Competition For Food Resources Research Articles

Reintroduction to the edge of its range: quenda (Isoodon fusciventer) to Wadderin Sanctuary in the eastern wheatbelt of Western Australia

Context Quenda (bandicoots, Isoodon fusciventer) have shown a major decline in range since European settlement, contracting to the more mesic coastal and forest zones in south-west Western Australia. Key actions to recover this species include broad-scale fox control, cat control and reintroductions. Most reintroductions have been to coastal and forest habitats. Aims To monitor the reintroduction of quenda to fox-free habitat of Wadderin Sanctuary in the wheatbelt of Western Australia, close to the eastern and drier margin of the species’ former range. Methods Relative abundance of the population was monitored over a 12-year period by regular standardised trapping throughout the sanctuary. Key results Quenda were reintroduced in 2010 and have persisted for >12 years. They were protected from fox predation by an exclusion fence, but were subject to a low level of cat predation for the first 8 years. Quenda showed both a ~20% drop in mean body condition over time and a trend of decreasing number of pouch young per female over time, likely a result of a succession of dry years and intra-and inter-specific competition for food resources. However, despite this, the index of abundance suggests that quenda numbers substantially increased, aided by high annual recruitment, in years following removal of the feral cat. Conclusions Quenda appear resilient at this site despite consecutive years of very low rainfall and apparent competition for food resources. Implications Quenda seem able to persist on the drier margin of their former range when protected from high levels of predation.

Reintroduction to the edge of its range: quenda (Isoodon fusciventer) to Wadderin Sanctuary in the eastern wheatbelt of Western Australia

Context Quenda (bandicoots, Isoodon fusciventer) have shown a major decline in range since European settlement, contracting to the more mesic coastal and forest zones in south-west Western Australia. Key actions to recover this species include broad-scale fox control, cat control and reintroductions. Most reintroductions have been to coastal and forest habitats. Aims To monitor the reintroduction of quenda to fox-free habitat of Wadderin Sanctuary in the wheatbelt of Western Australia, close to the eastern and drier margin of the species’ former range. Methods Relative abundance of the population was monitored over a 12-year period by regular standardised trapping throughout the sanctuary. Key results Quenda were reintroduced in 2010 and have persisted for >12 years. They were protected from fox predation by an exclusion fence, but were subject to a low level of cat predation for the first 8 years. Quenda showed both a ~20% drop in mean body condition over time and a trend of decreasing number of pouch young per female over time, likely a result of a succession of dry years and intra-and inter-specific competition for food resources. However, despite this, the index of abundance suggests that quenda numbers substantially increased, aided by high annual recruitment, in years following removal of the feral cat. Conclusions Quenda appear resilient at this site despite consecutive years of very low rainfall and apparent competition for food resources. Implications Quenda seem able to persist on the drier margin of their former range when protected from high levels of predation.

Assessing global carbon sequestration and bioenergy potential from microalgae cultivation on marginal lands leveraging machine learning

This comprehensive study unveils the vast global potential of microalgae as a sustainable bioenergy source, focusing on the utilization of marginal lands and employing advanced machine learning techniques to predict biomass productivity. By identifying approximately 7.37 million square kilometers of marginal lands suitable for microalgae cultivation, this research uncovers the extensive potential of these underutilized areas, particularly within equatorial and low-latitude regions, for microalgae bioenergy development. This approach mitigates the competition for food resources and conserves freshwater supplies. Utilizing cutting-edge machine learning algorithms based on robust datasets from global microalgae cultivation experiments spanning 1994 to 2017, this study integrates essential environmental variables to map out a detailed projection of potential yields across a variety of landscapes. The analysis further delineates the bioenergy and carbon sequestration potential across two effective cultivation methods: Photobioreactors (PBRs), and Open Ponds, with PBRs showcasing exceptional productivity, with a global average daily biomass productivity of 142.81mgL−1d−1, followed by Open Ponds at 122.57mgL−1d−1. Projections based on optimal PBR conditions suggest an annual yield of 99.54 gigatons of microalgae biomass. This yield can be transformed into 64.70 gigatons of biodiesel, equivalent to 58.68 gigatons of traditional diesel, while sequestering 182.16 gigatons of CO2, equating to approximately 4.5 times the global CO2 emissions projected for 2023. Notably, Australia leads in microalgae biomass production, with an annual output of 16.19 gigatons, followed by significant contributions from Kazakhstan, Sudan, Brazil, the United States, and China, showcasing the diverse global potential for microalgae bioenergy across varying ecological and geographical landscapes. Through this rigorous investigation, the study emphasizes the strategic importance of microalgae cultivation in achieving sustainable energy solutions and mitigating climate change, while also acknowledging the scalability challenges and the necessity for significant economic and energy investments.

