Prey Biomass Research Articles

First Capture of the Deep-Sea Careproctus bathycoetus (Liparidae) a Century After the Fish Was Described (North Pacific)—Revised Diagnosis and Notes on Ecology

The deep-sea snailfish Careproctus bathycoetus Gilbert et Burke, 1912 was described a century ago from a single specimen caught at a depth of 3292 m in the Kuril Basin (southern Sea of Okhotsk, western North Pacific). Until now, it was known from the holotype only. Therefore, the capture of another specimen is of great interest and provides new data on the morphology and ecology of the species. The second known specimen was collected by the international expedition “SohoBio” (2015) at a depth of 3305 m in the Kuril Basin near the type locality. This study provides a description of a rare fish, which allows us to improve the diagnosis of the species. Differences from other deep-sea snailfishes from the North Pacific Ocean are also given. At a depth of 3292–3305 m, the species lives in extreme conditions: complete darkness, temperature at about 1.9 °C, water pressure about 3300 ton/m2, low oxygen concentration, and low biomass of prey. Related Careproctus species can most likely be found in the abyssal depths of the neighboring Kuril–Kamchatka Trench.

Wolf population density: prey biomass limits via intrinsic factors

Whether gray wolf Canis lupus population density is limited intrinsically or extrinsically has occupied researchers for decades. Since 1983, prey biomass, an extrinsic factor, has been accepted as limiting, but that conclusion was recently challenged for unusually high wolf densities which were then said to be limited by behavioral, or intrinsic, factors such as intraspecific strife, dispersal, etc., below prey‐biomass constraints. That contention has been disputed, so disagreement remains. This article discusses the models involved, presents revised models that shed new light, and offers evidence that supports the conclusion that at least at densities below 79 wolves 1000 km−2, wolf numbers per area are limited by prey biomass. As wolf density increases, behavioral factors limit the density to the number of wolves the prey biomass will support. Extra wolves disperse, and wolf range expands. Thus, while wolf density is self‐limiting, the population is not.

Future impacts of reduced freshwater inflow and sea level rise on forage fish and their predators in Apalachicola Bay, Florida

Estuarine ecosystems often support large populations of forage fish, but these small-medium sized fish and the predators they feed may be affected by multiple climate change and human-induced stressors. In the Apalachicola Bay estuary, Florida, USA, reduced freshwater inflow and sea level rise are two prevalent stressors, and little is known about how these environmental changes might impact the forage fish species who inhabit the estuary. This study uses a food web model for Apalachicola Bay to simulate the impacts of future changes in water temperature and salinity on forage fish and predator species who inhabit the estuary. Water temperature and salinity conditions were based on previously developed simulations of reduced freshwater inflow and sea level rise in Apalachicola Bay from 2020 to 2049. These simulated environmental changes were applied as forcing functions in the food web model to drive shifts in species biomasses over time. This study centered on changes in biomass for two highly abundant forage fish species, juvenile silver perch (Bairdiella chrysoura) and juvenile pinfish (Lagodon rhomboides), as well as their major predators, spotted seatrout (Cynoscion nebulosus) and inshore lizardfish (Synodus foetens). These changes were assessed at both 10- and 30-year time intervals relative to 2019, along with an examination of forage fish consumption by their predators. Juvenile silver perch biomass increased across all scenarios and time scales, while juvenile pinfish biomass decreased. Consumption of juvenile silver perch by spotted seatrout increased across all scenarios and time scales, and consumption of juvenile pinfish by inshore lizardfish decreased, in concordance with the trends in prey biomass. Both spotted seatrout and inshore lizardfish biomasses decreased across future scenarios, though the high biomass of juvenile silver perch may have played a role in stabilizing the decline of spotted seatrout. Changes in forage fish biomasses and their impacts on predator species as a result of reduced freshwater inflow and sea level rise have implications for ecosystem productivity and the fisheries of the region.

Are Wild Prey Sufficient for the Top Predators in the Lowland Protected Areas of Nepal?

