Diet composition and foraging ecology of U.S. Pacific Coast groundfishes with applications for fisheries management

Determining the prey composition and foraging habitats of U.S. Pacific Coast groundfishes are specified management directives that have not received much scientific attention. To address this knowledge gap, we conducted a meta-analysis of the feeding ecology of 18 commercially important species and their life stages during a recent review of Pacific Coast groundfish essential fish habitat. A Major Prey Index was developed to evaluate relative importance among 47 prey taxa. Based on this metric, unidentified teleosts, euphausiids, and brachyuran crabs were the most important prey groups. When 14 generalized prey categories were used, fishes represented the dominant taxon (mean % weight or volume = 32.3) followed by shrimps (11.5), crabs (10.0), and euphausiids (9.5). PERMANOVA results indicated that species-specific differences were the primary source of dietary variability among tested variables (life stage, functional group, taxonomic group). Pacific Coast groundfishes mainly were characterized as mesopredators with estimated trophic levels ranging from 3.4 to 4.2. Foraging habitats differed significantly among functional (benthic, demersal, pelagic) and taxonomic (elasmobranch, roundfish, rockfish, flatfish) groups. Using hierarchical agglomerative cluster analysis, we identified a significantly distinct trophic guild that consumes mainly polychaetes and hard-shelled molluscs (juvenile, juvenile–adult Dover Sole; juvenile–adult English Sole) and another that specializes on euphausiids (juvenile Pacific Hake; juvenile–adult Darkblotched Rockfish). Our findings filled substantial data gaps in the trophic ecology and habitat-based management of commercially important species and can be used to inform future reviews of Pacific Coast groundfish essential fish habitat.     

The ecological significance of the zooplanktivores, snipefish Macroramphosus spp. and boarfish Capros aper, in the food web of the south-east North Atlantic

The diets of slender snipefish Macroramphosus gracilis, longspine snipefish Macroramphosus scolopax and boarfish Capros aper, three very abundant species on the Portuguese coast, were studied from samples collected between July 2002 and April 2003. Variations in the diet with fish size, season and area, as well as diet overlap and diversity, are explored in this study. The diets of slender snipefish and boarfish were mainly composed of copepods, with the main prey being Temora spp. and Calanus spp., respectively. Mysid shrimps were the most important food item in the diet of longspine snipefish. During the summer season, when the availability of different prey items was highest, the two species of snipefish and the boarfish fed on different prey. Temora spp. were the most important prey in the stomachs of slender snipefish in the summer on the south‐west coast, while Calanus spp. started appearing in the stomachs of boarfish in the spring in the north, increasing their abundance in the summer on the south and south‐west coasts. The abundance of mysids appeared to increase in the autumn on the south‐west coast, being at that time an important food item for both longspine snipefish and boarfish. For slender snipefish and boarfish, the differences in stomach species diversity were explained firstly by the season and then by the area and fish size. For longspine snipefish, the area did not explain the species diversity variability, season being the first variable determining the differences. Of all three species, slender snipefish was the one with highest diversity of stomach contents, particularly in spring and summer on the north and south‐west coasts. Diet overlap between species was very low. No predation on eggs and larval stages of fishes was found for any of these fish species. This work is the first to address the diets of snipefish species and boarfish in the south‐east North Atlantic, in a large spatio‐temporal coverage. These species are important prey for many commercial species on the Portuguese coast and, given their abundance, may have a great impact on zooplankton communities, thus assuming a pivotal position in marine food webs.     

