Trophic relations of the cephalopod Martialia hyadesi (Teuthoidea: Ommastrephidae) at the Antarctic Polar Front,Scotia Sea

Samples of the squid Martialia hyadesi were collected aboard two Japanese squid-jigging vessels carrying out commercial fishing trials at the Antarctic Polar Frontal Zone, north Scotia Sea, in February 1989. The dissected stomachs of 61 specimens were classified according to fullness and the contents were examined visually. Identifiable food items included fish sagittal otoliths, crustacean eyes, the lappets on euphausiid first antennule segments and cephalopod sucker rings. The most frequent items in the squid's diet were the myctophid fishes Krefftichthys anderssoni and Electrona carlsbergi, the euphausiid Euphausia superba and a hyperiid amphipod, probably Themisto gaudichaudi. A small proportion of the sample had been feeding cannibalistically. Total lengths of the fish prey were estimated from sagittal otolith size using published relationships. All fish were relatively small; 7 to 35% of squid mantle-length. However, it is possible that some heads of larger fish are discarded by the squid and so are not represented by otoliths in the stomach contents. Over the size range of squid in the sample there was no relationship between size of fish prey and size of squid. Similarly, when the squid sample was divided into groups according to prey categories: crustaceans, crustaceans+fish, fish, cephalopod, there was no evidence that dietary preference was related to squid size. The prevalence of copepod-feeding myctophids in the diet of this squid, which is itself a major prey item of some higher predators in the Scotia Sea, suggests that a previously unrecognised food chain: copepod-myctophid-M. hyadesi-higher predator, may be an important component of the Antarctic oceanic ecosystem.     

Fatty acid signatures of stomach contents reflect inter- and intra-annual changes in diet of a small pelagic seabird,the Thin-billed prion <Emphasis Type="Italic">Pachyptila belcheri</Emphasis>

In diet analyses of seabirds, fatty acid signatures (FAS) can be used to overcome biases due to differential digestion of prey and enable the analysis of very digested diet samples. We applied FAS analysis to stomach contents of a small sub-Antarctic seabird, the Thin-billed Prion Pachyptila belcheri, which feeds mainly on squid during incubation and on crustacea during chick rearing. This seasonal dietary switch of Thin-billed prions was reflected in differences in FAS in regurgitates, as were inter-annual differences in diet composition. A discriminant function analysis correctly classified 93.4% of cases with respect to year (2006–2008) and stage of the breeding cycle (incubation versus chick rearing). The dominant types of crustacea in the diet of Thin-billed prions (amphipods Themisto gaudichaudii, euphausiids, decapods Munida gregaria, and calanoid copepods) were distinguished well by characteristic FAS patterns. However, the FAS of the two main types of prey by volume, amphipods T. gaudichaudii and squid Gonatus antarcticus, were similar to each other. Although FAS were successfully applied in the analysis of prey in stomach contents of prions, FAS of some prey species were similar and may not be distinguishable from each other if used in quantitative diet analyses.     

Fish and squid in the diet of king penguin chicks,Aptenodytes patagonicus,during winter at sub-antarctic Crozet Islands

The diet of king penguins, Aptenodytes patagonicus, rearing chicks was studied during three consecutive austral winters (1990, 1991 and 1992) at Crozet Islands. The mean stomach content mass of the 47 samples was 503 g. Percentages of wet and reconstituted masses showed that both fishes (66 and 36%, respectively) and squid (34 and 64%) are important components of the winter diet. Juveniles of the demersal onychoteuthid squid Moroteuthis ingens form the bulk of the cephalopod diet, and this was the main prey by reconstituted mass (57%). Myctophid fish (lantern-fishes) accounted for most of the fish diet, constituting together 32% by mass. The three main species of myctophids eaten in summer by king penguins were either very rare in winter (Electrona carlsbergi) or accounted for a smaller proportion of the diet (Krefftichthys anderssoni = 1.5% by mass and Protomyctophum tenisoni = 4.6%). Five other myctophids, which are rarely consumed in summer, contributed 24% of the diet by mass in winter (Gymnoscopelus piabilis = 18.1%, Lampichthys procerus = 2.4%, G. nicholsi = 1.3%, and Metelectrona ventralis and Electrona subaspera = 1.0%). The greater diversity of prey in winter suggests a more opportunistic feeding behaviour at a time probably marked by a change in prey availability. Both the known ecology of the fish and squid prey and the barely digested state of some items suggest that in winter breeding adults forage in the outer shelf, upper slope and oceanic areas in the close vicinity of the Crozet Islands to feed their chicks. Finally, using king penguins as biological samplers, the present work provides novel data on the previously unstudied mesopelagic/epibenthic marine community in waters surrounding the Crozet Islands. Seventeen myctophid fish have been identified to species level. These include several poorly known species in the southern Indian Ocean. The occurrence of small, nearly intact, cephalopods in the diet of king penguins suggests that spawning grounds of four squid species may be located near the Crozet Archipelago.     

