Distribution patterns of larval myctophid fishes in the transition region of the western North Pacific

We examined the species composition and horizontal distribution of myctophid fish larvae in the transition region of the western North Pacific during the early summer. In total, 4,760 myctophid larvae were collected at 44 stations; 18 species of myctophids from 15 genera were collected, and the 8 most abundant species accounted for >95% of larvae. The distribution patterns of these larvae were well defined by the hydrographic structures of the study area including the Oyashio and Kuroshio fronts, the Subarctic Boundary, and a warm core ring. The horizontal distribution patterns of the eight dominant species were categorized into three groups: northern transition water (Stenobrachius nannochir, Tarletonbeania taylori, and Lampanyctus jordani), southern transition water (Symbolophorus californiensis, Diaphus theta, and Nannobrachium regale), and Kuroshio (Myctophum asperum and Diaphus garmani). The Subarctic Boundary defined the distributions of the northern and southern transition-water groups. The importance of areas of western North Pacific transition water as spawning and nursery grounds for subarctic, transitional, and subtropical myctophid fishes was indicated by the relationship between the horizontal distribution patterns of larvae, juveniles, and adults and the physical oceanographic structures.Communicated by T. Ikeda, Hakodate     

Herbivory by the myctophid fish Ceratoscopelus warmingii

During a study of midwater fish feeding in the oligotrophic North Pacific gyre in August 1978, nine specimens of a tropical-subtropical myctophid, Ceratoscopelus warmingii, were found to have been feeding on mats of diatoms, Rhizosolenia spp. Chemical analyses of the intestinal contents of several additional specimens showed significantly elevated levels of diatom degradation products. Therefore, C. warmingii, although known to feed on zooplankton, appears to be adapted for occasional herbivory. Such an adaptation is exceptional within a major ecological group of oceanic fishes that was previously thought to be exclusively carnivorous. Like omnivorous and herbivorous fishes in general, C. warmingii has a longer intestine than other myctophid species. As an adaptive response to competition from a diverse fish fauna in a low-productivity environment, occasional herbivory by C. warmingii runs counter to the theoretical expectation by expanding rather than narrowing the range of potential food types.     

Vertical distribution and feeding patterns of midwater fish in the central equatorial Atlantic

Fishes and zooplankton were obtained (March–April 1979 and partly in August 1974) from 45 hauls taken during the day and at night in the central equatorial Atlantic between Latitude 3°N and 2°S from the surface to 1250-m depth, using the RMT 1+8, a combined opening-closing plankton and micronekton trawl. The vertical distribution of 30 myctophid species is described. All species migrate in a diel pattern, Ceratoscopelus warmingii and Lampanyctus photonotus down to at least 1250 m. During daytime most species aggregated at 400-to 700-m depth, therefore only partly occupying the depth of the Deep Scattering Layer (400 to 500 m at 15 kHz). The feeding patterns of seven of the most abundant species were compared, with a total of 1 905 stomach contents being analysed. All seven species are regarded as opportunistic predators, which feed predominantly during the night on calanoid copepods. A total of 66 species of calanoid copepods were identified among the prey items, with smaller species definitely being in the minority. Stomachs of C. warmingii (700 to 1 250 m depth) and Lepidophanes guentheri (500 to 900 m depth) from daytime samples contained copepod species restricted to the upper 150 m of the water column, including Undinula vulgaris, Nannocalanus minor, and Euchaeta marina, thereby confirming an extended vertical migration of predators. Differences in diet and preferences between species in their total food spectrum are described.     

Interspecific comparisons of growth and diet among late larvae of three co-occurring clupeoid species in the Kii Channel,Japan

Growth and diet were compared among larvae of Japanese anchovy Engraulis japonicus, Japanese sardine Sardinops melanostictus and Pacific round herring Etrumeus teres. Compositions of prey items of the three species in the same month showed greater similarity than for the same species in different months. Prey size as well as prey taxa of the three species overlapped considerably with one another. Therefore, interspecific prey competition is likely in the case of limited food availability. The most abundant species tended to change from anchovy to round herring in early winter, from round herring to sardine in late winter and from sardine to anchovy in early spring, indicating a temporal segregation in use of the nursery grounds. Similar seasonal changes in growth rates were observed for the three species. Although interspecific prey competition is likely, the temporal segregation and similar temporal changes in growth rates could favor their coexistence.     

