Dominant Prey Items Research Articles

Habitat-specific effects of food abundance on the condition of ovenbirds wintering in Jamaica.

1. Food availability has been considered one of the most important factors limiting bird populations, yet the effects of food abundance on non-breeding insectivores has rarely been investigated. We studied the effects of food abundance on the body condition of ovenbirds (Seiurus aurocapillus L.), a sexually monomorphic, ground-foraging, Neotropical-Nearctic migrant warbler during two winters in three habitats on their wintering grounds in Jamaica. 2. Prey biomass decreased from early to late winter in all habitats. Concurrently, ovenbird body mass, corrected for differences in structural size, decreased significantly in five of six habitat-year combinations. Only in second growth scrub habitat in the 1995-96 winter did ovenbirds show no decrease in corrected body mass, and during this period there was no significant decrease in ant biomass, the dominant prey item of ovenbirds in all habitats. 3. Significant positive correlations were found between ovenbirds' rate of feather regrowth and the biomass of ants on their home ranges in early winter, and between overwinter change in ovenbird body mass and the biomass of ants on their home ranges in late winter. 4. The results of both the habitat- and home-range-based analyses suggest a similar threshold of ant biomass (2·5-3·0 mg m-2 ), below which ovenbirds did not maintain their body mass. 5. The results suggest that late winter rainfall mediates the biomass of prey abundance, which in turn affects the ovenbirds' overwinter body condition.

Effects of Otter Trawling on a Benthic Community in Monterey Bay National Marine Sanctuary

Bottom trawling is one of the most disruptive and widespread human-induced physical distur- bances to seabed communities and has become a global environmental concern. We used a comparative ap- proach to test the hypothesis that persistent otter trawling decreases bottom habitat complexity and biodiver- sity, increases the abundance of opportunistic species, and benefits prey important in the diet of some commercially valuable fish. We compared two similar and adjacent fishing areas at 180 m off central Califor- nia in Monterey Bay National Marine Sanctuary: one inside the three-mile coastal zone of restricted fishing with light levels of trawling and one beyond the three-mile limit with high levels of trawling. Differences in fishing effort between the two areas were confirmed and quantified by means of data and tow number statis- tics from Pacific Fishery Management Council (PFMC) Trawl Logbook records. We used still photography, video footage, bottom grab samples, and experimental trawling to compare the physical and biological pa- rameters of the two areas. The area with high levels of trawling had significantly more trawl tracks, exposed sediment, and shell fragments and significantly fewer rocks and mounds and less flocculent material than the lightly trawled area. Most invertebrate epifauna counted were significantly more abundant in the lightly trawled area. The density of the amphinomid polychaete, Chloeia pinnata , as well as that of oligochaetes, oph- iuroids, and nematodes, were higher every year in the highly trawled area, and there were significantly fewer polychaete species every year in the highly trawled area. Content analysis of fish guts showed that C. pinnata was a dominant prey item for some of the commercially important flatfishes in both lightly and heavily trawled areas. Our study provides evidence that high levels of trawling can decrease bottom habitat complex- ity and biodiversity and enhance the abundance of opportunistic species and certain prey important in the diet of some commercially important fishes. Our work also illustrates how constraints currently imposed on fisheries research by the near universal absence of true unfished control sites severely limit our ability to de- termine appropriate levels of harvest pressure for maintaining sustainable fisheries and marine biodiversity. Valid research in these areas will require marine reserves in which fishing effort and methods can be manip- ulated in collaborative studies involving fishers, researchers, and resource agencies.

