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Torstein Pedersen

Torstein Pedersen
UIT, The Arctic University of Norway · Department of Arctic and Marine Biology

Phd

About

101
Publications
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Introduction
I am currently studying how ecosystem dynamics of coastal and oceanic high latitude ecosystems are affected by climatic and antropogenic stressors. This involves ecosystem modelling (e.g. using Ecopth/Ecosim/Ecospace) and field sampling.

Publications

Publications (101)
Article
Since the 1990s, the density of the invasive red king crab Paralithodes camtschaticus has increased dramatically in coastal areas in northern Norway. We investigated its direct and indirect effects on food web structure and ecosystem properties (e.g. species biomasses and production) in the Porsanger Fjord in the study period 2009−2011 using 5 suba...
Article
Full-text available
The Barents Sea (BS) is a high-latitude shelf ecosystem with important fisheries, high and historically variable harvesting pressure, and ongoing high variability in climatic conditions. To quantify carbon flow pathways and assess if changes in harvesting intensity and climate variability have affected the BS ecosystem, we modeled the ecosystem for...
Article
Full-text available
The trophic position concept is central in system ecology, and in this study, trophic position (TP) estimates from stable-isotopes and an Ecopath mass-balance food web model for the Barents Sea were compared. Two alternative models for estimating TP from stable isotopes, with fixed or scaled trophic fractionation were applied. The mass-balance mode...
Article
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We compared stock origin, size- and age-distributions, and length growth rates derived from Atlantic cod otoliths from archaeological excavations at two sites in northern Norway: Vágar in Lofoten (68°12′N, ad 1156–1285) and the Værbukta site (70°57′N, ad 1450–1680). For comparison, modern otoliths were sampled during 1993–2001 from areas situated c...
Article
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We built a dynamic, spatial food web model for the Barents Sea, developed with Ecospace by including species’ habitat requirements and ecological interactions. The model was used to test the spatial shifts of different functional groups due to warming. We compared model-predicted and field-surveyed biomass of functional groups (FGs) spatial distrib...
Article
Full-text available
Predator–prey interactions in time and space determine stock productivity, making them an important consideration when managing marine resources, rebuilding stocks or considering reopening a fishery. We analysed fine‐scale diet data from surveys conducted in 2009–2010 and 2018–2019 in three fjords in northern Norway with geostatistical models inves...
Article
Numerical models of ecological systems are increasingly used to address complex environmental and resource management questions. One challenge for scientists, managers, and stakeholders is to appraise how well suited these models are to answer questions of scientific or societal relevance, that is, to perform, communicate, or access transparent eva...
Article
Full-text available
Adult anglerfish conduct annual migrations between spawning areas and feeding areas; for Faroese waters this migration has so far not been described. Therefore, anglerfish migration and distribution in Faroese waters was investigated by mark-recapture studies, including data storage tags, as well as data from scientific trawl surveys, commercial tr...
Article
Fish communities in the shallow waters (9–20 m depth) of outer Malangen (69o N), Northern Norway was studied to investigate effects of season, bottom substrate associations and population dynamic parameters on the fish assemblages. In four fieldtrips during one year at four locations, fish were sampled by trammel nets and bottom substrate compositi...
Conference Paper
Full-text available
The second Nansen Legacy workshop on best practices for ecological model evaluation, chaired by Benjamin Planque (IMR) was held at the University of Oslo on the 23-25th September 2019. The objective of the workshop was to develop a protocol for describing the evaluation of ecological models.
Article
Full-text available
The Nansen Legacy workshop on best practices for ecological model evaluation, chaired by Benjamin Planque (IMR) was held in Tromsø on the 6-7th November 2018. The objective of the workshop was to develop recommendations for best practice in evaluation of the performance of food-web simulation models (deliverable 4-4.1.1 of the Nansen Legacy project...
