Anders Klemetsen

UiT The Arctic University of Norway · Department of Arctic and Marine Biology

In a subarctic forest at Kvaløya, northern Norway, willow grouse Lagopus lagopus fed at snow level by clipping bits of twigs from mountain birch Betula pubescens during winter. Birch has two types of twigs ending in a terminal bud: long twigs with a smooth bark, and short twigs with rings of thicker bark. The grouse selected ringed twigs above smoo...

Disentangling the causes and consequences of ontogenetic niche shifts has been a pivotal challenge in ecology, aiming to enhance the understanding of biological processes that function at the individual, population, and community levels. Studies on ontogenetic dietary shifts have traditionally focused on short time scales, mostly including sampling...

Distinct swarms of Bosmina longispina (Leydig, 1860) (Crustacea: Cladocera) were visually observed and described in Gjøkvatn, a Norwegian forest lake at 69°N, in 1969 and again in 1996 and 2021. The repeated observations after many years show that Bosmina swarms occur regularly in the lake. The swarming is likely to be an anti-predation behaviour a...

Competition is assumed to shape niche widths, affecting species survival and coexistence. Expectedly, high interspecific competition will reduce population niche widths, whereas high intraspecific competition will do the opposite. Here we test in situ how intra-and interspecific competition affects trophic resource use and the individual and popula...

Littoral chydorids were sampled with a bottom sledge in Takvatn, a 15 km2 north Norwegian oligotrophic lake with poor vegetation. Three out of eight recorded species of chydorids were common, with abundance minima in late summer and maxima in autumn. Eurycercus lamellatus (O.F. Müller, 1776) and Acroperus harpae (Baird, 1835) were monocyclic, where...

We review three long‐term research programs performed over the last four decades on the ecology and management of oligotrophic lake systems with different fish communities at 69° N in Norway. Through whole‐lake perturbation experiments, intensive culling of stunted fish removed 35 tons (1984–1991) of Arctic charr Salvelinus alpinus in Takvatn (15 k...

A population of small-sized Arctic charr living their entire life cycle in deep water was recently found in Lake Skogsfjordvatn, Northern Norway. Their phenotype and life history closely resembles the profundal charr morph in another subarctic Norwegian lake, Fjellfrøsvatn. Fjellfrøsvatn has one littoral omnivorous and one small profundal benthivor...

Arctic charr (Salvelinus alpinus) is generally considered an inferior piscivore compared to brown trout (Salmo trutta). However, we demonstrate that a recently described profundal spawning piscivore PP-morph of Arctic charr in a subarctic lake has evolved typical piscivore traits (i.e. large jaws, robust skulls), similar to the co-occurring brown t...

Benthic invertebrate communities play a fundamental role in lake ecosystems, and the understanding of how those benthic communities are structured, particularly in terms of the identity and spatiotemporal distribution of their functional traits, is key to our understanding of how lake ecosystems work. In Takvatn, a subarctic lake in northern Norway...

Benthic invertebrate samples, taken in August and October 2000, 2001, 2002 at three sites in each of 13 streams (total 39 sites over a 200 km stretch of river), were used to: (i) classify the species/taxa into groups according to their occurrence; (ii) compare species/taxa richness and biodiversity across all sites; (iii) detect environmental varia...

p>Amundsen, P.-A., Smalås, A., Knudsen, R., Kristoffersen, R., Siwertsson, A. & Klemetsen, A. 2015. Takvatnprosjektet. Erfaringer fra forskning og kultivering av en overbefolka røyebestand. Rapport, UiT Norges arktiske universitet. 53 s. Overbefolka fiskebestander er et stort problem i mange av våre innsjøer. Det typiske kjennetegnet er en stor te...

The type localities for the Holarctic mayflies Metretopus borealis (Eaton, 1871) and Metretopus alter Bengtsson, 1930 are in northern Norway, between Kautokeino and Karesuando in Finnmark County for M. borealis and along the small stream, Råvatnbekken, in Målselv, Troms County for M. alter. By combining new sampling, records in reports and theses a...