Resource partitioning of a Mexican clam in species-poor Baltic Sea sediments indicates the existence of a vacant trophic niche

Invasive species are often generalists that can take advantage of formerly unexploited resources. The existence of such vacant niches is more likely in species-poor systems like the Baltic Sea. The suspension feeding wedge clam, Rangia cuneata, native to estuarine environments in the Gulf of Mexico, was sighted for the first time in the southeastern Baltic in 2010 and a few years later in the northern Baltic along the Swedish coast. To explore possible competition for food resources between R. cuneata and the three native clams inhabiting Baltic shallow soft bottoms, stable isotope and fatty acid analyses were conducted. There was no overlap between R. cuneata and any of the native species in either stable isotope or fatty acid niches. This suggests efficient partitioning of resources; multivariate analyses indicate that separation was driven mainly by δ13C and by fatty acids reflecting diatoms and cyanobacteria, respectively (e.g. 16:1ω7 and 18:3ω3). R. cuneata reflected seasonal variation in phytoplankton more than other clams reflecting higher trophic plasticity. In conclusion, the addition of R. cuneata to the Baltic shallow soft bottoms suggests the existence of a vacant trophic niche in these sediment habitats, however the long-term effects on other species and nutrient cycling requires further studies focusing on the population dynamics of R. cuneata and its impact on the Baltic Sea ecosystem.

Detailed analysis of prey taxonomic composition indicates feeding habitat partitioning amongst co-occurring invasive gobies and native European perch

One of the negative impacts of non-native invasive species on trophic interactions in an invaded ecosystem occurs via increased interspecific competition for food resources between the invader and local species of the same food niche. In freshwaters, there are usually several fish species that feed on similar food resources. Ponto-Caspian gobies are amongst the most successful and widespread invaders colonising European waterways. They have a wide food niche and an opportunistic feeding strategy, with a focus on benthic invertebrates and piscivory occurring occasionally mainly in the case of large individuals. Competition with native percids for food resources is predicted on the basis of high dietary overlap. However, studies published so far provide no unequivocal answer. In order to resolve this question, we conducted a comparative taxonomic analysis of gut content, with an emphasis on chironomids and amphipods, of the invasive monkey goby (Neogobius fluviatilis), racer goby (Babka gymnotrachelus) and the native Eurasian perch (Perca fluviatilis) occurring sympatrically in a large lowland European river, the Bug River in Poland. We found that each species forages in slightly different habitats, as indicated by the different composition of prey species in the gut content. This suggests feeding niche partitioning between the studied species facilitating their co-existence and reduction or avoidance of competition for food resources. Resource partitioning regarding prey types and foraging habitats is a mechanism for permitting the co-existence of closely-related alien gobies with similar food preferences in the invaded waters and co-occurrence with local species. This mechanism can contribute to their invasion success, as observed in European waters during the recent decades. We also demonstrate that precise prey identification to the lowest possible taxon is crucial to reveal the dietary overlap between co-occurring fish species and to predict the impact of alien invaders on native species through interspecific competition, as well as to recommend such an approach in studies upon fish foraging strategies.

Food resource competition between African wild dogs and larger carnivores in an ecosystem with artificial water provision.

