Feeding Tactics Research Articles

First finding of a dual-meaning X wave for phloem and xylem fluid ingestion: Characterization of Scaphoideus titanus (Hemiptera: Cicadellidae) EPG waveforms

The leafhopper Scaphoideus titanus (Hemiptera: Cicadomorpha: Cicadellidae), an invasive deltocephaline species introduced into Europe from North America, is the vector of the most important phytoplasma disease in European viticulture, flavescence dorée. In this first electropenetrography (EPG) study of S. titanus, we characterized its feeding waveforms and defined their biological meanings. Four typical waveform phases (pathway, X wave, sustained ingestion, and interruption) and four families within those phases (A, B, C, and N) were characterized using DC EPG technology. We proposed biological meanings for these waveforms based on excreta pH-ingestion correlations, presence of X waves, and comparison with previous AC, DC, and AC-DC EPG waveforms conducted on Cicadomorpha. We observed that sustained (i.e., >10min) ingestion by a deltocephaline leafhopper can occur from both xylem and phloem vascular cells. Waveform C2x represented ingestion of xylem fluid, and two waveforms represented behaviors when stylets were inserted into phloem sieve elements: C2p variant 1 (C2p-1), which may represent salivation (perhaps simultaneous with ingestion), and C2p variant 2 (C2p-2), which represented active ingestion. Furthermore, we found that the EPG-recorded X wave has a dual meaning by occurring prior to sustained ingestion from either phloem or xylem. This X wave was very similar in appearance to the model X wave of sharpshooters, an entirely different leafhopper subfamily, Cicadellinae. All cicadellines are obligate xylem-ingesters. Such a “dual-meaning X wave” will provide insights into how the feeding tactics of S. titanus relate to other sheath-feeding hemipterans, and will provide support for future research to clarify the role of this leafhopper as a vector of plant pathogens.

Mixed xylem and phloem sap ingestion in sheath-feeders as normal dietary behavior: Evidence from the leafhopper Scaphoideus titanus

In phytophagous piercing-sucking insects, salivary sheath-feeding species are often described as xylem- or phloem-sap feeding specialists. Because these two food sources have very different characteristics, two feeding tactics are often associated with this supposed specialization. Studying the feeding behavior of insects provides substantial information on their biology, ecology, and evolution. Furthermore, study of feeding behavior is of primary importance to elucidate the transmission ability of insects that act as vectors of plant pathogens. In this study, we compared the durations of ingestion performed in xylem versus phloem by a leafhopper species, Scaphoideus titanus Ball, 1932. This was done by characterizing and statistically analyzing electrical signals recorded using the electropenetrography technique, derived from the feeding behaviors of males and females. We identified three groups of S. titanus based on their feeding behavior: 1) a group that reached the phloem quickly and probed for a longer time in phloem tissue than the other groups, 2) a group that reached the xylem quickly and probed for a longer time in xylem tissue than the other groups, and 3) a group where individuals did not ingest much sap. In addition, the numbers and durations of waveforms representing ingestion of xylem and phloem saps differed significantly depending on the sex of the leafhopper, indicating that the two sexes exhibit different feeding behaviors. Males had longer phloem ingestion events than did females, which indicates that males are greater phloem feeders than females. These differences are discussed, specifically in relation to hypotheses about evolution of sap feeding and phytoplasma transmission from plant to plant.

Producers and scroungers: feeding-type composition changes with group size in a socially foraging spider

In groups of socially foraging animals, feeding behaviour may change with group size in response to varying cost-benefit trade-offs. Numerous studies have described group-size effects on group-average feeding behaviour, particularly emphasizing an increase in scrounging incidence for larger groups, where individuals (scroungers) feed from the food sources others (producers) discovered. However, individual variation in feeding behaviour remains unconsidered in the vast majority of these studies even though theoretical models predict individuals to specialize in feeding tactic and anticipate higher scrounger-type frequencies in larger groups. We combined group-level and individual-level analyses of group-size effects on social foraging in the subsocial spider Australomisidia ergandros Lending novel experimental support to model predictions, we found that individuals specialize in feeding tactic and that higher scrounging and lower producing incidence in larger groups were mediated through shifts in the ratio of feeding types. Further, feeding-type specialization was not explained by innate individual differences in hunting ability as all feeding types were equally efficient in prey capture when foraging alone. Context adaptivity of feeding behaviour might allow this subsocial species to succeed under varying socioecological conditions.

