Important Prey Items Research Articles

Diet, feeding, and niche overlap of west coast steenbras (Lithognathus aureti) and silver kob (Argyrosomus inodorus) in the northern Benguela.

In this study, we described and compared the diet, monthly feeding intensity, and condition of west coast steenbras (Lithognathus aureti) and silver kob (Argyrosomus inodorus) caught at a unique habitat in the northern Benguela. Stomach contents of 179 west coast steenbras and 114 silver kob caught from October 2020 to September 2022 were investigated. The peak in feeding intensity of west coast steenbras appeared to be opportunistic during winter and summer periods depending on food availability. The fish condition, however, peaked at the beginning (October) and at the end (April) of the austral summer spawning period, with the hepatosomatic index (HSI) at 1.5% and the condition factor (CF) at 0.022%. Seven prey taxa were found in the diet of west coast steenbras (bivalves, bony fishes, other mollusks, algae, crustaceans, cnidaria, and polychaetas) and six taxa in the diet of silver kob (bivalves, crustaceans, bony fishes, algae, starfish, and zooplankton), indicating generalist feeding behavior in both the species. The bivalves were the most important prey items in the diet of west coast steenbras (95.9% index of relative importance [IRI]). The most important prey items in the diet of silver kob were crustaceans (83.1% IRI) and bony fishes (16.0% IRI). Crustaceans were most important in the diet of small-to-medium-sized silver kob, whereas bony fishes were most important in the diet of larger silver kob(>75 cm), with significant differences of IRI% by size class. Schoener's index of niche overlap indicated a relatively low overall niche overlap (0.11) between west coast steenbras and silver kob. This allows them to coexist as their feeding habits allow them to occupy unique niches in the coastal reef and sandy habitat and reduce competition for resources.

Insights into the diet and feeding behavior of immature polar cod (Boreogadus saida) from the under-ice habitat of the central Arctic Ocean.

Polar cod (Boreogadus saida) is an endemic key species of the Arctic Ocean ecosystem. The ecology of this forage fish is well studied in Arctic shelf habitats where a large part of its population lives. However, knowledge about its ecology in the central Arctic Ocean (CAO), including its use of the sea-ice habitat, is hitherto very limited. To increase this knowledge, samples were collected at the under-ice surface during several expeditions to the CAO between 2012 and 2020, including the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The diet of immature B. saida and the taxonomic composition of their potential prey were analysed, showing that both sympagic and pelagic species were important prey items. Stomach contents included expected prey such as copepods and amphipods. Surprisingly, more rarely observed prey such as appendicularians, chaetognaths, and euphausiids were also found to be important. Comparisons of the fish stomach contents with prey distribution data suggests opportunistic feeding. However, relative prey density and catchability are important factors that determine which type of prey is ingested. Prey that ensures limited energy expenditure on hunting and feeding is often found in the stomach contents even though it is not the dominant species present in the environment. To investigate the importance of prey quality and quantity for the growth of B. saida in this area, we measured energy content of dominant prey species and used a bioenergetic model to quantify the effect of variations in diet on growth rate potential. The modeling results suggest that diet variability was largely explained by stomach fullness and, to a lesser degree, the energetic content of the prey. Our results suggest that under climate change, immature B. saida may be at least equally sensitive to a loss in the number of efficiently hunted prey than to a reduction in the prey's energy content. Consequences for the growth and survival of B. saida will not depend on prey presence alone, but also on prey catchability, digestibility, and energy content.

Moose in wolf diets across northeastern Minnesota

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

Detecting the invisible through DNA metabarcoding: The role of gelatinous taxa in the diet of two demersal Antarctic key stone fish species (Notothenioidei)

