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1.
John M. Logan Enrique Rodríguez-Marín Nicolas Goñi Santiago Barreiro Haritz Arrizabalaga Walter Golet Molly Lutcavage 《Marine Biology》2011,158(1):73-85
Atlantic bluefin tuna (Thunnus thynnus) are highly migratory predators whose abundance, distribution, and somatic condition have changed over the past decades.
Prey community composition and abundance have also varied in several foraging grounds. To better understand underlying food
webs and regional energy sources, we performed stomach content and stable isotope analyses on mainly juvenile (60–150 cm curved
fork length) bluefin tuna captured in foraging grounds in the western (Mid-Atlantic Bight) and eastern (Bay of Biscay) Atlantic
Ocean. In the Mid-Atlantic Bight, bluefin tuna diet was mainly sand lance (Ammodytes spp., 29% prey weight), consistent with historic findings. In the Bay of Biscay, krill (Meganyctiphanes norvegica) and anchovy (Engraulis encrasicolus) made up 39% prey weight, with relative consumption of each reflecting annual changes in prey abundance. Consumption of anchovies
apparently declined after the local collapse of this prey resource. In both regions, stable isotope analysis results showed
that juvenile bluefin tuna fed at a lower trophic position than indicated by stomach content analysis. In the Mid-Atlantic
Bight, stable isotope analyses suggested that >30% of the diet was prey from lower trophic levels that composed <10% of the
prey weights based upon traditional stomach content analyses. Trophic position was similar to juvenile fish sampled in the
NW Atlantic but lower than juveniles sampled in the Mediterranean Sea in previous studies. Our findings indicate that juvenile
bluefin tuna targeted a relatively small range of prey species and regional foraging patterns remained consistent over time
in the Mid-Atlantic Bight but changed in relation to local prey availability in the Bay of Biscay. 相似文献
2.
Ecologists primarily use δ15N values to estimate the trophic level of organisms, while δ13C, and even recently δ15N, are utilized to delineate feeding habitats. However, many factors can influence the stable isotopic composition of consumers,
e.g. age, starvation or isotopic signature of primary producers. Such sources of variability make the interpretation of stable
isotope data rather complex. To examine these potential sources of variability, muscle tissues of yellowfin tuna (Thunnus albacares) and swordfish (Xiphias gladius) of various body lengths were sampled between 2001 and 2004 in the western Indian Ocean during different seasons and along
a latitudinal gradient (23°S to 5°N). Body length and latitude effects on δ15N and δ13C were investigated using linear models. Both latitude and body length significantly affect the stable isotope values of the
studied species but variations were much more pronounced for δ15N. We explain the latitudinal effect by differences in nitrogen dynamics existing at the base of the food web and propagating
along the food chain up to top predators. This spatial pattern suggests that yellowfin and swordfish populations exhibit a
relatively unexpected resident behaviour at the temporal scale of their muscle tissue turnover. The body length effect is
significant for both species but this effect is more pronounced in swordfish as a consequence of their different feeding strategies,
reflecting specific physiological abilities. Swordfish adults are able to reach very deep water and have access to a larger
size range of prey than yellowfin tuna. In contrast, yellowfin juveniles and adults spend most of their time in the surface
waters and large yellowfin tuna continue to prey on small organisms. Consequently, nitrogen isotopic signatures of swordfish
tissues are higher than those of yellowfin tuna and provide evidence for different trophic levels between these species. Thus,
in contrast to δ13C, δ15N analyses of tropical Indian Ocean marine predators allow the investigation of complex vertical and spatial segregation,
both within and between species, even in the case of highly opportunistic feeding behaviours. The linear models developed
in this study allow us to make predictions of δ15N values and to correct for any body length or latitude differences in future food web studies. 相似文献
3.
