Hallvard Jensen
Research Scientist
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Authors
Paul Eric Aspholm Simo Maduna Juho Vuolteenaho Cornelya Klutsch Hallvard Jensen Ida Marie Bardalen Fløystad Ingrid Helle Søvik Ane-Sofie Bednarczyk Hansen Josefine Bergs Benedicte Beddari Helena Klöckener Snorre HagenAbstract
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Salmon-lice have the potential to change the behaviour and growth of their salmonid host species. Here, the baseline infection levels of salmon-lice of post-smolts (n = 815) and veteran migrants (n = 875) of sea-run Arctic charr (Salvelinus alpinus Linnaeus, 1758) were monitored over two successive years in a sub-Arctic Norwegian fjord without farming of salmonids. All Arctic charr were collected after the sea-migration period from a trap placed in the river, ascending to their overwintering freshwater habitat (Lake Laksvatn). The sea-lice infection showed a stable infection across the 2 years while increasing through the migration period and with the size of the wild sea-run Arctic charr. The prevalence of sea-lice infection was intermediate to high, and the intensities of sea-lice infections observed were generally modest, although some individuals had high infections. The relatively high infection of salmon-lice highlights the potential detrimental effects these parasites can have at both the individual and population level of such endangered sub-Arctic life-history strategies. A comparative study should be performed in fjords with aquaculture activity as focal points for salmon-lice, to investigate the impact farming have on sea-run Arctic charr populations.
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Hallvard JensenAbstract
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Lecture – ESS SURVEY UPDATE AND NEXT STEPS
Cornelya Klutsch, Paul Eric Aspholm, Hallvard Jensen, ...
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Juho Vuolteenaho Hallvard Jensen Cornelya Klutsch Helena Klöckener Helena Klöckener Birk Schulze Paul Eric AspholmAbstract
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Hallvard JensenAbstract
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Arctic charr and European whitefish are considered to be strong competitors in lakes, with the latter usually being the superior species. However, high niche plasticity and lake morphometry may suggestively facilitate resource partitioning and coexistence between charr and whitefish. Here, we explore the trophic niche utilization (diet and habitat use) of charr and whitefish co-occurring with brown trout in the deep and oligotrophic Lake Fyresvatnet, southern Norway (59°05’N, 8°10’E). Using CPUE, stomach contents and stable isotope analyses, a distinct resource partitioning was revealed between brown trout and the other two species. Brown trout typically occupied the littoral zone, feeding on benthic invertebrates, surface insects and small-sized whitefish. In contrast, charr and whitefish were predominantly zooplanktivorous, but diverged somewhat in habitat utilization as charr shifted seasonally between the profundal and the littoral zone, whereas whitefish were found in the upper water layers (littoral and pelagic habitats). Accordingly, the stable isotope values of carbon (δ13C) reflected a pelagic orientated prey resource use for both charr and whitefish, whereas brown trout had elevated carbon and nitrogen (δ15N) signatures that reflected their benthivore and piscivore diet, respectively. The findings suggest that charr may not rely upon the profundal zone as a feeding habitat but as a refuge area, and may coexist with whitefish if a third competitive and predatory species like brown trout co-occur in the lake. The study indicates that a general high habitat plasticity of Arctic charr may be essential in the presently observed coexistence with a competitively superior fish species like whitefish, and that a third fish species like brown trout may facilitate this particular fish community structure.
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Paul Eric Aspholm Bjørn Frantzen Tor-Arne Bjørn Hallvard Jensen Lars Ola Nilsson Eva Narten HøbergAbstract
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Hallvard Jensen Kimmo K. Kahilainen M. Vinni Karl Øystein Gjelland Tommi Malinen Chris Harrod Per-Arne AmundsenAbstract
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Hallvard JensenAbstract
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Hallvard JensenAbstract
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Hallvard Jensen Kimmo K. Kahilainen Per-Arne Amundsen Karl øystein Gjelland Anti Tuomaala Tommy Malinen Thomas BøhnAbstract
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