An Ecopath with Ecosim model of the Norwegian Sea and Barents Sea validated against time series of abundance

We here present a fitted and partly validated Ecopath with Ecosim model for the Norwegian Sea and Barents Sea. Ecopath mass-balance model parameters were obtained from the literature on Norwegian and Barents Sea organisms and from approximations. Predator-prey vulnerability parameters for Ecosim were fitted by driving a past state model balanced for the year 1950 from 1950 to 2000 and comparing the modelled biomass time series with series from VPA and acoustic surveys. Estimated fishing mortalities or reported catch were used to drive the modelled biomass through the 50-year period. The vulnerability parameters from the fitted 1950 model were then used as input for a simulation model balanced for the year 2000. The fits were reasonably good, and were improved after including fluctuation in the yearly phytoplankton production through a primary production forcing function. The fluctuating biomass trends characteristic for many of the short-lived groups in the model were better reproduced when including the primary production forcing function, suggesting that bottom-up control is important in this marine system. When evaluating the vulnerability parameters through a comparison between modelled and observed diet compositions, the parameter settings seemed reasonable for cod as a predator, but less so for haddock. The optimal long-term fishing pressure modelled in the model was consistent with advice from the International Council for the Exploration of the Sea (ICES) for the stocks for which values of target reference points are estimated.Her presenterer me ein Ecopath med Ecosim økosystemmodell for Norskehavet og Barentshavet som til dels er validert mot mengdemålingstidsseriar. Ecopath modellparametre på norskehavs- og barentshavsorganismar er henta frå litteraturen eller frå tilnærmingar viss ikkje annan informasjon er tilgjengeleg. Sårbarhetsparameteren som beskriv kor sårbart eit gitt bytte er for ein gitt predator, og som modellen er svært sensitiv ovafor, blei tilpassa ved å kjøra ein historisk modell balansert for året 1950 til 2000 og modellerte mengdemålingstidsseriar mot tidsseriar frå akustiske tokt eller VPA-kjøringar. Estimert fiskedødelighet eller rapportert fangst blei trekt frå biomassen for kvar modellert organismegruppe gjennom 50-årsperioden. Sårbarhetsparameteren blei ekstarhert ut frå den balanserte 1950-modellen, og blei deretter brukt inn i ein modell for det same området og med identiske organismegrupper, men balansert for året 2000. Samsvaret mellom den modellerte biomassen og den observerte var rimeleg god og blei forbedra ved å inkludera fluktuasjon i årleg planteplanktonproduksjon. Særleg den fluktuerande biomassen som er karakteristisk for fleire av dei pelagiske bestandane blei meir realistisk gjenskapt ved å inkludera primærproduksjonen, noko som indikerer at botn-opp kontroll er viktig i dette marine systemet. Den sensitive sårbarhetsparameteren blei delvis evaluert gjennom ein samanlikning mellom modellert og observert diettsamansetting hos torsk og hyse. Dietten til torsk blei rimeleg godt gjenskapt i modellen, men dietten for hyse i mindre grad. Optimalt fisketrykk ved langtidshausting som blei modellert med modellen balansert for år 2000, var konsistent med rådet frå det internasjonale råd for havforsking (ICES) for dei bestandane kor referansepunkt blir estimert

Survey report: Developing methods for abundance estimation of bluefin tuna in Norwegian waters

The major aim of this survey was to map and quantify distribution, school size and behaviour of Atlantic bluefin tuna (Thunnus thynnus) migrating to and feeding in Norwegian waters.The survey covered the region between Bergen and Molde, between 4th to 15th October, onboard hired vessel M. Ytterstad (75 m long) with promising preliminary results for acoustic methods for monitoring the distribution, abundance and behaviour of bluefin tuna in Norwegian waters.publishedVersio

Feeding ecology of Atlantic mackerel (Scomber scombrus) in the Norwegian Sea

Previous studies on Atlantic mackerel (Scomber scombrus) feeding during the highly migratory summer period are scarce. In this study we present detailed diet analyses and investigations of prey selection for Atlantic mackerel in relation to zooplankton distribution and hydrographical conditions in the Norwegian Sea in July 2004. A wide variety of prey organisms were found in the stomachs of mackerel in all water masses. According to dry weight was Limacina retroversa the principal prey in Coastal and Atlantic water masses. L. retroversa was presumably abundant in the Norwegian Sea and taken as secondary prey in the quest for more nutritious prey. Calanus finmarchicus was less important in all water masses than previously documented, also when combined with calanoidae copepod remainders, indicating that their descend to overwinter in deeper waters had already started in late July. Mackerel showed a size selective feeding behaviour and preferred larger prey species over smaller prey. Small copepods (< 1 mm) were numerous in the zooplankton samples in all water masses, especially Coastal and Atlantic, but were not present in the stomach samples. Furthermore, the three largest copepodite stages of C. finmarchicus (CIV – CVI) were selected over the three smallest stages (CI – CIII). Pronounced prey and size selection strongly suggests that mackerel performed particulate feeding. The potential feeding competition between mackerel and herring was also investigated. There was a clear difference in the diets of the two species. C. finmarchicus and L. retroversa were the main prey of mackerel, whereas herring preferred euphausiids and amphipods. These latter species normally swim in deeper waters and only enter the upper layers for feeding when protected by the dark. Moderate feeding by herring at the end of their feeding season and more active feeding by mackerel could explain the pronounced differences in the diet and lack of feeding competition between these two important planktivorous species

