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At least 541 records · Page 30Linked to original sources
USGS2016

Entrainment, retention, and transport of freely swimming fish in junction gaps between commercial barges operating on the Illinois Waterway

Large Electric Dispersal Barriers were constructed in the Chicago Sanitary and Ship Canal (CSSC) to prevent the transfer of invasive fish species between the Mississippi River Basin and the Great Lakes Basin while simultaneously allowing the passage of commercial barge traffic. We investigated the potential for entrainment, retention, and transport of freely swimming fish within large gaps (> 50 m 3 ) created at junction points between barges. Modified mark and capture trials were employed to assess fish entrainment, retention, and transport by barge tows. A multi-beam sonar system enabled estimation of fish abundance within barge junction gaps. Barges were also instrumented with acoustic Doppler velocity meters to map the velocity distribution in the water surrounding the barge and in the gap formed at the junction of two barges. Results indicate that the water inside the gap can move upstream with a barge tow at speeds near the barge tow travel speed. Water within 1 m to the side of the barge junction gaps was observed to move upstream with the barge tow. Observed transverse and vertical water velocities suggest pathways by which fish may potentially be entrained into barge junction gaps. Results of mark and capture trials provide direct evidence that small fish can become entrained by barges, retained within junction gaps, and transported over distances of at least 15.5 km. Fish entrained within the barge junction gap were retained in that space as the barge tow transited through locks and the Electric Dispersal Barriers, which would be expected to impede fish movement upstream.

Illinois↗
USGS2022

Condition of resident fish communities in the Eighteenmile Creek Area of Concern, New York

The lower 3.5 km of Eighteenmile Creek, a tributary to Lake Ontario in New York, was designated as an Area of Concern (AOC) in 1985 under the Great Lakes Water Quality Agreement due to extensive contamination of bed sediments by polychlorinated biphenyls (PCBs) and other toxicants. Five beneficial use impairments (BUIs) have been identified in this AOC, including degraded fish and wildlife populations. We surveyed fish communities in the Eighteenmile Creek AOC and in a comparable section of a nearby reference stream (Oak Orchard Creek) during June 2019 to infer whether legacy contaminants are currently impairing fish communities in the AOC to an extent that they differ from the regional reference condition. Estimates of community abundance, biomass, diversity, and fish condition from each system were compared using a noninferiority testing framework. Biomass, diversity, and fish condition in the Eighteenmile Creek AOC were similar or superior to that in Oak Orchard Creek, while abundance was 20% lower in the AOC. These findings and those of a 2007 sampling effort suggest that fish communities in the Eighteenmile Creek AOC are not impaired despite recent studies indicating that PCBs are bioaccumulating in fish tissues at 1–2 orders of magnitude above background levels. Future assessments in the Eighteenmile Creek AOC might focus on the condition of benthic macroinvertebrate communities and potential toxicity of local contaminants to piscivorous wildlife in order to fully address the remaining aspects of the fish and wildlife populations beneficial use impairment.

New York↗
USGS2021

Response of fish assemblages to restoration of rapids habitat in a Great Lakes connecting channel

Rapids habitats are critical spawning and nursery grounds for multiple Laurentian Great Lakes fishes of ecological importance such as lake sturgeon, walleye, and salmonids. However, river modifications have destroyed important rapids habitat in connecting channels by modifying flow profiles and removing large quantities of cobble and gravel that are preferred spawning substrates of several fish species. The conversion of rapids habitat to slow moving waters has altered fish assemblages and decreased the spawning success of lithophilic species. The St. Marys River is a Great Lakes connecting channel in which the majority of rapids habitat has been lost. However, rapids habitat was restored at the Little Rapids in 2016 to recover important spawning habitat in this river. During the restoration, flow and substrate were recovered to rapids habitat. We sampled the fish community (pre- and post-restoration), focusing on age-0 fishes in order to characterize the response of the fish assemblage to the restoration, particularly for species of importance (e.g. lake whitefish, walleye, Atlantic salmon). Following restoration, we observed a 40% increase in age-0 fish catch per unit effort , increased presence of rare species, and a shift in assemblage structure of age-0 fishes (higher relative abundance of Salmonidae, Cottidae, and Gasterosteidae). We also observed a “transition” period in 2017, in which the assemblage was markedly different from the pre- and post-restoration assemblages and was dominated by Catostomidae. Responses from target species were mixed, with increased Atlantic salmon abundance, first documented presence of walleye and no presence of lake sturgeon or Coregoninae.

