English
norskBlar i forfatter "Thorstad, Eva Bonsak"
Viser treff 1-20 av 40
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Area use and movement patterns of wild and escaped farmed Atlantic salmon before and during spawning in a large Norwegian river
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-02-02)We compared the within-river movements and distribution of wild and escaped farmed Atlantic salmon Salmo salar before and during spawning in the Namsen river system of Central Norway. A total of 74 wild and 43 escaped farmed salmon were captured at sea, tagged with radio transmitters and released. Based on our examinations, most, if not all salmon (farmed and wild) entering the River Namsen were ... -
Assessment of possible adverse consequences for biodiversity when planting vascular plants outside their natural range in Norway -(VKM)
(Research report; Forskningsrapport, 2021-06-25)We sow or plant vascular plant species on a large scale in revegetation and restoration projects in Norway today. Some of the species used are already found in Norway, but many of the species, subspecies or populations used though native are not local, that is, they are <i>regionally alien</i>. A regionally alien species is a species that is native to Norway (has been in Norway since 1800) somewhere ... -
Assessment of risk and risk-reducing measures related to the introduction and dispersal of the invasive alien carpet tunicate Didemnum vexillum in Norway
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-02-17)Didemnum vexillum is colonial sea squirt, a marine species which originates from the northwest Pacific; it was first recorded in Norway in November 2020. Didemnum vexillum is an alien species, meaning that it is a species that has been transferred from its original region to other regions of the world through human activity, and it had not previously been recorded in Norwegian waters. The species ... -
Assessment of the risk to Norwegian biodiversity from import and keeping of crustaceans in freshwater aquaria. Scientific Opinion of the Panel on Alien Organisms and Trade in Endangered Species of the Norwegian Scientific Committee for Food and Environment
(Research report; Forskningsrapport, 2021)The Norwegian Scientific Committee for Food and Environment (VKM) was requested by the Norwegian Environment Agency to assess the risk of negative impacts to biodiversity in Norway resulting from import of crustacean decapods for keeping in freshwater aquariums.<p> <p>VKM was asked to 1) list species of crayfish, crabs and shrimps that are currently kept in freshwater aquaria in Norway, and ... -
Assessment of the risks to honey bees and biodiversity in Norway posed by the predatory wasp species Vespa velutina and V. mandarinia - Scientific Opinion of the Panel on Alien Organisms and Trade in Endangered species of the Norwegian Scientific Committee for Food and Enviroment
(Research report; Forskningsrapport, 2022-02-21)Med varmere klima er det mulig at asiatisk geithams (Vespa velutina) kan spre seg til Norge. Det er usannsynlig at japansk geithams (Vespa mandarina) vil spre seg til Norge. -
Atferd og spredning av rømt oppdrettslaks og villaks i Namsen og andre elver. Resultater fra merking av laks i Namsfjorden og Vikna
(Research report; Forskningsrapport, 2013-04)Vi undersøkte atferd og spredning av rømt oppdrettslaks og villaks i Namsen og andre elver i Midt-Norge i 2012. Hovedmålsettingen var å skaffe kunnskap slik at man kan gjøre sikrere beregninger av den reelle andelen rømt oppdrettslaks i lakseelver. De ulike delmålene var å: Vurdere sikkerheten i dagens metoder for beregning av andel oppdrettslaks i gytebe-stander av villaks. Sammenligne ... -
Behaviour and habitat use of first-time migrant Arctic charr: novel insights from a subarctic marine area
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-13)Anadromous Arctic charr Salvelinus alpinus is a cold-adapted salmonid that is vulnerable to climate warming and anthropogenic activities including salmon farming, hydropower regulation, and pollution, which poses a multiple-stressor scenario that influences or threatens populations. We studied the horizontal and vertical behaviour of Arctic charr tagged with acoustic transmitters (n = 45, mean ... -
Biologiske undersøkelser i Altaelva 2005
(Research report; Forskningsrapport, 2006-05)Altaelva er ei av Norges beste elver for sportsfiske etter laks. Elva har en storvokst laksestamme, og en unik kultur og historie knyttet til laksefisket. Stortinget vedtok å utbygge og regulere elva for kraftproduksjon i 1978. Byggingen av kraftverksdammen ble igangsatt i 1983, og Alta kraftverk ble satt i drift i 1987. Det er gjennomført omfattende fiskebiologiske undersøkelser i vassdraget siden ... -
Diving and feeding of adult Atlantic salmon when migrating through the coastal zone in Norway