Predators of similar size often compete over prey. In semi-arid ecosystems where water is a limiting resource, prey availability can be affected by water distribution, which further increases resource competition and exacerbate conflict among predators. This can have implications for carnivore dietary competition. Hence, we evaluated the dynamics of food resource competition between African wild dogs and four competing predators (cheetahs, leopards, lions and spotted hyaenas) in different seasons and across areas with different waterhole densities in Hwange National Park, Zimbabwe. We used the frequency of occurrence of prey items found in predators' scats to analyse diet composition, overlap and prey preference. For most predators, kudu was most frequently consumed and preferred. Low and medium water-dependent prey (medium and small-sized) were mostly consumed by wild dogs, leopards and cheetahs. Wild dog diet overlap was high with all predators, particularly with hyaenas and lions. There were no seasonal differences in the predators diet. The diet overlap of wild dogs with lions was highest in the low waterhole density area, and wild dog diet composition did not differ significantly from the diet of lions and hyaenas. In the low waterhole density area, wild dogs and hyaenas broadened their niche breadth, and predators diet had a higher proportion of low water-dependent prey. A low density of waterholes increased food resource competition. However, high density of waterholes, where there is more prey availability, can increase the aggregation and density of predators, and hence, increase the risks involved in interspecific competition on wild dogs. To reduce food resource competition on wild dogs, we propose to conserve larger-bodied prey that are less dependent on water (e.g. kudu, reedbuck, eland and gemsbok). As the use of water pumping is common practice, we propose maintaining water management heterogeneity where prey which is less dependent on water can also thrive.

Traces of missing encrusters: borings reveal sclerobiont taphonomy in the Upper Ordovician (Katian) of the Cincinnati region, USA

ABSTRACT The abundant shells and hardgrounds in the Cincinnatian Group (Upper Ordovician, Katian) of the upper midwestern United States were commonly encrusted and bored by a variety of organisms. Numerous studies of these sclerobiont communities have provided valuable data for models of ecological succession, symbiosis, space and food resource competition, and taphonomy. An underlying assumption of this work is that most of the skeletal encrusters have remained in place, firmly attached to their hard substrates. This is especially the case with the most common encrusters, thick trepostome bryozoan and cystoporate skeletons, on their most common substrates, flat strophomenide brachiopods. We present evidence here, though, that these bryozoans were often dislodged from their brachiopod hosts, leaving no evidence of their attachment other than horizontal borings in semi-relief from organisms that excavated tunnels (Trypanites and Palaeosabella) at the interface of the brachiopod shell and attaching bryozoan. Similar borings are found on the bases of dislodged bryozoans and in bryoimmured mollusc external moulds. These borings along the bryozoan attachment surfaces caution us that there are significant numbers of missing skeletal encrusters on these hard substrates.

РАСПРЕДЕЛЕНИЕ И ДИНАМИКА ЧИСЛЕННОСТИ ИХТИОПЛАНКТОНА И РАННЕЙ МОЛОДИ ТЮЛЬКИ И ХАМСЫ В АЗОВСКОМ МОРЕ В 1993–2023 ГГ.

Background. Natural and anthropogenic factors have a major influence on the fish population status. In the Azov Sea, for the last 30 years, substantial changes in the environment have been observed and new exotic species of aquatic living organisms have been introduced, which affected reproduction of fish species. Relevance. To identify the driving forces behind the present dynamics of population abundance of European anchovy and Black and Caspian Sea sprat (tyulka), it is crucial to summarize the data collected during the annual ichthyoplankton surveys of the Azov Sea. This work is aimed at the assessment of the distribution of the ichthyoplankton and early juveniles of Black and Caspian Sea sprat (tyulka) and European anchovy in the Azov Sea area over time with regard to various environmental factors. Methods. Ichthyoplankton surveys are customarily conducted over the entirety of the Azov Sea in the middle of June, when eggs and larvae of Black and Caspian Sea sprat (tyulka) and European anchovy are caught at the highest quantities. Results. The dynamics of distribution and abundance variations for the early developmental stages of Black and Caspian Sea sprat (tyulka) and European anchovy under the influence of environmental factors, including ctenophores and scyphozoan jellyfishes, has been identified; a decrease in the survival rates of their jellyfishes juveniles in the present period of the Azov Sea salinization has been observed. Conclusion. In the context of increasing salinity of the Azov Sea waters, the main factors contributing to the reduced survival rates of the Black and Caspian Sea sprat (tyulka) larvae and fingerlings are the decrease in spawning ground area and competition for food resources with scyphozoan jellyfishes and ctenophores. In the case of the European anchovy larvae and fingerlings, the main factor affecting their abundance is a small number of breeders; food competition and predation of the scyphozoan jellyfishes and ctenophores are of secondary importance.