The numbers of divers, ducks, gulls, terns and waders in the 15 km2 oligotrophic lake Takvatn, North Norway, were estimated six times during 1983-2012. Systematic mapping surveys were done by boat within the first week after the ice-break in June. Twenty-one species were observed over the years and 12 were regarded as breeding on the lake. Red-brea...

In the search for the most variable non-human vertebrate on Earth, intraspecific variation of ten variable traits was compared among ten highly variable species. Mammals, birds and many reptiles, amphibians and fishes were excluded because most of the variation is among, and not within species. The focus was on northern fishes, where high intraspec...

In the study of mechanisms structuring fish communities, mixed competition–predation interactions where large predators feed on prey fish versus those in which small predators compete with prey fish for a shared prey have been the focus of substantial research. We used a long-term data set from a system inhabited by brown trout (Salmo trutta) (pred...

Introduced species can alter the topology of food webs. For instance, an introduction can aid the arrival of free-living consumers using the new species as a resource, while new parasites may also arrive with the introduced species. Food-web responses to species additions can thus be far more complex than anticipated. In a subarctic pelagic food we...

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Infections of the parasites Diphyllobothrium dendriticum, Diphyllobothrium ditremum, and Cystidicola farionis in Arctic charr (Salvelinus alpinus) from Takvatn, northern Norway, were followed throughout a 9-month overwintering period. The relative density of all three parasite species increased with the age of the host in response to ontogenetic sh...

The trophic niche and parasite infection of Arctic charr (Salvelinus alpinus) were explored in two lakes with sympatric burbot (Lota lota) and two lakes without burbot in subarctic Norway. The CPUE of burbot and charr were similar in one lake, but burbot had a low population density in the other. Burbot were benthivorous in both lakes. Other co-occ...

The salmonid arctic charr Salvelinus alpinus (L.) is one of the most widespread fishes in the world and is found farther north than any other freshwater or diadromous fish, but also in cool water farther south. It shows a strong phenotypic, ecological, and life history diversity throughout its circumpolar range. One particular side of this diversit...

Quantitative samples taken with a new colonisation sampler over three years demonstrated a macroinvertebrate community of 25 taxa in the stony littoral of Takvatn, North Norway. The spatial variance was density-dependent and the ‘index of aggregation’ varied in the range 1.01–1.73 for 13 common taxa. The distribution was significantly aggregated fo...

1. Inter-individual differences in trophic behaviour are considered important in the disruptive selection process for resource specialization and may represent an early phase in the evolution of polymorphism and adaptive radiation. Here, we provide evidence of high stability of individual trophic niches of a fish predator from a 15-year study. 2. I...

Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. Parasites used hosts at all trophic levels and increa...

The habitat and diet choice and the infection (prevalence and abundance) of trophically transmitted parasites were compared in Arctic charr and brown trout living sympatrically in two lakes in northern Norway. Arctic charr were found in all main lake habitats, whereas the brown trout were almost exclusively found in the littoral zone. In both lakes...

The study compares the resource utilization of two sympatric Arctic charr morphs over an annual period in a subarctic lake. The two morphs are reproductively isolated in time and place of spawning, and are referred to as the littoral and profundal morphs (L-morph and P-morph) according to their spawning habitats. Fish were sampled monthly (ice-free...

Many top-predator fish stocks in both freshwater and marine systems have collapsed as a result of overharvesting. Consequently, some of these communities have shifted into seemingly irreversible new states. We showed, for predators feeding on prey that exhibit food-dependent growth, that culling of fish prey may promote predator recovery. We remove...

1. Intraspecific competition for restricted food resources is considered to play a fundamental part in density dependence of somatic growth and other population characteristics, but studies simultaneously addressing the interrelationships between population density, food acquisition and somatic growth have been missing. 2. We explored the food cons...

Two reproductive isolated morphs of Arctic charr (Salvelinus alpinus), termed profundal and littoral charr according to their different spawning habitats, co-occur in the postglacial lake Fjellfrøsvatn in North Norway. All profundal charr live in deep water their entire life and have a maximum size of 14cm, while the littoral charr grow to 40cm. So...

