Fishery and Ontogenetic Driven Changes in the Diet of the Spiny Dogfish, Squalus acanthias, in Patagonian Waters, Argentina

The diet of the spiny dogfish in northern and central Patagonian waters was studied from the by-catch of the bottom trawling fisheries directed to Argentine hake Merluccius hubbsi and Argentine red shrimp Pleoticus muelleri between 1996 and 1998. Food habits were analyzed in relation to sex and maturity of sharks. Also, the relationship between diet and abundance of the main prey was explored. Intraspecific diet comparisons were performed. Differences in diet were found between immature individuals, mature males, and mature females. The Argentine shortfin squid Illex argentinus, the Argentine hake and ctenophores Pleurobrachia pileus were the most important prey for the spiny dogfish. Immature and small individuals were pelagic predators. After sexual maturity, the spiny dogfish shifted its diet. Mature and large individuals tended to reduce the consumption of ctenophores, and increase the consumption of demersal and benthic species. Previous diet studies on the spiny dogfish in 1984–1985 and 1994 indicated that the Argentine hake was the most important prey. In the present study, carried out in 1998, squid was the most important prey, followed by the hake. This diet change was related to the major decrease of hake due to overfishing and the increase of squid abundance between 1994 and 1999.     

PREY OF NORTHERN ROCKHOPPER PENGUINS AT GOUGH ISLAND,SOUTH ATLANTIC OCEAN

Klages, N. T., Brooke, M. de L. & Watkins, B. P. 1988. Prey of Northern Rockhopper Penguins at Gough Island, south Atlantic Ocean. Ostrich 59:162-165.

The diet of Northern Rockhopper Penguins Eudyptes chrysocome moseleyi breeding on Gough Island, south Atlantic Ocean was studied, during November 1984, 1985 and 1986 by stomach content analysis. Rockhopper Penguins fed chiefly on the euphausiids Thysanoessa gregaria, Euphausia lucens and E. similis. Fish and squid were of minor importance by mass but constituted the largest individual prey items.     

Diet and trophic position of two mackerel species in the archipelago of Madeira,Portugal

The Atlantic chub mackerel Scomber colias and the blue jack mackerel Trachurus picturatus are two abundant species in the Macaronesia region which includes the archipelago of Madeira, Portugal. Both are key species in the trophic web, being important prey for several local top predators, such as seabirds and marine mammals. Nonetheless, little is known about their feeding ecology in oceanic environments. In this study, the authors describe the seasonal variation in the diet of S. colias and T. picturatus in the oceanic region of Madeira throughout a year. Visual inspection of stomach contents revealed that S. colias fed on a broader range of prey groups than T. picturatus, but for both species, zooplankton (particularly calanoid copepods) and fish were the most important food items. The diet of S. colias included a higher proportion of fish, namely Atlantic saury Scomberesox saurus and S. colias, than that of T. picturatus, that included mostly the longspine snipefish Macroramphosus scolopax. T. picturatus consumed a higher proportion of decapods and other copepods. Seasonal variation was found in the diet of both species, with zooplanktonic species being more important in colder months (February to April) for S. colias and during warm months (May to October) for T. picturatus. Their diet in other seasons was dominated by fish. Although they consume similar prey, carbon and nitrogen stable isotope analysis of muscle of S. colias and T. picturatus showed little overlap in their diets, and T. picturatus showed higher δ¹⁵N and a narrower isotopic niche.     

Food habits of the smooth dogfish, Mustelus canis, dusky shark, Carcharhinus obscurus, Atlantic sharpnose shark, Rhizoprionodon terraenovae, and the sand tiger, Carcharias taurus, from the northwest Atlantic Ocean

Diet and feeding habits of the smooth dogfish, Mustelus canis, Atlantic sharpnose, Rhizoprionodon terraenovae, dusky, Carcharhinus obscurus, and the sand tiger, Carcharias taurus sharks, were investigated through analysis of stomach contents. Diet in M. canis was relatively homogeneous and was dominated by crustaceans, consisting mostly of rock crabs, Cancer irroratus. Diet in R. terraenovae was more heterogeneous and consisted largely of crustaceans and teleosts, in similar levels of prey importance. Use of cumulative prey curves as a measure of precision indicated that data were insufficient to fully describe the diets of C. obscurus and C. taurus. Nonetheless, these data suggested that both species are generalized feeders and consume a variety of teleost and elasmobranch prey. Further studies are necessary to fully characterize diet in these two species.     

