Diet composition of polar bears in Svalbard and the western Barents Sea

We estimated both the numerical and biomass composition of the prey of polar bears (Ursus maritimus) from 135 opportunistic observations of kills in Svalbard and the western Barents Sea collected from March to October 1984-2001. By number, the prey composition was dominated by ringed seals (Phoca hispida) (63%), followed by bearded seals (Erignathus barbatus) (13%), harp seals (P. groenlandica) (8%) and unknown species (16%). However, when known prey were converted to biomass, the composition was dominated by bearded seals (55%), followed by ringed seals (30%) and harp seals (15%). Results indicated that bearded seals are an important dietary item for polar bears in the western Barents Sea. We believe that different patterns of space use by different bears may result in geographic variation of diet within the same population.     

Feeding habits of harp seals (Phoca groenlandica) during early summer and autumn in the northern Barents Sea

The feeding habits of harp seals (Phoca groenlandica) in the Barents Sea were examined in studies conducted during June 1991, September 1990 and 1991, and October 1992. Analyses of stomach and intestinal contents were carried out and concurrent estimates of prey abundance were made using trawl gear. Harp seals appeared to feed at low intensity in the pack ice belt during the first half of June. There was little potential prey in the water column, but prawns (Pandalus borealis), capelin (Mallotus villosus) and polar cod (Boreogadus saida) were abundant close to the bottom. In September, the seals sampled in the northern pack ice areas of the Barents Sea fed on the pelagic amphipod Parathemisto libellula, krill (Thysanoessa spp.), prawns and, to a lesser extent, on fish species such as polar cod, sculpins (Cottidae) and snailfish (Liparidae). Trawling revealed that large quantities of Parathemisto libellala were present in the upper layers of the water column. Fish, mainly capelin and polar cod, were less abundant and occurred in deeper waters. In mid-October, the diet of seals in the northern Barents Sea consisted mainly of amphipods (Parathemisto sp.). Later in October, when increasing pack ice cover forced the harp seals to move south, the diet seemed to change from amphipods to fish prey, predominantly capelin and polar cod.     

Brucella sp. antibodies in polar bears from Svalbard and the Barents Sea

A prevalence of 5.4% of anti-Brucella sp. antibodies was found in plasma samples from 297 polar bears (Ursus maritimus) from Svalbard and the Barents Sea. Plasma was tested by the classical brucellosis tests Slow Agglutination of Wright (SAW), EDTA modified SAW and Rose Bengal test, as well as by an indirect Protein A ELISA. Only samples classified as positive in all tests were regarded as containing anti-Brucella sp. antibodies. A significant west to east increase in the proportion of bears with anti-Brucella sp. antibodies was found, with 3.6% (n = 253) at Svalbard (Spitsbergen, Nordaustlandet, Edge?ya, Barents?ya and Hopen), and 15.9% (n = 44) in the central Barents Sea. Anti-Brucella sp. antibodies were previously found in ringed seals (Phoca hispida) and harp seals (Phoca groenlandica) from the same geographical areas. The ringed seal is an important prey species for the Svalbard polar bear population, and may thus be a source of brucellosis for the bears. There are no indications of reproductive disorders caused by Brucella sp. or other infectious agents in our study polar bear population. Potential impacts of Brucella sp. exposure on individuals or the population are unknown.     

Pikeperch Sander lucioperca trapped between niches: foraging performance and prey selection in a piscivore on a planktivore diet

