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 ...

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)

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 ...

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 ...

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 ...