Article
Environmental stressors related to climate change and other anthropogenic activities are impacting Arctic marine ecosystems at exceptional rates. Within this context, predicting future scenarios of deep‐sea ecosystems and their consequences linked with the fate of coastal areas is a growing need and challenge. We used an existing food‐web model dev...
Article
Full-text available
Kelp forests produce large amounts of macroalgal detritus, ranging from whole plants to small particles (1 mm). The role of this kelp detritus in fueling deep-sea communities adjacent to healthy kelp forests was investigated in a region in the north of Norway by comparing the community structure and biodiversity of meio-, macro-, and megafauna in t...
Article
Full-text available
Animals employ various foraging strategies along their ontogeny to acquire energy, and with varying degree of efficiencies, to support growth, maturation and subsequent reproduction events. Individuals that can efficiently acquire energy early are more likely to mature at an earlier age, as a result of faster energy gain which can fuel maturation a...
Article
Full-text available
We investigated predation from an ambush predator (shorthorn sculpin) and two cruising predators (Atlantic cod and saithe) on bottom-settled 0-group cod and saithe juveniles in a fjord in northern Norway. Stomach contents of potential fish predators caught by gill net in shallow waters (depth of 3–10 m) during September in 2013–2015 were analysed....
Article
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Shorthorn sculpin (Myoxocephalus scorpius) and large cod (300–400 g body weight) are important predators on newly settled 0-group cod (Gadus morhua) and saithe (Pollachius virens) in Porsangerfjorden in northern Norway. The Atlantic wolffish (Anarhichas lupus) used to be abundant but is now very rare in the fjord. Video recorded experiments showed...
Preprint
Full-text available
Animals employ various foraging strategies along their ontogeny to acquire energy, and with varying degree of efficiencies, to support growth, maturation and subsequent reproduction events. Individuals that can efficiently acquire energy early are more likely to mature at an earlier age, as a result of faster energy gain which can fuel maturation a...
Article
Full-text available
This study investigates the temporal and spatial patterns of larval stages of the invasive red king crab (Paralithodes camtschaticus, RKC) and co-existing native brachyurans and anomurans in a Norwegian fjord. It is one of few field studies describing the larval stage of native and invasive brachyurans and anomurans in the southern Barents Sea. Lar...
Article
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Ongoing changes along the northeastern Atlantic coastline provide an opportunity to explore the influence of climate change and multitrophic interactions on the recovery of kelp. Here, vast areas of sea urchin‐dominated barren grounds have shifted back to kelp forests, in parallel with changes in sea temperature and predator abundances. We have com...
Article
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The spatial patterns in abundance and composition of benthic invertebrate larvae (meroplankton), the correlation between these patterns and environmental variables (temperature, salinity and chl a) and the relative abundance of meroplankton in the mesozooplankton community were investigated in the sub-Arctic Porsangerfjord, Norway (70° N). Zooplank...
Article
Full-text available
The aim of the present study was to test the hypothesis that the invasive red king crab Paralithodes camtschaticus may hamper capelin (Mallotus villosus) recruitment through egg consumption. Field studies (2005, 2006), laboratory experiments (2011), and models of consumption were applied. To explore the response of the predator to prey density, cra...
Article
Knowledge on the seasonal timing and composition of pelagic larvae of many benthic invertebrates, referred to as meroplankton, is limited for high-latitude fjords and coastal areas. We investigated the seasonal dynamics of meroplankton in the sub-Arctic Porsangerfjord (70°N), Norway, by examining their seasonal changes in relation to temperature, c...
Article
Herring from two unexploited fjord populations, Lake Rossfjord (LRH, n = 100) and Balsfjord (BFH, n = 420) in northern Norway, were sampled in 2014 and 2015. Life history characteristics were analysed and compared to the oceanic Norwegian spring-spawning herring (NSSH), and other Atlantic and Pacific herring stocks. Genetic studies have shown that...
