摘要:

AbstractBrook charr 15 months old were introduced in 1985 into one of two self‐contained basins of Batchawana Lake, Ontario, Canada, where they survived and reproduced. Population survival rates (ages ≥ 1) remained high (>50%) from 1986 to 1992. Annual growth rates peaked (Gx=3.1) the year following their introduction, and remained between 0.8 and 1.6 thereafter. Brook charr biomass (B) was highest, ∼ 55 kg ∼ ha−1in 1987 and 1990, and production (P) gradually declined from 80–90 in 1986–1987 to ∼ 30 kg‐ha−1‐year−1in 1990–1991. Initial high P:B ratios for brook charr, ∼ 3.0, declined and stabilized to ∼ 1.3 in the

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1995.tb00116.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractParr of the Atlantic salmon in subarctic River Teno, northern Finland (70°N, 28°E), are found to migrate to small tributaries that are not spawning areas for the adult salmon. The age distribution of the salmon differs significantly between these brooks and the natal rivers, the parr in the brooks being typically 2–4 years old, whereas those in the main rivers were mostly of age 0–2 years. The older fish were found in the uppermost regions of the brooks. The ratio of salmon to brown trout decreases towards the upper reaches of the brooks. At least some of the young salmon overwinter in the brooks. However, the number of fish and the area inhabited diminished towards the autumn in some occasions. It is suggested that this migratory behavior may be an adaptational phenomenon that could cause variation in survival among young salmon in the River

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1995.tb00117.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFish species richness was assessed by electrofishing and gillnetting in 16 lakes of the northeastern lowland in Germany (the Schorfheide biosphere reserve). The lakes range from 0.03 to 10.55 km2and support between 5 and 14 fish species. Species richness is significantly correlated with lake area in an exponential and a power model. Richness is also correlated with shoreline development and total dissolved solids. This supports the hypothesis that larger areas contain more species within a taxonomic group due to increased habitat diversity. The slope of the species‐area curve is low compared with most other studies of fish species richness in lakes, and the intercept value is high. This is interpreted as the result of high habitat and food diversity, lack of stress from abiotic factors, and the small regional species pool from which these lakes can be colonized. Two species inventories, one from the beginning of this century and one from the 1950s, are available for comparison. Average species richness did not change during the last decades. Species turnover rates were not related to the degree of anthropogenic eutrophication or to the intensity of fishery exploitation in these lakes. On the species level, however, one effect of accelerated eutrophication is apparent, the disappearance of 4 bottom‐living species from one to 6 of the study la

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1995.tb00118.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractCohorts of perch larvae, hatched within 24 h, developed into a bimodal body size distribution as early as 6 days after commencement of external food uptake. At this development stage, intra‐cohort cannibalism occurred among larval perch individuals of larval stage V (body size: 10.5±0.26 mm, 95% c. l.) on smaller siblings. In experimental trials the consumption rate (C: no. of prey/predator·hour) increased exponentially with size of predatory perch (L: mm) and at 21°C was expressed by the relationship log C=3.406·log L‐3.848 (n=10,r2=0.98,P<0.001). For predatory perch in larval stage V, consumption rate was reduced whenDaphnia pulexwere added, while not in later stages. Perch larvae experimentally forced to live as true piscivores without additional food items developed from stage V to stage IX (15.8±1.34 mm) within the same time as those fed onDaphniaalone, but with increased m

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1995.tb00119.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe food resource partitioning of Arctic charr (Salvelinus alpinusL.) and three‐spined stickleback (Gasterosteus aculeatusL.) were investigated in the littoral zone of lake Takvatn in northern Norway in the ice‐free period June–November. Charr and sticklebacks had different feeding habits. Sticklebacks ate several small benthic prey items that were never eaten by charr, and the sticklebacks' diet were dominated by the benthic microcrustaceans Chydoridae and Ostracoda, chironomid larvae and stickleback eggs. Small charr (20 cm) frequently ate both benthos, pelagic and terrestrial food. The diet overlap between small charr and sticklebacks was never larger than 0.6 (Schoener's index). The segregation in feeding habits indicates that small charr and sticklebacks are segregated in microhabitat when they are both in the littor

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1995.tb00120.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPredation is an important structuring force in many fish assemblages and may have large, direct lethal effects on prey fish populations but also may affect growth rate and survival indirectly through shifts in behavioral patterns. Some species appear more sensitive to predation and earlier studies in a limited set of Finnish ponds suggests that crucian carp (Carassius carassius) is very sensitive to predation, which results in changes in population size‐structure and density. In this study we tested the effect of piscivore presence or absence on crucian carp populations by using data from a large number (>600) of Swedish lakes across a wide geographical area and ranging in size from small ponds to large lakes (0.02–4400 ha). We also included a second species, tench (Tinea tinea), in our analyses. The population size structures of crucian carp and tench were clearly related to the presence or absence of piscivores. In lakes and ponds without piscivores. populations were dominated by small‐bodied individuals. When piscivores were present, populations consisted almost exclusively of large individuals. Densities of crucian carp and tench were much higher in ponds and lakes without piscivores. There were no differences in size structure or relative abundance when catches from electrofishing were compared with gill net catches, suggesting that our results are not an effect of a behavioral shift in the presence of pisci

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1995.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY