Total Number Of Prey Research Articles

Conspecific density drives sex-specific spatial wintertime distribution and hoarding behaviour of an avian predator

Most studies on intraspecific competition, i.e., competition among individuals of the same species, have been conducted during the breeding season. Yet, at northern latitudes, intraspecific competition is expected to be particularly strong under the harsh weather conditions of the non-breeding season with limited number of resources available per individual. We studied the food-hoarding behaviour of wintering Eurasian Pygmy Owls (Glaucidium passerinum) along with sex- and age-specific spatial distribution in relation to fluctuating main prey abundance (voles) and conspecific density using a 15-year dataset. In low vole abundance years, increasing conspecific density reduced the total prey number stored by an owl, suggesting high costs of exploitative competition. The distance between the stores of nearest neighbours was greater when both were females, suggesting that the spatial avoidance is driven by sex-specific competition. However, food stores of females had a larger amount of prey items, especially when the nearest neighbour was of the same sex. The number of stores hoarded by an owl increased with increasing conspecific densities. Distributing the prey items to multiple store-sites instead of one (shifting from larder-hoarding towards scatter-hoarding) can help to reduce the overall loss to potential pilfering when conspecific density is high. These results combined suggest that high conspecific density inflames sex-specific interference competition, rather than solely exploitative competition, and in turn drives the observed sex-specific spatial distribution. Adopting a sex-specific spatial distribution according to hoarding and aggressive behaviour can be a way to reduce the severity of intraspecific competition locally and could have cascading effects on the prey community.

Anthropogenic pressure on large carnivores and their prey in the highly threatened forests of Tanintharyi, southern Myanmar

AbstractThe Tanintharyi Region in southern Myanmar is rich in biodiversity yet is facing threats from varying degrees of anthropogenic pressure. In this research we examine how anthropogenic pressures are influencing large carnivores (tiger Panthera tigris, leopard Panthera pardus and dhole Cuon alpinus) and their major prey species (wild pig Sus scrofa, muntjac Muntiacus spp., sambar Rusa unicolor, gaur Bos gaurus and banteng Bos javanicus) in the Lenya Reserved Forest and adjacent areas of Sundaic forest. We used data from camera-trap surveys during May 2016–March 2018 and logistic regression to analyse the relationships between the presence of large carnivores and explanatory variables such as human disturbance, landscape variability and changes in prey distribution. Tiger presence was positively associated with the occurrence of gaur and distance to villages. The occurrence of prey did not explain the detection of leopards in the study area. We suspect this was because leopards have a broad diet, including arboreal primates, and their prey was not fully recorded in our camera-trap survey. Dholes were positively associated with wild pigs and the total number of prey but not associated with forest type and landscape variables. To restore the carnivore population and conserve the biodiversity of this area, effective protection of predators and habitat management for large ungulates are crucial.

Diet of the little Athene noctua (Scopoli, 1769) on the territory of Berehovo district (Transcarpathian region)

Objectives. The Little Owl is the most common owl in the Western Palearctic and its population is declining significantly in Europe. Therefore, conservation and study of this owl is an important issue in most European countries. Analysis of trophic patterns at the local level provides interesting and valuable information about the predator’s eating habits. The owl’s diet investigation allows us to analyze their potential adaptations to habitats with different levels of environmental transformation. Materials and Methods. We studied nutrition of the Little Owl Athene noctua, in agricultural lands of Berehove district of Transcarpathian region in Ukraine. In total, 1446 pellets were collected at 15 pellet stations in 2002–2020 and 2506 prey items were identified. The prey items represented 18 vertebrate species (16 species of small mammals of three orders Rodentia, Soricomorpha, Carnivora, as well as reptiles of the family Lacertidae and birds of the order Passeriformes and arthropods. Results. Vertebrates play a major role in feeding the Little Owl (over 99 % of total prey biomass in all of the studied sites). The common vole is the most common prey in the owl’s diet (52.1 % of the total prey number and 67.5 % of the biomass of the prey caught), as well as a high proportion of mice of the genus Apodemus and Sylvaemus. The contribution of invertebrates to total prey biomass is insignificant (0.3 %). A large number of invertebrates were observed in the diet of the Owl in summer and were almost completely absent in winter. Conclusions. According to our data, the Little Owl is a typical predator generalist in Transcarpathia. The 28 taxa found in the pellets show a wide range of food objects in a relatively small area, and high level adaptations to habitats with different levels of environmental transformation (agrosystems and anthropogenic areas).

Tunas off northwest Africa: The epipelagic diet of The Bigeye and Skipjack tunas

Tunas are among the most exploited top predators worldwide, with negative impacts on some of their stocks. Changes in their population abundance can impact marine food-webs and have the potential to alter entire ecosystems. To better understand the impacts of the exploitation of tuna stocks in the most critical habitats, basic knowledge on the diet of these species in each region is required. Here, we describe the diet of the two most fished tuna species in the archipelago of Madeira, the Bigeye tuna Thunnus obesus and the Skipjack tuna Katsuwonus pelamis, based on stomach contents analysis. To gain further insights into the diet, and also better assess the possible bias caused by the occurrence of live bait in stomachs, we compared tuna mercury values with those of two other predators with similar diets that are not directly targeted by fisheries, and with Bigeye and Skipjack tunas from other ocean basins. Bigeye tunas fed mostly on Atlantic chub mackerel Scomber colias and mackerel Trachurus sp., which together contributed with 85% of total prey weight. Only 7.5% of prey weight was constituted by mesopelagic prey, including myctophids and cephalopods. Skipjack tunas had an epipelagic diet (NF = 97%), with the Atlantic chub mackerel representing half of the total prey weight, despite Longspine snipefish Macroramphosus scolopax and Sand smelt Atherina sp. accounting for 62.9% of the total number of prey. There were interannual variations in diet likely linked to interannual pelagic community shifts. Bait did not bias the results of the stomach analysis of these tunas and bait species were observed to be part of the natural diet of both tuna species. Baseline data provided by this study should allow for more informed decisions for an efficient ecosystem-based fisheries management.

Feeding of fish inhabiting native and non-native macrophyte stands in a Neotropical reservoir

Owning to dissimilarity with native macrophytes, invasive macrophytes may negatively affect the diet and foraging efficiency of fishes. We evaluated the invertebrate availability, diet composition, and foraging efficiency of four fish species that use macrophytes as habitat in a native and a highly invasive macrophyte. The samples were taken in a reservoir in Brazil (22° 33′ S, 52°54′ W). We collected invertebrates and fishes simultaneously in macrophyte stands dominated by the invasive Poaceae Urochloa arrecta and the native Eichhornia azurea. We evaluated the foraging efficiency by the total number of prey consumed and by the degree of stomach fullness. We used an approach based on resampling procedures to compare differences in composition of invertebrates, composition of fish diet, and the similarity between invertebrates and fish diet. The abundance of invertebrates and the diet composition differed significantly between plants. On the other hand, fish foraging efficiency did not differ between macrophytes. Despite this lack of difference of foraging efficiency, the lower abundance of food items in the invasive macrophyte and the significant changes in fish diet suggest that U. arrecta is not a favorable feeding habitat for fishes, compared to the native E. azurea.

Long-Term Changes in the Importance of Aboriginal and Invasive Fish Species for Feeding of Predatory Fish of the Rybinsk Reservoir

