Extensive feeding on sockeye salmon Oncorhynchus nerka smolts by bull trout Salvelinus confluentus during initial outmigration into a small,unregulated and inland British Columbia river

Stomach contents were collected and analysed from 22 bull trout Salvelinus confluentus at the edge of the Chilko Lake and Chilko River in British Columbia, Canada, during spring outmigration of sockeye salmon Oncorhynchus nerka smolts. Twenty of the 22 (>90%) stomachs contained prey items, virtually all identifiable prey items were outmigrant O. nerka smolts and stomach contents represented a large portion (0·0–12·6%) of estimated S. confluentus mass. The results demonstrate nearly exclusive and intense feeding by S. confluentus on outmigrant smolts, and support recent telemetry observations of high disappearance rates of O. nerka smolts leaving large natural lake systems prior to entering high‐order unregulated river systems.     

Distribution, reproduction and feeding of the Greenland shark Somniosus (Somniosus) microcephalus, with notes on two other sleeper sharks, Somniosus (Somniosus) pacificus and Somniosus (Somniosus) antarcticus

The size and depth distribution, stomach contents and reproductive status of Somniosus ( Somniosus ) microcephalus, Somniosus ( Somniosus ) pacificus and Somniosus ( Somniosus ) antarcticus were examined from specimens collected from the North and South Atlantic, North and South Pacific, and the Southern Ocean. Specimens ranged in size from 42 to 480 cm total length, L _T, and were taken from depths of 35–1280 m. Stomach contents included coelenterates, gastropods, cephalopods, echinoderms, crustaceans, elasmobranchs, teleosts, penguins, marine mammals and human waste. Female S. ( S. ) microcephalus mature at c . 450 cm and S. ( S. ) antarcticus at c . 435 cm L _T; a female S. ( S. ) pacificus of 430 cm was mature. Male S. ( S. ) microcephalus mature at c . 300 cm, but male S. ( S. ) antarcticus may not mature until c . 400 cm L _T. The size at birth in these three species of Somniosus is c . 40 cm L _T.     

Influences of potential predictor variables on gastric evacuation in Atlantic cod Gadus morhua feeding on fish prey: parameterization of a generic model

The parameter values of a generic model of gastric evacuation were estimated from evacuation data on Atlantic cod Gadus morhua fed meals of four fish prey: herring Clupea harengus, sprat Sprattus sprattus, lesser sandeel Ammodytes tobianus and dab Limanda limanda. The effects on evacuation of photoperiod and pre-experimental treatment of prey were also tested. Freshly killed A. tobianus were evacuated from the stomach of G. morhua at a rate similar to the value estimated from conspecifics kept deep-frozen and subsequently thawed prior to the evacuation experiment. The evacuation rate in G. morhua exposed to continuous light did not differ from the rate obtained from fish maintained under a 12L:12D photoperiod. The evacuation rates estimated from the latter fish in the dark and light periods, respectively, were likewise similar. These results indicate that the resistance of prey to the digestive processes is not altered significantly by the pre-experimental treatment of prey and that there is no diurnal variation per se in the rate of evacuation for G. morhua. Therefore, it is believed that the present parameterization of the evacuation model should prove especially useful for studying the role of G. morhua as a top predator in natural systems.     

The food and feeding relationships of black oreo, Allocyttus niger, smooth oreo, Pseudocyttus maculatus, and eight other fish species from the continental slope of the south-west Chatham Rise, New Zealand

The food and feeding habits of black oreo and smooth oreo sampled at depths of 600–1200 m from the south-west Chatham Rise in 1983 are described, with notes on prey of eight other fish species. All these fish species fed benthopelagically. Black oreo preyed on hyperiid amphipods, salps and natant decapod crustaceans; smooth oreo on salps and amphipods. Dietary composition of both species changed with size of fish. Aspects of feeding relationships between the fish species were examined including dietary similarity and prey-size selection. Findings are compared with results of research on other New Zealand deepwater fish species.     