Mathematical Model of Phytoplankton Interspecific Competition for Food Resource

The phytoplankton in an aquatic ecosystem is the basis of its life activity and the main producing link. The functioning of phytoplankton in same time depends on environmental factors: mineral nutrition, photosynthetically active solar radiation, water temperature and other less significant ones. Sunlight is a stable factor, varying predictably over time and space. The water temperature is the small regulatory factor. Concentrations of mineral substances can change quite quickly and significantly, this much influences on plant organisms. Thus, mineral nutrition is a basic environmental factor of influence to phytoplankton. On the other hand, in large aquatic basin such as seas and oceanic areas the distribution of living organisms is very heterogeneous in space. These two aspects – nutrient and spatial heterogeneity – are the focus of this article. A model of competitive interaction is considered using the example of two species of phytoplankton. The phytoplankton move passively in water what is simulated by the diffusion process. The model contains one non-trivial stationary and spatially homogeneous equilibrium and two trivial ones, i.e. degenerate in at least one species of phytoplankton. Trivial equilibria are stable only in some “degenerate” situations. The non-trivial equilibrium in “normal” conditions is stable to temporal and spatial disturbances. The behavior of solutions near a nontrivial equilibrium for a stationary living environment and in cases of its nonstationary is studied. Perturbation of a nontrivial equilibrium in a stationary environment leads to relatively long-term deviations from equilibrium and a slow return to it. The instability of trivial equilibria increases the spatial heterogeneity of solutions. At the same time, the nontrivial equilibrium computationally demonstrates weak properties of global stability in time. The unsteadiness of the environment is simulated by the unsteadiness of the influx of nutrients. It has been shown that the distribution of nutrients can lead to significant heterogeneity in the distribution of individuals across the spatial habitat.

Active feeding of downstream migrating juvenile pink salmon (Oncorhynchus gorbuscha) revealed in a large Barents Sea river using diet and stable isotope analysis.

The recent, rapid spreading of non-native pink salmon Oncorhynchus gorbuscha in the North Atlantic area has raised concerns about their possible negative impacts on native salmonid species. Potential interactions include competition for food resources during the short freshwater phase of juvenile O. gorbuscha, but little is known about their feeding behavior in the newly occupied North Atlantic rivers. Using stable isotope and stomach content analyses, patterns of freshwater feeding of non-native O. gorbuscha fry were studied in a large Fennoscandian river, the Teno, that discharges to the Barents Sea. Changes in stable isotope values (δ13 C, δ15 N, δ34 S) and stomach contents from the period of emergence (April to mid-May) to estuarine entry (late May/June) were examined and provided both temporally integrated and short-term indicators of freshwater feeding dependency. In addition, the occurrence of juvenile O. gorbuscha and changes in their length and weight during their emergence/migration period were investigated. Juvenile O. gorbuscha were at the spawning grounds from April through to mid-May with abundance peaking in mid-May. Fish moved to the estuary by late May and their abundance decreased toward June, and their body size increased concurrently. Stomach analyses indicated no feeding activity in April-early May in the spawning areas, but the stomach fullness indices increased markedly in fish sampled in the estuary in May and June. The most important prey items in stomachs were Chironomidae and Ephemeroptera larvae. Significant changes in all analysed stable isotopes were detected among sample periods, with a peak in mid-May and June showing significantly lower values than other sample periods. A change from the higher values reflective of parental marine feeding to the lower values reflective of freshwater feeding indicated active in-river feeding by juveniles during the study period. The documented active freshwater feeding of non-native juvenile O. gorbuscha suggests potential resource competition with native fluvial fishes, particularly salmonids.

Global warming intensifies the interference competition by a poleward-expanding invader on a native dragonfly species.

Rapid climate warming has boosted biological invasions and the distribution or expansion polewards of many species: this can cause serious impacts on local ecosystems within the invaded areas. Subsequently, native species may be exposed to threats of both interspecific competition with invaders and temperature rises. However, effects of warming on interspecific interactions, especially competition between invader and native species remains unclear. To better understand the combined threats of biological invasions and warming, the effect of temperature on competitive interactions between two dragonfly species, the expanding Trithemis aurora from Southeast Asia and the Japanese native Orthetrum albistylum speciosum were assessed based on their foraging capacity. Although the stand-alone effect of temperature on foraging intake of the native dragonfly was not apparent, its intake significantly decreased with increasing temperatures when the invader T. aurora was present. Such reductions in foraging might lead to displacement of the native species through competition for food resources. This suggests that impacts of invader species against native species are expected to be more severe when interspecific competition is exacerbated by temperature rises.