AbstractGelatinous zooplankton (GZP), i.e., ctenophores, cnidarian medusae, chaetognaths, appendicularians and salps, are considered climate change winners. This becomes particularly obvious in the Southern Ocean, which has undergone a significant shift from a krill‐based to a salp‐based ecosystem over the last decades. A better knowledge on the role of gelatinous invertebrates as prey is needed to predict the impact of such a gelatinous shift. Until recently, GZP was considered as a “trophic dead end”. However, their true importance in diets has remained unresolved due to the rapid digestion of their watery and soft tissues in predators' stomachs. In this study, we want to validate the paradigm shift from GZP being considered as “survival food” to be considered a “regular” prey item for two demersal fish species (Notothenia rossii and N. coriiceps) of Potter Cove, South Shetland Islands, using a multimarker (COI and 18S) metabarcoding approach. We found that GZP taxa commonly occurred in the diets of both species, represented by pelagic tunicates (appendicularians, salps), cnidarians, chaetognaths and ctenophores. Salps were the most abundant prey group, preyed upon by each individual of both species, reaching 98.7% relative read abundance for 18S. We recovered a wide range of different taxa in their diets, from primary producers to highly abundant invertebrates, thus the two nototheniid species can be regarded as “natural samplers” of the ecosystem in study. Finally, we want to point out the importance of multimarker metabarcoding approaches for broad ecological assessments, given the differential amplification and sequencing success of different markers for specific groups and the unequal taxonomic coverage of the reference databases. The output of each marker was highly complementary, since an important prey item such as salps, was only detected with 18S, while other taxa (e.g., Arthropoda) were represented with a higher taxonomic resolution with COI.

Interactive effects between water temperature, microparticle compositions, and fiber types on the marine keystone species Americamysis bahia

Recently, there has been an increasing emphasis on examining the ecotoxicological effects of anthropogenic microparticles (MPs), especially microplastic particles, and related issues. Nevertheless, a notable deficiency exists in our understanding of the consequences on marine organisms, specifically in relation to microfibers and the combined influence of MPs and temperature.In this investigation, mysid shrimp (Americamysis bahia), an important species and prey item in estuarine and marine food webs, were subjected to four separate experimental trials involving fibers (cotton, nylon, polyester, hemp; 3 particles/ml; approximately 200 μm in length) or fragments (low-density Polyethylene: LDPE, polylactic acid: PLA, and their leachates; 5, 50, 200, 500 particles/ml; 1–20 μm). To consider the effects in the context of climate change, three different temperatures (22, 25, and 28 °C) were examined. Organismal growth and swimming behavior were measured following exposure to fragments and microfibers, and reactive oxygen species and particle uptake were investigated after microfiber exposure. To simulate the physical characteristics of MP exposure, such as microfibers obstructing the gills, we also assessed the post-fiber-exposure swimming behavior in an oxygen-depleted environment.Data revealed negligible fragment, but fiber exposure effects on growth. PLA leachate triggered higher activity at 25 °C and 28 °C; LDPE exposures led to decreased activity at 28 °C. Cotton exposures led to fewer behavioral differences compared to controls than other fiber types. The exposure to hemp fibers resulted in significant ROS increases at 28 °C. Microfibers were predominantly located within the gastric and upper gastrointestinal tract, suggesting extended periods of residence and the potential for obstructive phenomena over the longer term. The combination of increasing water temperatures, microplastic influx, and oxidative stress has the potential to pose risks to all components of marine and aquatic food webs.

Feeding habits of Pacific anchovy, Engraulis japonicus (Actinopterygii: Clupeiformes: Engraulidae), captured off the southern coasts of Korea

Understanding the feeding ecology of anchovies in the southern waters of Korea is crucial for improving ecosystem management. However, to date, few studies have examined seasonal changes in the diet of Pacific anchovy, Engraulis japonicus Temminck et Schlegel, 1846, in Korean waters, with the majority of these focusing on the larval and adult stages. The presently reported study provides updates on the feeding habits of E. japonicus off the southern coast of Korea. We analyzed 347 individuals. One-way analysis of similarity was performed to evaluate the differences in diet composition among size classes and seasons of E. japonicus, and correspondence analysis was conducted using the matrix of the percentage by number (%N) data for prey with occurrence of less than 10% to determine the distribution of prey across all size classes and each season. The diet of E. japonicus was investigated according to season and four size classes. The fork length of these specimens ranged from 5.4 to 14.1 cm. A total of 55 prey taxa of varying sizes between 0.33 mm (diatom Coscinodiscus spp.) and 5.8 mm (fish larvae) were recorded. Anchovies were exclusively planktivorous, and copepods were the most common prey, comprising 82.1% of the identified food items and 84.3% of anchovy stomach contents analyzed. However, their occurrence and abundance varied according to season and Pacific anchovy size class. According to the percentage of the index of relative importance (%IRI), the most important prey items were the copepods Calanus sinicus (48.0%), Paracalanus orientalis (31.7%), bivalve larvae (5.8%), Ditrichocorycaeus affinis (4.2%), and calanoid copepods (2.4%). Analysis of similarities and similarity percentage analysis indicated that a distinct diet of Pacific anchovy in the southern waters of Korea is potentially driven by differences in hydrological conditions. Correspondence analysis revealed that anchovies had the most significant impact on the differences between size classes. The results deepen our understanding of prey species diversity and intraspecific food competition off the southern coast of Korea.