Michigan, Ontario↗
USGS2024

Predicting the response of fish populations to changes in river connectivity using individual-based models

Barrier removal restores physical stream processes and improves accessibility of critical habitats to migratory fishes. Although increasing connectivity benefits stream systems and migratory fishes, barrier removals may also lead to increased production of undesirable or invasive migratory species, as well as myriad other concerns (e.g., reduced recreational opportunities). Few studies have predicted how migratory fish populations will respond to enhanced fish passage, despite being a critical step in the decision-making process. We developed an individual-based model framework to forecast the response of migratory fishes to changes in connectivity and applied the framework to six species under multiple fish passage scenarios for the FishPass project on the Boardman River, MI, which outlets into Lake Michigan. Population response to barrier removal was species-specific and varied based on initial population size and distribution within the watershed, number of fish passed upstream, and species life history traits. Species restricted to below the barrier prior to removal benefitted most; non-native species were found to have greater production potential under full passage scenarios than native Great Lakes species. With increasing passage of non-native Pacific salmonids, steelhead Oncorhynchus mykiss surpassed brook trout Salvelinus fontinalis as the system’s dominant species. Our results will inform decision-makers on management alternatives for fish passage on the Boardman River and our model framework can be modified, updated, and applied to additional river systems as more barrier removal projects are conducted in the future.

Michigan↗
USGS2012

Concentration, distribution, and translocation of mercury and methylmercury in mine-waste, sediment, soil, water, and fish collected near the Abbadia San Salvatore mercury mine, Monte Amiata district, Italy

The distribution and translocation of mercury (Hg) was studied in the Paglia River ecosystem, located downstream from the inactive Abbadia San Salvatore mine (ASSM). The ASSM is part of the Monte Amiata Hg district, Southern Tuscany, Italy, which was one of the world’s largest Hg districts. Concentrations of Hg and methyl-Hg were determined in mine-waste calcine (retorted ore), sediment, water, soil, and freshwater fish collected from the ASSM and the downstream Paglia River. Concentrations of Hg in calcine samples ranged from 25 to 1500 μg/g, all of which exceeded the industrial soil contamination level for Hg of 5 μg/g used in Italy. Stream and lake sediment samples collected downstream from the ASSM ranged in Hg concentration from 0.26 to 15 μg/g, of which more than 50% exceeded the probable effect concentration for Hg of 1.06 μg/g, the concentration above which harmful effects are likely to be observed in sediment-dwelling organisms. Stream and lake sediment methyl-Hg concentrations showed a significant correlation with TOC indicating considerable methylation and potential bioavailability of Hg. Stream water contained Hg as high as 1400 ng/L, but only one water sample exceeded the 1000 ng/L drinking water Hg standard used in Italy. Concentrations of Hg were elevated in freshwater fish muscle samples and ranged from 0.16 to 1.2 μg/g (wet weight), averaged 0.84 μg/g, and 96% of these exceeded the 0.3 μg/g (methyl-Hg, wet weight) USEPA fish muscle standard recommended to protect human health. Analysis of fish muscle for methyl-Hg confirmed that > 90% of the Hg in these fish is methyl-Hg. Such highly elevated Hg concentrations in fish indicated active methylation, significant bioavailability, and uptake of Hg by fish in the Paglia River ecosystem. Methyl-Hg is highly toxic and the high Hg concentrations in these fish represent a potential pathway of Hg to the human food chain.