Muscle tissue was collected for stable isotope analysis (SIA) from the main fish predators and their fish and cephalopod prey
from oceanic waters off eastern Australia between 2004 and 2006. SIA of δ15N and δ13C revealed that the species examined could be divided into three main trophic groups. A “top predator” group consisted mainly
of large billfish (Xiphias gladius and Tetrapturus audax), yellowfin (Thunnus albacares), bigeye (T. obesus) and southern bluefin (T. maccoyii) tunas and sharks; with mako (Isurus oxyrinchus) the highest. Below this tier was a second group composed of mid-trophic level fishes including albacore tuna (Thunnus alalunga), lancet fish (Alepisaurus ferox), mahi mahi (Coryphaena hippuris) and ommastrephid squid. Underlying both groups was a grouping of small fishes including myctophids, small scombrids and
nomeids as well as surface fishes including macrorhamphosids. These groupings were based largely on mean animal size which
showed a positive linear relation to δ15N (r
2 = 0.58). Some species showed significant ontogenetic variation in either δ15N (swordfish, lancet fish, yellowfin and albacore tuna) or δ13C (mako shark). We also noted a consistent latitudinal change in δ15N and δ13C at ~28°S for the top predator species, particularly albacore and yellowfin tuna. The differences were consistent with a
change from oligotrophic Coral Sea to nutrient rich Tasman Sea waters. These differences suggest that predatory fishes may
have extended residence time in distinct regions off eastern Australia. 相似文献
4.
Sea lions are generally considered opportunistic feeders. However, studies from different areas suggest their diet consists
mostly of four to five types of prey. Previous studies in Galapagos sea lions have identified at least three feeding strategies
for this species, suggesting diversification of their diet. Diet diversification is favored in organisms with relatively high
trophic position and subject to high intra-specific and low inter-specific competition. Zalophus wollebaeki meet these criteria as the only pinniped on San Cristobal Island, where three sea lion rookeries are located within 11 km:
a distance considerably shorter than their 41 km foraging range. To measure the degree of diet diversification, we used scats
and stable isotope analyses. A total of 270 scat samples from lactating females and 142 fur samples from sea lion pups were
collected during the breeding season 2006. The scat analysis identified distinct diets among rookeries, with minimal trophic
overlap (Cλ = 0.19), a trophic level TL = 4.5 (secondary–tertiary carnivore), and trophic breadth of a specialist predator (B
i
= 0.37). The mean δ15N and δ13C values were 13.07 ± 0.52 and −16.34 ± 0.37, respectively. No significant difference was found in the δ15N values from the sea lion rookeries, but differences were found inter- and intra-population in δ13C values for pups from different groups (ANOVA P < 0.05). Our results indicate that diet diversification is present in the Galapagos sea lion and may play important role
to the survival of the species in a habitat where pinniped populations are limited. 相似文献
5.
Ruth Fernández Susana García-Tiscar M. Begoña Santos Alfredo López Jose A. Martínez-Cedeira Jason Newton Graham J. Pierce 《Marine Biology》2011,158(5):1043-1055
Skin and muscle from 43 bottlenose dolphins (38 juveniles/adults, 5 calves) stranded in NW Spain were analysed to determine
whether stable isotope ratios (δ13C and δ15N) could be used to assess dietary variation, habitat segregation and population substructure. Results were compared with
published stomach contents data. Stable isotope ratios from 17 known prey species were also determined. Isotope ratios of
the main prey (blue whiting, hake) varied significantly in relation to fish body size. Dolphin calves showed significant heavy
isotope enrichments compared to adult females. Excluding calves, δ15N decreased with increasing dolphin body size, probably related to an ontogenetic shift in diet towards species at lower trophic
levels, e.g. on blue whiting as suggested by stomach content results. Bottlenose dolphins were divided into two putative populations
(North, South) based on previous genetic studies, and values of δ13C and δ15N differed significantly between these two groups, confirming the existence of population structuring. 相似文献
6.
