Opportunistic Feeding Research Articles

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.

The Box Crab Calappa hepatica as a Nuclear Species for the Opportunistic Foraging Behaviour of the Flowery Flounder, Bothus mancus, in the Indo-Pacific

Some predatory fishes may exhibit opportunistic feeding behaviour by exploiting potential prey that is distracted, displaced, or exposed by the activities of a third party that acts as a ‘nuclear’ species. Other fishes mostly perform the role of ‘nuclear’ species, but benthic invertebrates, such as octopuses, have also been reported. Crabs are rarely observed in this role, with only a few records from the tropical Atlantic Ocean. Here, we report the temporary association between two specimens of the flowery flounder, Bothus mancus (family Bothidae), and a box crab, Calappa hepatica (family Calappidae), from the Philippines, representing the first record of a crab–fish feeding association in the Indo-Pacific region.

High Resource Overlap and a Consistently Generalised Pattern of Interactions in a Bat-Flower Network in a Seasonally Dry Landscape.

Pollination is an ecosystem process that is crucial to maintain biodiversity and ecosystem function. Bats are important pollinators in the tropics and are an integral part of complex plant-pollinator interaction networks. However, network analysis-based approaches are still scarce at the plant species and bat community levels. We used metabarcoding to identify plant taxa present in pollen from fur and faecal samples collected across 1 year from three nectar-feeding bat roosts in central Mexico. We calculated the frequency of occurrence of plant taxa and assembled a zoocentric network of bat-plant interactions. We constructed a year-long network, encompassing the entire period of sampling, two seasonal networks comprising the wet and dry seasons, and six individual networks from sampling at two-month intervals across the year. Four species of nectar-feeding bats interacted with 36 plant species from 16 families. We found highly generalised interaction patterns across networks corresponding with opportunistic feeding behaviour by bats, with little seasonal variation in network structure. There was high resource overlap between bat species, and bats visited a diverse range of plant species even during periods with a high abundance of particular resources in the landscape. The diverse diet of nectar-feeding bats emphasises the importance of floristically rich natural habitats in the landscape to provide reliable foraging resources year-round in a seasonally variable system. While a generalised network structure is thought to increase robustness, further research is necessary to understand how fluctuations in pollinator abundance and diversity in the face of land use and climate change may impact bat-flower networks and the consequences to plant communities.

206 Effects of breed type and days on trial on feeding behavior in growing goats fed a total mixed diets using GrowSafe feeding technology

Abstract The objective of this study was to evaluate the effects of breed and days on trial (DOT) on feeding behavior traits in two breeds of growing goats. Nineteen female goats [n = 10 Alpine; n = 9 Spanish, with average initial ages of 360 d and 352 d, and body weight (BW) of 38.8 ± 2.8 kg and 35.5 ± 3.1 kg, respectively], were randomly assigned within the breed to one of two non-adjacent pens (5 goats/pen), each equipped with GrowSafe feed bunks. A pelletized total mixed ration (TMR) was fed twice per day and goats had ad libitum access to feed, water, and mineral block throughout the 84-d trial. Feeding behavior traits, including feed intake, bunk visit frequency (BVF), head-down duration (HDD), and dry matter intake (DMI) were collected daily using the GrowSafe feeding system. A 14-d interval was used to derive feed behavior traits of individual goats at 42, 56, 70, and 84 DOT. Data were analyzed using a repeated-measures model with a fixed effect of breed, DOT as a repeated measure, and breed x DOT interaction with pen as a random effect. Alpine goats had greater (P < 0.05) initial and final BW (37.6 kg and 51.7 kg, respectively) than Spanish goats (34.7 kg and 46.5 kg, respectively) although DMI (P = 0.10; 1.73 ± 0.31 and 1.39 ± 0.18 kg/d) did not differ. There was not a significant difference (P > 0.05) between breeds for frequency of bunk visits (21.1 vs. 18.6) and bunk duration (P > 0.05). Similarly, the effect of breed on DMI (27.1g/min vs. 22.8 g/min) was non-significant (P > 0.05). Furthermore, breed did not significantly (P > 0.05) affect HDD (31.3 min/d vs 31.9 min/d). However, there was a significant interaction (P < 0.05) between breed and DOT for HDD. In addition, significant differences (P < 0.05) were observed due to the length of DOT for BVD, bunk visit duration, HDD, and eating rate (g/min). Our results suggest that Spanish goats tended to visit feed bunks more frequently per day and tended to consume less feed per visit than their counterpart Alpine goats, and the feeding behaviors of goats change with age. However, further research is warranted to determine changes in the feeding behavior of goats in different production cycles.

