Distribution and population structure of the Chlorophthalmus agassizi (Bonaparte, 1840) on an unexploited fishing ground in the Greek Ionian Sea

The distribution and population structure of the shortnose green eye, Chlorophthalmus agassizi, were studied in the Greek Ionian Sea using data collected during experimental trawl surveys carried out from December 1996 to November 1997. The length–frequency distribution ranged between 45 and 201 mm total length (TL). The significant increase in average size linked with depth has been observed, supporting the general ‘bigger‐deeper’ phenomenon. Specifically, 1528 individuals were measured in the 300–400 m depth zone with a mean TL = 101 mm, 2351 individuals in the 400–500 m depth zone with a mean TL = 132 mm and 1889 individuals in the 500–600 depth zone with a mean TL = 145 mm. Age and growth of the population were determined by otolith readings. Twelve age groups were identified. The von Bertalanffy growth function (VBGF) parameters were L_∞=202.22 mm, K=0.20 and t_o=?1.6 years. Natural mortality was estimated at 0.285 per year, while total mortality was estimated at 0.65. The reproductive period of C. agassizi extends from spring to autumn, with greater activity in the summer.     

Diet and feeding strategy of blackmouth catshark Galeus melastomus

Diet and feeding strategy of the blackmouth catshark Galeus melastomus in the deep waters of the eastern Ionian Sea were investigated. Sampling was carried out using experimental bottom longline fishing at depths ranging from 300 to 855 m in summer and autumn 2010. Diet variability with fish size, season, area, sex and depth zone was tested and only season was found to significantly affect the diet of the species. Of the 870 stomachs examined, only 1·4% were empty. Cumulative prey curves showed that the sample sizes were adequate to describe the main prey items of the diet for both seasons. Prey identified belonged primarily to three major groups: fishes, cephalopods and dendrobranchiatan and caridean shrimps. In autumn, the above three major groups were found as principal prey, whereas in summer cephalopods followed by fishes were the principal prey and shrimps were found as secondary prey. SIMPER analysis indicated high dissimilarity between seasons and highlighted that Sepiolidae, Myctophidae, fishes, cephalopods, shrimps and other crustaceans contributed to seasonal differences in the diet of G. melastomus. The prey diversity index was higher in autumn than in summer. A high dietary overlap was observed between the two seasons. Galeus melastomus behaved as an opportunistic predator with a variety of unimportant prey in its diet. Feeding strategy indicated that G. melastomus holds a generalist niche with a considerable specialization at the individual level. This strategy seems to be an adaptation to a food‐scarce environment, as typified in deep‐water habitats.     

Feeding ecology of the endangered Valencia toothcarp,Valencia hispanica (Actinopterygii: Valenciidae)

Patterns of food resource utilisation by Valencia toothcarp were studied in a small coastal lagoon in the Iberian Peninsula, its most northern population. Emphasis was placed on feeding activity, diet composition, seasonal and intraspecific variation in diet and feeding strategy. Important features of the overall feeding pattern of the Valencia toothcarp are decreased feeding activity during winter, concentration on benthic invertebrates and narrow dietary breadth, with a focus on gammarid amphipods. The feeding of V. hispanica was independent of seasonal variation in food availability, because its main prey were much the same throughout the year. There were no differences in seasonal niche width and niche overlap between seasons was high. There are also no differences in diets between sexes, although diet composition, niche width and niche overlap differ between juvenile and adult fish. The Valencia toothcarp population from Santes Creus lagoon was formed by specialist individuals, with narrow niche widths, that fed on four preferential prey types, but also consumed some occasional prey.     

Variation of diet and food consumption of the scaldfish Arnoglossus laterna(Walbaum, 1792)

Although Arnoglossus laterna (Walbaum, 1792) is a common benthic fish in Portugal, several aspects of its feeding ecology remain incomplete. In this study, diet was examined and the food consumption estimated on inshore waters in the central coast of Portugal. The diet of the scaldfish included mainly mysids, amphipods and polychaetes, while the decapod Philocheras bispinosus Hailstone was the most frequent prey. Variation in the diet according to fish size (two size‐classes), sex and spawning/non‐spawning seasons was examined. Significant differences in diet composition were found between seasons, whereby the most frequently consumed prey in the non‐spawning season were crustaceans, while polychaetes and nemerteneans comprised most of its diet in the spawning season. The average value of the vacuity index was very similar between seasons (24.7% non‐spawning season and 25.0% spawning season). Diet overlap between size‐classes and sexes was high, but low between the two seasons. Food consumption of A. laterna was estimated based on diet characterization and evacuation rate. The estimate of the daily food consumption was 1.15 mg dry weight for the non‐spawning season and 1.67 mg dry weight for the spawning season. Significant differences in consumption rates were found between size‐classes and sexes. Larger individuals showed a higher consumption rate than smaller individuals. Females consumed more food than males in the non‐spawning season, while in the spawning season males consumed more than females.     

