Stomach Content Analysis Research Articles

Stomach content analysis of Euthynnus affinis, Auxis thazard and Auxis rochei of the coastal waters of Sri Lanka by DNA barcoding.

Analysis of the content of the gut of fish helps in the understanding of their inter- and intra-specific interactions, fish behaviour, condition and energy intake. The stomach contents of the commercially important neritic tuna species of Sri Lanka, kawakawa (Euthynnus affinis), frigate tuna (Auxis thazard) and bullet tuna (Auxis rochei) were analysed to determine their feeding habits and to identify prey species. The weighed stomachs of fish were dissected to reveal the types of prey found within. The prey was categorised into prey categories and each prey species was identified morphologically. Prey items which were partially digested were identified using DNA barcoding. The main prey category was small fish, followed by crustaceans and cephalopods. While the highest occurring prey category for E. affinis and A. rochei was fish, crustaceans dominated the A. thazard diet. DNA barcoding identified 11 prey items that were partially digested, which could not be identified to species-level morphologically. Of the prey items identified by DNA barcoding, four species of fish, three species of cephalopod and four species of crustaceans were identified. These prey item identifications confirmed that E. affinis, A. thazard and A. rochei are all nonspecific feeders. This exhibits the value of molecular tools in the identification of species which have lost their distinguishable features due to digestion. Further, it illustrates the predator-prey relationships between these species, aiding in the management of prey and predator populations, ensuring that both populations remain stable, helping in the maintenance of the balance of the ecosystem.

Trophic niche variation driven by water level fluctuations facilitates the co-occurrence of invasive tilapia species in a subtropical reservoir in China.

Investigating how multiple invasive fish species with similar ecological traits respond to different environmental conditions is crucial to understanding their successful invasion and coexistence. Here, we used stomach content analysis and stable isotope analysis to analyse the effects of water level fluctuation on the trophic niche plasticity of three dominant co-occurring invasive tilapia species (Coptodon zillii, Sarotherodon galilaeus, and Oreochromis niloticus) in the Shanmei Reservoir, southern China. We found that the tilapia species exhibited an iliophagous habit with dietary variations between the high-water (HW) and low-water (LW) level periods. During the LW period, tilapia fishes primarily fed on periphytic algae, whereas during the HW period, they reduced their consumption of epiphytic algae and increased their intake of plant remains. Biofilms were the most assimilated resource by the species during the LW period, whereas riparian plants dominated during the HW period. The niche width and niche overlap of the three tilapia species were significantly greater in the HW period than in the LW period. However, their trophic positions were not significantly affected by water level fluctuations. Our findings indicate that temporal variation in diet composition and trophic niche, driven by water level fluctuations, may favor food resource partitioning and facilitate the coexistence of these invasive tilapia species.

Comparative feeding habits of the invasive non-indigenous devil firefish Pterois miles and the indigenous scorpionfishes Scorpaena porcus, Scorpaena scrofa, and Scorpaena notata on the southwest coast of Türkiye, eastern Mediterranean

The feeding habits of the invasive alien devil firefish (Pterois miles) and the indigenous scorpaenids Scorpaena porcus, Scorpaena scrofa, and Scorpaena notata in the eastern Mediterranean Sea were investigated based on stomach content analysis. Furthermore, we examined whether these confamiliar species feed upon similar prey. Specimens were captured by professional fishers using trammel nets on the southwestern coast of Türkiye in the winter and summer of 2021. A total of 608 stomachs (286 P. miles, 112 S. porcus, 136 S. scrofa, and 74 S. notata) were investigated. The results demonstrate that the diet of P. miles included a total of 45 taxa, with 33 identified at the species level (27 indigenous, 6 non-indigenous), while those of the three congeneric scorpaenids included a total of 46 taxa and 37 identified species (30 indigenous, 7 non-indigenous). For P. miles, the highest index of relative importance (%IRI) values were determined for fish in both seasons (83.44% in winter, 93.82% in summer), with the damselfish Chromis chromis being the most preferred species. S. scrofa fed mainly on fish in winter and cephalopods in summer, whereas the diets of S. porcus and S. notata included mainly crustaceans in both seasons. In winter, P. miles exhibited a higher percentage of empty stomachs, demonstrating a significant difference in the vacuity index in different sampling seasons, while other scorpaenids did not exhibit statistically significant differences. This study also provides the northernmost record of the non-indigenous crab species Gonioinfradens giardi and the second record of the squat lobster Dactylonida curvimana in Türkiye. It also provides new reports of rarely observed fish species for the eastern Mediterranean, including Bellottia apoda and Odondebuenia balearica.