Seasonal, diel and ontogenetic variation in feeding patterns of small yellow croaker in the central Yellow Sea

Stomach contents of 1603 small yellow croaker Pseudosciaena polyactis , sampled from seasonal bottom trawl surveys in the central Yellow Sea between March 2001 and January 2002, were examined. The results showed that small yellow croaker was a carnivorous predator and >30 prey species were identified from stomach contents analysis. Crustaceans (mainly euphausiids and decapods) were the most important prey, occurring in 93·1% of the stomachs containing food, and accounting for 77·6% of the total food by mass. Feeding activity was highest in autumn and lowest in spring and winter. Decapods were more important in summer, whereas euphausiids were more important during other seasons. Ontogenetic differences were found in the diet composition and feeding activity within the range of size (standard length, L _S) studied. The importance of fishes and decapods increased with L _S, whereas euphausiids, copepods and amphipods decreased in importance with L _S. Dietary breadth increased markedly for adults. A positive relationship was found between L _S and prey size. In each season the maximum diel feeding activity occurred at 0800 and 2400 hours, indicating that there was crepuscular and nocturnal feeding by small yellow croaker.     

Diet and feeding strategy of blackmouth catshark Galeus melastomus

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

VARIABILITY IN THE DIET OF HARBOR PORPOISES (PHOCOENA PHOCOENA) IN SCOTTISH WATERS 1992–2003

Interannual, seasonal, and regional variation in the diet of porpoises, Phocoena phocoena , in Scottish (UK) waters was studied using stomach contents of animals stranded between 1992 and 2003. Most samples came from the east coast (including many porpoises killed by bottlenose dolphins), with smaller numbers from the west coast and from Shetland. The most important prey types, in terms of contribution by number and mass, were whiting ( Merlangius merlangus ) and sand eels (Ammodytidae). Multivariate analysis confirmed the existence of regional, seasonal, and interannual variation in diet, as well as differences ( i. e. , biases) related to cause of death. These differences were further explored using univariate analyses. Sand eels were more important in the summer months (quarters 2 and 3) and on the east coast, whereas gadids were more important in winter and in the Shetland area. Some, but not all, observed trends in the numerical importance and size of prey taken were consistent with trends in abundance and size of fish taken during research trawl surveys. There was some evidence that porpoises <1 yr old took more gobies (Gobiidae) and shrimps than did older porpoises. Clupeids (herring Clupea harengus and sprat Sprattus sprattus ) formed a relatively small proportion of the diet, but their importance varied from year to year. Although possible methodological biases prevent firm conclusions, it appears that the importance of clupeids in porpoise diet may have decreased since the 1960s, mirroring the decline in North Sea herring abundance. The recovery of the North Sea herring stock in recent years is not as yet reflected in porpoise diet.     

The diet of whiting Merlangius merlangus in the western Baltic Sea

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

Trophic ecology of the emerald notothen <Emphasis Type="Italic">Trematomus bernacchii</Emphasis> (Pisces,Nototheniidae) from Terra Nova Bay,Ross Sea,Antarctica

The trophic ecology of the emerald notothen Trematomus bernacchii was investigated using a sample of 284 specimens collected in the coastal waters of Terra Nova Bay (Ross Sea) during the summer season 1990–1991. The stomach-content analysis provided data on feeding habits and trophic niche breadth. Overall, 72 taxa of food items were identified; the most important as prey were infaunal and epifaunal polychaetes, amphipods and molluscs. Food of secondary importance comprised isopods, pycnogonids, fish and fish eggs. Several other taxa, such as euphausiids, mysids, decapods, echinoids, holothurians, priapulids and thaliaceans constituted food eaten in very small amounts and only occasionally. On the basis of their diet, T. bernacchii can be considered generalized feeders, with a wide niche breadth composed almost exclusively of benthic organisms. A cluster analysis was conducted to compare stomach-content data of subsamples selected on the basis of fish size and sampling depth, aiming to determine diet diversity and niche breadth, as well as factors involved in reducing intraspecific competition for food resources. Diet was different for fish sampled in shallow (90 m depth) and deeper waters (>90 m depth): while the first group fed mostly on bivalves (Adamussium colbecki) and amphipods, the latter preferred infaunal-epifaunal polychaetes. Conversely, fish size did not contribute significantly to diet diversification. According to our data and published data on feeding behaviour and sensory ecology, we conclude that in this species the intraspecific competition for food is reduced, either through habitat heterogeneity or different foraging strategies.     