Characteristics of foraging in the soft-bottom benthic starfish Luidia clathrata (echinodermata: Asteroidea): prey selectivity,switching behavior,functional responses and movement patterns

Summary Luidia clathrata show a strong preference for the infaunal bivalve Mulinia lateralis in Tampa Bay, Florida. Quantitative and qualitative changes in diet occurred over a 7-month period. Individuals may shift from intraoral macrofaunal feeding to intra- and extraoral detrital feeding during periods of low macrofaunal availability. In the laboratory L. clathrata showed switching behavior, feeding disproportionately on the most abundant of two simulataneously presented food models. This switching mechanism may be related to either contact-chemoreceptive rejection of lowdensity food or enhanced distance-chemoreception of high density food. The use of standardized food models eliminated the possibility that handling time was important in switching behavior. Both fed and starved individuals showed functional responses to changes in prey density. However starved individuals ingested greater numbers of prey and spent more time foraging than did fed individuals. Switching and functional response behaviors may be important in promoting nutritional uptake and in causing density-dependent mortality of prey populations. Movement patterns of L. clathrata are directional in the absence of bivalve prey, but become non-directional once patches of prey are encountered. This allows individuals to remain in areas of high prey density. Luidia clathrata has characteristics of an optimal forager, where energy is maximized per unit feeding time.     

Diet and foraging opportunism of the Guiana dolphin (Sotalia guianensis) in the Abrolhos Bank,Brazil

Diet analysis allows exploring how coastal dolphins interact with the environment and their role in the marine food webs. We studied the diet and feeding ecology of the Guiana dolphin, Sotalia guianensis, through analysis of stomach content from 42 animals stranded on the eastern coast of Brazil. A total of 1,336 semidigested prey items (fish, otoliths, cephalopod beaks, and crustaceans) were identified. Teleost fish comprised the most frequent food item (92% of the total), followed by cephalopods, and crustaceans. Prey belonged to 34 taxa and richness in individual stomachs varied from 1 to 15 prey taxa. Prey were generally small, but showed a significant trend to increase in size with dolphin length. The main prey of Guiana dolphins were demersal, estuarine, and sound-making fish such as catfish and sciaenids. No sex-related differences in diet were found. Diet composition varied seasonally and occurrence of prey items was coherent with breeding or high abundance periods of some fish species and squids. Our study shows the importance of demersal prey from estuarine and soft-sediment habitats to Guiana dolphin in the Abrolhos Bank and reveals that feeding habits are generalist and opportunistic, with diet reflecting the seasonal abundance and availability of prey.     

Feeding ecology of the critically endangered Valencia letourneuxi (Valenciidae)

Valencia letourneuxi is a critically endangered freshwater fish in urgent need of targeted conservation. Little information is however available on its life history and feeding ecology; therefore, food resource utilization by V. letourneuxi was studied in its most abundant known Greek population of Chiliadou stream. The diet of this population appears to be dominated by microcrustaceans, Dipteran larvae, Acari, and Mollusca. Its feeding is highly dependent on seasonal prey availability and diversity, with niche overlap being low only between winter and the rest of the seasons, indicating that only during winter its diet differs significantly in relation to the other seasons. There are no significant sex- and size-related dietary shifts. This V. letourneuxi population is characterized by a generalist feeding strategy and appears to consist mostly of individuals with broad niches. Its generalist feeding pattern and dietary flexibility permits it to fully exploit this very diverse and rich habitat and may account for the high local abundance of this population.     

Diet of the small-spotted catshark Scyliorhinus canicula in the Aegean Sea (eastern Mediterranean)

