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Browsing Artikler, rapporter og annet (arktisk og marin biologi) by Author
Now showing items 1-20 of 122
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Ampomah, Osei Yaw; Ofori-Ayeh, E; Solheim, Bjørn; Svenning, Mette M (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)[+][-]
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Amundsen, Per-Arne; Gjelland, Karl Øystein; Knudsen, Rune; DalsbØ, laina h; Lien, Cesilie; Evjen, jan knut (Research report; Forskningsrapport, 2012)[+][-]
Abstract: Pasvikvassdraget har siden 1991 vært gjenstand for omfattende økologiske studier i regi av Ferskvannsøkologisk faggruppe ved Universitetet i Tromsø. Undersøkelsene har særlig vært rettet mot å undersøke effektene av at lagesilda, en fremmed fiskeart for Nord-Norge, kom inn i vassdraget på slutten av 1980-tallet. For å få en grundig forståelse av økologien i vassdraget har studiene også omfattet andre viktige fiskearter, krepsdyrplankton og bunndyr. Samtidig har vi hatt et nært samarbeid med russiske forskere angående tungmetallforurensing fra de russiske Nikel-smelteverkene, og med finske forskere gjennom sammenlignende studier med fiskebestandene i Enaresjøen og andre innsjøer i den finske delen av vassdraget. Totalt sett har dette resultert i mye ny og interessant kunnskap om Pasvikvassdraget; kunnskap som bl.a. er dokumentert gjennom 36 internasjonale publikasjoner, 22 fagrapporter og populærvitenskapelige publikasjoner, fire doktorgradsavhandlinger og 12 masteroppgaver (se Appendiks 2 for detaljer). I perioden 2008 – 2011 har langtidsstudiene i Pasvikvassdraget vært fulgt opp gjennom et prosjekt finansiert av Norges forskningsråd (Miljø-2015 programmet; prosjektnr. 183984/S30). Denne rapporten er en populærvitenskapelig sammenfatning av kunnskapen som har fremkommet gjennom dette prosjektet, der det særlig har vært lagt vekt på de langsiktige effektene av lagesildas invasjon og viktige forvaltningsmessige implikasjoner. URI: http://hdl.handle.net/10037/4417 File(s) in this item: 1
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Amundsen, Per-Arne; Lafferty, Kevin D.; Knudsen, Rune; Primicerio, Raul; Kristoffersen, Roar; Klemetsen, Anders; Kuris, Armand M (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: 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 web with free-living and parasitic species, two fish species (arctic charr Salvelinus alpinus and three-spined stickleback Gasterosteus aculeatus) have known histories as deliberate introductions. The effects of these introductions on the food web were explored by comparing the current pelagic web with a heuristic reconstruction of the pre-introduction web. Extinctions caused by these introductions could not be evaluated by this approach. The introduced fish species have become important hubs in the trophic network, interacting with numerous parasites, predators and prey. In particular, five parasite species and four predatory bird species depend on the two introduced species as obligate trophic resources in the pelagic web and could therefore not have been present in the pre-introduction network. The presence of the two introduced fish species and the arrival of their associated parasites and predators increased biodiversity, mean trophic level, linkage density, and nestedness; altering both the network structure and functioning of the pelagic web. Parasites, in particular trophically transmitted species, had a prominent role in the network alterations that followed the introductions. URI: http://hdl.handle.net/10037/4974 File(s) in this item: 1
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Amundsen, Per-Arne; Salonen, Erno; Niva, Teuvo; Gjelland, Karl Øystein; Præbel, Kim; Sandlund, Odd Terje; Knudsen, Rune; Bøhn, Thomas (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: We explore the long-term developments in population biology and life history during the invasion and establishment of the fish species vendace Coregonus albula in a subarctic watercourse by comparing life-history traits and molecular genetic estimates between the source and the colonist population. The two populations exhibited highly contrasting life-history strategies. Relative to the source population, the colonist population was characterized by slower somatic growth rates, earlier sexual maturation at smaller individual size, higher mortality rates and a shorter life span. The two populations could also be significantly discriminated by the genetic markers. Limited founder effects were detected from heterozygote deficit and reduced allelic richness in the colonist population, but both populations were associated with relatively high genetic diversity. The study reveals that the invasion into a new environment induced large changes in life-history strategy, with typical r-selected traits being more prominent in the colonist than in the source population. We discuss the mechanisms that may explain the observed life-history differences between the source and the colonist population, and argue that the accelerated life history of the colonist population represents an adaptive pioneer strategy aimed at fast population increase during colonization and establishment. URI: http://hdl.handle.net/10037/4691 File(s) in this item: 1