A balanced equilibrium between carnivores and their prey is crucial for maintaining ecosystem sustainability. In this study, we applied the predator-prey power law equation to assess the balance between the biomass densities of carnivores and their wild prey within Nepal's lowland protected areas during 2013, 2018, and 2022. The estimated value of the power law exponent k for predator-prey biomass was 0.71 (95% CI = 0.39-1.05), indicating an approximate threefold increase in predator biomass density for every fivefold increase in prey biomass density. Consequently, this creates a systematically bottom-heavy predator-prey biomass pyramid. This finding, consistent with the k = 3/4 trophic biomass scaling across ecosystems, suggests that predator biomass is proportionally sustained by prey biomass, indicating a balance between top predators and their wild prey in Nepal's lowland protected areas. We further demonstrated it is possible to retain the overall power law exponent while jointly measuring intraguild competition between two predators with canonical correlation analysis. This understanding opens avenues for future research directed toward unraveling the factors that drive these consistent growth patterns in ecological communities.

Avian prey intake and breeding success parity of the powerful owl in dry, inland Victoria

AbstractApex predators are vulnerable to environmental changes which can cascade through trophic levels of an ecosystem. Investigating prey‐predator relationships is important for directing conservation efforts and understanding how species may respond to ecosystem changes. This case study examined the diet and breeding success of the threatened powerful owl Ninox strenua in central Victoria where the box‐ironbark forests have undergone widespread clearing, fragmentation, and degradation. The powerful owl preys predominantly on arboreal mammals, however, some birds are also consumed. By analysing the contents of regurgitated owl pellets of two owl pairs, we found that birds comprised 29.3% of all prey items and contributed the largest proportion of prey biomass for one pair (34.4%). All mammalian prey species identified in the pellet remains are dependent on tree hollows, which are now a scarce and competitive resource in box‐ironbark forests. Despite consuming a diet lower in mammalian prey than found in other studies, breeding success over five consecutive years was 1.4 chicks fledged per pair per year, which is notably higher than historical observations in the region and similar to powerful owls in other parts of their distribution. Our observations suggest that flexibility in prey selection enables powerful owls to occupy ranges that have undergone significant ecosystem change.

Diet variation and trophic impact of weakfish, Cynoscion regalis, within multiple marine habitats of the eastern United States.

Weakfish (Cynoscion regalis) is not federally managed but feeds on species of management and ecological interest. We examined the trophic ecology of weakfish in Chesapeake Bay and the coastal and offshore waters of the eastern United States. For these areas, we determined the dominant prey of weakfish; identified how much diet variation was explained by the factors: season, size class, and year; and quantified prey biomass removed by weakfish from 2007 to 2019. In general, diet composition was mostly dominated by Engraulidae, Osteichthyes (bony fishes), and Mysidacea, and significantly varied by season and size class in Chesapeake Bay and coastal waters, although this was less dramatic in Chesapeake Bay. The total amount of variance explained by the three factors was 23.1% (Chesapeake Bay) and 14.7% (coastal waters), with year not being a significant factor in explaining weakfish diet variation for these areas. Weakfish total prey biomass removal occurred primarily in coastal waters in the fall and small size class (annual mean: approximately 41,038 t; maximum: approximately 63,793 t). Highly opportunistic feeders, weakfish cannibalism also played an essential part of their diet. These results have implications for fisheries and ecosystem management of weakfish when considering ecological interactions in regulatory approaches, such as recruitment and cannibalism, competition with federally managed fishes, and the natural mortality of their prey.

Quantifying predation on benthos and its overlap with bottom fishing in the NW Atlantic

AbstractContinental shelves experience many human pressures with demersal fisheries central to disturbing the ocean floor. However, ecological processes such as predation rates of benthos and their relationship with bottom fishing are often unknown for large marine ecosystems. We examined the amount of benthos consumed by 14 benthivorous fishes, the overlap between benthos predation and bottom fishing (dredge and trawl gear), and temporal trends in benthivorous fish abundance and the number of fishing trips on the northeast US continental shelf. Mean annual predation (biomass of prey removed) and 95% confidence intervals ranged from .0002 (.0001–.0003) to 3967 (1761–7112) t per 10‐min area squared grid cell and prey taxa for these benthivorous fishes. Predation and bottom fishing had overlapping footprints of activity, which were slightly stronger for dredge gear. Trophic success (ratio of prey biomass eaten to the biomass of the benthivore community per grid cell) revealed more Bivalvia, Gammaridea, and Polychaeta eaten in areas targeted by trawling with more fish biomass. In contrast, dredging did not target fish biomass, but these areas had increased (Echinoidea, Gammaridea, and other benthos) or decreased (Ophiuroidea) trophic success relative to dredging footprint, suggesting habitat preferences for benthic prey and demersal fisheries have converged rather than diverged. Despite declines in bottom fishing, recent increases in benthivorous fish abundance and growing interest in ocean floor use suggest that fisheries managers should ensure benthivores have sufficient prey resources relative to their community size and human pressures to promote long‐term sustainability of demersal fisheries and healthy ecosystems.

