Forage Fish Research Articles

The untapped potential of seascape genomics in the North Pacific

Seascape genomics provides a powerful framework to evaluate the presence and strength of environmental pressures on marine organisms, as well as to forecast long term species stability under various perturbations. In the highly productive North Pacific, forage fishes, key trophic links across ecosystems, are also contending with a rapidly warming climate and a litany of associated oceanographic changes (e.g., changes in salinity, dissolved oxygen, pH, primary production, etc.). These changes can place substantial selective pressures on populations over space and time. While several population genomics studies have targeted forage fishes in the North Pacific, none have formally analyzed the interactions between genotype and environment. However, when population genomics studies provide collection location information and other critical data, it is possible to supplement a published genomic dataset with environmental data from existing public databases and perform “post hoc seascape genomics” analyses. In reviewing the literature, we find pertinent metadata (dates and locations of sample collection) are rarely provided. We identify specific factors that may impede the application of seascape genomics methods in the North Pacific. Finally, we present an approach for supplementing data in a reproducible way to allow for post hoc seascape genomics analysis, in instances when metadata are reported. Overall, our goal is to demonstrate – via literature review – the utility and importance of seascape genomics to understanding the long term health of forage fish species in the North Pacific.

A Package of Script Codes, POSIBIOM for Vegetation Acoustics: POSIdonia BIOMass

Macrophytes and seagrasses play a crucial role in a variety of functions in marine ecosystems and respond in a synchronized manner to a changing climate and the subsequent ecological status. The monitoring of seagrasses is one of the most important issues in the marine environment. One rapidly emerging monitoring technique is the use of acoustics, which has advantages compared to other remote sensing techniques. The acoustic method alone is ambiguous regarding the identities of backscatterers. Therefore, a computer program package was developed to identify and estimate the leaf biometrics (leaf length and biomass) of one of the most common seagrasses, Posidonia oceanica. Some problems in the acoustic data were resolved in order to obtain estimates related to problems with vegetation as well as fisheries and plankton acoustics. One of the problems was the “lost” bottom that occurred during the data collection and postprocessing due to the presence of acoustic noise, reverberation, interferences and intense scatterers, such as fish shoals. Another problem to be eliminated was the occurrence of near-bottom echoes belonging to submerged vegetation, such as seagrasses, followed by spurious echoes during the survey. The last one was the recognition of the seagrass to estimate the leaf length and biomass, the calibration of the sheaths/vertical rhizomes of the seagrass and the establishment of relationships between the acoustic units and biometrics. As a result, an autonomous package of code written in MATLAB was developed to perform all the processes, named “POSIBIOM”, an acronym for POSIdonia BIOMass. This study presents the algorithms, methodology, acoustic–biometric relationship and mapping of biometrics for the first time, and discusses the advantages and disadvantages of the package compared to the software dedicated to the bottom types, habitat and vegetation acoustics. Future studies are recommended to improve the package.

DNA metabarcoding of cloacal swabs provides insight into diets of highly migratory sharks in the Mid-Atlantic Bight.

The abundances of migratory shark species observed throughout the Mid-Atlantic Bight (MAB) during productive summer months suggest that this region provides critical habitat and prey resources to these taxa. However, the principal prey assemblages sustaining migratory shark biomass in this region are poorly defined. We applied high-throughput DNA metabarcoding to shark feces derived from cloacal swabs across nine species of Carcharhinid and Lamnid sharks to (1) quantify the contribution of broad taxa (e.g., invertebrates, fishes) supporting shark biomass during seasonal residency in the MAB and (2) determine whether the species displayed distinct dietary preference indicative of resource partitioning. DNA metabarcoding resulted in high taxonomic (species-level) resolution of shark diets with actinopterygian and elasmobranch fishes as the dominant prey categories across the species. DNA metabarcoding identified several key prey groups consistent across shark taxa that are likely integral for sustaining their biomass in this region, including Atlantic menhaden (Brevoortia tyrannus), Atlantic mackerel (Scomber scombrus), and benthic elasmobranchs, including skates. Our results are consistent with previously published stomach content data for the shark species of similar size range in the Northwest Atlantic Ocean, supporting the efficacy of cloacal swab DNA metabarcoding as a minimally invasive diet reconstruction technique. The high reliance of several shark species on Atlantic menhaden could imply wasp-waist food-web conditions during the summer months, whereby high abundances of forage fishes sustain a diverse suite of migratory sharks within a complex, seasonal food web.

