Stomach Content Analysis Research Articles

Seasonal changes in the dietary patterns and reproductive aspects of deep-water rose shrimp Parapenaeus longirostris in the central Adriatic Sea

The deep-water rose shrimp Parapenaeus longirostris is one of the most important commercial species caught by trawl fisheries in the Mediterranean Sea. The species has a warm-water affinity and its landings are increasing in the whole basin. Detailed information on its trophic ecology, niche width and role within demersal food webs is dated or lacking in the Adriatic Sea, the most exploited basin of the Mediterranean. Therefore, to detect seasonal changes in diet and trophic levels, seasonal samplings were conducted in this area from January to December 2021, collecting 400 specimens, and integrating information from both stomach content analysis and stable isotope analyses (SIA). To identify potential links between the biological cycle of the species and fluctuations in energy demand, seasonal changes in fullness, as a proxy of feeding intensity, and gonadosomatic and hepatosomatic indices were assessed. The deep-water rose shrimp is confirmed to be a benthic feeder that predominantly preys on molluscs, crustaceans, fish, echinoderms and polychaetes. According to SIA, P. longirostris is defined as a secondary consumer. Observed seasonal dietary changes precede the reproductive periods, likely due to the need for more energetic prey.

Utilisation of macroalgal habitats by juvenile rabbitfishes on an inshore reef

AbstractMacroalgal beds are increasingly recognised as nursery habitats for coral reef fish; however, the extent to which they are used as a source of food and/or a refuge from predation remains largely unexplored. Here, we investigate the distribution, feeding behaviour, diet, and predation risk for juvenile rabbitfish in macroalgal habitats on Orpheus Island, Great Barrier Reef. Visual surveys revealed that juvenile and adult Siganus doliatus had different among-habitat distributions with juveniles being largely restricted to the reef flat and positively associated with macroalgal cover, while adults were abundant on the reef crest. Focal feeding observations show that within macroalgal habitats, juvenile S. doliatus targeted epiphytes on Sargassum (80% of bites), with relatively few bites taken on turfs or the Sargassum itself (27% and 8%, respectively). These observations were supported by stomach content analyses with filamentous algae being the dominant item in the stomach content of both small (< 4 cm total length, TL; 58%) and large juvenile S. doliatus (> 4 cm TL; 47%). The stomach content of juvenile S. doliatus, S. canaliculatus, and S. spinus collected from macroalgal habitats was similar, consisting primarily of filamentous algae and detritus. We found no relationship between the abundance of potential predators and juvenile rabbitfishes across the study sites. Collectively, our results suggest that juvenile rabbitfishes are using macroalgal habitats on this, and potentially other, inshore reefs as a food source and add to a growing body of literature highlighting the importance of these habitats for the early life stages of reef fish.

Southernmost record and diet of Leptobrachella eos (Ohler, Woollen, Grosjean, Hendrix, Vences, Ziegler & Dubois, 2011) in Vietnam

Abstract The Rosy Litter Frog (Leptobrachella eos) is known from Thailand, Laos, and Vietnam. Knowledge about the natural history of this species is virtually lacking. As a result of our field work in Son La, Nghe An, and Ha Tinh provinces of Vietnam, we provide data on the food composition of L. eos for the first time. Using the stomach-flushing method, we analyzed stomach contents of 34 individuals (23 males and 11 females) from a total of 42 frogs, with stomachs of five males and three females (19%) being empty. A total of 13 prey categories were observed in the stomachs of L. eos, with 232 items, comprising 230 items of invertebrates and two unidentified items. The most important (IRI) groups among the prey of L. eos were Blattodea (26.31%), Araneae (17.26%), Orthoptera (13.21%), Coleoptera (12.39%), and Opiliones (10.09%). There was an overlap of 51.11 % in the diet between males and females, The trophic spectrum of males comprising 11 prey categories revealed to be wider than that of females comprising nine prey categories. Despite differences in diets between the sexes, Blattodea, Orthoptera, Araneae, Coleoptera, and Opiliones represented the most important prey category for all of them. In addition, we also report a new find of Leptobrachella eos, with a new subpopulation from Ha Tinh Province, Vietnam.