393 The role of on-animal sensors in understanding feed intake, behavior, and performance of grazing livestock

Abstract Intake by grazing animals is difficult to reliably measure in the field, particularly in more diverse grazing systems where pastures vary greatly across time and space in resource availability, which in turn leads to greater variation in animal time budgets and intake patterns. Advances in remote livestock monitoring (e.g., on-animal sensors, walk -over-weighing), and advanced analytics such as machine learning algorithms can contribute to the development of robust, adaptable tools for better understanding of animal performance and behavior in grazing systems. Many existing tools for predicting livestock production require estimates of feed intake, and while estimates based on forage sward characteristics have been developed and used for temperate, relatively homogenous pastures, they are less well defined for more diverse rangelands. These diverse pastures are more difficult to characterize due to their greater variation in quantity and quality; consequently, animal selectivity is greater in more variable pastures. However, such feedback loops between pasture diversity and animal behavior may not yet be adequately represented in biophysical models. On-animal sensors such as accelerometers and GPS devices can be used to develop new ways of assessing relative intake by providing accurate estimates of animal location and behavior profiles, such as the use of machine learning algorithms to detect how much time is spent grazing, walking, ruminating, or resting. Measurements of animal behavior could then be combined with other animal-based methods such as walk-over-weighing and fecal NIR to improve estimates of intake and production for a wide range of extensive grazing environments. Sensor-derived measurements of animal movement could also be used to improve estimates of the energetic costs of grazing, thereby improving estimates of energy available for growth. As an example, data on recent activity and paddock use from on-animal sensors could be entered into a model to estimate current feeding requirements, then combined with weather and pasture quality forecasts. The ensuing baseline could then be used to explore the potential variability of these projections and generate a range for possible expected performance over the next month or season. This approach could be repeated over time, and animal performance and behavior measures used to update model estimates and improve forward projections. These methods could also be used in conjunction with estimates of animal energy requirements to provide real-time prediction of relative feed intake, which would provide a step-change in modelling livestock production in extensive grazing systems. For these approaches to be successful, additional calibration data are needed across a wide variety of environments and species, and the tools must be cost-effective to implement. In summary, on-animal measurements provide an adaptable, data-driven approach that could be integrated with existing tools to improve our understanding of feed intake, behavior, and performance of grazing animals.

Opportunistic predatory feeding behaviour of Munida intermedia A. Milne-Edwards & Bouvier, 1899 targeting juveniles of Lepidopus caudatus (Euphrasen, 1788) in the north-western Mediterranean Sea

The genus Munida, inhabits various marine habitats and exhibits versatile feeding behaviour. This study explored the behavioural patterns of Munida intermedia, shedding light on its opportunistic behaviour and competitive interactions within its ecological niche. In 2018, during an investigation using a remotely operated vehicle (ROV), carried out on the Méjean shoal (north-western Mediterranean Sea), at 397 m depth, specimens were observed engaging in opportunistic predatory feeding, targeting juveniles of the bathypelagic silver scabbardfish Lepidopus caudatus. Our findings underscore the dynamic nature of M. intermedia feeding habits and the significant role of competitive interactions within its habitat, highlighting the role of video technology in capturing real-time information.

Feeding habits of splendid alfonsino Beryx splendens in the vicinity of Kuroshio, the south of Japan