Survey report from the CODFUN 2016114 Barents Sea survey 5.-11. oktober 2016

The survey is part of the project “The cod – capelin interaction in the Barents Sea: spatial dynamics in predator prey overlap and functional response (CODFUN)” funded by the Norwegian Research Council (NRC project number 243676/E40). The CODFUN project was motivated by the need to update and improve the current formulation of the functional response of cod used in the capelin assessment model. The functional response is the relationship between the feeding rate of individual predators and density of prey. Functional response, together with density of predators and prey is used to calculate natural mortality. In all natural environments, there is spatial heterogeneity in densities of prey and predators and their overlap. This heterogeneity becomes a very important determinant of natural mortality due to predation. The aim of the CODFUN project is to quantify and explain spatial heterogeneity in the capelin-cod interaction at different spatial scales in the Barents Sea. The aim of the survey was to study spatial variation at the scale of individual cod and capelin schools. We aimed at quantifying attack rates of cod on capelin using acoustics, and to estimate proportion of successful attacks using stomach samples from trawl catches and handline. Furthermore, we aimed to relate variation in attack rates to variation in capelin densities and light conditionspublishedVersio

Antarctic krill and ecosystem monitoring survey off the South Orkney islands in 2018

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Testing of trawl-acoustic stock estimation of spawning capelin 2022

This report describes the fourth in a series of trawl-acoustic monitoring surveys of the spawning stock of capelin during the migration to the coast. The survey is a response to a proposal from the industry to evaluate the possibility of using winter monitoring of maturing capelin as an input to the capelin assessment and advice. The timing and geographic coverage of the survey are such that the results would be relevant to use for advice given that the output is reliable. Pre-defined areas off the Troms and Finnmark coast were covered using two vessels, Vendla surveying the eastern part and Eros the western part. A stratified random transect design was originally adopted with two complementary zig-zag grids, the first going in a west-east and the second in an east-west direction over the same strata. However, the high capelin abundances north of Varangerhalvøya lead to changes in the design, and a new stratum with increased effort covering the area with high abundance. The biomass estimate we present is based on the second coverage, but evaluation of the mobility of the fish can be done by comparing the coverages. Echo sounders with frequencies from 18-333 kHz were run together with sonars, and target trawls were carried out on significant pelagic aggregations. Capelin abundance was estimated using 38 kHz data. The median biomass of maturing capelin in the coverage area based on 500 bootstrap runs was estimated at 426 618 tons, with a CV of 42%. The 5% lower and 95% upper confidence limits were 167 555 and 757 229 tons, respectively. The confidence bands overlap with the prediction from the autumn 2021, but the wide confidence interval shows that the survey result is uncertain. The high uncertainty despite the good survey coverage is likely due to the very patchy distribution. Capelin aggregations recorded north of Varanger in the eastern coverage area totally dominated in the estimate. Capelin concentrations were also observed in the west, in areas associated with Fugløybanken and Malangsgrunnen, but the capelin abundance in these areas seemed to decrease over the survey period. Capelin at age 3 dominated in the samples and were estimated to constitute more than 6 times the biomass of the other age groups combined. The 3-year-olds had an average length of 15.5 cm and weight 16.3 g. Maturation had progressed further in the western than the eastern area similar as last year, and quite a high proportion of the females sampled towards the end of the survey in the western area were spent. We undertook 7 stations with a submersible probe measuring acoustic target strength of capelin. Preliminary results indicate that the target strength and acoustic frequency response of capelin this year were more in accordance with expectations for capelin than last year. A thorough evaluation of this survey series and its usefulness as input to the capelin advice will be prepared for the capelin benchmark in June this year.publishedVersio

Antarctic krill and ecosystem monitoring survey off the South Orkney Islands in 2018

Environmental monitoring along set transect lines off South Orkney Islands, Southern Ocean. Executed annual surveys (since 2011) to collect acoustic and biological data on krill, other macro zooplankton and data on krill predators from sector 48.2 in the Southern Ocean.publishedVersio

Impact of herring spawning behaviour on acoustic abundance estimates

Spawning dynamics of Norwegian spring spawning herring was studied in south western Norway 29 March to 3 April 2000 using hydroacoustics. The horizontal distribution of the spawning layers shifted in a south-easterly direction during the study period indicating directional spawning. A diurnal spawning pattern was found, with layers of spawning herring recorded at night from 18 to 24 UTC (= local time - 2 hours), few herring recordings during the night from 24 to 06, and most herring recorded pelagically during the day. Recorded fish density was highest in the period 15 to 18 and lowest from 21 to 03, and schools staying pelagically had higher density than bottom layers. The observed behaviours are likely to influence acoustic abundance estimates, particularly when surveying during the night towards the end of the spawning season