Feeding habits of the juvenile striped weakfish, Cynoscion guatucupa Cuvier 1830, in Bahía Blanca estuary (Argentina): seasonal and ontogenetic changes

The aim of this study was to analyze the feeding habits of the juvenile striped weakfish, Cynoscion guatucupa Cuvier, from Bahía Blanca estuary, Argentina. C. guatucupa is one of the most important regional fishing resources although in the last 10 years landings have greatly decreased. The year class strength of fish as well as stock size and yield are determined during the early life stages. Knowledge about the diet of young C. guatucupa may therefore contribute to our better understanding of the influence that the changes occurring in the biota of the estuary exert on the abundance fluctuations of this species. To this end, we investigated the ontogenetic and seasonal dietary changes of C. guatucupa between 1.00 and 12.99 cm total length (age 0+), and we related them to changes in habitat use and prey selection. Two dietary shifts were found during ontogeny. The first shift, at approximately 4 cm total length, involved a change from demersal-pelagic prey (mysid shrimps) to demersal-benthic prey (Peisos petrunkevitchi Burkenroad). The second shift, at approximately 8 cm total length, involved a progressive increase in ichthyophagy (mainly an increase consumption of the Argentine anchovy Engraulis anchoita Hubbs & Marini). Seasonal dietary changes were also found. They evidenced the changes in the availability of organisms. In autumn, the chaetognath Sagitta friderici Ritter-Zahoni, P. petrunkevitchi, and E. anchoita were the dominant prey items; in winter, the copepod Labidocera fluviatilis Dahl along with S. friderici, mysids, and P. petrunkevitchi constituted the majority of the diet; and, in summer, mysids were the most important prey item consumed. Selectivity data showed that whereas some prey items, such as the copepods Acartia tonsa Dana and Paracalanus parvus (Claus) and S. friderici, were consistently negatively selected by all size classes throughout the year, other prey items, such as fish larvae, mysids, and P. petrunkevitchi,were selected in one season and avoided in another. Additional dietary seasonal differences observed in our research indicate that the limited food supply and the low water temperatures are limiting factors for winter juveniles in BahÕa Blanca estuary. These factors may also directly influence the more-than-10 cm total length seaward migration of large numbers of C. guatucupa that is registered at the end of every autumn.     

Feeding ecology of Urophycis brasiliensis on the Uruguayan coast of the Río de la Plata estuary

The Brazilian codling (Urophycis brasiliensis) is the target of an important artisanal fishery in Uruguay. In the present study we analysed the feeding habits of this species over a 2‐year cycle. The samples were obtained from landings of the artisanal fishery at two sites on the Uruguayan coast: one representing a transitional habitat between estuarine and marine conditions (Piriápolis), the other representing a typical marine ecosystem (La Paloma). Different approaches were considered (Index of Relative Importance, IRI; graphical methods and multivariate techniques of cluster analysis and Principal Component Analysis). The ontogenetic changes in the diet were also assessed. Stomach contents of 870 individuals were analysed and a total of 24 prey species identified. The shirmp Artemesia longinaris has the highest IRI (89.9%) score followed by Cynoscion guatucupa (IRI = 4.3%). Molluscs were only marginally represented (IRI < 0.01%). Both the graphical method of Cortés and the method of Amundsen indicate the specialization of Brazilian codling to A. longinaris. However, a trend to a generalist diet evolves in bigger fishes, which also consume fishes in important quantities, mainly C. guatucupa. Moreover, opportunism is occasionally present both seasonally and spatially, and responds to variations of the availability of prey items throughout its distribution. U. brasiliensis predation plays an important role in the trophic dynamics of the SW Atlantic ecosystem. It is dependent on shrimp for feeding, a reason for an integrated management of coastal habitat and fisheries of both resources. The dependence of Brazilian codling, mainly when it is small, on shrimp calls for an integrated management of both the coastal habitat and fisheries.     

