Prey Energy Density Research Articles

Prey selection by the common dolphin: Fulfilling high energy requirements with high quality food

Which characteristics define the prey species constituting the diet of a given predator? Answering this question would help predict a predator's diet and improve our understanding of how an ecosystem functions. The aim of this study was to test if the diet of common dolphins, Delphinus delphis, in the oceanic Bay of Biscay reflected prey availability or a selection shaped by prey energy densities (ED). To do this, the community of potential prey species, described both in terms of relative abundance and energy densities, was compared to the common dolphin diet in this area. This analysis of a predator's diet and its prey field revealed that the common dolphin selected its diet on the basis of prey energy densities (significant values of Chesson's index for ED>5kJg−1). High-energy prey were positively selected in the diet [e.g. Notoscopelus kroeyeri, ED=7.9kJg−1, 9% of relative abundance in the environment (%Ne); 62% of relative abundance in the diet (%Nd)] and low-energy prey disregarded (Xenodermichthys copei, ED=2.1kJg−1, 20%Ne, 0%Nd). These results supported the hypothesis that common dolphins selected high energy density prey species to meet their energetically expensive life style and disregard prey organisms of poor energy content even when abundant in the environment.

A review of estimates of daily energy expenditure and food intake in cormorants ( Phalacrocorax spp.)

Daily energy expenditure (DEE) and daily food intake (DFI) are key parameters in estimating population level consumption by cormorants. A number of different methods are still employed in estimating these parameters along with different estimates for assimilation efficiency (if used) and prey energy density. The pellet/fish size reconstruction and percent adult body weight methods underestimate DFI for a number of reasons including an implied underestimation of DEE. In the absence of study-specific data, an assimilation efficiency of 0.80 and prey energy density of 5.42 kJ∙g − 1 are recommended. The bioenergetic model for field metabolic rate from Ellis and Gabrielsen (2002) is recommended for adults during the nesting season and their model for basal metabolic rate (BMR × 2.5) is recommended for adults or sub-adults outside the nesting season. Comparisons between empirical and bioenergetic models for chick DFI are also made with recommendations on estimating DFI.

Are the dynamics of gastric evacuation of natural prey in a piscivorous flatfish different from what is going on in a gadoid?

Despite the fact that the stomach of turbot Psetta maxima is a curved tube that forms a half circle, it was demonstrated that gastric evacuation in this predatory flatfish fed natural prey closely followed the surface-dependent cylinder model developed from studies on gadoids with a straight stomach. Evacuation experiments were performed on two size groups of P. maxima fed sandeel Ammodytes tobianus as well as on P. maxima fed brown shrimp Crangon crangon at three different temperatures. This enabled the provision of a gastric evacuation model for studies on P. maxima, which takes into account the effects of the explanatory variables predator size, temperature, prey energy density and resistance of prey to the digestive processes in the stomach. Basically, the cylinder model predicts that a square-root function accurately describes gastric evacuation, which is inconsistent with the conclusion of a previous study on P. maxima that evacuation of A. tobianus is essentially linear with time. Use of the cylinder model to the values of the explanatory variables presented in the latter study, however, gave accurate predictions of the actually acquired evacuation data, which points to the generic value of the model.

Changes in mercury bioaccumulation in an apex predator in response to removal of an introduced competitor

We evaluated methylmercury (MeHg) concentrations in native apex predators, lake trout Salvelinus namaycush before and after the large-scale removal of introduced predators, smallmouth bass Micropterus dolomieu in a 270 ha Adirondack lake. Previous studies show that removing competitors can result in increased growth and decreased mercury concentrations in remaining fish. Instead, we observed a significant increase in lake trout MeHg concentrations despite observed increases in lake trout growth. Bioenergetics simulations predicted similar increases in lake trout MeHg concentrations. Higher MeHg in prey fish (post-removal diet) relative to invertebrates (pre-removal diet) was the most important factor increasing lake trout MeHg concentrations. However, this effect was counteracted by increased lake trout growth (i.e., growth dilution) likely due to a combination of decreased foraging costs and an increase in prey energy density. These data provide evidence for a mechanism (diet shift due to reduced competition) by which changes in food web structure can influence MeHg concentrations in top predators.