Trends in larval densities, spawning timing, and site quality of capelin (Mallotus villosus) across bays and habitats in Newfoundland, Canada

Abstract Capelin is a short-lived forage fish species that underwent a population collapse in 1991 on the Newfoundland and Labrador Shelf, Canada (Northwest Atlantic Fisheries Organization Divisions 2J3KL) and has not recovered. The collapsed stock is characterized by delayed spawning timing and low recruitment. As year-class strength is set early in life, long-term larval monitoring at an intertidal spawning site in Trinity Bay (TB) is used as a proxy for stock-wide recruitment. Capelin spawn at both intertidal and subtidal habitats; however, there is minimal larval information from bays with a high incidence of subtidal spawning. We aimed to (i) compare inter-annual trends in temperatures, timing of spawning, and annual larval densities between two northeastern bays [TB and Notre Dame Bay (NDB)] and (ii) compare habitat quality metrics and larval densities between subtidal and intertidal sites in NDB. The date of first spawning in TB and NDB was positively correlated, suggesting that years with delayed spawning are experienced shelf-wide. While larval density was lower in NDB compared to TB, inter-annual trends were similar. In NDB, larval densities at both intertidal and subtidal spawning habitats were similar within a year, but temperatures and the proportion of dead eggs were lower at subtidal sites. These habitat quality metrics, however, were not related to annual larval density. These findings improve our knowledge on sources of capelin productivity, including the potential importance of subtidal spawning to recruitment dynamics.

Seasonal variation in activity and nearshore habitat use of Lake Trout in a subarctic lake

BackgroundIn lake ecosystems, predatory fish can move and forage across both nearshore and offshore habitats. This coupling of sub-habitats, which is important in stabilizing lake food webs, has largely been assessed from a dietary perspective and has not included movement data. As such, empirical estimates of the seasonal dynamics of these coupling movements by fish are rarely quantified, especially for northern lakes. Here we collect fine-scale fish movement data on Lake Trout (Salvelinus namaycush), a predatory cold-water fish known to link nearshore and offshore habitats, to test for seasonal drivers of activity, habitat use and diet in a subarctic lake.MethodsWe used an acoustic telemetry positioning array to track the depth and spatial movements of 43 Lake Trout in a subarctic lake over two years. From these data we estimated seasonal 50% home ranges, movements rates, tail beat activity, depth use, and nearshore habitat use. Additionally, we examined stomach contents to quantify seasonal diet. Data from water temperature and light loggers were used to monitor abiotic lake conditions and compare to telemetry data.ResultsLake Trout showed repeatable seasonal patterns of nearshore habitat use that peaked each spring and fall, were lower throughout the long winter, and least in summer when this habitat was above preferred temperatures. Stomach content data showed that Lake Trout acquired the most nearshore prey during the brief spring season, followed by fall, and winter, supporting telemetry results. Activity rates were highest in spring when feeding on invertebrates and least in summer when foraging offshore, presumably on large-bodied prey fish. High rates of nearshore activity in fall were associated with spawning. Nearshore habitat use was widespread and not localized to specific regions of the lake, although there was high overlap of winter nearshore core areas between years.ConclusionsWe provide empirical demonstrations of the seasonal extent to which a mobile top predator links nearshore and offshore habitats in a subarctic lake. Our findings suggest that the nearshore is an important foraging area for Lake Trout for much of the year, and the role of this zone for feeding should be considered in addition to its traditional importance as spawning habitat.

The potential of insects as alternative animal protein source for livestock feeding

The livestock industry as an important component of general agriculture is a key contributor to economic growth and development of any nation. In addition to having the capacity for earning revenue for the governments, it provides employment, food, farm energy, manure, fuel and transport. Currently, important protein ingredients for animal feed are fish meal, processed animal proteins and soybean meal. However, in the European Union the use of processed animal proteins in animal feed is prohibited due to the TSE legislation, globally land availability for soya cultivation is limited, while marine overexploitation has reduced the abundance of small pelagic forage fish from which fish meal and fish oil is derived. The growing scarcity of resources to produce these increasingly demanded ingredients has doubled prices during the last five years, while it already represents 60-70% of production costs. So, alternative (animal) protein sources for livestock and aquaculture are urgently needed.Insects are such an alternative animal protein source, which can sustainably reared on organic side streams. Reasons are that they have a favorable feed conversion efficiency, likely because they are cold-blooded. Insects contain between 30% and 70% protein on a dry matter basis. The protein content of the insect species is within the soybean/fish meal range and fat content is higher especially compared to (defatted) soybean meal. This review, however highlighted the environmental, health, livelihood and social benefits of insects. Recent efforts in feeding livestock, challenges limiting the use of insects as feed ingredients and moreover, the strategies for commercial production of insects as feed ingredients just to mention a few of the potentials of using insects for feeding livestock.

