Browsing Brage IMR by Author "Johnsen, Espen"

Now showing items 1-20 of 27

    • 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 ...

    • 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 ...

    • 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, ...

    • Fish diversity data from the Barents Sea Ecosystem Survey 2004-2019 

      Johannesen, Edda; Wienerroither, Rupert; Mørk, Herdis Langøy; Husson, Berengere; Holmin, Arne Johannes; Johnsen, Espen; Dolgov, Andrey; Prokhorova, Tatiana (Rapport fra havforskningen;2021 - 15, Research report, 2021)
      Assessing and improving the status of biodiversity are main targets of international agreements such as the Convention on Biological Diversity and the associated Aichi Biodiversity Targets for 2020. Here we present fish ...

    • Fishery management as exact science 

      Hamre, Johannes; Hamre, Kristin; Johnsen, Espen (Preprint, 2014-03-05)
      The main objective in research on sustainable fishery management is to understand the effects of fisheries on the resources and predict the Maximal Sustainable Yield. The von Bertalanffy growth model, commonly used in stock ...

    • In situ calibration of observatory broadband echosounders 

      Ona, Egil; Zhang, Guosong; Pedersen, Geir; Johnsen, Espen (Peer reviewed; Journal article, 2020)
      Today, numerous scientific echosounders are used as continuously monitoring systems in ocean observatories. These echosounders are usually calibrated in shallow water, either in laboratory tanks or at random ocean docks ...

    • Kunnskapsstatus for havsil i norsk sone av Nordsjøen 

      Johnsen, Espen; Sørhus, Elin; de Jong, Karen; Lie, Kai Kristoffer; Grøsvik, Bjørn Einar (Rapport fra havforskningen;2021 - 33, Research report, 2021)
      Tobis eller havsil er en nøkkelart i økosystemet i Nordsjøen, og viktige gyte- og leveområder for havsil er identifisert som særlig verdifulle og sårbare områder (SVO) i Nordsjøen. Rapporten oppsummerer eksisterende kunnskap ...

    • Measurements of underwater noise radiated by commercial ships at a cabled ocean observatory 

      Zhang, Guosong; Forland, Tonje Nesse; Johnsen, Espen; Pedersen, Geir; Dong, Hefeng (Journal article; Peer reviewed, 2020)
      Measurements of underwater noise radiated under ship normal operations are presented. The acoustic data, from the cabled ocean observatory, are analyzed under each identified ship passage, which was obtained by the Automatic ...

    • Measuring distribution and density of sprat in Årdalsfjorden with a kayak drone - 15-16 August 2020 

      Johnsen, Espen; Totland, Atle; Kvamme, Cecilie (Rapport fra havforskningen;2020 - 28, Research report, 2020)
      Sprat is a key species in several Norwegian fjords, as an important prey for fish, sea mammals and sea birds. The sprat populations are monitored with routine acoustic-trawl surveys using a large research vessel, which ...

    • StoX applied to cod and haddock data from the Barents Sea NOR-RUS ecosystem cruise in autumn - Swept area abundance, length and weight at age 2004-2017 

      Johannesen, Edda; Johnsen, Espen; Johansen, Geir Odd; Korsbrekke, Knut (Fisken og Havete;2019 - 6, Research report, 2019)
      North East Arctic cod and haddock are the largest stocks of these species in the world. Data from the Barents Sea NOR-RUS ecosystem cruise (BESS) in autumn is used as input to the assessment of these species. Here, we used ...

    • StoX: An open source software for marine survey analyses 

      Johnsen, Espen; Totland, Atle; Skålevik, Åsmund; Holmin, Arne Johannes; Dingsør, Gjert Endre; Fuglebakk, Edvin; Handegard, Nils Olav (Journal article; Peer reviewed, 2019)
      Scientists across the globe conduct survey programs to monitor and characterize abundance, population structure, biodiversity and geographical distributions. To assess the state of marine fish and zooplankton, population ...