Diet of the ringed seal (<i>Phoca hispida</i>) in Greenland

Analysis of 454 stomachs of ringed seals (Phoca hispida) collected from the Inuit hunt in six municipalities in West Greenland and 30 alimentary tracts collected by scientists in East Greenland, showed seasonal and regional differences in the diet. In Northwest and East Greenland polar cod (Boreogadus saida) and Arctic cod (Arctogadus glacialis) were the most dominant prey items. In contrast, seals in central West Greenland mainly preyed upon amphipods (Parathemisto spp.), capelin (Mallotus villosus), redfish (Sebastes sp.) and squid (Gonatus sp.), while capelin was the most important prey item in Southwest Greenland. The material from Uummannaq demonstrates seasonal variations, as euphausiids were common in spring, and snailfish (Liparis spp.) dominated from October through January, where after snailfish disappeared with the formation of fast ice. No age related differences in the diet were found in stomach samples from Avanersuaq, but in Upemavik crustaceans were more abundant in stomach samples from younger immature seals. Greenland halibut (Reinhardtius hippoglossoides) was only present in samples from seals older than 4 years. In Upemavik Arctic cod was the dominant prey item for seals caught in May at the iceedge, whereas polar cod dominated the samples from seals caught in open water.

Diet of the Red-Cockaded Woodpecker in the Apalachicola National Forest

Most territories of the largest population of red-cockaded woodpeckers (Picoides borealis; RCWs) in the western district of the Apalachicola National Forest (ANF) do not meet the current foraging-habitat requirements in the recovery plan for this species. We suspect that more information about the relation between the diet of the RCW and its habitat is needed and would permit development of better guidelines for the ANF and other populations. We studied diets of adult and nestling RCWs and their relation to variation in habitat. We found that ants were the dominant prey item by biomass (58%). Additional major items in stomachs of adult RCWs were other arthropods, fruits and seeds, and wood. Of the 4 species of ants present in samples, 74% of the biomass consisted of eggs, larvae, pupae, and adults of the arboreal ant Crematogaster ashmeadi. Territories burned more frequently had pine trees (Pinus spp.) with a higher diversity of ant species and lower proportions of trees occupied by C. ashmeadi than did territories burned less frequently. Also, stomach samples from adult male woodpeckers at frequently burned sites had lower proportions of ants, including C. ashmeadi. More information is needed about the dynamics of interspecific relations within arthropod communities of longleaf pine trees (P. palustris), the importance of ants to the ecology of the RCW, and the relevance of variation in habitat to diets of RCWs.

Field estimates of food consumption of the searobin Prionotus punectatus (Bloch, 1797) on the continental shelf off Ubatuba, southeastern Brazil

Daily ration and population food consumption of juvenile and adult searobin Prionotus punctatus (54-314 mm total length) were estimated for the southeastern Brazilian shelf off Ubatuba (23°35'S, 45°00'W). Samples were collected during 24hour-tisheries in three periods during 1987/88. P. puctatus is a diurnal invertebrate feeder, its maximum stomach fullness occurred during the afternoon. Instantaneous gastric evacuation rates were estimated from the data, and daily ration was subsequently computed for total food intake, as well as the dominant prey items, comparing the results off three widely-used methods. The total daily ration for juveniles (total length< 150 mm, average mass 15 g) was estimated at 11.6% body wet mass in January 1987 (summer). The daily ration for adults ranged from 2.7-3.4% body wet mass in winter July 1988 (average body mass 80.6 g), and from 3.1-4.1 % body wet mass in summer December 1988 (average body mass 110.0 g). The mean food consumption rate of the population was estimated at about 17 year-I, corresponding to a gross efficiency of 7.3%.

Interannual Variation in the Diet of the Antarctic Prion Pachyptila desolata at South Georgia

SummaryThe diet of the Antarctic Prion Pachyptila desolata was examined using food samples regurgitated by adult birds during five breeding seasons at Bird Island, South Georgia. In all years the diet was mainly crustaceans, with a small proportion of myctophid fish and trace amounts of cephalopods. Antarctic krill Euphausia superba was the dominant prey item in three years and was replaced by calanoid copepods, especially Rhincalanus gigas and Calanoides acutus, in two years of low krill abundance. Differences in the prey species taken and observations of foraging behaviour suggest that in years of low krill availability Antarctic Prions forage closer inshore, taking copepods by filtering surface water through their palatal lamellae. By switching to feeding on copepods Antarctic Prions are apparently able to maintain a comparable level of reproductive success, unlike most other krill feeding species which suffer much reduced reproductive performance in years of reduced krill availability.