Feeding ecology of the Common Tern Sterna hirundo in a wintering area in southern Brazil

The wintering diet of Common Terns Sterna hirundo was studied by using 714 pellets collected on roosting sites at the mouth of the Lagoa dos Patos and on adjacent coastal beaches, in Rio Grande do Sul, southern Brazil, from March 1999 to February 2000. A total of 12 340 individual prey items of 35 different food types was found. Fish was the most important food type in the diet, constituting 32% by number and 93% by mass. Insects contributed 67% by number but only 3% by mass. The main food types were sciaenid fishes Paralonchurus brasiliensis, Micropogonias furnieri, Cynoscion guatucupa and Macrodon ancylodon. Several of these are important commercial species; fisheries potentially impact food availability to the terns, and terns may contribute significantly to the natural mortality of these fishes. Clupeiform fishes, the urophycid fish Urophycis brasiliensis and flying ants (Camponotus sp.) were also important. Species composition of the diet (food types), both by number and by mass, differed significantly between months. Prey sizes ranged in length from 12.7 mm to 217.4 mm. The average estimated total length of fish taken was 77.7 mm, but the mean differed significantly among prey species. The importance of demersal sciaenids to the diet of the Common Tern, a surface predator, may be explained by their association with aquatic predators, especially adult Bluefish Pomatomus saltatrix and Striped Weakfish Cynoscion guatucupa, and the Franciscana Dolphin Pontoporia blainvillei, which drive these fish to the surface. The occurrence of flying ants in the diet was related to offshore winds, which carried these insects out to sea. The occasional high availability of insects possibly changed the cost/benefit relationship of several food types, causing diet changes. The high number of prey species, the temporal variations in the composition of the diet and the wide range of prey sizes are evidence of the high dietary plasticity of the Common Tern, at wintering areas in southern Brazil.     

Diet composition of the juvenile chub mackerel (Scomber japonicus) in the Aegean Sea (Izmir Bay, Turkey)

Stomach contents of 296 juvenile chub mackerel (Scomber japonicus Houttuyn, 1782) specimens were examined based on samplings carried out in Izmir Bay (Aegean Sea, Turkey) during 2001. In terms of percentage weight (W%), fishes were the main food during summer and autumn. Thaliaceans (Salpa sp.) constituted the most important food source in winter, whereas planktonic crustaceans (Amphipoda, Copepoda) were the main prey during spring. According to the Bray–Curtis similarity index, diet of the chub mackerel was 64.1% similar during the summer, winter and autumn seasons.     

Food habits of genetically identified pine marten (<Emphasis Type="Italic">Martes martes</Emphasis>) expanding in agricultural lowlands (NW Italy)

We assessed the diet of pine marten (Martes martes) expanding in the heavily human-altered agricultural plain of the River Po, northern Italy. Between February 2008 and November 2009, surveys were carried out twice a week during seasonal sampling sessions of three to four consecutive weeks. To distinguish the faecal samples from those of sympatric carnivores, a polymerase chain reaction-restriction fragment length polymorphism method was applied. The availability of small mammals was assessed by the analysis of 59 barn owl (Tyto alba) pellets. A total of 109 pine marten faeces were analysed. Its diet consisted of fruit, rodents, lagomorphs and birds. Seasonal variation occurred for fruit, which prevailed in summer, and rodents, which were more preyed upon in autumn. In winter, the diet of the pine marten was almost totally based on vertebrates, and lagomorphs were the main source of protein in summer. Use of small mammals differed significantly from their availability, voles, particularly bank vole Myodes glareolus, being preferred to mice (Apodemus sp.) and rats (Rattus sp.). Medium-size mammals formed about 18% of pine marten diet, a value generally reported for high-latitude habitats. In agricultural areas, the pine marten proved to be an opportunistic predator, able to face the reduced availability of small mammals by preying upon medium-size prey and fruit.     