Monte Amiata↗
USGS2016

Hg concentrations in fish from coastal waters of California and Western North America

The State of California conducted an extensive and systematic survey of mercury (Hg) in fish from the California coast in 2009 and 2010. The California survey sampled 3483 fish representing 46 species at 68 locations, and demonstrated that methylHg in fish presents a widespread exposure risk to fish consumers. Most of the locations sampled (37 of 68) had a species with an average concentration above 0.3 μg/g wet weight (ww), and 10 locations an average above 1.0 μg/g ww. The recent and robust dataset from California provided a basis for a broader examination of spatial and temporal patterns in fish Hg in coastal waters of Western North America. There is a striking lack of data in publicly accessible databases on Hg and other contaminants in coastal fish. An assessment of the raw data from these databases suggested the presence of relatively high concentrations along the California coast and in Puget Sound, and relatively low concentrations along the coasts of Alaska and Oregon, and the outer coast of Washington. The dataset suggests that Hg concentrations of public health concern can be observed at any location on the coast of Western North America where long-lived predator species are sampled. Output from a linear mixed-effects model resembled the spatial pattern observed for the raw data and suggested, based on the limited dataset, a lack of trend in fish Hg over the nearly 30-year period covered by the dataset. Expanded and continued monitoring, accompanied by rigorous data management procedures, would be of great value in characterizing methylHg exposure, and tracking changes in contamination of coastal fish in response to possible increases in atmospheric Hg emissions in Asia, climate change, and terrestrial Hg control efforts in coastal watersheds.

Science of the Total Environment↗
USGS2025

Cleaner cuts: Farmed fish and skin-off fillets are lower in per- and polyfluoroalkyl substances (PFAS)

The ubiquitous occurrence and persistence of per- and polyfluoroalkyl substances (PFAS) in all environmental matrices and biota poses significant health risks to humans. Fish consumption is one of the main pathways humans are exposed to PFAS, yet general patterns in factors influencing PFAS content in fish fillets remain unknown. We assembled information on PFAS content (total quantified PFAS, PFOS, PFOA, and others) in fish fillets to assess the effect of fish origin (marine, freshwater, wild, or farmed), fillet type (skin-on or skin-off), and lipid content on PFAS variation across environments at a global scale. We found that these factors influenced PFAS contents in fish fillets, with concentrations reaching up to 2149 ng•g wet mass −1 (WM). Specifically, PFOS and PFOA in skin-off fillets were consistently lower in farmed than wild fish across freshwater and marine environments. In freshwater wild fish, PFOS was lower in skin-off fillets than skin-on fillets at group and species levels, and multiple PFAS showed an inverse relationship with the lipid content of skin-off fillets, though the slopes showed varying steepness depending on the carbon chain length and functional group of the PFAS. However, the high variability of PFAS content across sites in aquatic environments and the complexity of PFAS bioaccumulation mechanisms in fish tissues may lead to variable results at a fine scale (i.e. , species level); this highlights general patterns of factors influencing PFAS bioaccumulation that may inform the management of human exposure to PFAS through dietary consumption.

Science of the Total Environment↗
USGS2010

Stress and fish reproduction: The roles of allostasis and hormesis

This paper is a review of the effects of stress on reproduction in fishes. I hope to further the development of the concepts of allostasis and hormesis as relevant to understanding reproduction in general and in fish in particular. The main contentions I derive in this review are the following: Stressors affect fish reproduction in a variety of ways depending on the nature and severity of the stressor. The effects are transduced through a hormonal cascade initiated by perception of the stressor and involving the hypothalamus-pituitary-interrenal axis, the catecholamines, and also cytokines. Mounting a stress response and resisting a stressor is an energetically costly process, including costs associated with allostasis, attempting to reset homeostatic norms. Responses in emergency situations (e.g., being chased by a predator or a net) can be different from those where fish can cope (e.g., being in a more crowded environment) with a stressor, but both situations involve energy re-budgeting. Emergency responses happen in concert with the onset of energy limitations (e.g., the fish may not eat), while coping with allostatic overload can happen in a more energy-rich environment (e.g., the fish can continue to eat). Low levels of stress may have a positive effect on reproductive processes while greater stress has negative effects on fish reproduction. The concept of hormesis is a useful way to think about the effect of stressors on fish reproduction since responses can be nonmonotonal, often biphasic.