Influence of depth and season on the diet of the deep-water aristeid Aristeus antennatus along the continental slope (400 to 2300 m) in the Catalan Sea (western Mediterranean)

The composition of the diet of the deep-sea aristeid shrimp Aristeus antennatus (Risso, 1816) was determined based on the analysis of 1578 stomach contents. Samples were collected using bottom trawls during 1984 to 1989 along the deep continental slope (380 to 2266 m) in the Catalan Sea (Western Mediterranea). A. antennatus displayed a high feeding activity on a large variety of endobenthic and epibenthic invertebrates, whereas benthopelagic prey were supplementary to its diet. The shrimp's diet varied mainly as a function of depth. Various preferred prey items on the middle slope (Calocaris macandreae, Cirolana borealis, Abra longicallus) disappeared from its diet below 1300 m, coinciding with the transtion boundary between different taxocenoses in the Catalan Sea. Less mobile prey and inert remains (mainly pteropods) contributed a progressively larger share of the diet of Aristeus antennatus with increasing depth. The importance of seasonality in the changes in diet decreased with increasing depth, and was relatively high only in the upper middle slope (down to 1000 m depth), where two seasonal dietary groups were detected. The most distinct seasonal changes in diet were among benthopelagic prey. The diet of A. antennatus in the submarine canyons mainly consisted of endobenthic prey (large polychaetes, ophiuroids). The higher stomach-fullness values and less diversified diet in this area were probably related to high productivity in the submarine canyons.     

Diets of fishes of the upper continental slope of eastern Tasmania: content,calorific values,dietary overlap and trophic relationships

Diets of 15 species of demersal and pelagic fishes on the upper continental slope (420 to 550 m) were determined, based on samples taken every two months over 13 mo (April 1984 to April 1985) off eastern Tasmania. The calorific contribution of each prey item to the diets was determined. The fish could be divided into four trophic categories: pelagic piscivores, epibenthic piscivores, epibenthic invertebrate feeders and benthopelagic omnivores. Dietary overlap between the groups was low. The pelagic piscivores Apogonops anomalus, Trachurus declivis, Brama brama, Lepidopus caudatus and Macruronus novaezelandiae primarily consume the shelf-break myctophid Lampanyctodes hectoris; their diet is narrow, with a large overlap between species. The epibenthic piscivores Deania calcea and Genypterus blacodes both take a greater variety of prey, but have little dietary overlap. The fish feeding on epibenthic invertebrates, Coelorinchus sp. 2 and Centriscops humerosus, obtain most of their energy from benthic Crustacea and Ophiuroidea, supplemented with Lampanyctodes hectoris; the diet is broad, with little overlap. Among the benthopelagic omnivores (Cyttus traversi, Coelorinchus sp. 4, Lepidorhynchus denticulatus, Neocyttus rhomboidalis, Helicolenus percoides, Epigonus denticulatus and E. lenimen), most diets are broad and show slight overlap. All but E. denticulatus consume significant quantities of Lampanyctodes hectoris as well as Crustacea, particularly Polychaeta, Euphausiacea and Pyrosoma atlanticum. Seasonal changes in diet occurred in G. blacodes, T. declivis, Lepidopus caudatus, Coelorinchus sp. 4, Lepidorhynchus denticulatus, H. percoides, E. denticulatus and E. lenimen; these were related to changes in abundance of particular prey species, not to alterations in feeding habits. Only three species, Lepidopus caudatus, Coelorinchus sp. 2 and H. percoides, showed significant diel feeding periodicity. Ontogenetic dietary changes were evident in Cyttus traversi, Coelorinchus sp. 2, Lepidorhynchus denticulatus and H. percoides. Cyttus traversi and H. percoides progressively changed from crustaceans to fish as their size increased. The diets of size classes within species showed little overlap, except for Lepidorhynchus denticulatus, which eats chiefly euphausiids and Lampanyctodes hectoris at all sizes. In addition to describing the diets and trophic relationships of 90% of the fish biomass, the results emphasize the importance to the entire fish community of mesopelagic food resources, particularly Lampanyctodes hectoris. Many benthopelagic species undertake extensive vertical migrations in search of prey, thus playing a major role in the transport of energy from midwater regions to the benthos of the continental slope.     