Movement behavior, habitat selection, and functional responses to habitat availability among four species of wintering waterfowl in California

IntroductionHabitat selection analyses provide a window into the perceived value of habitats by animals and how those perceptions compare with other animals, change across time, or change in relation to availability (termed functional responses). Habitat selection analysis and functional responses can be used to develop strategies to avoid habitat limitations, guide habitat management, and set attainable conservation goals. GPS relocations of marked animals are the principal data used in habitat selection analysis. The accuracy and frequency with which tracking devices collect data are increasing and may result in non-stationary point processes that result from latent behaviors previously unidentifiable in sparse data.MethodsWe investigated non-stationary step length distributions and integrated a two-mixture model of animal movement with step selection analysis to identify patterns of activity among four species of co-occurring waterfowl that winter in the Central Valley of California, United States. We evaluated relative strength of selection and compared functional responses across a range of habitat types for two goose and two dabbling duck species.ResultsGoose species (greater white-fronted goose [Anser albifrons] and lesser snow goose [Anser caerulescens caerulescens]) used habitats similarly and displayed similar functional responses with habitat availability. Northern pintail (Anas acuta) displayed functional responses for habitats that provided primary food resources and sanctuary from hunting that were more similar to geese than to mallard (Anas platyrhynchos), which expressed a more generalist pattern of habitat selection.DiscussionOur results define conditions where food resource competition between geese and ducks could operate, which indicate that some species may be more impacted than others. Specifically, early season food limitation may manifest more strongly in snow geese due to longer movements and stronger functional response with rice availability. Late season limitations may manifest in northern pintail, which remain reliant on rice later but may not be reflected in habitat selection patterns due to a consistent functional response with rice availability. We show that multiple movement processes present in high-resolution data can be used to obtain a variety of information about animal behavior and that subsequent step selection analyses may demonstrate unique functional responses relative to alternate habitat selection methods that warrant additional investigation.

Spatio-temporal patterns of human-carnivore conflict and mitigation in Pakistan

Human-carnivore conflict is a noteworthy rural livelihood issue as livestock of local communities living around protected areas are depredated by wild carnivores, which are the persecuted by local communities, in response. The current study aimed at investigating the patterns, perception, economic losses, and mitigation of human wildlife conflict in Pakistan through meta-analysis of published literature and using the questionnaire survey method. We retrieved data from the published and unpublished sources, and from records of provincial wildlife departments. In addition, we also collected empirical data from different households falling in the range of targeted carnivore species and filled 331 semi-structured questionaries. Based on the activities and home range of the predator species, conflict density maps for each predator species were developed. Our analysis revealed that five major carnivore species are involved in the human-wildlife conflict, namely Asiatic black bear (Ursus thibetanus), Himalayan brown bear (Ursus arctos), common leopard (Panthera pardus), grey wolf (Canis lupus) and snow leopard (Panthera uncia). About 7214 livestock heads were reportedly lost during past two decades because of these five carnivore species. The domestic goat depredation was maximum (51.08 %, n = 3685), followed by sheep (27.09 %, n = 1954), cow (11.37 %, n = 820), buffalo (2.34 %, n = 169), dogs (2.05 %, n = 148), poultry (0.87 %, n = 63), donkey (4.28 %, n = 348), and horse (0.37 %, n = 27), causing a total financial loss of USD 1.87 million. Maximum livestock depredation occurred in summer season (50.79 %), at night (59.92 %) time and outside the village (51.22 %). Majority of the people showed negative attitude towards the predators, and they did not know about the conservation status and the authorities to report for conservation of the predator species. Most of the respondents were unaware about the possible management of the predator species for the co-existence of human and wildlife in the same landscape. However, majority of respondents (38.3 %) thought that livestock depredation by carnivore species can be controlled through payment of insurance compensation to the person who lost its livestock during carnivore attacks, followed by restoration of natural habitat (20.1 %), translocation of predator (16 %), and improved husbandry practices like predator proof corals (8 %). The study concludes that buffer zones of the protected areas are the hotspots for human- wildlife conflict and to avoid such conflict in future, special mitigation measures should be adapted, and regulations should be developed to minimize the niche overlap of the livestock and wildlife prey species, thereby to avoid any competition for food resources.