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

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

Food habits of the longnose skate, <Emphasis Type="Italic">Raja rhina</Emphasis> (Jordan and Gilbert, 1880), in central California waters

Feeding studies can provide researchers with important insights towards understanding potential fishery impacts on marine systems. Raja rhina is one of the most common elasmobranch species landed in central and northern California demersal fisheries, yet life history information is extremely limited for this species and aspects of its diet are unknown. Specimens of R. rhina were collected between September, 2002 and August, 2003 from fisheries-independent trawl surveys. Percent Index of Relative Importance values indicated that the five most important prey items in 618 stomachs of R. rhina were unidentified teleosts (31.6% IRI), unidentified shrimps (19.6% IRI), unidentified euphausiids (10.9% IRI), Crangonidae (7.4% IRI), and Neocrangon resima (6.0% IRI). There were significant dietary shifts with increasing skate total length and with increasing depths. Smaller skates ate small crustaceans and larger skates ate larger fishes and cephalopods. With increasing depths, diet included bentho-pelagic teleosts and more cephalopods and euphausiids. The findings of this study are consistent with previous researchers that report similar diet shifts in skate species with size and depth.     

Spatial variation in abundance of prey and diet of trumpeter (Pelates sexlineatus: Teraponidae) associated with Zostera capricorni seagrass meadows

Abstract The diet of juveniles of Pelates sexlineatus was examined at six estuaries, separated by tens to hundreds of kilometres, and two sites within each estuary, separated by hundreds of metres to kilometres. Fish were collected in Zostera capricorni seagrass meadows along the coast of New South Wales (Australia). Spatial variability in diet was compared with the abundance of prey. Pelates sexlineatus had a broad diet (27 different prey) but generally preferred crustaceans (harpacticoid copepods, gammarid amphipods, ostracods and tanaids), although at some sites other prey items were important (e.g. polychaetes, nematodes and foraminiferans). Composition of the diet varied among estuaries and between sites. Proportional representation of the different size of prey eaten by the three sizes of juveniles (40‐ 54 , 55–74 and 75–94 mm standard length) was similar. Fish generally preferred prey smaller than 1 mm. Abundance of prey also varied at both spatial scales. At five of the 12 sites, there was a significant correlation between abundance of prey in the seagrass meadows and abundance of prey in the diet. Variation in the composition of the diet was partly explained by spatial variation in abundance of prey. When crustaceans were not abundant in the seagrass, P. sexlineatus had a broad diet, taking both benthic and planktonic prey items. It is concluded therefore that trophic linkages between P. sexlineatus and benthic invertebrates may vary greatly with spatial scales from hundreds of metres to hundreds of kilometres, and are strongly related to availability of prey in seagrass habitats.     

Seasonal variation in the diet of Redshank Tringa totanus in the Odiel Marshes,southwest Spain: a comparison of faecal and pellet analysis

Capsule Redshank diet from southern Europe during migration shows spatial and seasonal variations.

Aims To assess seasonal variation in Redshank diet at a major passage site, and to compare data derived from analysing pellets or faeces.

Methods At the Odiel Marshes in 2001, pellets from spring migration (39), autumn migration (121) and midwinter (15) were analysed, together with faecal samples from autumn (84).

Results The abundance of different invertebrate groups in pellets varied between seasons. In spring, Chironomus salinarius pupae and larvae dominated by volume, followed by Ephydridae larvae and the beetle Paracymus aenus. Polychaetes and molluscs dominated in autumn, and isopods in midwinter. In autumn, chironomid larvae, Mesembryanthemum nodiflorum seeds and Artemia cysts were relatively more abundant in faeces, whereas polychaetes, isopods, molluscs and cestode cysticercoids were more abundant in pellets. Harder and/or larger items were thus relatively more abundant in pellets than faeces. Pellet analysis gave more emphasis to mudflat prey, and faeces to saltpan prey.