Direct effect of artificial warming on communities is stronger than its indirect effect through body mass reduction

Theory predicts that morphological and bioenergetic constraints due to temperature‐induced body size reduction can modulate the direct effects of warming on biotic interactions, with consequent effects on trophic cascades and biomass distribution. However, these theoretical predictions have rarely been tested empirically. Our aim was to distinguish the indirect effects of warming‐induced body size reductions from the direct effects of warming on community structure. We conducted a mesocosm experiment manipulating factorially 1) body size reduction in the medaka fish Oryzias latipes using two populations raised for several generations under contrasted climate conditions and 2) warming (+4°C), to test their independent and interactive effects on the structure of prey and primary resource communities, the predator–prey biomass ratio and the biomass size spectra. We further dissected the effects of seasonal temperature variation from the effects of constant artificial warming. We found that the indirect effects of warming (i.e. fish body size reduction) on composition and structure of communities as well as their biomass size spectra were of marginal amplitude compared to the direct effects of seasonal temperature variation and constant warming. There were no changes in community composition in response to fish body size reduction or constant warming. However, the density of macroinvertebrates and zooplankton were maximal at intermediate seasonal water temperatures and lower in constantly‐heated mesocosms. Contrastingly, phytoplankton was not strongly affected by seasonal temperature or warming, but rather responded to grazing effects of zooplankton. Finally, we found a reduction in predator–prey biomass ratio under warming and at the warmest seasonal temperature, inducing a steeper slope of the biomass size spectra under increasing seasonal (but not constant) temperature. We conclude that the direct effects of climate change on freshwater communities are stronger than its indirect effects mediated by body mass reduction.

Community structure of whole pelagic copepods along the Kuroshio: Increase in the abundance and size in the north frontal area of the Kuroshio axis near the Japanese archipelago

The Kuroshio ecosystem is an important nursery ground for various fish species. Because the prey biomass and composition influence the recruitment of larval and juvenile fish, we investigated the variation in the abundance, carbon biomass, and community structure of copepods, which are the main prey for larval and juvenile fish, along the Kuroshio from the eastern coast of Taiwan to the Boso Peninsula, Japan from 8–November 24, 2015, using 100 μm-meshed plankton net samples. We identified two groups of stations (A and B) by the cluster analysis based on the composition and abundance for adult copepods (Q-mode). The total copepod abundance and carbon biomass were higher in Group A than in Group B. Of the dominant species assemblages classified by cluster analysis (R-mode), the abundance of species assemblages S2b and S3, which were composed of small-sized species (e.g., Oithona and Oncaea species), did not differ between Groups A and B, indicating that they were distributed abundantly throughout the Kuroshio region. On the other hand, the species assemblages (S1 and S2a) including the medium-sized calanoid copepods of coastal species and subtropical species (e.g., Paracalanus aculeatus and Clausocalanus furcatus) contributed to the high abundance and biomass of Group A. Group A occurred in the north-frontal area of the Kuroshio axis near the Japanese archipelago where chlorophyll a was high. This indicates that the community was changed by the bottom-up processes driven by nutrient supply from the subsurface layer in the north-frontal area. These results show that although the small-sized copepods were usually dominant in numerical abundance in the Kuroshio region as well as other oligotrophic oceans, the medium-sized copepods were an important component in the copepod community in water with high primary production. We concluded that the ecosystem in the north-frontal area downstream of the Kuroshio might provide optimal prey environments for diverse fish larvae and juveniles.

The trophic strategy of the European honey‐buzzard Pernis apivorus during breeding: extravagant specialization or ingenious solution?