Distribution and demographics of mysids (Crustacea: Mysida) as prey for gray whales (Eschrichtius robustus) in northwest Washington state.

The movement and distribution of gray whales (Eschrichtius robustus) during the feeding season is likely dependent on the quality of foraging opportunities and the distribution of prey species. These dynamics are especially important to understand for the Pacific Coast Feeding Group (PCFG) of gray whales which spend the feeding season along the coast from northern California, USA through northern British Columbia, Canada. In Washington state, no previous work has been done to describe available gray whale prey. The main goal of this research was to initiate studies on an important gray whale prey item in northwest Washington, mysid shrimp (Mysida), by establishing a baseline understanding of mysid swarm demographics in the area and investigating patterns in gray whale and mysid presence. Prey samples were collected during June through November 2019 and June through September 2020 using a vertically-towed plankton net at seven sites in the Strait of Juan de Fuca and seven sites in the Pacific Ocean in areas where gray whales were known to feed. Mysids collected in the samples were counted and the sex, length, species, maturity, and gravidity were documented. Patterns in gray whale and mysid co-occurrence were explored through data visualization. Seven species of mysids were observed in the survey area. In 2019, the number of mysids per tow increased steadily through the season, the most abundant species of mysids were Holmesimysis sculpta and Neomysis rayii, and sampled mysids averaged 4.7 mm in length. In 2020, mysids were abundant in tow samples in June and July but were not abundant in the remaining months of the sampling season. The average length of mysids in 2020 was 13.3 mm, and a large portion were sexually mature males and brooded females identified as H. sculpta. Throughout the survey area, the majority of whale sightings occurred later in the season in 2019 and earlier in the season in 2020, coinciding with the trends of sampled mysids. This study provides the first description of mysid swarm composition and temporal variation in northwest Washington. Tows were dominated by a similar assemblage of mysid species as what is observed in other areas of the PCFG range. The differences in sampled mysid assemblages between years, and the presence of whales in the survey area in times and at sites where samples with high mysid counts were collected, suggest evidence for interesting predator-prey dynamics that warrant further investigation.

Larval Lake Whitefish (Coregonus clupeaformis) zooplankton consumption remains constant despite variation in prey densities in western Lake Erie

Abstract Larval fish growth and survival could be limited or reduced due to patchiness of zooplankton densities, even in productive aquatic systems. Recent declines in Lake Whitefish (Coregonus clupeaformis) populations prompted research to identify underlying mechanisms controlling survival at early life stages. In Lake Erie, the bottleneck window controlling year-class strength of Lake Whitefish likely occurs during the first growing season, suggesting that availability of important prey could influence year-class strength. Therefore, spatial and temporal larval Lake Whitefish distribution, diet, and prey utilization were evaluated in western Lake Erie. The pelagic Lake Whitefish larval period in the western basin extends from April 1 to May 15 with most larvae concentrated nearshore at the surface both day and night. Cyclopoid copepods were the most important prey item; however, calanoid copepods and Cladocera were consistently consumed, indicating that copepods and Cladocera were important larval Lake Whitefish prey items. Copepod and Cladocera biomass were the highest nearshore, overlapping with the highest larval Lake Whitefish densities. However, the amount of food consumed by larvae was consistent in all areas, suggesting that offshore areas in western Lake Erie with relatively low zooplankton biomass harbor enough food to satiate larval Lake Whitefish. Therefore, it is unlikely that prey availability limits survival through means of starvation during the larval phase.

Trophic Interactions of European Hake Merluccius merluccius (Linnaeus, 1758) in Benthic Communities off the Moroccan Mediterranean Coastline: Seasonal and Ontogenetic Shifts.