Interannual fluctuations in acoustic biomass estimates and in landings of small pelagic fish populations in relation to hydrology in the Strait of Sicily

The main results of research work carried out since 1998 with regard to the application of hydro-acoustic technologies for the evaluation of biomass and distribution of small pelagic fish species off the southern coast of Sicily are presented, taking into account information from hydrology and from ecology of the fish populations targeted. The biomass estimates and the population‐density charts presented concern the two main species, i.e. sardine Sardina pilchardus (Walbaum, 1792) and anchovy Engraulis encrasicolus (Linnaeus, 1758). Both the sardine and anchovy populations experienced large inter-annual fluctuations, with biomass estimates ranging from 6000 to over 36,000 tonnes (t) (sardine) and from about 7000 to 23,000 t (anchovy). Acoustic estimates are largely consistent with landings recorded in Sciacca (the main fishing port for small pelagic species in the study area) during the year following the evaluation surveys. In addition, trends in sardine and anchovy biomass estimates appears to be negatively correlated with the mean sea surface temperature calculated over the time intervals January–September (sardine) and June–November (anchovy) of the preceding year, which correspond to larval and juvenile growth periods of target species. Observed patterns would suggest the importance of enrichment processes relevant to the survival of early stages, so determining recruitment success and finally higher population sizes.     

Feeding ecology of five fishes from the mid-slope micronekton community off southern Tasmania, Australia

We examine the feeding ecology of characteristic micronekton species inhabiting the mid-slope region (~700 to 1,500 m depths) off southern Tasmania. Five fishes, Diaphus danae, Hygophum hanseni, Lampanyctus australis (Myctophidae), Phosichthys argenteus (Phosichthyidae) and Chauliodus sloani (Chauliodontidae), were sampled by depth-stratified midwater trawling on a diel and seasonal basis. Overall, 74 prey taxa were identified from 2,132 stomachs. Euphausiids (mostly Euphausia spinifera and E. similis) and calanoid copepods (mostly Pleuromamma species) were the main prey of the three myctophids; P. argenteus ate fishes and decapods in addition to the euphausiids, while C. sloani ate only fishes. Copepods were less important in the diets of larger D. danae, L. australis and P. argenteus and were replaced by euphausiids in the myctophids and by fishes in P. argenteus. In autumn, when euphausiid biomass increased six-fold, all three myctophids and P. argenteus fed most intensively and consumed a high proportion of euphausiids. The three myctophids appeared to feed nocturnally. Differences in the timing and duration of feeding corresponded to differences in their spatio-temporal overlap with key prey. Daily rations of H. hanseni (1.93% dry-weight biomass) and L. australis (1.43%), estimated from data on stomach fullness, were typical for temperate myctophids and higher than that of the non-migratory P. argenteus (0.43%). The vertical flux of near-surface plankton production to the mesopelagic food web is based primarily on diel feeding in the upper water column (<500 m) rather than consumption of species that migrate seasonally into the deeper mesopelagic zone. Because species such as P. argenteus and C. sloani feed above the third trophic level, their predators, including the commercially important orange roughy, are feeding between levels four and five.     

Comparison of the food of Triphoturus mexicanus and T. nigrescens,two lanternfishes of the Pacific Ocean