CURRENT APPROACHES TO PREVENTING CHILDHOOD OBESITY

Obesity prevention is a priority in health care. The paper gives the results ofstudies of the prevention of overweight and obesity in childhood. It discusses specific practical recommendations concerning antenatal prophylaxis, a balanced diet, complementary food, and infant feeding tactics. Inclusion of functional foods as an important component of dietary measures to prevent obesity is warranted.

Sensory-Motor Systems of Copepods involved in their Escape from Suction Feeding.

Copepods escape well by detecting minute gradients in the flow field; they react quickly, and swim away strongly. As a key link in the aquatic food web, these small planktonic organisms often encounter suction-feeding fish. Studies have identified certain hydrodynamic features that are created by the approach of this visual predator and the generation of its suction flow for capturing food. Similarly, studies have identified certain hydrodynamic features that evoke the evasive response of copepods. This is a review of the copepod sensory motor system as pertains to understanding their response to suction-feeding fish. Analyses of the reaction time, threshold sensitivity, structure of sensors, and evasive behavior by this key prey of fish can be useful for evaluating the effectiveness of feeding tactics in response to suction flow. To illustrate, we present results comparing a copepod from a fishless lake (Hesperodiaptomus shoshone) to a copepod from a rich fishing ground (Calanus finmarchicus). We designed a flow mimic that produces a realistic mushroom-cap-shaped flow field and realistic accelerations of flow; the copepods treated the mimic as a threat and performed jumps directed up and away from the siphon. Calanus finmarchicus responded at an average threshold strain rate of 18.7/s, escaped at 0.46 m/s, and traveled 5.99 mm, most frequently as a single jump. Hesperodiaptomus shoshone responded at a strain rate of 15.1/s that is not significantly different, escaped more slowly at 0.22 m/s and traveled a shorter distance of 3.01 mm using a series of hops. The high variability noted in the initial angle of the body and the maximum change in body angle suggests that unpredictability in the escape maneuver is another aspect of the tactic of copepods. The speed of the escape by small copepods 2-3 mm long is overwhelmed by the speed of the attack by the much larger, faster fish; if the copepod reacts when it is within the fish's arena of capture (<1.5 mm from mouth), it will be eaten. The copepod, however, has an acutely sensitive array of mechanosensors that perceive the flow field of the fish at distances of 3-6 mm, or outside the fish's range of capture. The copepod also has a rapid and strong locomotory response, thereby increasing the odds that the copepod will survive-but speed is unlikely to be the best tactic for staying alive. Instead, the copepod accelerates from 61.3 to 96.5 m/s(2) or more than 20 times stronger than the lunge of a fish. This collection of capabilities of copepods enables them to remain one of the most abundant multicellular organisms on our planet.

Flexibility in foraging strategies of Brown Skuas in response to local and seasonal dietary constraints

The Brown Skua Stercorarius antarcticus lonnbergi is an opportunistic species that displays a high degree of flexibility in foraging tactics. We deployed glo- bal positioning system (GPS) and immersion (activity) loggers on breeding Brown Skuas of known sex, body size and condition at Admiralty Bay, King George Island with the aim to examine the impacts of spatial and seasonal fluctuations in prey availability on movement and foraging behavior. We also investigated whether reversed sexual size dimorphism (females larger than males) in this species leads to differences between sexes in foraging behavior and whether this or other factors contribute to variation in breeding success. Analysis of the GPS data highlighted the high degree of plasticity in foraging behavior among individuals. Although most Brown Skuas were flexible in their feeding tactics, this was not enough to ensure a suc- cessful breeding season, as few pairs fledged chicks. Dur- ing early chick rearing, Brown Skuas spent most of their time on land, feeding almost exclusively on penguin chicks. By late chick rearing, when the availability of penguins had diminished, Brown Skuas supplemented the food obtained on land by traveling to the ocean. All for- aging trips to sea occurred during daylight, mostly during the early morning. Despite marked sexual size dimorphism, we failed to find any difference in foraging tactics between males and females. Furthermore, although laying date affected the number of chicks hatched (earlier pairs were more successful), no relationship was found between breeding success and male or female body size, condition or degree of dimorphism within pairs.