Conclusion Pellet and faecal analysis give different results for wader diet, and it is useful to combine the two methods. However, they show significant correlations both in diet range and rank abundance of prey items. Redshank diet shows much seasonal and spatial variation in southern Europe.     

东海北部大管鞭虾的食性

根据对2009年6月至2010年5月在东海北部采集到的720尾大管鞭虾胃含物的分析,对不同季节、性别、个体大小以及发育条件下大管鞭虾的摄食习性进行了研究.结果表明: 东海大管鞭虾的饵料生物共有43种(包含未鉴定种),甲壳类、有孔虫类和多毛类为其主要的摄食群类,在食物中所占的数量百分比分别为34.7%、29.4%和12.4%.大管鞭虾的饵料组成具有明显的季节波动,春季以有孔虫、藻类和无脊椎卵为主要食物;夏、秋季以有孔虫、鱼类和多毛类为主要食物;冬季则以多毛类和有孔虫类为主要食物.其摄食强度在春季和夏季较高,秋季较低.不同甲长的个体食性变化显著,小于24 mm的个体主食有孔虫类和藻类,24 mm以上的个体主食有多毛类和十足类;随着性腺发育雌性个体摄食等级呈现减弱的趋势,表明大管鞭虾摄食活动受到繁殖周期的影响.不同性别和不同季节大管鞭虾的食物重叠指数均较高,与栖息环境饵料资源的波动有关.大管鞭虾的营养级为2.67,属低级肉食性动物.     

东海北部大管鞭虾的食性

根据对2009年6月至2010年5月在东海北部采集到的720尾大管鞭虾胃含物的分析,对不同季节、性别、个体大小以及发育条件下大管鞭虾的摄食习性进行了研究.结果表明: 东海大管鞭虾的饵料生物共有43种(包含未鉴定种),甲壳类、有孔虫类和多毛类为其主要的摄食群类,在食物中所占的数量百分比分别为34.7%、29.4%和12.4%.大管鞭虾的饵料组成具有明显的季节波动,春季以有孔虫、藻类和无脊椎卵为主要食物;夏、秋季以有孔虫、鱼类和多毛类为主要食物;冬季则以多毛类和有孔虫类为主要食物.其摄食强度在春季和夏季较高,秋季较低.不同甲长的个体食性变化显著,小于24 mm的个体主食有孔虫类和藻类,24 mm以上的个体主食有多毛类和十足类;随着性腺发育雌性个体摄食等级呈现减弱的趋势,表明大管鞭虾摄食活动受到繁殖周期的影响.不同性别和不同季节大管鞭虾的食物重叠指数均较高,与栖息环境饵料资源的波动有关.大管鞭虾的营养级为2.67,属低级肉食性动物.     

Distribution of antarctic zooplankton around Elephant Island during the austral summers of 1988, 1989, and 1990

Year to year variation and vertical distributions of epipelagic Zooplankton around Elephant Island and King George Island were examined with samples collected with bongo nets and a 1 m² MOCNESS during the austral summers (Jan–Feb.) of 1988, 1989 and 1990. Copepods were the major components of epipelagic Zooplankton (in numbers) with dominance of Metridia gerlachei (1988 and 1989) and small calanoids and cyclopoids (1990). Euphausiids and salps were the next most abundant groups. The percent composition of euphausiids decreased from 1988 to 1990 while that of salps increased. The abundance of salps exceeded euphausiids and major taxa of copepods in 1990. Local patches of polychaetes and amphipods were also found. Statistically significant annual variations with increased numbers in 1990 were found by analyses of variance in total abundance, abundances of copepods, salps, chaetognaths and amphipods, but abundances of euphausiids, polychaetes and fishes showed no significant annual variations. When the study area was divided geographically, horizontal variability in abundance within each year showed no significance in total abundance, abundances of copepods, euphausiids, amphipods and fishes, but significance in salps, polychaetes and chaetognaths. Results of site clustering based on covariances of abundances of eleven major taxa were well matched, though not perfect, with the distribution of surface water temperatures which could be used as a tracer of source water masses suggesting that spatial variation was related to hydrodynamic conditions. Factor analyses showed that annual and spatial variations in abundance were mainly caused by only two taxa, Metridia gerlachei and salps (mostly Salpa thompsoni). These two taxa were responsible for about 60% and 30% of total variance, respectively, and were useful indicators of the interannual variation. That is, 1988 and 1989 were the years of M. gerlachei, and 1990 was the year of salps. From vertically stratified MOCNESS samples, it was shown that the major taxa in this study area were active vertical migrators. While most samples obtained by relatively shallow tows (uppermost 100 m depth) were composed of exclusively one or two taxa, those from relatively deep tows (down to 200 m) showed various patterns of vertical stratification suggesting that the patterns of vertical migration were species specific. Species specific ontogenetic vertical migration associated with elevated habitat temperatures also seemed to be responsible for the annual variation in zooplankton distribution in the upper water column.     