Evaluating a microalga (Schizochytrium sp.) as an alternative to fish oil in fish-free feeds for sablefish (Anoplopoma fimbria)

Alternative feeds are critical for the sustainable expansion of the marine finfish aquaculture industry. The industry uses wild-caught forage fish as a primary ingredient in farmed fish feeds. Alternative ingredients are needed to safeguard fisheries' sustainability and future aquaculture development. While there have been successes in alternative feeds, it is necessary to improve the existing options and identify alternative ingredients with higher concentrations of omega-3 polyunsaturated fatty acids (PUFAs). This study was designed to test a microalga, Schizochytrium sp., as a feed ingredient for sablefish (Anoplopoma fimbria) using six test diets. There were two fish-ingredient control diets: +FM+FO, which contained both fishmeal and fish oil, and −FM+FO, which contained fish oil, but no fishmeal. The remaining four diets contained alternative lipids and were completely fish-free. FF Flax contained flax oil as the only lipid source replacing fish oil. FF LowSc, FF ModSc, and FF HighSc contained a low, moderate, and high level of Schizochytrium sp. to replace fish oil, with flax oil content decreasing as the microalga increased. After a 20-week trial, sablefish growth differed across the feed treatments, with fish fed the high microalga-inclusion diet (FF HighSc) performing similarly to fish fed the fish-ingredient controls. Fulton's K condition factor, dry feed intake (DFI), and lipid productive value (LPV) were also influenced by treatment. For the four fish-free diets, specific growth rate increased with increasing inclusion of Schizochytrium sp. in the feed. Fillet fatty acid profiles were similarly influenced by diet treatment, generally reflecting the fatty acid profiles of the feed. Total fillet PUFAs were higher in sablefish from the fish-free treatments than the control treatments, with DHA increasing with increasing inclusion of dietary Schizochytrium. In contrast, EPA was higher in fillets from both fish-ingredient control treatments compared to fillets from the fish-free treatments, yet EPA remained higher than expected in sablefish fed the fish-free diets. Histologic evaluation of sablefish distal intestine and liver demonstrated that the microalga-inclusion diets were well tolerated and did not cause histomorphological changes in the tissues. These results suggest Schizochytrium sp. can increase PUFA concentrations in fish fillets without compromising fish health and growth, making it a viable ingredient for alternative sablefish feeds.

A mixed-species shoal including fewer heterospecifics is preferred by jack mackerel Trachurus japonicus juveniles

Mixed-species shoals of fishes were reported from various environments such as coral reefs and temperate lakes. The driving mechanism of forming mixed-species shoal can be either haphazard or a preferential choice by an individual. Here, we tested if jack mackerel Trachurus japonicus, a temperate marine pelagic fish, could choose a shoal composition using vision based on a choice experiment. Shoal preference of jack mackerel juveniles was evaluated by presenting shoals comprising one to four heterospecifics (half-lined cardinal Ostorhinchus semilineatus) out of four shoal members to the focal fish. When both conspecific and heterospecific shoals were presented to a single jack mackerel, the focal fish showed a preference for the conspecific rather than heterospecific shoal, indicating that they can choose a conspecific shoal based on the visual information. However, when a focal fish encountered both conspecific and mixed-species shoals including fewer heterospecifics (one out of four individuals), the latter was preferred. The result implies that jack mackerel can judge a preferable composition of shoal using visual information. The inclusion of fewer heterospecifics may be exploiting oddity effects, whereby minority species are exposed to relatively high vulnerability to predators, as well as resulting in reduced competition for food while maintaining predator vigilance in a shoal.

