Prey Volume Research Articles

Spatial and temporal variability in the distribution and diet of the gudgeon (Eleotridae: Hypseleotris spp.) in a subtropical Australian reservoir

The diurnal distribution and diet of Hypseleotris spp. was examined over a 14-month period in Maroon Dam, a productive subtropical reservoir in south-east Queensland, Australia. Three distinct size classes of Hypseleotris were observed. The smallest (<16 mm standard length (SL)) fish undertake a vertical diurnal migration in the pelagic throughout the year, spending daylight hours near the surface and night hours in deeper waters. The diet of this size class consists almost exclusively of zooplankton (98.6% total prey volume), with cladocera and copepoda dominating the identifiable prey items. A larger (12–20 mm SL) size class group of subadult/adult fish occupies the near-shore littoral throughout the daylight hours but moves out of the sampled area during the night. The diet of this size class is more diverse (zooplankton 58.5%, macro-invertebrate 25.0%, other 16.5%). The largest size class (>20 mm SL) of adult Hypseleotris remains in the near-shore littoral throughout seasonal and diurnal cycles and has a more eclectic diet than the other two size classes (zooplankton 28.8%, macro-invertebrate 28.9%, other 42.3%). Spatial and temporal differences in the distribution and diet of these three size class groups are discussed with reference to the abundance and availability of suitable prey, intraspecific competitive exclusion, predator avoidance and water quality.

Ontogenetic change in the diet of the pond frog, Rana nigromaculata

I analyzed 478 diet samples of Rana nigromaculata across its natural size range to examine the dietary changes of this species during postmetamorphic ontogeny. As the frogs increased in size, they increased total diet volume, but decreased the number of prey items. Also, individuals ontogenetically increased the mean, minimum and maximum prey volume in the stomach. The mean volume of the major prey taxa consumed by the frogs varied considerably. Small prey, such as ants and dipterans, were found less frequently as the size of the frogs increased, but large prey, such as beetles and orthopterans, were more frequently recovered from larger frogs. These results suggest that ontogenetic diet change should be considered when the structure of an anuran community is investigated using food niche analysis.

Relationships among vertically structured in situ measures of turbulence, larval fish abundance and feeding success and copepods on Western Bank, Scotian Shelf

Using vertically stratified data of the abundance of silver hake (Merluccius bilinearis) larvae and concentrations of copepods collected in the field, we examine relationships among the vertical distribution of larval fish, their potential prey, feeding success and water column turbulence. Water column turbulence and associated stratification parameters were estimated from: (i) in situ measures of turbulent kinetic energy dissipation (ɛ) provided by an EPSONDE profiler; (ii) in situ wind speed; (iii) the Richardson number (Ri); and (iv) the buoyancy frequency (N2). Small (< 5 mm total length) silver hake were more abundant in the least turbulent waters (i.e. at a minimum in the rate of dissipation of turbulent kinetic energy, ɛ < 10–7 W kg−1; Ri > 0.25; N2 > 0.001 (rad s–1)2). Partial correlations amongst ɛ, N2 and small hake larvae were significant only for N2. The abundance of larger (> 5 mm total length) hake larvae was positively correlated with depth and was not associated with either ɛ or N2. Vertical distributions of three potential prey (classified by stage) were variable. Early stage copepodids were positively correlated with N2 and negatively correlated with ɛ. We found no evidence of diel distribution patterns for small (< 5 mm total length) hake larvae or for any of the developmental stages of the copepods examined. Neither estimate of water column turbulence inferred from wind speed nor from Ri was meaningfully related to in situ estimates of ɛ or to larval fish abundance. Feeding success, measured either as prey items (gut)–1, average prey length, or total prey volume (gut)–1, was not related to predicted encounter rates between days. However, the average prey length (gut)–1 was significantly (P < 0.01) related to water column turbulence. These conflicting results suggest that the relationship between larval feeding and the environment is more complicated than assumed. We conclude that without substantial high resolution in situ examination of the relationship between the vertical distributions of turbulence, larvae and their prey, the growing acceptance in the secondary literature that turbulence has a positive and biologically meaningful effect on trophic interactions between fish and their zooplankton prey (a generalization based largely on modelling and laboratory experiments) is premature.

