Effects of discharge and local density on the growth of juvenile Atlantic salmon Salmo salar

The study explored the combined effects of density, physical habitat and different discharge levels on the growth of juvenile Atlantic salmon Salmo salar in artificial streams, by manipulating flow during both summer and winter conditions. Growth was high during all four summer trials and increased linearly with discharge and mean velocity. Differences in fish densities (fish m^?3) due to differences in stream volume explained a similar proportion of the variation in mean growth among discharge treatments. Within streams, the fish aggregated in areas of larger sediment size, where shelters were probably abundant, while growth decreased with increasing densities. Fish appeared to favour the availability of shelter over maximization of growth. Mean growth was negative during all winter trials and did not vary among discharge treatments. These results suggest that increased fish densities are a major cause of reduced summer growth at low discharge, and that habitat‐mediated density differences explain the majority of the growth variation across habitat conditions both during summer and winter.     

Predicting tree biomass growth in the temperate–boreal ecotone: Is tree size,age, competition,or climate response most important?

As global temperatures rise, variation in annual climate is also changing, with unknown consequences for forest biomes. Growing forests have the ability to capture atmospheric CO₂ and thereby slow rising CO₂ concentrations. Forests’ ongoing ability to sequester C depends on how tree communities respond to changes in climate variation. Much of what we know about tree and forest response to climate variation comes from tree‐ring records. Yet typical tree‐ring datasets and models do not capture the diversity of climate responses that exist within and among trees and species. We address this issue using a model that estimates individual tree response to climate variables while accounting for variation in individuals’ size, age, competitive status, and spatially structured latent covariates. Our model allows for inference about variance within and among species. We quantify how variables influence aboveground biomass growth of individual trees from a representative sample of 15 northern or southern tree species growing in a transition zone between boreal and temperate biomes. Individual trees varied in their growth response to fluctuating mean annual temperature and summer moisture stress. The variation among individuals within a species was wider than mean differences among species. The effects of mean temperature and summer moisture stress interacted, such that warm years produced positive responses to summer moisture availability and cool years produced negative responses. As climate models project significant increases in annual temperatures, growth of species like Acer saccharum, Quercus rubra, and Picea glauca will vary more in response to summer moisture stress than in the past. The magnitude of biomass growth variation in response to annual climate was 92–95% smaller than responses to tree size and age. This means that measuring or predicting the physical structure of current and future forests could tell us more about future C dynamics than growth responses related to climate change alone.     

Social dominance and body size in Atlantic salmon parr, Salmo solar L.

Dominance relationships between pairs of Atlantic salmon parr of known size were assessed at various times during their first year of life. In tests conducted between first feeding and early July, the larger of two fish was dominant in only 54% of pairs, regardless of the magnitude of the size difference between the fish. In September, there was a stronger association between size and status, especially in pairs with a large size differential, where the dominant was larger in 72% of cases. In groups of parr tested in April of the following year, there was no relationship between size and status, the larger of two fish being dominant in 48% of cases, regardless of the magnitude of the size differential. This result suggests that status in early social interactions may depend on behavioural properties rather than size and that the larger size of dominant fish reported in a number of salmonids might be a consequence and not a cause of high status.     

Variations in juvenile growth, energy allocation and life-history strategies of two populations of Arctic charr in North Norway

Within the populations of Arctic charr Salvelinus alpinus in Storvatn and Rungavatn, Norway, fish that attained the largest size in the late parr stage migrated as 4+ smolts, fish that attained a medium size became 5+ smolts, and the smallest parr became lake residents. Within the last 2 years of the parr stage, those that became anadromous had a lower growth rate during the winter and early summer than those that became resident, and vice versa in late summer. Thus, anadromous fish grew faster in the parr stage, but in years prior to migration, their growth pattern seemed to differ from that of parr that became resident. Due to early size differences between parr that became anadromous or resident, it is suggested that some of the basis for the decision to smoltify or not in charr depends on the growth rate through the whole parr stage, but with significant modification by the local environment. Rungavatn parr had a significantly higher population density (5 ×), higher lipid content and mortality, an earlier maturation, a lower rate of growth, and only one-third the degree of anadromy than those from Storvatn. It is suggested that the two charr populations have evolved different life-history adaptations due to unequal growth, energy allocation and competition opportunities in the lakes.     