Marianne Robert Laurent Dagorn Jean Louis Deneubourg David Itano Kim Holland 《Marine Biology》2012,159(4):907-914
Several lines of evidence indicate that aggregations of yellowfin tuna associated with floating objects are more frequently
composed of small animals than larger ones. Also, the diet of small yellowfin tuna caught at anchored fish aggregating devices
(FADs) around Oahu, Hawaii, was found to shift quite rapidly when these fish reached approximately 50 cm FL. In order to test
for ontogenetic changes in aggregation behavior, we tagged and released two distinct size classes of yellowfin tuna in an
array of anchored FADs around Oahu, Hawaii. Twenty-four yellowfin tuna 30–39 cm FL and 16 yellowfin tuna 63–83 cm FL were
tagged with acoustic transmitters and released near anchored FADs equipped with automated acoustic receivers. Fish in the
smaller size class stayed about 2.5 times longer at individual FADs than the larger fish (mean 4.05 days vs. 1.65 days) and
displayed larger horizontal movements within the array. However, the durations of unassociated phases, residence times in
the entire FAD array, percentage of time spent associated with FADs and numbers of movements between FADs did not show any
difference between the two size groups. The observed size-dependent behavior is discussed in terms of physiological abilities,
diet segregation and anti-predator behavior. 相似文献
7.
To test the hypothesis that stable isotope ratios from marine organisms vary, the δ15N and δ13C values from fish and squid collected in Alaskan waters were measured across years (1997, 2000, and 2005), seasons, geographic
locations, and different size/age classes, and between muscle tissue and whole animals. Temporal, geographic, and ontogenetic
differences in stable isotope ratios ranged from 0.5–2.5‰ (δ15N) to 0.5–2.0‰ (δ13C). Twenty-one comparisons of stable isotope values between whole organisms and muscle tissue revealed only four small differences
each for δ15N and δ13C, making costly and space prohibitive collection of whole animals unnecessary. The data from this study indicate that significant
variations of stable isotope values from animals in marine systems necessitates collection of prey and predator tissues from
the same time and place for best interpretation of stable isotope analysis in foraging ecology studies. 相似文献
8.
The feeding ecology of Merluccius hubbsi was investigated in 2 regions of SE Brazil. The major food sources for the hakes were fish, crustaceans, and squid. In the
upwelling system of Cabo Frio, the diet was very similar in the summers of 2001/2002 and spring 2002; fish were the most important
prey followed by crustaceans. In Ubatuba, euphausiids were an important prey during the winter 2001 (100 m), while in the
summer 2002, fish and amphipods predominated in the diet in the shallower site (40 m) and squid in the deeper site (100 m).
The hakes showed temporal differences in stable isotope signatures in both regions, while C:N ratios varied only in Cabo Frio.
δ15N and δ13C (bulk and corrected for lipid content) increased with fish length, which seems to be related to the increasing importance
of fish and decreasing importance of euphausiids and amphipods in the diet of larger hakes. The mean trophic level of 3.7
for M. hubbsi was estimated using δ15N of bivalves as baseline and the fractionation of 3.4‰ between trophic levels. 相似文献
9.
Stomach content analyses are commonly used to study both fish feeding behaviour and trophic conditions. However, the interpretation of such data depends on fish foraging behaviour for a given environment and how representative the stomach contents are to the prey distribution. Tuna feeding behaviour was studied within the context of a research programme conducted in French Polynesia. Tuna prey distribution was characterised using acoustic measurements and pelagic trawls; thereafter, this distribution was compared with the stomach contents of tuna caught using an instrumented longline. Acoustic, pelagic trawling and stomach content analyses give complementary elements to describe the pelagic trophic habitat and to better understand tuna-prey relationships. The classic concept of a reduced food availability for tunas in the tropical pelagic environment seems relative. Tunas able to dive enough during daytime to exploit the migrant micronektonic species secure a source of regular food. This is particularly true of bigeye tuna (Thunnus obesus), which have ecophysiological capacities for this purpose. The behaviour of albacore tuna (T. alalunga), which dive >400 m in depth, remains less clear, as little is known about their vertical behaviour. Lastly, yellowfin tuna (T. albacares), which are distributed in more superficial waters, can better exploit the biomass of juvenile fish and crustaceans exported from the reefs. Analysis of the stomach fullness of tuna caught by longline, a passive gear, generally showed an empty state. This result suggests that most tuna foraging on large prey aggregations present in the study area are quickly satiated and escape longline capture and sampling. A consequence is that studies of tuna feeding behaviour based on longlining may be biased, particularly when large aggregations of prey are present such as in convergence zones. Another potential consequence is that longline tuna catch rates could differ according to prey richness. Longline tuna catch rates may sometimes reflect the relative abundance of prey rather than relative tuna abundance. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00227-001-0776-3. 相似文献
10.
