Forage Fish Research Articles

Evaluating top-down, bottom-up, and environmental drivers of pelagic food web dynamics along an estuarine gradient.

Identification of the key biotic and abiotic drivers within food webs is important for understanding species abundance changes in ecosystems, particularly across ecotones where there may be strong variation in interaction strengths. Using structural equation models (SEMs) and four decades of integrated data from the San Francisco Estuary, we investigated the relative effects of top-down, bottom-up, and environmental drivers on multiple trophic levels of the pelagic food web along an estuarine salinity gradient and at both annual and monthly temporal resolutions. We found that interactions varied across the estuarine gradient and that the detectability of different interactions depended on timescale. For example, for zooplankton and estuarine fishes, bottom-up effects appeared to be stronger in the freshwater upstream regions, while top-down effects were stronger in the brackish downstream regions. Some relationships (e.g., bottom-up effects of phytoplankton on zooplankton) were seen primarily at annual timescales, whereas others (e.g., temperature effects) were only observed at monthly timescales. We also found that the net effect of environmental drivers was similar to or greater than bottom-up and top-down effects for all food web components. These findings can help identify which trophic levels or environmental factors could be targeted by management actions to have the greatest impact on estuarine forage fishes and the spatial and temporal scale at which responses might be observed. More broadly, this study highlights how environmental gradients can structure community interactions and how long-term data sets can be leveraged to generate insights across multiple scales.

Anatomical hooking location and bleeding occurrence in northern pike (Esox lucius) caught in recreational catch-and-release angling in a lake with reduced prey fish availability

Catch-and-release (C&R) is a common practice in recreational angling for northern pike (Esox lucius), whereby the angler releases the fish back into the water after capture with the expectation that it will survive with negligible stress and physical injuries. This may not always be the case, as hooking in critical anatomical locations, such as gills, esophagus, and stomach, increases the frequency of bleeding at the hook wound and has been recognized as a key determinant of post-release mortality in pike. Several factors (e.g. bait type and size, hook characteristics, and fish length) can influence the risk of hooking in critical locations, and the fish’s willingness to strike the fishing lure/bait may largely depend on previous feeding history and associated motivation to feed. In this respect, food deprivation and greater feeding motivation can be expected to result in an intensified response and more forceful attacks on fishing lures/baits, which could increase the risk of hooking injuries in sensitive tissues, as the fish may ingest the hook more deeply. Here, we assess the hooking location and bleeding occurrence in pike caught on soft plastic shads and baitfish in a shallow eutrophic lake. The prey fish density of this lake, primarily common roach (Rutilus rutilus), has been substantially reduced by seining as part of a lake restoration project. Experimental angling sessions took place at the end of 2020 and 2022, approximately 1–2 months and 25–26 months after the initial reduction in prey fish density, respectively. Removal of roach from the lake was also done regularly by seining after the angling sessions in 2020. Pike angled in 2022 had significantly lower body condition than individuals caught in 2020, indicating that mass removal of roach from the lake resulted in food shortage. The risk of hooking in critical locations (herein defined as hooking in gills and back of mouth) was not associated to angling year, body condition, or length of the pike. However, across the two angling years, the incidence of hooking in critical locations was higher for soft plastic shads compared to baitfish (24.2% versus 7.4%). Pike caught on soft plastic shads also bled more frequently than individuals caught on baitfish (19.7% versus 6.2%), most likely due to the fact that hooking in the gills almost exclusively occurred with soft plastic shads. Bleeding propensity was also not related to angling year, body condition, or fish length. Hence, the present study found no evidence that long-term reductions in food availability and resulting declines in body condition influence how pike strike and ingest fishing lures/baits, at least not in a manner that increases the risk of hooking injuries in sensitive locations. Instead, bait type seems to play the largest role for the observed bleeding patterns. We recommend that future studies investigate the potential effects of C&R angling on the post-release survival of pike with reduced body condition due to limited food availability.