Trophic relationships of white-chinned petrels from Crozet Islands: combined stomach oil and conventional dietary analyses

The diet of white-chinned petrels Procellaria aequinoctialis breeding at the Crozet Archipelago (southern Indian Ocean) was studied using two complementary methods: lipid analysis of stomach oils as trophic markers together with the conventional dietary approach (i.e., stomach content analysis). Objectives were (1) to investigate the adult diet when they feed for themselves by analyzing stomach oil lipids, and (2) to compare the lipid signature of chick and adult oils. Stomach oils mainly consisted of triacylglycerols (TAG), diacylglycerol-ethers (DAGE) and wax esters (WE) (66, 14 and 11%, respectively). The dietary origin of TAG and WE was evaluated by linear discriminant analyses with fatty acid and fatty alcohol fractions. Analyses evidenced that stomach oils did not originate from Antarctic krill, but instead from myctophid fish, thus demonstrating the importance of mesopelagic fish in the nutrition of adult petrels. This result was consistent with the identification of digested remains of myctophids recovered from adult stomach contents after long foraging trips. Large amounts of a rare lipid class, DAGE (up to 76% of total lipids), were identified in two stomach oils, together with fresh remains of the squid Gonatus antarcticus (99% by mass), suggesting that DAGE could have the potential to be trophic markers of cephalopods. Moreover, six oils probably originated from Patagonian toothfish, thus confirming strong interactions between white-chinned petrels and fisheries. Comparison between chick and adult stomach oils indicated no major differences in their biochemical composition suggesting an identical dietary origin of oils, mainly myctophids. Both adult and chick oils can therefore be used to determine the feeding ecology of adult birds when they feed far away from their breeding grounds. Finally, food analysis of chick samples and adult samples collected after short and long trips indicated different foraging grounds during the two kinds of trips, and also between long trips performed in subtropical and Antarctic waters.     

Food of emperor penguins (Aptenodytes forsteri) in the western Ross Sea, Antarctica

The diet of the emperor penguin Aptenodytes forsteri in the western Ross Sea during spring was investigated by analysis of stomach contents sampled at three different localities. At Cape Washington, emperor penguins feeding chicks consistently preyed on fishes (89 to 95% by mass) and crustaceans (5 to 11%) over the four spring seasons examined. By far the commonest prey was the Antarctic silverfish Pleuragramma antarcticum (89% of the fish prey); the remainder of fish prey were mainly unidentified juveniles of different species of channichthyid fishes. Three species dominated the crustacean part of the diet, i.e. the gammarid amphipods Abyssorchomene rossi/plebs (30% of the crustacean prey) and Eusirus microps (22%), together with the euphausiid Euphausia crystallorophias (24%). At Coulman Island and Cape Roget, fishes, mainly P. antarcticum, formed the bulk of the food (88 and 93% by mass, respectively), crustaceans were minor prey (2.5 and 0.4%), and the squid Psychroteuthis glacialis accounted for a small but significant part of the food (3.5 and 0.8%). This study emphasizes the importance of the small, shoaling pelagic fish Pleuragramma antarcticum as a key link between zooplankton and top predators, including seabirds, in the food web and marine ecosystem of the Ross Sea. Received: 20 May 1997 / Accepted: 8 October 1997     

Isolation of cellulolytic microbes from the intestinal tract of the pinfish,Lagodon rhomboides: size-related changes in diet and microbial abundance