AbstractGut contents and nitrogen isotope ratio (δ15N) analyses were conducted on splendid alfonsino Beryx splendens collected in the vicinity of Kuroshio from May 2015 to November 2016 (n = 708) to identify their feeding habits in the Western North Pacific. Micronektonic fish, shrimp, and squid were the dominant prey species, with the Decapoda Acanthephyra quadrispinosa, Prehensilosergia prehensilis, Cephalopoda Enoploteuthis chunii, Chiroteuthis calyx, Teleostei Sigmops gracilis, and Gonostoma elongatum. These micronektons are common in the Kuroshio Current; thus, B. splendens is a possible opportunistic feeder. Gut content weight (GCW), occurrence (%O) of fish and squid, and δ15N were significantly increased with the fork length (FL) of B. splendens. Only the %O of shrimp does not show a significant relationship with the FL of B. splendens. These indicated the ontogenetic shift of dominant prey from shrimp to fish. Fattened specimens could also prey on a greater number of fish. The seasonality of GCW and %O values was high in spring and autumn and low in summer and winter. This seasonality indicated that the feeding habits of B. splendens are controlled by primary productivity in the surface layer and/or by maturity. When the Kuroshio flowed in the north of Hachijojima Island, the GCW was significantly increased, and some organisms, including C. calyx, G. elongatum, and S. gracilis, were preyed on more. While the offshore area of the Kuroshio has low productivity, B. splendens can actively prey in this area, indicating that it is an important feeding ground for this species.

Culicoides biting midges feeding behaviour as a key for understanding avian Haemoproteus transmission in Lithuania.

Investigations of host feeding behaviour in haematophagous insects are critical to assess transmission routes of vector-borne diseases. Understanding if a certain species has ornithophilic or mammalophilic feeding behaviour can facilitate future studies focused on pathogens transmission to and from certain host species. Culicoides Latreille (Diptera: Ceratopogonidae) are vectors of several pathogens, which include arboviruses, bacteria and parasites to a considerable diversity of vertebrate hosts. However, most of the studies focused on feeding habits target Culicoides species that could transmit the Bluetongue virus, consequently with a mammalophilic feeding behaviour, leaving aside the Culicoides species that are involved in the transmission of vector-borne parasites to birds, such as Haemoproteus Kruse (Haemosporida: Haemoproteidae). This study aimed to investigate the source of blood meals of wild-caught Culicoides using molecular-based methods and to correlate our findings with the reports of Haemoproteus parasites in Culicoides species. Engorged Culicoides females were collected using ultraviolet (UV)-light traps at seven different localities in Lithuania in 2021-2023. Biting midges were dissected, and the abdomens of engorged females were used for molecular investigation of the blood meal source. A polymerase chain reaction (PCR) protocol that amplifies a fragment of the Cytochrome B gene of vertebrates was used. Obtained sequences were compared to available information in GenBank database to confirm the source of the blood meal. In total, 258 engorged Culicoides females, representing nine different species, were analysed. The source of blood meal was identified in 29.1% of them with most of the insects having fed on birds (74.7%) and the remaining on mammals (25.3%). Culicoides segnis Campbell, Pelham-Clinton was the only species to feed exclusively on birds; Culicoides from the Obsoletus group, C. pallidicornis Kieffer and C. punctatus Latreille were found to feed exclusively on mammals; C. festivipennis Kieffer, C. kibunensis Tokunaga and C. pictipennis Staeger had an opportunistic feeding behaviour, with the first two preferably feeding on birds. Due to their feeding behaviour and the presence of Haemoproteus parasites reported in the literature, C. festivipennis, C. kibunensis, C. pictipennis, and C. segnis play an important role in the transmission of those avian vector-borne parasite in the wild. These Culicoides species were already confirmed as being able to support the development of several Haemoproteus species and lineages. Future studies focused on understanding the epidemiology of avian pathogens transmitted by Culicoides should target these species.

Diet variation and trophic impact of weakfish, Cynoscion regalis, within multiple marine habitats of the eastern United States.

Weakfish (Cynoscion regalis) is not federally managed but feeds on species of management and ecological interest. We examined the trophic ecology of weakfish in Chesapeake Bay and the coastal and offshore waters of the eastern United States. For these areas, we determined the dominant prey of weakfish; identified how much diet variation was explained by the factors: season, size class, and year; and quantified prey biomass removed by weakfish from 2007 to 2019. In general, diet composition was mostly dominated by Engraulidae, Osteichthyes (bony fishes), and Mysidacea, and significantly varied by season and size class in Chesapeake Bay and coastal waters, although this was less dramatic in Chesapeake Bay. The total amount of variance explained by the three factors was 23.1% (Chesapeake Bay) and 14.7% (coastal waters), with year not being a significant factor in explaining weakfish diet variation for these areas. Weakfish total prey biomass removal occurred primarily in coastal waters in the fall and small size class (annual mean: approximately 41,038 t; maximum: approximately 63,793 t). Highly opportunistic feeders, weakfish cannibalism also played an essential part of their diet. These results have implications for fisheries and ecosystem management of weakfish when considering ecological interactions in regulatory approaches, such as recruitment and cannibalism, competition with federally managed fishes, and the natural mortality of their prey.

