Kayak Drone – a silent acoustic unmanned surface vehicle for marine research

Advancements in technologies have led to a rapid development of unmanned surface vehicles (USV) for marine ecosystem monitoring. The design, size, and scientific payload of the USVs differ as they are built for different purposes. Here, we present the design criteria and detailed technical solutions of a prototype USV which has been built to fulfill the following experimental and operational needs; the USV should be used for inshore and shallow water acoustic monitoring, offshore comparison of echo sounder recordings from the USV and research vessels, monitor natural fish schooling behavior and seabird-fish behavioral interactions. The prototype has been built over a period of 5 years with steadily quality improvements. As the hull is based on an expedition double kayak, the USV is named Kayak Drone, and we aimed at building the Kayak Drone using of-the-shelf hardware and existing open-source software. This allowed for the development of a modular and well-functioning USV at a relatively low cost. The Kayak Drone produces very little noise and in situ experiments show that the Kayak Drone can record echo sounder data of fish near the surface without disturbing their natural distribution and behavior. One in situ study shows that the Kayak Drone could navigate within a couple of meters from swimming puffin and other seabirds without triggering escape. These results demonstrate that the Kayak Drone can be utilized to produce unbiased survey estimates for fish distributed in shallow waters and near the surface, which is very important for many fish stock assessments and managements. Furthermore, it can also be used as a tool to observe the predation by seabirds on fish schools without interfering with their natural interspecific behavior, which traditionally has been very difficult. The use of the Kayak Drone is not restricted to these tasks, and we foresee that the Kayak Drone can be utilized in many different experiments where a silent platform is needed.publishedVersio

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

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 surveys since the 1980s. The time series have provided vital input to stock assessments and are widely used in studies of ecology and biodiversity. The objectives of this study were to evaluate the technical specifications of the vessels and trawls used, to examine effects of modifications on catching efficiency, and to assess implications of these modifications over time. We find that the demersal trawl data collected in South Africa are not comparable with those of Namibia and Angola, and that the time series of Angola and Namibia contain inherent differences in terms of catchability of bottom dwellers. The introduction of smaller bobbins gear on the RV Dr. Fridtjof Nansen in 1994 increased the catchability of bottom-dwelling species, and catch rates of monkfish and sole were higher in surveys with commercial vessels than the RV Dr. Fridtjof Nansen. We recommend that temporal trends are interpreted with caution and that time series for the three countries are viewed in isolation

Råd for tobisfiskeriet i norsk sone for 2022 - Tobistokt i Nordsjøen 27. april-12. mai 2022

Tobistoktet i 2022 viser at rekrutteringen (ettåringer) av havsil (tobis) i sørlige del av norsk sone av Nordsjøen er lavere enn middels, men individvekten for disse ettåringene er høyere enn gjennomsnittet i tidsserien og ca. 14% høyere enn i 2021. For de eldre individene er vekten omtrent gjennomsnittlig, og en del høyere enn i fjor. Bestanden har en god geografisk spredning sør for 57°30’, mens nord for dette er bestanden kritisk lav. Under toktet har mattilgangen for tobis vært relativt god i de sørlige områdene der tobismagene inneholdt mye hoppekreps og andre dyreplankton. I de mer nordlige områdene var det vesentlig mindre mat i magene.publishedVersio

A new model for simulating growth in fish

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 accumulated time as an independent variable. As a result the B&H model has to assume constant fish growth. However, growth in fish is highly variable depending on food availability and environmental conditions.We propose a new growth model where the length increment of fish living under constant conditions and unlimited food supply, de- creases linearly with increasing fish length until it reaches zero at a maximal fish length. The model is independent of time and includes a term which accounts for the environmental variation. In the present study, the model was validated in ze- brafish held at constant conditions. There was a good fit of the model to data on ob- served growth in Norwegian spring spawning herring, capelin from the Barents Sea, North Sea herring and in farmed coastal cod. Growth data fromWalleye Pollock from the Eastern Bering Sea and blue whiting from the Norwegian Sea also fitted reasonably well to the model, whereas data from cod from the North Sea showed a good fit to the model only above a length of 70 cm. Cod from the Barents Sea did not grow according to the model. The last results can be explained by environmental factors and variable food availability in the time under study. The model implicates that the efficiency of energy conversion from food decreases as the individual animal approaches its maximal length and is postulated to represent a natural law of fish growth

Fishery management as exact science

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 assessment, is suboptimal for the calculation of yield, because it cannot be integrated to omit time from the equation. Here, we present a new model to be used as the scientific basis to calculate yield and provide advices for optimal ecological harvesting strategies. The model builds on the principle of exact science and utilizes population measurements from scientific acoustic trawl surveys as input in a real population dynamical model. The model expands the theory of relativity to include the transition of biomass into energy and will improve simulation models used in fisheries science

The relationship between physical activity at school and in their spare time

Hensikten med denne studien var å undersøke sammenhengen mellom intensitetsnivået i kroppsøvingstimene og fysisk aktivitetsnivå på fritiden hos 3. klasseelever på videregående skole. Resultat: Ingen signifikante sammenhenger ble funnet mellom noen av variablene. Sammenheng mellom kjønn og intensitetsnivå i kroppsøvingsundervisning ble ikke observert

Estimering av akustiske indekser med CV for torsk og hyse fra vintertoktet i Barentshavet 1994-2017 med Sea2Data programvaren StoX

Source at https://www.hi.no/publikasjoner/andre_publikasjoner/fisken_og_havet/2018/nb-no.English: The Sea2Data software StoX was applied to estimate acoustic indices with CVs for Northeast Arctic cod and haddock from the Barents Sea winter survey in 1994 to 2017. The indices are compared to indices previously estimated by the BEAM software. In most years the StoX indices for cod are quite similar to those obtained by BEAM, while they are somewhat higher for haddock. The largest deviations were mainly found for age groups with low indices and/or in years with raising of the indices.Norwegian: 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 programmet BEAM. I de fleste år er StoX indeksene for torsk nokså like BEAM indeksene, mens de er noe høyere for hyse. De største forskjellene var hovedsakelig for aldersgrupper med lave indekser og/eller i år med skalering av indeksene

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

Source at http://hdl.handle.net/11250/2562514The Sea2Data software StoX was applied to estimate acoustic indices with CVs and length and weight at age for Northeast Arctic saithe from the Norwegian coastal survey Varanger - Stad in 2013 to 2017. The indices are compared to indices previously estimated by the BEAM software, and differences are mainly explained by different strata areas.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 tidligere estimert med programmet BEAM, og forskjeller er i hovedsak forklart ved forskjeller i strata-areal

In situ calibration of observatory broadband echosounders

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 before deployments. If the systems are used for quantitative measurements by the observatories, they should be calibrated at the operating depths to consider the environmental effects on the calibration parameters. In this article, a simple in situ calibration method is presented, which was recently applied to one of the nodes of the Norwegian Lofoten-Vesterålen ocean observatory, when the research vessel with dynamic positioning system suspended and moved the calibration sphere between the vessel and the transducer. The calibration results of a 70-kHz split-beam echosounder demonstrate that this method can be applied to the cabled observatories.publishedVersio