The European hake, Merluccius merluccius (Linnaeus, 1758), is one of the most important resources for Mediterranean fisheries. Due to its pivotal role in energy transfer from lower to higher trophic levels, this species is a crucial component of the ecosystem's functioning. The ecological role of Merluccius merluccius, off the Moroccan Mediterranean Sea (southern Alboran Sea), was investigated, exploring seasonal and ontogenetic shifts, geographical variations in prey composition, and feeding strategy. Between November 2020 and July 2022, a total of 402 hake specimens were collected by oceanographic bottom trawl surveys (MEDITS) that were carried out during warm and cold seasons to assess their diet and feeding habits. The sample was analyzed according to fish sizes and seasons, and qualitative/quantitative feeding indices were calculated. The trophic spectrum of Merluccius merluccius included 24 prey items in total, mainly belonging to Osteichthyes (12), Crustacea (10), Cephalopoda (1), and Polychaeta (1), suggesting a generalist behavior of this predator as in numerous regions of the Mediterranean Sea, with several species that occasionally occurs in its diet. In the Moroccan Mediterranean Sea, Osteichthyes proved to be the most important prey item (%IRI = 78.56) among the different zoological groups, followed by Crustacea (%IRI = 16.22). The other food items were occasionally and randomly consumed, and cannibalism was low (0.8%). Hierarchical cluster analysis and nonmetric multidimensional scaling (nMDS) showed different feeding habits of two main groups separated at 60% similarity: small specimens <10 cm TL, primarily feed on zooplanktonic prey, while medium and large specimens hold a diet based on Osteichthyes with crustaceans. Furthermore, a significant positive relationship between hake and fish prey size was confirmed. Seasonally, mesopelagic Osteichthyes were the main food prey in the summer season, while pelagic species were predominant during the autumn. SIMPER analysis revealed that the prey items contributing the most to the differences between seasons and length classes were Engraulis encrasicolus, Micromesistius poutassou, Boops boops, Macroramphosus scolopax, gobids, Gadiculus argenteus, and most of Crustacea. The diet does not appear to be influenced by sex (>0.05). A trophic level (TROPH) of 4.1 was calculated, indicating that the species is a top predator (quaternary consumers). The TROPH values ranged between 2.58 and 4.38 from juveniles to adults, increasing asymptotically with the size of specimens. In contrast to what has previously been found in other Mediterranean regions, where ichthyophagous hake feed mostly on pelagic Osteichthyes, such as Engraulis encrasicolus, Sardina pilchardus, and Micromesistius poutassou, the study points up the vital role played by Atlantic horse mackerel Trachurus trachurus for hake diet in the Moroccan Mediterranean Sea. Information on the feeding ecology of fish species as provided in this study is essential to improve ecosystem conservation in accordance with multispecies approach to fishery management, leading to a better understanding of the role of hake in the Moroccan Mediterranean Sea demersal communities.

Food Selectivity in Juvenile Three-Spined Stickleback Gasterosteus aculeatus L. (Gasterosteidae) at Nursery Grounds in the White Sea

The spatial and temporal variability in the dietary preferences of juvenile three-spined stickleback Gasterosteus aculeatus were studied across the typical coastal habitats of Keret Archipelago, Kandalaksha Bay(the White Sea). The sampling of fish using a beach seine was conducted in the late July–early August period and in late August. Additionally, zooplankton samples were collected to conduct a quantitative assessment of the abundance of potential prey items. The similarity percentage (SIMPER) analysis was applied to the data obtained from the stomach content and revealed the five planktonic taxa most prominently contributing to the diet of juvenile sticklebacks. Among these, the copepod Temora longicornis was the most important prey item at marine sites, while Acartia longiremis dominated the diet of fish in the marine lagoon. The calculation of the selectivity index revealed that some taxa (such as A. longiremis) were always avoided by juvenile fish, whereas the selectivity of some taxa increased in late August. In general, juvenile sticklebacks demonstrated a pronounced individual variation in their selectivity, even when a particular prey item was selected positively during the whole period of study. Our data highlight that despite the predominant consumption of easily available prey by juvenile sticklebacks, they demonstrate taxonomic- and size-specific prey selectivity.

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.