Article
Full-text available
Understanding the trophic ecology of an invasive species is important for risk assessment. The red king crab Paralithodes camtschaticus is both a valuable fishery resource and a potential threat to native biota in the Barents Sea. We combined gut content analysis and stable carbon and nitrogen isotope analysis to study feeding strategy, variation i...
Article
Despite slight but significant differences in size of male and female Common Guillemots Uria aalge and previously published sex differences in parental behaviour, foraging ranges and diving behaviour, no evidence of sex-specific differences in choice or size of fish caught for chicks or for self-feeding was found among adults caught in a North Norw...
Presentation
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http://prezi.com/wvioovtabqho/?utm_campaign=share&utm_medium=copy&rc=ex0share Abstract In the subarctic Porsangerfjord in northern Norway, the abundance of the invasive red king crab (Paralithodes camtschaticus) has increased dramatically since 2006 and it has now become a benthic predator and the major fishery target in this ecosystem. Porsangerfj...
Poster
Full-text available
The Balsfjord herring stock spawns in the intertidal zone in Balsfjord (69oN), northern Norway and shows spawning dynamics that is very different from the adjacent Norwegian spring spawning herring. To investigate the spawning dynamics and the environmental conditions at the spawning area, we conducted field studies (2014, 2015). We applied survey...
Article
Full-text available
Year-class strength of Barents Sea capelin has been monitored closely since the early 1970s and during this ∼45 years period three short periods of almost total recruitment failure leading to three stock collapses have been observed. These events triggered much attention since there was a large commercial fishery for capelin, but also because of ob...
Article
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Maturation, reproduction and early life history of Lophius piscatorius was investigated in Faroese waters. Length at first maturity (L50) was 58 cm for males and 84 cm for females, corresponding to an age of about four years for males and seven years for females. The proportions of females and males were similar in fish less than 55 cm long, and we...
Article
Large offshore and small inshore populations of Atlantic cod Gadus morhua L. display differences in migratory patterns and settling regimes, but little is known about possible differences in spawning behaviour. Cod presumably of the Norwegian coastal cod type were therefore sampled during 7 spawning seasons (2002-2013) in Malangen, northern Norway....
Article
Understanding predator–prey relationships and resource overlap between sympatric species is fundamental for enhanced scientific knowledge and management. This study compared the trophic ecology of three small demersal fishes (Artediellus atlanticus, Myoxocephalus scorpius, and Leptagonus decagonus) using stomach data and stable isotope analyses. Al...
Article
The Black-legged Kittiwake Rissa tridactyla population is declining throughout its North Atlantic range. In Norway, the species is classified as Endangered on the Norwegian Red List. Studies of diet are one important requirement for effective management of any species. Because it is easier to sample, chick diet has often been considered a proxy for...
Poster
Full-text available
Two spawning waves were identifed for the Balsfjord herring in the intertidal zone in 2014. Spawning on macroalgae in the intertidal was likely to cause large microclimate and temperature fluctuations in the egg environment, increased predation from seabirds, but reduced predation from fish and sea urchins. Preliminary results on egg mortality is p...
Article
To investigate the reliability of age–length growth estimates of anglerfish Lophius piscatorius in Faroese waters, results from illicia age determination, length frequency and mark-recapture analyses were compared. Features of the illicium, such as the time of deposition and sizes of the benthic and first annual zones, width and the marginal increm...
Conference Paper
The introduced red king crab (Paralithodes camtschaticus) has become an abundant predator of the benthic community along the north Norwegian coast, potentially altering community structure and competing with other native predators. Previous diet studies based on stomach analysis (SA) found soft bottom communities to be the main foraging areas of th...
Article
Full-text available
The invasive red king crab Paralithodes camtschaticus preys on lumpsucker Cyclopterus lumpus eggs. We tested the hypothesis this egg consumption may hamper the recruitment of lumpsucker. Methods applied included field work, laboratory experiments and modelling of egg consumption. Crabs were sampled and feeding behaviour was studied by means of a re...
