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  • 1
    Electronic Resource
    Electronic Resource
    An experimental test of the genetic component of the ontogenetic habitat shift in Arctic charr (Salvelinus alpinus) (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Ecology of freshwater fish 7 (1998), S. 0 
    Details
    ISSN: 1600-0633
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract— Fry of the Arctic charr, Salvelinus alpinus, were experimentally stocked into a small fish-free lake to test the hypothesis that the size-dependent habitat shift from the epibenthic to the pelagic habitat is genetically determined. The charr originated from a nearby lake inhabiting predatory brown trout Salmo trutta. The cohort of stocked charr was investigated for three years. The Arctic charr started to exploit the pelagic habitat in their first summer at a size of 7–9 cm in contrast to about 15 cm in the donor lake. In the next two summers, the pelagic fraction of the cohort increased. The main fraction lived in epibenthic areas, utilizing the same prey as pelagic charr. Water temperature moderated the habitat use of juveniles such that they avoided warm (〉16°C) waters and resided in cool, deep areas. The result was consistent with the hypothesis of a tradeoff between feeding benefit and the predation risk producing spatial segregation of Arctic charr and demonstrated that the fish can facultatively respond to predation risk and adjust the size at which they migrate to the pelagic zone to feed on zooplankton.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0633.1998.tb00187.x
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  • 2
    Electronic Resource
    Electronic Resource
    Gill raker structure and selective predation on zooplankton by particulate feeding fish (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 47 (1995), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The relationship between the gill raker structure of planktivorous fish (number, distance between gill rakers and length) and selective feeding on different species and size classes of zooplankton was studied. Gill raker structure was measured for brown trout Salmo trutta, Arctic charr Salvelinus alpinus, whitefish Coregonus lavaretus, roach Rutilus rutilus, bleak Alburnus alburnus, and three-spined stickleback Gasterosteus aculeatus. All species are facultative planktivorous fish and occur commonly in Scandinavian lakes. The effect of gill raker structure was studied by comparing prey found in fish stomachs with the availability of zooplankton from several lakes. Gill raker length and distance were significantly correlated with fish length. Although gill raker structure differed among species, all fish species selected the larger zooplankters. The minimum size of cladoceran species found in fish stomachs was much smaller than the distance between gill rakers. Despite great differences in gill raker spacing, the minimum size ingested of Daphnia galeata and Bosmina longispina was similar for all predators. The hypothesis that small zooplankton are strained and retained by the gill rakers in particulate feeding planktivorous fish, particularly in salmonids and roach, is rejected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1995.tb01937.x
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  • 3
    Electronic Resource
    Electronic Resource
    A 27-year study of brown trout population dynamics and exploitation in Lake Songsjøen, central Norway (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 57 (2000), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: From 1968–1984 (period I), a brown trout Salmo trutta, population in a 70-ha oligotrophic lake in central Norway was exploited using larger mesh gill-nets selectively removing the larger fish. From 1985–1994 (period II), intermediate sized fish were removed using smaller-mesh sizes gill-nets. Fishing mortality and CPUE were correlated positively with effort and numbers of fish 〉3 years old for period II. The gill-net catchability was correlated negatively with spawner biomass and number of trout 〉3 years old. The significant positive correlation between natural mortality and stock biomass and spawning stock biomass indicated density-dependent mortality. The significant correlation between spawning stock and recruitment described by the Ricker model, indicated density-dependent recruitment of 1-year-old trout. The fishing regimes in the two periods affected the population dynamics and density differently. Selective removal of smaller fish permitted the larger fish to survive, and was beneficial in reducing fish density and maintaining stocks at low levels, consequently, achieving the expected increase in fish growth rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2000.tb00483.x
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  • 4
    Electronic Resource
    Electronic Resource
    Habitat use, size and age structure in sympatric brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) stocks: resistance of populations to change following harvest (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Ecology of freshwater fish 5 (1996), S. 0 
    Details
    ISSN: 1600-0633
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract– Habitat use and population dynamics in brown trout Salmo trutta and Arctic charr Salvelinus alpinus were studied in an oligotrophic lake over a period of 10 years. Previous studies showed that the species segregated by habitat during summer. While brown trout occupied the surface water down to a depth of 10 m, Arctic charr were found deeper with a maximum occurrence at depth 10–15 m. Following the removal of a large number of intermediate sized fish in 1988–89, habitat segregation between the species broke down and Arctic charr were found in upper waters, while brown trout descended to deeper waters. The following year, both species were most frequently found in surface waters at depths of 0–5 m. During the last four years, the species reestablished their original habitat segregation despite another removal experiment of intermediate-sized fish in 1992–1994. The removal of fish resulted in an increased proportion of large (≥ 25 cm) fish in both species. Furthermore, the charr stock responded by reduced abundance and increased size-at-age. The results revealed plasticity and strong resistance to harvest populations of brown trout and Arctic charr. This is probably due to internal mechanisms of intraspecific competition within each population, which result in differential mortality among size classes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0633.1996.tb00036.x