Changes in reproductive strategy in the ruffe during a period of establishment in a new habitat

The pattern of maturation, body size and fecundity was examined in a population of ruffe ( Gymnocephalus cernuus L.) three times during a period of rapid growth, and eventual stabilization, following its introduction to a new habitat. When the ruffe were less common, maturing ruffe were relatively large and immature ruffe relatively small, compared with when the ruffe were abundant. Intermediate ruffe population size showed a maturation pattern intermediate between these two extremes. It is suggested that this pattern of maturation is a response of the ruffe population to changing growth opportunity induced by changing intraspecific competition. This fluctuating maturation pattern is interpreted in terms of a threshold-dependent maturation trigger, operating on the rate of accumulation of energy and a trade-off between somatic growth and gonad development. When the ruffe population was large, high intraspecific competition resulted in low opportunity for growth; only fish with the highest rate of food acquisition were able to mature in a given year–the investment in gonadal tissue reducing somatic growth. When the ruffe population was low, the high rate of energy acquisition in the population resulted in the triggering of maturation, even at small size, only the very smallest fish remaining immature. High growth opportunity allowed maturing fish to develop gonad and maintain somatic growth. The pattern of size related fecundity also changed over the three periods. When growth opportunity was low, size related fecundity was greater than when opportunity for growth was high. This suggests that maturing females faced with poor growth conditions compensated by increasing egg number for a given body size either by decreasing egg size or by increasing total investment in ovarian tissue.     

Phenotypic Correlation of Juvenile Growth Rate between Different Consecutive foraging Environments in a Salmonid fish: A Field Experiment

Many organisms occupy considerably different environments during individual's lifespan. We are interested in how the phenotypic characteristics that are favourable in the earlier environment predict fitness in the later environment. High predictability of fitness between the two consecutive environments suggests that the either the same traits are favored in both environments, or that the favourable traits are genetically correlated. In this study, we ask how similarity of consecutive foraging environments affects the phenotypic correlation of juvenile brown trout growth rate. More specifically, we used a genetically narrow stock of hatchery-bred fish to contrast individual growth rates between high and low density hatchery environments, and thereafter between hatchery and natural lake environment. As expected, growth rate was highly dependent on the environment, and the fish showed considerable phenotypic plasticity. Furthermore, we found a strong positive correlation in growth rate between similar foraging environments, for example, between high and low density hatchery stocks, and between hatchery and a lake with small fish as main prey. However, hatchery growth did not predict growth rate in lakes where fish had to forage on bottom-dwelling invertebrates. Our results suggest that when the consecutive environments differed dramatically with respect to traits that fish use for foraging, relative performance of individual fish changed, earlier performance not being an accurate predictor of performance in the new environment. In this case, fitness of the fish was determined by an environment-specific set of traits that were not the same between the two consecutive environments. The result indicates that assessment of individual performance may be highly environment specific in trout. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of body size on sympatric shelter use in over‐wintering juvenile salmonids

The study tests two hypotheses: (1) the degree of shelter dominance in Atlantic salmon Salmo salar and brown trout Salmo trutta increases progressively with increasing size differential between heterospecific fish in a pair and (2) shelter dominance, standardized to size differential, correlates with aggression. The results support the first but not the second hypothesis, suggesting that the fitness consequences of high growth performance during the summer are likely to become evident during winter. At this time of year, when mortality is high among both Atlantic salmon and brown trout, shelter dominance may increase the chances of survival.     

Does social status within a dominance hierarchy mediate individual growth,residency and relocation?