Effect of food quality on escape performance of Daphnia

Food quality (e.g. the presence of cyanobacteria) may affect the behavior, morphology and life history of cladocerans. However, little is known about how diet quality may affect the effectiveness of Daphnia's behavioral defenses against predators. Here we test the hypothesis that the presence of non-toxic cyanobacteria in Daphnia's diet reduces its ability to escape fish attack. The animals cultured under two different food quality regimes (green alga vs. cyanobacteria) were subjected to two types of predation experiments. In the first, we tested Daphnia's ability to avoid a predator whose feeding was simulated using a pipette, while in the second we tested Daphnia's ability to escape when confronted with a foraging fish (Poecilia reticulata). In both types of experiments, the ability to avoid predator attack was greater in Daphnia fed high quality green algae than in Daphnia fed low quality cyanobacteria.. We conclude that low food quality can affect the fitness of Daphnia not only by slowing their growth and reproduction rates, but also by increasing their susceptibility to predation.

The circumpolar impacts of climate change and anthropogenic stressors on Arctic cod (Boreogadus saida) and its ecosystem

Arctic cod (Boreogadus saida) is the most abundant forage fish in the Arctic Ocean. Here we review Arctic cod habitats, distribution, ecology, and physiology to assess how climate change and other anthropogenic stressors are affecting this key species. This review identifies vulnerabilities for different life stages across the entire distribution range of Arctic cod. We explore the impact of environmental (abiotic and biotic) and anthropogenic stressors on Arctic cod with a regional perspective in a scenario up to the year 2050 and identify knowledge gaps constraining predictions. Epipelagic eggs and larvae are more vulnerable to climate change and stressors than adults. Increased water temperatures, sea-ice decline, altered freshwater input, acidification, changing prey field, increased interspecific competition, new predators, and pollution are the principal stressors that will affect Arctic cod populations. Detrimental effects are likely to be greater in regions characterized by the advection of warmer Atlantic and Pacific waters. In contrast, Arctic cod may benefit from ocean warming in colder areas of the High Arctic. The risk from fisheries is moderate and primarily limited to bycatch. Overall, a decrease in suitable habitat and an associated decline in total Arctic cod biomass are predicted. In most Arctic seas, the relative abundance of Arctic cod within the fish community will likely fluctuate in accordance with cold and warm periods. A reduced abundance of Arctic cod will negatively affect the abundance, distribution, and physiological condition of certain predators, whereas some predators will successfully adapt to a more boreal diet. Regional management measures that recognize the critical role of Arctic cod are required to ensure that increased anthropogenic activities do not exacerbate the impacts of climate change on Arctic marine ecosystems. Ultimately, the mitigation of habitat loss for Arctic cod will only be achieved through a global reduction in carbon emissions.

Spawning characteristics of blue sprat (Spratelloides gracilis) in the waters of Penghu, central Taiwan Strait

Blue sprat (Spratelloides gracilis) is an economically valuable species that inhabits the central Taiwan Strait. However, despite the implementation of a local management scheme involving a closed season between 1 May and 1 June, the annual catch has rapidly decreased over the decades. Thus, the efficacy of the implemented regulations must be investigated. This study sought to clarify the reproductive biology, spawning ground, and behavior of this species in the waters of Penghu. In total, 6,549 specimens were collected between March 2021 and September 2022. Considering gonadosomatic index, group maturity, and oocyte diameter, we found that the spawning season (March–September) peaked in April; new cohorts were distinctly recruited after the spawning peak. The distribution of the spawning ground (latitude, 23°41′N to 23°43′N; longitude, 119°32′E to 119°39′E) was determined by considering the fishing area of mature females and DNA analysis of adhered eggs. We further noted shoals of fish darting in the bottom water without clear schooling movement, females’ abdomen frequently contacting substrata for eggs able to attach on during oviposition, and males releasing sperms making water milky white; these indicate that S. gracilis exhibits promiscuous spawning behavior. Our findings may facilitate the management and conservation of S. gracilis in this region.

Lingering Effects of Legacy Industrial Pollution on Yellow Perch of the Detroit River.

We used yellow perch (Perca flavescens) captured at four sites differing in legacy industrial pollution in the Lake St. Clair-Detroit River system to evaluate the lingering sublethal effects of industrial pollution. We emphasized bioindicators of direct (toxicity) and indirect (chronic stress, impoverished food web) effects on somatic and organ-specific growth (brain, gut, liver, heart ventricle, gonad). Our results show that higher sediment levels of industrial contaminants at the most downstream Detroit River site (Trenton Channel) are associated with increased perch liver detoxification activity and liver size, reduced brain size, and reduced scale cortisol content. Trenton Channel also displayed food web disruption, where adult perch occupied lower trophic positions than forage fish. Somatic growth and relative gut size were lower in perch sampled at the reference site in Lake St. Clair (Mitchell's Bay), possibly because of increased competition for resources. Models used to determine the factors contributing to site differences in organ growth suggest that the lingering effects of industrial pollution are best explained by trophic disruption. Thus, bioindicators of fish trophic ecology may prove advantageous to assess the health of aquatic ecosystems. Environ Toxicol Chem 2023;42:2158-2170. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Loss of sea ice and intermittent winds alter distributions and diet resources of young forage fish in the Chukchi sea