O17 Effect of shade and water on competition for food resources

O17 Effect of shade and water on competition for food resources

Understanding carnivore interactions in a cold arid trans-Himalayan landscape: What drives co-existence patterns within predator guild along varying resource gradients?

Predators compete for resources aggressively, forming trophic hierarchies that shape the structure of an ecosystem. Competitive interactions between species are modified in the human-altered environment and become particularly important where an introduced predator can have negative effects on native predator and prey species. The trans-Himalayan region of northern India has seen significant development in tourism and associated infrastructure over the last two decades, resulting in many changes to the natural setting of the landscape. While tourism, combined with unmanaged garbage can facilitate red fox (Vulpes vulpes), it also allows free-ranging dogs (Canis lupus familiaris), an introduced mesopredator to thrive, possibly more than the native red fox. We look at the little-known competitive dynamics of these two meso-carnivores, as well as their intra-guild interactions with the region's top carnivores, the snow leopard (Panthera uncia) and the Himalayan wolf (Canis lupus chanco). To study interactions between these four carnivores, we performed multispecies occupancy modeling and analyzed spatiotemporal interactions between these predators using camera trap data. We also collected scat samples to calculate dietary niche overlaps and determine the extent of competition for food resources between these carnivores. The study found that, after controlling for habitat and prey covariates, red fox site use was related positively to snow leopard site use, but negatively to dog and wolf site use. In addition, site use of the dog was associated negatively with top predators, that is, snow leopard and Himalayan wolf, while top predators themselves related negatively in their site use. As anthropogenic impacts increase, we find that these predators coexist in this resource-scarce landscape through dietary or spatiotemporal segregation, implying competition for limited resources. Our research adds to the scant ecological knowledge of the predators in the region and improves our understanding of community dynamics in human-altered ecosystems.

The effects of river regulation on diet diversity, dietary niche overlap and foraging habitat preferences of two sympatric plover species

During migration waders use a variety of microhabitats and a wide range of prey to supply their nutritional requirements. Most of them form multispecies flocks, which may result in increased competition for resources. In this study, we compare the abundance of potential prey for Ringed and Little Ringed plovers at unregulated and regulated stretches of the Vistula River. We also observed plovers and assigned them to the habitat in which they foraged and compare the diet, dietary niche overlap and foraging habitat preferences of these two plover species. The larger species, the Ringed Plover, foraged more often in invertebrate abundant habitats, yet exclusively on the three most abundant prey species, while the smaller species expanded its diet to include invertebrate species of low abundance and in suboptimal habitats. In the regulated river section, below the dam, the diet of the Little Ringed Plover was more diverse, and the dissimilarity of both plovers’ diets was much higher than in the regulated section. The unregulated river section offered richer foraging grounds and both species showed similar proportions of primary prey items in their diets here resulting in greater dietary niche overlap and weaker resource partitioning. Our study shows that river regulation increases competition for food resources due to a lower abundance of potential prey and has an influence on diet diversity and foraging habitat preferences of smaller, less competitive plover species.

Status of a stocked Atlantic salmon population in Lake Huron

In 2011, the Michigan Department of Natural Resources (MDNR) expanded stocking of Atlantic salmon (Salmo salar) in Lake Huron to enhance fishing opportunities following Chinook salmon (Oncorhynchus tshawytscha) abundance declines. Currently, little is known about the population produced from this stocking. We fit an assessment model to harvest data from Michigan jurisdictional waters to estimate Atlantic salmon population dynamics and abundance. Because of potential biases in MDNR creel survey harvest estimates, a survey was e-mailed to online purchasers of a 2019 Michigan fishing license asking about where and when Atlantic salmon were harvested to correct creel harvest estimates. Anglers were also asked about catch-and-release angling and tested on their ability to identify Lake Huron salmonids. Creel harvest estimates overlapped spatially and temporally with 42% of survey reported Atlantic salmon harvest. After correcting creel harvest estimates, total abundance of Atlantic salmon in 2019 was estimated at approximately 392,000 fish with a peak abundance of approximately 406,000 fish. Anglers released 27% of caught fish and correctly identified Atlantic salmon 28% of the time. To assess the occurrence of food resource competition, differences in condition (i.e., expected weight at length) were evaluated. Condition was higher in later years than in earlier years despite abundance increases. Our results suggested that past stocking established a population of approximately 400,000 Atlantic salmon with evidence suggesting that fish were finding sufficient food resources. Future Atlantic salmon management efforts may be improved by quantifying post-stocking survival rates and other sources (e.g., charter, Canadian) of harvest.