Geographical variations in the trophic ecology of Japanese anchovy, Engraulis
japonicus, inferred from carbon and nitrogen stable isotope ratios 总被引:1,自引:0,他引:1
Carbon and nitrogen stable isotope ratios of Japanese anchovy (Engraulis japonicus) and their stomach contents were examined and compared among various regions around Japan. Geographical variations in the
isotope ratios were found between inshore and Pacific offshore regions. While most of the anchovy samples had isotope ratios
around −17.6‰ for δ13C and 10.0‰ for δ15N as median values, higher (more enriched) isotope values were found in the anchovy sampled from inshore regions. On the contrary,
lower (more depleted) values were found mostly in the anchovy from the Pacific offshore region including the Kuroshio Extension
and Kuroshio-Oyashio transition zones. Higher carbon isotope ratios in the inshore regions may reflect a carbon source from
benthic primary producers in addition to phytoplankton possibly through the consumption of the larvae of benthic organisms
such as bivalves or decapods, which were found in the stomach contents of the inshore anchovy. Variations in the nitrogen
isotope ratio may reflect not only differences in the trophic level of prey species, but also variations in the baseline level
of food webs. Stable isotope ratios are potentially a useful tool for understanding the stock/population structure and migration
of anchovy. The present findings indicate the potential importance of the “inshore–offshore” variations in the biology of
Japanese anchovy populations in the northwestern Pacific waters. 相似文献
11.
We present the first quantitative analyses of dolphinfish (Coryphaena hippurus) foraging habits and trophic interactions with co-occurring yellowfin (Thunnus albacares) and albacore (T. alalunga) tunas in the Southern New England region of the western North Atlantic Ocean. Fish caught by recreational anglers in offshore waters of Massachusetts were sampled during the summers of 2007–2010. Diet analysis revealed that shortfin squid (Illex illecebrosus) and small pelagic crustaceans were principal prey to dolphinfish, yellowfin tuna, and albacore tuna. A wide variety of Sargassum-associated fishes were also important to dolphinfish and yellowfin tuna diets. Dietary (Schoener’s index: 0.82–0.86) and isotopic niche (isotopic ellipse overlap: 53.6–64.7 %) overlap was high, and dolphinfish and tunas occupied equivalent trophic positions (TP = 3.4–3.6). Relative prey size in dolphinfish and yellowfin tuna diets exhibited convergence with ontogeny. Overall, dolphinfish had the greatest isotopic niche width, which was twice as large as yellowfin tuna and three times as large as albacore tuna; dolphinfish also consumed the greatest range of prey sizes. Results quantify dolphinfish trophic interactions in the western Atlantic near the northern extent of their geographical range, and are relevant for ecosystem-based management of the offshore pelagic guild in the context of shifting fish populations and fisheries in response to climate and ecological change. 相似文献
12.