Loss of sea ice alters habitat for organisms that function as energetic links in Arctic food webs. To address the impacts of such changes on lower trophic levels we focus on forage fish during the early life stages (polar cod: Boreogadus saida and saffron cod: Eleginus gracilis) and copepods (Calanus spp. and Pseudocalanus spp.) in the Chukchi Sea with differing reliance on sea ice environments. We assess distributions throughout years of varying ice extent (2010–2013, 2015, 2017–2018) and diet resources during unprecedented warm years (2017, 2018) using stable isotope analyses (bulk δ13C and δ15N and δ13C compound-specific isotope analysis of amino acids). Calanus spp. and polar cod were found at relatively higher latitudes in closer proximity to recent sea ice, whereas saffron cod were rare and Pseudocalanus spp. were ubiquitous. Polar cod juveniles, but not larvae, were more common in open water, suggesting that low ice and northward ocean currents interact to influence juvenile distributions. Low summer sea ice also coincided with northward expansion of warm Pacific-origin water across the shelf. Stable isotope δ13C values reflected this latitudinal variation in water masses as well as inshore-offshore gradients due to convergence of ocean currents. When summer sea ice was absent during 2017, juvenile polar cod were dispersed across the shelf, abundances were low for both copepod taxa, isotopic niche was reduced for polar cod, and carbon sources for some larval polar cod reflected boreal-associated phytoplankton. Distributions and isotopic patterns suggest that under low ice conditions, along-shelf wind reversals and weak currents can lead to dominance of Pacific-origin water, mixing of organisms from various source locations, and reductions in sea ice-influenced environments. Northward expansion of subarctic water masses and organisms across the Chukchi shelf alters basal resources for lower trophic levels and modifies pelagic habitats to more uniformly resemble lower latitude marine ecosystems.

Quantifying inter-annual variability on the space-use of parental Northern Gannets (Morus bassanus) in pursuit of different prey types.

Spatial planning for marine areas of multi-species conservation concern requires in-depth assessment of the distribution of predators and their prey. Northern Gannets Morus bassanus are generalist predators that predate several different forage fishes depending on their availability. In the western North Atlantic, gannets employ different dive tactics while in pursuit of different prey types, performing deep, prolonged U-shaped dives when foraging on capelin (Mallotus villosus), and rapid, shallow, V-shaped dives when foraging on larger pelagic fishes. Therefore, much can be inferred about the distribution and abundance of key forage fishes by assessing the foraging behaviour and space-use of gannets. In this study, we aimed to quantify space-use and to determine areas of suitable foraging habitat for gannets in pursuit of different prey types using habitat suitability models and kernel density utilization distributions. We deployed 25 GPS/Time-depth recorder devices on parental Northern Gannets at Cape St. Mary's, Newfoundland, Canada from 2019 to 2021. To assess the influence of environmental variables on gannets foraging for different prey types, we constructed three different habitat suitability models: a U-shaped dive model, and two V-shaped dive models (early and late chick-rearing). Suitable foraging habitat for capelin, deduced by the U-shaped dive model, was defined by coastal, shallow waters with flat relief and sea surface temperatures (SST) of 11-15° C. Suitable habitat for early V-shaped dives was defined by shallow and coastal waters with steep slope and SST of 12-15°C and ~18°C, likely reflecting the variability in environmental preferences of different prey species captured when performing V-shaped dives. Suitable habitat for late V-shaped dives was defined by shallow coastal waters (<100m depth), as well as waters deeper than 200 m, and by SST greater than 16°C. We show that space-use by gannets can vary both within and between years depending on environmental conditions and the prey they are searching for, with consequences for the extent of potential interaction with anthropogenic activities. Further, we suggest regions defined as suitable for U-shaped dives are likely to be critical habitat of multi-species conservation concern, as these regions are likely to represent consistent capelin spawning habitat.