Feeding Habits of the Endangered Ozark Big-Eared Bat (Corynorhinus townsendii ingens) Relative to Prey Abundance

Feeding habits of the endangered Ozark big-eared bat (Corynorhinus townsendii ingens) in eastern Oklahoma, USA, were studied from July 1987 through July 1988. Diets were determined from microscopic analysis of fecal pellets and compared with arthropods collected in Malaise traps. Although lepidopterans comprised only 21.5% of the available prey, they occurred in > 90% of the pellets examined and accounted for > 85% of the volume of prey consumed. Dipterans, coleopterans, and homopterans occurred in 18.3%, 10.6%, and 6.7% of the feces, respectively, but each accounted for < 5% of the volume of prey consumed. Trichopterans, hymenopterans, and neuropterans also were found in feces but in trace amounts. Our results support the classification of C. t. ingens as a moth specialist, but additional insights are needed to fully understand how its feeding tactics conform to the allotonic frequency hypothesis (i.e., avoiding detection by eared moths). Conservation of this highly endangered North American bat will require, in part, maintenance of habitats capable of supporting abundant populations of Lepidoptera.

Factors influencing the partitioning of food resources among six fish species in a large embayment with juxtaposing bare sand and seagrass habitats

Six abundant fish species were collected from a large embayment during both day and night and at bimonthly intervals for a year. Gerres subfasciatus and Upeneus tragula occurred mainly over bare sand, while Psammoperca waigiensis, Centrogenys vaigiensis and Apogon victoriae lived mainly in seagrass ( Amphibolis antarctica) and A. rueppellii often migrated from seagrass to over bare sand at night. All species except U. tragula fed at night, as well as during the day. The overall dietary compositions of the six species were significantly different from each other, even when the species occurred in the same habitat. G. subfasciatus and U. tragula consumed greater volumes of errant polychaetes, which could be readily targeted in a substrate that does not contain dense rhizome mats. In contrast, P. waigiensis, C. vaigiensis and A. victoriae ingested greater volumes of carid decapods, which are particularly abundant in seagrass and, thus, within the water column. Furthermore, when A. rueppellii moved at night from seagrass to over sand, the consumption of carid decapods declined, whereas that of polychaetes and particularly mysids, which are very abundant over bare sand, increased. However, the composition of the prey consumed by different species within the same habitat also often varied markedly. For example, unlike U. tragula, G. subfasciatus ingested not only sedentary polychaetes, but also considerable volumes of errant polychaetes, reflecting its ability to use a combination of vision and its highly protrusible mouth to target prey both on and just below the substrate surface. Differences in the types and range of prey ingested by the six species could often be related to differences in the overall size, width and/or protrusibility of the mouth. Furthermore, dietary breadth was greatest in species with the largest mouth dimensions. The diets of three species underwent diel changes that could be related to differences in foraging mode and/or prey availability. Thus, a use of vision to detect prey would account for the greater consumption during the day of copepods by G. subfasciatus and of small teleosts by A. rueppellii, while the nocturnal emergence of amphipods and/or tanaids from the substrate explains their greater ingestion by G. subfasciatus, A. victoriae and A. rueppellii at night. Although the smaller individuals of each species consumed larger volumes of prey, such as copepods and mysids, and the larger fish ingested greater volumes of prey, such as decapods and teleosts, the extent of the size-related changes in diet varied markedly amongst species.

Size Selective Feeding in Cyclidium glaucoma (Ciliophora, Scuticociliatida) and Its Effects on Bacterial Community Structure: A Study from a Continuous Cultivation System.

Three aspects of size selective feeding by the scuticociliate Cyclidium glaucoma were studied in continuous cultivation systems. Firstly, grazing-induced changes in abundance, biomass, and size structure of a bacterial community were investigated. Secondly, we studied possible grazing-protection mechanisms of bacteria as a response to permanent presence of the predator. And finally, we were looking for potential feedback mechanisms within this predator-prey relationship, i.e., how the ciliate population reacted to a changed, more grazing-protected bacterial community. The first stage of the cultivation system consisted of the alga Cryptomonas sp. and the accompanying mixed bacterial community. These organisms were transferred to two second stage vessels, a control stage without ciliates and a second one inoculated with C. glaucoma. After the first week, the abundance of bacteria in the latter decreased by 60% and remained stable until the end of the experiment (65 d), whereas bacterial biomass was less affected (393 mg C L-1 during days 0-7, 281 mg C L-1 afterwards). The mean bacterial cell volume doubled from 0.089 mm3 to 0.167 mm3, which was mainly due to increasing cell widths. During the whole investigation period formation of colonies or filaments was not observed, but we found a clear feedback of ciliates on bacterial size. An increase in bacterial cell volume was always followed by a decline of the predator population, resulting in a yet undescribed type of microbial predator-prey relation. Literature and our own data on the optimal food size range grazed by C. glaucoma showed that bacterial cell width rather than length was responsible for that observed phenomenon. Finally, we suggest that uptake rates of spherical latex beads give only limited information on truly ingestible prey volumes and that prey geometry should be considered in future studies on size selective feeding of protists.