Pinfish, Lagodon rhomboides (Linneaus), undergo a gradual ontogenetic dietary shift during their first year of life, marked by an increase in the consumption of plant material. To determine if this shift in diet was associated with a change in the microbial flora of the intestinal tract that may assist in degradation of plant material, stomach contents were analyzed and microbes in the intestinal tract were isolated from fish ranging from 20 to 139 mm standard length. These fish were collected from Core Sound, North Carolina, USA between March and September 1991. Plant material increased from 16% of dry weight of stomach contents in pinfish under 40 mm standard length (SL) to 65% in pinfish above 120 mm SL, confirming previous observations of a diet-related ontogenetic change in L. rhomboides. Comparison of the total cultivatable facultative and anaerobic microbial flora isolated from the intestinal tract contents of pinfish ranging in size from 26 to 139 mm SL showed a 10-fold increase between fish <40 and fish >40 mm SL, with maximum population densities of approximately 2x10⁷ colony forming units (CFU) g^-1 of intestine including contents. The percentage of microbial isolates examined capable of hydrolyzing carboxymethylcellulose (CMC) increased from 12% in fish <40 mm SL to 13 to 50% in fish >40 mm SL, although there was no strict increase with increasing fish size classes. Although the percentage of CMC-hydrolytic microbial isolates varied with respect to fish SL, the percentage of skim-milk hydrolytic (proteolytic) isolates remained relatively constant (4% of total isolates) irrespective of fish SL and dietary composition. Results presented in this study document the first isolation of carboxymethylcellulase producing microbes from the intestinal tract of any fish and demonstrate that the ontogenetic dietary shift in L. rhomboides is paralleled by qualitative and quantitative changes in the intestinal microbial community. The use of strict anaerobic sampling methods in the preparation of intestinal contents from wild-captured fresh specimens was essential in obtaining these isolates.     

Foraging, prey capture, and gut contents of the mesopelagic narcomedusa Solmissus spp. (Cnidaria: Hydrozoa)

Narcomedusae are the most common group of medusae in the mesopelagic depths of Monterey Bay, California. Numerous capture events of various prey taxa were recorded in situ and analyzed using the Monterey Bay Aquarium Research Institute's remotely operated vehicle "Ventana". In situ video analysis of the stomach contents of 82 Solmissus incisa and S. marshalli revealed 88 identifiable prey items. Most (88%) were gelatinous animals. Of these gelatinous prey, 60.3% were ctenophores, 20.5% were cnidarians, 12.8% were salps, 3.8% were chaetognaths, and 2.6% were polychaetes. Euphausiids accounted for 11.4% of the diet, but they were probably captured adventitiously, as the gut contents of ctenophore prey. The tentacle-first foraging behavior of the narcomedusae is an effective way to capture large, comparatively fast-moving prey, because the fluid disturbance caused by swimming is decoupled from the area of prey capture. This behavior contrasts with the prevailing models of feeding behavior in medusae. Stealth predation may be the dominant mode of capturing prey by medusae in the mesopelagic depths of the oceans.     

Temporal changes in feeding habits and daily rations of<Emphasis Type="Italic"> Hoplostethus mediterraneus</Emphasis> in the bathyal Ionian Sea (eastern Mediterranean)

Data on the diet, feeding habits and daily rations of Hoplostethus mediterraneus Cuvier, 1829 in the bathyal eastern Ionian Sea (Mediterranean Sea) are presented. A total of 430 specimens collected by bottom trawls at depths ranging from 473 to 603 m during four 24-h day–night sampling cycles covering the four annual seasons was examined. H. mediterraneus diet consisted of pelagic and vagile epibenthic prey, mainly crustaceans, and was dominated by benthopelagic natantian decapods (83.35% IRI, index of relative importance). Seasonal changes in diet were apparent and related to seasonal fluctuations in suprabenthic and zooplanktonic prey in the environment. Diel patterns in stomach fullness and trends in diel feeding cycles are discussed in relation to the vertical migratory movements of available prey (i.e. suprabenthos and zooplankton). Daily-ration estimates were determined by evacuation-rate models and ranged from 0.143% to 0.397% WW/WW. Overall, daily-ration estimates were within the range of the daily consumption of other deep-sea fish. Deduced from diet contents, we found a constant gross energy intake (305–316 kcal g^–1) during all seasons. As a possible response to the reproductive peak of mature females observed in summer, H. mediterraneus increases its food consumption, which, in turn, is coupled with an increase in food availability.Communicated by S.A. Poulet, Roscoff     