Modeling the Marine Resources Consumed in Raising a King Penguin Chick: An Energetics Approach

Accurate estimates of penguin energetics would represent an important contribution to our understanding of the trophodynamics of the Southern Ocean ecosystem and our ability to predict effects of environmental change on these species. We used the heart rate-rate of oxygen consumption technique to estimate rate of energy expenditure in adult king penguins raising a chick, in combination with data from the literature on changes in adult mass, chick energy requirements, and prey energy density. Our model estimated a variety of energetic costs and quantities of prey consumption related to raising a king penguin chick during the austral summer. The total energy requirements of a king penguin chick at the Crozet Archipelago from hatching until reaching a mass of 8 kg 90 d later is 271 MJ, representing the consumption of 38.4 kg of myctophid fish. A successfully breeding male requires 0.78 kg d(-1) of fish during the entirety of the incubation period and 1.14 kg d(-1) during the subsequent 90 d of chick rearing. Assuming the same energy requirements for females, the estimated 580,000 pairs of king penguins that breed successfully at Crozet each year, together with their chicks, consume a total of around 190,000 tons of fish during the incubation and summer rearing periods combined. If, due to depletion of fish stocks, the diet of breeders and chicks during the summer becomes identical to the typical diet of adults during the austral winter, the mass of prey required by both adults and chicks combined (where the chick still reaches 8 kg after 90 d) would increase by more than 25%.

Comparisons between Consumption Estimates from Bioenergetics Simulations and Field Measurements for Walleyes from Oneida Lake, New York

AbstractDaily consumption was estimated from the stomach contents of walleyes Sander vitreus collected weekly from Oneida Lake, New York, during June‐October 1975, 1992, 1993, and 1994 for one to four age‐groups per year. Field rations were highly variable between weeks, and trends in ration size varied both seasonally and annually. The coefficient of variation for weekly field rations within years and ages ranged from 45% to 97%. Field estimates were compared with simulated consumption from a bioenergetics model. The simulation averages of daily ration deviated from those of the field estimates by −20.1% to +70.3%, with a mean across all simulations of +14.3%. The deviations for each time step were much greater than those for the simulation averages, ranging from −92.8% to +363.6%. A systematic trend in the deviations was observed, the model producing overpredictions at rations less than 3.7% of body weight. Analysis of variance indicated that the deviations were affected by sample year and week but not age. Multiple linear regression using backwards selection procedures and Akaike's information criterion indicated that walleye weight, walleye growth, lake temperature, prey energy density, and the proportion of gizzard shad Dorosoma cepedianum in the diet significantly affected the deviations between simulated and field rations and explained 32% of the variance.

Annual prey consumption of a dominant seabird, the common murre, in the California Current system

Abstract Roth, J. E., Nur, N., Warzybok, P., and Sydeman, W. J. 2008. Annual prey consumption of a dominant seabird, the common murre, in the California Current system. – ICES Journal of Marine Science, 65: 1046–1056. Information compiled from the literature on population size, diet composition, field metabolic rate, prey energy densities, and assimilation efficiency is used to estimate annual prey consumption by common murres (Uria aalge), between Cape Blanco, OR, and Point Conception, CA, USA. The population consumed an estimated 172 313 t of prey based on population estimates and diet data from the mid- to the late 1980s, including 50 125 t consumed by breeding adults, 36 940 t by non-breeding birds during the breeding season, 85 098 t by all birds during the wintering period, and 150 t by dependent chicks before their leaving the breeding colonies. The population in the mid-2000s consumed 225 235 t of prey based on population estimates from 2004, including 65 516 t consumed by breeding adults, 48 283 t by non-breeding birds during the breeding season, 111 226 t by all birds during the wintering period, and 210 t by chicks at breeding colonies. Monte Carlo simulations indicated that the coefficients of variation around our overall prey consumption estimates were ±14.4% for the 1980s and ±13.2% for the 2000s.