Influence of biotic and abiotic environmental factors on feeding of the predatory fish in the Rybinsk Reservoir in 1953−2012 has been analyzed. It is revealed that the feeding spectrum of the majority of piscivores (sander Sander lucioperca, burbot Lota lota, pike Esox lucius and adult perch Perca fluviatilis) includes 16−18 fish species, while only seven in Volga sander Sander volgensis. Three aboriginal fish species (perch, ruff Gymnocephalus cernuus and roach Rutilus rutilus) and two invasive species (European smelt Osmerus eperlanus and Black-Azov tyulka Clupeonella cultriventris) are the main food items for piscivores. In some years, these species accounted for 97% of the total number of prey. Introduction and naturalization into the reservoir of smelt (during the period of climatic norm) and Black-Azov tyulka (during regional climate warming) considerably changed proportions of species serving as potential prey for predatory fish. During these periods, the share of invasive species in the ration of pelagic zone piscivores was increasing, but this increase was not proportional to the abundance of these prey species. After decline in abundance of smelt and tyulka (while, at the same time, these species were still dominant) their shares in the feeding of predators decreased, while the role of more available mass aboriginal species increased again. It is revealed that predatory fish are selective to certain prey items: sander, Volga sander, and large perch prefer to feed on perch yearlings; burbot, on yearlings of perch and on ruff; and pike, on roach.

Temporal changes in prey composition and biomass delivery to African Crowned Eagle nestlings in urban areas of KwaZulu-Natal, South Africa

Globally urban areas are expanding rapidly and this usually has negative effects on biodiversity. Despite this, some species manage to persist in urban areas, as is the case with African Crowned Eagles Stephanoaetus coronatus in KwaZulu-Natal, South Africa. As relatively little is known about African Crowned Eagle nestling diet, especially about how it changes with nestling age, we investigated this with nest camera-traps. We analysed temporal changes in prey composition and biomass delivery during the nestling stage. We also recorded which adults provisioned and attended the nest. The main prey fed to nestlings were Rock Hyrax Procavia capensis and Hadeda Ibis Bostrychia hagedash. Adult males did most of the food provisioning, especially at the start of the nestling period. We found a decrease in total prey number and biomass with nestling age. This may be caused by changing requirements of nestlings. Furthermore, delivering fewer prey at later nestling stages may be a facilitating mechanism to enhance fledging of the nestling. Although the total number of prey brought to the nest decreased, we found an increase in numbers of Vervet Monkey Chlorocebus pygerythrus in the diet with nestling age. This indicated an increase in larger prey being delivered to the nests as the nestling aged. We suggest that this could be caused by increased participation in hunting by the larger female as her nest attendance time decreased as the nestling aged. We conclude with emphasising the importance of protecting the Durban Metropolitan Open Space System (D’MOSS) zones for the persistence of this Near Threatened raptor species, and populations of its prey in urban areas for its breeding success.

Pitcher plant facilitates prey capture in a sympatric congener

Carnivorous plants avoid below-ground competition for nitrogen by utilizing an alternative nitrogen resource—invertebrate prey, but it remains unclear if sympatric carnivorous plants compete for prey resources. The aim of this study was to investigate if exploitative prey-resource competition occurs between the two sympatric pitcher plant species, Nepenthes rafflesiana and N. gracilis in Singapore. We first investigated if prey-resource partitioning occurs between these two species, and then investigated niche shift in N. gracilis by examining its pitcher contents along an in situ gradient of N. rafflesiana interspecific competition. Our results showed clear evidence of resource partitioning between the two species, but contrary to the expectation of competition, proximity to N. rafflesiana pitchers correlated with higher total prey numbers in N. gracilis pitchers. Our multivariate model of prey assemblages further suggested that N. rafflesiana facilitates N. gracilis prey capture, especially in several ant taxa that are trapped by both species. Concurrently, we found strong evidence for intraspecific competition between N. gracilis pitchers, suggesting that prey resources are exhaustible by pitcher-predation. Our results show that resource partitioning can be associated with facilitative interactions, instead of competition as is usually assumed. Facilitation is more typically expected between phylogenetically distant species, but divergences in resource acquisition strategies can permit facilitation between congeners.