The diet and diving behaviour of the ringed seal (Pusa hispida) in Kangia (Ilulissat Icefjord), Greenland

AbstractThis study uses telemetry and stomach content analysis to describe the ringed seals’ dive pattern and prey selection within Kangia (Ilulissat Icefjord), Greenland, where the ringed seals are known to be exceptionally large and genetically distinct. Data from twenty-four ringed seals (Pusa hispida) tagged in Kangia, with satellite relay data loggers from 2012 to 2020, were used to describe the dive patterns. The transmitters were active between 28 and 270 days and showed that subadults most frequently dove to around 150 m. Adult males frequently dove to this depth, but they also had a second frequently visited depth at around 400 m, some adults significantly deeper. Adult males generally dove deeper than females and adult seals showed deeper dives during the winter, a feature that was less prominent in subadults. The stomach content from ringed seals (n = 108) harvested in Kangia by subsistence hunters revealed that polar cod (Boreogadus saida), capelin (Mallotus villosus), mysids (Mysis oculata, M. littoralis, M. Polaris) and shrimps (mainly Pandalus borealis) were the dominant prey. Shrimps were observed more often in adults, likely due to the frequently visited dive depth of around 400 m, whereas mysids were more observed in small subadult seals. The stomach content from harp seals (Pagophilus groenlandicus) and Greenland halibut (Reinhardtius hippoglossoides) caught in Kangia also showed a strong niche overlap with the ringed seals. These findings outline the unique ecological adaptations and the importance of Kangia as a critical habitat of ringed seals.

Changes in the Diet of an Invasive Predatory Crab, Chionoecetes opilio, in the Degrading Benthic Community of an Arctic Fjord.

The introduction of a new species can lead to substantial changes in a new ecosystem. Local and introduced species' survival depends on their ability to adapt to the new environment. Studying such adaptations is often hindered by multiple factors affecting the ecosystem. The introduction of a large predatory snow crab, Chionoecetes opilio, into the Kara Sea, is a unique invasive species affecting an otherwise undisturbed ecosystem. The crab has caused drastic changes in the macro- and megabenthic taxonomic structure, abundance, and biomass of the most common species in an Arctic fjord, Blagopoluchiya Bay. Stomach content and stable isotope analysis were applied to study crabs' feeding habits. As the abundance of the most common prey items diminished, the crabs switched to other less accessible food. Prior to substantial changes in benthic communities, the diet of the snow crabs was similar to that of other invaded and native areas, where animal food predominates. However, with the degradation of the ecosystem, detritus contribution has substantially increased. The changes in prey items did not change the crab's trophic status, and they continued to feed within the same trophic niche. In the depleted benthic communities of Blagopoluchiya Bay, the snow crab is forced to use all available food sources.

Evidence for resource partitioning in weakfishes from a coastal upwelling ecosystem

Resource partitioning plays an important role in supporting species coexistence. In a coastal upwelling ecosystem two weakfish species, Cynoscion guatucupa and C. jamaicensis co-occur and are key commercial species. The present study aimed to provide a comprehensive assessment of the feeding ecology of both species, including to; (i) quantitatively assess diet, (ii) evaluate ontogenetic and seasonal diet variations, and (iii) estimate dietary overlap in the context of competition or resource partitioning, using an integrated approach combining stomach content (SCA) and stable isotope analyses (SIA). Our results revealed that both C. guatucupa and C. jamaicensis prey mainly on pelagic fish and shrimp with ontogenetic and seasonal changes in diet detected. Weakfishes consume a large proportion of similar prey throughout the year and high isotopic niche overlap confirmed the SCA results. Despite the similar use of food resources by both species, the availability and abundance of prey promoted by seasonal upwellings and the possible spatial segregation between C. guatucupa and C. jamaicensis may promote their co-occurrence in an upwelling ecosystem. Due to their commercial value and fisheries importance in the southwestern Atlantic, these results contribute insights to support sustainable fisheries management.

Niche partitioning of invasive Amur sleeper (Perccottus glenii) amongst native fish communities in three different freshwater ecosystems

The invasive fish, Amur sleeper, poses a significant and growing threat to Central European freshwater ecosystems. Despite its rapid spread, the ecological implications of its invasion have been poorly explored. Recent findings confirm its presence in various Estonian freshwater systems, raising concerns about its imminent expansion into larger lakes. To better understand its potential ecological impacts, we explored the isotopic niche of the Amur sleeper in comparison with native fish species co-existing in three Estonian freshwater ecosystems. We employed carbon and nitrogen stable isotope analyses alongside gut content analyses. Our findings show that the Amur sleeper’s diet in newly-invaded Estonian water bodies predominantly comprises benthic macroinvertebrates, although it may also include fish, confirming its role as a predator in the local food web. Notably, Amur sleeper populations exhibited clear isotopic niche partitioning in three invaded ecosystems. A logistic regression model, based on stomach content analyses, revealed an ontogenetic diet shift from benthivorous to piscivorous feeding habits from small to large specimens. Amur sleeper exhibits voracious, non-selective feeding habits, which can negatively impact native freshwater communities. The ability to occupy a distinct isotopic niche, with minimal overlap with native fish populations, may reduce interspecific competition, facilitating the spread and establishment of Amur sleeper in newly-invaded habitats. Managing the spread of this invasive species thus becomes even more critical to safeguard the integrity of native aquatic ecosystems.