What determines demographic growth in green anacondas? Strong interactions among vertebrates in a neotropical ecosystem

IntroductionTrophic cascades can produce important effects on a community where some species may have strong effects on other parts of the community up, down the food chain, or both. Top predators are often controlled from the bottom-up by the abundance of their prey base while prey animals are often controlled from the top-down. Studies of trophic interactions in the tropics suggest that the trophic chains are longer because of the high productivity; and because of the high diversity there is abundant intraguild redundancy which results in weak interactions.MethodsWe studied the effect of bottom-up forces affecting the population of green Anaconda (Eunectes murinus) in the Venezuelan llanos; looking at net primary productivity, precipitation, and the abundance of an important prey item, Capybara (Hydrochaeris hydrochaeris).ResultsOur data show a strong interaction of these variables on the percentage of Anacondas that reproduce in a given year (here forth breeding ratio). In particular Capybara abundance has a strong effect. Capybara abundance itself is also under strong bottom-up influence determined by precipitation and Net Primary Productivity.DiscussionThese strong interactions are not what is expected from a tropical ecosystem. We also found an unexpected strong influence of precipitation and primary productivity on Anaconda breeding ratio not related to the abundance of Capybara, likely affecting abundance of other prey or affecting non-trophic variables. This later evidence supports the notion that there is redundancy in tropical food chains and, strong as the effect of Capybara abundance might be, Anacondas do not entirely rely on them.

Mice population dynamics and structure over time and space after wildfires

AbstractRodents respond quickly to changes in habitat structure after wildfires. They constitute important prey items for vertebrate predators and influence vegetation structure and regeneration. Assessing the population dynamics of rodents in burnt areas, whether individuals originate from in situ survival or from ex situ immigration, is therefore a key question in understanding the recovery of trophic networks after disturbance. This study aimed to identify the recovery strategies of rodent populations in recently burnt forests in the Mediterranean basin using body condition, reproductive output, sex ratios, and distance covered by wood mice and Algerian mice. Sampling stations were set up at increasing distances from the perimeter of recently burnt areas. Rodents were captured using Sherman traps and measured. Wood mice and Algerian mice lived syntopically within the recently burnt areas studied, the former species being more abundant and the second one selecting drier areas. Results indicated that time since fire, shrub cover, and distance to the perimeter of the burnt area influenced wood mice and Algerian mice population structures. Adult female wood mice mainly remained close to the burnt area perimeter, due to this species' matriarchal structure, while juvenile males dispersed farther into the burnt area. Adult females were also recaptured more frequently than other age and sex categories over time, whereas males covered greater distances. These findings suggest that the recovery strategy of these widespread Mediterranean rodents is mainly driven by ex situ immigration from unburnt areas. These results will be useful for post‐fire management decisions such as non‐intervention, salvage logging or the conservation of open areas, given that mice are a fundamental component of the ecosystem. Results also suggest that management should focus on maintaining good connectivity between burnt and adjacent unburnt areas to support mice populations and facilitate other longer‐term conservation benefits.

Flow Augmentations Modify an Estuarine Prey Field

Zooplankton density and community composition in estuaries can be affected by variation in freshwater inputs, with important implications for higher trophic levels. In the San Francisco Estuary, management agencies have initiated autumn flow augmentations in the form of changes to reservoir releases or to exported water from the South Delta to increase and improve available habitat for endangered Delta Smelt, Hypomesus transpacificus, during the season when their body condition most influences fecundity. Autumn flow augmentation only occurs in years with higher precipitation, effectively moving the Low-Salinity Zone (LSZ) downstream to key foraging habitats for Delta Smelt in Suisun Bay and Suisun Marsh. To assess whether augmented flow enhanced prey resources for Delta Smelt, we compared autumn zooplankton abundance, biomass, spatial distribution, and community composition in years when flow was augmented (2017, 2019) with reference years when flow was not augmented (2018, 2020). In augmented years, we detected higher total zooplankton abundance and altered community composition in Suisun Bay and Suisun Marsh. Increased freshwater in these regions was associated with higher abundance of Pseudodiaptomus forbesi, a preferred prey of Delta Smelt, while species associated with higher salinities—Acartiella sinensis and Tortanus dextrilobatus—were less abundant. Thus, autumn flow augmentations can influence foraging habitat and prey availability for Delta Smelt, underscoring the complex responses of estuarine zooplankton communities to changes in response to flow and salinity regimes. This study is management- relevant because it shows that important Delta Smelt prey items increase in downstream regions when X2 is lower. Whether that results in a response in Delta Smelt abundance remains to be seen.