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-23)Atlantic salmon post-spawners from a population in northern Norway were tagged with data storage tags (N = 773), and the depth use and diving behaviour of recaptured individuals within the coastal zone were examined, both on their outward migration to sea (N = 44) and their return to the natal river after overwintering at sea (N = 34). In addition, the stomach contents of 909 returning adults caught ... -
Diving behaviour of Atlantic salmon at sea: effects of light regimes and temperature stratification
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-07-04)The diving behaviour of adult Atlantic salmon Salmo salar L. post-spawners in the Norwegian and Barents Seas was monitored with pop-up satellite archival tags (PSATs) and data storage tags (DSTs). Salmon from the 3 studied populations showed similar depth use patterns: tagged specimens spent most of their time near the surface (mean of 82% of the time at depths <10 m), with occasional short deep ... -
Effects of salmon lice on sea trout
(Research report; Forskningsrapport, 2014) -
Fish populations, gill net catches and gill net selectivity in the Lower Orange River, Namibia, from 1995 to 2001
(Research report; Forskningsrapport, 2007-01)The Orange River: The lower part of the Orange River forms the border between Namibia and South Africa from the mouth of the river and 580 km upstream. The river origins in the Lesotho Highlands, and runs for approximately 2300 km from the source to the Orange River Mouth at Oranjemund (Namibia) and Alexander Bay (South Africa), where it discharges into the Atlantic Ocean. The total Orange ... -
Fiskebiologiske undersøkelser i Altaelva 2010
(Research report; Forskningsrapport, 2011)Altaelva er ei av Norges beste elver for sportsfiske etter laks. Stortinget vedtok i 1978 å utbygge og regulere elva for kraftproduksjon. Byggingen av kraftverksdammen ble igangsatt i 1983, og Alta kraftverk ble satt i drift i 1987. Omfattende fiskebiologiske undersøkelser er gjennomført i vassdraget siden 1981. Formålet har vært å dokumentere eventuelle endringer i laksebestanden, finne årsakene ... -
Growth of invasive pink salmon (Oncorhynchus gorbuscha) at sea assessed by scale analysis
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-01)Invasive pink salmon (Oncorhynchus gorbuscha) has been present in variable, but low, numbers in Norwegian waters since c. 1960, but beginning in 2017 their numbers have exploded in rivers in northern Norway, with considerable numbers also recorded in rivers in southern Norway and other countries bordering the North Atlantic. Analysis of pink salmon scales from two rivers draining to the western ... -
Homing behaviour of Atlantic salmon (Salmo salar) during final phase of marine migration and river entry
(Journal article; Tidsskriftartikkel; Peer reviewed, 2013)Little is known about Atlantic salmon behaviour during the last phase of the marine homing migration and subsequent river entry. In this study, 56 adult Atlantic salmon in the Alta Fjord in northern Norway were equipped with acoustic transmitters. Salmon generally followed the coastline, but their horizontal distribution was also affected by wind-induced spreading of river water across the fjord. ... -
Impacts of a weir and power station on downstream migrating Atlantic salmon smolts in a German river
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-10)Weirs are barriers built across rivers for a wide range of other purposes than hydropower production. Like hydropower installations, weirs can negatively impact fish migrations. Downstream migration and mortality of Atlantic salmon smolts were studied during passage of a weir and power station by tagging 227 smolts with radio transmitters. Extra loss of smolts due to the weir and adjacent reservoir ... -
Impacts of salmon lice on mortality, marine migration distance and premature return in sea trout
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-06)Brown trout <i>Salmo trutta</i> (L.) is a facultative anadromous species, where a portion of individuals in populations with access to the sea perform migrations to use the richer feeding resources. We investigated the effect of salmon lice <i>Lepeophtheirus salmonis</i> (Krøyer 1837) infestation on the survival and behaviour of wild trout post-smolts (average fork length = 180 mm) during their ... -
Keeping close to the river, shore and surface: the first marine migration of brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) post-smolts
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-23)Acoustic telemetry was utilized to track 49 brown trout (<i>Salmo trutta</i>) and 37 Arctic charr (<i>Salvelinus alpinus</i>) first-time migrants of wild origin [post-smolts; mean LF (fork length): 169 and 172 mm] in a large fjord in northern Norway. The <i>S. trutta</i> were registered at sea for more than twice the time of the <i>S. alpinus</i> (medians of 54 and 22 days, respectively). Both species ... -
Klimaendringer og virkninger på hovedøkosystem skog.
(Research report; Forskningsrapport, 2022-04-29)