Spatial and Temporal Variability in the Diet of Anadromous Arctic Charr, Salvelinus Alpinus, In Northern Labrador

Spatial and temporal variation in the diet of anadromous Arctic charr, Salvelinus alpinus, was determined from over 2500 prey-containing stomachs collected from three stock complex areas in northern Labrador. Based on the percent wet mass, sand lance, Ammodytes spp., capelin, Mallotus villosus, and sculpins, Triglops spp. and Myoxocephalus spp., were the most important components of the diet in the Voisey stock complex, with capelin, sand lance, and hyperiid amphipods, Parathemisto spp., dominating in the Nain region. In contrast, hyperiid amphipods and sculpins were the main prey items in the more northern Hebron–Saglek complex indicating that diet differs among stocks, and at times over limited spatial scales. The relative importance of prey varied with size of predator. Mean weight of charr has declined over time (p < 0.01), and for one stock complex, is highly correlated with the average quantity of capelin found in the stomachs (r = 0.66, p < 0.001). Dietary shifts observed in anadromous charr in some areas of northern Labrador could be associated, in part, with changes in the distribution of capelin in the northwest Atlantic Ocean, possibly as a result of anomalous ocean climate conditions.     

Do abiotic and ontogenetic factors influence the diet of a generalist predator? Feeding ecology of the Pacific spiny dogfish (<Emphasis Type="Italic">Squalus suckleyi</Emphasis>) in the northeast Pacific Ocean

Stomach contents from 1221 Pacific spiny dogfish (Squalus suckleyi) were collected from the Gulf of Alaska over 2004–2006 and analyzed to determine predominant prey species. Pacific spiny dogfish in the Gulf of Alaska have a variable diet suggesting that they are generalist feeders. Of the 68.30% of stomachs with prey contents, the most important prey groups based on the percent prey-specific index of relative importance (%PSIRI) were shrimp (27.06%), cephalopods (17.16%), and forage fish (17.11%). Remaining components of the diet were inconsistent. Commercially valuable species, such as salmon, Oncorhynchus spp., and rockfish, Sebastes spp. constituted only 2.37% and 1.51% of the diet of Pacific spiny dogfish, respectively. Diet diversity was not significantly influenced by spatial, temporal or ontogenetic factors; however, trophic level of prey and average prey item weight varied both interannually and with ontogeny. With increasing size, Pacific spiny dogfish incorporate larger prey items into their diet, and diet composition may be driven more by seasonal availability and prey size than any other factors.     

Trophic Behavior of Two Perlidae Species (Insecta,Plecoptera) in a River in Southern Spain

Two Perlidae species, Dinocras cephalotes and Perla bipunctata, were studied in a river in Spain with the objectives of: a) describing their diets; b) detecting differences between size classes; c) analyzing niche breadth; and d) assessing the degree of niche overlap between both species and size classes. Dinocras cephalotes and Perla bipunctata nymphs fed mainly on Baetidae and immature Chironomidae. We did not detect significant differences in the quantity of ingested detritus, algae, and leaf pieces. Niche breadth was very low, although both species presented a high niche overlap. P. bipunctata seems to select some prey items throughout its nymphal development, whereas D. cephalotes augments its diet with other prey items as it grows. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diet and feeding strategy of smooth butterfly ray Gymnura micrura in northeastern Brazil

The purpose of the present study was to analyze the diet of the smooth butterfly ray Gymnura micrura using qualitative and quantitative approaches to describe the feeding spectrum as well as ecological aspects related to feeding and niche width. The rays were obtained through monthly sampling as by‐catch from bottom trawl fisheries in northeastern Brazil from August 2007 to July 2008. A total of 286 stomachs were sampled, of which 176 contained food items. G. micrura is a predator in the region that feeds intermittently on large whole prey items, followed by a long period of digestion with simply little or no feeding activity. A low diversity of food items was found in the G. micrura diet, with an absolute predominance of teleosts, especially the roughneck grunt Pomadasys corvinaeformis. It is suggested that the species has a narrow feeding niche and a high degree of specialization. This presumed high degree of feeding specialization is discussed and the findings are compared in light of similar studies for closely related species, allowing to propose the family as primarily constituting piscivorous rays.     