Diet of the Mexican Fringe-Toed Lizard (Uma exsul)

Seasonal differences in environmental conditions, such as precipitation, appear to regulate food diversity and abundance, and thereby indirectly influence changes in the diet of some lizards (Ballinger and Ballinger, 1979). Whitford and Creusere (1977) showed that the availability of insect prey varied according to the distribution and amount of rain throughout the year, and Maury (1995) found that variability in prey diversity and abundance was correlated with the effect of precipitation on primary productivity. The diet of the genus Uma remains somewhat unclear (D. S. Turner and C. R. Schwalbe, unpbul.). Commonly, it has been considered a carnivore, or perhaps opportunistic omnivore, but the data are contradictory. In Sonora (Mexico), Ortega-Rubio et al. (1995) found no plant matter in the diet of Uma notata. They reported a purely insect diet. In sharp contrast, a study of the more distantly related Mexican species, Uma paraphygas, found plant parts in nearly 56% of the 153 lizards examined, providing more than 40% of the total prey volume for adult males in two of four seasons (Gadsden and PalaciosOrona, 1997). The purpose of our paper is to describe seasonal variation in the diet of an endemic Mexican lizard species, Uma exsul, and to investigate sexual differences in diet. The study was conducted in the sand dune systems within the Mapimian subprovince of the Chihuahuan Desert (25023'N, 103?30'W), in the dry Laguna de Viesca in southwestern Coahuila, Mexico (1100 m elevation; INEGI, 1988). The vegetation is dominated by Larrea tridentata and Suaeda nigrescens (Instituto Nacional de Estadistica, Georgrafia e Informatica, 1988). Average monthly temperature ranges from 13?C in January to 28?C during the summer. Average annual rainfall is 200 mm but varies greatly among years (Schmidt, 1979). In 1992, adult U. exsul were noosed or shot with BB rifles each month (8.3 + 4.0 individuals each month), immediately placed on ice, and subsequently preserved in 10% formalin. Lizards were collected between 1000 and 1600 h. Monthly samples for each season were combined (winter = January-March, spring = April-June, summer = July-September, and autumn = October-December). Stomach contents were removed, and food items

Ontogeny of diet changes in a tropical benthic carnivorous fish, Parupeneus barberinus (Mullidae): relationship between foraging behaviour, habitat use, jaw size, and prey selection

Parupeneus barberinus forages on benthic invertebrates using a wide range of foraging modes, including vigorous digging in the substratum, resulting in considerable disturbance to the benthos. Polychaetes were the most important prey item for all size classes, but fishes less than 120 mm total length consumed more small ostracods and nematodes than did larger fishes. Fishes greater than 120 mm total length consumed mostly bivalves, and fishes over 240 mm total length consumed mostly bivalves and crabs. A morphological examination of the feeding apparatus suggested that the size of important prey items consumed was determined by gape height and jaw width. Prey available to different size classes of fishes was determined by combining information on microhabitat use, foraging behaviours, and prey volumes in the substratum. Small fishes spent more time foraging on the reef flat and slope, compared with larger fishes that foraged mostly on the reef edge and base. In addition smaller fishes foraged mostly in the upper 2 cm of sediment, whereas larger fishes often foraged to depths of 10 cm. Selection ratios showed that different size classes of fishes selectively extracted different prey items from the substratum. Small fishes showed a preference for ostracods whereas large fishes selected for bivalves and crabs. Although polychaetes were the dominant prey item for all size classes, they were consistently selected against.

Estimation of larval fish prey volume: mensuration formulae for copepod nauplii

Prey volume measurements are used to determine feeding bioenergetics and transfer of energy between trophic levels. Quantitative estimation of larval fish feeding success often depends on accurate estimates of prey volume inside the gut. Many marine fish larvae begin their lives feeding on copepod nauplii. Various methods and formulae have been proposed to estimate bodily volume of this diverse and difficult to identify group of organisms. We estimated the mean square error and average error for six different single-measurement formulae used to calculate bodily volume for two stages (NI and NIV) of three different copepod genera found in the eastern Bering Sea (<it>Metridia, Oithona</it> and<it>Pseudocalanus</it>). Each method used an assumed or empirical relationship among the three bodily dimensions (length, width and depth). Methods that assume a single geometric model and fixed bodily proportions for al nauplii are shown to be poor estimators of bodily volume. Mensuration methods must take into account the variety of body forms and changes in proportions during development for accurate estimation of bodily volume. It is possible, however, to reduce the number of measurements needed (i.e. to assume fixed bodily proportions) if one accounts for differences among taxa and developmental stages.