The foraging behaviour of planktivorous pikeperch Sander lucioperca during their first growing season was analysed. Field data showed that S. lucioperca feed on extremely rare prey at the end of the summer, suggesting the presence of a bottleneck. In experiments, foraging ability of planktivorous S. lucioperca was determined when fish were feeding on different prey types (Daphnia magna or Chaoborus spp.) and sizes (D. magna of lengths 1 or 2·5 mm) when they occurred alone. From these results, the minimum density requirement of each prey type was analysed. The energy gain for three different foraging strategies was estimated; a specialized diet based on either large D. magna or Chaoborus spp. or a generalist diet combining both prey types. Prey value estimates showed that Chaoborus spp. should be the preferred prey, assuming an energy maximizing principle. In prey choice experiments, S. lucioperca largely followed this principle, including D. magna in the diet only when the density of the Chaoborus spp. was below a threshold value. Splitting the foraging bout into different sequences, however, resulted in a somewhat different pattern. During an initial phase, S. lucioperca captured both prey as encountered and then switched to Chaoborus spp. if prey density was above the threshold level. The prey selection observed was mainly explained by sampling behaviour and incomplete information about environmental quality, whereas satiation only had marginal effects. It was concluded that the observed diet based on rare prey items was in accordance with an optimal foraging strategy and may generate positive growth in the absence of prey fish in suitable sizes.     

Copepod communities off Franz Josef Land (northern Barents Sea) in late summer of 2006 and 2007

Copepods are considered to be the main component of the Arctic marine zooplankton. We examined the copepod distribution and diversity off Franz Josef Land (northern Barents Sea) in August 2006 and 2007. A total of 18 and 14 copepod taxa were identified from the sampling layers (100–0 m or bottom–0 m) in 2006 and in 2007, respectively. There were no significant differences in the total copepod abundance between the years (means ± SE: 118,503 ± 24,115 individuals m⁻² in 2006 vs. 113,932 ± 28,564 individuals m⁻² in 2007). However, the copepod biomass in 2006 (4,518 ± 1,091 mg C m⁻²) exceeded clearly the value in 2007 (1,253 ± 217 mg C m⁻²). The copepod community showed low species richness and diversity in both years (Simpson index D: 0.34 and 0.38, respectively). Biomass of the large and small copepod species strongly decreased from 2006 to 2007. The total abundance of copepods was negatively correlated with water temperature in 2006 and positively correlated with salinity in 2007. The patchiness in copepod distribution was associated with local hydrography and temperature conditions.     

Linking prey composition of haddock Melanogrammus aeglefinus to benthic prey availability in three different areas of the northern North Sea

The feeding strategy and prey selection of haddock Melanogrammus aeglefinus related to the benthic infauna in the field were investigated in three different study areas (boxes) in the northern North Sea in 2007. The stomach contents of M. aeglefinus were dominated by invertebrates in all three boxes, mainly echinoderms and polychaetes, similar to the benthic communities in the field. Prey densities in the field significantly determined prey selection and, thus the feeding strategy of M. aeglefinus appeared highly opportunistic. Other prey characteristics, such as the position in the sediment or its palatability, had no significant effect on the selection process although trends were apparent that tubicolous polychaetes of the family spionids, especially Spiophanes kröyeri and Spiophanes bombyx as well as the tentaculate Phoronis spp., were not consumed and potentially avoided due to their ability to withdraw below the feeding depths or due to chemical deterrents. High abundances of echinoderm species with hard calcareous shells in the M. aeglefinus stomachs, such as the ophiurid Ophiocten affinis and the echinoid Echinocyamus pusillus, indicated their use as grinding elements. A gradual shift from benthos to fish feeding with increasing M. aeglefinus size was not found.     

The importance of a main dish: nestling diet and foraging behaviour in Mediterranean blue tits in relation to prey phenology