Article
Full-text available
We sampled 0-group juvenile Atlantic cod Gadus morhua L. within fjords and offshore in northern Norway from 1994 to 2008 using different gears for the 3 sampling depths: shore seine (0-3 m), pelagic trawl (various depths), and bottom trawl (>80 m). Frequencies of alleles at the Pan I locus (4218 fish analysed) showed highly significant differences...
Article
We investigated stable nitrogen (δ15N) and carbon (δ13C) isotope signatures in haddock Melanogrammus aeglefinus in Ullsfjord, Norway, and found evidence of an ontogenetic shift as a result of growth but in the absence of other morphological changes. Stable isotope signatures and trophic level (TL) changed significantly from a pelagic signature and...
Article
Full-text available
The Norwegian population of the Common Guillemot Uria aalge has declined by >95% since the 1960s, and is classified as critically endangered in the Norwegian Red List. Much of the recent decline has been attributed to reduced food availability, but without extensive documentation of adult diet. Instead, chick diet has been considered a proxy of adu...
Article
Full-text available
Pedersen, O. P., Pedersen, T., Tande, K. S., and Slagstad, D. 2009. Integrating spatial and temporal mortality from herring on capelin larvae: a study in the Barents Sea. – ICES Journal of Marine Science, 66: 2183–2194.Barents Sea herring and capelin are commercially very important fish stocks. We investigate the spatial and temporal mortality rate...
Article
Full-text available
Predation has been suggested as a cause of substantial mortality of fish larvae to the degree that it might influence recruitment. This field-based study concludes that juvenile herring (Clupea harengus) as small pelagic predator can significantly affect mortality rates of the planktonic larvae of capelin (Mallotus villosus) in the Barents Sea. Sur...
Article
The Barents Sea capelin stock is, potentially, the largest capelin stock in the world, with a maximum biomass in the range of 6–8 million tonne. The main spawning grounds for this capelin stock are along the coast of northern Norway. By modeling and fieldwork, this study addresses the interaction between mesoscale physical process and newly hatched...
Article
The Sørfjord, Norway, and the Gulf of St. Lawrence, Canada, are two sub-arctic ecosystems with similar trophic structure. However, in the Gulf of St. Lawrence, severe exploitation of groundfish stocks has lead to important shifts in the trophic structure. In the Sørfjord, the situation is different: fishing pressure is much lighter. Our hypothesis...
Article
Atlantic Puffin (Fratercula arctica) chick growth, diet, feeding rate and early survival and adult body condition were quantified on Hornøya, North Norway in 2002 and 2003 after a long-term change in diet from large Capelin (Mallotus villosus) and Sand Lance (Ammodytes spp.) in the early 1980s to smaller, poorer quality gadids, Sand Lance and Herri...
Article
Full-text available
Stable isotopes of ¹³C and ¹⁵N were used to examine food sources and trophic structure of 65 taxa, representing 19 ecological groups, in a high-latitude ecosystem. Discrimination was made between pelagic and benthic carbon sources, where feeding in most cases reflected the habitat. Trophic levels from these analyses, TLN, were compared with corresp...
Article
A 27 compartment model of the food-web in Sørfjord, northern Norway was balanced using the mass-balance model Ecopath based on data from Sørfjord and adjacent fjord areas. Sørfjord is a lightly exploited high-latitude fjord ecosystem with cod as the main piscivore. During 1993–1996, the biomass of planktivore fish was low, and the pelagic community...
Article
Otolith microstructure analysis was applied to known age capelin larvae (Mallotus villosus) in order to examine the formation of daily increments. In two validation experiments, newly hatched yolk sac larvae were stocked into eight 10 m3 plastic bags where environmental conditions were kept as natural as possible. The bags were terminated after 35-...
Article
The movement patterns of released hatchery-reared fish determine the geographical scale at which a population may be enhanced, while the movement patterns of wild fish affect the management strategies of wild populations. This article investigates (1) if movement patterns differ between hatchery reared and wild cod, and (2) if the movement patterns...