Enrollment, retention, and inclusivity of Marine Stewardship Council (MSC) eco-labelling certifications

In the past twenty years, seafood sustainability certifications have been heralded as a complement to traditional government-based fisheries management. However, certifying organizations such as the Marine Stewardship Council (MSC) have often struggled to reach fisheries in the Global South, which are less likely to already have strong top-down management practices. To further understand how MSC’s recruitment may be inhibited in different regions and nations, we developed a random forest machine-learning model which identified MSC-enrolled and unenrolled fisheries with 79% accuracy based on 36 socioeconomic characteristics. Fisheries from countries with high Human Development Indices (HDI) and those targeting high biomass regions were much more likely to enroll, reflecting a lack of socioeconomic and geographic diversity among program fisheries. Almost a third of all issued MSC certifications have also been voluntarily withdrawn, and using a similar predictive model, we found withdrawals were most likely in fisheries in overharvested regions, regardless of HDI, and those that targeted forage fish species. Results suggest MSC has struggled to recruit fisheries outside of particular regions, such as Alaska and the far North Atlantic, and to retain fisheries in need of harvest controls or other significant changes in management practices. Considering the organization’s Theory of Change and existing case studies, we outline a potential program-wide mismatch between where MSC certifications are most likely to occur, and where they are most likely to successfully generate improvements.

Potential environmental and nutritional benefits of replacing ruminant meat with forage fish

Dietary changes can affect both human health and the environment. Reducing meat consumption, especially ruminant meat, has been proven to significantly reduce greenhouse gas (GHG) emissions, reduce agricultural land use, and improve human health. Whereas the shift to a plant-based diet from meat is by far the most commonly investigated dietary change pattern, nutrient-rich forage fish with a low carbon footprint is receiving increasing interest from a global food system perspective. In this study, we attempted to fill the current research gap to better understand the environmental and nutritional impacts of forage fish as a substitute for ruminant meat by 2050. We developed environmental- and nutrient-based consumption scenarios for meat substitution. Global ruminant meat demand and potential forage fish supply were projected using a global economic model and catches over the last few decades. We found that the potential forage fish supply could replace 10 % of global ruminant meat consumption, resulting in global ruminant-related reductions in total GHG emissions and land use by up to 15 % and 10 %, respectively, by 2050. Such a dietary change could also increase the intake of essential nutrients, such as omega-3 fatty acids (DHA and EPA), vitamin B12, and calcium, especially in deficient regions. Our analyses highlight the potential of forage fish as part of a portfolio of sustainable dietary solutions, while effective fisheries management and sociocultural acceptance of forage fish consumption are necessary to realize the potential of forage fish.

Diel vertical migration in Pacific sand lance (Ammodytes personatus)—a pelagic forage fish associated with benthic substrates

AbstractDiel vertical migration (DVM) in marine organisms is an evolved response to maximize foraging opportunities and minimize predation risk. This pattern in vertical distribution is a widely observed phenomenon and common in pelagic forage fish species. Modelling these dynamics has important relevance to understanding marine ecosystem dynamics, predator–prey interactions, and marine food webs. We examine DVM in sand lance—an ecologically important taxa of forage fishes throughout northern hemisphere marine systems and target of commercial fisheries. Much remains unknown about their diurnal emergence from sediments. We apply data from autonomous stereo-camera deployments and tank observations to provide new insight to DVM patterns in Pacific sand lance (Ammodytes personatus). We model emergence curves using beta regression models with random effects, depicting important differences in the shape of ascent and descent. Our observations and analyses document crepuscular movement patterns, suggesting pelagic foraging occurs primarily at dawn and dusk. Results suggest critical light thresholds are necessary to initiate and maintain pelagic foraging. Results also suggest the importance of seasonality and life stage, such that adult fish exhibit reduced pelagic foraging in the fall relative to juvenile fish. These results constitute a comprehensive evaluation of DVM in this species, better define the physical drivers, and mathematically depict the pattern and shape of emergence timing.