Trophic traits of Grammostola vachoni, a tarantula (Araneae : Theraphosidae) from Argentina

This is the first study about trophic traits of Grammostola vachoni, a threatened theraphosid spider endemic to the mountain systems of central Argentina. Four prey types were used in experiments: crickets, cockroaches, beetle larvae and adult beetles. Grammostola vachoni was observed to eat at a rate of about once every 11 days, with the mean total number of prey consumed per spider during the experimental period being 2.7. Latency to the first attack was similar for crickets, cockroaches and beetle larvae, but was shorter for adult beetles. Feeding time was significantly longer for crickets and beetle larvae. Mass gain was significantly different among prey types. Feeding effectiveness and ingestion rate were significantly higher for crickets. A significant positive correlation for feeding effectiveness and ingestion rate with prey mass and the initial spider mass was also found.

What do <i>Anolis</i> eat?: evaluation of sexual dimorphism and geographic variation in the diet of <i>Anolis ventrimaculatus</i> (Squamata: dactyloidae) in Colombia

Anolis lizards exhibit high morphological diversity, partially related to variation in structural resource use, that probably influences foraging behavior and prey selection of individuals and species. Anoles are largely insectivorous: most species are generalists/opportunists and few are specialists. Dietary differences between sexes and among individuals from different populations have been observed in several species. Sexual size dimorphism, spatial niche divergence between sexes and species, competition and food availability are some of the factors responsible for these differences. We characterized the diet of Anolis ventrimaculatus (Squamata: Dactyloidae), a species with sexual size and shape dimorphism, widely distributed in highland Colombian environments. Stomach and proximal intestinal content of preserved adults were analyzed. Prey items were classified to order and, when possible, to family. A. ventrimaculatus eats variable preys (mostly Hymenoptera, Coleoptera, and insect larvae) and is classified as a generalist/opportunist. Vegetal debris, shed skin, and stones presumably were ingested incidentally. Diets of males and females are similar. Sexual dimorphism and geographic variation in the diet were minimal. Males and females exhibited differences in total number and percentage of use of frequently consumed prey (Orthoptera and Hymenoptera), and these differences varied among localities. Total prey numbers consumed by females also varied among localities, whereas consumption of Coleoptera and Orthoptera varied in both sexes. Differences in prey size could explain the variation in prey number between sexes, with males probably ingesting larger items. Variation in prey availability (most likely attributable to differences in structural microhabitat use), sample sizes and dates of collecting events could explain minor geographic variation in some aspects of the foraging ecology in this species.

Life traits and predatory potential of Antilochus coqueberti (Fab.) (Heteroptera: Pyrrhocoridae) against Dysdercus koenigii Fab.

The red cotton bug, Dysdercus koenigii Fab., and its specialized predator Antilochus coquebertii (Fab.), are among the most abundant insects in Asian cotton agro-ecosystems. To gauge the potential of using A. coquebertii to control D. koenigii in cotton, we tested the role of feeding on cotton leaves in development of the predator, prey stage preference and characterized the functional response of the predator to prey density under laboratory conditions. Antilochus coquebertii exhibited an active hunting strategy indicative of using both olfactory and visual orientation. Immature stages of the predator successfully developed and reproduced when offered D. koenigii or cotton leaves with D. koenigii. However, A. coquebertii nymphs failed to develop past the third instar when feeding on cotton leaves alone. The food regime did not significantly affect body size of the predator. Mated male and female adults live long when fed with D. koenigii. Total number of prey consumed by an adult predator during 15-days observation reveals not much deviation when offered D. koenigii or cotton leaves with D. koenigii. The adults of A. coquebertii killed a maximum of six D. koenigii adults per day, and were preying on D. koenigii populations in a density dependent manner (showed a type II functional response). We argue that A. coquebertii has considerable potential for the biological control of the red cotton bug D. koenigii.