Fatty acid signatures and stomach contents of four sympatricLakeTrout: assessment of trophic patterns among morphotypes inGreatBearLake

AbstractSympatric diversification inLakeTrout is generally linked to differences in habitat use (especially depth) as a result of foraging on different prey items. However, extensive sympatric divergence has taken place in the shallow waters (≤30 m) ofGreatBearLake, with multipleLakeTrout morphs varying in head and fin characteristics. To investigate diet partitioning as a potential explanatory mechanism for this diversification, we assessed trophic characteristics and relationships among four sympatric shallow‐water morphs ofLakeTrout via analyses of fatty acids and stomach contents. Fatty acids and stomach contents both identifiedLakeTrout,Cisco andMysisas key prey items inLakeTrout diets. Interestingly, terrestrial invertebrates were also seasonally important among morphs, reflecting temporal variability of available prey in this arctic lake. Some diet partitioning was observed among morphs;Morph 1 was characterised as a generalist,Morph 3 was more benthic‐oriented, andMorphs 2 and 4 were mainly pelagic feeders. Of the latter,Morph 4 was the most specialised, whereasMorph 2 exhibited alternative feeding tactics of benthic cannibalistic and pelagic piscivorous feeding. Our findings demonstrate that complementary dietary methods can elucidate habits of opportunistic feeders, a task that can often be problematic, given their complex and variable diets. Our results add new information and perspectives on the current model ofLakeTrout differentiation, demonstrating niche partitioning based on benthic versus pelagic habitat use and generalist versus specialist feeding tactics.

At-sea associations in foraging little penguins.

Prey distribution, patch size, and the presence of conspecifics are important factors influencing a predator’s feeding tactics, including the decision to feed individually or socially. Little is known about group behaviour in seabirds as they spend most of their lives in the marine environment where it is difficult to observe their foraging activities. In this study, we report on at-sea foraging associations of little penguins (Eudyptula minor) during the breeding season. Individuals could be categorised as (1) not associating; (2) associating when departing from and/or returning to the colony; or (3) at sea when travelling, diving or performing synchronised dives. Out of 84 separate foraging tracks, 58 (69.0%) involved associations with conspecifics. Furthermore, in a total of 39 (46.4%), individuals were found to dive during association and in 32 (38.1%), individuals were found to exhibit synchronous diving. These behaviours suggest little penguins forage in groups, could synchronise their underwater movements and potentially cooperate to concentrate their small schooling prey.

Coordinated feeding behavior of the Guiana dolphin, Sotalia guianensis (Cetacea: Delphinidae), in southeastern Brazil: a comparison between populations

The coordinated feeding tactics used by delphinids are influenced by differences in the distribution of prey species, season, and opportunities for social learning. In the present study, we compared the coordinated feeding behavior of two populations of the Guiana dolphin, Sotalia guianensis, in southeastern Brazil, and how these feeding tactics vary seasonality and in the presence of calves. We observed eight types of coordinated feeding tactics, which differed in frequency and in the mean number of individuals engaged in them, and between both areas. Feeding tactics used to herd and capture prey were the most frequent and engaged a greater number of individuals, suggesting that these tactics are better for capturing fish that gather in larger schools. Furthermore, the seasons influenced the occurrence of different prey items, which in turn modified the feeding tactics of the dolphins. In the Ilha Grande Bay we observed that bouts lasted longer and larger groups engaged in the feeding tactics, which may be associated with the seasonal spawning of larger schooling fish such as Sardinella brasiliensis (Steindachner, 1879) (Teleostei: Clupeidae). However, in the Sepetiba Bay, we observed longer feeding bouts and a smaller number of individuals engaged in the feeding tactics during autumn-winter. This may be associated with the fact that the most abundant prey species, Micropogonias furnieri (Desmarest, 1823) (Teleostei: Sciaenidae), gathers in small schools. Calves were present in 95% of all coordinated feeding tactics that occurred in the Ilha Grande Bay and in approximately 61% of feeding tactics in the Sepetiba Bay, suggesting that these areas are important for social learning. This study provides more information about feeding tactics and improves knowledge of the coordinated behavior of Sotalia guianensis (Van Beneden, 1864).