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

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

Regional and temporal variation in diet and provisioning rates suggest weather limits prey availability for an endangered raptor

Understanding variation in food requirements of wild animals is of central importance in population ecology and conservation, as it helps to identify where and when food may be limiting. Studies on diet variation or prey provisioning rates may give useful insights when direct information on prey availability is lacking. We assess spatial and temporal variation in the diet of an endangered predator, the Black Harrier Circus maurus. This raptor is endemic to southern Africa and specializes on small mammals but also feeds on birds and reptiles as alternative prey. Using data on 1679 prey identified in 953 pellets collected in inland and coastal regions from 2006 to 2015, we show that diet composition changed little throughout the breeding season in the coastal region, whereas there was a marked seasonal decline in the occurrence of small mammal prey in the inland region, with a concomitant increase in alternative prey. The proportion of small mammals in the diet declined with increasing maximum temperature, the latter being highest at the inland region late in the breeding season. Using camera recordings at nests in 2014, we further analysed daily patterns of prey provisioning to nestlings. A marked reduction in small mammal provisioning rates occurred during the middle of the day in the hotter inland region but not in the cooler coastal region. Reduced availability of the primary prey, small mammals, in hotter conditions, through a reduction in activity or overall abundance, could explain these patterns. Finally, we show a positive relationship between winter rainfall and interannual differences in the proportion of small mammals in the diet of Black Harriers breeding in the coastal region, suggesting relationships between diet and prey abundance that are mediated through rainfall. We discuss the need to consider spatial variation in food availability in conservation strategies.     

Food and Feeding Habits of Flounder <Emphasis Type="Italic">Paralichthys Orbignyanus</Emphasis> (Jenyns, 1842) in Bahía Blanca Estuary,Argentina

Specimens of flounder Paralichthys orbignyanus (Jenyns, 1842) were collected in Bahía Blanca estuary between February 1997 and January 1998, and their feeding habits were examined in relation to season and size class. The stomach contents of 823 specimens, ranging from 70 to 875 mm total length, were analysed. Their diet included organisms from 17 taxa. The highest vacuity index values were found during autumn and winter. The stomach fullness index indicated that flounders increased their feeding activity between October and March, reaching a highest point in February and decreasing after February. Fish were the primary prey item in frequency, number and weight, followed by crustaceans, such as shrimps and crabs. A seasonal and size class variation was detected in the diet. During summer all-size flounders consumed mainly fish. In autumn, for all-size classes the main food were fish and crustaceans even though fish were dominant in terms of biomass. In spring, crustaceans (mysids Arthromysis magellanica (Cunningham), shrimps Artemesia longinaris Bate, and prawns Pleoticus muelleri (Bate)) were the dominant prey in terms of number and biomass for flounders ≤ 450 mm TL. Size classes larger than 451 mm TL fed on crustaceans and fish though the most important prey item in terms of biomass was fish. In Bahía Blanca estuary,P. orbignyanus evidenced mainly an ichthyophagou – carcinophagous diet. The results collected from the present study lead to conclude that P. orbignyanus shows, in this region, a clear preference for fish.     