The impact of multi-type artificial reef habitats on the feeding ecology and trophic niche of dominant rocky reef fish species (Hexagrammos otakii and Sebastes schlegelii)

Large-scale artificial reef constructions have been carried out in the coast of northern Yellow Sea, which has effectively enhanced populations of rocky reef fish species. However, there is a lack of evidence regarding the differences in community composition among different types of artificial reef habitats. This study scrutinizes the foraging dynamics and ecological niche partitioning of Hexagrammos otakii and Sebastes schlegelii, which are two representative rocky reef fish species in the northern Yellow Sea. Stomach content analysis indicates that H. otakii exhibits a more diverse diet compared to S. schlegelii, with both species achieving the highest dietary diversity within concrete reef habitats. When factoring in body size, the dietary diversity for fish in the 0–15 cm size class was found to be the greatest within rock reef habitat, while larger individuals exhibited higher diversity within ship artificial reef habitats. The prey composition results demonstrate spatial differentiation patterns consistent across all size classes, with these discrepancies predominantly situated between ship and concrete or rock artificial reef habitats. The taxa driving these differences varied with fish species and body size, encompassing various prey categories such as Decapoda, Teleost, Polychaeta and Amphipod. Findings from the Stable Isotope Mixing Model (SIMMR) revealed significant dietary variations linked to species, habitat type and size class, which were fundamentally in agreement with the stomach content analysis. Niche analysis disclosed that overall niche breadth for both fish populations was largest in concrete artificial reef habitat. This suggests that each reef type caters to specific fish size classes, showcasing distinct spatial and interspecific variations in foraging tactics.

Trophic Ecology of the Pyjama Shark Poroderma africanum (Gmelin, 1789) Elucidated by Stable Isotopes.

Sharks may occupy both intermediate and upper levels of marine food webs. They are overfished worldwide and constitute one of the largest portions of the bycatch. The removal of top-predator species has negative cascading effects on the entire food web, causing the "mesopredator release" phenomenon, which leads to an increase in mesopredators with consequent changes in the ecosystem's energetic balance. Despite their important ecological role, information on their trophic ecology is limited. This essential information can be obtained through the analysis of stomach contents and, more recently, by using less invasive techniques, such as the stable isotope analysis of muscle tissue, obtained through biopsies. Here, we analysed the trophic ecology of the pyjama shark or striped catshark Poroderma africanum, an endemic species of South Africa, by means of SIA. The results obtained from SIA were analysed using the R SIMMR and SIBER packages to estimate the contribution of potential food sources to the diet and to evaluate the extent of the trophic niches. The SIMMR outputs showed that adults select more benthic prey than juveniles, which consume more planktonic species, with juveniles being more generalist than adults, according to SIBER outputs. As assessed by IUCN, the population of P. africanum is increasing, and given its role as mesopredator, future monitoring efforts could be crucial to elucidating their potential effects in marine food webs.

Multi-disciplinary approach identifies pelagic nutrient linkage by sawsharks

Quantifying the trophic role of a species is key to understanding its ecology and ecological role. Their trophic role can influence community composition, ecosystem stability, and nutrient transport and cycling between habitats through ingestion, egestion, and excretion, which requires an understanding of species diet and habitat use. Despite the regular occurrence of sawsharks in Australian temperate fisheries, there remains limited information on their trophic ecology or habitat use, but they are assumed to be benthic consumers. We used fatty acid and stable isotope profiles along with stomach content analysis to investigate the trophic ecology of two sympatric species of sawsharks, the common sawshark (Pristiophorus cirratus) and southern sawshark (Pristiophorus nudipinnis) in south-eastern Australia. Stable isotope analysis of δ13C, δ15N, and δ34S in sawshark muscle revealed that P. nudipinnis fed at a higher trophic level than P. cirratus, and mixing models and stomach contents indicated P. nudipinnis was surprisingly reliant on pelagic and benthopelagic prey sources. In contrast, P. cirratus preyed on more benthic invertebrate species, not found in P. nudipinnis. This bentho-pelagic partitioning between species was supported by P. nudipinnis fatty acid profiles having higher levels of tracers associated with dinoflagellate basal sources (16:1/16:0, 22:6ω3) than P. cirratus, indicating a reliance on pelagic food webs. These data demonstrate that sawsharks are mesopredators that play a substantial role linking pelagic and benthic food webs and highlights the value of incorporating multiple biochemical tracers to provide a comprehensive representation of an animal’s trophic ecology and role in and between ecosystems.