R. W. Brill B. A. Block C. H. Boggs K. A. Bigelow E. V. Freund D. J. Marcinek 《Marine Biology》1999,133(3):395-408
We measured the horizontal and vertical movements of five adult yellowfin tuna (Thunnus albacares, estimated body mass 64 to 93 kg) near the main Hawaiian Islands, while simultaneously gathering data on oceanographic conditions
and currents. Fish movements were recorded by means of ultrasonic depth-sensitive transmitters. Depth–temperature and depth–oxygen
profiles were measured with vertical conductivity–temperature–depth (CTD) casts, and the current-velocity field was surveyed
using an acoustic Doppler current profiler (ADCP). Large adult yellowfin tuna spent ≃60 to 80% of their time in or immediately
below the relatively uniform-temperature surface-layer (i.e. above 100 m), a behavior pattern similar to that previously reported
for juvenile yellowfin tuna, blue marlin (Makaira nigricans), and striped marlin (Tetrapturus audax) tracked in the same area. In all three species, maximum swimming depths appear to be limited by water temperatures 8 C°
colder than the surface-layer water temperature. Therefore, neither large body mass, nor the ability to maintain elevated
swimming-muscle temperatures due to the presence of vascular counter-current heat exchangers in tunas, appears to permit greater
vertical mobility or the ability to remain for extended periods below the thermocline. In those areas where the decrease in
oxygen with depth is not limiting, the vertical movements of yellowfin tuna, blue marlin and striped marlin all appear to
be restricted by the effects of water temperature on cardiac muscle function. Like juvenile yellowfin tuna, but unlike blue
marlin and striped marlin, adult yellowfin tuna remained within 18.5 km of the coast and became associated with floating objects,
including anchored fish-aggregating devices (FADs) and the tracking vessel. Like juvenile yellowfin tuna, large adult yellowfin
repeatedly re-visit the same FAD, and appear able to navigate precisely between FADs that are up to 18 km apart. The median
speed over ground ranged from 72 to 154 cm s−1. Neither speed nor direction was strongly influenced by currents.
Received: 27 March 1998 / Accepted: 13 November 1998 相似文献
13.
Rocío Moreno Lluís Jover Ignacio Munilla Alberto Velando Carola Sanpera 《Marine Biology》2010,157(3):545-553
The widespread omnivory of consumers and the trophic complexity of marine ecosystems make it difficult to infer the feeding
ecology of species. The use of stable isotopic analysis plays a crucial role in elucidating trophic interactions. Here we
analysed δ15N, δ13C and δ34S in chick feathers, and we used a Bayesian triple-isotope mixing model to reconstruct the diet of a generalist predator,
the yellow-legged gull (Larus michahellis) that breeds in the coastal upwelling area off northwest mainland Spain. The mixing model indicated that although chicks
from all colonies were fed with a high percentage of fish, there are geographical differences in their diets. While chicks
from northern colonies consume higher percentages of earthworms, refuse constitutes a more important source in the diet of chicks from western colonies. The three-isotope mixing model revealed
a heterogeneity in foraging habitats that would not have been apparent if only two stable isotopes had been analysed. Moreover,
our work highlights the potential of adding δ34S for distinguishing not only between terrestrial and marine prey, but also between different marine species such as fish,
crabs and mussels. 相似文献
14.
Mariela Pajuelo Karen A. Bjorndal Kimberly J. Reich Michael D. Arendt Alan B. Bolten 《Marine Biology》2012,159(6):1255-1267
Most studies on the foraging ecology of loggerhead turtles (Caretta caretta) have focused on adult females and juveniles. Little is known about the foraging patterns of adult male loggerheads. We analyzed
tissues for carbon and nitrogen stable isotopes (δ13C and δ15N) from 29 adult male loggerheads tracked with satellite transmitters from one breeding area in Florida, USA, to evaluate
their foraging habitats in the Northwest Atlantic (NWA). Our study revealed large variations in δ13C and δ15N and a correlation between both δ13C and δ15N and the latitude to which the loggerheads traveled after the mating season, thus reflecting a geographic pattern in the
isotopic signatures. Variation in δ13C and δ15N can be explained by differences in food web baseline isotopic signatures rather than differences in loggerhead trophic levels.