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Andersen, Johan (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)[+][-]
Abstract: Sites at various distances from eutrophic and mesotrophic lakes and fens on the island Öland in southern Sweden were systematically surveyed in summer (May–August) and autumn (late September–October) to elucidate the hibernation sites of wetland carabid beetles. Thirty-five of 47 wetland species were found in their winter quarters. In areas ≤50 m from the lakes and fens, the observed as well as the estimated number of hibernating wetland species was higher in mesic to dry sites than in wet or moist open sites. Very few overwintering beetles were detected far (≥120 m) from the water. There was no significant difference in the frequencies of macropterous and dimorphic (brachypterous) species and individuals hibernating close to, and more distantly from, water. Individuals of small species hibernated closer to water than larger ones. At least in Scandinavia, there is no convincing evidence that wetland species hibernate far away from water, migrating by flight. A considerable number of the species that were collected in their winter quarters are rare and red- listed in at least one of the Scandinavian countries. Winter quarters situated in mesic and dry meadows and woodland close to lakes and fens had the highest number of red-listed species. Therefore, it is of fundamental importance to protect such sites. Threats to the integrity of the current habitats are logging and various transformations of meadows, e.g. digging and removal of large objects such as stones. Cessation of grazing by cattle may also have a negative effect. URI: http://hdl.handle.net/10037/4024 File(s) in this item: 1
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Asante, Daniel Kwaku Addo (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)[+][-]
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Aschan, Michaela; Helle, Kristin; Williams, Thomas (Journal article; Tidsskriftartikkel; Peer reviewed, 27-Jun-2008)[+][-]
Abstract: The relationship between temperature, latitude, and depth and the distribution and relative abundance of chondrichthyans along the northern coast of Norway was examined based on catches made in scientific trawls north of 628N from 1992 to 2005. It appears that Chimaera monstrosa, Etmopterus spinax, Squalus acanthias, and Galeus melastomus were more abundant in the south, and Amblyraja radiata more common in the north. Between 1992 and 2005, the distribution and relative abundance did not appear to change significantly, although average water temperatures rose during the period. Current fishing levels do not appear to be impacting the populations of the more common species, but the status of species rarely found in the survey catches is unclear. Description: Authors' final draft, post refereeing. Reprinted with permission. Published version available at publisher's site: http://dx.doi.org/10.1093/icesjms/fsn103 URI: http://hdl.handle.net/10037/2336 File(s) in this item: 1
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Barraquand, Frederic; Murrell, David J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: Dispersal theory generally predicts kin competition, inbreeding, and temporal variation in habitat quality should select for dispersal, whereas spatial variation in habitat quality should select against dispersal. The effect of predation on the evolution of dispersal is currently not well-known: because predation can be variable in both space and time, it is not clear whether or when predation will promote dispersal within prey. Moreover, the evolution of prey dispersal affects strongly the encounter rate of predator and prey individuals, which greatly determines the ecological dynamics, and in turn changes the selection pressures for prey dispersal, in an eco-evolutionary feedback loop. When taken all together the effect of predation on prey dispersal is rather difficult to predict. We analyze a spatially explicit, individual-based predator-prey model and its mathematical approximation to investigate the evolution of prey dispersal. Competition and predation depend on local, rather than landscape-scale densities, and the spatial pattern of predation corresponds well to that of predators using restricted home ranges (e.g. central-place foragers). Analyses show the balance between the level of competition and predation pressure an individual is expected to experience determines whether prey should disperse or stay close to their parents and siblings, and more predation selects for less prey dispersal. Predators with smaller home ranges also select for less prey dispersal; more prey dispersal is favoured if predators have large home ranges, are very mobile, and/or are evenly distributed across the landscape. URI: http://hdl.handle.net/10037/4749 File(s) in this item: 1