Models for estimating feed intake in small ruminants

This review deals with the most relevant limits and developments of the modeling of intake of sheep and goats reared intensively and extensively. Because small ruminants are normally fed ad libitum, voluntary feed intake is crucial in feeding tactics and strategies aimed at optimal animal production. The effects of genetic, neuroendocrine, hormonal, feed and environmental factors on voluntary feed intake were discussed. Then, several mathematical models to estimate dry matter intake (DMI) were examined, with emphasis on empirical models for sheep and goats in intensive farm systems or in extensive areas under pasture or rangeland conditions. A sensitivity analysis of four models of prediction of DMI in housed lactating dairy sheep and meat sheep breeds was also presented. This work evidenced a large variability in the approaches used and in the variables considered for housed sheep and goats. Regarding the estimation of feed intake for grazing sheep and browsing goats, the accuracy of estimates based on empirical models developed so far is very low when applied out of the boundaries of the studied system. Feeding experiments indoors and outdoors remain fundamental for a better modeling and understanding of the interactions between feeds and small ruminants. However, there is a need for biological and theoretical frameworks in which these experiments should be carried out, so that appropriate empirical or mechanistic equations to predict DMI could be developed.

Functional trophic composition of the ichthyofauna of forest streams in eastern Brazilian Amazon

This study aimed to describe the functional organization of the ichthyofauna of forest streams from northeastern Pará State, Brazil, based on behavioral observation of species' feeding tactics. Seven streams were sampled between June and November, 2010, during snorkeling sessions, totaling 91h 51min of visual censuses at day, dusk, and night periods. Seventy three species distributed in six orders, 26 families and 63 genera were observed, with dominance of Characiformes, followed by Siluriformes. From information gathered by ad libitum observations, each species was included in one of 18 functional trophic groups (FTGs), according to two main characteristics: (1) its most frequently observed feeding tactic; and (2) its spatial distribution in the stream environment, considering their horizontal (margins or main channel) and vertical (water column) dimensions. The most frequent FTGs observed were Nocturnal invertebrate pickers (9 species), Diurnal channel drift feeders (8 spp.), Diurnal surface pickers (7 spp.), and Ambush and stalking predators (6 spp.). The FTGs herein defined enable a comparative analysis of the structure and composition of ichthyofauna in different basins and environmental conditions, which presents an alternative approach to the use of taxonomic structure in ecological studies. The ichthyofauna classification based in FTGs proposed in this study is compared to three other classifications, proposed by Sazima (1986), Sabino &amp; Zuanon (1998) and Casatti et al. (2001).

Arctic charr (Salvelinus alpinus): a case study of the importance of understanding biodiversity and taxonomic issues in northern fishes

Charrs, fishes of the genus Salvelinus (Salmonidae), comprise about 7–20+ species important in the ecosystems and fisheries of Arctic and sub-Arctic waters. Charrs vary by life-history type (anadromous vs. lacustrine), are noted for variability in morphology, colouration and feeding and habitat use across their range, and occur from temperate regions to the northernmost areas of land. Charr diversity is manifested as an often confusing array of taxonomic and functional diversity. Components of taxonomic diversity include unresolved species’ complexes, subspecies, glacial lineages and genetic stocks. Features associated with functional diversity include semi-distinct life history variants and differential habitat and feeding tactics resulting in distinctive growth forms. Complex periglacial histories, allopatric and sympatric diversification processes, founder effects, hybridisation and introgression have contributed to the observed variability and complexity. The categorisation of taxonomic and functional diversity and understanding their roles, drivers and vulnerabilities underpins conservation and management efforts for taxa and their ecosystems. In that context, Arctic charr is an excellent example of diversity and the many levels of difficulties associated with determining the significance of diversity. Despite recently increased scientific efforts, resolving the nature and importance of charr diversity remains both a challenge and a priority because rapid anthropogenically driven change, especially climate change, is altering ecosystems and biodiversity faster than diversity can be inventoried, its importance understood and protective measures developed.