Feeding strategy and prey selectivity in common minke whales (Balaenoptera acutorostrata) foraging in the southern Barents Sea during early summer

Stomach content samples from 33 minke whales (Balaenoptera acutorostrata), caught during Norwegian commercial whaling between May-June 1998, were collected in four sub-areas in the southern Barents Sea. Simultaneously, a comprehensive resource survey was conducted in order to identify and estimate the abundance of potential prey items for the whales in the four sub-areas. Krill (Thysanoessa sp. and Meganyctphanes norvegica) dominated the diet in all but one sub-area although pelagic fish such as capelin and herring also contributed significantly. The minke whales displayed monophagus feeding in all sub-areas investigated, including the medium-scale area resulting from pooling of all sub-areas. The small-scale resource surveys revealed significant variations in absolute and relative prey abundance between sub-areas, while the temporal (1-7 days) variations in relative prey biomass within sub-areas appeared to be less significant for all prey items, except herring (Clupea harengus) and perhaps capelin (Mallotus villosus). Krill was by far the most important prey item available in all areas, followed by either herring, cod (Gadus morhua) or saithe (Pollachius virens), depending on sub-area and survey. Although minke whale prey preference appeared to vary greatly in space, some new features of minke whale foraging behaviour were evident. Minke whales showed a strong preference for capelin, whereas gadoids (cod, haddock (Melanogrammus aeglefinus) and saithe) appeared to be avoided by the whales. Krill appeared to have been either avoided, fed upon randomly or were the preferred prey depending on sub-area and analyses level.

Three forms of killer whales (Orcinus orca) in Antarctic waters

This paper provides field descriptions and biological observations of three different forms of killer whale (Orcinus orca) that occur in Antarctica based on field observations and a review of available photographs. Identifications were based on the relative size and orientation of the white eyepatch and the presence or absence of a dorsal cape. Type A (presumably the nominate form) has a medium-sized eyepatch oriented parallel to the body axis, no dorsal cape, it occurs mainly off-shore in ice-free water, has a circumpolar distribution and apparently preys mainly upon Antarctic minke whales (Balaenoptera bonaerensis). Type B also has an eyepatch oriented parallel to the body axis, but the eyepatch is at least twice as large as in Type A, it has a dorsal cape, mainly inhabits inshore waters, regularly occurs in pack-ice, is distributed around the continent and is regularly sighted in the Antarctic Peninsula area. Although it may also prey upon Antarctic minke whales and possibly humpback whales (Megaptera novaeangliae), seals seem to be the most important prey item. Type C has a small, forward-slanted eyepatch, a dorsal cape, inhabits inshore waters and lives mainly in the pack-ice; it occurs mostly off East Antarctica, and to date it has been recorded feeding only on Antarctic toothfish (Dissostichus mawsoni). Type C appears to be referable to Orcinus glacialis as described by Berzin and Vladimirov (1983). Although similar ecological specialisations have been reported for sympatric killer whale populations in the Northeast Pacific (i.e. an inshore mammal-eater, an inshore fish-eater and an offshore form), the extent of morphological divergence, habitat segregation and, perhaps, reproductive isolation, appears to be more pronounced among Antarctic populations. Although under a Biological Species Concept these forms appear to warrant separate species status, it will be important to show that this interpretation is consistent with results of molecular genetic analyses and additional morphological studies.

Feeding ecology of broadbill swordfish (Xiphias gladius) in the California current.

The feeding ecology of broadbill swordfish (Xiphias gladius) in the California Current was described based on analysis of stomach contents collected by fishery observers aboard commercial drift gillnet boats from 2007 to 2014. Prey were identified to the lowest taxonomic level and diet composition was analyzed using univariate and multivariate methods. Of 299 swordfish sampled (74 to 245 cm eye-to-fork length), 292 non-empty stomachs contained remains from 60 prey taxa. Genetic analyses were used to identify prey that could not be identified visually. Diet consisted mainly of cephalopods but also included epipelagic and mesopelagic teleosts. Jumbo squid (Dosidicus gigas) and Gonatopsis borealis were the most important prey based on the geometric index of importance. Swordfish diet varied with body size, location and year. Jumbo squid, Gonatus spp. and Pacific hake (Merluccius productus) were more important for larger swordfish, reflecting the ability of larger specimens to catch large prey. Jumbo squid, Gonatus spp. and market squid (Doryteuthis opalescens) were more important in inshore waters, while G. borealis and Pacific hake predominated offshore. Jumbo squid was more important in 2007-2010 than in 2011-2014, with Pacific hake being the most important prey item in the latter period. Diet variation by area and year probably reflects differences in swordfish preference, prey availability, prey distribution, and prey abundance. The range expansion of jumbo squid that occurred during the first decade of this century may particularly explain their prominence in swordfish diet during 2007-2010. Some factors (swordfish size, area, time period, sea surface temperature) that may influence dietary variation in swordfish were identified. Standardizing methods could make future studies more comparable for conservation monitoring purposes.