Article
Effects of climatic variability on recruitment of fish stocks have been linked to variation in mortality rates of fish larvae. In this study, it was attempted to test the hypothesis that 0-group Northeast Arctic cod has a significant effect on mortality rates of Barents Sea capelin larvae. Surveys were carried out in June/July in 2002 (58 stations,...
Article
Recruitment of capelin in the Barents Sea fail when juvenile herring and cod are abundant and the potential for feeding competition of wild sympatric capelin and herring larvae and small cod juveniles were investigated. The frequency of gut evacuation after capture of capelin larvae were also studied in mesocosms. Small capelin larvae (<35mm length...
Article
Two methods for estimating digestion rate were evaluated and the digestion rate to disappearance was estimated to be 0.30 h(-1) for herring Clupea harengus feeding on capelin Mallotus villosus larvae. Due to high individual variability in feeding rates in schooling fish species, groups should be fed in separate tanks and stomach contents collected...
Article
Stomach contents from lesser sandeel Ammodytes marinus and herring Clupea harengus caught at one and three stations, respectively, were analysed to investigate predation intensity on capelin Mallotus villosus larvae. Most capelin larvae were found in the anterior sections of the stomachs close to the oesophagus, indicating that rapid digestion rate...
Article
Full-text available
Macrobenthic invertebrate biomass, productivity (P/(B) over bar ratio) and production were estimated for a high-latitude fjord ecosystem, Sorfjord, North Norway. A model including individual weight, temperature, depth, taxonomical group, tidal-zone position, faunal category, motility and habitat was used to estimate P/(B) over bar ratios, and produ...
Article
Full-text available
Stomach samples of minke whale ( Balaenoptera acutorostrata) and cod ( Gadus morhua) were collected on the northeastern parts of the Finnmark coast, northern Norway, in 1998 and 1999 to investigate prey preference, niche overlap and niche width for the two species. A survey to estimate prey abundance was also conducted. Prey preference, niche overl...
Article
Metamorphosis in cod, Gadus morhua L., was investigated with respect to morphological changes in the alimentary tract (mouth, stomach and pyloric caeca) and external characters (finfold and fin development). Morphometric measurements and histological investigations were made on both larvae and juveniles and all fish lengths are given as standard le...
Article
The Tana river, in northern Norway has the largest wild Atlantic salmon stock in the world. Each summer more than 1 million smolts, representing nearly 20% of the total number of Atlantic salmon smolts produced annually in Norwegian rivers, descend through the large estuary of this river. Several marine fishes feed in the estuary during the summer...
Article
A total of 293 shorthorn sculpins Myoxocephalus scorpius from Tromsø, northern Norway, were sampled between November 1998 and April 1999 to determine sex, total length, age, growth, maturity and mortality. Females grew to larger sizes (L∞=26·9 v. 18·5 cm), matured later (2 v. 1 year of age) at larger size (maturation length=16 v. 14 cm LT), and had...
Article
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 wi...
Article
In the summers of 1981 and 2000, 288 goosanders Mergus merganser were sampled in the estuary of the River Tana in northern Norway, which has the largest wild Atlantic salmon Salmo salar stock in the world. Based on 2308 otoliths found in their stomach contents, sandeels Ammodytes sp. were found to be the dominant prey, and only one pair of Atlantic...
Article
We studied whether incorporation of terms for environmental factors (temperature, herring and 0-group cod) into the stock recruitment functions for the Barents Sea capelin (Mallotus villosus) would increase the ability to predict recruitment. We also investigated the effects of alternative estimates of the capelin spawning stock (SSB) and juvenile...
Article
We studied whether incorporation of terms for environmental factors (temperature, herring and 0-group cod) into the stock recruitment functions for the Barents Sea capelin (Mallotus villosus) would increase the ability to predict recruitment. We also investigated the effects of alternative estimates of the capelin spawning stock (SSB) and juvenile...