Migratory-derived resources induce elongated food chains through middle-up food web effects

BackgroundSeasonal movements of animals often result in the transfer of large amounts of energy and nutrients across ecosystem boundaries, which may have large consequences on local food webs through various pathways. While this is known for both terrestrial- and aquatic organisms, quantitative estimates on its effects on food web structure and identification of key pathways are scarce, due to the difficulty in obtaining replication on ecosystem level with negative control, i.e. comparable systems without migration.MethodsIn this study, we estimate the impact of Arctic charr (Salvelinus alpinus) migration on riverine ecosystem structure, by comparing multiple streams with strictly resident populations above natural migration barriers with streams below those barriers harboring partially migratory populations. We compared density estimates and size structure between above and below populations. Diet differences were examined through the analysis of stomach contents, changes in trophic position were examined by using stable isotopes. To infer growth rate of resident individuals, back-growth calculation was performed using otoliths.ResultsWe find higher densities of small juveniles in partially migratory populations, where juvenile Arctic charr show initially lower growth, likely due to higher intraspecific competition. After reaching a size, where they can start feeding on eggs and smaller juveniles, which are both more frequent in partially migratory populations, growth surpasses that of resident populations. Cannibalism induced by high juvenile densities occurred almost exclusively in populations with migration and represents an altered energy pathway to the food web. The presence of large cannibalistic charr feeding on smaller ones that have a similar trophic level as charr from strictly resident populations (based on stomach content) coupled with steeper δ15N-size regression slopes illustrate the general increase of food chain length in systems with migration.ConclusionsOur results thus suggest that the consumption of migration-derived resources may result in longer food chains through middle-up rather than bottom-up effects. Furthermore, by occupying the apex of the food chain and feeding on juvenile conspecifics, resident individuals experience reduced competition with their young counterparts, which potentially balances their fitness with migratory individuals.

Verifying the Diet of the Slender Racer, <i>Orientocoluber spinalis</i> (Peters, 1866), Rare, Threatened, and Endangered Across Northeast Asian Countries

Understanding the diet of a species provides important information on various aspects of its ecology. Diet studies are few on the reptile species, of which observation frequency is very low, due to the great difficulty of sampling. We investigated the diet of Orientocoluber spinalis, a long and slender small grassland snake with high rarity and a high extinction risk across northeast Asian countries, by applying regurgitated stomach content analysis and metabarcoding analysis using a developed O. spinalis blocking primer. Among 19 diet samples, which were mainly collected on islands along the west coast of the Korean Peninsula, we determined the food sources of 13 samples, which consisted of four small vertebrate species, the Tsushima smooth skink (Scincella vandenburghi), mountain grass lizard (Takydromus wolteri), Japanese keelback (Hebius vibakari), and lesser white-toothed shrew (Crocidura shantungensis). Among them, O. spinalis most frequently fed on S. vandenburghi (10 of 13 cases). Our results show that O. spinalis mainly forages small reptiles and mammals in grasslands adjoining to lowland forests and could be beneficial for conservation in the field and rearing of this vulnerable species in the facilities.

Incorporating ecological heterogeneity and intraspecific variation differentiates complex interactions between apex predators and stocked fish

Ecological heterogeneity and intraspecific variation can impact energy flow from the base of the food web to top predators. We evaluated the effect of intraspecific variation on estimates of lake trout (Salvelinus namaycush) consumption of stocked kokanee (lacustrine sockeye salmon, Oncorhynchus nerka) in a 390 ha oligotrophic lake with two distinct basins. Lake trout stomach content analyses, stable isotope niche space, and catch rates indicated high intraspecific variation in resource use across habitats and basins. Intraspecific variation and ecological heterogeneity were incorporated into two bioenergetics modeling approaches; one lake-wide model, and one partitioned model that accounted for differences in lake trout diet composition and population size across habitats. The ecologically partitioned model highlighted that lake trout consumption was primarily in the epilimnion of one basin, while the lake-wide, unpartitioned model performed similarly but failed to provide ecological context for where that consumption occurred. Incorporating ecological heterogeneity and intraspecific variation into bioenergetic models can more accurately represent top predators foraging patterns across habitats and inform management actions to mitigate impacts to stocked fish.