Laboratory‐bred Longfin Smelt produced offspring in the first year in captivity

AbstractObjectiveThis study aims to develop the culture methods for Longfin Smelt Spirinchus thaleichthys in a laboratory setting, achieving the first production of a fully captive second generation (F2). The objective includes understanding the critical factors influencing the breeding and maturation of this species in captivity, contributing to conservation efforts and potential revival of this threatened species.MethodsLongfin Smelt broodstock were collected from the San Francisco Estuary and reared in controlled conditions at the University of California Davis Fish Conservation and Culture Laboratory (FCCL). The study involved spawning of wild broodstock, rearing of first generation (F1) progeny to adulthood, and subsequent spawning to produce F2 offspring. Key variables such as salinity, temperature, and diet were carefully managed throughout the process. Fertilization and hatching rates were calculated, and the larvae were reared using the same methods to closely monitor and understand their growth and development.ResultFirst generation Longfin Smelt successfully matured and spawned at age 1, earlier than commonly observed in the wild. From five crosses, four produced viable offspring. The study recorded a range of fertilization rates (10–40%) and high hatching rates (75–97%). Salinity was identified as a critical factor in both larval development and adult maturation. While initial larval survival was challenging, the larval rearing system used in this study proved effective.ConclusionThe study represents a major breakthrough in the cultivation of Longfin Smelt, showing that it is possible to complete their life cycle under controlled conditions. It has provided valuable understanding of the maturation and breeding processes in these fish, with an emphasis on the influence of salinity. These outcomes are crucial for conservation strategies, offering the potential to help establish a refuge population and laying the groundwork for further research aimed at refining captive breeding methods for this species.

Impact of climate variability on moonfish (Mene maculata) catch rate in the waters off southwestern Taiwan

AbstractA commercially significant small coastal forage fish, moonfish (Mene maculata), accounts for almost 98% of Taiwanese purse seine capture, primarily in the southwestern Taiwan region. Research indicates that climate indices affect coastal fish catch and dispersal, while the link between moonfish and climatic variability in this region is still unclear. This study found that the delayed period of Pacific Decadal Oscillation (PDO), North Pacific Oscillation (NPO) and North Pacific Gyre Oscillation (NPGO) affect moonfish distribution and catch rates off southwestern Taiwan. Understudied are the environmental factors connected to these oscillations and their delayed consequences on moonfish catch rates. We focussed on Taiwan purse seiner capture rates (catch per unit effort or CPUE) of moonfish in southwestern Taiwan from 2014 to 2020 and delayed oscillation occurrences up to 5 years to better understand these processes. CPUE demonstrated a 3 to 4‐year positive connection (r > 0.5) with NPGO, NPO and PDO. The region's moonfish catch rates were most affected by NPGO with a 4‐year lag, followed by a 3‐year lag of PDO and lastly a 4‐year lag of NPO, according to the results of generalized additive models (GAMs). All the three oscillations had the greatest impact on moonfish catchability when a lag of >2 years was present. Between 2014 and 2020, moonfish CPUE fluctuated, peaking in 2019. The climatic parameters that affect moonfish in southwestern Taiwan and the Taiwanese purse seine fisheries catches are shown by this study.

Thiamine Deficiency M74 Developed in Salmon (Salmo salar) Stocks in Two Baltic Sea Areas after the Hatching of Large Year-Classes of Two Clupeid Species—Detected by Fatty Acid Signature Analysis