Food-resource partitioning among fish species from a first-order stream in northwestern Paraná, Brazil

This study addressed the feeding ecology of fish fauna from a first-order stream located in a rural area. The purposes were to evaluate the influence of interspecific, seasonal and spatial factors on the diet, examine the dietary overlap, and determine the predominant food sources. Sampling was conducted in December 2007, September 2008, and March 2009, in three 50-m stretches of Itiz stream (upstream, intermediate, and downstream), through electrofishing. A total of 1,102 stomach contents were analyzed from 14 species, by the volumetric method. In general, allochthonous resources were predominant in the diets. Astyanax aff. fasciatus, Astyanax aff. paranae, Astyanax bockmanni, and Bryconamericus aff. iheringi consumed a higher proportion of plant remains, and Bryconamericus stramineus consumed predominantly Hymenoptera. The diets of Cetopsorhamdia iheringi, Characidium aff. zebra, Imparfinis schubarti, and Trichomycterus sp. consisted of aquatic insects, especially immature forms of Trichoptera, Ephemeroptera, Plecoptera, and Diptera. Hypostomus ancistroides, Hisonotus sp., Poecilia reticulata, and Rineloricaria aff. pentamaculata exploited mainly detritus, while Rhamdia quelen used a variety of items, predominantly terrestrial insects. Detrended Correspondence Analysis (DCA) showed a clear distinction among the species, with different morphology and feeding tactics. The Multi-Response Permutation Procedure (MRPP) supported this differentiation, and also indicated significant spatial and temporal variations in the dietary composition; the Indicator Value Method (IndVal) indicated the main items that contributed to these differences. The diet overlap among species was low (&lt; 0.4) to around 78% of pairs, and the mean value did not vary significantly among the sites or between hydrological periods within each site. According to the null model of Pianka’s index, the values for dietary overlap were significantly higher than expected at random, showing evidence of resource sharing. This was related to the availability of allochthonous resources, highlighting the importance of riparian vegetation as a source of these resources for maintaining the fish fauna of the stream.

Alternative egg-feeding tactics in Telmatherina sarasinorum, a trophic specialist of Lake Matano’s evolving sailfin silversides fish radiation

Feeding specialisation is a typical feature of adaptive animal radiations. Different kinds of feeding specialisations have evolved in the endemic sailfin silversides species flock in Lake Matano (Central Sulawesi, Indonesia), including egg-feeding. The present study focuses on Telmatherina sarasinorum, a sailfin silverside species feeding on the eggs of related Telmatherina antoniae. Stomach content analyses supported T. antoniae eggs to be the dominant food item, independent of daytime. We hypothesized that the egg-feeders use alternative tactics for maximising egg consumption under varying densities of both, spawning T. antoniae pairs and competing conspecific egg-feeders. Focal behavioural observations were applied to describe different feeding tactics and to analyse feeding success and the related costs in terms of competitive interactions. Egg-feeders followed single courting pairs of T. antoniae or, alternatively, they switched between different spawning pairs. Following-behaviour, covering one or more spawning events of the host species, was positively related to enhanced egg consumption. Compared to feeding by switching frequently among different spawning pairs, the following tactic came at the cost of likewise increased competition. Behavioural observations suggest that some males monopolize courting pairs of T. antoniae and gain increased amounts of eggs compared to others avoiding competition by switching among pairs. The present results confirm that egg-feeding is a distinct trophic specialisation in T. sarasinorum and increase the scale of behavioural specialisation in Lake Matano’s evolving Telmatherina radiation.

Jellyfish Support High Energy Intake of Leatherback Sea Turtles (Dermochelys coriacea): Video Evidence from Animal-Borne Cameras