The availability of food, and hence energy, is known to influence the abundance, habitat choice and growth of individuals. In contrast, there is a paucity of knowledge on how the interaction of energy supply and social status determines patterns of residency and movement. This study tests whether the presence of conspecifics and an individual’s social status in relation to food supply influence the fitness and movement of a drift-feeding fish (Galaxias fasciatus). Using an information-theoretic approach (AIC), our analysis indicated that the most parsimonious model of fish movement among pools was one that included food supply, social rank and fish relative growth rate. Our results indicated that subordinate fish relocated more frequently compared to dominant fish, most likely as a consequence of intra-specific competition that limited the access of these smaller fish to resources and constrained their growth. Our results suggest that energy constraints may force individuals to explore new habitats in an effort to find more energetically profitable patches. We conclude that intra-specific competition mediated through the social hierarchy amongst closely interacting individuals plays a key role in determining individual growth, residency and relocation.     

Aggression and growth depression in juvenile Atlantic salmon: the consequences of individual variation in standard metabolic rate

In aquaculture, competitive interactions for food are a major source of growth rate variation, since they result in aggressive individuals acquiring a disproportionate amount of food and growing faster. Consequently, such competition increases the variance and skew of the size distribution of fish. In Atlantic salmon Salmo salar acquaculture, rearing is often initiated with juveniles of uniform size. However, the initial factors allowing fish to out-compete others of the same size is unclear. This study shows that individual differences in standard metabolic rate (SMR) may contribute to differences in aggression between juvenile Atlantic salmon. Fish were segregated into three holding tanks on the basis of differences in relative SMR aggression was highest in the tank containing high SMR fish, and lowest in a low SMR group. However, there were no significant differences in mean growth between the three treatments, although the skew of the size distribution was much less in the low SMR group than in the high SMR group. Therefore, although mean growth was not improved in the low SMR group by excluding high SMR fish, their growth subsequently showed less variability, possibly as a consequence of fewer despotic individuals gaining disproportionate access to food.     

Interacting effects of temperature and density on individual growth performance in a wild population of brown trout

相似文献   

Periphyton growth as an indicator of eutrophication; an experimental approach

Growth of periphyton was studied in the Archipelago Sea (Finland) during summer 1994 as a part of the annual monitoring control of fish farms. Experimental growth plates (Whatman GF/C filters) were incubated (two weeks) at 213 sites in different parts of the Archipelago Sea and in the coastal area north of the Archipelago Sea. At each site incubations were repeated two or three times during the summer (July 4- -September 1). The growth of periphyton was measured as the amount of chlorophyll a (mg m-2) extracted from the incubation plates. The growth varied significantly among different parts of the study area. The strongest growth was observed in the inner archipelago and in areas with high fish production and relatively slow water exchange. In the outer archipelago, rapid water exchange ensured good mixing of nutrients from fish farms and other sources into relatively large water volumes. The local impacts of nutrient loading thus remained too low to be detected by measuring nutrient concentrations or periphyton growth. Periphyton growth was positively correlated with concentrations of total nitrogen, total phosphorus and chlorophyll a in the productivity layer (approximately 2 × Secchi depth). A significant inverse correlation was also shown between periphyton growth and Secchi depth. Archipelago areas with different levels of eutrophication could satisfactorily be distinguished in this study. The results were consequent with previous classifications of the eutrophication levels in the Archipelago Sea. Periphyton studies thus are a useful addition to conventional monitoring programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Resource seasonality and fish diets in an Illinois stream

Synopsis The purpose of this study was to evaluate the intensity of competition for food among 9 species of stream fishes that primarily eat aquatic invertebrates. The taxonomic and size composition, and numerical abundance of aquatic invertebrates were monitored for one year using drift and benthic samples. Diet data were obtained from stomachs of fishes captured at the same time and place that invertebrate sampling was done. Diet characteristics examined included taxonomic and size composition, number of prey per fish, and diet breadth. Drifting invertebrates were more abundant early in the year (March–June) than later (July–January). The summer-early fall scarcity of invertebrates was especially notable among those>3.6 mm long, which comprised the bulk of prey found in fish stomachs. Average prey size eaten by a fish species was positively correlated with fish mouth size, but interspecific overlap in prey size was extensive. Cyprinids as a group (5 species) ate proportionally fewer small (< 3.6 mm long) prey from July to January than did the centrarchids and stonecat. Taxonomic compositions of available invertebrates and fish diets varied markedly among sampling dates, but the use of prey taxa by fishes was not correlated with the availability of those taxa. Use of aquatic prey taxa was generally similar among fish species, but cyprinids as a group ate proportionally more terrestrial prey from July to January than did the centrarchids and stonecat. Diet breadths for all species increased as food levels declined, indicating that these fishes experienced resource depression. Food scarcity was evidently more severe for cyprinids since their stomachs contained few prey through the summer and fall relative to the centrarchids and stonecat. Though the fish species studied probably compete for food in the summer and fall, this competition did not account for the community structure observed.     