Prey (chiefly euphausiids and copepods) eaten by two myctophids (lanternfishes) are compared from incidence in fish stomachs and from abundance in the environment. One lanternfish species, Triphoturus mexicanus, lives in the California Current, and the other, T. nigrescens, lives in the central Pacific Ocean. Although these two environments are very different physically and biologically, the feeding habits of the two lanternfishes are surprisingly similar. Prey biomass is 94% euphausiids, 3% copepods, and 3% other organisms for T. mexicanus and 88% euphausiids, 4.5% copepods, and 7.5% other organisms for T. nigrescens; the difference between the fish species is not significant when tested statistically. The two fishes resemble one another in frequency distributions of ingested copepod individuals, copepod species, euphausiid individuals, and euphausiid species. During a single diurnal feeding period, both fishes eat a variety of copepod species but tend to eat only a single species of euphausiid. T. mexicanus grows to twice the length of T. nigrescens and eats proportionally larger euphausiids; however, both fishes eat copepods having the same median size. The frequencies of euphausiid species in the diets of both fishes differ from the frequencies in the environment. The chief differences between the feeding habits of the two lanternfishes are that T. nigrescens, in comparison to its congener, eats a greater variety of organisms during one diurnal feeding period and captures smaller euphausiids. The feeding patterns for each lanternfish species are consistent over distances of hundreds of kilometers and over many years of sampling.     

Resource-partitioning and predation impact of a low-latitude myctophid community

This study, based on data collected during summer 1985 in the eastern Gulf of Mexico, examined the degree of overlap in two prime niche parameters, space and food, in 17 of the most abundant myctophid species which inhabit the epipelagic zone at night. Cluster-analyses of vertical distribution information and diet characteristics revealed that while large groups of species overlapped (>60%) in either vertical distributions or diet, when both niche parameters were considered together, little interspecific or intraspecific (size class) overlap occurred. Our data suggest that for myctophids trophic competition is reduced through resource-partitioning, although with considerable overlap at niche boundaries. Niche separation presumably is the result of competition during the evolution of the ecosystem and is maintained presently as diffuse competition: the effect on a species of the combined competition from all other species at that trophic level. We suggest that the large degree of niche overlap enables the packing of over 50 myctophid species in the epipelagic zone at night. Our calculations indicate that myctophid predation nightly removes 2% of the zooplankton biomass. Myctophid predation is selective in that greatest pressure is on certain size classes and types of prey (copepods, ostracods and euphausiids). In the case of copepods, impact is greatest on the larger, more mature stages and hence on the breeding population. It is estimated that myctophids account for at least one-third of the daily production of zooplankton removed from the epipelagic zone by micronekton in the eastern Gulf.     

Comparative studies on the metabolism of shallow-water and deep-sea marine fishes. I. White-muscle metabolism in shallow-water fishes

Maximal rates of oxygen consumption in vitro have been measured under standardized conditions at three test temperatures (5°, 15°, and 25°C) on minced preparations of white muscle from 39 species of shallow-water marine teleost fishes. These fishes came from four different geographic areas, two with cool average water-temperatures (near 15°C: coastal southern California, Galápagos Islands) and two with warm average water-temperatures (near 25°C: Hawaiian Islands; Bermuda). The group includes species covering much of the range of variation to be found among the teleosts with respect to five additional variables: phylogenetic position, type of environment, body weight, activity level, and growth stage. The purpose of the work is to provide part of a base line of tissue-metabolism data on shallow-water fishes for comparison with similar results from deep-sea species. Major conclusions from statistical analyses of the results are: four groups of shapes of oxygen-uptake rate versus temperature curves exist: normal, flat, dipped and peaked. Over 50% of curves are normal. Intra-group differences, contributing significantly to the total variance of the results at given test temperatures, are: cool versus warm average environmental temperatures primarily for epipelagic species; epipelagic versus non-epipelagic environments; very active species versus all others; juvenile stages versus adults. In each case, the subgroup first mentioned shows higher muscle oxygen-uptake rates than the other subgroup. Variables not contributing significantly to the total variance are phylogenetic position and body weight. Physiological and ecological implications of these results are discussed.     