Insectivorous birds rely on a short period of food abundance to feed their young; they must time their reproduction to match the timing of Lepidoptera larvae, their main prey. Apart from the net result (i.e. birds are timed or mistimed with respect to the food's peak), an important aspect is the possible influence of other factors, such as the seasonality of the environment or the abundance and diversity of species contributing to the caterpillar peak, on birds' phenology and their ability to cope well with unpredictable food supplies. In a 2-year study, we explored the seasonal variation of nestling diet in Mediterranean blue tits Cyanistes caeruleus and how reproductive parameters (nestling condition, provisioning rates) are affected by the phenology and composition of food. We also examined the influence of the synchrony between offspring needs and caterpillar peak in shaping the composition of the nestlings' diet. We found that the effect of synchrony on nestling condition varied between years which may be partially due to differences in food peak attributes. The adequacy of birds' timing in relation to prey phenology affected foraging decisions; those birds that were not able to correctly adjust their timing were forced to rely on less preferred prey (tortricids). In this sense, we found that relative contribution of tortricids (smaller caterpillars but easier to get) and noctuids (preferred prey but more difficult to find) to the diet influenced nestling condition and parental provisioning effort; parents performed fewer feeding events and reared heavier nestlings as the contribution of noctuids to the diet increased. The relationship between the proportion of caterpillars and nestling mass was curvilinear, whereas that parameter was negatively affected by the percentage of pupae. Our results show how changes in diet composition may contribute to explain the effect of mismatching on birds' breeding performance.     

夏季南海北部纤毛虫群落组成及其水平分布

在2007年中国科学院南海海洋研究所南海北部开放航次期间,设计了两条纤毛虫采样断面(X断面、Y断面),共13个站位,涵盖了珠江冲淡水区、粤东上升流区和陆坡开阔海区,旨在对纤毛虫的种类组成和空间分布及其影响因素进行探讨。共检出4纲8目22属38种纤毛虫,其中种类数最多的属是砂壳目拟铃虫属(9种),其次是急游目急游属(5种)。本航次中纤毛虫主要是砂壳目纤毛虫(27种),共鉴定出砂壳虫15属27种。纤毛虫优势种为蚤状中缢虫Mesodinium pulex(18.1%),其次是丁丁急游虫Strombidium tintinnodes(9.7%),盾形拟铃虫Tintinnopsis urula(5.8%)。纤毛虫种类数和丰度从近岸向外海逐渐减少,纤毛虫种类数与温度(R2=0.53,P0.05)和盐度(R2=0.43,P0.05)呈负相关,随着温度的升高,纤毛虫种类数逐渐降低。纤毛虫丰度与温度和盐度相关性并不明显,这可能由于受上升流的影响,近岸上升流高盐区存在着纤毛虫丰度较为丰富的情况。叶绿素a浓度与纤毛虫种类数(R2=0.36,P0.05)和纤毛虫丰度(R2=0.36,P0.05)呈正相关,近岸浮游植物生物量高,纤毛虫种类丰富,丰度大,叶绿素a沿纵断面降低,纤毛虫种类数和丰度也降低。     

Climatic determinants of diet and foraging behaviour in baboons

Baboons (Papio spp.) are characterised by a large degree of variation in foraging behaviour and dietary composition. Previous analyses have suggested that much of this can be traced to differences in ecological conditions between sites. The proximate mechanism underlying these relationships is assumed to be mediated via the impact of climatic conditions on food availability, and ultimately the impact that this has on dietary composition. This paper examines these relationships more explicitly. Data from 15 baboon populations were used to assess the relationship between foraging variables and dietary composition. Only feeding time showed significant relationships with dietary composition, with percentage of time spent feeding decreasing with proportion of fruit in the diet, and increasing with the proportion of subterranean items. No relationships were found between diet composition and moving time or day journey length, although significant relationships were found between these variables and group size. The proportions of feeding time spent feeding on fruit, subterranean items and leaves were functions of the ecological conditions experienced by that population, although no relationships were found for the percentage of feeding time devoted to flowers or animal material. The relationships between the proportion feeding time spent on fruits, leaves and subterranean items and ecological variables could be best explained through understanding the way in which bush and tree level vegetation respond to the climatic environment and the impact this has on fruit availability. In this respect, temperature and seasonality are the key climatic parameters. This provides good support for the idea that the proximate mechanism underlying the relationship between foraging time and ecological variables is mediated via the impact of the climatic environment on vegetation structure and food availability. Similar factors have been proposed to explain much of the geographic variation in species diversity, suggesting that these relationships have far wider relevance and may account for much of the observed geographical variation in mammalian behaviour.     