This article provides insight into the trophic strategy of a little‐known top predator and allows for a better understanding of the selective pressures that shape its diet. We studied the diet of European honey‐buzzards, a raptor specialized in consuming social wasp brood. The ratio of predator to prey biomasses is one of the highest among raptors. Considering the prey size and ingestion rate hypothesis, we investigated the honey‐buzzard's preferences for native and exotic eusocial vespid species. We also described other prey items in the diet and how diet changes throughout the breeding season. We installed trail cameras in 24 honey‐buzzard nests in north‐western Spain in 2018–2021. We estimated the proportion and daily rate of delivery of native common‐wasps, invasive Asian‐hornets, reptiles, and birds and the honey‐buzzard's preferences for vespid species. We performed LMMs, GLMMs, and CLMMs to analyse relationships between response variables and predictors. Honey‐buzzards mainly consumed vespids (82% of prey). Common‐wasps and Asian‐hornets were almost the only two vespids consumed. The invasive hornet was the second most consumed prey, but common‐wasps were preferred. Vespids became more important as the age and number of nestlings increased. Our results suggest that this diet is the adaptive result of the conflict between being a median‐sized insect‐eating nidicolous raptor and collecting enough morsels for the growth of its nestlings. This would allow them to deliver a relatively large amount of biomass to the nest with a high ingestion rate. We discussed implications of our findings for the management of the invasive wasp.

Top-down effects of intraspeciflic predator behavioral variation.

Among-individual variation in predator traits is ubiquitous in nature. However, variation among populations in this trait variation has been seldom considered in trophic dynamics. This has left unexplored (a) to what degree does among-individual variation in predator traits regulate prey populations and (b) to what degree do these effects vary spatially. We address these questions by examining how predator among-individual variation in functional traits shapes communities across habitats of varying structural complexity, in field conditions. We manipulated Chinese mantis (Tenodera sinensis) density (six or twelve individuals) and behavioral trait variability (activity level by movement on an open field) in experimental patches of old fields with varying habitat complexity (density of plant material). Then, we quantified their impacts on lower trophic levels, specifically prey (arthropods > 4mm) and plant biomass. Predator behavioral variability only altered prey biomass in structurally complex plots, and this effect depended on mantis density. In the plots with the highest habitat complexity and mantis density, behaviorally variable groups decreased prey biomass by 40.3%. In complex plots with low mantis densities, low levels of behavioral variability decreased prey biomass by 32.2%. Behavioral variability and low habitat complexity also changed prey community composition, namely by increasing ant biomass by 881%. Our results demonstrate that among-individual trait variation can shape species-rich prey communities. Moreover, these effects depend on both predator density and habitat complexity. Incorporating this important facet of ecological diversity revealed normally unnoticed effects of functional traits on the structure and function of food webs.

Seasonal trophic niche width and overlap of mottled sculpin and brown trout in a regulated high‐elevation river

AbstractIn temperate ecosystems, resource availability fluctuates seasonally due to changes in environmental conditions and productivity. Intra‐ and inter‐specific trophic niche overlap under resource limitation is a measure of competitive interactions and influences species coexistence and community dynamics, but patterns of this overlap are influenced by anthropogenic activities. To investigate seasonal trophic niche dynamics of coexisting fish species in a flow‐altered river, we analysed prey resources, stomach content samples and stable isotope signatures of mottled sculpin Cottus bairdii and juvenile brown trout Salmo trutta in the Blue River, Colorado, USA, a high‐elevation oligotrophic river. Prey biomass (i.e. benthic macroinvertebrates) peaked in spring and declined through summer and autumn. Stomach content and stable isotope analysis results showed that diet composition of mottled sculpin and brown trout varied seasonally in response to changes in prey availability. Stomach content analysis results revealed that in autumn, both species exhibited the highest frequency of empty stomachs and expanded population trophic niches due to increased inter‐individual diet variation despite decreased individual trophic niche breadth. Inter‐specific trophic niche overlap was relatively high across all seasons, but the lowest degree of overlap occurred in autumn of both years when prey availability was lowest. Isotopic analysis revealed similar trends to stomach content analysis, of wider isotopic niches and reduced overlap in autumn compared to spring. Our data indicated that seasonal variation affected individual‐ and population‐level trophic niche dynamics and inter‐specific niche overlap between mottled sculpin and brown trout. This trophic segregation under resource limitation may serve as a mechanism that facilitates species coexistence in a flow‐regulated, oligotrophic river.