A new snow leopard record reflects the value of remote protected areas for connectivity

AbstractAs wildlife becomes more isolated in human-dominated and rapidly changing environments, species conservation requires investment in landscape connectivity. Identifying stepping stones (discrete areas of suitable habitat that facilitate the movement of dispersing individuals) can help meet connectivity goals. We report the occurrence of the snow leopard Panthera uncia in Ikh Nart Nature Reserve, Mongolia, over 250 km from the nearest known population, one of the easternmost records for the species. Ikh Nart Nature Reserve lies within a region considered highly resistant to movement but harbours high densities of argali sheep Ovis ammon and Siberian ibexes Capra sibirica, both important prey items for snow leopards. This occurrence reveals a new distribution record for the species, the capacity of the species to move across low-quality environments, the value of investment in community conservation and collaborative park management, and the role of remote protected areas such as Ikh Nart Nature Reserve as stepping stones for facilitating population expansion and broader connectivity to other potentially suitable but unoccupied areas.

Parasites and prey of the nursehound shark Scyliorhinus stellaris (Linnaeus, 1758): Insights into hidden trophic web interactions in the Mediterranean Sea.

The metazoan parasite community and the stomach contents of the nursehound shark Scyliorhinus stellaris from the Gulf of Naples (central Mediterranean Sea) were studied. The nursehound shark harboured a poor parasite community composed of a species of gill monogenean (Hexabothrium appendiculatum) and three intestinal cestode taxa (Acanthobothrium coronatum and two unidentified species of the genera Yamaguticestus and Scyphophyllidium), all represented by adult stages. Hosts were mostly parasitized by individuals of A. coronatum, which was the most abundant species and contributed to almost 80% of the total number of parasites found. Conversely, other trophically transmitted parasites (i.e., Yamaguticestus sp. and Scyphophyllidium sp.) showed low prevalence and abundance. The parasite infracommunity was poor, showing low values of species richness, total mean abundance, and diversity indices. Overall, 52 prey items belonging to 13 taxa were identified in the stomach contents. Cephalopods were the most important prey items (represented by nine taxa) and the most diverse and abundant group. In the multivariate space provided by a principal component of mixed data (PCAmix), nursehound sharks distributed along two main axes, related to individual traits (first axis) and stomach contents (including empty ones, second axis). A logistic regression based on the first two axes of the PCAmix showed a significant influence of host individual traits and, to a lesser extent, of stomach contents, regarding the probability of being infected by A. coronatum. Alongside specific traits already associated with parasites transmission, our results highlight the importance of cephalopods in transferring cestode infections through trophic web interactions in the top-predator nursehound shark.

Comparative trophic ecology of two sympatric guitarfishes Pseudobatos (Chondrichthyes, Rhinobatidae) from Southeast Brazil, southwestern Atlantic.

The present study compares the trophic ecology of two guitarfishes (Pseudobatos percellens and Pseudobatos horkelii) from the continental shelf of the São Paulo State, Brazil, caught by the bottom pair trawls between 2007 and 2009. These two sympatric species are under different threat categories, "Vulnerable" and "Critically Endangered," respectively, according to Brazilian agencies. Thus, any study considering trophic ecology parameters is pivotal in understanding the trophic ecology role of such species in the ecosystem. The authors analysed 500 stomachs of P. percellens and 108 of P. horkelii, quantifying with dietary indexes: numerical (%N), gravimetric (%W), frequency of occurrence (%FO) and the prey-specific index of relative importance (%PSIRI). For P. percellens and P. horkelii, 26 and 14 different prey items were found, respectively. Crustacea and Teleostei were the most important prey items for both species, indicating a specialist feeding behaviour due to their low niche amplitude. The results provide evidence related to ontogenetic dietary shift in P. percellens and individual-level diet specialization in both species. These two benthic-demersal elasmobranchs are important mesopredators (3,7 for P. percellens, and 3,5 for P. horkelii) in the study area, with high trophic-level values.