夏、秋季渤海小型底栖动物类群组成及分布特征

分别于2011年6月和11月,搭载"东方红2号"科学调查船在渤海海域(37.0°—40.0°N,118.0°—122.0°E)进行了小型底栖动物的取样,对小型底栖动物类群组成、丰度、生物量、空间分布及其与环境因子的关系进行了研究。结果表明:研究海域小型底栖动物分布不均匀,表现为黄河口附近及近岸海域小型底栖动物丰度显著低于其他海域。小型底栖动物6月平均丰度高于11月,分别为(1012.7±519.1)个/10 cm~2和(829.5±385.8)个/10 cm~2, 6月平均生物量低于11月,分别为(570.8±307.6)μg干重/10 cm~2和(661.3±310.9)μg干重/10 cm~2。两个航次共鉴定出18个小型底栖动物类群,其中自由生活海洋线虫为最优势类群,分别占小型底栖动物总丰度的95.0%和90.3%,占小型底栖动物总生物量的67.4%和45.3%。其他数量上较重要的类群还有底栖桡足类、多毛类、动吻类和双壳类等。其中,多毛类丰度具有显著的季节差异,其11月丰度高于6月。两个航次分别有93.6%(6月)和91.1%(9月)的小型底栖动物分布在0—5 cm的表层沉积物内,没有表现季节性垂直迁移。对小型底栖动物生物数据与环境因子的相关分析结果显示,小型底栖动物的丰度与沉积物中值粒径、含水率呈显著负相关,与有机质含量呈极显著负相关,表明这三个因子是决定研究海域小型底栖动物分布的重要因素。小型底栖动物群落组成与环境因子的BIOENV相关分析表明,水深、有机质含量的组合能够最好地解释小型底栖动物群落结构的差异。与渤海海域30年来的小型底栖动物研究比较发现,在过去30年里,渤海小型底栖动物(包括海洋线虫)丰度逐渐增加,而其中的底栖桡足类丰度却在逐渐减少。沉积环境的变化以及人类干扰是引起渤海海域小型底栖动物丰度变化的重要因素。     

Recent phytoplankton productivity of the northern Bering Sea during early summer in 2007

Although the northern Bering Sea is one of the most productive regions in the northern North Pacific Ocean and currently considered a declining productivity region, no recent primary productivity measurements have been collected in this region. Phytoplankton productivity was measured in the northern Bering Sea in 2007 using a dual ¹³C–¹⁵N isotope tracer technique to quantify present rates of primary productivity and to assess changes under recent environmental conditions in this area. We found that large diatoms (mostly Fragilaria sp.) dominated the phytoplankton during the initial part of the cruise, whereas unidentified nano + pico phytoplankton largely dominated at the surface about 2 weeks later (at “revisited stations”). At the 1% light depth, diatoms and Phaeocystis sp. were the dominant species, whereas diatoms and unidentified nano + pico cells were dominant at the revisited sites. Based on nitrate and ammonium uptake rates, the estimated f-ratios (the ratio of nitrate uptake rate/nitrate + ammonium uptake rates of phytoplankton) were high (0.65–0.74), indicating that nitrate was an important nitrogen source supporting primary production in the northern Bering Sea during the cruise in 2007. Compared with previous studies performed several decades ago, we found significantly lower chlorophyll-a concentrations and carbon uptake rates of phytoplankton in the northern Bering Sea in 2007. This is consistent with recent studies that have shown lower rates of production in the Chukchi Sea and declines in benthic biomass and sediment oxygen uptake in the northern Bering Sea.     