It’s Time for Dinner, a Particular and Seasonal Feeding Habit of a Threatened Troglobitic Catfish from Brazil, Rhamdiopsis krugi Bockmann & Castro 2010 (Ostaryophysi, Siluriformes)

Rhamdiopsis krugi is a highly specialized troglobitic (exclusively subterranean) catfish endemic to the phreatic water bodies of twelve caves located within two separated metasedimentary basins in the region of Chapada Diamantina, Bahia state, Brazil. This species is included in the List of Endangered Fauna of Brazil, under the Vulnerable category—VU. In general, troglobites have different strategies for searching for food and reproductive partners, as well as unique behaviors. Knowledge of the reproductive periods, as well as its feeding habits, provides fundamental data for effective protection and species conservation. Biological aspects related to feeding habits and reproduction of R. krugi were addressed across six annual cycles, considering both dry and rainy seasons. For this, stomach content analysis, using the frequency of occurrence and volumetric index methods, as well as observation of the sex ratio and stage of maturation of the gonads were carried out for 148 individuals of R. krugi sampled in eight caves in Chapada Diamantina. Stomach volumes correlated with reproduction aspects across the dry and rainy seasons. These populations showed opportunistic carnivorous feeding habits, consuming both autochthonous and allochthonous items, with a preference for foraging in submerged guano deposits, which demonstrates the catfish’s strong dependence on bats. Regarding sex ratios, there was no marked seasonality; however, in rainy seasons, there was a higher proportion of maturing females, showing a reproductive tendency. During these periods, there was also a significantly higher number of stomachs with contents, showing seasonality in the diet. Specialized diet and dependence on rainy periods, especially in diet, corroborate the fragility of R. krugi, especially considering the changes in rainfall regimes in Brazil, with dry seasons exceeding eight months per year in the last ten years.

A Deep Dive into the Trophic Ecology of Engraulis ringens: Assessing Diet Through Stomach Content and Stable Isotope Analysis

Our study investigates the trophic ecology of the anchoveta (Engraulis ringens). The anchoveta plays a key role in the Greater Humboldt Ecosystem and is extensively exploited by countries from the south-eastern Pacific Ocean. For a comprehensive study of trophic ecology, we employed a combined approach that included stomach content analysis, stable isotope analysis, and scaled mass index of body condition. Our results showed that the multivariate composition of the diet varies significantly between life stage and fishing zones in Chile. Copepods and euphausiids emerged as the dominant prey found in the stomachs across all fisheries zones. Stable isotope analysis revealed significant differences among different zones. The scaled mass index values were higher in the northern zone compared to the southern zones, for both juveniles and adults. This research carries significant implications for fisheries management and conservation efforts, such as the development of targeted management strategies that address variations in the trophic structure of anchoveta across different life stages and fishing zones.