Fatty acid evidence for the importance of myctophid fishes in the diet of king penguins, Aptenodytes patagonicus

We tested the usefulness of the fatty acid signature-method in investigating the diet of seabirds in conjunction with the conventional technique of stomach-content analysis. We compared the fatty acid composition of subcutaneous white adipose tissue (SWAT) of king penguin chicks (Aptenodytes patagonicus) during fattening periods to that of total lipids from their food. In both spring and autumn, the fatty acid composition of chick SWAT was identical to that of the dietary lipids. Because the diet of adult king penguins feeding for self-maintenance (i.e. not for their chicks) was essentially unknown, we subsequently analysed their SWAT fatty acid patterns after premolting and prebreeding foraging trips (during which they build up large energy reserves). The fatty acid composition of SWAT from adults was identical to that of chick adipose tissue and food. King penguin diet and SWAT were characterized by high levels of very long-chain mono-unsaturated fatty acids (20 to 24 carbon atoms, 16 to 23% by mass) and (n-3) poly-unsaturated fatty acids (19 to 27%); these consisted mainly of 20:1n-9 (5 to 8%) and 22:1n-11 (5 to 8%), and 22:6n-3 (10 to 13%) and 20:5n-3 (3 to 9%), respectively. Prey items identified from chick stomach contents indicated that the bulk of the food was oceanic myctophid fishes, mainly Electrona carlbergi, Krefftichthys anderssoni and Protomyctophum tenisoni. The fatty acid composition of four other species of myctophid fishes was similar to that of penguin diet and SWAT, but markedly different from that measured for a squid species and that reported for crustaceans. These findings indicate that adult king penguins prey on myctophid fish not only to feed their chicks but also for their own nutrition. The fatty acid signature-technique is therefore a reliable method to gain information on the food and feeding ecology of seabirds when more conventional techniques are of limited value. Such information is important to the understanding of trophic relationships between key species of the ecosystems, and also to provide insight into the nature of avian adaptations to the marine environment. Received: 11 December 1997 / Accepted: 25 July 1998     

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.     

Size matters: variation in the diet of chick and adult crested terns

We investigated ontogenetic, temporal and spatial patterns in the composition and size of prey in the diet of crested terns, Sterna bergii. Diet analyses indicated that crested terns are a generalist predator on surface-schooling clupeids (Australian anchovy Engraulis australis, sardine Sardinops sagax and blue sprat Spratelloides robustus), Degens leatherjacket Thamnaconus degeni, southern sea garfish Hyporhamphus melanochir, Australian herring Arripis georgianus, slender bullseye Parapriacanthus elongatus and barracouta Thyrsites atun. Ontogenetic differences in prey size indicated that adults are constrained in their foraging behaviour during the early chick-provisioning period by the need to self feed and select smaller prey that can be ingested by their chicks. Chicks consumed significantly higher proportions of clupeids than adults, which consumed mainly Degens leatherjackets and barracouta, suggesting that adults may select higher quality prey for their chicks compared to what they consume themselves. Spatial differences in prey composition were driven by differing proportions of sardine, Australian anchovy and Degens leatherjacket and could reflect local differences in the abundances of these prey. The size of prey taxa consumed by adults also reflected a North–South gradient in prey size. The large component of juvenile sardine in the diet of crested terns suggests future dietary measures may inform fisheries managers about changes in local juvenile sardine abundance. These data could assist in highlighting any fishery-related decreases in sardine recruitment and help ensure commercial fishing practices address principals of Ecologically Sustainable Development developed for Australian fisheries.     

Foraging behavior of a generalist marine top predator,Japanese cormorants (<Emphasis Type="Italic">Phalacrocorax filamentosus</Emphasis>), in years of demersal versus epipelagic prey

To examine the behavioral adjustment of a generalist marine top predator to variability of their prey, we studied the foraging behavior of Japanese cormorants (Phalacrocorax filamentosus) breeding at Teuri Island, Hokkaido, in years of contrasting demersal and epipelagic prey composition. We used radio telemetry and ship-based surveys to determine behavior and at-sea distribution during three summers (1996–1998). The cormorants fed on epipelagic anchovy (Engraulis japonicus) and sandlance (Ammodytes personatus) in 1998 (year of epipelagic diet), while they fed on benthic rock fish (Sebastes spp.) and flatfish (Pleuronectidae) and nearshore-living naked sandlance (Hypophychus dybowskii), as well as epibenthic greenling (Hexagrammidae) in 1996 and 1997 (year of demersal diet). Cormorants engaged in larger feeding groups, visited more feeding sites, and stayed at each feeding site for a shorter period in the year of epipelagic diet than in the years of demersal diet. The cormorants made long foraging trips and fed in the mainland coastal habitat, distant from the colony, in the years of demersal diet. Individual radio-tracked birds fed over the wide area between the islands and mainland, in the year of epipelagic diet, while most individuals specialized in mainland or island coastal habitats in the years of demersal diet. Behavioral adjustment of Japanese cormorants might allow them to exploit both unpredictable epipelagic and predictable benthic prey efficiently.Communicated by T. Ikeda, Hakodate     