The diet of the small-spotted catshark Scyliorhinus canicula, captured in the Aegean Sea by bottom-trawl from 2006 to 2012, was investigated with respect to sex, maturity condition, sampling location and season. The stomach contents of 432 specimens, measuring from 144 to 517?mm in total length, were analysed. The cumulative prey curve showed that the sample size was adequate to describe the species’ diet, which was quantified using the percentage gravimetric composition (%W). The identified prey items belonged to eight major groups: Teleostei, Chondrichthyes, Crustacea, Cephalopoda, Annelida, Echinodermata, phanerogams and macroalgae, with Teleostei, Crustacea and Cephalopoda being the most consumed in both females (%W?=?48.1, 16.0 and 31.4, respectively) and males (%W?=?33.9, 31.6 and 29.8, respectively). Higher diet diversity was observed in males than females, in immature individuals than mature ones, regardless of sex, as well as in spring in comparison to autumn and winter. Feeding intensity seemed to be influenced mainly by sex and maturity condition. No significant dietary overlap was observed for all possible combinations of the factors examined. Gut indices were compared between the two sexes with females showing statistically significantly higher median relative gut length, as well as a longer gut than males of the same length. Based on the diet composition, S. canicula can be considered a generalist predator consuming, with geographical differentiation, a wide variety of benthic taxa. The estimated fractional trophic level (τ?=?4.22) classified the species as a carnivore with a preference for Teleostei and Cephalopoda, thus confirming its key role in the food web.     

Diets of the African Civet Civettictis civetta (Schreber, 1778) in selected coffee forest habitat,south‐western Ethiopia

Feeding ecology of the African civet, Civettictis civetta (Schreber, 1778), was studied in selected coffee forest habitat for two seasons between December 2012 and October 2013. The study was conducted in Limu Seka district, south‐west Ethiopia. Faecal analysis was employed to assess the diet spectrum, seasonal abundance and relative importance of food items. Over 55 different food items were identified from the analysis of 387 scat samples collected during the dry and wet seasons. In the coffee forest habitat, African civets showed omnivorous feeding habit with plant‐to‐animal diet biomass ratio of 1 : 1.36. A slight diet specialization was observed during the wet season (BA = 0.46) favouring animal prey. However, during the dry season, they showed generalist feeding habit (BA = 0.87) with more plant biomass in their diet. With over 64% occurrence and 14.4% biomass, coffee berries significantly contributed to the civets dry season plant diets. The excreted coffee beans, after civets ingested ripe coffee berries, are the tastiest product used by farmers for consumption and market. Seasonal collection of civet coffee from coffee forest floor economically supports the farmers while increasing the importance of civets in the habitat and hence contributing for its conservation.     

Optimization of foraging and diet by the piscivorous Othos dentex (Serranidae)

The aim of this study was to determine the dietary characteristics and mouth morphology of Othos dentex and to use these data, together with in situ observations of feeding behaviour, to elucidate how foraging and diet are optimized by this piscivorous serranid. Seasonal spear and line fishing over reefs in south‐western Australia yielded 426 O. dentex (total length, L_T, 183–605 mm), among which the stomachs of 95 contained food. The food in the stomachs of 76 fish was sufficiently undigested to be seen to contain, almost invariably, a single fish prey, which was typically identifiable to family and often to species. The prey of O. dentex, which were measured (L_T), represented 10 families, of which the Labridae and Pempheridae constituted nearly two‐thirds of the prey volume. Two‐way crossed analysis of similarities of volumetric data for stomach contents showed that the dietary compositions of the different length classes of O. dentex in the various seasons were significantly related to length class of prey, but not to prey family, length class within the various prey families or season. Furthermore, an inverse (Q‐mode) analysis, including one‐way analysis of similarities, showed that the patterns in the prey consumed by the different length classes of O. dentex in the various seasons were related more strongly to length class than prey family. The former trend is exemplified in a shade plot, by a marked diagonality of the length classes of prey with increasing predator size. The ingestion of typically a single teleost prey, whose body size increases as that of O. dentex increases, reduces the frequency required for seeking prey, thus saving energy and reducing the potential for intraspecific competition for food. The ability of O. dentex to ingest large prey is facilitated by its possession of a very large gape, prominent recurved teeth, dorsal and independently‐moveable eyes, cryptic colouration and effective ambush behaviour. Othos dentex has thus evolved very cost‐effective mechanisms for optimizing its foraging and diet.     

Feeding ecology of the Iberian lynxLynx pardinus in eastern Sierra Morena (Southern Spain)

The feeding ecol ogy of the critically endangered Iberian lynxLynx pardinus Temminck, 1827, was studied in the most important remnant population, located in eastern Sierra Morena (Sierra de Andujar Natural Park, Spain). Three hundred sixty scats were collected from October 2001 through Sep tember 2002. RabbitsOryctolagus cuniculus dominated the lynx diet, as showed by frequency of occurrence (94%) and percent age of volume (91%). Red-legged partridgesAlectoris rufa were the most important secondary prey. No significant seasonal variation was observed regarding the diet preferences of the lynx. No difference was found in lynx diet by comparing two areas with high and low rabbit availability. Juvenile rabbits were positively selected when they were available, during late winter, spring and early summer.     