Interpopulation variation in predator foraging behaviour promotes the evolutionary divergence of prey

Despite intensive investigation of the role of predation on evolutionary processes, few studies have questioned the possibility of the evolutionary divergence of prey populations in response to interpopulation variation in predator foraging behaviour. In an interaction between a seed-predatory insect, the camellia weevil (Curculio camelliae), and its host plant, the Japanese camellia (Camellia japonica), I tested whether the evolutionary differentiation of the plant's defensive trait, pericarp thickness, was related to the interpopulation variation in the foraging behaviour of female weevils. I found that the preference of weevils for the plant fruit based on pericarp thickness varied across 13 populations in Japan. Importantly, variation in weevil behaviour explained interpopulation variation in pericarp thickness and the direction/strength of natural selection on the trait. Overall, I show that adaptive foraging of predators can result in the evolutionary divergence of predator-prey interactions.     

Species composition and structure of the ichthyofauna of the Barents Sea

The species composition and brief characteristic of some elements of structure of the ichthyofauna of the Barents Sea within its geographic boundaries are represented. During the whole historic period of observations in the Barents Sea, 182 species and subspecies of fish were recorded, belonging to 59 families, 28 orders, and 5 classes. Most species and subspecies belong to the boreal complex (59.3%), occur principally in the bottom layers (56.6%), more than a half feed on bottom and demersal invertebrates (52.2%), and are commercial species (52.7%). In the Barents Sea, 21 species and subspecies are commercial. Their ration in catches depends on the integral impact of natural and anthropogenous factors. In the arctic zone of the Barents Sea, the part of noncommercial species makes by biomass 1.18%; in the boreal zone—0.26%; in the Pechora Sea—10.6%.     

Food of introduced mosquitofish: ontogenetic diet shift and prey selection

The mosquitofish Gambusia holbrooki of Lake Banyoles, Catalonia, Spain, were strictly littoral. Their population was dominated by females throughout the year, except in spring when males were more common. Their diet was based on littoral cladocerans, particularly Chydorus sphaericus, Scapholeberis ramneri, Ceriodaphnia reticulata , and Pleuroxus laevis , and nematoceran (basically chironomid) adults. There was a large variety of prey of terrestrial (collembolans, ants) or aquatic neustonic origin ( S. ramneri , emerging nematoceran adults), showing the microhabitat of mosquitofish closely linked to the water surface. In contrast to other studies, terrestrial insects were not especially important in summer. In addition to seasonal and between-site variation, there was an ontogenetic diet shift from microcrustaceans, particularly cladocerans (smallest fish also using diatoms and copepod nauplii) to larger prey, namely nematoceran adults. However, there was an unusual, inverse relationship between fish length and the size of two prey ( S. ramneri and the collembolan Sminthurides sp.), paralleling the overall increase in mean prey size.     

Diving behaviour in relation to water temperature in the southern elephant seal: foraging implications

Summary A time-depth-temperature recorder provided a continuous record of diving by a female southern elephant seal in relation to water temperature for 27 days (1939 dives) after completion of moult. Mean maximum dive depth was 391±2.6 m and the overall maximum was 775 m. Dives lasted on average 17.5±0.09 min. Most dives showed a rapid descent to the discontinuity between the cold surface water and warmer deep water. Consequently the seal spent 57% of its time while diving at a depth of 200–400 m when it may have been foraging. This strongly suggests that the seal was exploiting a food source at the discontinuity between vertically stratified water masses. The water temperature data also indicated that the seal was diving in waters south of the Antarctic Polar Front and at some distance from the northern edge of the pack ice. The seal spent 88% of its time under water. Normal surface intervals between dives lasted an average of 2.1 ± 0.1 min whereas 16 extended surface intervals (>10 min duration) lasted 32.7±4.6 min. Dives were deeper during the day than at night and all but one extended surface interval occurred at night. The pattern of dives was similar to records from northern elephant seals but this is the first study to show how diving behaviour relates to water temperature.     