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Berge, Jørgen; Båtnes, Anna Solvang; Johnsen, Geir; Blackwell, Susan; Moline, Mark A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: This study examines the composition and activity of the planktonic community during the polar night in the high Arctic Kongsfjord, Svalbard. Our results are the first published evidence of bioluminescence among zooplankton during the Arctic polar night. The observations were collected by a bathyphotometer detecting bioluminescence, integrated into an autonomous underwater vehicle, to determine the concentration and intensity of bioluminescent flashes as a function of time of day and depth. To further understand community dynamics and composition, plankton nets were used to collect organisms passing through the bathyphotometer along with traditional vertical net tows. Additionally, using a moored bathyphotometer closed to the sampling site, the bioluminescence potential itself was shown not to have a diurnal or circadian rhythm. Rather, our results provide evidence for a diel vertical migration of bioluminescent zooplankton that does not correspond to any externally detectable changes in illumination. URI: http://hdl.handle.net/10037/4975 File(s) in this item: 1
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Berge, Jørgen; Gabrielsen, Tove M; Moline, Mark A.; Renaud, Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: Before man hunted the large baleen whales to near extinction by the end of the nineteenth century, Arctic ecosystems were strongly influenced by these large predators. Their main prey were zooplankton, among which the calanoid copepod species of the genus Calanus, long considered key elements of polar marine ecosystems, are particularly abundant. These herbivorous zooplankters display a range of adaptations to the highly seasonal environments of the polar oceans, most notably extensive energy reserves and seasonal migrations to deep waters where the non-feeding season is spent in diapause. Classical work in marine ecology has suggested that slow growth, long lifespan and large body size in zooplankton are specific adaptations to life in cold waters with short and unpredictable feeding seasons. Here, we challenge this understanding and, by using an analogy from the evolutionary and contemporary history of the avocado, argue that predation pressure by the now nearly extinct baleen whales was an important driving force in the evolution of life history diversity in the Arctic Calanus complex. URI: http://hdl.handle.net/10037/4976 File(s) in this item: 1
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Bårdsen, Bård-Jørgen; Henden, John-André; Fauchald, Per; Tveraa, Torkild; Stien, Audun (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)[+][-]
Abstract: Empirical work suggest that long-lived organisms have adopted risk sensitive reproductive strategies where individuals trade the amount of resources spent on reproduction versus survival according to expected future environmental conditions. Earlier studies also suggest that climate affects population dynamics both directly by affecting population vital rates and indirectly through long-term changes in individual life histories. Using a seasonal and state-dependent individual-based model we investigated how environmental variability affects the selection of reproductive strategies and their effect on population dynamics. We found that: (1) dynamic, i.e. plastic, reproductive strategies were optimal in a variable climate. (2) Females in poor and unpredictable climatic regimes allocated fewer available resources in reproduction and more in own somatic growth. This resulted in populations with low population densities, and a high average female age and body mass. (3) Strong negative density dependence on offspring body mass and survival, along with co-variation between climatic severity and population density, resulted in no clear negative climatic effects on reproductive success and offspring body mass. (4) Time series analyses of population growth rates revealed that populations inhabiting benign environments showed the clearest response to climatic perturbations as high population density prohibited an effective buffering of adverse climatic effects as individuals were not able to gain sufficient body reserves during summer. Regularly occurring harsh winters ‘harvested’ populations, resulting in persistent low densities, and released them from negative density dependent effects, resulting in high rewards for a given resource allocation. URI: http://hdl.handle.net/10037/4089 File(s) in this item: 1