Habitat Characteristics Associated with the Distribution and Abundance of Histrionicus histrionicus (Harlequin Ducks) Wintering in Southern New England

Histrionicus histrionicus (Harlequin Ducks) that winter along the east coast of North America are listed as a population of special concern in Canada, and they use several coastal wintering sites in southern New England that are subject to varying degrees of urbanization. We studied patterns of habitat use by Harlequin Ducks at 12 known wintering sites in southern New England. An average of 327 ± 114 Harlequin Ducks were found at the sites during the winters of 2001–2003. More Harlequin Ducks wintered at sites south of Cape Cod, MA that had greater mollusk (709,133 ± 504,568 versus 97,154 ± 72,427 kcal ha−1) and crustacean (27,907 ± 16,312 versus 1412 ± 1675 kcal ha−1) prey energy density, and a higher index of hunting activity (2.4 ± 1.2 versus 1.4 ± 0.5) than sites to the north. We used logistic regression analysis at 12 sites inhabited by Harlequin Ducks and 12 nearby sites of similar geomorphology that did not support Harlequin Ducks to identify habitat characteristics that best explained their distribution in southern New England. Our analysis identified two habitat characteristics that affected the likelihood a site was used by Harlequin Ducks: 1) the proportion of residential, commercial, and industrial land use within a 100-m radius of the perimeter of the site; and 2) distance to the nearest Harlequin Duck wintering site. However, other factors, including those related to their extremely low population size, need to also be considered as recommendations are developed for the conservation of east coast Harlequin Ducks.

Satiation and compensation for short-term changes in food quality and availability in young Steller sea lions (Eumetopias jubatus)

Foraging theory predicts that animals should proportionately increase their food intake to compensate for reduced food energy content and (or) prey availability. However, the theoretical intake levels will, at some point, exceed the digestive capacity of the predator. We tested the ability of Steller sea lions, Eumetopias jubatus (Schreber, 1776), to compensate for short-term changes in prey energy density and availability, and quantified the maximum amount of food a young sea lion could consume. Five 1–2-year-old captive Steller sea lions were offered either herring (high energy) or capelin (low energy) each day or every second day. When prey were available on a daily basis, the sea lions compensated for differences in the energy content of herring and capelin by consuming sufficient quantities of each (8.3 vs. 14.0 kg·d–1, respectively) to maintain equivalent gross energy intakes. When herring was available only on alternate days, the sea lions increased their consumption by 52% to 11.5 kg·d–1, which was not sufficient to maintain an average gross intake equal to that maintained when herring was available every day. When capelin was available only on alternate days, some animals increased their intake for a few days, but average intake (15.2 kg·d–1) was far below levels observed during daily feeding. Generally, the sea lions appeared to reach their digestive limit at a level equivalent to 14%–16% of their body mass. Our findings suggest that Steller sea lions can alter their food intake in response to short-term changes in prey quality or availability, but that these variables can quickly combine to necessitate food intake levels that exceed the physiological digestive capacities of young animals.

Evaluation of a Mysis bioenergetics model

Direct approachesfor estimating the feeding rate of the opossum shrimp Mysis relicta can be hampered by variable gut residence time (evacuation rate models) and non-linear functional responses (clearance rate models). Bioenergetics modeling provides an alternative method, but the reliability of this approach needs to be evaluated using independent measures of growth and food consumption. In this study, we measured growth and food consumption for M. relicta and compared experimental results with those predicted from a Mysis bioenergetics model. For Mysis reared at 10°C, model predictions were not significantly different from observed values. Moreover, decomposition of mean square error indicated that 70% of the variation between model predictions and observed values was attributable to random error. On average, model predictions were within 12% of observed values. A sensitivity analysis revealed that Mysis respiration and prey energy density were the most sensitive parameters affecting model output. By accounting for uncertainty (95% CLs) in Mysis respiration, we observed a significant improvement in the accuracy of model output (within 5% of observed values), illustrating the importance of sensitive input parameters for model performance. These findings help corroborate the Mysis bioenergetics model and demonstrate the usefulness of this approach for estimating Mysis feeding rate.