Small pelagic fish in the shallow Wadden Sea show opportunistic feeding with a strong benthic link

Abstract Small pelagic fish (SPF) are crucial in marine food webs, transferring energy from plankton to higher trophic levels. This study focuses on herring (Clupea harengus) and sprat (Sprattus sprattus), addressing knowledge gaps in their feeding ecology in a nursery area, the Dutch Wadden Sea. We conducted a year-long, monthly survey, and used DNA metabarcoding to analyse zooplankton samples and stomach contents of two size classes of herring and sprat. Intra-, interspecific, and seasonal variations in fish condition, stomach fullness, and diet composition, along with selective feeding, were studied. Our study showed that condition and diet composition of herring and sprat, along with zooplankton density, exhibited a clear seasonal pattern. Juvenile herring and sprat displayed opportunistic feeding behaviour, rather than showing distinct prey selection. Besides copepods, we regularly observed (larvae of) benthic invertebrates in their diet. This emphasizes the crucial role of SPF as energy transfer agents, not solely between trophic levels, but also from benthic to pelagic habitats. Furthermore, fish post-larvae were part of the diet of larger herring (10–15 cm). Because of its unprecedented temporal and taxonomical detail, this study advances the understanding of seasonal dynamics of dominant components at the base of the Wadden Sea food web.

Design and Implementation of Bulk Feeders Using Voice Coil Motors

Design and Implementation of Bulk Feeders Using Voice Coil Motors

Diet of the European Pond Turtle (Emys orbicularis) in Anzali Lagoon (South Caspian Sea)

This study explored the diet and food composition of the European Pond Turtle, Emys orbicularis, population in Anzali Lagoon, located in the South Caspian region. A total of 186 turtles were captured during both the pre- and post-breeding seasons to analyse their stomach contents. The analysis revealed that the diet primarily consisted of Arthropoda (76.2%), followed by Mollusca (12.2%), fish (4.6%), aquatic plant material (6.0%), and Annelida (0.9%). The average number of food items during the breeding season was 14 per sample, which significantly decreased to 2.5 in the post-breeding season. On average, male turtles consumed three food items, while females consumed six during the study period. The Pianka Index indicated a high degree of dietary overlap among males, females, and juveniles. Moreover, the Shannon Index revealed food item diversity values of 1.1 for males, 0.94 for females, and 0.62 for juveniles. These findings suggest that the European Pond Turtle in Anzali Lagoon is an opportunistic feeder, with its diet ranging from carnivorous to omnivorous, depending on environmental conditions, season changes, and food availability.

High trophic specialization structures the epi- to bathypelagic fish community in the Bay of Biscay

The deep-pelagic ecosystem is characterized by significant environmental gradients, particularly in food resources. The absence of primary production below the epipelagic zone leads to a decrease in food resources with depth. Two opposite feeding strategies have been described for this community in response to this decline in food resources: stochasticity, with species adopting opportunistic feeding strategies with a generalist diet, and determinism, with species segregating and specializing to mitigate strong interspecific competition through niche partitioning. To test these aspects, we analyzed the isotopic niches of 16 fish species using stable isotope analysis of carbon and nitrogen carried out on muscle samples. The data were collected in canyons of the Bay of Biscay between 25 and 1335 m. Our primary objective was to identify isotopic niche segregation or overlap and determine whether species sharing similar isotopic niches show depth-based segregation by grouping them into trophic guilds and comparing their depth distribution with trawl data. We then used null model comparisons to test whether competition resulted in smaller values of isotopic niche size and overlap within each depth assemblage compared to those obtained by chance. We found that several species with similar isotopic niches were segregated based on depth. The comparison with null models showed that competition drove species to reduce niche size and specialize to avoid strong interspecific competition in the epi- to bathypelagic layers. Utilizing isotopic diversity indices weighted by biomass, our calculation showed significant divergence within the community, indicating that species with the highest biomass had extreme isotopic values. The high degree of specialization of species raises concerns about their vulnerability to various pressures, including climate change and exploitation. At the community level, this vulnerability is also a concern in maintaining the integrity of ecological processes.