The endangered leatherback turtle is a large, highly migratory marine predator that inexplicably relies upon a diet of low-energy gelatinous zooplankton. The location of these prey may be predictable at large oceanographic scales, given that leatherback turtles perform long distance migrations (1000s of km) from nesting beaches to high latitude foraging grounds. However, little is known about the profitability of this migration and foraging strategy. We used GPS location data and video from animal-borne cameras to examine how prey characteristics (i.e., prey size, prey type, prey encounter rate) correlate with the daytime foraging behavior of leatherbacks (n = 19) in shelf waters off Cape Breton Island, NS, Canada, during August and September. Video was recorded continuously, averaged 1:53 h per turtle (range 0:08–3:38 h), and documented a total of 601 prey captures. Lion's mane jellyfish (Cyanea capillata) was the dominant prey (83–100%), but moon jellyfish (Aurelia aurita) were also consumed. Turtles approached and attacked most jellyfish within the camera's field of view and appeared to consume prey completely. There was no significant relationship between encounter rate and dive duration (p = 0.74, linear mixed-effects models). Handling time increased with prey size regardless of prey species (p = 0.0001). Estimates of energy intake averaged 66,018 kJ•d−1 but were as high as 167,797 kJ•d−1 corresponding to turtles consuming an average of 330 kg wet mass•d−1 (up to 840 kg•d−1) or approximately 261 (up to 664) jellyfish•d-1. Assuming our turtles averaged 455 kg body mass, they consumed an average of 73% of their body mass•d−1 equating to an average energy intake of 3–7 times their daily metabolic requirements, depending on estimates used. This study provides evidence that feeding tactics used by leatherbacks in Atlantic Canadian waters are highly profitable and our results are consistent with estimates of mass gain prior to southward migration.

Benefits for dominant red deer hinds under a competitive feeding system: food access behavior, diet and nutrient selection.

Social dominance is widely known to facilitate access to food resources in many animal species such as deer. However, research has paid little attention to dominance in ad libitum access to food because it was thought not to result in any benefit for dominant individuals. In this study we assessed if, even under ad libitum conditions, social rank may allow dominant hinds to consume the preferred components of food. Forty-four red deer hinds (Cervus elaphus) were allowed to consume ad libitum meal consisting of pellets of sunflower, lucerne and orange, and seeds of cereals, corn, cotton, and carob tree. The meal was placed only in one feeder, which reduced accessibility to a few individuals simultaneously. During seven days, feeding behavior (order of access, time to first feeding bout, total time spent feeding, and time per feeding bout) were assessed during the first hour. The relative abundance of each meal component was assessed at times 0, 1 and 5 h, as well as its nutritional composition. Social rank was positively related to the amount of time spent feeding during the 1st h (P = 0.048). Selection indices were positively correlated with energy (P = 0.018 during the 1st h and P = 0.047 from 1st to 5th) and fat (only during the 1st h; P = 0.036), but also negatively with certain minerals. Thus, dominant hinds could select high energy meal components for longer time under an ad libitum but restricted food access setting. Selection indices showed a higher selectivity when food availability was higher (1st hour respect to 1st to 5th). Finally, high and low ranking hinds had longer time per feeding bout than mid ones (P = 0.011), suggesting complex behavioral feeding tactics of low ranking social ungulates.

Two different feeding tactics of young-of-the-year perch, Perca fluviatilis L., inhabiting the littoral zone of the lowland Sulejow Reservoir (Central Poland)

The feeding pattern of young-of-the-year (YOY) fish was investigated in a field experiment in the sparsely vegetated littoral zone of the Sulejow Reservoir in June 2007. Perch received special emphasis in this study. During the study period, the part of the reservoir selected to conduct the research was densely inhabited by YOY fish (up to 20 individuals per square metre). The dominant YOY species were perch (Perca fluviatilis) and roach (Rutilus rutilus). Analyses of stomach/gut contents showed that large zooplankters and benthic prey contributed significantly to the diet of YOY fish. For perch, two distinct feeding tactics were observed. Fish collected by trapping in unvegetated gaps among beds of macrophytes preyed almost exclusively on daphnids and copepods, whereas individuals seined in shallow water among macrophytes ate mostly the larvae of benthic insects. The observed division of YOY perch into two feeding groups may indicate an attempt to decrease the level of both intra-specific competition among the cohort's members and inter-specific competition between perch and roach.