Food resource utilization by juvenile Baltic cod Gadus morhua:a mechanism potentially influencing recruitment success at the demersal juvenile stage?

Pelagic and demersal juvenile Baltic cod Gadus morhua L. were collected during surveys in the Bornholm Basin (Baltic Sea) in autumn 1994. Stomach contents were examined for prey compo- sition in order to evaluate the potential importance of the pelagic and demersal habitats for recruitment success. Juvenile cod less than 40 mm fed exclusively on pelagic prey such as copepods and cladocer- ans. Between 40 and 50 mm the juveniles began to consume benthic prey such as mysids and amphipods; however, copepods were still the dominant food organisms. Between 50 and 70 mm the dominant prey items consumed were mysids and amphipods, with copepods comprising a minor com- ponent of the diet. Between 70 and 160 mm the juveniles' diet was composed exclusively of benthic prey with an increase in prey diversity. Mysids were slightly less important in the diet, while the abun- dance of polychaetes, decapods and fish increased with fish size. Amphipods remained almost constant in the diet of juveniles above 60 mm in length. These results indicate that a major change in food resource utilization started to occur at a fish length of 40 mm, with the main change taking place at approximately 50 mm, suggesting that juvenile Baltic cod make the transition to the benthic habitat at this length. This change in food preference is also reflected in the size of the prey items and the num- bers of prey consumed. Pelagic juveniles consumed much smaller prey than their demersal con- specifics. Neither prey size nor prey numbers consumed by pelagic and small demersal juveniles from this study differed from prey reported to be taken by juvenile cod of corresponding size in the Atlantic and the North Sea. However, prey organisms consumed by demersal juvenile Baltic cod larger than 90 mm were much smaller, and prey numbers much higher, than those reported to be consumed by juveniles in other areas. The apparent overlap in food resource utilization among the different size groups of demersal juveniles observed in this study suggests that in years with low prey abundance, or high abundance of pelagic juveniles, strong intra-specific competition for food resources may affect the recruitment success of Baltic cod.

Diet and Feeding Behavior of Two Dragonets <i>Calliurichthys japonicus</i> and <i>Repomucenus huguenini</i> in Tosa Bay, Southern Japan

Diet and food selectivity of Calliurichthys japonicus and Repomucenus huguenini were investigat ed from March 1992 to February 1993 in Tosa Bay, Kochi Prefecture. The diet of C. japonicus was com posed of polychaetes, amphipods, gastropods, ophiuroids, bivalves, cumaceans, and other small ben thic animals. Amphipods were abundant in number both in spring and winter months, while poly chaetes and ophiuroids were the most dominant in autumn and summer, respectively. Calliurichthys japonicus actively selected gastropods and showed a more randomized feeding character than R. huguenini. In R. huguenini, polychaetes and amphipods were the most dominant prey items throughout the year. Polychaetes were most abundant in number from spring to autumn, while the amphipods dominated in winter. Although R. huguenini had a similar diet to that of C. japonicus, R. huguenini had a more selective and specialized diet than the C. japonicus, and actively selected decapods, isopods , ostracods, and cumaceans. The difference in feeding habits between the two species may be attributed to their difference in adult body-size and their ability to visually differentiate prey at their different death distributions.