Prey Consumption by a Large Aggregation of Barn Owls in an Agricultural Setting

Author(s): Browning, Mark; Cleckler, John; Knott, Kayla; Johnson, Matthew | Abstract: Barn owls produce large numbers of young, will nest in close proximity, are easily attracted to nest boxes, and occasionally form dense colonies. Their diet consists largely of various species of rodent pests. These characteristics suggest barn owls could contribute to pest control in agriculture. Studies have been conducted in Israel and Malaysia, but little quantitative research has documented their effectiveness. This study measured the effect of a population of barn owls on a rodent population in a 40-ha vineyard near Sacramento, California. In 2011, 11 of 20 boxes were occupied by breeding pairs, fledging 40 young. In 2012, 18 of 24 owl boxes were occupied, fledging 66 young; and in 2013, three of 24 boxes were occupied, fledging nine young. Nocturnal observations revealed the owls hunted the study area heavily. Monthly pocket gopher surveys using the mound-count method indicated that gophers declined on the vineyard with barn owl boxes relative to a control vineyard without barn owl boxes. Pellet analysis showed diet was composed mainly of Botta’s pocket gophers (70.4%) and California voles (26.2%). An infrared camera recorded 316 deliveries to a nest with three chicks (105.3 per chick) over the first eight weeks. Using these figures, and adding conservative estimates of adult consumption over the 165-day breeding season, and adult and fledgling consumption prior to dispersal, the total number of prey taken over the three breeding seasons was estimated to be 30,020 rodents. Cost comparison analysis showed an average cost of $8.11 per pocket gopher trapped versus $ 0.34 per rodent taken by barn owls.

Mesopredator foraging success in eelgrass (Zostera marina L.): Relative effects of epiphytes, shoot density, and prey abundance

In seagrass habitats, structural complexity influences predator foraging success and prey survival by moderating encounter rates and behaviors of predators and prey. Studies of the effects of structural complexity on predator–prey interactions typically vary seagrass shoot density, biomass, or architecture. Filamentous epiphytic algae commonly grow on seagrass blades and add structure to seagrasses, but the effect of epiphytes on the outcome of predator–prey interactions has rarely been explored. This study determined the relative effects of simulated seagrass epiphytes, eelgrass (Zostera marina) shoot density, and prey density on the foraging behaviors of a common predator, the juvenile giant kelpfish Heterostichus rostratus (Girard, 1854) and on escape responses of their prey, grass shrimp Hippolyte californiensis (Holmes, 1895). Juvenile giant kelpfish hunted for grass shrimp in a laboratory experiment in which two levels of grass shrimp density were crossed with three levels of structural complexity (low density artificial eelgrass, low density artificial eelgrass with artificial epiphytes, and high density artificial eelgrass). Increased structural complexity had variable effects on juvenile kelpfish activity levels, but enhanced their success at catching prey after detection, resulting in no net effect of structural complexity on the total number of prey captured. Grass shrimp made fewer escape attempts in high vs. low structural complexity, which may have enhanced kelpfish foraging success because kelpfish rarely pursued fleeing prey. Prey density did not influence kelpfish behaviors or the total amount of prey they consumed. These results suggest that it is important to consider how different forms of habitat complexity affect the mechanisms by which predators hunt for prey in structured marine habitats.

Dietary habits of the Black-legged mongoose Bdeogale nigripes (Mammalia: Carnivora) in the rainforest of Southeastern Nigeria

The Black-legged mongoose Bdeogale nigripes is a poorly studied carnivore (family Herperstidae) found only in Central African rainforests. In Southeastern Nigeria, its known range is strictly limited to the localities close to the Cameroon border and just east of the Cross River. This article reports some original data on the diet of B. nigripes, the first objectively positive data on this species according to the analysis of their stomach contents. Moreover, these are the first data collected in Nigeria, including the first known record west of the Cross River. B. nigripes seems to be slowly expanding its range westward. Most of its prey were vertebrates, mainly mammals, followed by reptiles and birds. Invertebrate prey was also found, mainly insects, followed by centipedes. In terms of their frequency of occurrence, insects and other arthropods (50.48%) were consumed significantly more often than any other type of prey. Both arthropods (88.88%) and mammals (88.88%) were almost always present in the examined stomachs. Larger prey (mammals), such as Cricetomys emini (1.9% of the total number of prey) and Xerus erythropus (0.95%) were occasionally preyed upon, as well as small snakes (1.9%). Comparing these results with the limited information available thus far, it is evident that there are more prey taxa, in addition to food categories, than previously estimated, and overall this demonstrates that arthropods and mammals are the most commonly consumed prey, the first because they are certainly more numerous, while the latter are far more significant in terms of biomass. In fact, the analysis indicates that mammals (79.21%), and especially large rodents (59.23%), were the main contributors in terms of biomass. Conversely, small prey, in particular arthropods, some of which are tiny, are of decidedly low trophic significance (5.43%).

