Browsing Brage IMR by Author "Johnsen, Espen"

A new model for simulating growth in fish

Hamre, Johannes; Johnsen, Espen; Hamre, Kristin (Journal article; Peer reviewed, 2014-01-16)

A real dynamic population model calculates change in population sizes indepen- dent of time. The Beverton & Holt (B&H) model commonly used in fish assessment includes the von Bertalanffy growth function which has age or ...

Acoustic classification in multifrequency echosounder data using deep convolutional neural networks

Brautaset, Olav; Waldeland, Anders Ueland; Johnsen, Espen; Malde, Ketil; Eikvil, Line; Salberg, Arnt-Børre; Handegard, Nils Olav (Peer reviewed; Journal article, 2020)

Acoustic target classification is the process of assigning observed acoustic backscattering intensity to an acoustic category. A deep learning strategy for acoustic target classification using a convolutional network is ...

Adaptive mass formations in fish shoals founded in conflicting motivation

Johnsen, Espen; Skaret, Georg (Journal article; Peer reviewed, 2008-04-21)

The organising principles behind adaptive collective formations in animals are not well understood. Here we document that persistent vertical hourglass formations occur during the critical spawning period in huge shoals ...

An evaluation of the bottom trawl surveys in the Benguela Current Large Marine Ecosystem

Axelsen, Bjørn Erik; Johnsen, Espen (Journal article; Peer reviewed, 2014-07-02)

Demersal fish, shrimp and cephalopod assemblages on the continental shelves and slopes off Angola, Namibia and the southern and western coasts of South Africa have been monitored in terms of fisheries-independent trawl ...

Assessments for management of living marine resources in the Barents Sea and adjacent waters – a focus on methodology

IMR; PINRO (IMR/PINRO Joint Report Series;3/2014, Research report, 2015)

CRIMAC - Annual Report 2020

Ona, Egil; Handegard, Nils Olav; Pedersen, Geir; Forland, Tonje Nesse; Tenningen, Maria; Johnsen, Espen (Research report, 2021)

Diel vertical movements determine spatial interactions between cod, pelagic fish and krill on an Arctic shelf bank

Skaret, Georg; Johansen, Geir Odd; Johnsen, Espen; Fall, Johanna Jennifer Elisabeth; Fiksen, Øyvind; Englund, Gøran; Fauchald, Per; Gjøsæter, Harald; Macaulay, Gavin; Johannesen, Edda (Peer reviewed; Journal article, 2020)

Predator-prey spatial interactions are essential to understand ecosystem processes like predation rates and trophic interaction strength. In marine systems, such spatial interactions are highly dynamic and difficult to ...

Diurnal variation models of bottom trawl survey catches parameterised by using commercial CPUE data

Johnsen, Espen (ICES CM Documents;2004/R:41, Working paper, 2004)

Introduction: Diurnal variation is observed in almost all marine surveys and can cause biased abundance and length frequency estimates. Symmetric logistic models developed by Hjellvik et al. (2001) were utilized to ...

Early ontogeny of the lesser sandeel (Ammodytes marinus)

Perrichon, Prescilla; Bjelland, Reidun Marie; Durif, Caroline; Fiksdal, Ingrid Uglenes; Johnsen, Espen; Skiftesvik, Anne Berit; Cresci, Alessandro; Browman, Howard; Sørhus, Elin (Peer reviewed; Journal article, 2023)

Background Lesser sandeel (Ammodytes marinus) is widely distributed in North Sea ecosystems. Sandeel acts as a critical trophic link between zooplankton and top predators (fish, mammals, sea birds). Because they live buried ...

Estimation of acoustic indices with CVs for cod and haddock in the Barents Sea winter survey 1994 – 2017 applying the Sea2Data StoX software.

Mehl, Sigbjørn; Aglen, Asgeir; Johnsen, Espen; Skålevik, Åsmund (Fisken og Havet;5-2018, Research report, 2018)

Sea2Data programmet StoX er brukt til å estimere akustiske indekser med CV for nordøstarktisk torsk og hyse fra vintertoktet i Barentshavet i 1994 til 2017. Indeksene er sammenlignet med indekser tidligere estimert med ...