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Certain, Gregoire; Skarpaas, Olav; Bjerke, Jarle Werner; Framstad, Erik; Lindholm, Markus; Nilsen, Jan-Erik; Norderhaug, Ann; Oug, Eivind; Pedersen, Hans-Christian; Schartau, Ann Kristin; van der Meeren, Gro Ingleid; Aslaksen, Iulie; Engen, Steinar; Garnåsjordet, Per-Arild; Kvaløy, Pål; Lillegård, Magnar; Yoccoz, Nigel; Nybø, Signe (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)[+][-]
Abstract: The magnitude and urgency of the biodiversity crisis is widely recognized within scientific and political organizations. However, a lack of integrated measures for biodiversity has greatly constrained the national and international response to the biodiversity crisis. Thus, integrated biodiversity indexes will greatly facilitate information transfer from science toward other areas of human society. The Nature Index framework samples scientific information on biodiversity from a variety of sources, synthesizes this information, and then transmits it in a simplified form to environmental managers, policymakers, and the public. The Nature Index optimizes information use by incorporating expert judgment, monitoring-based estimates, and model-based estimates. The index relies on a network of scientific experts, each of whom is responsible for one or more biodiversity indicators. The resulting set of indicators is supposed to represent the best available knowledge on the state of biodiversity and ecosystems in any given area. The value of each indicator is scaled relative to a reference state, i.e., a predicted value assessed by each expert for a hypothetical undisturbed or sustainably managed ecosystem. Scaled indicator values can be aggregated or disaggregated over different axes representing spatiotemporal dimensions or thematic groups. A range of scaling models can be applied to allow for different ways of interpreting the reference states, e.g., optimal situations or minimum sustainable levels. Statistical testing for differences in space or time can be implemented using Monte-Carlo simulations. This study presents the Nature Index framework and details its implementation in Norway. The results suggest that the framework is a functional, efficient, and pragmatic approach for gathering and synthesizing scientific knowledge on the state of biodiversity in any marine or terrestrial ecosystem and has general applicability worldwide. URI: http://hdl.handle.net/10037/4026 File(s) in this item: 1
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Chittenden, Cedar Marget; Biagi, Carlo; Kondo, Hidehiro; Davidsen, Jan Grimsrud; McKnight, Allison; Grimsrud, anette sophie; Raven, Peter; Pedersen, ole petter; Rikardsen, Audun; Shrimpton, Mark; Zuehlke, Brett; McKinley, Scott; Devlin, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2010)[+][-]
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Chittenden, Cedar Marget; Ewart, David; Anderson, Shannon; Jensen, Jenny Lovisa Alexandra; Balfry, Shannon; Downey, Elan; Eaves, Alexandra; Saksida, Sonja; Smith, Brian; Vincent, Stephen; Welch, David; McKinley, Scott (Journal article; Tidsskriftartikkel; Peer reviewed, 2010)[+][-]
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Davidsen, Jan Grimsrud; Rikardsen, Audun H.; Finstad, B; Økland, Finn; Thorstad, E.B.; Mo, TA (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)[+][-]
Description: This is the accepted manuscript version of the article. Published article available at http://dx.doi.org/10.1111/j.1095-8649.2011.02943.x URI: http://hdl.handle.net/10037/3641 File(s) in this item: 1
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Plantalech Manel-la, Nuria; Davidsen, Jan Grimsrud; Thorstad, E.B; Økland, F.; Sivertsgård, Rolf; McKinley, R.S; Finstad, B. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)[+][-]
Abstract: The migratory behaviour of hatchery-reared Atlantic salmon, Salmo salar L., post-smolts during the first phase of the marine migration was examined to assess their susceptibility to salmon lice, Lepeophtheirus salmonis (Krøyer), infestations. Swimming depths of eight post-smolts relative to the measured salinity and temperature were monitored for an average of 11.4 h following release outside the mouth of the River Eio using depth sensitive acoustic transmitters. Vertical salinity and temperature distributions were simultaneously recorded along the migratory route. Mean swimming depth was 1.7 m (individual mean 0.5–2.1 m). There was no overall preference among all the post-smolts for specific salinity concentrations. Typically post-smolts migrated the majority (68%) of their time at salinities <20 psu (brackish water), and as a result outside the reported salinity tolerances of sea lice. Furthermore, post-smolts chose the warmest water layer during their coastal migration. Description: This is the final draft post refereeing version of the article. Published version available at http://dx.doi.org/10.1111/j.1365-2400.2009.00658.x URI: http://hdl.handle.net/10037/2015 File(s) in this item: 1
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Thorstad, EB; Davidsen, Jan Grimsrud; Økland, F.; Rikardsen, Audun; Halttunen, Elina; Letcher, B.H,; Skardhamar, Jofrid; Næsje, Tor (Journal article; Tidsskriftartikkel; Peer reviewed, 03-Dec-2009)[+][-]