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.

Pollen-feeding in a giant pelobatid tadpole from the late Oligocene of Enspel, Germany

AbstractWe examined the gut contents of a fossil giant pelobatid tadpole from the late Oligocene of Enspel, Germany, and discovered that it contains mainly pollen from spruce (Picea) but also pollen from pine (Pinus), beech (Fagus), and elm (Ulmus). Pollen in the gut of the fossil tadpole and other plant fossil records from this locality suggest that the regional vegetation around Enspel was characterised by mixed conifer and broadleaved forests with a prominent deciduous angiosperm component. Palaeoclimatic estimations indicate that the area endured a fully humid warm temperate climate with a hot to warm summer and a distinct temperature difference between seasons. The pollination period of potential modern analogues of the plant taxa discovered in the gut of the fossil tadpole hints that it was feeding on pollen floating on the water surface of the ancient Enspel Lake during late spring or earliest summer. Comparable analyses from the guts of extant pelobatid tadpoles have shown a broad spectrum of food remains, including whole/or parts of algae, protists, protozoans, macrophytes, rotifers, crustaceans, and pollen. It seems that living pelobatid tadpoles are indiscriminate and opportunistic feeders able to adapt and change their feeding behaviour according to the available food source. The time of origin and evolution of pollen feeding in tadpoles is obscure. Our discovery indicates that pelobatid tadpoles were already feeding on pollen in the late Oligocene, and the amount and purity of pollen filling the gut suggests intentional surface feeding.

Management of dairy heifers in Uruguay

Management practices during the rearing of dairy heifers should allow an adequate body growth and reproductive development to attain puberty several months before the first conception. Proposed target age and body weight (BW) at first calving for Holstein heifers are between 22-24 months and 82% of mature BW, respectively, for which heifers must conceive at around 15 months of age with 60% of their mature BW. Pre- and postweaning feeding level has effects on feed efficiency, behavior, energy metabolism and body and reproductive development, while social environment during rearing, specifically the social dominance and social regroupings, is known to affect energy metabolism, feeding behavior and body and reproductive development of the heifer. In Uruguay, the information published regarding the management of the dairy heifer is scarce. The aim of this review is to briefly assess the main factors affecting the onset of puberty, and to present an integrative approach of the information generated in Uruguay regarding the effects of modifying the feeding level and social environment during the rearing period on body development, metabolism, and onset of puberty in dairy heifers. In addition, we make a proposal of knowledge gaps that should be addressed in future studies.

Living at depth: ecophysiological condition of Boreomysis arctica in autumn and winter in the St. Lawrence estuary and gulf.

Mysids, besides krill, play a significant role in energy transfer and carbon sequestration. The ecology of coastal species is better understood than that of deep dwelling species such as Boreomysis arctica. The objectives of this study were to quantify spatiotemporal variations in body condition and the trophic level of B. arctica in autumn and winter, under sea-ice conditions in the St. Lawrence system, using a multimarker approach. We sampled along a 1000km transect. Mean abundances in winter were higher in the estuary compared to the Gulf of St. Lawrence. Body condition, measured as total lipid content, was higher in winter than in autumn. Lipids of B. arctica were mainly composed of wax esters, thereby B. arctica is richer in energetic lipids compared to the three dominant krill species. We also observed seasonal differences in the trophic level of B. arctica, revealing carnivorous behavior in autumn compared to omnivory in winter. High intra-specific variability in both energetic strategy and feeding behavior was found that is potentially due to opportunistic feeding. Energy rich reserves suggest that B. arctica could act as a valuable prey for both benthic and pelagic consumers and thus playing a key role in bentho-pelagic energy transfer.

Microplastic in an apex predator: evidence from Barn owl (Tyto alba) pellets in two sites with different levels of anthropization.