Diet and feeding selectivity of a benthivorous fish in streams: responses to the effects of urbanization

This study evaluated the diet and feeding selectivity of the catfish Imparfinis mirini in streams with different degrees of urbanization and the effect of rainfall on the availability of prey. The diet was based especially on Chironomidae and Trichoptera. Significant spatial differences in diet were found between the streams; the diet of the fish was similar in the rural and peri‐urban streams, and differed from that in the urban stream. Seasonality was an unimportant factor affecting the species' diet, which did not differ significantly between the rainy and dry periods in any of the streams. Fish from the urban stream fed more according to what was available in the environment, while fish from the peri‐urban and rural streams showed higher degrees of selectivity. The results indicate that environmental conditions influenced the diet and prey selection of this species in response to the differences in diversity and abundance of the food organisms. They indicate that trophic studies of benthivorous fishes, such as I. mirini, may represent an alternative way to assess human effects on streams.     

Long‐term changes in the feeding of Pollachius virens on the Scotian Shelf: responses to a dynamic ecosystem

The diet and feeding ecology of pollock Pollachius virens from the Scotian Shelf and Bay of Fundy in the north‐west Atlantic changed over the last few decades, which was associated with decreases in euphausiid abundance. Stomach contents data for 2078 pollock collected during the 1958–1967 period and for 1230 pollock collected during the 1996–2002 period indicated that pollock diet contained fewer euphausiids and feeding activity decreased. During the early period, euphausiids were present in 65% of the pollock stomachs that contained food and only 9% of these stomachs in the recent period. The decrease of euphausiids was not wholly offset by an increase in piscivory, since there was little increase in the frequency of fish prey in the diet or in the fullness index for this prey type. Empty stomachs were significantly more common in the recent period during both the winter and summer. The decreased occurrence of euphausiids in stomach samples coincided with a significantly decreased abundance of this prey, suggesting that the near‐absence of euphausiids in recently collected pollock stomachs reflected prey abundance. Concurrent with changes in diet and feeding intensity, the condition or 'plumpness' of pollock significantly declined from the early to the late sampling periods.     

Diets and trophic‐guild structure of a diverse fish assemblage in Chesapeake Bay,U.S.A.

Dietary habits and trophic‐guild structure were examined in a fish assemblage (47 species) of the Chesapeake Bay estuary, U.S.A., using 10 years of data from >25 000 fish stomachs. The assemblage was comprised of 10 statistically significant trophic guilds that were principally differentiated by the relative amounts of Mysida, Bivalvia, Polychaeta, Teleostei and other Crustacea in the diets. These guilds were broadly aggregated into five trophic categories: piscivores, zooplanktivores, benthivores, crustacivores and miscellaneous consumers. Food web structure was largely dictated by gradients in habitat (benthic to pelagic) and prey size. Size classes within piscivorous species were more likely to be classified into different guilds, reflecting stronger dietary changes through ontogeny relative to benthivores and other guilds. Relative to predator species and predator size, the month of sampling had negligible effects on dietary differences within the assemblage. A majority of sampled fishes derived most of their nutrition from non‐pelagic prey sources, suggesting a strong coupling of fish production to benthic and demersal food resources. Mysida (predominantly the opossum shrimp Neomysis americana) contributed substantially to the diets of over 25% of the sampled predator groups, indicating that this species is a critical, but underappreciated, node in the Chesapeake Bay food web.     

Exchange between littoral and pelagic waters in a stratified lake due to wind-induced motions: Lake Kinneret, Israel

We used field data and three-dimensional numerical simulations to investigate the exchange processes between the lake boundaries (littoral) and lake interior (pelagic) due to wind-induced motions in Lake Kinneret, Israel. The field data showed large-scale metalimnion oscillations with amplitudes up to 10 m in response to westerly diurnal winds, the existence of a well-defined turbidity intrusion into the metalimnion of the lake and a benthic boundary layer (BBL). The observed vertical and horizontal movements of the turbidity were explained by the vertical and horizontal advection associated with basin-scale wave motions and a residual circulation set up by the basin-scale motions and the wind field. The horizontal advective transport in the metalimnion, associated with the velocities induced by the basin-scale mode-two Poincaré wave, provided the primary control for the exchange between the lake boundaries and lake interior on daily time scales. Detailed comparison of simulation results with both temperature and velocity profiles revealed excellent agreement for time scales from hours to days. The validated numerical model was used to extract the residual motions that provided the secondary exchange flows, in the various regions of the lake on time scales from days to weeks. The residual motion in the surface layer consisted of a combination of an anticlockwise gyre in the western half of the lake and a weak clockwise gyre along the eastern boundary that were forced by the curl of the wind field. In the metalimnion, residual motions were predominantly forced by the basin-scale internal wave motions and an anticlockwise gyre established itself throughout the whole basin. Lastly in the BBL, residual motions consisted of an anticlockwise gyre, but the geographic distribution was patchy. Together these results provide new insight into a proper characterization of the processes underlying the flux paths of water and particles between the lake boundaries and lake interior. Handling editor: L. Naselli-Flores     