Fish recruitment, dispersal, and trophic interactions in a heterogeneous lotic environment

I examine how dispersal of juvenile creek chubs (Semotilusatromaculatus) from beaver ponds into adjacent stream environments interacts with temporal abiotic variability to influence fish foraging, growth, and long-term persistence in the lotic ecosystem. Minnow trapping in upstream and downstream beaver ponds, along with weir traps used to monitor directional movement, indicated that most chubs colonized the stream from the downstream beaver pond. Large annual fluctuations in density of age 0 creek chubs occurred in the stream over a 10-year sampling period. Multiple regression analysis indicated that stream temperature, precipitation, and the density of reproductive creek chubs were not correlated with summer density of age 0 chubs in the stream. The factor most strongly associated with increased density of age 0 creek chubs was creation of the downstream beaver pond during the 6th–7th years of the study, suggesting dispersal from the pond was the primary factor determining age 0 fish density in the stream. Most individuals in the strong year classes neither persisted in the stream through their first winter nor resulted in an increased abundance of older age classes in later years. Comparison of age 0 fish density in summer to the proportion of fish surviving to age 1 in spring suggested that overwinter mortality was density dependent. Furthermore, a comparison of the size structure for age 0 individuals in summer to age 1 individuals the following spring indicated that winter mortality was size dependent. Experiments in an artificial stream adjacent to the natural channel revealed that fish growth was strongly density dependent, decreasing as fish density increased across both spring and summer, and elevated and low discharge. The decline in invertebrate prey captured by the fish and the subsequent decline in fish growth appeared to be particularly pronounced under low discharge in summer. Changes in juvenile creek chub density had no significant effect on benthic insect or crustacean abundance, suggesting that exploitative competition for limited invertebrate drift resources was a more important cause of density- dependent growth than depressed local benthic invertebrate abundance. These results suggest that lotic regions adjacent to beaver ponds act as potential reproductive “sinks” for dispersing juveniles confronting seasonal and flow-mediated restrictions on resource acquisition and growth, and the occurrence of seasonal bottlenecks to their survival, especially harsh winter conditions. Received: 9 September 1996 / Accepted: 8 August 1997     

Temporal and spatial variation in potential and realized growth rates of age‐0 year northern rock sole

The possibility of prey limitations on the growth performance of age‐0 year northern rock sole Lepidopsetta polyxystra was evaluated at three sites along the north‐east coast of Kodiak Island, Alaska, U.S.A., by comparison of observed to potential growth rates. Growth potential was measured in the laboratory across the range of temperatures encountered by this species during the first summer of life. Growth potential ( g _L, mm day⁻¹) increased with water temperature (T) between 2 and 13° C, according to: g _L = 0·0151 + 0·3673·log₁₀(T). There were significant differences in growth rate between the three field sites such that Holiday Beach fish were 7·1 mm longer than Shakmanof Beach fish by mid‐September, with Pillar Creek Cove fish of intermediate size. Temperature differences between sites accounted for less than half of this variation. The remainder may have been related to differences in prey availability among the sites in association with observed differences in sediment characteristics. In addition to the spatial variability, there was significant monthly variation in growth performance. Realized growth rates between July and August were in excess of 85% of potential. Between August and September, however, realized growth fell to 43–71% of potential indicating a decline in conditions for growth. The spatial variation in growth rates was not density‐dependent as the site with the highest fish densities (Holiday Beach) also supported the highest growth rates. The available data indicates that for this subtidal species, interannual variation in growth may be more important than site variation.     