Effects of currents and temperature on ecosystem productivity in Unimak Pass, Alaska, a premier seabird and biodiversity hotspot

Understanding bio-physical relationships for areas of high biodiversity in marine systems can illuminate potential impacts of environmental change on concentrations of marine life. A biodiversity hotspot of singular significance in the North Pacific Ocean is Unimak Pass, Alaska, where millions of seabirds, hundreds of cetaceans, and thousands of pinnipeds concentrate each summer to forage on rich zooplankton and forage fish resources. We synthesized a large number of disparate datasets from different sources to examine the effect of current flows and temperature on productivity across trophic levels in Unimak Pass on the seasonal time scale. Our results verify the importance of these factors. This study is one of few to investigate how seabird reproductive success may vary relative to ocean currents, and corroborates other studies showing trait-mediated responses of seabirds to variation in oceanographic conditions, but at the local scale of an Aleutian pass. Somewhat surprisingly, seabird species with larger foraging ranges appeared to respond most to variability in ocean parameters at the seasonal scale. Our hypothesis that spring conditions promote summer productivity was not supported. Instead, contemporaneous conditions in summer had more and stronger effects on seabird production and foraging density. An important caveat of our study is that these relationships remain mechanistically poorly understood due to a lack of data on lower trophic levels and corresponding information on prey use and other aspects of trophic ecology across species. Nonetheless, we have shown that the breeding success of some seabird species on Aiktak Island, as well as seasonal average foraging densities of migratory shearwaters and other species, track currents and temperature variability in Unimak Pass, and may thus be useful as ecological indicators to the robustness of local pelagic food webs, and therefore ecosystem status assessments, in the region.

Surface and subsurface oceanographic features drive forage fish distributions and aggregations: Implications for prey availability to top predators in the US Northeast Shelf ecosystem.

Forage fishes are a critical food web link in marine ecosystems, aggregating in a hierarchical patch structure over multiple spatial and temporal scales. Surface-level forage fish aggregations (FFAs) represent a concentrated source of prey available to surface- and shallow-foraging marine predators. Existing survey and analysis methods are often imperfect for studying forage fishes at scales appropriate to foraging predators, making it difficult to quantify predator-prey interactions. In many cases, general distributions of forage fish species are known; however, these may not represent surface-level prey availability to predators. Likewise, we lack an understanding of the oceanographic drivers of spatial patterns of prey aggregation and availability or forage fish community patterns. Specifically, we applied Bayesian joint species distribution models to bottom trawl survey data to assess species- and community-level forage fish distribution patterns across the US Northeast Continental Shelf (NES) ecosystem. Aerial digital surveys gathered data on surface FFAs at two project sites within the NES, which we used in a spatially explicit hierarchical Bayesian model to estimate the abundance and size of surface FFAs. We used these models to examine the oceanographic drivers of forage fish distributions and aggregations. Our results suggest that, in the NES, regions of high community species richness are spatially consistent with regions of high surface FFA abundance. Bathymetric depth drove both patterns, while subsurface features, such as mixed layer depth, primarily influenced aggregation behavior and surface features, such as sea surface temperature, sub-mesoscale eddies, and fronts influenced forage fish diversity. In combination, these models help quantify the availability of forage fishes to marine predators and represent a novel application of spatial models to aerial digital survey data.

Yangtze finless porpoise (Neophocaena asiaeorientalis) prey fish diversity based on environmental DNA metabarcoding

Abstract Knowledge of the feeding habits of the Critically Endangered Neophocaena asiaorientalis (Yangtze finless porpoise, YFP) is vital for the management and protection of this species. However, stringent protections implemented in 2020 dictate that only non‐invasive methods may be used to gain information. Therefore, environmental DNA (eDNA) metabarcoding was used to obtain YFP prey diversity and community structures from different environmental samples collected from YFP habitat in April 2021. Sampling strategies for using eDNA to monitor the YFP were explored. Of the 63 fish species detected, more species were detected in samples from surface water than in samples from deeper water and sediment, but the diversity and community structures of fish in the samples from surface water, deeper water, and sediment did not significantly differ. The number of YFP sequences in the main lake area of Poyang Lake was significantly higher than that in other sampling areas. The YFP sequence number, operational taxonomic unit (OTU) number, and OTU occurrence frequency in surface water samples were higher than those in deeper water samples. Eighteen previously verified species of YFP prey fishes were detected, with more species detected in water samples than in sediment samples. The sequence numbers of the YFP and their prey fishes Ctenopharyngodon idella, Pseudolaubuca engraulis, and Tachysurus argentivittatus were significantly positively correlated, indicating that YFP preferentially selected these three species. Surface water samples yielded good results for the convenient and non‐invasive eDNA metabarcoding method of monitoring the feeding habits of this flagship species and for identifying early signals of YFP responses to changes in prey fish communities. The creation of critical conservation areas, eDNA monitoring standards, and emergency rescue plans are vital for YFP conservation.