A gastric evacuation model for three predatory gadoids and implications of using pooled field data of stomach contents to estimate food rations

The general applicability of the square root model to describe gastric evacuation in predatory gadoids independently of meal size was verified through experiments on whiting Merlangius merlangus, saithe Pollachius virens and cod Gadus morhua fed different fish and crustacean prey. Gastric evacuation rate was related by a negative power function to energy density of fish prey over an extended range from 3·4 to 11·5 kJ g‐1 of the effector variable. Gastric evacuation of crustacean prey seemed to depend on the characteristics of their exoskeleton. Gastric evacuation of mixed meals composed of fish prey with different energy densities could be described as a function of the overall energy density. The evacuation rate of each of the prey could be described directly by their share of the stomach content. A full gastric evacuation model including predator size, temperature and prey energy density was established for whiting, saithe and cod. It was demonstrated that estimates of food rations might be severely biased by use of mean values for prey composition and total mass of stomach contents.

The effects of predator size, temperature, and prey characteristics on gastric evacuation in whiting

No effect of prey size on gastric evacuation rate was found in whiting Merlangius merlangus.Prey energy density explained most of the data variation among fish prey, and evacuation time increased by a factor 1·6–1·7 with prey energy density increasing from 3·4 to 5·6 kJ g−1. The power model expanded to include predator size, temperature, and prey energy density could describe gastric evacuation in whiting fed fish prey. Krill Meganyctiphanes norvegica was evacuated at a rate similar to fish prey of equal energy density, while the evacuation of brown shrimp Crangon crangon took almost twice as long.

Kokanee Foraging: ADaphniain the StomachIs Worth Two in the Lake

Abstract We estimated percent dry matter per unit biomass of ambient Daphnia spp. and of Daphnia spp. (both predominately D. pulex) from stomachs of kokanee Oncorhynchus nerka to test the hypothesis that kokanee can reduce the water content of their prey. Percent dry matter of consumed Daphnia did not differ from that of ambient Daphnia in May–June, but was approximately double that of ambient Daphnia in July and August. We also found that percent dry matter of zooplankton in kokanee stomachs did not increase with decreasing gut fullness. Consequently, water reduction probably occurred during ingestion and enabled kokanee to pack a larger number of prey into their stomachs. The results suggest that kokanee may be able to capture twice as many Daphnia per unit time than previously predicted. Additionally, consumption estimates from a bioenergetics model that used wet-mass energy density of prey derived from field samples resulted in P-values (proportion of maximum consumption) greater than 1.0, whereas wet...

Important prey species of marine vertebrate predators in the northwest Atlantic:proximate composition and energy density

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 164:13-20 (1998) - doi:10.3354/meps164013 Important prey species of marine vertebrate predators in the northwest Atlantic: proximate composition and energy density John W. Lawson1,*, Alexandra M. Magalhães2, Edward H. Miller1,2 1Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, Newfoundland A1C 5S7, Canada 2Biology Department, Memorial University of Newfoundland, St. John's, Newfoundland A1C 3X9, Canada *E-mail: johnwl@morgan.ucs.mun.ca Prey energy density values are crucial inputs to bioenergetic consumption models. Vertebrate predators in the northwest Atlantic consume a variety of prey species, but the proximate composition (PC; proportions of lipid, protein, ash and water) and energy density (ED; kJ g-1) of prey, and their variability, are known poorly. In this study, key prey species from Newfoundland and Labrador were studied: Atlantic cod Gadus morhua, American plaice Hippoglossoides platessoides, sand lance Ammodytes dubius, Arctic cod Boreogadus saida, northern shrimp Pandalusborealis, redfish Sebastes spp., Greenland halibut Reinhardtius hippoglossoides, squid Illexillecebrosus and Gonatus fabricii, capelin Mallotus villosus, Atlantic herring Clupea harengus and daubed shanny Lumpenus maculatus. PC and ED varied greatly among species and were influenced by size, season, geography and year. Herring, capelin and G. fabricii had the highest ED, whereas Atlantic cod, plaice, sand lance and shrimp had the lowest. Halibut and I. illecebrosus increased in ED with size. EDs of capelin and redfish varied seasonally; that of plaice and sand lance did not. Herring and halibut had higher ED in the early 1990s than in recent years. Such variation in prey ED has important implications for digestive efficiency, foraging energetics, and dietary preferences of vertebrate predators. Proximate composition · Energy density · Capelin · Cod · Atlantic Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 164. Publication date: April 09, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Variation in assimilation efficiency and digestive efficiency of captive harp seals (Phoca groenlandica) on different diets