Apparent predation on ichthyoplankton by zooplankton and fishes in nearshore waters of southern California

Plankton collected at discrete depths in Santa Monica Bay, California, USA, during January 1982 were examined for fish eggs and larvae that had been attacked or consumed by zooplankton. The bongo net remained open for only 3 min and samples were preserved within 5 min of capture. Juvenile and adult fishes that had been captured by otter trawl and preserved within 20 min of capture were examined for ingested fish eggs and larvae. Three copepods (Corycaeus anglicus, Labidocera trispinosa, and Tortanus discaudatus), one euphausid larva (Nyctiphanes simplex), one amphipod (Monoculoides sp.), and an unidentified decapod larva were found attached to fish larvae in the preserved plankton samples (attachment to 23% of the fish larvae was observed in one sample). Overall, about 5% of the white croaker (Genyonemus lineatus) larvae and 2% of the northern anchovy (Engraulis mordax) larvae had attached zooplankton predators. Most fish larvae with attached zooplankton predators were small. We found no indication of zooplankton predation on fish eggs. Few fish eggs and larvae were found in the digestive tracts of juvenile or adult fishes, and the ingested fish larvae were relatively large. The discussion considers apparent preyspecificity of the zooplankton predators as well as potential biases that may be associated with preserved samples collected by nets.     

Structure and function of the stomachless digestive system in three related species of New World silverside fishes (Atherinopsidae) representing herbivory, omnivory, and carnivory

We explored possible diet-related specializations in the digestive tract of stomachless fishes by summarizing the diets, verifying the absence of a stomach, and comparing gut lengths, microvilli surface areas, and activities of five digestive enzymes in four taxa of silversides from southern California coastal waters. For the comparisons, we examined these gut features in Atherinops affinis from both estuarine and kelp-forest habitats, and Atherinopsis californiensis and Leuresthes tenuis from open coastal habitats. A. affinis was found to be primarily herbivorous in estuaries and carnivorous in kelp forests, whereas As. californiensis was shown to be somewhat omnivorous but mainly carnivorous, and L. tenuis strictly carnivorous. Estuarine A. affinis exhibited the longest gut, largest microvilli surface area, and highest amylase and maltase activities, all arguably reflecting responses to an algal diet. In contrast, kelp-forest A. affinis displayed the highest trypsin activity and generally similar microvilli surface areas and aminopeptidase, amylase, and maltase activities to the two other carnivorous taxa. All four taxa showed similar lipase activities that compared closely with published values for other fishes. Taken together, our results reveal striking differences in gut structure and function among the four taxa, but especially between the estuarine and kelp-forest populations of A. affinis. Further studies are required to assess the roles of genetic variation and phenotypic plasticity in explaining the differences in these herbivorous and carnivorous taxa.     

Comparative studies on the metabolism of shallow-water and deep-sea marine fishes. II. Red-muscle metabolism in shallow-water fishes