Stomach content analysis indicates multi decadal trophic stability in a temperate coastal fish food web, western Dutch Wadden Sea

Information about stomach content composition of fish species of a temperate coastal fish community (western Dutch Wadden Sea) over the period 1930–2019 was analysed to reconstruct long-term trends in trophic position of individual species. Stomach data were not evenly distributed but clustered both with respect to years as well as fish species. For 18 fish species, all being omnivorous and belonging to different functional groups (pelagic, benthopelagic, demersal) and guilds [(near)-resident, juvenile marine migrants, marine seasonal visitiors], prey consumption and trophic position over time could be analysed. Prey occurrence in the stomachs of different fish species showed variability over time, most likely due to fluctuations in prey abundance, but without a trend. For all species, individual fish showed variablity in trophic position in the order of 1 unit or even more both within and between years. However, in all 18 species, no significant trend in mean trophic position over time could be found, despite the serious anthropogenic stress (pollution, eutrophication events, climate change) and the decrease in fish abundance in the area during the last 50 years. The present study does not indicate any changes in trophic position of individual species in the western Dutch Wadden Sea over the last 80 years. At the community level, trophic structure varies due to interannual fluctuations in species composition and year-to year fluctuations in the relative abundance of the various fish species. At the ecosystem level the trophic role of the fish community has been degraded due to the decrease in total fish biomass in the area.

Combining biotracer and stomach contents analysis to understand trophic dynamics in the northern Gulf of Mexico

The northern Gulf of Mexico (nGOM) is a taxonomically rich ecosystem. Previous work based on a meta-analysis of stomach contents data has shown the trophic connectivity of predators and prey to be substantial. However, the trophic dynamics of many economically and ecologically important species are still not well understood. Sportfish, such as Spotted Seatrout (Cynoscion nebulosus), Red Drum (Sciaenops ocellatus), and Southern Flounder (Paralichthys lethostigma), support recreational fisheries throughout the region. Gulf Menhaden (Brevoortia patronus), a high biomass forage fish with the region's largest commercial fishery, is considered an important forage species. In this study, we use information from meta-analysis of stomach contents and stable isotope analysis to investigate the importance of prey taxa, including Gulf Menhaden, for nGOM nearshore predators. Stomach contents and stable isotope analyses are generally evaluated independently, with stomach contents used to directly identify trophic interactions, while stable isotopes of carbon (δ13C) and nitrogen (δ15N) provide insight into a consumer's long-term feeding habits. We used a multispecies trophic model, EcoDiet, developed by Hernvann et al. (2022), that integrates information of both stomach contents and stable isotopes into a single framework to estimate trophic link probabilities and diet proportions. Data in the model include n = 41 predators, n = 173 prey, and n = 497 unique predator and prey interactions. The results indicate that nGOM nearshore predators are generalists using the diverse prey base, and in concordance with previous findings, there is no single Menhaden-dependent predator. Our findings better quantify the trophic interactions of the highly diverse nGOM region and have important implications regarding future ecosystem modeling and management considerations for the Gulf Menhaden stock.

Octopus diet during the settlement period using DNA metabarcoding

The settlement phase is a challenging period for meropelagic octopus, as they adapt to their new life in the sea bottom after a planktonic period. Their ecology and trophic interactions with the surrounding fauna in the wild are practically unknown. To understand their predatory role in the littoral zone, the diet of recently settled Octopus vulgaris from a Mediterranean sandy bottom was studied through molecular methods. Amphipods were present in all the analysed stomach contents, with a total of 20 amphipod taxa recorded as prey. Jassa slatteryi and Microprotopus maculatus were the most commonly found amphipod species. Hydrozoans, decapod crustaceans, cephalopods and bivalves followed amphipods in importance. Niche breadth index assigned to small recently settled octopus the role of a specialised predator, increasing the diversity of prey as they grow. Larger juveniles displayed a higher number of prey taxa suggesting a decreasing predatory specialisation with octopus size and an ontogenetic shift in trophic ecology from diet mainly based on amphipods to a richer diet. The considerable arm elongation and the strong muscular arm crown development after settlement probably allow the juvenile benthic octopus to develop ambush predation and speculative hunting, increasing the range of potential benthic prey species along its adaptation to the benthos.Graphic abstract