Phenotypic plasticity in sex allocation and body size leads to trade-offs between male function and growth in a simultaneously hermaphroditic fish

Phenotypic plasticity in sex allocation enables organisms to maximize reproductive success in variable environments, and thus may generate different sex allocation patterns among populations that experience different mating opportunities. In this experiment, I test whether sex allocation is phenotypically plastic in Serranus tortugarum, a simultaneously hermaphroditic fish, by using reciprocal transplants among four reef study sites with populations at high and low densities and significant differences in sex allocation. Fish transplanted across different densities were predicted to alter sex allocation and body size through trade-offs in investments to somatic growth and male and/or female reproduction. As a control for effects of transplanting, I also transplanted fish across study sites with the same densities and marked and returned fish to their original study sites. As predicted, sex allocation and body size shifted significantly for fish transplanted across different densities but not for those transplanted across the same densities. Separate analyses revealed that the treatment effect on sex allocation was driven strongly by a reduction in male investment by fish transplanted from high to low density, and this reduction in male investment was accompanied by an increase in body size. Fish transplanted from low to high density did not appear to change either male or female investments, but they were smaller than transplants from low to low density. A trade-off between male and female function was not evident, but phenotypic plasticity in body size suggested a trade-off between growth and male function when sex allocation is adjusted. Large-scale empirical tests of sex allocation in the field are relatively rare, and the results of this experiment give novel insights into how animals respond to a change in mating opportunities under natural conditions. The effects of logistical problems associated with fieldwork, such as mortality of experimental animals, are considered in the discussion.     

Effects of varying temperature and food availability on growth and reproduction in first‐time spawning female Atlantic cod

The somatic growth, sexual maturation and fecundity of individually marked first‐time spawning female Atlantic cod Gadus morhua were examined under different varying temperature and feeding regimes over the months preceding spawning. A negative correlation between somatic and oocyte growth was found, reflecting the changing energy allocation pattern. Nevertheless, the somatic growth of mature individuals was at least as high as those of immature fish over the period of vitellogenesis. Potential fecundity was positively correlated with body size, but neither temperature or feeding regime significantly affected this relationship. Consequently, fish with unlimited feeding opportunity invested more energy into somatic growth during vitellogenesis compared to those held under a restricted ration. This indicated that once Atlantic cod had made the decision to invest in first reproduction, they allocated a certain amount of energy relative to their size into egg production and any surplus was invested into somatic growth. Low temperature led to an arrest in the onset of vitellogenesis and significantly affected the number of females that matured.     

Ontogeny of sexual development in the roach (Rutilus rutilus) and its interrelationships with growth and age

The roach (Rutilus rutilus) has become a sentinel species for the study of sexual disruption in wild fish populations as a consequence of exposure to endocrine disrupting chemicals (EDCs). Little is known, however, about the normal ontogeny of sexual development in this species. Here, we analyzed the ontogeny of sexual development in captive‐bred roach and assessed how growth rate and fish size affected the timing of both sexual differentiation and sexual development over a 2‐year period. Ovarian differentiation was first recorded at 68 days post‐fertilization (dpf) and this preceded testicular differentiation (first recorded at 98 dpf). In contrast, sexual maturation occurred at an earlier age in males (300 dpf) compared with females (728 dpf). No differences in body size (length or weight) were recorded between male and female roach until the fish were 415 dpf. Studies on three populations of roach which grew at different rates showed that the timing of sexual differentiation was highly variable and more related to fish size than to fish age. Time to sexual maturation was also variable among populations but, subsequent to their first year of life, gonadal status was less well associated with fish size. Interestingly, the sex ratio of the population was biased towards females in populations that grew more rapidly during early life. The findings presented here provide a valuable foundation of work to support both field‐ and laboratory‐based assessments on the effects of EDCs, and other stressors, on sexual differentiation and development in the roach. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Ontogenetic shifts in the diets of juvenile Chinook Salmon: new insight from stable isotopes and fatty acids