The secret meal of Antarctic mesopelagic fish (Myctophidae: Electrona) revealed by multi-marker metabarcoding

IntroductionIn the Southern Ocean, myctophids are the most successful pelagic fish group in terms of diversity, biomass, and abundance. They play a crucial role in linking primary consumers and coupling carbon flux between surface and mesopelagic depths. Understanding their trophodynamics is key to assessing pelagic ecosystem resilience under environmental change. Conventional stomach content analyses indicate that myctophids predominantly feed on crustaceans, such as copepods and euphausiids, but are less effective at detecting easily digestible, soft-bodied organisms like gelatinous zooplankton (GZP) and pteropods. MethodsThis study used multimarker (COI Leray-XT and 18S v1-v2) DNA metabarcoding to analyze the diets of two abundant myctophids in the Scotia Sea, Electrona antarctica and Electrona carlsbergi.Results and discussionWe found a diverse diet dominated by copepods and euphausiids, followed by pteropods and GZP in terms of frequency of occurrence and relative read abundances. Within the GZP, salps and appendicularians were major components of the diet for E. carlsbergi, while hydrozoans were prominent in E. antarctica. With regards seasonal and spatial variability in the dietary contribution of GZP, E. carlsbergi consumed primarily appendicularians, chaetognaths, and hydrozoans during spring (2006) in the northern region, and more salps (predominantly Ilhea racovitzai) and other cnidarians in autumn (2009) in the southern region. Our study reveals the dietary diversity of myctophid fish as well as the importance GZP consumption as a key trophic pathway in the Southern Ocean.

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.

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.

Feeding Habits of Striped Piggy Fish, Pomadasys stridens (Forsskål, 1775) in the Persian Gulf

The stomach contents of Pomadasys stridens were studied monthly in the Persian Gulf (Hormozgan province) from October 2020 to October 2021. The stomach contents analysis of 591 fish included a wide variety of food items such as bony fish, crustaceans, molluscs, echinoderms, plant materials, annelid worms, and miscellaneous materials. Although the food component percentage differed marginally between sexes, it was not statistically significant (P=0.19). The vacuity index revealed that P. stridens is a gluttonous species (19.5 %) and the amount of this index was not significantly different in both sexes, length classes, or months. The food preference varied by size: in younger fish, the dominant food item was fish prey, followed by unknown materials, crustaceans, and plant material, and in larger fish (often including sex-determined fish), the food preference shifted to mostly molluscs, crustaceans, and mixed food groups. These preferences also differed significantly across sexes and months (P<0.05). The Penaeid shrimps made up a major portion of P. stridens` diet. Therefore, any change in the stocks of each prey and their predators can have a significant effect on their exploitation potential in the region.

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.

Food web ecology of Lahontan cutthroat trout

Reyes-Avila AD, Moore BC, Jones BW, Taylor TN. 2024. Food web ecology of Lahontan cutthroat trout. Lake Reserv Manage. XX:XXX–XXX. The diet of the Lahontan cutthroat trout (LCT; Oncorhynchus henshawi) introduced in Omak Lake is an example of fish adaptation to new ecosystems, providing more information for successful stocking. Our research aimed to elucidate the role of LCT in the Omak Lake food web, identifying and quantifying the main prey taxa in LCT diets throughout life stages. We investigated potential dietary limitations to support the sustainability and subsistence of LCT and assist management decisions for the sport fishery. Samples were collected seasonally during spring (2018–2021), summer (2019–2021), and autumn (2019–2021). Trout were divided into groups by age. We identified and quantified short-term prey consumption via stomach content analysis (SCA). Stable isotope analysis (SIA) of nitrogen and carbon (δ15N, δ13C) elucidated longer term predator/prey food web relationships. We found that juvenile LCT (1–2 yr; 150–299 mm) diets included aquatic and terrestrial invertebrates (57%). We observed an ontogenetic dietary transition to piscivory at about 2–4 yr (300–450 mm). Fish were a primary diet source (64%) for adult LCT (>4 yr; >450 mm); however, aquatic, and terrestrial invertebrates were still utilized, particularly in the spring season. The largest LCT (>600 mm) consumed mainly fish (>72%). According to SCA, the 5 largest dietary sources for LCT of all ages were peamouth > Coleoptera > LCT-cannibalized > longnose sucker > Odonata. Diptera were found in all LCT age groups, and terrestrial macroinvertebrates were an important seasonal food source. The SIA and SCA results revealed LCT’s dietary plasticity and suggested prey fish scarcity may limit the growth of larger LCT (Beauchamp et al. 2007).

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.