General and Comparative Endocrinology↗
USGS2017

Mercury bioaccumulation in estuarine fishes: Novel insights from sulfur stable isotopes

Estuaries are transitional habitats characterized by complex biogeochemical and ecological gradients that result in substantial variation in fish total mercury concentrations (THg). We leveraged these gradients and used carbon (δ 13 C), nitrogen (δ 15 N), and sulfur (δ 34 S) stable isotopes to examine the ecological and biogeochemical processes underlying THg bioaccumulation in fishes from the San Francisco Bay Estuary. We employed a tiered approach that first examined processes influencing variation in fish THg among wetlands, and subsequently examined the roles of habitat and within-wetland processes in generating larger-scale patterns in fish THg. We found that δ 34 S, an indicator of sulfate reduction and habitat specific-foraging, was correlated with fish THg at all three spatial scales. Over the observed ranges of δ 34 S, THg concentrations in fish increased by up to 860% within wetlands, 560% among wetlands, and 291% within specific impounded wetland habitats. In contrast, δ 13 C and δ 15 N were not correlated with THg among wetlands and were only important in low salinity impounded wetlands, possibly reflecting more diverse food webs in this habitat. Together, our results highlight the key roles of sulfur biogeochemistry and ecology in influencing estuarine fish THg, as well as the importance of fish ecology and habitat in modulating the relationships between biogeochemical processes and Hg bioaccumulation.

California↗
USGS2012

MERGANSER: an empirical model to predict fish and loon mercury in New England lakes

MERGANSER (MERcury Geo-spatial AssessmeNtS for the New England Region) is an empirical least-squares multiple regression model using mercury (Hg) deposition and readily obtainable lake and watershed features to predict fish (fillet) and common loon (blood) Hg in New England lakes. We modeled lakes larger than 8 ha (4404 lakes), using 3470 fish (12 species) and 253 loon Hg concentrations from 420 lakes. MERGANSER predictor variables included Hg deposition, watershed alkalinity, percent wetlands, percent forest canopy, percent agriculture, drainage area, population density, mean annual air temperature, and watershed slope. The model returns fish or loon Hg for user-entered species and fish length. MERGANSER explained 63% of the variance in fish and loon Hg concentrations. MERGANSER predicted that 32-cm smallmouth bass had a median Hg concentration of 0.53 μg g -1 (root-mean-square error 0.27 μg g -1 ) and exceeded EPA's recommended fish Hg criterion of 0.3 μg g -1 in 90% of New England lakes. Common loon had a median Hg concentration of 1.07 μg g -1 and was in the moderate or higher risk category of >1 μg g -1 Hg in 58% of New England lakes. MERGANSER can be applied to target fish advisories to specific unmonitored lakes, and for scenario evaluation, such as the effect of changes in Hg deposition, land use, or warmer climate on fish and loon mercury.