Maximal rates of oxygen consumption in vitro have been measured under standardized conditions at three test temperatures (5°, 15°, 25°C) on minced preparations of red muscle from 10 species of shallow-water marine teleost fishes. These fishes came from three different geographic areas, two with cool average water temperatures (near 15°C: coastal southern California, Galápagos Islands) and one with warm average water temperatures (near 25°C: Hawaiian Islands). The group is made up of post-juvenile or adult epipelagic fishes, which are moderately or very active in terms of their locomotor activities. A large part of the range of phylogenetic diversity among the teleosts is represented, as is the body weight range from a few grams to several kilograms. The purpose of the work is to provide part of a set of tissue-metabolism data on shallow-water fishes for future comparison with similar results from deep-sea species. Of 8 complete curves for oxygen uptake rate versus temperature (R-T curves), 6 are normal in shape (Q₁₀1.5), 1 is normal but with a low Q₁₀, and 1 is partly flat, partly normal. The differences between the species in terms of both absolute positions and slopes of the R-T curves are not related in any consistent way to any of the three testable variables: phylogenetic position, long-term adaptation temperature, and body size. The red muscles of a variety of adult epipelagic fishes, at ecologically realistic temperatures, are shown to be exceptions to the general rule that tissues of ectothermous lower vertebrates have lower metabolic rates than comparable tissues of non-torpid endothermous higher vertebrates. This circumstance probably is a major factor in the great capacities for sustained high-speed swimming shown by most epipelagic fishes. Other physiological and ecological implications of the results are discussed.     

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.     

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.     

Trophic ecology of the stomiid (Pisces: Stomiidae) fish assemblage of the eastern Gulf of Mexico: Strategies,selectivity and impact of a top mesopelagic predator group

The trophic ecology of the stomiid assemblage (Pisces, Stomiiformes, Stomiidae) in the eastern Gulf of Mexico, a region with physical and biological characteristics typical of oligotrophic low-latitude regimes, was investigated. Over 1400 specimens representing 69 species and 17 genera were examined. Four patterns of feeding were evident among the abundant stomiids: (1) myctophid predation; (2) zooplankton/small micronekton predation; (3) penaeidean shrimp predation; and (4) copepod/micronekton predation. One rare species preyed on cephalopods. Il was concluded that stomiids exhibited a high level of prey-selectivity, particularly considering the broad range of prey types available in the eastern Gulf of Mexico. The absence of numerically dominant potential prey (e.g.Cyclothone spp., sternoptychids) in the diets of piscivorous stomiids is possibly a function of feeding periodicity coupled with stomiid vertical migration. Stomiids may feed at night in the upper 200 m on vertically migrating myctophids while disregarding co-occurring nonmigrating prey during the daytime. Integration of stomiid abundance and diet data suggests that: (1) stomiids are the dominant upper trophic-level predators of the Gulf of Mexico mesopelagial, (2) stomiids inflict the highest predation impact on myctophids in low-latitude midwater ecosystems, and (3) the historic use of predation-avoidance arguments to explain certain mesopelagic phenomena (e.g. vertical migration, ventral photophores) appears to be substantiated by estimates of stomiid predation-impact. The stomiids may serve as key trophic mediators in the transfer of energy from the mesopelagial to the bathyand benthopelagial.     

Recherches sur la situation trophique d'un groupe d'organismes pélagiques (Euphausiacea). V. Relations avec les thons

The examination of stomach contents of large subsurface tunas caught by long-line fishing, as well as of those of micronektonic fishes which they had eaten, allows us to assess the role played by euphausiids in food webs concerning these fishes. Long-line tunas do not utilize euphausiids as food because, in the tropical Pacific Ocean, their feeding activity is restricted to light hours, i.e., to a time when large euphausiids which could serve as potential prey, occupy deeper (below 400 m) water layers. Euphausiids constitute approximately 10% of the total food ingested by epipelagic micronektonic fishes which, in turn, are preyed upon by tunas; these fishes, measuring usually 30 to 60 mm in total length, are fast swimmers and are rarely collected by pelagic trawls. Among this ichthyofauna, the main predators of euphausiids appear to be Gempylidae (Diplospinus multistriatus), Paralepididae, and Bramidae (Collybus, Taractes, Pteraclis). Euphausiids ingested by these fishes chiefly belong to the genera Stylocheiron (64%) and Nematoscelis (15%). This means that the fishes which serve as prey for tunas are able to utilize for food only organisms which inhabit subsurface (0 to 400 m) layers during daytime and not those (Euphausia, Thysanopoda) which remain at this time in the deeper layers and rise to the subsurface only at night. Therefore, these fishes, like tunas themselves, appear to display their main feeding activity in the 0 to 400 m water layer and during daytime.