Digestive efficiency (DE) is influenced by many factors including food type or quality. Assimilation efficiency (AE) and DE of 12 captive harp seals (Phoca groenlandica) were estimated for five prey types in large outdoor seawater tanks. In trials of > 9 days' duration, the seals were fed Atlantic cod (Gadus morhua), Arctic cod (Boreogadus saida), Greenland halibut (Reinhardtius hippoglossoides), Atlantic herring (Clupea harengus), and capelin (Mallotus villosus). Fish were marked with inert tracers so that faecal samples could be matched to individual animals. AE (digestibility of dry matter) was estimated from the relative concentration of Mn2+in food and faeces. DE (digestible energy) was estimated from the relative concentrations of both Mn2+and energy in food and faeces. AE and DE values were high, but varied among the fish species (DE: Atlantic cod 93.5%; Arctic cod 93.5%; halibut 94.7%; capelin 95.7%; herring 96.6%). Both estimates of digestive efficiency were positively correlated with prey energy density. For most prey, AE and DE were not correlated with meal size, number of prey in a meal, size of prey, or seal body mass. However, digestive efficiency was greater in seals fed smaller Atlantic cod, or meals of greater mass. Quantifying estimates of digestive efficiency is important for formulating energy-based population consumption models, and so should be improved. It is recommended that more pinniped species be studied in captivity, that experiments last longer, and that the number of individuals studied be increased so that individual differences can be investigated.

Notes: Estimating the Energy Density of Daphnid Prey for Use with Rainbow Trout Bioenergetics Models

Abstract Energy densities and percent dry matter of zooplankton were estimated from both field collections and from stomach contents of rainbow trout Oncorhynchus mykiss. Dry-mass energy densities were similar for zooplankton collected from the field and from fish stomachs, averaging 22.7 kJ/g. The percent dry matter of zooplankton from fish stomachs was approximately twice that of zooplankton from field collections, although species composition was similar. Energy density of wet zooplankton was consequently twice as high in fish stomachs as it was in field collections. These results indicate that the wet-mass energy density of zooplankton prey used in fish bioenergetics models should be increased over values that have been reported in the literature.

Food energy requirements of the harp seal (Phoca groenlandica) population in the Barents and White Seas

The harp seal (Phoca groenlandica) population of the Barents and White seas has probably decreased from about one million individuals to half this size the last few years. Energy requirements of the population have been estimated by use of the simulation model SEAERG. In this model the energy requirements of an individual seal from each age group is multiplied with the group size and summed to provide the requirements of the population. In addition to population size and age structure the total food and energy requirement is sensitive to individual activity levels as well as metabolic levels and other specified physiological functions. The interactions between the seal population and fisheries depends on the caloric density of the prey species which varies with season and location. Realistic simulations of interactions between seals and fisheries require more information about spatial and temporal variations in the prey selection of harp seals than is available today. Present estimates indicate average maintenance requirements of about 13,600 and ll,150kcal/day for adult female and male harp seals respectively. The high value for the females is due to the costs of pregnancy and lactation. With a mean energy density of prey of 1500 kcal/kg, the corresponding food consumption is 9 kg/day for females and 7.4 kg/day for males.

Corroboration of a Bioenergetics Model for Sockeye Salmon

We constructed a bioenergetics model for sockeye salmon Oncorhynchus nerka and evaluated its sensitivity to parameter error. When used to predict annual growth, the model was most sensitive, in declining order of importance. to changes in the intercept of the dependence of consumption on body weight, the proportion of maximum consumption, the energy density of prey, low temperature and its associated proportion of maximum consumption in the temperaturedependence function, the intercept of the energy density relationship to predator weight, and the intercept of the relationship between body weight and respiration. Estimates of consumption from the model, when consumption was constrained by fixed growth, were quite insensitive to perturbation of all parameters except the energy density of prey. We computed consumption rates and energy budgets with the model and compared these with independently derived estimates for populations in Lake Dalnee, USSR; Lake Washington, USA; and Babine Lake, Canada. The close agreement of estimates from the model to independent estimates of prey consumption and energy budgets for three different populations indicated that the model may be widely applicable to other populations. Performance of the model can be enhanced further if the frequency with which water temperature and mean body weight data are collected is increased for each cohort of interest.