Occupancy estimation and modeling in monitoring tigers with implications for conservation and management

The tiger (Panthera tigris) is highly endangered through out its range and one of the impediments to effective tiger conservation is the lack of simple and cost effective methods for monitoring of wild tiger populations. With an aim to find a rapid, cost effective, and statistically robust methodology to take quick management decisions, observations of tiger and co-predator sign in administrative subunits (beats) of the Similipal Tiger Reserve, located between 200 28’ and 220 08’ North latitude, and 860 04’ and 860 37’ East longitude in India, were subjected to an occupancy estimation and modeling analysis. Several environmental factors were identified as covariates with explanatory power for the pattern of observations of tiger sign. Most important of these were the proportion of the area of the beat that is classified as disturbed habitat, the distance between the beat and the nearest inhabited place, and the total number of prey observed in the beat in a separate set of surveys for ungulates and other tiger prey species. The results of this analysis have clear management implications for the reserve, with beats classifiable into four categories, each with its own target strategy for increasing tiger abundance. These categories are: highest concern, reduce disturbance, increase prey protection, and maintain current protection. This study suggests that occupancy estimation and modeling from surveys of large mammalian predator sign is a simple cost-effective statistically robust methodology that can be performed by the management staff of a reserve and can be used to engage members of the local population in conservation.

Natural prey of the crab spiderXysticus marmoratus(Araneae: Thomisidae) onEryngiumplants

The natural prey of medium-sized juvenile (ca. 3 mm) crab spiders Xysticus marmoratus Thorell 1875 inhabiting Eryngium biebersteinianum plants was studied on the Absheron Peninsula, Azerbaijan. The percentage of specimens found feeding on prey was low (3.4%). Xysticus marmoratus is a polyphagous predator with representatives of four arthropod orders found in its diet. The primary food of X. marmoratus was ants (Formicidae), which accounted for 83.3% of the total number of prey. The length of prey killed by X. marmoratus ranged between 0.87–7.50 mm (mean 2.96 mm) and constituted from 28.5–300.0% (mean 96.9%) of the length of their captors. The most frequently captured size group of prey was 50–70% the length of the spiders.

Food resources and foraging habits of the common shrew,Sorex araneus: does winter food shortage explain Dehnel's phenomenon?

It is widely assumed that winter is a critical time for homeotherms because of decreased ambient temperatures coupled with reduced food supply. Shrews are excellent models for investigating overwintering strategies, not only because of their particularly small size, high energy requirements relative to their size and short fasting endurance, but also the dramatic reduction in body size (Dehnel's phenomenon) exhibited by soricine shrews in northern temperate winters. The cause of Dehnel's phenomenon is poorly understood but food supply is implicated. To test the hypothesis that winter at higher latitudes is a period of food shortage for small homeotherms, we compared feeding habits of common shrews,Sorex araneus, and abundance and biomass of their prey in winters and summers in northeastern Poland using scat analysis combined with pitfall and ground core sampling for invertebrates. Ground‐surface activity and numbers of invertebrates in pitfall traps were greatly reduced in winter but, contrary to prediction, no significant differences between winter and summer were found in total numbers and biomass of prey invertebrates in ground core samples. However, certain prey types changed seasonally with respect to numbers, biomass and distribution in the soil profile, which was reflected in shrews’ food composition and foraging behaviour. Dehnel's phenomenon appears not to be caused by reduction in total prey numbers and biomass, at least in our study area. Smaller body mass coupled with lowering of absolute food requirements may have important survival value in winter with its reduced numbers of certain major prey coupled with increased difficulty of locating and extracting invertebrates within the soil profile resulting in higher energetic costs of foraging.