Ontogenetic diet shifts of bull-rout, Myoxocephalus scorpius (L.), in the south-western Baltic Sea

The stomach contents of 533 bull‐rout, Myoxocephalus scorpius (L.), were collected during February–March and October–November 1997 in the south‐western Baltic Sea in order to study the feeding ecology and investigate diet changes between seasons and with the increasing size of the fish. The isopod Mesidotea entomon, and herring Clupea harengus, were the dominant species in the diet, accounting for 99% in weight of all bull‐rout sampled in spring and autumn. Mysis mixta was frequent but less important in weight; analysis of the ontogenetic diet shift showed the presence of M. mixta essentially in the smaller size‐classes. Herring was eaten almost exclusively by individuals larger than 21 cm total length; its importance increased with increasing size of bull‐rout. The isopod M. entomon was abundant in all size‐classes examined. Prey‐size and the size of the principal prey, M. entomon, showed a significant increase with increasing bull‐rout size. The diet shift from mysids to fish was followed by a change in the weight‐length relationship. Cluster analysis confirmed two distinct size groups of >26 cm and <24 cm. In conclusion, the data indicate that the diet of bull‐rout partially overlaps with that of herring in the first trophic stage, and with that of cod in the second part of the bull‐rout life cycle.     

Characterization of feeding habits,prey diversity and diet overlap of two sympatric species: Bronze catfish,Netuma bilineata (Valenciennes, 1840) and blacktip sea catfish,Plicofollis dussumieri (Valenciennes, 1840) in the northern Arabian Sea

This study describes the diet composition, diet overlap and prey diversity in two economically and ecologically important marine catfish species: the bronze catfish (Netuma bilineata) and the blacktip sea catfish (Plicofollis dussumieri) collected between January and December 2015 from the northern Arabian Sea coast of Pakistan. Stomach data of 342 bronze catfish and 283 blacktip sea catfish were examined. Diet composition and feeding strategy of each species by identification of stomach contents were weighed and enumerated. Both species primarily consumed teleosts, Brachyura and small amounts of a wide variety of prey items; however, specialization was a more common trait for the bronze catfish than for the black tip sea catfish. The Morisita‐Horn index showed considerable diet overlap in percentage of mean weights (0.847) than in numbers (0.612) between co‐prey pairs of both species. The highest Bray‐Curtis similarity between the southwest monsoon (SWM) and south inter monsoon (SIM) was observed in bronze catfish and lowest between autumn inter monsoon (AIM) seasons in both species. While Bray‐Curtis dissimilarity was observed, both species share diet niches and diet overlap. The present study evaluation of the feeding strategy and potential competition between two sympatric species of marine catfishes can provide the framework for their conservation and management in the region.     

Diet and feeding habits of Economidichthys pygmaeus (Perciformes: Gobiidae) in Lake Pamvotis,NW Greece

The purpose of the study was to define the diet composition, feeding preferences, seasonal, size and sex related changes in diet, feeding strategy and diel cycle of Economidichthys pygmaeus. Important features of the overall feeding patterns of the goby include (i) feeding activity, (ii) bottom habits and (iii) consumption of food items to identify the dietary breadth. Stomach contents of 533 specimens, 13.42–48.65 mm total length (TL), collected by hand net (2 mm mesh size) from October 2006 to September 2007 were analyzed. The percentage of 76 empty stomachs (14.26%) did not vary significantly with season. The food composition suggested that the goby is a carnivorous fish. Prey items identified in the stomachs belonged to four major groups: Crustaceans, Insects, Mollusca and Plants. Copepods were the most important (%IRI = 57.51), especially in fish larger than 23 mm TL. Chironomids (%IRI = 43.23) constituted the main prey for fish <23 mm TL. Diet composition showed little seasonal variation. Copepoda dominated the diet in autumn and winter (43.4%; 82.4%) and were replaced by Chironomidae larvae in spring (39.7%) and summer (47.7%). During the reproductive season, large males show a narrow food spectrum as opposed to large females, reflecting the different activity pattern exhibited by males and females during the breeding season, since the former supports parental care. According to the modified Costello graphical method, specialist individuals form the goby population that feeds on two preferential prey types (e.g. Copepods, Chironomids). Nevertheless, they consume some occasional prey (e.g. Cladocera, Insects, Gastropods). The species foraged chiefly at night and early morning, during lower light intensity. The highest feeding activity recorded at night (02.00 hours) and during early morning (08.00 hours) could be related to the cryptic behaviour displayed by the species.     