Lipid-related thiamine (vitamin B1) deficiency of Baltic salmon (Salmo salar), the M74 syndrome, is generally caused by feeding on abundant young sprat (Sprattus sprattus) in the Baltic Proper, the main foraging area of these salmon. In 2014, a strong year-class of sprat was hatched in the Baltic Proper, and a strong herring (Clupea harengus) year-class was hatched in the Gulf of Bothnia, where herring is the dominant salmon prey. The fatty acid (FA) signatures of prey fish in muscle or eggs of second sea-year spawners suggested that 27% of wild River Simojoki and 68% of reared River Dal salmon remained in the Gulf of Bothnia in 2014 instead of continuing to the Baltic Proper. In 2016, 23% of the M74 females of the River Simojoki and 58% of the River Dal originated from the Gulf of Bothnia, and 13% and 16%, respectively, originated from the Baltic Proper. Some salmon from the River Neris in the southern Baltic Proper had also been feeding in the Gulf of Bothnia. In general, low free thiamine (THIAM) concentration in eggs was associated with high lipid content and high docosahexaenoic acid (DHA, 22:6n−3) and n−3 polyunsaturated FA (n−3 PUFA) concentrations in muscle but not in eggs. A higher THIAM concentration and lower proportions of DHA and n−3 PUFAs in Arctic Ocean salmon eggs, despite higher egg lipid content, indicated that their diet contained fewer fatty fish than the Baltic salmon diet. Hence, M74 originated by foraging heavily on young fatty sprat in the Baltic Proper or herring in the Gulf of Bothnia.

Forage fish: Pacific herring in Alaska

Forage fish: Pacific herring in Alaska W. Scott Pegau and Hayley Hoover discuss the plight of forage fish, with a particular emphasis on understanding the lack of recovery of Pacific herring in Prince William Sound, Alaska. Pacific herring (Fig. 1) are food for fish, birds, and marine mammals and are an important subsistence and commercial fisheries resource. They are among the most numerous forage fishes in Prince William Sound, Alaska, yet their population is a small fraction of what it was in the late 1980s. The biomass dropped from around a peak of over 140 metric tons to about 20 metric tons in a few years in the early 1990s (Fig. 2). The drop was most likely the result of a disease outbreak. Since then, the population has remained around 20 metric tons except for a recent decline to about five metric tons.

Linking climate stressors to ecological processes in ecosystem models, with a case study from the Gulf of Alaska

Abstract As climate stressors are impacting marine ecosystems and fisheries across the world, ecosystem models that incorporate environmental variables are increasingly used to inform ecosystem-based fisheries management. The assumptions around the mechanistic links between climate stressors and the biological processes in these models are important, but the implications for model outcomes of which stressors are captured and how they affect modeled biological processes are seldom explored. Using a whole-ecosystem model (Atlantis) for the Gulf of Alaska, we explore the effects of capturing physical (increased temperature) and biogeochemical (decreased low trophic level productivity) climate stressors, and disentangle the effects of each stressor on the productivity of forage fish, groundfish, and fish-eating seabirds. We then test the effects of alternative model specifications of temperature-driven habitat determination and bioenergetics. Increased temperature resulted in increased weight-at-age and higher natural mortality, while decreased productivity resulted in decreased weight-at-age and higher natural mortality. Model specification of temperature dependence of movement and spawning influenced model outcomes, and decoupling these processes from temperature led to overly optimistic biomass predictions. As the use of ecosystem models to inform fisheries management becomes more operational, we illustrate that the assumptions around the links between climate stressors and ecological processes influence model outcomes.

An updated end-to-end ecosystem model of the Northern California Current reflecting ecosystem changes due to recent marine heatwaves.

The Northern California Current is a highly productive marine upwelling ecosystem that is economically and ecologically important. It is home to both commercially harvested species and those that are federally listed under the U.S. Endangered Species Act. Recently, there has been a global shift from single-species fisheries management to ecosystem-based fisheries management, which acknowledges that more complex dynamics can reverberate through a food web. Here, we have integrated new research into an end-to-end ecosystem model (i.e., physics to fisheries) using data from long-term ocean surveys, phytoplankton satellite imagery paired with a vertically generalized production model, a recently assembled diet database, fishery catch information, species distribution models, and existing literature. This spatially-explicit model includes 90 living and detrital functional groups ranging from phytoplankton, krill, and forage fish to salmon, seabirds, and marine mammals, and nine fisheries that occur off the coast of Washington, Oregon, and Northern California. This model was updated from previous regional models to account for more recent changes in the Northern California Current (e.g., increases in market squid and some gelatinous zooplankton such as pyrosomes and salps), to expand the previous domain to increase the spatial resolution, to include data from previously unincorporated surveys, and to add improved characterization of endangered species, such as Chinook salmon (Oncorhynchus tshawytscha) and southern resident killer whales (Orcinus orca). Our model is mass-balanced, ecologically plausible, without extinctions, and stable over 150-year simulations. Ammonium and nitrate availability, total primary production rates, and model-derived phytoplankton time series are within realistic ranges. As we move towards holistic ecosystem-based fisheries management, we must continue to openly and collaboratively integrate our disparate datasets and collective knowledge to solve the intricate problems we face. As a tool for future research, we provide the data and code to use our ecosystem model.