The biology of the skates Raja wallacei and R. pullopunctata (Batoidea: Rajidae) on the Agulhas Bank, South Africa

Aspects of the biology of Raja wallacei and R. pullopunctata were investigated using data collected in 1995 and 1996 from research and commercial trawls on the Agulhas Bank, South Africa. Age and growth parameters were investigated by examination of bands on the vertebral centrum. Estimates of Von Bertalanffy parameters for R. wallacei were L ∞ = 405.40 mm disc width (DW), K = 0.27 and t 0 = −0.08 years for males and L ∞ = 435.23 mm DW, K = 0.26 and t 0 = −0.21 years for females. For R. pullopunctata, the estimates were L ∞ = 770.50 mm DW, K = 0.10 and t 0 = −2.37 years for males and L ∞ = 1 326.75 mm DW, K = 0.05 and t 0 = −2.20 years for females. Growth was significantly different between sexes for both species. The oldest aged R. wallacei and R. pullopunctata were 15 and 18 years respectively. The length at first maturity was approximately 350 mm DW or 7 years of age for R. wallacei and 600 mm DW or 9 years of age for R. pullopunctata. The length-at-50% maturity for R. wallacei was 395 mm DW for males and 400 mm DW for females. R. wallacei fed primarily on benthic teleosts and crustaceans. There were significant differences (p < 0.05) in the diet between research- and commercially caught fish, in terms of percentage frequency of occurrence and volume of prey.

Effects of habitat fragmentation on provisioning rates, diet and breeding success in two species of tit (great tit and blue tit).

The aim of this study was to examine the effects of forest fragmentation on the ability of parent birds to provide their young with an adequate food supply. To examine whether prey population densities of the great tit (Parus major L.) and the blue tit (P. caeruleus L.) vary between study areas in different forest size classes we compared provisioning rates and chick diet and related these parameters to breeding success. We filmed 217 nests over two breeding seasons and collected data on frass fall as a general estimate of caterpillar availability. Nests which were attended by none or one parent only during filming (n = 46) were excluded from the analyses. In both years and for both species feeding rates were highest in the smallest fragments and lowest in the large forest. There was also a suggestion that differences in feeding rates between areas vary between years. We found no consistent tendency for prey size to change with forest size, although both species brought slightly smaller prey items to the nest in the smallest forest fragments and feeding rates correlated negatively with prey size. Caterpillars were the main item fed to nestlings, in both species. We found no evidence to suggest that either frass fall or the proportion of caterpillars in the diet varied with forest size. There was also no correlation between mean frass fall and the total number of caterpillars brought to the nests, in either species. Breeding success, as measured by clutch size, brood size, fledging weight and fledging success, did not differ between the small fragments and the large forest, in either species. There was also no relationship between provisioning rate (as concerns volume of prey fed to nestlings and the quality of chick diet) and breeding success parameters. In conclusion, this study does not suggest suboptimal foraging or breeding conditions in small fragments compared to a nearby large forest, for either species.

Patterns of pisciviory by resident predatory reef fish at One Tree Reef, Great Barrier Reef

Patterns of piscivory were investigated among five abundant species of predatory fish at One Tree Reef, Great Barrier Reef, Australia. The guts of two lutjanids Lutjanus carponotatus and Lutjanus fulviflamma, two labrids Cheilinus diagrammus and Thalassoma lunare, and a serranid Epinephelus quoyanus were examined for type, length, number and volume of prey at two times of the day: sunrise and sunset. Each of these species consumed fish, but only T. lunare and the two lutjanids consumed recruit-sized fish. This information is important because there is often scepticism as to whether large predators (&gt;200 mm TL) such as lutjanids consume new recruits. Only in the lutjanids were there differences in the number and volume of prey present in the gut at sunrise and at sunset; at sunset, few lutjanid specimens contained prey, whereas at sunrise 98% of specimens contained prey. This result, in conjunction with studies of nocturnal activity, suggest that patterns of predation pressure inferred from daylight observations of predator abundance may have little relevance to actual patterns of predation at local scales.