Environmental and human factors influencing rare plant local occurrence, extinction and persistence: a 115-year study in the Mediterranean region

Aim Assessing whether environmental and human factors influenced the spatial distribution and the dynamics of regionally rare plant species since the late nineteenth century, and whether these spatial and temporal patterns of rare species occurrences differ according to their chorology (level of endemism and biogeographic affinity). Location An area extending over 6250 km² in the French Mediterranean Region. Methods We used two botanical surveys achieved in 1886 and in 2001, and considered species rare if occurring in only one or two sites in the study area. Each rare species was assigned to a group of endemism level (restricted endemic, non‐endemic), and of biogeographic affinity (Mediterranean, South/Central European, Mountain, Eurosiberian). A 1 × 1 km grid was applied to the study zone. Generalized linear models were developed to study the spatial distribution and the fate of rare species occurrences (local extinction vs. local persistence between 1886 and 2001), as a function of environmental and human variables. Multivariate analyses were used to test whether the spatial distribution and the fate of rare species occurrences differed according to their chorology. Results In 2001, rare species as a whole tended to occur at higher altitude, in zones dominated by semi‐natural open habitats, and where cultivated area had decreased in the last 30 years. Between 1886 and 2001, rare species were the most prone to local extinction in zones where human population density, cultivated area and livestock density had increased the most. Between 1886 and 2001, rare species had a higher probability of local persistence in zones of high altitude and steep slope, on basic bedrocks and with low cultivated area. Rare species with Mountain and Eurosiberian affinities occurred in marginal habitats in the study region, i.e. on gneiss‐micaschist bedrocks and at high altitudes, whereas Mediterranean and South/Central European rare species occupied more varied environmental conditions. Between 1886 and 2001, Eurosiberian rare species showed high rates of local extinction whereas Mediterranean rare species had a significantly higher probability of local persistence. Restricted endemic species mostly occurred in zones of high slope, low human population density, and where cultivated area had decreased in the last 30 years. Occurrences of restricted endemics remained significantly stable between 1886 and 2001. Main conclusions Environmental and land‐use changes that occurred over the twentieth century in the Mediterranean Basin had significant impacts on the spatial distribution and on the long‐term dynamics of rare species occurrences. Urbanization and recent agriculture intensification, occurring mainly in coastal plains and littoral zones, caused most local extinctions of rare species from 1886 to 2001. Local populations of Eurosiberian species, which reach their range limits in marginal zones of the Mediterranean, also appear to be highly vulnerable. Conversely, most restricted endemic species occur in habitats with harsh topography and low human disturbance and have a higher potential of local persistence.     

Size selective feeding and its limitations for the black rockfish, Sebastes inermis, in a demersal fish assemblage of Onagawa Bay, northeastern Japan

The size selective feeding of the black rockfish, Sebastes inermis, in a demersal fish assemblage of Onagawa Bay, located in northeastern Japan, was studied using laboratory experiments and stomach content analysis of the dominant demersal fish coexisting with the black rockfish in Onagawa Bay. The preferred food size of the black rockfish was determined in the laboratory experiments. The average food size taken by the black rockfish (150–227 mm long) under natural conditions was much smaller than that taken by fish in laboratory experiments (148–158 mm sized). The most preferred size of food taken by fish in laboratory experiments was rarely found under natural conditions. Analysis of the competition coefficients of fish species in the fish assemblage based on stomach content analysis suggested that the degrees to which the preferred food size was found depended upon the foods availability, by competition with other fish species and by the feeding ability of the fish. Intra- and inter-specific competition in a fish assemblage might be limiting factors on the food size selection of fish under natural conditions.     