New England↗
USGS2023

Evolutionary and ecological correlates of thiaminase in fishes

Thiamine (vitamin B 1 ) is required by all living organisms in multiple metabolic pathways. It is scarce in natural systems, and deficiency can lead to reproductive failure, neurological issues, and death. One major cause of thiamine deficiency is an overreliance on diet items containing the enzyme thiaminase. Thiaminase activity has been noted in many prey fishes and linked to cohort failure in salmonid predators that eat prey fish with thiaminase activity, yet it is generally unknown whether evolutionary history, fish traits, and/or environmental conditions lead to production of thiaminase. We conducted literature and GenBank BLAST sequence searches to collect thiaminase activity data and sequence homology data in expressed protein sequences for 300 freshwater and marine fishes. We then tested whether presence or absence of thiaminase could be predicted by evolutionary relationships, trophic level, omega-3 fatty acid concentrations, habitat, climate, invasive potential, and body size. There was no evolutionary relationship with thiaminase activity. It first appears in Class Actinoptergyii (bony ray-finned fishes) and is present across the entire Actinoptergyii phylogeny in both primitive and derived fish orders. Instead, ecological factors explained the most variation in thiaminase: fishes were more likely to express thiaminase if they fed closer to the base of the food web, were high in polyunsaturated fatty acids, lived in freshwater, and were from tropical climates. These data provide a foundation for understanding sources of thiaminase leading to thiamine deficiency in fisheries and other organisms, including humans that eat uncooked fish.

Scientific Reports↗
USGS2019

Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan

To understand the impact reduced mercury (Hg) loading and invasive species have had on methylmercury bioaccumulation in predator fish of Lake Michigan, we reconstructed bioaccumulation trends from a fish archive (1978 to 2012). By measuring fish Hg stable isotope ratios, we related temporal changes in Hg concentrations to varying Hg sources. Additionally, dietary tracers were necessary to identify food web influences. Through combined Hg, C, and N stable isotopic analyses, we were able to differentiate between a shift in Hg sources to fish and periods when energetic transitions (from dreissenid mussels) led to the assimilation of contrasting Hg pools (2000 to present). In the late 1980s, lake trout δ 202 Hg increased (0.4‰) from regulatory reductions in regional Hg emissions. After 2000, C and N isotopes ratios revealed altered food web pathways, resulting in a benthic energetic shift and changes to Hg bioaccumulation. Continued increases in δ 202 Hg indicate fish are responding to several United States mercury emission mitigation strategies that were initiated circa 1990 and continued through the 2011 promulgation of the Mercury and Air Toxics Standards rule. Unlike archives of sediments, this fish archive tracks Hg sources susceptible to bioaccumulation in Great Lakes fisheries. Analysis reveals that trends in fish Hg concentrations can be substantially affected by shifts in trophic structure and dietary preferences initiated by invasive species in the Great Lakes. This does not diminish the benefits of declining emissions over this period, as fish Hg concentrations would have been higher without these actions.

Lake Michigan↗
USGS2025

Relationships between larval fish drift, time of day and discharge in an Ozark stream

We examined the relationship between larval fish numbers and discharge during a high flow event in Bear Creek, Arkansas, a small Ozark stream. Additionally, we examined the relationship between fish numbers and time of day, and the spatial distribution of families and size classes. A total of 3,083 fish from five families were collected. Leuciscidae was the dominant family collected, followed by Percidae, and Catostomidae. Larval fish in Bear Creek were not susceptible to increased discharge from the flood event, as all three families exhibited strong significant negative relationships to discharge at night when discharge began to decline. Larval fish in Bear Creek drifted significantly more at night than during the day, with the exception of large percids, which exhibited no diel pattern. Leuciscidae and small Percidae showed a spatial pattern of distribution across the stream at night, with higher drift densities in near shore nets. The results from our study indicate that fish drift in Bear Creek was an active process, with most larval fish drifting in response to decreased light intensity. We suggest future studies consider the effects of flood intensity on larval fish drift relative to diel periodicity.

Arkansas↗
USGS2014

Sampling characteristics and calibration of snorkel counts to estimate stream fish populations