Diet of the hatchetfish Sternoptyx diaphana

Sternoptyx diaphana Hermann is a non-migrating hatchetfish inhabiting the mesopelagic zone between 300 and 1500 m in temperate to tropical oceanic regions. An analysis is presented of the diet of this species, collected from 5 oceanic faunal provinces—the Pacific Subantarctic, and 4 subregions of the North Atlantic Ocean. Stomach analyses of 20 to 40 mm specimens revealed considerable intra-trawl (fish to fish), intraregional (Station to station), and inter-regional variation in size and composition of the diet. Generic composition of stomach contents differed noticeably from region to region, with the highest degree of faunal affinity being only 38%. The dominant food items both in terms of biomass and abundance also varied inter-regionally, with fish, euphausiids, or decapods predominant by weight; and euphaussids, copepods, or amphipods most prevalent by number. Differences in size distribution of food items from region to region were also noted. S. diaphana from regions of cooler overlying water masses fed on fewer but larger prey items, and diet was less diverse than that of fish from warmer waters. The diet consists primarily of omnivorous and carnivorous prey, and there is evidence that larger specimens feed on larger food items. The broad size-distribution and taxonomic spectrum of the prey, features of functional morphology, and low density as inferred from trawl catches, indicate that S. diaphana is a predator of limited pursuit capability. Feeding strategy appears to involve capture of the nearest available prey within its immediate vicinity.     

Comparative foraging ecology and ecological niche of a superabundant tropical seabird: the sooty tern Sterna fuscata in the southwest Indian Ocean

Over 6-million pairs of sooty terns Sterna fuscata breed once a year in the southwest Indian Ocean, mostly on three islands of the Mozambique Channel (Europa, Juan de Nova and Glorieuses) and in the Seychelles region. Seasonal reproduction in either winter or summer is the dominant strategy in the area, but non-seasonal reproduction also occurred in some places like at Glorieuses Archipelago. The feeding ecology of the sooty tern was investigated during the breeding seasons to determine whether terns showed significant differences in their trophic ecology between locations. Regurgitations were analyzed to describe the diet of individuals when breeding, and stable isotopes and mercury concentrations were used to temporally integrate over the medium-term of the trophic ecology of both adults and chicks. Overall, the diet was composed of fish, flying squid and fish larvae in different proportions. At Europa and Aride in the Seychelles, where winter reproduction occurs, large epipelagic prey like flying fish or squid dominated the diet. At Juan de Nova, sooty terns reproduce in summer and rely mostly on fish larvae. At Glorieuses (non-seasonal breeding), the diet was intermediate with fish larvae and flying squid being important prey items. The stable-carbon and nitrogen isotope values in blood confirm the differences observed in dietary analysis, and demonstrate different feeding strategies between colonies. δ¹³C values of feathers showed spatial segregation between birds from the Mozambique Channel and the Seychelles region. Terns from the Seychelles had also higher δ¹⁵N values. Feather δ¹³C values also suggest a significant shift from summer to wintering habitat for birds from Juan de Nova. This study emphasizes the high phenotypic plasticity of the species, which may explain its numerical dominance in all tropical waters of the World’s Ocean.     

Different food preferences in four sympatric deep-sea Macrourid fishes

Feeding habits of the four most abundant deep-sea demersal trawl-caught macrourids on Chatham Rise, New Zealand, were examined from stomach contents. Two species were predominantly benthic foragers: Coelorinchus bollonsi on infaunal and epifaunal polychaetes, and C. aspercephalus on epifaunal crustaceans; and two species were predominantly mesopelagic foragers; C. oliverianus on calanoid copepods, and Lepidorhynchus denticulatus on mesopelagic crustaceans. The most important predictors of diet variability were identified using distance-based linear models and included areal predictors in all four species, fish size in C. aspercephalus, C. bollonsi and L. denticulatus, and sample year in C. bollonsi. Cluster analyses showed that the diets of C. aspercephalus and C. bollonsi were most distinct. There was a greater interspecific similarity in diet in the spatial and fish size subgroups of C. oliverianus and L. denticulatus, than at the species level. Failing to account for areal, temporal, and ontogenetic variability in diets may bias evaluations of resource competition.     