Abstract –  Habitat and diet of Arctic charr Salvelinus alpinus (L.) were studied by monthly sampling from late autumn to early summer in Linnévatn, Svalbard (78°3′N, 13°50′E). This is the first year-round study of a population of charr in the High Arctic, with samples being taken every 5–7 weeks. The ice cover lasted for more than 9 months, from m...

The food resource partitioning of Arctic charr (Salvelinus alpinus L.) and three-spined stickleback (Gasterosteus aculeatus L.) 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 we...

Spatial and temporal migratory behaviour of wild Atlantic salmon smolt (Salmo salar L.) was investigated at the River Utsjoki, a tributary of the sub-Arctic River Tana, using submerged video cameras that covered the entire water column across the river. The matrix of cameras provided information on the exact time, position in water column, and swim...

Juvenile salmon density was related to invertebrate density in 13 streams within the River Tana, northern Norway. There were only small, nonsignificant, differences in benthic density between streams with and without juvenile salmon. All streams with a high density of juvenile salmon had low benthic densities at the stream mouth. Juvenile salmon we...

The sub-arctic Lake Fjellfrøsvatn, northern Norway, has two morphs of Arctic charr that are reproductively isolated because they spawn 5 months apart. The smaller morph (≤14 cm LF) is confined to the profundal zone of the lake and the larger morph is mainly littoral. Three hypotheses were tested: (i) the offspring of the profundal Arctic charr grow...

Mean values ±95% CL of the upper incipient (TIL) and ultimate (TUL) lethal temperatures, determined at five acclimation temperatures (TA), increased for TIL from 19.2 ± 0.4° C (TA 0.5° C) to 21.0 ± 0.4° C (TA 20° C), and for TUL from 22.6 ± 0.1° C (TA 0.5° C) to 26.6 ± 0.4° C (TA 20° C). Mean values were close to those obtained for Arctic charr ale...

Relationships between the degree of anadromy, sex ratio and parr growth of Arctic charr Salvelinus alpinus were investigated in Lake Storvatn in Hammerfest town, by estimating the densities of resident and anadromous charr in the lake, and by comparing the smolt characteristics of fish captured in the outlet river with those of fish of the same age...

– The objective was to compare juvenile salmon density in 20 streams throughout the very large River Tana, northern Norway, and to relate variation in density to a suite of environmental factors. Four sampling sites were electrofished in each stream (one at the mouth of the stream and three within the stream) in August and October 2000, 2001, 2002....

Two whitefish morphs have been identified in lakes in northern Norway from a bimodal distribution of gill raker numbers: a sparsely- and a densely-rakered. Habitat choice and feeding ecology of whitefish were studied in five lakes with the two morphs living in sympatry, and in five lakes harbouring only the sparsely-rakered morph. In sympatry, the...

A long-term field study of a perturbed host–helminth system provides indirect evidence that a long-lived swimbladder nematode, Cystidicola farionis, induces mortality of Arctic charr, Salvelinus alpinus. The prevalence and abundance of this parasite has changed little over the period from 1987 to 1999. The cumulative numbers of L3-stage larvae stea...

Between 1984 and 1989, the experimental removal of 31 tons (666000 fish) of stunted Arctic charr, Salvelinus alpinus, from Takvatn in northern Norway, had strong effects on the populations of Arctic charr, brown trout, Salmo trutta, and three-spined sticklebacks, Gasterosteus aculeatus. The littoral catch per unit effort (CPUE) of charr had decreas...

Overpopulation and stunting is a management problem in many boreal whitefish populations. Typically, there is an accumulation of old, small-sized and heavily parasitized fish. In an attempt to alleviate this problem and to initiate a commercial fishery in the 25 km2 lake Stuorajavri, northern Norway, a large-scale fish removal programme was carried...

The zooplankton of two neighbouring lakes, situated in northern Norway (69 07 N), was studied during the ice-free season of 1994. Zooplankton structure and seasonal dynamics are compared, and the importance of biotic interactions and seasonality (temperature and photoperiod) as determinants of the observed patterns is evaluated in light of collecte...