Food habits of the shortfin mako, Isurus oxyrinchus, off the southwest coast of Portugal

The shortfin mako, Isurus oxyrinchus, is caught in the eastern North Atlantic as a regular bycatch of the surface-drift longline fishery, mainly directed towards swordfish, Xiphias gladius. Stomachs of 112 shortfin mako sharks, ranging in size from 64 cm to 290 cm fork length, showed teleosts to be the principal component of the diet, occurring in 87% of the stomachs and accounting for over 90% of the contents by weight. Crustaceans and cephalopods were also relatively important in this species’ diet, whereas other elasmobranchs were only present in lower percentages. Meal overlap was observed in half of the sampled sharks. No clear trend of prey size selectivity was found, despite smaller individuals seeming incapable of pursuing larger and faster prey. The retention of small prey was also observed in the diet of all sizes of shark. Seasonality in food habits was in accordance with the current availability of food items. The observed vacuity index of 12% is comparable to foraging ecology studies using gillnetting and appears not to be influenced by baited longline gear. Morphological relationships of the digestive system might add important information to the foraging ecology studies and to ecosystem modelling.     

THE DIET OF THE CURLEW SANDPIPER AT LANGEBAAN LAGOON,SOUTH AFRICA

Puttick, G. M. 1978. The diet of the Curlew Sandpiper at Langebaan Lagoon, South Africa. Ostrich 49:158-167.

Nereid worms (mainly Ceratonereis erythraensis) and the hydrobiid gastropod Assiminea globulus were the most important prey items throughout the year for Curlew Sandpipers Calidris ferruginea feeding at Langebaan Lagoon. Other important items were the amphipod Urothoe grimaldi, the crabs Hymenosoma orbiculare and Cleistostoma edwardsii and dipteran larvae (Stratiomyidae). Immature Curlew Sandpipers took smaller prey items than adult birds. The diet of male and female birds differed in the proportion, sue and range of prey items taken.     

Diet of spiny dogfish, Squalus acanthias Linnaeus, on the east coast, South Island, New Zealand

Stomach content data from 7283 spiny dogfish, Squalus ucunthius Linnaeus, from east coast South Island of New Zealand are presented. The major dietary components based on occurrence were 60% crustaceans and 15% fish. The principal food items were the post-larval phase of the squat lobster, Munida greguria Fabricius (30%), and the euphausiid, Nyctiphanes australis Sars (20%). Commercial fish species contributed to less than 5% of the diet. Diet of dogfish varied with dogfish size and sex. Compared to northern hemisphere studies, spiny dogfish in this study area had (1) a high proportion of crustaceans in their diet, (2) a relatively low percentage of empty stomachs, (3) a relatively high incidence of cannibalism.     

Trophic interactions between brown and south polar skuas at Deception Island,Antarctica

It is broadly accepted that the brown skua (Stercorarius antarcticus lonnbergi) competitively excludes the south polar skua (S. maccormicki) from penguin colonies when breeding sympatrically, forcing the latter to feed on marine resources. The purpose of this work was to examine the diets and trophic niche breadths of each species where they co-occur and to determine the degree of overlap. To this end, we analyzed 169 pellets of brown skuas, collected in two different areas (20 individuals), and 152 of south polar skuas, collected in three different areas (18 individuals), on Deception Island, South Shetland Islands, Antarctica, during the austral summer 2000. Pellet analysis often underestimates the amount of easily digestible prey, but allows for comparisons of the relative contributions of different items in the diet. South polar skuas at our study locations consumed seven different food items and had a trophic niche breadth of 0.133 compared to brown skuas that fed on 10 different items and had a trophic niche breadth of 0.078. The niche overlap between the species was 82.1%. Penguins were the principal food source of both species, however, brown skuas fed mostly on chicks, while south polar skuas fed on adults (carcasses). The use of different age classes of penguins as a food source offers an alternative to competitive exclusion, allowing the coexistence of these species on Deception Island.     