Changes in the diet of a recovering Eurasian otter population between the 1970s and 2010

ABSTRACT Diet is an essential element for understanding how the Eurasian otter (Lutra lutra) is re‐colonizing its former range in England following a population decline observed in the 1950s to 1970s. Otter spraints from the River Glaven catchment (north Norfolk, eastern England) were collected seasonally between 2009 and 2010 from three habitat types (ponds, ‘retenus’ (small in‐stream reservoirs), and stream stretches). Feeding tactics of the otter were compared between habitat types and, using previously published data, with regard to seasonal changes since the 1970s when the species was in decline. Otter diet composition varied greatly, with predation on aquatic invertebrates, crayfish, fish, and tetrapods. Fruit seeds were also found in the spraints. Diet generally reflected habitat, with northern pike (Esox lucius) remains found in spraints from ponds and retenus, whereas European eel (Anguilla anguilla) and gudgeon (Gobio gobio) were prominent in spraints from stream sections. Trophic diversity was particularly high in spraints collected next to ponds. Between the 1970s and the present, crayfish, brown trout (Salmo trutta), cyprinids, Eurasian perch (Perca fluviatilis), birds and mammals increased in prominence, whereas eel and threespine stickleback (Gasterosteus aculeatus) decreased, with notable seasonal variations between the study periods. Otter spraints revealed few prey preferences, with only that for gudgeon being ecologically relevant. The consumption of popular sport fishes, in particular common carp (Cyprinus carpio), has given rise to conflicts between recreational anglers and otter conservationists, but no demonstrated preference for carp was observed in the present study. Overall, otters have increased their consumption of ‘less preferred’ (i.e. lower energetic value) food types, and because the species normally preys on the most abundant species available, this suggests declines in ‘preferred’ prey types. These dietary shifts could contribute to otter dispersal and re‐colonization of parts of its original European range where food availability may be higher. © 2012 Crown copyright.

Evaluation of Species-Specific Dissimilarities in Two Marine Fish Species: Mercury Accumulation as a Function of Metal Levels in Consumed Prey

The aim of this research was to compare mercury (Hg) accumulation (total and organic) and tissue distribution in two marine fish species with contrasting feeding tactics. Thus, juvenile specimens of European sea bass and Golden grey mullet were surveyed in an estuary historically affected by Hg discharges. Total Hg was preferentially accumulated in intestine, muscle, and liver, whereas gills and brain presented the lowest Hg levels observed in both species. Significant differences between species were only verified for muscle, with D. labrax's levels being greater than L. aurata's. Muscle accounted for >87% of the Hg relative tissue burden, whereas liver did not exceed 11%. Organic Hg accumulation occurred mainly in liver and muscle, with D. labrax evidencing significantly greater loads. Moreover, organic Hg in consumed prey items was also significantly greater in D. labrax. Accumulation of organic Hg in liver, intestine, and muscle seemed to vary as a function of the consumed prey items contamination, suggesting fish feeding strategies as the dominant factor determining metal accumulation. For both fish species, a stable ratio was observed between Hg increments from the reference to the contaminated site, possibly indicating that the organic Hg content of diet may regulate the internal levels of this contaminant. Thus, this ratio might prove to be a useful contamination predictor tool in early life stages of fish.

Coordinated feeding tactics of the Guiana dolphin, Sotalia guianensis (Cetacea: Delphinidae), in Ilha Grande Bay, Rio de Janeiro, Brazil

Differences in distribution, prey species, season and social learning opportunities influence the feeding tactics used by marine mammals. Here, we analyze the coordinated feeding behavior of the Guiana dolphin, Sotalia guianensis (Van Bénéden, 1864, Delphinidae) and its relation to seasonality and the presence of calves. In a total of 201 feeding bouts, we observed four types of coordinated feeding tactics, which differed in frequency and in mean number of engaged individuals. Tactics in which dolphins used their bodies to herd and capture prey were the most frequent, presenting a higher frequency and engaging a higher number of individuals, suggesting that these tactics are better for capturing fishes which form larger schools. Furthermore, the seasons influenced the feeding behavior used by dolphins. During spring-summer, a longer duration of bouts and a larger number of individuals engaged in the feeding tactics was observed, which may be related to the seasonal spawning of larger schooling fish, such as Sardinella brasiliensis (Steindachner, 1879). Calves were present in 95% of all coordinated feeding tactic occurrences. This study indicates a complete preference of dolphins for coordinating their actions to capture prey and for the first time reports the presence of calves in the coordinated tactics and jumps. This broadens the current knowledge of the Guiana dolphin feeding tactics.