Stable isotope analysis may help elucidate residency and migration patterns and identify foraging sea turtle subpopulations
in the NWA due to the isotopically distinct habitats used by these highly migratory organisms. 相似文献
15.
Pelagic seabirds are central place foragers during breeding and variation in foraging trip duration and range reflect differences
in diet and chick provisioning, through the exploitation of divergent habitats of varying productivity. We tested whether
these relationships hold in small procellarriids by equipping chick-rearing Cook’s petrel Pterodroma cookii (200 g) with geolocation-immersion loggers, conducting isotope analysis of blood and measuring chick meal mass following
foraging trips of varying duration. Cook’s petrel tracked during chick rearing from Little Barrier Island (LBI) and Codfish
Island (CDF), New Zealand had larger maximum ranges during longer foraging trips. Blood nitrogen isotope signatures (δ15N) of adults were significantly higher after foraging trips of longer duration, but not of greater maximum range. There was
no significant relationship between blood carbon isotope signatures (δ13C) and foraging trip characteristics. Proportion of time spent on the sea surface and the mass of the meal brought back to
chicks were consistently greater for Cook’s petrel with larger maximum ranges, which in the case of birds from CDF coincided
with productive subtropical convergence zone habitats. As predicted, trip duration reflected divergent foraging behaviours
in Cook’s petrel during breeding. We suggest that the availability of different prey is a key factor governing at-sea distributions
and dietary composition of this species. 相似文献
16.
Stable 13C and 15N isotope analyses of scale, bone, and muscle tissues were used to investigate diet and trophic position of North Atlantic bluefin tuna (Thunnus thynnus Linnaeus) during residency in the northwest Atlantic Ocean off the northeast coast of the United States. Adult bluefin tuna scales collected from fish between June and October 2001 were significantly enriched in 13C compared to both muscle and bone across all months, while muscle was significantly enriched in 15N compared to either bone or scale throughout the same period. In muscle tissue, there was evidence of a shift over the summer from prey with 13C values (–17 to –18) that were characteristic of silver hake (Merluccius bilinearis) to species with 13C values of –20 to –21 that were similar to Atlantic herring (Clupea harengus) and sandlance (Ammodytes americanus). Depletion of 15N values in adult scales and bone compared to muscle tissue may be explained by bone and scale samples representing juvenile or life-long feeding habits, isotopic routing, or isotopic differences in amino acid composition of the three tissue types. Adult bluefin tuna were estimated to be feeding at a trophic position similar to pelagic sharks in the northwest Atlantic Ocean, while the trophic positions of yellowfin tuna (Thunnus albacares), albacore tuna (Thunnus alalunga), and juvenile bluefin tuna were indicative of a diet of up to a full trophic position below adult bluefin tuna. The close relationship between the juvenile bluefin 15N values and those of suspension feeders suggests that nektonic crustaceans or zooplankton may contribute significantly to the diet of bluefin tuna, a food source previously overlooked for this species in the northwest Atlantic Ocean.Communicated by J.P. Grassle, New Brunswick 相似文献
17.
Ana Paula Madeira Di Beneditto Cristina Maria Magalhães de Souza Helena Amaral Kehrig Carlos Eduardo Rezende 《Marine Biology》2011,158(10):2209-2217
The feeding preferences of the coastal dolphins Pontoporia blainvillei and Sotalia guianensis in south-eastern Brazil (21o18′S–22o25′S) were assessed through the prey’s index of relative importance (IRI), total mercury
concentration (Hgtot), and stable isotopic (δ15N and δ13C) to compare their efficiency in the discrimination of prey contribution to the predators’ diet. The IRI was the best tool
to describe the dolphins’ preference, while Hgtot and δ15N seemed to be efficient as a trophic marker when the diet is made up of prey of varying sizes, as observed in S. guianensis. Both dolphins presented lighter δ15N than their prey species, which is an unusual pattern. However, as the sample size to isotope ratios analysis was small,
especially to the dolphins, the results should be considered with caution, and further studies are necessary to corroborate
these findings. The δ13C values characterized a typical coastal food chain, confirming the preferential area of these species. 相似文献
18.