Between family variation in EPA and DHA storage among Atlantic salmon (Salmo salar) fed a fish oil-free diet

Biosynthesis and storage of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is under dietary and genetic control in Atlantic salmon (Salmo salar). Enhanced EPA and DHA biosynthesis and storage may improve utilization, and thus reduce marine forage fish oil use in aquafeeds. To determine phenotypic variability in EPA and DHA tissue content and growth performance, 50 families (n = 30 salmon/family, 48 g/fish initial weight) of Atlantic salmon (Saint John River strain) were reared in freshwater and fed either a fish oil (FO) control diet or FO-free diet. After 16 weeks, body size was recorded. Salmon fed the FO-free diet overall showed significantly lower growth performance compared to salmon fed the FO control diet, regardless of family. To determine the relationship between growth and FA content, the five families with the highest and the five families with the lowest weight gain were sampled for tissue and liver FA analysis. There was a significant interaction between growth and diet. The family x diet interaction was significant for final weight, final length, weight gain, growth rate and feed conversion ratio. Among the five fastest growing families, there was a significant family effect for EPA and DHA storage in the liver but not for muscle. Among the five slowest growing families, by comparison salmon had similar liver DHA and EPA content, independent of diet treatment. Family and diet were interacting factors that determine EPA and DHA storage in liver. Certain fast-growing families also had significantly higher DHA content in liver and muscle. This study demonstrates the potential for selecting families that can better utilize a diet without marine forage fish oil.

Demographic response of osprey within the lower Chesapeake Bay to fluctuations in menhaden stock

Forage fish support the largest fisheries in the world and play a vital role in marine food webs by transferring energy from plankton to consumers within higher trophic levels. Growing commercial demand for these species and concern for the impact of over harvest on predator populations has driven a paradigm shift in management objectives from maximizing economic return to the establishment of ecosystem-based limits on harvest rates. How well current harvest policy supports noncommercial species like piscivorous birds remains poorly understood. We investigated the relationship between osprey breeding performance within the lower Chesapeake Bay and a menhaden stock index during a period (1974-2021) when the menhaden index fluctuated over 35-fold. Reproductive rate (young/pair/year), brood provisioning (fish/10-h) and the proportion of menhaden in the diet all declined during the study period. Indicators of food stress including brood reduction and nest failure increased during the study period. The population transitioned from reproductive surplus (demographic source) to reproductive deficit (demographic sink). A significant relationship between reproductive rate and the menhaden index suggests that osprey population viability requires that the menhaden stock be restored to 1980s levels. Current ecological reference points based on the food requirements of predatory fish are unlikely to protect the osprey population. We suggest the establishment of menhaden or reproductive thresholds designed to allow osprey to meet demographic targets (1.15 young/pair/year).

Collective dynamics in active solids

After 25 years of research activity, the physics of collective motions -- flights of starlings, shoals of fish, micro-swimmers or artificial walkers -- is well understood. Here, we describe a new form of self-organization, emerging from the coupling between elasticity and activity: collective actuation, the solid counterpart of collective movements.