Variability in resource use of sympatric cowfish Aracana aurita and A. ornata in southeastern Australian waters

Sympatric species that share morphological similarities tend to diversify their prey resources to coexist. The striped cowfish (Aracana aurita) and ornate cowfish (A. ornata) live together on the continental shelf from western to southern Australia including Tasmanian waters. The present study analyzed stomach contents and stable isotope ratios (δ13C and δ15N) to investigate the use of food resource between the two species collected in Tasmanian waters, Australia. In total, 139 A. aurita and 46 A. ornata were collected from 2014 to 2018. The small size class of A. aurita (<140 mm SL) mainly consumed polychaetes and amphipods, while its large size class (≥140 mm SL) preyed more on bivalves and crustacean decapods. The main prey items of the small size class of A. ornata (<140 mm SL) were amphipods and crabs. No differences in diet were observed between the sexes of either species. Stable isotope analyses showed significant differences in δ15N and δ13C between the two species, but not between the two size classes of A. aurita (ANOVA, P < 0.05). Integrating analyses of stomach contents and stable isotopes indicated that the two species preferred different food resources based on different trophic sources. Consequently, although the habitats of the two species overlap, both species can co-exist through dietary segregation.

Ontogenetic, Spatial and Inter-Annual Variability in the Diet of European Hake Merluccius merluccius Linnaeus, 1758, in the North Aegean Sea

This study contributes to filling knowledge gaps regarding recent information on the diet of the European hake, Merluccius merluccius Linnaeus, 1758, in the Greek seas, particularly its ontogenetic shifts and its spatiotemporal variability. The trophic preferences of M. merluccius were investigated in the North Aegean Sea during the summers of 2019 to 2023 with visual stomach content analysis to assess its composition, diversity, and variability across body-size classes, years, and subareas. The identified prey are functionally diverse and in many cases also primary targets for local fisheries. The ontogenetic trophic niche of hake was characterized by two distinct shifts, delineated by 10 and 50 cm body-size thresholds. Cephalopods were a prevalent dietary component for large hake individuals. The intermediate body-size classes demonstrated greater trophic niche breadth concerning prey diversity and absolute prey-size ranges. A feeding strategy characterized by the specialization of individuals was also revealed. The effect of the temporal and spatial context on the hake diet was occasionally correlated with spatiotemporal variations in the sizes of their populations. In conclusion, ontogenetic and spatiotemporal variability in the hake diet were found to be significant and should be considered in the data collection design and analyses of the trophic interactions of the species.

Feeding ontogeny and trophic ecology of the shortfin mako shark, Isurus oxyrinchus, on the west coast of Baja California Sur, Mexico

Certain shark species are considered top predators, which bestows them with important roles in the trophic dynamics of marine ecosystems. The present study describes the ecology and ontogeny feeding of the shortfin mako shark Isurus oxyrinchus along Baja California Sur, Mexico, through stomach content analysis (SCA) and stable isotope analysis (SIA). A total of 272 stomachs and 39 muscle samples of I. oxyrinchus were analyzed. The SCA indicated that I. oxyrinchus has a wide trophic spectrum, with a consumption preference for Dosidicus gigas, Prionotus albirostris, and Scomber japonicus; however, feeding differences by sexes and sexual maturity stages were evidenced. The SCA indicated that I. oxyrinchus is a specialist consumer (Bi = 0.10) occupying high trophic positions (TP: 4.7–5.2). SIA reflected isotopic signals between –17.3 ‰ and –15.7 ‰ for δ13C and 15.5 ‰ and 19.5 ‰ for δ15N, but with some differences by maturity stages in δ15N (Young-of-the-year = 16.4 ± 0.66 ‰, Juveniles = 18.1 ± 0.13 ‰, adults = 18.3 ± 0.56 ‰). The SIA suggests that this species has a wide isotopic niche (SEAC: 1.08 ‰2) and occupies high TP (3.9–6.2). In conclusion, I. oxyrinchus presents segregation by sex and maturity stages, shows ontogenetic changes in habitat use and prey selection related to the physical characteristics of the zone (bathymetry), and plays important roles in the trophic dynamics of marine ecosystems.

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.