The Potential of the Bull Chub (Nocomis raneyi) as a Predator of the Zebra Mussel (Dreissena polymorpha) in Mid-Atlantic Coastal Rivers

-The feeding ecology and pharyngeal teeth of the bull chub (Nocomis raneyi) were investigated to determine whether the species could potentially crush and ingest zebra mussels (Dreissena polymorpha), should this mollusk become established in coastal rivers of the mid-Atlantic United States. We hypothesized that if bull chubs could crush mollusks similar in size and shell thickness to zebra mussels, bull chubs could successfully prey upon zebra mussels. The introduced Asiatic clam (Corbicula fiuminea) was used as a surrogate for the zebra mussel. Gut content analysis of larger (TL = 126 mm+) bull chubs from the James River, Virginia, revealed that mollusks were a dominant prey item, and Asiatic clams were ingested by bull chubs >125 mm TL. Shell thicknesses of zebra mussels and Asiatic clams of equivalent shell lengths were compared, and Asiatic clam shells were significantly thicker (P < 0.001) than zebra mussel shells. Because bull chubs ingest and crush the thicker-shelled Asiatic clam, the fish could successfully prey upon the zebra mussel if it becomes established in coastal rivers of the mid-Atlantic United States.

Amino acid profile in natural prey of sole— Solea solea

The amino acid profile of the dominant prey items of the sole natural diet was analysed; differences in the quantity and proportions of non-essential and essential amino acids between the sexes were determined. The highest level of total amino acid was found in Upogebia from F. Callianassidae. The prey items with a higher proportion of essential amino acids are Callianassidae, Glyceridae and Apseudidae. As a higher quantity of prey was found in the female stomach contents, a higher level of amino acids was found in the female diet. Differences between the sexes in essential amino acid proportions in sole spring diet have not been found. In both sexes, phenylalanine, histidine and lysine are the most abundant essential amino acids and valine the least abundant.

Predation on Juvenile Salmonids by Smallmouth Bass and Northern Squawfish in the Columbia River near Richland, Washington

Abstract The importance of juvenile salmonids in the diet of smallmouth bass Micropterus dolomieu and northern squawfish Ptychocheilus oregonensis was examined at a 6-km stretch of the Columbia River. Piscivorous fish were sampled with electrofishing gear on 4 d (May 2–3 and June 20–21, 1990) during emigration of juvenile anadromous salmonids. Sixty-two smallmouth bass and 69 northern squawfish were collected for diet analysis. Juvenile salmonids made up 59% of smallmouth bass diet by weight and were present in 65% of the stomachs of smallmouth bass. By a meal turnover method, smallmouth bass were estimated to consume from 1.4 (May 2–3) to 1.0 (June 20–21) salmonids per predator daily. Crayfish were the dominant prey item (41.4% by weight) of northern squawfish, but juvenile salmonids (28.8%) were also important. Northern squawfish consumed from 0.55 (May 2–3) to 0.34 (June 20–21) salmonids per predator daily. Smallmouth bass and northern squawfish consumed mostly subyearling Chinook salmon Oncorhynchus t...

Evidence for Yellow Perch Predation on Bythotrephes Cederstroemi in Southern Lake Michigan

Zooplankton and yellow perch ( Perca flavescens) were collected on 7 August 1990 in Lake Michigan at sites near Michigan City, Indiana, to determine abundance of Bythotrephes cederstroemi and to attempt to document possible predation by yellow perch. Zooplankton analysis revealed the concentration of Bythotrephes was highest in shallow near-shore water at 5 m (15/m 3) but dropped sharply at 10 m (2/m 3) and 15 m (1/m 3) sample sites. Stomach analyses of 48 yellow perch ranging in length from 80 to 179 mm revealed four fish had empty stomachs, four had nearly empty stomachs, 17 had half-full stomachs, and 23 had full stomachs. Bythotrephes was the dominant prey item, occurring in 95% of the stomachs which contained food. Numbers of Bythotrephes ranged from 0–323 per stomach with a mean of 48 (SD = 59). Diptera larvae and pupae were also important food items during this time occurring in 77% of the stomachs containing food. Diptera and other zooplankton were relatively more important than Bythotrephes to yellow perch < 100 mm maximum total length but Bythotrephes was eaten by all of the fish ≥ 100 mm and tended to be the major food item consumed by the larger fish. These data reveal Bythotrephes is an easily captured food source for yellow perch in extreme southern Lake Michigan.