Variation in the diet composition of a generalist predator, the red fox, in relation to season and density of main prey

Diet composition of a generalist predator, the red fox (Vulpes vulpes) in relation to season (winter or summer) and abundance of multi-annually cyclic voles was studied in western Finland from 1983 to 1995. The proportion of scats (PS; a total of 58 scats) including each food category was calculated for each prey group. Microtus voles (the field vole M. agrestis and the sibling vole M. rossiaemeridionalis) were the main prey group of foxes (PS = 0.55) and they frequently occurred in the scats both in the winter and summer (PSs 0.50 and 0.62, respectively). There was a positive correlation between the PSs of Microtus voles in the winter diet of foxes and the density indices of these voles in the previous autumn. Other microtine rodents (the bank vole Clethrionomys glareolus, the water vole Arvicola terrestris and the muskrat Ondatra zibethicus) were consumed more in winter than in summer. The unusually high small mustelid predation by red foxes (PS = approx. 0.10) in our study area gives qualitative support for the hypothesis on the limiting impact of mammalian predators on least weasel and stoat populations. None of the important prey groups was preyed upon more at low than at high densities of main prey (Microtus voles). This is consistent with the notion that red foxes are generalist predators that tend to opportunistically subsist on many prey groups. Among these prey groups, particularly hares and birds (including grouse), were frequently used as food by foxes.     

Diet of the nominate Southern Grey Shrike Lanius meridionalis meridionalis in the north of its range (Mediterranean France)

Capsule In this region the diet is mainly cold-blooded prey, mostly insects such as beetles.

Aims To describe the diet of this newly separated, poorly documented and endangered species.

Method Diet was inferred from pellet analysis, collected during a single breeding and winter period in the steppe of the Crau.

Results A total of 5409 prey were identified from 257 pellets. Vertebrates were seldom taken, except by adults (small passerines) during the fledgling period. High seasonal differences were found. Hymenoptera were largely consumed in autumn, Arachnida in autumn and winter, Orthoptera in summer and autumn and Lepidoptera larvae in winter and spring and by fledglings. Nevertheless, Coleoptera were ingested in large proportions all year round. Carabidae were the main prey in winter and Melolonthidae were especially important for adults during the nestling period, as were Cetoniidae for the fledglings.

Conclusion Small mammals and small birds were less exploited in France and Spain (L. m. meridionalis) than in Israel (L. m. elegans or L. m. aucheri), whereas the opposite might be expected, following a north–south climatic gradient. Thus, the nominate subspecies L. m. meridionalis differed in diet from L. m. elegans or L. m. aucheri.     

Dietary comparisons of six skate species (Rajidae) in south-eastern Australian waters

The diet of six skate species caught as bycatch in south-eastern Australian waters was examined over a 2-year period. The skates were segregated into two regions (continental shelf and continental slope) based on prey species and depth of capture. The shelf group consisted of four species, Dipturus sp. A, D. cerva, D. lemprieri and D. whitleyi, while the slope group comprised two species, Dipturus sp. B and D. gudgeri. The two groups varied in feeding strategies with the shelf species generally occupying a broader feeding niche and preying on a larger diversity of prey including a variety of crustaceans (brachyurans, anomurans, achelates, carideans and dendobranchiates), cephalopods, elasmobranchs and teleosts. Within the slope group, Dipturus sp. B and D. gudgeri were more specialised. Dipturus sp. B preyed primarily on anomurans (galatheids) and bachyurans (homolids), whereas D. gudgeri preyed primarily on teleosts. A size related change in diet was evident for all species with the exception of D. gudgeri in which all sizes preyed predominantly on teleosts. Smaller representatives of the four shelf species all preyed on numerous amounts of caridean shrimps, in particular Leptochela sydniensis. In contrast, the continental slope species, Dipturus sp. B consumed anomurans when small, shifting to brachyurans with increasing size. Of the six skate species examined in this study, three were secondary consumers (trophic level <3) and the remaining three tertiary consumers (trophic level >4). Although ANOSIM found significant differences in dietary composition between species within groups, there was some overlap in prey species amongst co-existing skates, which suggests that there is some degree of resource partitioning amongst them.     