Estimation of acoustic indices with CVs for Northeast Arctic saithe in the Norwegian coastal survey 2003-2017 applying the Sea2Data StoX software.

Mehl, Sigbjørn; Johnsen, Espen; Skålevik, Åsmund; Aglen, Asgeir (Fisken og Havet;1-2018, Research report, 2018)

Sea2Data programmet StoX er brukt til å estimere akustiske indekser med CV og lengde og vekt ved alder for nordøstarktisk sei fra det norske kysttoktet Varanger – Stad i 2013 til 2017. Indeksene er sammenlignet med indekser ...

Evaluering og opprydding av offisielle gytekart

Sivle, Lise Doksæter; Johnsen, Espen (Rapport fra Havforskningen;12-2016, Research report, 2016-02)

English: Institute of Marine Research (IMR) presents maps of fish distributions and spawning areas for a large number of fish stocks. The maps are used by different organizations and research programs, and are important ...

Fangstprøvelotteriet 2020 – erfaringer og resultat

Høines, Åge Sigurd; Johnsen, Espen; Kvamme, Cecilie; Nøttestad, Leif; Otterå, Håkon Magne; Salthaug, Are; Stenevik, Erling Kåre; Svendsen, Bjørn Vidar (Rapport fra havforskningen;2022 - 4, Research report, 2022)

Etter at vi startet opp med fangstprøvelotteriet i 2018 har vi sett en gradvis og betydelig forbedring i prøvetakingen fra de kommersielle pelagiske fiskeriene. Vi ser likevel et stort forbedringspotensial framover siden ...

Fangstprøvelotteriet 2021 - erfaringer og resultat

Høines, Åge Sigurd; Diaz, Justine Emmanuelle; Heggebakken, Lise; Hellenbrecht, Lea Marie; Johnsen, Espen; Kvamme, Cecilie; Nøttestad, Leif; Salthaug, Are; Skaret, Georg; Stenevik, Erling Kåre; Svendsen, Bjørn Vidar; Tonheim, Susanne; Otterå, Håkon Magne (Rapport fra havforskningen;2023 - 8, Research report, 2023)

Etter at vi startet opp med fangstprøvelotteriet i 2018 har vi sett en gradvis og betydelig forbedring i prøvetakingen fra de kommersielle pelagiske fiskeriene. Vi ser likevel et stort forbedringspotensial framover siden ...

Fangstprøvelotteriet 2022 - erfaringer og resultat

Skaret, Georg; Diaz, Justine Emmanuelle; Heggebakken, Lise; Hellenbrecht, Lea Marie; Høines, Åge Sigurd; Johnsen, Espen; Kvamme, Cecilie; Nøttestad, Leif; Salthaug, Are; Stenevik, Erling Kåre; Svendsen, Bjørn Vidar; Tonheim, Susanne; Otterå, Håkon Magne (Rapport fra havforskningen;2023 - 60, Research report, 2023)

Etter at vi startet opp med fangstprøvelotteriet i 2018 har vi sett en gradvis og betydelig forbedring i prøvetakingen fra de kommersielle pelagiske fiskeriene, og i 2022 mottok vi totalt sett ca 70% av de bestilte prøvene. ...

Final report for the REDUS project - Reduced Uncertainty in Stock Assessment

Olsen, Erik Joel Steinar; Aanes, Sondre; Aldrin, Magne Tommy; Breivik, Olav Nikolai; Fuglebakk, Edvin; Goto, Daisuke; Handegard, Nils Olav; Hansen, Cecilie; Holmin, Arne Johannes; Howell, Daniel; Johnsen, Espen; Jourdain, Natoya; Korsbrekke, Knut; Ono, Kotaro; Otterå, Håkon Magne; Perryman, Holly Ann; Subbey, Samuel; Søvik, Guldborg; Umar, Ibrahim; Vatnehol, Sindre; Vølstad, Jon Helge (Rapport fra havforskningen;2021 - 16, Research report, 2021)

The REDUS project (2016-2020) has been a strategic project at the Institute of Marine Research (IMR) aimed at quantifying and reducing the uncertainty in data-rich and age-structured stock assessments (e.g., cod, herring, ...