A note on the diet and feeding selectivity of juvenile riverbream, Acanthopagrus berda (Forskal, 1775), in a subtropical mangrove creek

The diet and food selectivity of juvenile (< 100 mm S.L.) Acanthopagrus berda were investigated in Beachwood creek, north of Durban. Fish and benthic samples were taken from November 1986 to September 1987. The diet of juvenile A. berda was varied but crustaceans, mainly amphipods, were the dominant prey item. Ivlev's (1961) electivity index revealed a positive selection for amphipods, tanaids and fish scales.

Summer Feeding Patterns of White Perch, Channel Catfish, and Yellow Perch in the Susquehanna River, Maryland

Abstract Diel feeding patterns of white perch, yellow perch, and channel catfish were investigated by electroshocking in the lower Susquehanna River during the summer and early fall of 1982 and 1983. On several occasions, ambient densities of benthic and drifting invertebrates were also estimated. Stomach content analysis identified that trichopterans, primarily Cheumatopsyche sp., were the dominant prey item, accounting for at least 40% of diet biomass for each fish species. The amphipod Gammarus fasciatus and chironomids accounted for more than 40% of the yellow perch and channel catfish diets, respectively, but contributed less than 10% to the diet of the other fish species. Diurnal feeding patterns were most apparent for yellow perch, whose feeding was limited almost exclusively to daylight hours. Species composition and relative abundance in the diets of all three fish were more like the composition and abundance of the benthos than of the drift, suggesting that most foraging occurred on the bottom rather than in the water column. The timing and composition of drift did not appear to be related to prey selection by any of these fish species.

Diets of Young King and Spanish Mackerel Off the Southeast United States

The diet of larval and post-larval (n = 95 and 307), and juvenile (n = 489 and 508) king (Scomberomorus cavalia) and Spanish mackerel (S. maculatus) from the Gulf of Mexico and southeastern Atlantic coastal waters of the U.S. consisted principally of fishes. Carangids, clupeids, and engraulids occurred in 23, 7 and 9% of larval and post-larval king mackerel stomachs and in 20, 40 and 7% of larval and post-larval Spanish mackerel stomachs, respectively. Sciaenids were also common in king mackerel, occurring in 21% of the stomachs. Prey fishes included the genera Cynoscion, Caranx, and Anchoa, and the species Opisthonema oglinum. Invertebrates, principally small crustaceans and nudibranch larvae, occurred infrequently in the diets of both species, but more so in Spanish mackerel than king mackerel. The dominant prey items for juvenile mackerels from the Atlantic were engraulids, clupeids, balistids, and squids, collectively accounting for 73.3% by volume of the diet of king mackerel and 88.8% of Spanish mackerel. More invertebrates occurred in the diet of juvenile Spanish mackerel than king mackerel, but they accounted for a smaller volume, i.e., 2.1% as compared to 5.4% for the Atlantic fish. Chi-square tests indicated significant differences between the diets of juvenile mackerel from the Gulf of Mexico and the Atlantic coast.

Ulcers associated with larval Anisakis simplex B (Nematoda: Ascaridoidea) in the forestomach of harbour porpoises Phocoena phocoena (L.)

Anisakis simplex B larvae and adults occurred in the forestomach of 7 of 10 Phocoena phocoena found drowned in cod nets in the winters (November–January) of 1977–1978, 1980–1981, 1981–1982, and 1983–1984, along the Scottish east coast. A cluster of third- and fourth-stage larvae was found in one large, crater-like ulcer in the wall of the ventral "hemisphere" of the forestomach in five porpoises. A sixth infected animal had one large ulcer bearing a larval nematode cluster, plus, at a separate site in the ventral hemisphere, an aggregation of six very small ulcers, three of which contained larvae. The remaining infected porpoise harboured a large multiple ulcer at a single site in the ventral hemisphere, each of its five craters bearing a cluster of larvae. Adult male and female nematodes were apparently "free" in the forestomach lumen. One third-stage larva of Contracaecum sp. was the only other parasite found in the gastrointestinal tract of the 10 porpoises. Whiting (Merlangius merlangus) was the dominant prey item, and may have been the source of A. simplex B infection.