Feeding habits of invasive American mink (Neovison vison) in northern Germany—potential implications for fishery and waterfowl

In order to collect ecological data of invasive American mink (Neovison vison) at a fishpond area in northeastern Germany, we conducted a telemetry study in which 14 mink were radio-tracked. During this project, 2,502 scats from radio-tracked individuals were collected in the period from October 2003 to October 2005. Investigated mink principally prey on fish, small mammals and birds (eggs inclusive), whereas amphibians, reptiles and invertebrates were caught infrequently. Analysing mink scats of different seasons, we found significant seasonal variations of diet composition. In spring, fish, mammals and birds were hunted in similar amounts. During summer, birds made up the main part of the diet followed by mammals. In autumn, the proportion of birds in the mink diet decreased, whereas fish gained in importance. This trend continued during the winter period, when mink preyed almost exclusively on fish. Amphibians, crustaceans, insects, molluscs and reptiles were found only occasionally in scat samples. Among birds, the mink preyed mainly on the Eurasian Coot (Fulica atra) followed by the Mallard (Anas platyrhynchos). Mammalian prey was clearly dominated by the water vole (Arvicola terrestris) and among fish, mink hunted especially perch (Perca fluviatilis), roach (Rutilus rutilus) and carp (Cyprinus carpio). Results clearly demonstrate that mink is an opportunistic predator, which hunts its prey according to availability and vulnerability, respectively. Despite the high portions of fish in their autumn and winter diet, the economic damage caused by mink seems to be negligible. However, high predation rates on birds during the breeding season indicate a potential negative impact of mink on waterfowl.     

The diet of native and invasive fish species along the eastern Mediterranean coast (Osteichthyes)

The opening of the Suez Canal in 1869 enabled the invasion of more than 100 alien fish species into the Mediterranean. The aim of the present study was to compare the diet of native and alien fish species and to identify possibly shared food resources. We examined the diet composition of 13 of the most abundant fish species (6 alien, 7 native) on shallow soft bottom off southern Israel. All 13 species are omnivorous/carnivorous. The native fish exhibited a wider diversity of food types than the aliens. Alien fish prey upon and are preyed by native species as well as by other alien fish. A high level of diet overlap was found among some species, the aliens Saurida lessepsianus and Scomberomorus commerson overlapped with the native Synodus saurus; and the alien Nemipterus randalli with the native species Pagrus caeruleostictus, Lithognathus mormyrus and Pagellus erythrinus. The identified diet overlap is discussed, and the possibility of competitive interactions between these species is considered.     

Winter ecology of Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) and brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) in a subarctic lake,Norway

We studied habitat choice, diet, food consumption and somatic growth of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) during the ice-covered winter period of a subarctic lake in northern Norway. Both Arctic charr and brown trout predominantly used the littoral zone during winter time. Despite very cold winter conditions (water temperature <1°C) and poor light conditions, both fish species fed continuously during the ice-covered period, although at a much lower rate than during the summer season. No somatic growth could be detected during the ice-covered winter period and the condition factor of both species significantly declined, suggesting that the winter feeding rates were similar to or below the maintenance requirements. Also, the species richness and diversity of ingested prey largely decreased from summer to winter for both fish species. The winter diet of Arctic charr <20 cm was dominated by benthic insect larvae, chironomids in particular, and Gammarus lacustris, but zooplankton was also important in December. G. lacustris was the dominant prey of charr >20 cm. The winter diet of brown trout <20 cm was dominated by insect larvae, whereas large-sized trout mainly was piscivorous, feeding on juvenile Arctic charr. Piscivorous feeding behaviour of trout was in contrast rarely seen during the summer months when their encounter with potential fish prey was rare as the small-sized charr mainly inhabited the profundal. The study demonstrated large differences in the ecology and interactions of Arctic charr and brown trout between the winter and summer seasons.     