Winter diet shift of long-beaked common dolphins (Delphinus capensis) feeding in the sardine run off KwaZulu-Natal, South Africa

Unpredictable inter-annual variations in the timing, spatial extent and intensity of the sardine run (Sardinops sagax) have been documented in recent years along the coastline of KwaZulu-Natal, South Africa. This study aimed to determine whether variations in the availability of sardine were reflected in the diet and condition of common dolphins (Delphinus capensis) over the past three decades. Stomach contents from 95 common dolphins incidentally caught between 2000 and 2009 were analysed and compared to historical data collected between 1972 and 1992. A shift in the principal prey species consumed by the dolphins was observed over the past 30 years. Prior to 1992, sardine comprised up to 49 % of the total stomach contents by mass, whilst chub mackerel (Scomber japonicus) was the dominant prey recorded in the stomach contents between 2000 and 2009 (66 %). As common dolphins prey on locally abundant fish species, this dietary shift may indicate changes in the availability of the most abundant fish prey. Stable isotope analyses of tooth tissue revealed no significant changes in the δ¹⁵N and δ¹³C isotopic ratios over the past three decades (P = 0.283 for N and P = 0.922 for C). Blubber thickness as a percentage of body length and blubber weight as a percentage of total body weight were assessed as indicators of animal condition. No significant changes in proportional blubber weight or blubber thickness were seen over the last 40 years (1970–2009) for all age cohorts. This species appears to be well adapted to cope with changes in prey species availability, without impacting on body condition.     

Age-related shifts in the diet composition of southern elephant seals expand overall foraging niche

Southern elephant seals are important apex predators in a highly variable and unpredictable marine environment. In the presence of resource limitation, foraging behaviours evolve to reduce intra-specific competition increasing a species’ overall probability of successful foraging. We examined the diet of 141 (aged 1–3 years) juvenile southern elephant seals to test the hypotheses that differences between ages, sexes and seasons in diet structure occur. We described prey species composition for common squid and fish species and the mean size of cephalopod prey items for these age groups. Three cephalopod species dominated the stomach samples, Alluroteuthis antarcticus, Histioteuthis eltaninae and Slosarczykovia circumantarcticus. We found age-related differences in both species composition and size of larger prey species that probably relate to ontogenetic changes in diving ability and haul-out behaviour and prey availability. These changes in foraging behaviour and diet are hypothesised to reduce intra-specific food competition concomitant with the increase in foraging niche of growing juveniles.     

Natural feeding activity of the crab Callinectes ornatus (Portunidae) in Ubatuba Bay (São Paulo, Brazil): influence of season, sex, size and molt stage

The natural diet of Callinectes ornatus in Ubatuba Bay, Ubatuba (SP), Brazil, was studied. Influence of season, sex, size and molt stage variation in the diet were also described. Specimens were collected monthly over a period of 1 year, in Ubatuba Bay, using a fishing boat equipped with a double rigged net. The relative degree of stomach fullness, frequency of occurrence, and quantitative scoring (percentage) were determined. Digested material, crustaceans, sediment and mollusks were the principal items of the diet. Echinoderms, annelids, plants, and fishes were also notable prey items, and other food categories (foraminiferans, cnidarians, worms and bryozoans) occurred in low percentages. A non-significant difference was found in many items during seasonal analysis, i.e. plants, foraminiferans, cnidarians, bryozoans and digested material were present at highest percentages during summer and autumn, while crustaceans and echinoderms were consumed in larger amounts during the spring and winter. Males and females consumed a similar diet, although ovigerous females showed a greater tendency to feed on items with soft tissues (fish, squid, shrimp). Juveniles fed more on sedentary and calcareous items than did adults, showing a significant tendency to reduce consumption of foraminiferans, annelids, bryozoans, echinoderms and sediment as the animal increased in size, accompanied by an elevation in the consumption of plants, crustaceans and fish. These crabs are opportunistic predators with a preference for crustaceans and mollusks that is correlated with the availability of prey and the ontogenetic phase of the predator. Received: 21 January 2000 / Accepted: 2 October 2000     

Using fatty acid analysis to elucidate the feeding habits of Southern Ocean mesopelagic fish

Fatty acid biomarkers were used to investigate the feeding ecology of 17 mesopelagic fish species occurring in the Southern Ocean. Fatty acid signatures of species where little or no dietary information exists were compared to fatty acid signatures of species of known diets in order to elucidate their trophic position. Principal component analysis grouped species of known diets into two clusters with amphipods and copepods comprising the main prey species, respectively. Although the majority of species of unknown diet were grouped with either of these feeding guilds, a third cluster comprising only Gymnoscopelus bolini was identified suggesting a significantly different diet for this species. Electrona antarctica also exhibited significant changes in fatty acid signatures with size. Furthermore, discriminant analysis of the four most abundant species classified species with a 90% success rate thus validating the usefulness of fatty acid signatures when trying to resolve the trophic position of species where no or little dietary information exists.     