Feeding habits of dolphinfish (Coryphaena hippurus) in the southeastern Gulf of California,Mexico

The objective of the study was to identify key elements of the feeding ecology of the dolphinfish, which is a high tropic predator important for sport and artisanal fishing in the Mexican Pacific. Feeding habits were investigated during the years 2000–2003. This species is seasonal in the southern Gulf of California and probably remains there because of the abundant prey. The contents of 232 dolphinfish stomachs were analyzed, identifying 98 prey species, although only eight of these were well‐represented in the diet. The most important prey by weight was the fish Hemiramphus saltator, however by number and frequency of occurrence was the crustacean Hemisquilla californiensis. No differences in the diet were found between males and females, although there was an ontogenic diet shift between seasons. There was no relationship between dolphinfish size and prey size, because dolphinfish fed preferentially on prey with an average size of 4.7 cm.     

Lipid‐rich zooplankton subsidise the winter diet of benthivorous Arctic charr (Salvelinus alpinus) in a subarctic lake

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Feeding habits of ocellate spot skate,Okamejei kenojei (Müller & Henle, 1841), in coastal waters of Taean,Korea

The feeding habits of Okamejei kenojei were studied using 592 specimens collected in the coastal waters of Taean, Korea from April 2008 to March 2009. O. kenojei is a bottom‐feeding carnivore that consumes mainly shrimp, fishes, and crabs. Its diet also includes small quantities of amphipods, mysids, cephalopods, euphausiids, copepods, isopods, and polychaetes. The total length (TL) of individuals in this study ranged from 8.2 to 49.0 cm. Cluster analysis based on %IRI (index of relative importance) identified three size classes. Group A (< 20 cm TL) ate primarily caridean shrimp and amphipods; group B (20–30 cm TL) ate exclusively shrimp; and group C (> 30 cm TL) ate penaeoidean shrimp, fishes, and crabs. O. kenojei showed ontogenetic changes in feeding habits. Although shrimps were the primary food consumed by all size groups, the proportion of shrimp in the total diet decreased and the consumption of fishes and crabs gradually increased with the body size of O. kenojei. Size of the prey organisms also increased. Smaller individuals fed mainly on small prey, such as amphipods, mysids, and small shrimp, whereas larger individuals preferred larger prey, such as larger shrimp, fishes, and crabs. The size‐related diet breadth and the percentage of empty stomachs were significant; the diet breadth gradually increased with body size, whereas the percentage of empty stomachs decreased. Seasonal changes in the O. kenojei diet were not significant, but shrimp constituted 97.3% of the summer diet by %IRI. Seasonal changes in diet breadth and the percentage of empty stomachs were not significant.     

The diet of whiting Merlangius merlangus in the western Baltic Sea

The diet of whiting Merlangius merlangus in the western Baltic Sea was investigated and compared to the diet in the southern North Sea. Clupeids were important prey in both areas, but especially in the western Baltic Sea where they constituted up to 90% of the diet of larger individuals. Gobies, brown shrimps and polychaetes were the main prey of juveniles in the western Baltic Sea, while a wider range of species were consumed in the North Sea. The shift to piscivory occurred at smaller sizes in the western Baltic Sea and the fish prey consumed was proportionately larger than in the southern North Sea. Estimates of prey abundance and food intake of M. merlangus are required to evaluate its predatory significance in the western Baltic Sea, but its diet suggests that it could be just as significant a fish predator here as in the southern North Sea.     

Feeding of <Emphasis Type="Italic">Ctenocalanus citer</Emphasis> in the eastern Weddell Sea: low in summer and spring,high in autumn and winter

The feeding activity and diet of the small dominant Antarctic copepod, Ctenocalanus citer, were studied throughout the seasonal cycle from samples taken during several “Polarstern” cruises to the eastern Weddell Sea. Two indices of feeding activity were used, percentage of copepods with food inside and length of the faecal pellets. C. citer guts contained food throughout the year thus confirming the year-round activity of this species without diapause. Both indices demonstrated a seasonal pattern of foraging, unusual for a predominantly herbivorous copepod: high-feeding activity in autumn–winter and low in spring–summer. Our results suggest that feeding is at least partially decoupled from the phytoplankton bloom. Diet of C. citer was assessed by analyzing the gut contents. The bulk of the recognizable food in the guts of all copepodite stages consisted of small-sized phytoplankton, and no evidence of switching to a more carnivorous diet at low-phytoplankton concentrations was obtained. Usage of ice-associated algae was proposed to explain high winter-feeding activity. This knowledge of seasonal feeding patterns fills in a gap in our understanding of the life-cycle strategy of C. citer.