Trophic behaviour of juvenile reef fishes inhabiting interlinked mangrove–seagrass habitats in offshore mangrove islets

Stable isotope (δ¹³C and δ¹⁵N) and gut content analyses were used to investigate size‐related feeding habits of four reef fishes (the beaugregory Stegastes leucostictus, the french grunt Haemulon flavolineatum, the schoolmaster snapper Lutjanus apodus and the yellowtail snapper Ocyurus chrysurus) inhabiting an offshore (non‐estuarine) mangrove islet off Belize, Central America. Comparisons of isotopic niche space and Schoener diet similarity index suggested a low to moderate degree of niche overlap between fish size groups. The δ¹³C gradient between mangrove and seagrass prey as well as results of Bayesian mixing models revealed that sampled fishes relied mostly on seagrass prey items. Only small and large juveniles of the carnivorous species L. apodus derived a part of their diet from mangroves by targeting mangrove‐associated Grapsidae crabs and fish prey, respectively. Isotopic niche shifts were particularly obvious for carnivorous fishes that ingested larger prey items (Xanthidae crabs and fishes) during their ontogeny. The utilization of mangrove food resources is less than expected and depends on the ecology and life history of the fish species considered. This research highlights that mangrove‐derived carbon contributed relatively little to the diets of four fish taxa from an offshore mangrove islet.     

Inter-annual variation in the diet of female southern rockhopper penguin (Eudyptes chrysocome chrysocome) at Tierra del Fuego

Inter-annual variation in the diet of female southern rockhopper penguins (Eudyptes chrysocome chrysocome) at Staten Island was studied during the early chick-rearing period to investigate the components of the diet and highlight some points of the possible food web in the study area. Gregarious crustaceans, small juveniles of squid and octopus, fish larvae and juvenile fish dominated the diet. There was a high degree of variability in the relative contribution of the different prey taxa during the three seasons studied. Overall, crustaceans were by far the most abundant in terms of number. Cephalopods contributed less to numbers, while fish was the least represented of the prey item in 2 years. Inter-annual variation in the proportion of prey items consumed was apparent only for some prey species: Thysanoessa gregaria, Gonatus antarcticus, Themisto gaudichaudii, Harpagifer bispinis and Salilota australis. These data suggest variability in the prey resources at sea during the study period and a subsequent opportunism of this penguin species to exploit what is differentially available. In terms of the food web in the area, we suggest an apparent relationship in the availability between T. gaudichaudii and G. antarcticus, and between T. gaudichaudii and H bispinnis. These relationships emphasise the importance of understanding food web interactions, especially those involving multiple trophic levels, when determining the role of upper-trophic level predators in marine systems.     

Diet of the Long-eared Owl,Asio otus,in Central Anatolia (Aves: Strigidae)

In a one-year study on the diet of the Long-eared Owl, Asio otus, in the area of Karap?nar in Central Anatolia, 5324 prey items were recovered from 3314 pellets collected at monthly intervals. At least 7 species of mammals belonging to Insectivora (Crocidura suaveolens) and Rodentia (Allactaga williamsi, Cricetulus migratorius, Meriones tristrami, Mescocricetus brandti, Microtus guentheri, M. sp., Mus macedonicus) were identified. Rodentia were dominant and contributed 93.8% of the number of prey items of the Long-eared Owl. Microtus guentheri accounted for 83.9% of the rodent remains. The diet pattern was more diverse in summer, when some 24% of the diet consisted of non-mammal prey items (birds, insects).     