Snorkeling is a versatile technique for estimating lotic fish population characteristics; however, few investigators have evaluated its accuracy at population or assemblage levels. We evaluated the accuracy of snorkeling using prepositioned areal electrofishing (PAE) for estimating fish populations in a medium-sized Appalachian Mountain river during fall 2008 and summer 2009. Strip-transect snorkel counts were calibrated with PAE counts in identical locations among macrohabitats, fish species or taxa, and seasons. Mean snorkeling efficiency (i.e., the proportion of individuals counted from the true population) among all taxa and seasons was 14.7% (SE, 2.5%), and the highest efficiencies were for River Chub Nocomis micropogon at 21.1% (SE, 5.9%), Central Stoneroller Campostoma anomalum at 20.3% (SE, 9.6%), and darters (Percidae) at 17.1% (SE, 3.7%), whereas efficiencies were lower for shiners ( Notropis spp., Cyprinella spp., Luxilus spp.) at 8.2% (SE, 2.2%) and suckers (Catostomidae) at 6.6% (SE, 3.2%). Macrohabitat type, fish taxon, or sampling season did not significantly explain variance in snorkeling efficiency. Mean snorkeling detection probability (i.e., probability of detecting at least one individual of a taxon) among fish taxa and seasons was 58.4% (SE, 6.1%). We applied the efficiencies from our calibration study to adjust snorkel counts from an intensive snorkeling survey conducted in a nearby reach. Total fish density estimates from strip-transect counts adjusted for snorkeling efficiency were 7,288 fish/ha (SE, 1,564) during summer and 15,805 fish/ha (SE, 4,947) during fall. Precision of fish density estimates is influenced by variation in snorkeling efficiency and sample size and may be increased with additional sampling effort. These results demonstrate the sampling properties and utility of snorkeling to characterize lotic fish assemblages with acceptable efficiency and detection probability, less effort, and no mortality, compared with traditional sampling methods.

North American Journal of Fisheries Management↗
USGS2016

Upstream movements of Atlantic Salmon in the Lower Penobscot River, Maine following two dam removals and fish passage modifications

The Penobscot River Restoration Project (PRRP), to be completed in 2016, involved an extensive plan of dam removal, increases in hydroelectric capacity, and fish passage modifications to increase habitat access for diadromous species. As part of the PRRP, Great Works and Veazie dams were removed, making Milford Dam the first impediment to federally endangered Atlantic Salmon Salmo salar . Upstream habitat access for Atlantic Salmon is dependent upon successful and timely passage at Milford Dam because nearly all suitable spawning habitat is located upstream. In 2014 and 2015, a total of 73 adult salmon were radio-tagged to track their upstream movements through the Penobscot River to assess potential delays at (1) the dam remnants, (2) the confluence of the Stillwater Branch and the main stem of the Penobscot River below the impassable Orono Dam, and (3) the Milford Dam fish lift (installed in 2014). Movement rates through the dam remnants and the Stillwater confluence were comparable to open river reaches. Passage efficiency of the fish lift was high in both years (95% and 100%). However, fish experienced long delays at Milford Dam, with approximately one-third of fish taking more than a week to pass in each year, well below the Federal Energy Regulatory Commission passage standard of 95% within 48 h. Telemetry indicates most fish locate the fishway entrance within 5 h of arrival and were observed at the entrance at all hours of the day. These data indicate that overall transit times through the lower river were comparable to reported movement rates prior to changes to the Penobscot River due to the substantial delays seen at Milford Dam. The results of this study show that while adult Atlantic Salmon locate the new fish lift entrance quickly, passage of these fish was significantly delayed under 2014–2015 operations.

Maine↗
USGS2017

Recruitment phenology and pelagic larval duration in Caribbean amphidromous fishes

Amphidromous fishes are major components of oceanic tropical island stream ecosystems, such as those of the Caribbean island, Puerto Rico. Fishes with this life history face threats related to the requirement for connectivity between freshwater and marine environments during early life stages. Pelagic larval duration and recruitment phenology are 2 early life-history processes that are crucial for the biology, ecology, conservation, and management of amphidromous fishes. However, these processes are understudied in the Caribbean in general and have never been quantified in Puerto Rico. We quantified recruit abundance, recruitment phenology, and pelagic larval duration of several Caribbean amphidromous fish species in multiple rivers in Puerto Rico and explored the effects of environmental variables on recruit abundances. Two fish taxa—sirajo goby ( Sicydium spp.) and River Goby ( Awaous banana )—were exceptionally abundant as postlarvae and recruited to Caribbean rivers in pulsed migration episodes that were periodic at annual and lunar scales. Sirajo goby and River Goby recruit abundances varied among rivers, were greater at sunrise than at sunset, and were positively related to river discharge. The pelagic larval duration of 4 fish taxa ranged from a minimum of 28 d to a maximum of 103 d with means between 43 ± 7 d (SD) and 65 ± 11 d. We identified the last-quarter moon phase during the months of June through January as periods of maximum amphidromous fish recruitment to freshwater streams. The results and conclusions of our study can be applied to identify critical times to maintain river–ocean connectivity and stream flow for the benefit of the amphidromous fish population dynamics, stream ecology, and natural resources of the Caribbean.

