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

Testing of trawl-acoustic stock estimation of spawning capelin 2020

This report describes the second in a series of three 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 they 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 western part and Eros the eastern part. A stratified random transect design was 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. The ultimate biomass estimate combines the two coverages, but evaluation about the mobility of the fish can be done by comparing the coverages. The final geographical allocation of survey effort was decided based on information from the scouting vessel Hovden Viking which covered the area a week prior to the main survey. Echo sounders with frequencies from 18-200 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 total biomass of maturing capelin in the coverage area was estimated at 62 298 tons, with a CV of 38%. The 5% lower and 95% upper confidence limits were 26 655 and 104 305 tons, respectively. The result is in accordance with the prediction from the autumn 2019, but the high CV and wide confidence interval show that the survey result is uncertain. The high uncertainty despite the good survey coverage is likely due to the very patchy distribution of the capelin. In addition, in the western coverage area which had most of the capelin recordings, there was a big difference in both estimate and distribution in the return east-west coverage compared to the west-east. This underlines the high mobility of the capelin when it is in this state of migration. The strong dynamic was also evident last year and makes the monitoring of the capelin spawning migration challenging. Mean length of the capelin was 16.2 cm, mean weight 22.3 g, and maturation had progressed further in the western than the eastern area which was the opposite of what was observed last year. Methodological investigations including target strength measurements and testing of the autonomous Sailbuoy were carried out successfully and are described in the report. A thorough evaluation of the survey series and its usefulness as input to the capelin advice will be done after the third survey in this series is completed.Testing of trawl-acoustic stock estimation of spawning capelin 2020publishedVersio

StoX: An open source software for marine survey analyses

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 surveys are often repeated annually using standardized sampling protocols and analysis techniques to establish trustworthy stock status. However, although transparency and repeatability are recognised as important principles of this process, it is often difficult to obtain comprehensive documentation of metadata and data processing steps. This is particularly challenging for workflows that include manual processing steps. StoX was principally built to process research‐vessel survey data, and we have included several standard survey estimation models. The software was developed to be robust and versatile and aimed at the open source community, such that users could easily build their own models. StoX is fully integrated with R to utilize the large number of R‐packages and enable any StoX function and stock estimation model to be controlled using R. There has been a large need for a freely available software for research–vessel survey estimation, and StoX is tested in surveys carried out in four continents and is the official tool for many important fish stock surveys. The basic workflow and transparency principles of StoX, together with a customizable GUI, makes StoX applicable for any geographically coded surveys. Future versions of StoX will include statistical models to estimate the catch composition in commercial fisheries. In fields such as conservation management, there is also a need to document the estimation methods, and additional estimation and analyses models, including biodiversity indices are currently implemented. In parallel, we envision a closer web service integration with existing international and national data centres.publishedVersio

Testing of trawl-acoustic stock estimation of spawning capelin 2021

This report describes the third 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 they 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 western part and Eros the eastern part.Testing of trawl-acoustic stock estimation of spawning capelin 2021publishedVersio

Does seismic have an effect on zooplankton? - Field study at Ekofisk with RV Kristine Bonnevie

Toktnr: 2022611Does seismic have an effect on zooplankton? - Field study at Ekofisk with RV Kristine BonneviepublishedVersio

Migratory behaviour of reared Norwegian coastal cod and north east Arctic cod

This paper is based on experiments to test if differences in migratory behaviour of Norwegian coastal cod and north east Arctic cod is related to parental origin or, alternatively, is related to the environmental experienced during the premature stages. Earlier experiments have shown that when wild fish from the two groups are transplanted and released at a new location, their behaviour after release differ distinctly. The two groups of cod in the present study were raised in captivity under identical conditions. Mature fish were tagged with acoustic transmitters and their behaviour studied during a week's period after release. Methods and design were the same as in the earlier experiments, and the results signified no behavioural differences between the two groups of fish. This might be an indication of strong environmental influence on migratory behaviour in cod. The number of released fish were low and the results have to be verified by new trials

A stationary acoustic system for monitoring undisturbed and vessel affected fish behaviour

Thorough knowledge of the dynamics of natural fish behaviour and distribution within a survey and among surveys is fundamental for reliability of time series of abundance indices. Further, vessel/trawl affected avoidance may greatly affect density estimates from trawl and acoustic surveys. Means for monitoring behaviour of fish during surveys or in special experiments have been limited, time consuming and expensive. This paper describes an acoustic buoy system for monitoring undisturbed distribution and behaviour of fish as well as avoidance reactions of fish in relation to passing surveying or trawling vessel. Operation and results from the first trials are described. The buoy could easily be operated in connection with a standard trawl haul, prolonging the haul time with approximately 30 minutes for launching, retrieval and extra cruising distance. Information on fish distribution and behaviour , i.e. vertical and horizontal movements, is stored in the buoy and can easily be downloaded for later processing and analysis. Observations on cod demonstrated avoidance away from the vessel of variable intensity