This contribution reports the analysis of a sample of landlocked arctic charr collected with gillnets in Svartvatnet, Svalbard, 1964. This is the first scientific sample from a landlocked charr population from Svalbard. We found a very prominent modal group of large, old and sexually adult fish of both sexes. Their length ranged from 15 to 62 cm, b...

This contribution reports the analysis of a sample of landlocked Arctic charr collected with gillnets in Svartvatnet, Svalbard, 1964. This is the first scientific sample from a landlocked charr population from Svalbard. We found a very prominent modal group of large, old and sexually adult fish of both sexes. Their length ranged from 15 to 62 cm, b...

A dwarf charr that is remarkably distinct from the normal charr morph was recently discovered in the subarctic lake Fjellfrøsvatn, in northern Norway. It spends its entire life cycle in deep water and spawns under a thick cover of snow and ice. There is no size overlap between sexu ally mature fish of the two morphs (8-13 cm FL versus >16 cm), and...

S. alpinus of Lake Takvatn, N Norway used all major habitats of the lake in the icefree season. Charr in the profundal, the pelagic and the littoral habitats differed with respect to age and size and the population displayed a regular pattern of ontogenetic habitat shifts in the lake. From 1984-89, 666 000 charr were removed by intensive fishing wi...

Arctic char Salvelinus alpinus once occurred at high densities in the pelagic zone of Takvatn. An intensive fish stock reduction program begun in 1984 reduced the catches of pelagic Arctic char by approximately 60% from 1981 to 1986. The crustacean plankton was dominated by Bosmina longispina, Cyclops scutifer, and Eudiaptomus graciloides. With the...

This paper outlines different production strategies for farming Arctic char Salvelinus alpinus in Norway. Economics and marketing are also discussed. Based on recent results, the use of wild Arctic char for smolt production may represent an alternative to intensive smolt production. In addition, the effects on the remaining wild fish populations of...

Long-rough dab were sampled during a period of one year at two stations situated 35 km apart in Balsfjorden, North Norway. The dab had ingested a total of 40 different prey taxa; 19 taxa were found at both stations. The polychaetes Nephtys sp., Maldanidae (mainly Maldane sarsi), Owenidae (mainly Galathowena oculata), the amphipod Arrhis phyllo- nyx...

Before 1984, Takvatn, a 14.2-km2 oligotrophic lake in northern Norway, held a dense population of stunted Arctic char Salvelinus alpinus. A large-scale, intensive fishing program with baited funnel traps was initiated in 1984. In the 6-year period from 1984 to 1989, 666,000 individuals or 31.3 tonnes of Arctic char were removed from the lake. The e...

Stomach contents analyses and other biological information of Arctic charr (Savelinus alpinus (L.)), brown trout (Salmo trutta L.) and small Atlantic salmon (S. salar L.) caught 1982–85 close to the elv estuary (69N) on the island of Senja, N. Norway are presented, and extracts of a 1975–85 fishing log given. this appears to be the first case study...

Stomach contents weights in a study of Arctic charr (Salvelinus alpinus L.) were not normally distributed. This may have implications for the field estimation of consumption rates and also indicates that a more extensive handling of stomach content data is needed. Fish were sampled every 3 h throughout 24 h periods. The stomach contents showed very...

The polar, isolated Bear Island is rich in rivers, lakes and ponds. Arctic charr is the only fish species, and the freshwater biota are of exceptionally low diversity. The charr probably immigrated in early postglacial times. Today only landlocked population seem to exist. Anadromy is prevented by steep river outlets to the sea following land uphea...

Some 72 different animal taxa were recorded in the stomachs of Gadus morhua. Of these 11 taxa made up the principal prey. Deep water prawn Pandalus borealis, capelin Mallotus villosus and small krill Thysanoessa spp. were the most important. The others were the polychaete Nephtys sp., the mysids Erythrops sp. and Michteimysis mixta, the amphipods A...