Species identification of fish shoals using coupled split-beam and multibeam echosounders and two scuba-diving observational methods

Species identification remains crucial for interpreting acoustic backscatter delivered by active acoustic methodologies. The study took place in a Marine Protected Area where highly restricted areas were present such as no take zones. We used an innovative methodology coupling split-beam and multibeam echosounders to detect and classify monospecific fish shoals (i.e. schools or aggregations). Species identifications were realised by underwater visual censuses made by scientific divers. Two experimental protocols, where the divers gave the identifications instantaneously thanks to a communication wireframe, were tested: three roving scuba divers locating the shoals or a towed scuba diver directly behind the vessel. Energy responses, 3-D morphological, shape indexes and spatial descriptive variables of multiple independent samples of 4 observed fish species shoals (Atherina sp., Boops boops, Chromis chromis and Spicara maena) were calculated from the acoustic data. According to their behaviour and feeding strategy, significant differences in the acoustic variables were found between species. The combined use of acoustic data from both echosounders significantly improved the fish species classification. They were well discriminated using a Linear Discriminant Analysis (LDA), including for B. boops, C. chromis and S. maena, which were all observed in aggregations. Finally, we used this LDA model to allocate species to unknown shoals monitored by acoustics methods in the studied site, highlighting the interest of our methodology to predict bentho-pelagic and pelagic fish distributions in shallow waters. We suggest that these acoustic methods to discriminate fish species could provide valuable insights for marine management and decision-making.

Chronic social isolation affects feeding behavior of juvenile zebrafish (Danio rerio).

Many organisms exhibit social behaviors and are part of some scheme of social structure. Zebrafish are highly social, shoaling fish and therefore, social isolation may have notable impacts on their physiology and behavior. The objective of this study was to evaluate the effects of social isolation on feed intake, monoaminergic system related gene expression, and intestinal health of juvenile zebrafish fed a high-inclusion soybean meal based diet. At 20 days post-fertilization zebrafish were randomly assigned to chronic isolation (1 fish per 1.5 L tank) or social housing (6 fish per 9 L tank) with 18 tanks per treatment group (n = 18). Dividers were placed between all tanks to prevent visual cues between fish. Zebrafish were fed a commercial fishmeal based diet until 35 days post-fertilization and then fed the experimental high-inclusion soybean meal based diet until 50 days post-fertilization. At the end of the experiment (51 days post-fertilization), the mean total length, weight, and weight gain were not significantly different between treatment groups. Feed intake and feed conversion ratio were significantly higher in chronic isolation fish than in social housing fish. Expression of monoaminergic and appetite-related genes were not significantly different between groups. The chronic isolation group showed higher expression of the inflammatory gene il-1b, however, average intestinal villi width was significantly smaller and average length-to-width ratio was significantly higher in chronic isolation fish, suggesting morphological signs of inflammation were not present at the time of sampling. These results indicate that chronic isolation positively affects feed intake of juvenile zebrafish and suggest that isolation may be useful in promoting feed intake of less-palatable diets such as those based on soybean meal.

Length–weight relationships of the French pikes Esox spp. (Teleostei, Esocidae)

Length–weight relationships for Pike Esox aquitanicus and Esox lucius from France are provided. A total of 9070 specimens were collected, measured and weighted from 1981 to 2022 throughout France by Departmental Angling Federations and the French Agency of Biodiversity during their survey by electrofishing. For all species, the values of b are 2.960 for E. aquitanicus and 2.987 for Esox lucius. We hypothetize this difference by the poor environment where live the Aquitanian pike with no abundant available food and small prey fish species which do not contribute to good conditions for the growth. The study provides the first reference of length–weight relationships for E. aquitanicus.

Reproduction and commercial cultivation of chinese perch <i>Siniperca chuatsi</i> in conditions of a warm-water farm

A breeding stock of chinese perch was gotten in a warm-water farm located in the southern Far East of Russia, where the experiment is conducted on growing this species up to three years. Combined method of growing in tanks, warm-water fry ponds and cages was used for growing the fingerlings, but two- and three-year old perches were kept in cages only and fed with live and non-living low-value forage fish. There were attempts to train two-year-old perch to feed on wet artificial pellets. By the end of the experiment, three-year-old chinese perches of two size groups had the body weight of 700−880 g with the maximum of 1600 g. Feed costs for the growth of two- and three-year-old fish in the growing seasons were 2.7−3.9 and 5.3−5.6 kg per 1 kg gain, respectively; their survival was 98−100 %. In 2023, the two-year-old perches weighing 0.5−1.1 kg were used for the first time in spawning and their offspring were raised to an average weight of 60 g.