Influence of season on the feeding habits of the common sole Solea solea

The object of the study was to determine whether the composition of the diet of sole Solea solea Linnaeus, 1758 throughout the year is influenced only by the presence and abundance of prey or whether in addition it is influenced by a selection procedure resulting from its energetic and nutritional needs. Feeding habits were established by examining the stomach contents of males and females throughout the year. We recorded the presence or absence of each prey item and identified dominant, occasional and accidental prey. Differences in the seasonal composition of the basic diet were analysed (chisquare). Throughout the year, the diet consisted mainly of crustaceans, except in autumn when polychaetes were the most abundant prey. Significant differences (chisquare) in feeding habits were established between seasons and between sexes in each season. Some of the dominant prey (Ampeliscidae and Callianassidae) live exclusively in estuaries and bays, and occur in highest abundance during winter, the season in which sole enter estuaries to spawn. These prey items were present in higher numbers in the stomach contents of the sole during this period, reflecting the dependence of its diet on prey availability.     

Species composition, biomass and vertical distribution of micronekton over the mid-slope region off southern Tasmania, Australia

Seasonal sampling was carried out based on day/night, vertically stratified tows (100 or 125 m strata) in the upper 900 m of the water column over the mid-slope commercial fishing grounds south of Tasmania. A large midwater trawl (105 m² mouth area) was used with an opening/closing cod-end. Subtropical convergence and subtropical species dominated the fauna, but many less abundant, more widely-distributed species were also present. Fishes, which contributed 89% of micronekton biomass and 135 of 178 species, were dominated by the Myctophidae (48% biomass and 48 species). Twenty micronekton species made up 80% of the total biomass. Overall, the micronekton fish biomass in this region was 2.2 g m⁻² wet weight. A pronounced day/night shift in the distribution of biomass was attributable to diel migratory species. During the day, <0.2% of the total micronekton biomass was found in 0 to 300 m; most biomass was below 400 m, with peaks at 400 to 525 m and 775 to 900 m. At night, 53% of the biomass was found in 0 to 300 m, with progressively less in each deeper stratum. The vertical ranges of individual species typically exceeded 400 to 500 m during the day and night and were non-coincident, although nyctoepipelagic migrators were concentrated in the surface 200 m at night. Distinct epipelagic, lower and upper mesopelagic assemblages were identified, and patterns of epipelagic migration, limited migration and non-migration were categorised for species from each of the lower and upper mesopelagic assemblages. The vertical distribution of these assemblages was coincident with the primary water masses: subantarctic mode water (∼250 to 600 m) and antarctic intermediate water (below ∼700 m). The flux of migrating micronekton, estimated at 0.94 to 3.36 g C m⁻² yr⁻¹ to the lower mesopelagic and 1.14 to 4.06 g C m⁻² yr⁻¹ to the upper mesopelagic, appeared to be considerably outweighed by the consumption needs of aggregated mid-slope benthopelagic predators. We suggest that advection of mesopelagic prey in antarctic intermediate water may sustain aggregated populations of orange roughy (Hoplostethus atlanticus) and other predators on the micronekton in mid-slope depths at this site. Received: 2 April 1997 / Accepted: 21 August 1997     

Feeding biology of <Emphasis Type="Italic">Ophiura sarsii</Emphasis> Lütken, 1855 on Banquereau bank and the effects of fishing

Ophiura sarsii was collected in May/June from Banquereau Bank off Nova Scotia, Canada as part of the benthic fauna analyzed in a 2 year clam dredging-impact experiment. In total, 529 O. sarsii specimens were analyzed; 174 (33%) had stomach contents while the rest were empty. Ophiura sarsii is a trophic generalist feeding on at least 31 taxa (52% identified to species) drawn from four phyla: Arthropoda (81.8%), Annelida (13.2%), Mollusca (3%), and Cnidaria (1.5%). However, the diet was largely restricted to two amphipod families (Ampeliscidae and Lysianassidae), accounting for 54–70% of stomach contents at any one sampling period. This diet provides indirect evidence for carnivory. Limited spatial and temporal heterogeneity in the proportion of animals feeding showed no consistent pattern. Where diet composition differed (ANOSIM) it was attributed to the proportion of lysianassid and ampeliscid amphipods consumed. Dredging introduced new dietary items, although diet composition was not significantly altered.