Moose in wolf diets across northeastern Minnesota

AbstractThe moose (Alces alces; mooz in Anishinaabemowin, Ojibwe language) population has recently declined in Minnesota, USA, and gray wolf (Canis lupus; ma'iingan) predation is likely a contributing factor. We analyzed diet composition of gray wolves in northeastern Minnesota during 2011–2013 to evaluate the importance of moose as prey and seasonal and regional variations in wolf diet. We identified frequency of occurrence of prey items and biomass consumed in 1,000 wolf scats collected on and adjacent to the Grand Portage Indian Reservation and Voyageurs National Park and within the 1854 Ceded Territory (greater northeastern Minnesota). White‐tailed deer (Odocoileus virginianus; waawaashkeshiwag [plural]), moose, and beaver (Castor canadensis; amikwag [plural]) composed the majority of wolf diet, with moose as the primary prey in Grand Portage (35–54% of diet by biomass across seasons) and deer the primary prey in the 1854 Ceded Territory (46–62%) and Voyageurs (63–79%). Relative importance of prey species differed by study area and season. Moose calves were an important prey item in spring in the 1854 Ceded Territory (12% of diet by biomass) but not in Grand Portage or Voyageurs. Although calves were not a majority of wolf diet by biomass, many calves were preyed upon by wolves (30% of calves born each year in Grand Portage), thus affecting recruitment in a declining moose population. Deer fawns composed 12% of wolf diet in spring and 10% in summer in Grand Portage and 19% in summer in Voyageurs. Beaver composed 16% of wolf diet by biomass in spring and 14% in summer in Grand Portage and composed 22% of wolf diet in spring and 30% in summer in Voyageurs. At most prey densities, moose were preferred and deer avoided in Grand Portage and the 1854 Ceded Territory and beaver were preferred in Voyageurs. Our results can be used in conjunction with predation and prey studies to evaluate the effect of wolves on prey populations.

Prey dynamics and breeding performance in a generalist predator: The differential role of prey density, biomass, and effective consumption rates

The breeding performance of predators is influenced by the differential consequences of prey density, prey biomass and effective consumption rates. Using camera traps at nests, we investigated whether changes in prey abundances caused functional and/or numerical responses of the common buzzard (Buteo) in a Mediterranean woodland region. After determining 1150 prey delivered to the nests by adults, we found that the biomass of prey caught was not a good indicator of its influence on individual life history traits such as productivity. Indeed, the consumption of small mammal prey, despite representing only 11% of the biomass delivered, had a much greater influence on buzzards' productivity than the consumption of snakes, which made up 47% of the biomass delivered. Live trapping evidenced that small mammals were roughly preyed according to its availability in the field, and their abundance in spring was directly related to buzzards' productivity and inversely related to hatching dates. Small mammals – mostly mice – can be considered as very suitable prey, owing quick handling times, profitability, and high energy intake. Our results pointed out the relevance of mice on buzzards' breeding performance, and altogether with the outstanding role of open-land small mammals on buzzards' demography during autumn-winter, suggested a key role of small mammals on buzzards’ ecology throughout the year cycle in the Mediterranean area studied. These findings have important implications for our understanding of the foraging strategies of generalist species and the role that habitat and environmental factors play in shaping them.

Africa's overlooked top predator: Towards a better understanding of martial eagle feeding ecology in the Maasai Mara, Kenya