Potentiality of natural live food organisms in shrimp culture: A review

The aquaculture industry is growing quickly due to increased fish consumption and a decline in wild fish catch. About half of the world's seafood demand for human consumption is now met by farmed seafood. The aquafeed market is expanding along with the aquaculture sector. Some of the elements in shrimp feed are derived from terrestrial plants and low-value forage fishes (fish meal). It is impossible to produce more fish meals since doing so would harm the ocean's environment and sustainability. The reduction in shrimp feed cost can also be done by introducing low-cost, environment-friendly ingredients in shrimp feed formulation. Therefore, new and ecologically friendly shrimp (Litopenaeus vannamei) feed component sources must be created. Live food organisms are a preferable option for this since they provide a variety of essential amino acids and beneficial triglycerides like fat, vitamins, and colors in their cell metabolites. Microalgae biomasses also represent feasible ingredients for shrimp feed sources. Their distinctive variety of bioactive chemicals can enhance color and pellet quality, act as a bulk element in shrimp feed, and boost the viability of farmed species. Live food organisms have a great economic potential since they have the highest biomass productivity of all photosynthetic organisms. In addition to giving farmers and exporters a better choice for feeding their fish, the availability of on-grown live food would also open up the prospect of improving the performance and quality of the fish and shrimp through bioencapsulation. This review study examines the possibility of generating natural food biomass as a component in shrimp feed.

The combined effects of acidification and acute warming on the embryos of Pacific herring (Clupea pallasii)

Anthropogenic climate change is projected to affect marine ecosystems by challenging the environmental tolerance of individuals. Marine fishes may be particularly vulnerable to emergent climate stressors during early life stages. Here we focus on embryos of Pacific herring (Clupea pallasii), an important forage fish species widely distributed across the North Pacific. Embryos were reared under a range of temperatures (10-16°C) crossed with two pCO2 levels (600 and 2000 μatm) to investigate effects on metabolism and survival. We further tested how elevated pCO2 affects critical thermal tolerance (CTmax) by challenging embryos to short-term temperature fluctuations. Experiments were repeated on embryos collected from winter and spring spawning populations to determine if spawning phenology corresponds with different limits of environmental tolerance in offspring. We found that embryos could withstand acute exposure to 20°C regardless of spawning population or incubation treatment, but that survival was greatly reduced after 2-3 hours at 25°C. We found that pCO2 had limited effects on CTmax. The survival of embryos reared under chronically warm conditions (12°, 14°, or 16°C) was significantly lower relative to 10°C treatments in both populations. Oxygen consumption rates (MO2) were also higher at elevated temperatures and pCO2 levels. However, heart contraction measurements made 48 hours after CTmax exposure revealed a greater increase in heart rate in embryos reared at 10°C compared to 16°C, suggesting acclimation at higher incubation temperatures. Our results indicate that Pacific herring are generally tolerant of pCO2 but are vulnerable to acute temperature stress. Importantly, spring-spawning embryos did not clearly exhibit a higher tolerance to heat stress compared to winter offspring.

Persisting in extreme environments: What are the drivers of body conditions of introduced fish in high mountain lakes?