The influence of hunger and predation risk on group cohesion in a pelagic fish, walleye pollock Theragra chalcogramma

Variation in the intensity of schooling behavior in fishes suggests that the benefits of aggregation are balanced by certain costs. We examined the proximity of group members to each other in juvenile walleye pollock, Theragra chalcogramma, under different environmental conditions. Food availability, simulated by a gradient of six ration treatments, had a major influence on group cohesion, with increasing dispersion as food level decreased. Group cohesion also decreased at night relative to daytime levels. Small juveniles (x=53 mm TL) maintained on high rations were highly responsive to the potential threat of a predator, with groups becoming more cohesive and remaining so for up to an hour after the initial threat. A chronic threat (continual presence of predators) resulted in tighter group cohesion than an acute threat (single simulated attack). Small juveniles maintained on low rations were less responsive to predation threats and recovered quickly, supporting the hypothesis that hunger induces risk-taking behavior. Large juveniles (x=149 mm TL) did not change their degree of aggregation in response to either type of predation threat. An overall plasticity in the degree of cohesiveness among group members indicates that walleye pollock are capable of gradually modifying their schooling behavior according to the environmental context.     

Biological control of the western flower thrips,Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in glasshouse sweet peppers with Orius spp. (Hemiptera: Anthocoridae). A comparative study between O. niger (Wolff) and O. insidiosus (Say)

In a comparative study for biocontrol of the western flower thrips (WFT) in commercial sweet peppers Orius spp. effectively controlled WFT. The introduced native Orius niger had replaced the introduced imported Orius insidiosus by the end of the growing season.     

Establishment of dominance relationships in gilthead sea bream Sparus aurata juveniles during feeding: effects on feeding behaviour, feed utilization and fish health

In gilthead sea bream Sparus aurata held in groups of two, five or 10 fish, social hierarchies were observed. Subordinate S. aurata were characterized by elevation of basal levels of plasma cortisol, together with a reduced immunological potential. Subordinate fish also showed lower feed intake, feed utilization and lower growth. Fatty acid composition was also affected by social status, with a lower content of saturated acids, oleic and eicosapentaenoic, in muscle and liver of fish considered as subordinate. Results show that social hierarchy acts as a stressor in S . aurata .     

The impact of dietary restriction, intermittent feeding and compensatory growth on reproductive investment and lifespan in a short-lived fish

While dietary restriction usually increases lifespan, an intermittent feeding regime, where periods of deprivation alternate with times when food is available, has been found to reduce lifespan in some studies but prolong it in others. We suggest that these disparities arise because in some situations lifespan is reduced by the costs of catch-up growth (following the deprivation) and reproductive investment, a factor that has rarely been measured in studies of lifespan. Using three-spined sticklebacks, we show for the first time that while animals subjected to an intermittent feeding regime can grow as large as continuously fed controls that receive the same total amount of food, and can maintain reproductive investment, they have a shorter lifespan. Furthermore, we show that this reduction in lifespan is linked to rapid skeletal growth rate and is due to an increase in the instantaneous risk of mortality rather than in the rate of senescence. By contrast, dietary restriction caused a reduction in reproductive investment in females but no corresponding increase in longevity. This suggests that in short-lived species where reproduction is size dependent, selection pressures may lead to an increase in intrinsic mortality risk when resources are diverted from somatic maintenance to both growth and reproductive investment.     

Influence of feeding a fish oil-containing diet to young,lean, adult dogs: effects on lipid metabolites,postprandial glycaemia and body weight

The aim of this study was to determine the effect of feeding a fish oil (FO)-containing diet on lipid and protein metabolism, postprandial glycaemia and body weight in young, lean, adult dogs. Eight female Beagles were randomly assigned to one of two isonitrogenous and isoenergetic diets, Control or FO, in a crossover design. At the beginning of the experiment and at 30 and 60 d, a baseline blood sample was collected and the dogs then were fed their daily ration. Nitrogen balance began at 07:00 h on day 63 of each experimental period and ended at 07:00 h on day 69. On day 66 of each period, a single dose (7.5 mg/kg) of ¹⁵N-glycine was administered orally to each dog via gelatin capsule. Postprandial glycaemia did not differ between treatments or among sampling days within treatment. Cholesterol concentration was increased (p < 0.05) on the Control treatment throughout the experiment when compared to values of day 0. Dogs fed the FO treatment had higher plasma triglyceride and ghrelin concentrations than those fed the Control treatment. Body weight and food intake did not differ between dietary treatments. Faecal excretion was increased (p < 0.05) in the FO treatment. Dry matter digestibility was decreased (p < 0.05) and fat digestibility tended (p < 0.10) to decrease in the FO treatment. Overall, feeding a FO-containing diet showed a protective effect against the rise of plasma cholesterol and it increased plasma ghrelin concentration. However, FO supplementation did not appear to affect protein metabolism or postprandial glycaemia in adult lean dogs.     