Ontogenetic and spatiotemporal variability in anchoveta Engraulis ringens diet off Peru

In this study, historical data available since 1954 were used to get new insight to ontogenetic and spatiotemporal variability in Peruvian anchovy or anchoveta Engraulis ringens diet. Whatever the period, E. ringens foraged mainly on macrozooplankton and the importance of euphausiids in E. ringens diet appears directly related to euphausiids abundance. This bottom‐up effect is also observed at smaller scale because the euphausiids fraction increased with E. ringens total length and euphausiids accessibility. Selecting the largest prey, the euphausiids, provides an energetic advantage for E. ringens in its ecosystem where oxygen depletion imposes strong metabolic constraints on pelagic fishes. This study illustrates the plasticity of E. ringens that allows it to cope with its highly variable environment.     

On the food of the European eel, Anguilla anguilla (L.), in the upper zone of the Tagus estuary, Portugal

The estuarine food habits of the European eel, Anguilla anguilla (L.), in the upper zone of the Tagus estuary have been studied through the analysis of 210 specimens collected during 1988. Eels, measuring from 136 to 627 mm in total length, fed on prey organisms ranging from 2.0 to 76.0 mm in length. Amphipods and the shore crab, Carcinus maenas (L.), were the most important food items found. In more saline muddy bottom areas polychaetes, bivalves and shrimp increased their importance as prey, replacing the amphipods as preferential food. Fish were always a secondary, although significant, prey item. The occurrence of seasonal variations in eels' diet could be attributed to fluctuations in prey densities. There was evidence of a close relationship between the quantity of prey organisms in the benthos and the composition of eels' stomach contents, but a certain degree of food selection based on size, concealment capacity and motility of prey, was found.     

Comparative Feeding Ecology of Two Sympatric Greenling Species, <Emphasis Type="Italic">Hexagrammos otakii</Emphasis> and <Emphasis Type="Italic">Hexagrammos agrammus</Emphasis> in Eelgrass <Emphasis Type="Italic">Zostera marina</Emphasis> Beds

Synopsis Feeding ecology was compared between sympatric greenling species, Hexagrammos otakii and H. agrammus in the eelgrass beds in Jindong Bay, Korea, from January to December. These two species had similar diets composed of crustaceans, polychaetes, gastropods and fishes; both species consumed primarily crustaceans throughout study periods. H. otakii, however, fed a greater proportion of polychaetes and fishes than H. agrammus. H. agrammus had a greater proportion of gastropods in their diets. The diet of both species underwent size-related changes; smaller individuals of H. otakii and H. agrammus consumed amphipods (gammarid amphipods and caprellid amphipods), while larger individuals of H. otakii ate polychaetes and fishes and those of H. agrammus fed mainly on gastropods and crabs. The diet of H. otakii underwent seasonal changes; H. otakii consumed mainly polychaetes and fishes during January and February 2002 but amphipods during March and May 2002. H. agrammus, however, ate mainly gastropods and crabs all seasons. H. otakii underwent also a significant diel changes that could be related to difference of prey availability. Thus the nocturnal emergence of gammarid amphipods, polychaetes and fishes explained their greater consumption by H. otakii. Dietary breadth of both species was lower in the smallest individuals (<5 cm SL) and in March and April 2002. This was due to the disproportionate dry mass attributable to the consumption of amphipods by both H. otakii and H. agrammus. Dietary overlap of both species was relatively moderate to high, in particular in <9.9 cm SL (0.62 – 0.71) from May to July 2002 (0.63 – 0.71). This is coincident with higher abundances of crabs, caridean shrimps and polychaetes in the study area, and it was assumed that these prey species were not limited resources. Higher dietary overlap was correlated with an abundance of a shared resource and did not indicate the interspecific competition between H. otakii and H. agrammus.