Sex differences in grey seal diet reflect seasonal variation in foraging behaviour and reproductive expenditure: evidence from quantitative fatty acid signature analysis

1. Intraspecific variation in diet can be an important component of a species niche breadth. We tested the hypothesis that sex differences in seasonal foraging behaviour and energy storage of sexually size dimorphic grey seals Halichoerus grypus (Fabrisius 1971) are reflected in differences in the diet and niche breadth. Diet composition was estimated for 496 adult (226 males, 270 females) and 91 juvenile (46 males/45 females; all 6 months old) grey seals sampled between 1993 and 2000 using quantitative fatty acid signature analysis. Niche breadth and overlap were estimated using the Shannon-Weaver diversity index (H') and the Morisita-Horn index (C(H)), respectively. 2. Sand lance Ammodytes dubius (Reinhardt 1837) and redfish Sebastes sp. (Cuvier 1829) accounted for a high proportion of the diet in both sexes and age groups. However, the diets of adult males were significantly more diverse across all seasons (H': males 0.36 +/- 0.007 vs. females 0.28 +/- 0.007) and less energy dense in spring (male 5.3 +/- 0.07 kJ g(-1) vs. females 5.6 +/- 0.09 kJ g(-1)) than those of adult females. 3. Season and sex explained most of the observed variation in adult diets, but there were significant sex-season interactions. These differences were most evident during the post-breeding (spring) foraging period when energy acquisition is important to female recovery of nutrient stores needed to support pregnancy. Females selected fewer and higher quality prey species in spring than males. 4. There were no sex differences in the diets of juvenile grey seals. Although many of the species overlapped with those eaten by adults, juvenile niche breadth (H': 0.41 +/- 0.014, n = 91) was significantly broader than that of adults (H': 0.30 +/- 0.011, n = 115). Juvenile diets were also of lower energy density (5.3 +/- 0.04 kJ g(-1)) than those of adults (5.6 +/- 0.09 kJ g(-1)), suggesting less selectivity in these young and relatively na?ve predators. 5. Sex-specific seasonal changes in diet correspond to seasonal changes in diving behaviour and rate of body energy accumulation of adult males and females. Sex-specific reproductive requirements appear to be a primary factor generating the intraspecific variation in the seasonal foraging ecology of this large marine carnivore. However, sex differences in the breadth and energy content of diets also suggest the influence of body-size dimorphism as a factor shaping the diet of this species.     

Ontogenetic diet shifts and prey selection in nursery bound lemon sharks, Negaprion brevirostris, indicate a flexible foraging tactic

Ontogenetic variations in shark diet are often qualitatively inferred from dietary analysis and hindered by high levels of unidentified prey or small sample sizes. This study focused on nursery bound lemon sharks (Negaprion brevirostris, n?=?396), enabling some control over the confounding variables of prey choice associated with ontogeny. Nursery bound lemon sharks exhibited weak ontogenetic variation in dietary composition with high levels of dietary overlap. Variation in prey preference of lemon sharks with ontogeny was complex, but revealed a continuous shift from predominantly opportunistic benthic foraging as neonates to more selective piscivory with increasing shark size while in the nursery. Lemon sharks demonstrated a discrete ontogenetic shift in the number of prey consumed and stomach content weight (Kruskal-Wallis tests p?<?0.01), as well as prey size (ANOVA, p?<?0.001). All sizes of sharks exhibited positive size selection of prey (Mann?CWhitney U tests, p?<?0.01). However, the lack of size preference by all but the largest lemon sharks for their major prey (yellowfin mojarra, Gerres cinereus), suggests neonate sharks, while capable of occasionally foraging on large prey, are relatively inept opportunistic foragers. This was evident in high diet breadth, low diversity of consumed prey and lower trophic level than larger sharks. This study represents the first quantitative analysis of ontogenetic variation in prey preference and size selection in sharks, indicating a flexible foraging tactic in lemon sharks and the importance of hunting ability and predator size in prey choice.