Diet of the Chilean sandperch, Pinguipes chilensis (Perciformes, Pinguipedidae) in southern Chile

A study of the Pinguipes chilensis Valenciennes 1833 diet was carried out on 414 specimens captured on the Talcahuano, Chile coastline (36°41′S; 73°06′E) between October 1998 and March 2000. P. chilensis, endemic to the southeast Pacific (from Tumbes, Peru to Magallanes, Chile), is confirmed as a general predator over a wide trophic spectrum including 61 taxa. Crustaceans (mostly mysids, but also a wide variety of decapods) made up the principal dietary component, followed by fish and annelids. Prey belonging to Mollusca, Ophiuroidea, Echinoidea, Rhynchocoela, Sipunculida, Echiura and Urochordata were also present. There were no significant differences between male and female diets, although they shared only 32 prey. A significant dietary difference was found, however, between analysed size groups: specimens under 30 cm total length (TL) preyed mainly on the amphipod, Ampelisca araucana; those over 30 cm TL preyed on the mysid, Neomysis sp.; and those over 40 cm TL on fish, annelids, molluscs and echinoderms. Seasonal differences, due in large part to the dynamics of the prey species, were also found to be significant. Crustaceans were the predominant prey throughout the study with the exception of autumn, when fish were the most common prey.     

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.     

What is out there: diversity in feeding of gentoo penguins (Pygoscelis papua) around the Falkland Islands (Southwest Atlantic)

During austral spring 2000, the diet of Gentoo penguins, Pygoscelis papua, was studied and compared to prey availability, assessed by trawl and plankton surveys, in waters adjacent to a number of colonies along the coast of West Falkland. There was good agreement in size and abundance of key prey species in the penguin diet and from the plankton and trawl surveys. The diet of birds breeding adjacent to shallow sheltered waters was dominated by demersal species, in particular crustaceans, Munida spp. whilst birds breeding adjacent to deeper exposed waters generally preyed upon pelagic species of fish, Falkland herring Sprattus fuegensis and squid, Moroteuthis ingens. Gentoo penguins generally foraged at depths of up to 30 m, relatively close to the coast, and illustrated a certain degree of selection of prey species where possible, thus providing evidence that they are not fully opportunistic predators.     

Competition and coexistance between Glossiphonia complanata and Helobdella stagnalis (Glossiphoniidae: Hirudinoidea)

Summary The prey utilization of Glossiphonia complanata and Helobdella stagnalis from Bruce Lake, Alberta, Canada was examined quantitatively using serological techniques. While considerable prey range overlap occurred between the species, niche overlap was low during the winter, peaked in March and declined through the summer. Temporal differences in feeding and intraspecific weight class differences in prey utilization were found in both species but more distinctly in G. complanata. It is suggested that co-existance of G. complanata and H. stagnalis is based on adjustments of weight class food resource partitioning on a temporal basis.     

The diet ofEnoplus brevis (Nematoda) in a supralittoral salt marsh of the North Sea

The gut content of nearly 2000 specimens ofEnoplus brevis was quantitatively analysed.E. brevis is an opportunistic omnivore. Main food categories found were cyanobacteria, diatoms, oligochaetes, nematodes, and rotifers. With a few exceptions, the diet of females and males was identical. Predominantly, juveniles fed on cyanobacteria and adults on animal prey. Experiments revealed that living oligochaetes are attacked and preyed upon. The quantities of the food categories eaten byEnoplus varied according to their ambient abundance, both temporarily and spatially on a small scale. At least the nematode prey was strongly selected: some species were significantly preferred and others avoided.     

Feeding ecology of the vulnerable aoudad (Ammotragus lervia) in north-western Sahara

The feeding ecology of the aoudad (Ammotragus lervia) was investigated for the first time in north-western Sahara, Djebel Antar (Bechar province, Algeria), from autumn 2015 to summer 2016. Microhistological analyses of faeces revealed an annual diet composed of 23 identified taxa belonging to 16 plant families. The highest species diversity was recorded in spring and summer (23 species), despite a marked consumption of two species: Vachellia tortilis (17.7%) and Avena sterilis (14.0%); diet diversity was lower in autumn and winter (16 species), including mainly Teucrium polium (14.7%, 21.0%) and Gymnocarpos decander (19.7%, 10.0%). The main plant parts consumed during these seasons were stems (77.7%, 65.3%), while leaves and inflorescences were mostly consumed during spring and summer (54.7%, 52.3%). Forbs dominated the aoudad's diet, with 46.3% average relative abundance, including mainly T. polium, Limoniastrum feei, and Chrysanthemum macrocarpum. Woody plants including mainly V. tortilis and G. decander accounted for 33.3% (50.0% in autumn), and grasses including A. sterilis and H. murinum for 20.4% (32.0% in summer). Based on this diet, A. lervia can be classified as a “generalist mixed-feeder.”     