Prey capture in orb weaving spiders: are we using the best metric?

Orb spiders are commonly used to study many ecological and behavioral questions, due in part to the ease of working with their webs. The frequency distributions of prey captured by spiders are often compared among species or individuals to search for evidence of competition, effects of experimental manipulations, etc. In most instances, smaller insects are extremely common compared to larger prey, presenting a critical flaw in how such comparisons are analyzed because natural selection acts upon web evolution through the biomass, rather than total number, of prey captured. The ''rare, large prey'' hypothesis, developed for Zygiella x-notata (Clerk 1757), suggests that orb spiders derive the bulk of their energy not from common prey, but rather from a small subset of the largest possible insects. If correct, then orb webs should be designed to facilitate the capture of these insects, which are essential for spider fitness, even though they rarely fly into webs. Here, I test the generality of the ''rare, large prey'' hypothesis by comparing the frequency and biomass of large prey in 38 studies of the diets of 31 species of orb spiders in four different families. I define large prey as insects at least 66% as long as the spiders capturing them. The 38 studies included both large and small species of spiders, living in both tropical and temperate habitats. Large insects accounted for only 17% of the total number of prey captured by spiders, but contributed 85% of the total consumable biomass. The ''rare, large prey'' hypothesis thus can apparently be generalized across orb spiders. Future experiments need to account for the disproportionate influence of these large insects on spider fitness and on how to effectively measure these rare events. More importantly, the ''rare, large prey'' hypothesis provides a new framework in which to better understand variation in the web spinning behaviors of spiders.

Predation on Juvenile Pacific Salmon Oncorhynchus spp. in Downstream Migrant Traps in Prairie Creek, California

AbstractDownstream migrant traps are a widely applied fishery management tool for sampling anadromous Pacific salmon Oncorhynchus spp. and steelhead O. mykiss smolts along the West Coast of North America and elsewhere, yet predation on juvenile salmonids in traps has not been studied quantitatively. We assessed the frequency of occurrence and abundance of juvenile salmonids in the stomachs of coastal cutthroat trout O. clarkii clarkii, coho salmon O. kisutch, steelhead, and prickly sculpin Cottus asper (>70 mm fork length) captured in traps and in nearby stream habitats. All four predator species took juvenile salmonids with much greater frequency in traps than in stream habitats. Among free‐swimming predators, only coastal cutthroat trout were observed with salmonid fry in their stomachs, but they took fewer salmonid prey and appeared to rely more heavily on insect prey than did coastal cutthroat trout captured in traps. Predators consumed up to 25% of the available prey over a broad range of prey abundances. Over the course of the study, predators consumed 2.5% of all salmonid fry captured in traps, but this fraction ranged from less than 1% to more than 10% in any given year. The number of prey taken in traps increased with predator length and with prey abundance in traps, and predation in traps peaked during the period of most intense downstream migration by salmon fry. In contrast, live‐box design and trap location had little or no effect on the total number of prey taken by individual predators. We estimated that the predation mortality of juvenile salmon increased by 0.5–1.0% due to in‐trap predation (i.e., a 9–10% relative increase over natural predation rates). We found no evidence that predators selected for prey on the basis of species. These results should motivate additional research on methods that reduce or eliminate predation in trap live‐boxes and protocols for efficiently measuring predation associated with the trapping of downstream migrants.Received May 11, 2010; accepted November 29, 2010

Change in prey selectivity during the larval life of Atlantic cod in the southern Gulf of St Lawrence

Atlantic cod larvae showed strong selectivity for the medium-size calanoid copepod Pseudocalanus spp. Naupliar stages comprised 62.4% of total prey number in the gut of first-feeding larvae. Selectivity shifted to Pseudocalanus spp. females at the mid-larval stage, representing 43% of all prey ingested by > 12 mm larvae.