Raptors exert top‐down influences on ecosystems via their effects on prey population dynamics and community composition. Most raptors are sympatric with other predators, thus complicating our understanding of their relative influence in these systems. Estimates of kill rates and prey biomass recycling have been used as predation metrics that allow quantitative comparison among species and assessment of the relative role of single species within complex food webs. Few studies have produced findings of kill rates or prey biomass recycling for raptors. We used a supervised machine learning algorithm to behaviourally classify high resolution accelerometer informed GPS locations of tagged adult non‐breeding martial eagles Polemaetus bellicosus in the Maasai Mara region of Kenya to estimate kill rates and prey biomass recycling. Eagle locations classified as feeding were clustered using distance and time thresholds to identify kills and calculate kill rates. Identified kill sites were quickly ground‐truthed to confirm kills and identify prey species. We estimated kill rates for martial eagles at 0.59 kills day‐1 for males and 0.38 kills day‐1 for females, and we estimated biomass recycling per ground‐truthed kill at 1796 g for males and 3860 g for females. From our sample of identified ground‐truthed kills, ‘gamebirds' was the most frequently recorded prey category for male eagles and ‘small ungulates' was the most frequently recorded prey category for female eagles. These results position martial eagles close to sympatric mammalian top predators in trophic pyramids and provide evidence for their classification as a top predator.

Food Composition of the Little Owl Athene noctua in Farmland Areas of South East Poland

The feeding ecology of the Little Owl (Athene noctua) was studied in farmlands of southeast Poland, which is dominated by monocultural farms. 3065 prey dissected from pellets were collected at 13 pellet stations between 1999 and 2001 through 7 seasons in total. Mammals were found to dominate both in total number (54.3% of caught prey) and total biomass (93.0% of caught prey) while insects comprised 43.0% of the number, but only 1.1% of the prey biomass. However, the proportion of insects reached up to 62% in certain seasons. Coleopteran beetles dominated the insect fraction representing 98.3% of the number and 87.9% of the insect biomass. Our study also illustrated that in some seasons, the prey composition included taxa related to intensive agricultural management. The food composition of the Little Owls from the examined Polish sites is more similar to Eastern and Southern populations than to Northern and Western populations of Little Owls in Europe.

Estimating relative per capita predation rates from molecular gut content analysis

The problem of estimating predation rates from molecular gut content data has been challenging. Previous work showed how per capita predation rates could be estimated from quantitative molecular gut content data using the average prey quantity in the predator, the decay rate of the prey in the predator and a conversion constant to convert measured prey quantity into prey numbers or biomass. Based on this previous work, we developed and illustrated a method to estimate relative per capita predation rates for a single prey species consumed by one predator species. This method does not require estimation of either the decay rate of the prey in the predator or the conversion constant. We describe how gut content data from qPCR, quantitative ELISA, metabarcoding and unassembled shotgun reads (Lazaro) can be used to estimate relative per capita predation rates. The method was used to estimate the relative per capita predation rate in a laboratory feeding trial to evaluate the precision and accuracy of the method using Lazaro data. Ten independent estimates were statistically similar, but precision was related to the number of observed prey reads. We estimated the relative per capita predation rate by the ant Pheidole flavens on another ant Pheidole tristis in a field experiment and by the ladybeetle Hippodamia convergens on the aphid Lipaphis pseudobrassicae on organic production farms. We found that higher P. flavens activity-density was associated with lower relative per capita predation rates, therefore indicating lower predation rates on P. tristis. The absence of variation among farms in relative per capita predation by H. convergens suggested that the farms were biological replicates. Using relative per capita predation rates can provide a rapid way to assess how a predator–prey interaction changes over space and time and may help identify factors that limit or enhance biological control of pests.

Comparison of DNA metabarcoding and morphological diet analysis of lumpfish (Cyclopterus lumpus) as methods of estimating sea lice cleaning efficacy inside commercial Atlantic salmon (Salmo salar) sea cages