Abstract: To study smolt behaviour and survival of a northern Atlantic salmon (Salmo salar) population during river descent, sea entry and fjord migration, 120 wild S. salar were tagged with acoustic tags and registered at four automatic listening station arrays in the mouth of the North Norwegian River Alta and throughout the Alta Fjord. An estimated 75% of the post-smolts survived from the river mouth, through the estuary and the first 17 km of the fjord. Survival rates in the fjord varied with body length, and ranged from 97.0–99.5% per km. On average, the post-smolts spent 1.5 days (36 h, range 11–365 h) travelling from the river mouth to the last fjord array, 31 km from the river mouth. The migratory speed was slower (1.8 bl sec-135 ) in the first 4 km after sea entry compared to the next 27 km (3.0 bl sec-136 ). Post-smolts entered the fjord more often during the high or ebbing tide (70%). There was no clear diurnal migration pattern within the river and fjord, but most of the post-smolts entered the fjord at night (66%, 2000–0800 hours), despite the 24 h daylight at this latitude. The tidal cycle, wind-induced currents and the smolts‟ own movements seemed to influence migratory speeds and routes in different parts of the fjord. A large variation in migration patterns, both in river and fjord, might indicate that individuals in stochastic estuarine and marine environments are exposed to highly variable selection regimes resulting in different responses to environmental factors on both temporal and spatial scales. Post-smolts in northern Alta Fjord had similar early marine survival rates to those observed previously in southern fjords; however fjord residency in the north was shorter. Description: This is the accepted version (authors' final draft post review) of the paper, reprinted with permission. Published version available at http://dx.doi.org/10.1111/j.1095-8649.2009.02423.x URI: http://hdl.handle.net/10037/2431 File(s) in this item: 1
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Thorstad, EB; Davidsen, Jan Grimsrud; Økland, F.; Rikardsen, Audun; Halttunen, Elina; Letcher, B.H,; Næsje, Tor; Skardhamar, Jofrid (Conference object; Konferansebidrag, 14-Sep-2009)[+][-]
Description: Poster presentation at the Eight Conference on Fish Telemetry held in Europe, Umeå, Sweden, 14-18 September 2009 URI: http://hdl.handle.net/10037/2458 File(s) in this item: 1
article.pdf (7.631Mb) -
Davidsen, Jan Grimsrud; Plantalech Manel-la, Nuria; Thorstad, E.B; Rikardsen, Audun H.; Økland, F.; Sivertsgård, Rolf; Finstad, B; McKinley, R.S; Diserud, O. H. (Journal article; Tidsskriftartikkel; Peer reviewed, 22-Jun-2008)[+][-]
Abstract: Eight hatchery-reared Atlantic salmon Salmo salar post-smolts, implanted with acoustic depth sensing transmitters and manually tracked for 5-12 h in the Hardangerfjord (Norway), spent most of their time (49-99%) at 1-3 m depth during the day, whereas four of seven fish tracked were found close (<0.5 m) to the surface at night, with a strong negative cross-correlation between general swimming depth and surface light intensity. Hence, the actual swimming depth of post-smolts during their early marine migration may depend on the light conditions, although the individual variation in vertical movement pattern was large. No cross-correlations were found between light intensity and swimming depth during daytime periods with rapid changes in light intensity, indicating that other factors than light intensity were important in initiating the irregular dives that were recorded down to 6.5 m depth. Description: Dette er forfatternes aksepterte versjon. This is the author’s final accepted manuscript. URI: http://hdl.handle.net/10037/2227 File(s) in this item: 1
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Strand, Jo Espen Tau; Davidsen, Jan Grimsrud; Jørgensen, Even Hjalmar; Rikardsen, Audun (Journal article; Tidsskriftartikkel; Peer reviewed, 16-Nov-2010)[+][-]
Abstract: Two groups of migrating wild Atlantic salmon (Salmo salar) smolts caught within a 1 week interval in the River Alta, northern Norway, were tagged with acoustic transmitters and measured for gill Na+, K+ -ATPase activity in order to compare their smolt status with timing of sea entry. The first group of smolts had low levels of gill Na+, K+ -ATPase activity and resided in the lower part of the river twice as long as the second group that had high levels of gill Na+, K+ -ATPase activity. This indicates that early migrating smolts may not be completely physiologically adapted for salt water and delay their sea entry, thereby also synchronizing their seaward migration with the later migrating smolts. Description: This article is published with open access at Springerlink.com URI: http://hdl.handle.net/10037/2838 File(s) in this item: 1
article.pdf (161.8Kb)
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