Effect of carbohydrate on age-related feeding behaviors and longevity in adult black cutworm,Agrotis ipsilon (Lepidoptera: Noctuidae)

Age-related consumption and longevity were monitored in the laboratory for adultA. ipsilon fed either a 1M sucrose solution or water. An additional group was completely starved. Adults consumed sucrose solution and water just after eclosion; the percentage feeding daily and the mean daily consumption for females and males fed sucrose solution declined with time, whereas the percentage feeding daily and the mean daily consumption of those fed water increased with time. Total consumption was significantly higher for those fed sucrose solution (P<0.01) because they lived longer, but consumption per day averaged over the entire adult stage was not significantly different between those fed sucrose solution and those fed water (P>0.05). Mean longevity was significantly extended for females and males fed sucrose solution over those fed water or starved (P<0.01). Moreover, consumption of either fluid was significantly correlated with extended longevity in all groups (P<0.05). These data on fluid consumption by adultA. ipsilon are discussed relative to posteclosion migratory activities.     

Variation in social information use: the influences of information reliability and mass on decision making in a group‐living fish Gambusia affinis

The effect of the reliability of available social information was assessed by examining whether the age of social information changes its effects on a foraging decision in a group‐living fish Gambusia affinis. Individuals switched their patch preference when faced with social information that conflicted with personal information in general; the age of the social information, however, did not significantly influence preference for feeding patch. The mass of decision makers was positively correlated with their use of available social information, with heavier individuals exhibiting a greater difference in patch preference than lighter individuals, suggesting that large and small G. affinis trade‐off the benefits of information acquisition and the costs of competition from conspecifics differently.     

New records of a rare species of spariform fish Acanthopagrus schlegelii (Bleeker, 1854) (Osteichthyes: Sparidae) from Russian waters of the sea of Japan, with notes on the taxonomy of the genus Acanthopagrus Peters, 1855

A rare species of the spariform fish Acanthopagrus schlegelii from Russian waters is described. The synonymy of this species and the related literature data are analyzed. It is suggested that two species occur in Russian waters that differ in body coloration: A. schlegelii and A. czerskii.     

Experimental increase of flying costs in a pelagic seabird: effects on foraging strategies,nutritional state and chick condition

A central point in life history theory is that parental investment in current reproduction should be balanced by the costs in terms of residual reproductive value. Long-lived seabirds are considered fixed investors, that is, parents fix a specific level of investment in their current reproduction independent to the breeding requirements. We tested this hypothesis analysing the consequences of an experimental increase in flying costs on the foraging ecology, body condition and chick condition in Cory’s shearwaters Calonectris diomedea. We treated 28 pairs by reducing the wing surface in one partner and compared them with 14 control pairs. We monitored mass changes and incubation shifts and tracked 19 foraging trips per group using geolocators. Furthermore, we took blood samples at laying, hatching and chick-rearing to analyse the nutritional condition, haematology, muscle damage and stable isotopes. Eighty-day-old chicks were measured, blood sampled and challenged with PHA immune assay. In addition, we analysed the effects of handicap on the adults at the subsequent breeding season. During incubation, handicapped birds showed a greater foraging effort than control birds, as indicated by greater foraging distances and longer periods of foraging, covering larger areas. Eighty-day-old chicks reared by treated pairs were smaller and lighter and showed a lower immunity than those reared by control pairs. However, oxygen demands, nutritional condition and stable isotopes did not differ between control and handicapped birds. Although handicapped birds had to increase their foraging effort, they maintained physical condition by reducing parental investment and transferred the experimentally increased costs to their partners and the chick. This result supports the fixed investment hypothesis and is consistent with life history theory.