Abstract Salmonids are introduced in various ecosystems, including mountain lakes characterised by extreme environmental constraints. Although these constraints can affect salmonid body condition through direct and indirect pathways, they remain seldom explored despite their importance for understanding salmonid fitness and long‐term establishment. In order to fill this gap, we firstly fitted species‐specific weight–length relationships for three salmonid species in nine mountain lakes, and compared their allometric coefficients with those of 362 salmonid populations worldwide to identify potential differences in growth trajectory of salmonids in the studied lakes. We then investigated how thermal characteristics and lake morphometry could influence salmonid body conditions, both directly and indirectly through salmonid density, the presence of forage fish and resource densities. We calculated salmonid relative body condition Kn and used a structural equation model (SEM) to disentangle these direct and indirect effects. The values of allometric coefficients for the three species did not differ from those of most salmonids worldwide although ontogenetic changes in Salvelinus alpinus weight gain was observed. Kn differed significantly among the populations studied. The strongest effects were related to direct and indirect effects of lake morphometry, while thermal characteristics had mostly indirect effects on Kn. The strength and the sign of the indirect effects of morphometry and temperature were mediated by the direct effects of resource and salmonid densities on Kn. Kn estimates were greater in lakes with shallow basin slopes than those with steep slopes. Shallow basin slopes probably provide habitats that support high prey availability and require lower energy expenditure by salmonids compared to lakes with steep slopes dominated by pelagic habitats. Complementarily, higher winter and summer temperatures favour Kn by supporting higher prey densities and longer periods of feeding activity. Our results may help managers to select lakes that optimise sustainability of salmonid populations based on the joint effects of basin morphometry and the expected thermal modifications induced by global change.

Plastic, It's What's for Dinner: A Preliminary Comparison of Ingested Particles in Bottlenose Dolphins and Their Prey.

Microplastic ingestion was reported for common bottlenose dolphins (Tursiops truncatus) inhabiting Sarasota Bay, FL, USA, a community that also has prevalent exposure to plasticizers (i.e., phthalates) at concentrations higher than human reference populations. Exposure sources are currently unknown, but plastic-contaminated prey could be a vector. To explore the potential for trophic exposure, prey fish muscle and gastrointestinal tract (GIT) tissues and contents were screened for suspected microplastics, and particle properties (e.g., color, shape, surface texture) were compared with those observed in gastric samples from free-ranging dolphins. Twenty-nine fish across four species (hardhead catfish, Ariopsis felis; pigfish, Orthopristis chrysoptera; pinfish, Lagodon rhomboides; and Gulf toadfish, Opsanus beta) were collected from Sarasota Bay during September 2022. Overall, 97% of fish (n = 28) had suspected microplastics, and GIT abundance was higher than muscle. Fish and dolphin samples contained fibers and films; however, foams were common in dolphin samples and not observed in fish. Suspected tire wear particles (TWPs) were not in dolphin samples, but 23.1% and 32.0% of fish muscle and GIT samples, respectively, contained at least one suspected TWP. While some similarities in particles were shared between dolphins and fish, small sample sizes and incongruent findings for foams and TWPs suggest further investigation is warranted to understand trophic transfer potential.

Unconfined fishway design, implementation, and assessment for the emerald Shiner (Notropis atherinoides) in the Upper Niagara River, New York

An engineered seawall in need of repair along the Upper Niagara River in Buffalo, NY, was previously identified as a hydrodynamic barrier to the migration of a small but important prey fish, the emerald shiner (Notropis atherinoides), and its connection to the upstream environs of Lake Erie. This study proposed a novel unconfined fishway design to be incorporated into existing plans for rehabilitation of the seawall at Broderick Park. The proposed fishway was developed using a two-dimensional depth-averaged numerical model, it was explored by placing the target fish into a physical model, and the constructed demonstration project was assessed using field measurements and observations. The numerical model showed that modular baffles attached to the seawall reduced the nearshore flow velocities to about 0.4 to 0.6 m s−1, which was within the acceptable range of velocities for the upstream migration of the emerald shiners. The physical experiments demonstrated that most emerald shiners chose to swim toward, within, or close to the proposed fishway in the presence of higher flow velocities within the main channel region. The proposed fishway design was integrated into the seawall repair as part of a demonstration project supervised by the US Army Corps of Engineers-Buffalo District. Post-construction assessment of the installation showed that (1) the modular baffles reduced time-averaged flow velocities near the seawall and water surface, (2) while very few shiners were observed swimming along the pre-construction seawall, large numbers were observed swimming upstream within this reduced flow velocity corridor created by the baffles, and (3) the structural integrity of the installation proved to be durable and resilient to extremely harsh environmental conditions. This study explored a new approach to fishway design for the passage of relatively small fish in large rivers, and it effectively melded fishway requirements into seawall restoration in concert with the expectations of multiple stakeholders.