and it samples a bigger area that includes many different microhabitats. The substrate method is cost-effective, especially for P. brasiliana, but by sampling a small area, its estimates can be highly affected by local heterogeneity. The substrate method is not recommended for M. olfersii, as it underestimated both its density and biomass.

The management of species that occur in low densities is a conservation concern worldwide across taxa with consequences for managers and policymakers. The distribution boundary at the upper extent of fish in North America receives extra attention because stream reaches with fish are managed differently and often have more protections than fishless reaches. Here, we examine the relative reliability of water environmental DNA (eDNA), polymerase chain reaction (PCR)‐amplified for Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) to detect the upper extent of fish across streams as a potential management tool compared to standard electrofishing methods. We provide estimates of fish detection probabilities from eDNA analyses, and probabilities of detection for both eDNA field samples and quantitative PCR (qPCR) given covariates of habitat characteristics and fish densities from electrofishing. We present a primer and probe based on the cytochrome oxidase I gene using qPCR to detect trout DNA across water samples from 60 forested streams in the Pacific Northwest, USA using high‐resolution spatial sampling. In 28% of streams, the upper extent of fish matches between methods. In over half of the streams, Coastal Cutthroat Trout eDNA was detected above the electrofishing last‐fish boundary. Although some detections could be attributed to false‐positive errors, eDNA results extend the upstream, leading edge of fish by 50–250 m from the electrofishing boundary. In 20% of the streams, detections of last‐fish occurred higher in the stream network with electrofishing rather than eDNA, but generally by only 50 m. Modeled results revealed that the occurrence of trout eDNA was higher in wider‐stream locations and that eDNA detections occurred at lower electrofishing densities (<5 trout per 50 linear m). We also showed that three replicate eDNA samples were sufficient to capture trout eDNA when eDNA was present. Although eDNA constitutes an effective addition to approaches to delimit the upper extent of fish, its effectiveness depends on previous knowledge of the last‐fish boundary to apprise where to start sampling and targeting fish species anticipated to be last‐fish. We present evidence that eDNA is a valuable tool in investigating fish distributions taking its place alongside traditional high‐effort catch–release tools. [ABSTRACT FROM AUTHOR]