THE DIET AND IMPLICATIONS OF DIETARY CHANGE OF CAPE GANNETS ON BIRD ISLAND,ALGOA BAY

Batchelor, A. L. & Ross, G. J. B. 1984. The diet and implications of dietary change of Cape Gannets on Bird Island, Algoa Bay. Ostrich 55:45-63.

The diet of the Cape Gannet Sula capensis breeding on Bird Island, Algoa Bay, South Africa, was investigated. Approximately 2000 regurgitations representing 13300 prey items were examined. Twenty-three teleost and two cephalopod species were recorded in the diet. More than 90 % of the numerical composition consisted of the three species Pilchard Sardinops ocellata, Anchovy Engraulis capensis and Saury Scomberesox saurus. The proportions of these three species in the diet changed during the sampling periods. These changes were not related to the implied migration patterns of these species. Chick growth rates were investigated in conjunction with the dietary study. These results indicated that Cape Gannet chicks on a diet of Pilchard and/or Anchovy were more likely to fledge successfully than those on a diet of Stockfish Merluccius capensis or Saury. These observations were based on differences in growth rate, and peak and fledgling mass, The data suggest that Pilchard is a preferred prey species and its presence or absence in regurgitationsMayreflect a similar situation on the feeding grounds. The observed increase in the Bird Island gannet populationMaybe related to the availability of high-quality food and consequent reduced pre-breeding mortality. In the absence of historical dietary data, further detailed population dynamics studies are required to support this supposition.     

THE DISTRIBUTION, ABUNDANCE AND SELECTED PREY OF THE HARBOR SEAL, PHOCA VITULINA CONCOLOR, IN SOUTHERN NEW ENGLAND

The seasonal distribution and abundance of harbor seals occurring south of Maine were documented by counting the number of seals at traditional haulout locations. The average number of seals counted during each survey in Massachusetts and New Hampshire was 3,560 ± 255 (95% CI), 1983–1987. The maximum number of seals counted on any individual survey was 4,736 individuals. Fifty percent of all the surveys since January 1985 have resulted in counts greater than 4,000 seals reflecting a 27% increase in the abundance of seals in our study area since that date. Seventy-five percent of the seals in southern New England are located at haulout sites on Cape Cod and Nantucket Island. The largest aggregation of seals in the eastern United States occurs mid-winter at Monomoy Island and adjacent shoals. A single high count of 1,672 seals occurred at this site during the study period. An additional 271–374 seals were also counted in Rhode Island, Connecticut and eastern Long Island Sound during surveys conducted in March 1986 and 1987. The American sandlance Ammodytes americanus was the single dominant prey item of harbor seals in waters adjacent to Cape Cod based on the modified frequency of occurrence of each prey species in scat samples collected from three haulout sites on Cape Cod between 1984–1987. During January and February sandlance was the near exclusive prey item at Monomoy (99%, n= 80). During March and April, the frequency of Atlantic herring Clupea harengus increased in the scat samples at this site. Regional differences in the diet of seals reflect distinct prey communities throughout the study area. Since 1986, the percent occurrence and importance of sandlance in the diet of seals has decreased, reflecting an overall decrease in abundance of this prey species in waters adjacent to Cape Cod. In spite of fluctuations in abundance, and regional differences in the diet of seals throughout the study area, sandlance still comprised a minimum 55% of the total prey species of harbor seals throughout the study area.     

Temporal variations in the diet of pearly razorfish Xyrichtys novacula (Osteichthyes: Labridae)

The diet of pearly razorfish Xyrichtys novacula, caught monthly along the shores of the Island of Lampedusa, appeared to be mainly composed of crustaceans, followed by colonial ascidians, molluscs and polychaetes. Among prey, sand dwellers and phanerogam‐associated species were recorded. In winter months, the diet was characterized by a small number of prey items, dominated by colonial ascidians, while in spring and summer a wider prey array was recorded. Dietary indices show that X. novacula do not strictly exploit benthic prey but also pelagic organisms, such as copepods. This feeding behaviour reached its peak in March and October, when the abundance of primary consumers was at its highest after phytoplankton blooms. Furthermore, X. novacula caught prey organisms according to their availability and seasonal patterns during their life cycles, irrespective of fish size.