Food Preference of Bullet Tuna (<i>Auxis rochei</i> Risso, 1810) in Prigi Coast of Trenggalek Regency, East Java

As a commercial fish, bullet tuna is constantly caught in purse seine fisheries to provide economic benefits for coastal communities. Biological information such as food preference has to be known due to their sustainability in the future. This research aims to figure out the food composition and preference of bullet tuna (Auxis rochei Risso, 1810) in Prigi Coast, Trenggalek Regency East Java. A total of 294 fish landed by purse seine fishermen have been collected from March up to May 2018. Each individual was measured in its total length and weight, then was dissected for sex determination, measured the length of intestine, and analyse the stomach content. The data analysis encompasses frequency distribution of total length, relative gut length, frequency of occurrence, index of preponderance, trophic level, niche breadth, and food overlapping. The research result indicates that the main foods of Auxis rochei are fish and crustacean, while the complementary and additional foods were copepod, mollusc, annelid, and debris. Bullet tuna was a carnivorous fish with the trophic level of 3.7 and shows the existence of competition for food resources. Overlapping of feeding occurred in the 19-20 cm long group against the 23-24 cm long group in male fish and the 19-20 cm size group against the 21-22 cm length group in female fish. Bullet tuna use the same feed resources among the size groups of fish, where females use feed over a wider area than males.

Invasive Brook Stickleback Culaea inconstans minimally alters the trophic ecology of four native fishes in Wyoming, USA

Invasive species introductions are a primary threat facing populations of native freshwater fishes. There are multiple mechanisms by which an invader can affect native species, with competition for food resources being one mechanism that can lead to declines in the distribution and abundance of native species. Invaders that are trophic generalists may cause shifts in the trophic ecology of native species and may be better suited for long-term persistence amid environmental stochasticity. Therefore, trophic studies can provide valuable information on the risk an invader poses to native species. Brook Stickleback Culaea inconstans is an invasive fish species in Wyoming whose effect on native fish assemblages is poorly understood. Our goal was to understand the potential for competitive interactions between Brook Stickleback and native fishes. We used stable isotopes of carbon (ẟ13C) and nitrogen (ẟ15N) to evaluate the feeding ecology of Brook Stickleback relative to four native fishes, and to explore whether native fish isotopic niches changed in sympatry with Brook Stickleback. We hypothesized that the isotopic niche of Brook Stickleback would be larger than that of native fishes, suggesting broader resource use. Additionally, we hypothesized that the isotopic niche of native fish populations sympatric with Brook Stickleback would contract. We did not find support for our hypotheses as the isotopic niche of Brook Stickleback was not substantially different from that of native fishes. Further, the isotopic niche of native fishes was not substantially affected by Brook Stickleback presence. As a result, we do not currently see evidence of Brook Stickleback altering the trophic ecology of native fish species. Our results provide insight to the effects of a small-bodied invasive fish species on native fishes in a previously unstudied region, and can help managers prioritize management actions to conserve native fishes.

Assessment of the impact of polar bears on the grouping of pacific walruses at the Cape Vankarem rookery during the summer-autumn period in 2017–2021

The aim of this work is to assess the impact of polar bears (Ursus maritimus Phipps, 1774) on the distribution, abundance, and migration activity of Pacific walrus (Odobenus rosmarus divergens Illiger, 1815) on the coastal rookery Cape Vankarem (Chukotka Autonomous District) during the period from August to October 2017–2021.Also, based on the analysis of data on the number of walruses and bears on the rookery and analysis of photographs, we tried to assess the physical condition of predators, the degree of their attachment to the rookery, i. e. to determine how the age and sex composition of the bear group at the rookery changes during the development of walrus migration activity on the Cape Vankarem rookery. It has been established that: along with anthropogenic influence, polar bears are one of the main factors scaring walruses on the Cape Vankarem coastal rookery; immature bears spend significantly more time at the rookery than adult females with pups or adult males; the physical condition of the majority of bears is good, but the adult males are more frequently below average in fatness; while in the rookery, no food and space competition for food resources was observed between bears.