We provided a classification tree modeling framework for investigating complex feeding relationships and illustrated the method
using stomach contents data for yellowfin tuna (Thunnus albacares) collected by longline fishing gear deployed off eastern Australia between 1992 and 2006. The non-parametric method is both
exploratory and predictive, can be applied to varying size datasets and therefore is not restricted to a minimum sample size.
The method uses a bootstrap approach to provide standard errors of predicted prey proportions, variable importance measures
to highlight important variables and partial dependence plots to explore the relationships between explanatory variables and
predicted prey composition. Our results supported previous studies of yellowfin tuna feeding ecology in the region. However,
the method provided a number of novel insights. For example, significant differences were noted in the prey of yellowfin tuna
sampled north of 20°S in summer where oligotrophic waters dominate. The analysis also identified that sea-surface temperature,
latitude and yellowfin size were the most important variables associated with dietary differences. The methodology is appropriate
for delineating ecosystem-level trophic dynamics, as it can easily incorporate large datasets comprising multiple predators
to explore trophic interactions among members of a community. Broad-scale relationships among explanatory variables (environmental,
biological, temporal and spatial) and prey composition elucidated by this method then serve to focus and lend validity to
subsequent fine-scale analyses of important parameters using standard diet methods and chemical tracers such as stable isotopes. 相似文献
19.
Leatherback turtles, Dermochelys coriacea, are highly migratory, spending most of their lives submerged or offshore where their feeding habits are difficult to observe.
In order to elucidate the foraging ecology of leatherbacks off Massachusetts, USA, stable isotope analyses were performed
on leatherback tissues and prey collected from 2005 to 2009. Stable isotope ratios of nitrogen and carbon were determined
in whole blood, red blood cells, blood plasma, muscle, liver, and skin from adult male, female, and subadult leatherbacks.
Isotopic values were analyzed by body size (curved carapace length) and grouped by sex, and groups were tested for dietary
differences. Gelatinous zooplankton samples were collected from leatherback foraging grounds using surface dip nets and stratified
net tows, and prey contribution to leatherback diet was estimated using a two-isotope Bayesian mixing model. Skin and whole
blood δ13C values and red blood cell δ15N values were correlated with body size, while δ13C values of red blood cells, whole blood, and blood plasma differed by sex. Mixing model results suggest that leatherbacks
foraging off Massachusetts primarily consume the scyphozoan jellyfishes, Cyanea capillata and Chrysaora quinquecirrha, and ctenophores, while a smaller proportion of their diet comes from holoplanktonic salps and sea butterflies (Cymbuliidae).
Our results are consistent with historical observations of leatherback turtles feeding on scyphozoan prey in this region and
offer new insight into size- and sex-related differences in leatherback diet. 相似文献
20.
Cephalopod beaks retrieved from stomachs of dead emperor penguin chicks at Pointe Géologie, Terre Adélie, provide information
on taxonomic and size composition of the penguin’s squid diet, on the trophic range of the squid species preyed upon and on
the fractional trophic impact of the penguin on the whole food web. Emperor penguins prey upon four squid species (Psychroteuthis glacialis, Kondakovia longimana, Gonatus antarcticus, Alluroteuthis antarcticus) and do not take squid larger than 480 mm mantle length. Larger squid live either below the penguin’s diving range or are
beyond its handling capacity. Nitrogen stable isotope ratios indicate that squids cover a range of about two trophic levels
(2.5–8‰ δ15N). The impact of the emperor penguin, however, concentrates on the upper part of this range, about 68% of its squid prey
being >6‰ δ15N. The principal components of the emperor’s diet, fish, krill and squid, differ distinctly in average trophic level. Consequently
the trophic position of the emperor penguin changes accordingly with diet composition and may differ by almost one trophic
level between different emperor penguin colonies. 相似文献