Plastic pollution in terrestrial and freshwater environments and its accumulation along food chains has been poorly studied in birds. The Barn owl (Tyto alba) is an opportunistic and nocturnal apex predator feeding mostly on small mammals. In this note, we reported evidence of microplastics (MPs) contamination in Barn owl pellets collected, for the first time, in two sites with different levels of anthropization (low: natural landscape mosaic vs. high extensive croplands). The following polymers have been recorded: polyvinylchloride (PVC), polyethylene (PE), expanded polyester (EPS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyester (PL), viscose, and starch-based biopolymer. We found significant higher MPs frequency in the most anthropized site. Our results suggest that pellet' analysis may represent a cost-effective method for monitoring MP contamination along food chains in terrestrial ecosystems.

Southern Ocean humpback whale trophic ecology. II. Influence of fasting and opportunistic feeding on skin stable isotope values of migrating whales

Many baleen whale species migrate between low-latitude breeding grounds and high-latitude feeding grounds, with increasing evidence that humpback whales Megaptera novaeangliae utilise supplemental feeding sites in temperate regions while migrating. The diet of whales while migrating is often unknown, and the impact that temperate feeding and/or fasting has on biochemical tracers used to investigate diet remains unclear. The aims of this study were to (1) determine whether prey consumption at supplemental feeding sites could be detected by carbon (13C) and nitrogen (15C) stable isotope analysis of skin; (2) obtain information on diet during migration; and (3) ascertain the impact of potential fasting on stable isotope values of baleen whales. Skin samples were taken from the eastern Australian humpback whale population on Antarctic feeding grounds and 2 sites on the southward migration route (a sub-tropical site and a temperate site) across 2 yr. At the sub-tropical site, 13C and δ15N were consistent with the last place of foraging 5 mo earlier. One exception was the higher (0.5 ‰) δ15N value in 2011, suggesting that in some years, potentially when blubber reserves are insufficient, δ15N may be influenced by fasting. In both years, skin 13C and δ15N values at the temperate site were higher than those from the Antarctic and sub-tropical sites, indicating that a feeding signal from temperate zones had likely been incorporated, with whales feeding on fish and krill. Importantly, supplemental feeding while migrating could affect the interpretation of whale diet on feeding grounds if sampled early in the season.

Trophic niche overlap of deep-sea fish species revealed by the combined approach of stomach contents and stable isotopes analysis in the Central Tyrrhenian Sea

Understanding the trophic ecology of marine ecosystems is a key challenge given that they are subject to anthropogenic pressures that can alter the integrity of the food web. The bathyal zone of the Central Tyrrhenian Sea is characterized by an high level of community biodiversity, heavy anthropogenic pressure and thus represents a fundamental environment for the study of trophic relationships between demersal fish species which live in sympatry, but this basin still remains data deficient. To fill this information gap, we investigated the trophic niche overlap of four deep-sea fish species, Galeus melastomus, Helicolenus dactylopterus, Lepidorhombus boscii, and Trisopterus capelanus, in the Central Tyrrhenian Sea using an integrated approach of stomach content and stable isotopes analysis (δ13C and δ15N). Our analysis revealed that the blackmouth catshark G. melastomus displays a wide trophic niche with considerable overlap with other fish species, as it consumed diverse prey including fish, crustaceans, and cephalopods, thus proving a generalist and opportunistic feeding behavior. The blackbelly rosefish H. dactylopterus exhibits a narrower isotopic trophic niche comprising mainly benthic crustaceans and so suggesting a marked specialism in feeding strategy. The diet of the four-spotted megrim L. boscii showed a marked overlap with that H. dactylopterus, as these species shared a similar benthic habit and relied upon a similar pool of resource. The poor cod T. capelanus showed a diverse diet comprising both prey captured close to the bottom, especially decapod and mysid crustaceans, and bathypelagic prey, mainly Osteichthyes, Myctophidae, and amphipod Hyperiidae, with an intermediate partially segregated isotopic niche width. The combination of stomach content analysis and stable isotopes analysis provided the first characterization of the trophic relationships, shedding light on the trophic niche overlap of these four ecologically important deep sea fish species. The diets of the four investigated species showed similarities in the composition of prey, but also differences which allows them to partially reduce competition. This information may be of crucial relevance for the development of effective management and conservation strategies for the bathyal Mediterranean environment.