Article
The reproduction and life history events of the shorthorn sculpin Myoxocephalus scorpius were studied in an unexploited high latitude population in Tromsø, northern Norway. Shorthorn sculpins were sampled from November 1998 to March 1999 to determine sex ratio, spawning period, oogenesis, fecundity, embryogenesis and hatching. Spawning occurred bet...
Article
An assessment model was developed of a coastal cod population integrating data on catch-at-age from commercial catches and survey data and tag returns from commercial and survey trawl fisheries. Cod were tagged during the period 1990–1995 and recaptured in the commercial and research survey. Quarterly trawl surveys were conducted during 1990–1996,...
Article
Full-text available
We investigate how cod feeding data may be included into a recently developed age-structured model for a coastal cod population in a small fjord in northern Norway. The model integrates data from mark-recapture experiments, trawl-surveys and commercial catches. The fjord population has high biomass density (2-3 tonnes km 2 ) and low fishing mortali...
Poster
Full-text available
The stock-recruitment relationship was investigated for the year classes 1973-2000 of the Barents Sea capelin (Mallotus villosus). The fit of the stock-recruitment functions, such as Ricker and Beverton & Holt were investigated by adding temperature and predation by herring and 0 group cod as parameters. The models were fitted to different time ser...
Article
In order to evaluate the potential of cod enhancement in a north Norwegian fjord, 4842 hatchery-reared cod juveniles (14-23 cm in length) were tagged and released into Stalvikbotn in 1988, a 10 km(2) area sill fjord in Northern Norway. Wild cod were tagged to serve as a reference group for the hatchery-reared group. At the time of release, the size...
Article
Growth, recruitment and age and length at sexual maturity of Coastal cod (CC) were investigated in a North Norwegian fjord system in the period 1989-1994. There were marked differences between inner (S›rfjord) and outer (Ullsfjord) areas of the fjord system. In the inner part, growth was slower and the population was more dominated by the numerous...
Article
This study describes how 30 Great Cormorants Phalacrocorax carbo carbo managed to catch sufficient food for their daily energetic needs under conditions of reduced daylight and cold while wintering north of the Arctic Circle. Activity observations showed that the Great Cormorants' daily foraging pattern was generally bimodal, with morning and eveni...
Article
Atlantic cod have been a primary target for marine stock enhancement since the 1880s. In the early part of this period, hatched larvae were released in Norway, the USA and Canada. The last larval releases were conducted in Norway in 1971, and a century of cod larvae releases were halted without any clear evidence of benefit. Since the early 1980s,...
Article
The purpose of this study was to evaluate fishing gears designed to catch live cod in order to tag a representative part of the cod populations in two fjords in northern Norway. Hand line, fish pots and fyke nets were used at shallow rocky bottom (<50 m depth); in deeper waters, bottom and pelagic trawls were used. Fish pots were more efficient in...
Chapter
This study addresses the role played by cormorants as predators in a cod enhancement area in S›rfjord, North Norway in January-March 1996 and October 1996-March 1977. An analysis is made of otoliths from fish found in 135 pellets of indigestible food remains regurgiated by 30 cormorants roosting in the fjord, and of fish caught in an independent fi...
Chapter
As part of an enhancement programme aimed at evaluating whether released reared cod would contribute to increase yield and spawning stock of local cod populations, groups of hatchery-reared coastal cod (about 30 cm in length) and wild cod were tagged and released into the S›rfjord-Ullsfjord system (69§45ïN, 19§45ïE) during 1994. We investigated the...
Article
Full-text available
Cod juveniles settling in shallow water and recruiting to coastal cod (CC) stocks have lower vertebrae number than juveniles settling in deep water and recruiting to Northeast Arctic cod (NAC) stock. We investigated whether the differences in vertebrae number in CC and NAC were caused by genetic differences or by exposure to different temperatures...