Variations in marine prey availability and nutritional quality can affect juvenile salmon growth and survival during early ocean residence. Salmon growth, and hence survival, may be related to the onset of piscivory, but there is limited knowledge on the interplay between the prey field, environment, and salmon ontogeny. Subyearling Chinook Salmon (Oncorhynchus tshawytscha) and their potential prey were sampled in coastal waters off Willapa Bay, USA to explore this issue. Three seasonal prey assemblages were identified, occurring in spring (May), early summer (June – July), and late summer (August – September). The onset of piscivory, based on salmon stomach contents, fatty acids, and stable isotopes occurred later in 2011 compared to 2012, and coincided with the appearance of Northern Anchovy (Engraulis mordax). Salmon fork length (FL) and carbon isotope values (δ¹³C) increased with a fatty acid biomarker for marine phytoplankton and decreased with a freshwater marker, indicating dietary carbon sources changed as salmon emigrated from the Columbia River. Salmon FL also increased with nitrogen isotope ratios (δ¹⁵N), trophic position, and a fatty acid marker for piscivory – a consequence of the ontogenetic shift in diet to fish. Salmon grew faster and obtained larger size and condition by September 2011 compared to 2012, which was related to inter-annual differences in ocean conditions and the duration over which Northern Anchovy were available. Our results support the idea that juvenile salmon growth depends on the onset and duration of piscivory, suggesting both of these factors may be important components of lifetime growth and fitness.     

Competitive ability is related to metabolic asymmetry in juvenile rainbow trout

Of 55 size–matched pairs of juvenile rainbow trout Oncorhynchus mykiss , each consisting of one high and one low relative metabolic rate fish (relative size difference <5%), the high relative metabolic rate fish was dominant in 36 pairs (65·5%), significantly more often than expected by chance. The probability of a fish winning was related to its relative metabolic rate (measured prior to introduction into the test arena); the higher the relative metabolic rate of a fish compared to its opponent, the greater its probability of being dominant. In the 36 pairs of fish where the low relative metabolic rate fish was the subordinate, its competitive ability was significantly correlated with how closely the two fish were matched in terms of their relative metabolic rates. The smaller the difference between the relative metabolic rates of the dominant high relative metabolic rate fish and subordinate low metabolic rate fish, the greater the competitive ability and feeding success of the low relative metabolic rate subordinate. However, no such relation was found in the 19 pairs of fish where the high relative metabolic rate fish was the subordinate. In these pairs, the competitive ability of the subordinate high relative metabolic rate fish was correlated with its size relative to its dyad partner. The larger the dominant low relative metabolic rate fish, the lower the competitive ability of the subordinate high relative metabolic rate fish.     

Foraging and breeding performance of Japanese cormorants in relation to prey type

Seabirds are high trophic predators in marine ecosystems and are sensitive to change in food supply and thus seabirds can be used as monitors of the marine environment. In order to study the foraging responses of Japanese cormorants Phalacrocorax filamentosus breeding at Teuri Island, Hokkaido to changes in fish availability, the diet was assessed from the regurgitations of parents and chicks, and diving behavior was measured by using time-depth recorders. Breeding performance (brood size, chick growth, breeding success) was monitored using conventional methods to study their breeding responses. Japanese cormorants changed the diet and foraging behavior over four summers. The birds fed mainly on epipelagic schooling fish when they were available and on demersal fish when pelagic fish availability was low. They tended to dive deeper and longer in a year when they fed mainly on demersal fish than the other years, reflecting the change in the depth distribution of prey fish. Chick growth rate did not differ among years, but fledging success was lower in the years of demersal fish as their meal delivery rate was low. When epipelagic schooling fish were considered scare, parents maintained chick growth by reducing brood size. High variability and unpredictability in pelagic fish abundance are key factors affecting the foraging and breeding performance of Japanese cormorants, which could potentially be used to monitor fish resources.