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

AbstractThe 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 sandlanceAmmodytes americanuswas 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 herringClupea harengusincreased 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.

Diet of the Barn Owl, Tyto-Alba, in the Tanami Desert, Northern Territory

The diet of the barn owl was determined by analysing egested pellets collected from the Tanami Desert. These data were also used to examine the distribution of small mammals in the region. Rodents were the dominant prey items, forming more than 74% of prey biomass in all samples. The dominant rodent species were those that undergo large fluctuations in population size. Notomys alexis was the dominant prey item in 15 of the 17 samples. In all samples, one or two species of rodents formed 47-100% of prey biomass. Dasyurids were relatively minor prey items, forming less than 12% of prey biomass in all samples. It is suggested that this is a reflection of their abundance relative to rodents. Bats, birds, lizards and insects combined formed less than 14% of prey biomass in all but one sample (24%). Behavioural and life-history characteristics of prey appear to affect their susceptibility to predation. The analysis of pellets proved to be a useful supplementary technique to conventional methods of surveying small mammals. All species of small mammal that could be expected were identified in owl pellets. Notomys amplus was recorded in pellets but not collected by conventional techniques.

Use of enclosures to detect the contribution of particular zooplankton to growth of young-of-the-year yellow perch (Perca flavescens Mitchell).

Densities of the cladoceran, Holopedium gibberum, were manipulated in 18 enclosures containing juvenile (age 0+) yellow perch (Perca flavescens) and mean-lake densities of other zooplankton. In enclosures, where nearlake densities of all zooplankton species including Holopedium were maintained, young-of-the-year perch grew significantly heavier and longer than in experimental enclosures where Holopedium was excluded. Holopedium comprised between 15-45% of the diet (wet weight) of perch in the first 2 weeks of July in the control treatment (Holopedium at or near ambient lake densities) and only 3-7% of total biomass ingested in the experimental treatment (Holopedium density selectively reduced). Predation on Holopedium decreased dramatically after the 2nd week of July in the control treatment after which Chaoborus, chironomids, and Sida became dominant prey items (by weight) of juvenile perch. These findings suggest that growth and survivorship of age 0+ perch in Precambrian Shield lakes may be coupled to Holopedium abundance. Thus, utilization of Holopedium by young-of-the-year yellow perch may affect recruitment of this species since overwintering survivorship, range of accessible prey sizes or species, and vulnerability of juvenile perch to predation by larger fish depend on body size, which is reduced when Holopedium is excluded from the diet.

相模湾シラス漁場におけるカタクチイワシの食性

In order to clarity food habits of Japanese anchovy in the Shirasu (anchovy larvae) fishing ground within Sagami Bay, gut contents were analysed during the period of July through October, 1984. This period was the major fishing season for Shirasu. The prey organisms in the guts consisted of 7 kinds of zooplankton. Copepoda were the most dominant prey items, Among others, Oithona comprised 67 numerical percentage of total prey organisms detected in the guts. Food preference of larval and juvenile anchovies was found to change with increase in lengths: TL 20-25mm size-class chiefly fed on O. davisae and Evadne, 26-30mm size-class on Paracalanidae and Penilia in addition to the former two items, and anchovy over 31mm fed on Oncaea, Microsetella, Bivalvia larvae and so on. Seasonal abundance of O. davisae in anchovy guts changed with the density of O. davisae in the bottom layer of the fishing ground. According to change of food preference with growth, anchovy probably moved from one region, where O. davisae was abundant, to the other region where another zooplankton was distribut-ed, so that the school seemed to be composed of almost the same size of anchovy.