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of stocking of piscivorous brown trout, Salmo trutta L., on stunted Arctic charr, Salvelinus alpinus (L.) (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Ecology of freshwater fish 3 (1994), S. 0 
    Details
    ISSN: 1600-0633
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: To study the effects on a stunted freshwater population of Arctic charr, Salvelinus alpinus (L.), two groups of large (26–45 cm) individually tagged brown trout, Salmo trutta L., were released and recaptured with gillnets after 1, 7, 11 and 63 weeks. One group of trout was trained on a fish diet before release, and the other, reared on commercial dry pellets, served as a control. Specific growth rates in both groups were negative 1 week after release and approached zero after 63 weeks. Condition factor and internal fat content decreased during the experiment. Although only 11% of the trout stomachs examined contained fish prey, charr represented 79% of the total stomach weight content. Gillnet samples of charr before and 63 weeks after the release of trout indicated a decreasing population size of charr. Individual growth and mean length of charr increased after release of trout, especially for charr at age 4 years. After the release of trout, 35% of the charr were longer than 20 cm as compared with 6% before the release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0633.1994.tb00107.x
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  • 6
    Electronic Resource
    Electronic Resource
    Size-scaling of zooplankton foraging in Arctic charr (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of fish biology 62 (2003), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Prey capture rate (number of prey s−1) and the mode of feeding of Arctic charr Salvelinus alpinus were studied by performing foraging experiments with two sizes (1·1 and 1·8 mm) of Daphnia longispina prey. Arctic charr were particulate feeders at all densities tested. Adjusted for the effect of prey density, the capture rate showed a hump-shaped relationship with Arctic charr size for both sizes of D. longispina. Estimated attack rates (a) also tended to show a hump-shaped relationship with fish size. The estimated size-scaling exponent of the attack rate function, however, was relatively small, implying small changes in attack rate over fish sizes. Simultaneous estimations of a and handling time were used in combination with published data on fish metabolism and dry mass rations of prey to estimate maintenance resource density of prey as a function of Arctic charr mass. Maintenance resource densities increased monotonically with Arctic charr size, and rapidly as optimum fish size relative to attack rate on prey was passed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1095-8649.2003.00071.x
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  • 7
    Electronic Resource
    Electronic Resource
    Piscivory by brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.) in Norwegian lakes (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 41 (1992), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Size and frequency of occurrence of prey of brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.) were recorded in 13 Norwegian lakes during 1973–1990. Piscivores usually comprised less than 5% of the total population. Arctic charr were less piscivorous than brown trout. Trout and charr became piscivorous at 13 and 16 cm length, respectively. These size thresholds were similar to those of other facultative piscivorous freshwater fish species. When present, three-spined sticklebacks, Gasterosteus aculeatus (L.), were preferred by all length groups of piscivorous brown trout and Arctic charr. Length of prey increased with increasing predator length, and the mean body length of prey was about 33 and 25% of predator length for trout and charr, respectively. Yearlings of charr were not recorded as prey.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1992.tb03172.x
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  • 8
    Electronic Resource
    Electronic Resource
    Book reviews (1956)
    Springer
    International review of education 2 (1956), S. 92-101 
    Details
    ISSN: 1573-0638
    Source: Springer Online Journal Archives 1860-2000
    Topics: Education
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01416841
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  • 9
    Electronic Resource
    Electronic Resource
    Introduction: Aspects of school failure (1957)
    Springer
    International review of education 3 (1957), S. 129-134 
    Details
    ISSN: 1573-0638
    Source: Springer Online Journal Archives 1860-2000
    Topics: Education
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01417277
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  • 10
    Electronic Resource
    Electronic Resource
    Coexistence with similar life cycles in two species of freshwater copepods (Crustacea) (1990)
    Springer
    Hydrobiologia 208 (1990), S. 187-199 
    Details
    ISSN: 1573-5117
    Keywords: life cycles ; coexistence ; competition ; diapause ; humic lakes ; hydrography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two species of freshwater cyclopoid copepods, Cyclops scutifer Sars and Mesocyclops leuckarti (Claus), with different ecological requirements, coexist in three humic ponds near the timberline in boreal forests in south-central Norway. The life cycle in both species is basically regulated by complete depletion of oxygen during the long winter. There is a short period of reproduction in spring followed by a rapid development during summer and autumn to advanced instars, capable of diapause when oxygen depletion starts in early winter. Both species have an exclusive 1-yr cycle. The long winter under anoxic conditions is passed in diapause as large copepodids (late developmental instars) with usually no individuals left in the plankton. Even if co-occurring in the same habitats with similar life cycles, there is a temporal and spatial segregation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007784
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