Lumpfish (Cyclopterus lumpus) are often used as cleaner fish inside salmonid sea cages for biological control of ectoparasitic sea lice. We compared traditional morphological diet assessments with DNA metabarcoding as methods of estimating lumpfish cleaning efficacy as a function of its size, and of its ingestion of alternative prey. Traditional morphological analysis was performed on 122 ethanol-preserved stomachs. The stomachs were removed in the field - following eDNA protocols – from lumpfish collected from industrial Atlantic salmon sea cages in southern Newfoundland. Morphological stomach analysis gave semi-quantitative estimates of prey counts and/or biomass at the order or family level; it showed that shorter lumpfish ate more gammarid amphipods whereas longer lumpfish ate more formulated feed pellets designed for salmon. No sea lice were confidentially morphologically identified in the lumpfish stomachs. In contrast, COI metabarcoding was able to confidently identify the presence of the salmon louse (Lepeophtheirus salmonis) in 61 of 82 successfully barcoded lumpfish stomachs. Metabarcoding showed that diurnally-migrating krill and gammarid amphipods were present in more stomachs in 2018 whereas formulated feed pellets – identified from COI sequences classified as domestic poultry and non-indigenous fish species - were present in more stomachs in 2020. We argue that, when weighed by the total number of reads, the counts per stomach of the number of Global Estimated Sequence Variants (ESV) classified as a particular prey species could be used to estimate the single-species indices of abundance needed for lumpfish breeding values. The number of ESVs classified as the salmon louse could be used to estimate an index of lumpfish cleaning efficacy. As proof-of-concept, we show that 83% of the variance in the number of Norwegian krill heads observed per stomach was explained by two weighed covariates: 1) Norwegian krill ESV counts and 2) lumpfish stomach contents weight.

Effects of insecticide spray drift on arthropod prey resources of birds in grasslands in Minnesota

AbstractSoybean aphid (Aphis glycines) insecticides are used throughout the Upper Midwest and Great Plains regions of North America, including the farmland region of Minnesota, USA, to combat insect pests. These broad‐spectrum, foliar spray insecticides have the potential to drift beyond target fields into nearby grassland cover where birds and other insectivores forage. Arthropods serve important roles in grassland ecology and are susceptible to mortality and sublethal effects from exposure to these pesticides. Our objective was to assess effects of soybean aphid insecticides on grassland arthropods, especially those that are important in grassland bird diets. We measured the abundance, consumable biomass, and family richness of insects and spiders in grasslands adjacent to soybean fields in an agricultural landscape. Soybean fields were treated with chlorpyrifos and lambda‐cyhalothrin, which were the 2 most common foliar pesticides used to control soybean aphids in Minnesota. We compared measures at focal sites to samples collected at reference sites adjacent to corn fields not sprayed for aphids during 3 periods in mid‐to‐late summer: 1–3 days before spraying, 3–5 days post‐spraying, and 19–21 days post‐spraying. The abundance of arthropods in focal grasslands was lower 3–5 days after pesticide applications. Coleoptera family richness at focal sites was also lower than at reference sites 3–5 days after pesticide applications. These measures 19–21 days after application were similar to pre‐spraying levels, indicating that arthropod populations rebounded during this period. Measures of consumable dry biomass, bird prey abundance, bird prey biomass, family richness of Araneae, family richness of Hemiptera, and family richness of Orthoptera were not different between focal and reference sites after spraying. Our results reveal that reductions in arthropod food abundance for grassland birds are associated with pesticide applications up to 5 days after spraying. We suggest that natural resource managers factor proximity to row crop fields and susceptibility to pesticide drift into decisions about where to add grassland cover to landscapes.

Evidence for adaptive strategies in larval capelin on the northeastern coast of Newfoundland, Canada

Abstract Fish species with high mortality during early life may maximize fitness using adaptive strategies to time hatching to match favorable environmental conditions (match/mismatch) or extending spawning/hatching to disperse risk (bet-hedging). We examined support for these strategies in a collapsed forage fish, capelin (Mallotus villosus), in coastal Newfoundland (2018–2021). Capelin shift from spawning at warm, intertidal to cool, subtidal (15–40 m) habitats in warmer years, with unknown recruitment consequences. We hypothesized that match/mismatch (specifically, Coastal Water Mass Replacement Hypothesis) would be supported if densities of recently hatched larvae showed pulses that overlapped with high prey and low predator densities. Generalized additive models revealed that larval densities increased with zooplankton prey biomass, but were not influenced by predator biomass or temperature, contrasting with pre-collapse studies and providing equivocal support for match/mismatch. Protracted larval emergence and previously documented high variability in larval traits supported a bet-hedging strategy. Larval condition (i.e. length, yolk-sac diameter) did not differ between habitats but varied among years, where the highest proportion of larvae in poor condition was from the intertidal site in the warmest year (2018). Findings suggest that spawning habitat shifts may have limited impact on stock recovery relative to year-specific environmental conditions that influence larval condition.