Analysis of dietary overlap in Antarctic fish (Notothenioidei) from the South Shetland Islands: no evidence of food competition

A dietary overlap analysis between notothenioid species was carried out among three fish assemblages in the South Shetland Island area. Using Tyler's (1972) method, the re-occurrence of main and secondary prey among fish predators was 33% in summer and 37% over the year at Potter Cove, 25% in summer and 7% in winter at Admiralty Bay, and 20% in autumn/winter around Elephant Island. Likewise, using the "S" index of Linton et al. (1981), the diet similarity between most species pairs is <50%. This relatively low dietary overlap may be explained by the about equally divided occurrence of generalised feeders and specialised feeders, with no evidence of competition among them. The fishes' trophic niches seem to be separated by depth and prey taxa. These findings are compared with other Antarctic fish communities and those in similar non-Antarctic cold marine ecosystems.     

Characterization of feeding habits,prey diversity and diet overlap of two sympatric species: Bronze catfish,Netuma bilineata (Valenciennes, 1840) and blacktip sea catfish,Plicofollis dussumieri (Valenciennes, 1840) in the northern Arabian Sea

This study describes the diet composition, diet overlap and prey diversity in two economically and ecologically important marine catfish species: the bronze catfish (Netuma bilineata) and the blacktip sea catfish (Plicofollis dussumieri) collected between January and December 2015 from the northern Arabian Sea coast of Pakistan. Stomach data of 342 bronze catfish and 283 blacktip sea catfish were examined. Diet composition and feeding strategy of each species by identification of stomach contents were weighed and enumerated. Both species primarily consumed teleosts, Brachyura and small amounts of a wide variety of prey items; however, specialization was a more common trait for the bronze catfish than for the black tip sea catfish. The Morisita‐Horn index showed considerable diet overlap in percentage of mean weights (0.847) than in numbers (0.612) between co‐prey pairs of both species. The highest Bray‐Curtis similarity between the southwest monsoon (SWM) and south inter monsoon (SIM) was observed in bronze catfish and lowest between autumn inter monsoon (AIM) seasons in both species. While Bray‐Curtis dissimilarity was observed, both species share diet niches and diet overlap. The present study evaluation of the feeding strategy and potential competition between two sympatric species of marine catfishes can provide the framework for their conservation and management in the region.     

Niche overlap and habitat use at distinct temporal scales among the California sea lions (Zalophus californianus) and Guadalupe fur seals (Arctocephalus philippii townsendi)

The aim of this study was to determine the trophic level, trophic breadth, and dietary overlap of two species of otariids (Zalophus californianus and Arctocephalus philippii townsendi) at the San Benito Islands in Baja California, Mexico, using scat analysis, and stable isotope analyses (SIA) of carbon and nitrogen in pup hair and dental collagen. Scat samples were collected during summer and winter. The most important prey for both species during summer was squid, comprising 74% of the A. p. townsendi diet and 45% of that of Z. californianus. In winter, squid was 87% of the A. p. townsendi diet, whereas fish was the predominant food (76%) for Z. californianus. Both species were specialist feeders and reached maximum trophic overlap during the summer (C_H = 0.9). SIA of the hair of otariid pups showed significant differences in δ¹⁵N (P = 0.001), coinciding with A. p. townsendi's greater consumption of squid. The average δ¹³C value was significantly lower for A. p. townsendi (?16.3‰ ± 0.2‰), reflecting the species' consumption of squid from pelagic habitats, whereas that of Z. californianus (?15.9‰ ± 0.3‰) was significantly higher, reflecting their consumption of benthic fish. Difference in habitat use was confirmed in δ¹³C values of dental collagen.