Puerto Rico↗
USGS2022

Fish-inspired segment models for undulatory swimming

Many aquatic animals swim by undulatory body movements and understanding the diversity of these movements could unlock the potential for designing better underwater robots. Here, we analyzed the steady swimming kinematics of a diverse group of fish species to investigate whether their undulatory movements can be represented using a series of interconnected multi-segment models, and if so, to identify the key factors driving the segment configuration of the models. Our results show that the steady swimming kinematics of fishes can be described successfully using parsimonious models, 83% of which had fewer than five segments. In these models, the anterior segments were significantly longer than the posterior segments, and there was a direct link between segment configuration and swimming kinematics, body shape, and Reynolds number. The models representing eel-like fishes with elongated bodies and fishes swimming at high Reynolds numbers had more segments and less segment length variability along the body than the models representing other fishes. These fishes recruited their anterior bodies to a greater extent, initiating the undulatory wave more anteriorly. Two shape parameters, related to axial and overall body thickness, predicted segment configuration with moderate to high success rate. We found that head morphology was a good predictor of its segment length. While there was a large variation in head segments, the length of tail segments was similar across all models. Given that fishes exhibited variable caudal fin shapes, the consistency of tail segments could be a result of an evolutionary constraint tuned for high propulsive efficiency. The bio-inspired multi-segment models presented in this study highlight the key bending points along the body and can be used to decide on the placement of actuators in fish-inspired robots, to model hydrodynamic forces in theoretical and computational studies, or for predicting muscle activation patterns during swimming.

Bioinspiration & Biomimetics↗
USGS2024

A transferable approach for quantifying benthic fish sizes and densities in annotated underwater images

1. Benthic fishes are a common target of scientific monitoring but are difficult to quantify because of their close association to bottom habitats that are hard to access. Advances in image-acquisition technologies, machine vision, and deep learning have made capturing and quantifying fishes with cameras increasingly feasible. We present a method and open-source software called ‘FishScale’ to estimate benthic fish lengths, numeric abundance, and biomass density in underwater environments assessed with down-looking monocular images. 2. ‘FishScale’ estimates fish abundances and size frequencies from near-nadir monocular images where fish have already been semantically segmented. The software accounts for lens distortion, underwater magnification effects, and fish body curvature to automatically estimate fish lengths and the areas of images where they were captured. Numeric and biomass density are estimated through a deterministic machine vision algorithm that requires a user-provided length-weight relationship for species of interest and calibration images. 3. Results from validation studies show that lengths and weights can be estimated with high accuracy and precision for round goby ( Neogobius melanostomus ) captured in distorted action camera images, and from large-bodied lake trout ( Salvelinus namaycush ) imaged with a machine vision camera. The real-world utility of the approach is demonstrated in a case study estimating round goby abundances and size frequencies along a 10.7-km transect surveyed with an autonomous underwater vehicle in Lake Michigan, USA. 4. Our validation studies demonstrate that the approach estimates benthic and benthopelagic fish lengths and weights with little bias and good accuracy and precision for species with much different body shapes and sizes. The method is applicable to data collected using a variety of nadir imaging approaches with widespread applications to fisheries monitoring and quantification of any species or object for which nadir images and working distances between the camera and feature of interest are available.

Illinois, Indiana, Michigan, Wisconsin↗