Food habits and ontogenetic diet shifts of the litter dwelling frog proceratophrys boiei (wied)

Here is described the diet of Proceratophrys boiei (Wied, 1825), a leaf litter frog of the Atlantic Forest, and test for relationships between frog size and prey size and type. The diet was determined by stomach content analysis. In 38 frogs, was found 76 prey items belonging to 23 taxa. Insects predominate in the diet and the most frequent categories were coleopterans (39.4% of total volume) and orthopterans (25.0%). There was a positive correlation between frog size and volume of prey taken. The most important ontogenetic shift in prey type was an increase in the consume of coleopterans and insect larvae with increasing frog size.

Feeding ecology of Mediterranean razorfish Xyrichthys novacula in the Tyrrhenian Sea (Central Mediterranean Sea)

The stomach contents of 196 razorfish (Xyrichthys novacula), collected in the Tyrrhenian Sea (Ponza Island, Italy) between July and December 1994, were examined in order to assess the diet and to analyse size-related dietary variation of the species. The diet of X. novacula showed a strict relationship with well-sorted fine sand (SFBC) benthic species, mostly Mollusca and Echinodermata, as pointed out by the analysis at the specific level of the stomach contents. Mollusca Pelecipoda, essentially Acanthocardium tuberculatum and Echinodermata, with Echinocardium cordatum, made up 90% of the volume of prey of X. novacula. Mysidacea and Gastropoda were frequent but volumetrically less important. The study showed that male and female X. novacula were not effectively segregated by trophic dimension in the study area. The niche overlap between males and females in prey composition was pronounced, as evidenced by the significantly high values of Schoener's index with larger males that showed a greater tendency towards predation of large prey. The increment in length (L.I.) in males, despite a decrease in the percentage body weight increment (B.W.I.), could represent the result of a male reproductive feature: the lack of sperm competition allows the males much more energy to devote to growth than do that of the females of this species.

The effects of fire on the frillneck lizard (Chlamydosaurus kingii) in northern Australia

Abstract A population of frillneck lizards, Chlamydosaurus kingii, was monitored by radio telemetry and mark‐recapture techniques between April 1991 and April 1994, as part of a landscape‐scale fire experiment, in Kakadu National Park, Northern Territory. The study aimed to investigate both the short‐ and longer‐term effects of fire on a lizard species in a tropical savanna where fires are frequent and often annual. Frillneck lizards are able to survive fires that occur in the first few months of the dry season by remaining perched in trees. A high level of mortality (29%) occurred during late dry‐season fires, along with changes in their behavioural response to fire: sheltering in either larger trees or hollow termite mounds. Food is more accessible after fires due to the removal of ground vegetation. This is reflected in greater volume and diversity of prey in stomach contents after fires. This increase is more pronounced after late dry‐season fires, possibly due to increased accessibility of prey caused by more complete vegetation removal. Frillneck lizards show an overall preference for trees with a dense canopy cover located in an area with a low density of grass. Fire has an effect on this relationship. Frillneck lizards in habitat unburnt for a number of years tend to perch in trees with a smaller canopy, whereas lizards in annually burnt habitat perch in trees with a dense canopy. Volume and composition of lizard stomach contents was broadly similar among fire treatments over a 2 year period, although termites were more predominant in stomach contents of lizards in unburnt habitat. Wet‐season body condition is lower in lizards from unburnt habitat, although the reason for this is unclear. These results demonstrate the importance of different fire intensities and regimes on the ecology of a lizard species in a tropical savanna.

Ecological Differences in Tropical Sympatric Skinks (Mabuya macrorhyncha and Mabuya agilis) in Southeastern Brazil

Ecological Differences in Tropical Sympatric Skinks (Mabuya macrorhyncha and Mabuya agilis) in Southeastern Brazil

Foraging ecology in the lizard Anolis oculatus (Iguanidae) from Dominica, West Indies

In general, populations of Anolis lizards on West Indian islands face few predators, are at high density and are thought to be limited by food. This paper describes how the foraging ecology of Anolis oculatus, a solitary species confined to the island of Dominica, Lesser Antilles, varies with habitat and season in relation to the quantity and quality of available food.Availability of invertebrate food (determined using pitfall traps and sticky traps) was greater in a dry scrub woodland site, Cabrits National Park (CNP), compared with a montane rainforest site, Palmiste Ridge. In the former, there were general increases in abundance, volumes of softbodied prey and sizes of invertebrates from dry season to wet season. Concomitant dietary changes, as determined principally by stomach flushing, included an increase (by volume) in the proportion of soft‐bodied prey. Dietary analyses confirmed the importance of ants (Formicidae) in the diet of A. oculatus, although for large individuals (mainly adult males) at the rainforest site, soft‐bodied prey such as Oligochaeta and Orthoptera were, in volumetric terms, more important. Prey capture observations showed that large A. oculatus fed mainly above ground. Anolis oculatus at the montane rainforest site used higher perch heights than those in dry scrub woodland, although in both habitats, small individuals (mainly juveniles) fed mainly at ground level on ants. In the dry season in CNP, the diet (in volumetric terms) of smaller Anolis was dominated by hardbodied prey such as ants, springtails (Collembola), barklice (Psocoptera) and beetles (Coleoptera). large Anolis used springtails and barklice to a lesser extent, resulting in relatively low food niche overlap values between size classes and a reduced potential for intraspecific competition compared with the wet season.

Ontogenetic diet shifts of age‐0 smallmouth bass (Micropterus dolomieu Lacepède) in the New River, West Virginia, USA

AbstractLarval and juvenile smallmouth bass (Micropterus dolomieu Lacepède; 8.5–85.0 mm total length (TL)) were collected from 2 sites in the New River, West Virginia, in the late spring and early summer to document diet shifts during early ontogeny. The first foods of smallmouth bass (TL = 9 mm) were primarily Chironomidae and microcrustaceans (primarily Copepoda). Other aquatic insects, primarily Ephemeroptera, became more abundant in the stomachs as TL increased. A shift in the proportions and types of prey consumed began at approximately 15 mm TL and was primarily attributed to fin development and increased mouth size. Foraging success, measured by number of prey per stomach, stomach fullness, and average prey volume was lower for first‐feeding smallmouth bass than for later life stages. Mouth width appeared to restrict the size of prey consumed by larval smallmouth bass, but the maximum prey width never approached the mouth width for fish longer than 35 mm TL.

Comparative feeding, growth and movements of Atlantic salmon (Salmo salar) parr from riverine and estuarine environments

Abstract– The diet composition, movcments and growth of Atlantic salmon parr rearing in the estuary of Western Arm Brook, Newfoundland were compared with those of parr from riverine habitats over 2 years. Estuarine parr consumed a variety of prey, including many freshwater taxa (mainly insects), which indicated a dependence on freshwater drift from the river. Prey of estuarine origin (amphipods and sticklebacks) were increasingly consumed between spring and autumn. Prey volume per fish and number of prey per fish increased significantly for estuarine parr between spring and autumn, suggesting an improvement in food availability. Riverine parr, however, realized a general decrease in both parameters between spring and autumn. The recapture of 16% (n= 131) of the 829 parr marked in the estuary in 1987 and 1988 indicated a directed movement toward the head of the estuary and river mouth, as also suggested by the diet analysis. Parr from outer estuary sites were very mobile compared with parr from the estuary site closest to the river mouth, which behaved more like parr in the river proper in displaying strong site fidelity. Movement patterns of parr were primarily along the shoreline. Individual growth rates were highly variable in both environments but especially in the estuary. The mean growth of estuarine parr was 0.23 mm. d−1 between May and October with some evidence of fastest growth having occurred in late spring and early summer (approx. 0.4 mm. d−1); mean growth rate of riverine parr was slower, at 0.12 mm. d−1. The results are discussed in the context that estuarine rearing by salmon parr represents an alternative life‐history tactic for the species in river systems in eastern Canada.

The relationship between cladoceran body size and the growth of underyearling roach (Rutilus rutilus) (L.) in two shallow lowland lakes: a mechanism for density-dependent reductions in growth

Large planktonic Cladocera are typically the most important components of the diet of underyearling roach. Selection for large species and individuals by fish can result in a shift in the species composition of the cladoceran community as well as a reduction in the mean size of the individuals of large species and in the assemblage as a whole. Laboratory experiments demonstrated that underyearlings feeding on Daphnia hyalina smaller than 1 mm in length has a significantly lower intake of prey volume per unit time than when feeding on prey greater than 1.5 mm. A decrease in the nutritional quality of zooplankton prey, brought about by increasing predation pressure is suggested as the mechanism for density-dependent reductions in the growth of underyearling roach in eutrophic water bodies.