Field demonstration of a novel towed, area bubble-plume zooplankton (Calanus sp.) harvesting approach

SINTEF post https://www.sintef.no/en/publications/publication/?pubid=CRIStin+1097811.This paper presents field experiment results of using a new technology to harvest copepods (Calanus sp.) in the ocean by bubble upwelling. Two largo-scale bubble rafts, a 21 m2 and a flexible 75 m2 bubble raft with tow parallel and perpendicular sparger elements, respectively, were field tested in areas with high, upper 25-m water column Calanus densities. Measured bubble-driven upwelling velocities (Vup) at different air flows (Q) and depths (z0), found Vup-(f21 under stratified marine conditions, in agreement with other results for stratified conditions. Bubble trawls significantly enhanced Calanus concentrations in the upper water column, as much as 1416% integrated over the upper 2·m, with the best results for the tow-transverse raft, which also was tested under unstratified seas. Bubble trawl perfonnance aJso was related to stratification with the highest enhancement for the lowest stratification. Catch species analysis showed reduced bycatch. Thus, this new harvesting technology showed a potential to develop an economically robust, environmentally benign, and sustainable fishery on a renewable resource at lower trophic levels in the food web, within the context of ecosystem-based managemen

New active fishing gear Report from project workshop in Hirtshals, Dec. 14-15 2009

A few initial ideas for new active fishing gear concepts based on trawl and seine were presented at a workshop in Hirtshals, 14-15 December 2009. These initial concepts are described and the comments and feedback from the workshop participants included in this report. The outcome of the workshop is summarized in the form of a matrix (Table 4.1) of specific concepts and gear configurations that are to be followed up in the further work and tests in the project. Such a matrix provides both a clear overview of the concepts/configurations to be followed up, and a structured way to evaluate and systemize them wrt. applications and combinations in specific fisheries and for specific vessels. The further concept development consists of planning further model tank tests of these concepts and configurations, including establishing a set of relevant user oriented criteria for what makes a concept or configuration interesting or not for implementation in actual fishing. This will decide how the further tests should be carried out, what should be varied and measured etc. Also, the project should use the matrix to start proposing a set of one or a few of the gear concepts that may be realistic to have on board a specific or a typical vessel.publishedVersio

Nye konsept for drivstoff- og fangsteffektive aktive fiskeredskap basert pa trål og snurrevad

Prosjektet New fuel and catch efficient active fishing gear concepts based on trawl and seine ble initiert for å se på mulige synergier og gevinster ved å kombinere trål og snurrevad teknologi og operasjon. Prosjektet har bestått av flere delprosjekt med forskjellig faglig innhold og fokus. Resultater inkluderer vitenskapelige publikasjoner rundt rammebetingelser for og effekter av redskapsvalg, to nye redskapskonsept (notdesign) som kan anvendes som pelagisk trål, semi-pelagisk trål og som snurrevad ved forskjellige rigginger, fremskritt innen numerisk simulering av snurrevad, og resultater for bl.a. bunnkontaktkrefter og hydrodynamiske laster på forskjellige redskapselementer. Nytteverdien for næringen består i den potensielle gevinsten ved økt fleksibilitet og mer optimal tilpasning av redskap og operasjon i forhold til en aktuell fangstsituasjon, både mht. fangsteffektivitet, energibruk og miljøpåvirkning, og ved konkrete modeller og kunnskap som implementeres både i beregningsverktøy og redskapsutvikling fremover.Norges Forskningsråd;FHFpublishedVersio

Kinematics in Regular and Irregular Waves based on a Lagrangian Formulation

Kinematics in two-dimensional regular and irregular swface waves is described based on the Lagrangian form of the equations of motion, with particular emphasis 011 the conditions in the so-called splash zone in irregular waves. A practical method for accurate calculation of kinematics in broad-banded irregular waves is developed based on Gerstner's wave theory, and theoretical calculations are compared with laborat01:y wave data. A review of basic hydrodynamics has also been called for, and is presented from a Lagrangian as well as Eulerian point of view. The results of the analytical study and the study of the wave data question the applicability of certain universally accepted fluid dynamical principles. The basic equations of fluid motion are presented on Eulerian and Lagrangian form, including the general Lagrangian form of the Laplacian. The relations governing vortex motion are also presented, including the theorems of Helmholtz, Kelvin and others on the rate of change of vorticity and circulation. Rotation of fluid elements is also studied from a Lagrangian point of view, showing that vorticity is not suited to express how a fluid element actually rotates about itself. It is found reason to question the common Lagrangian form of the continuity equation, namely that the Jacobian must be constant and that it in general can be set equal to 1, since this requirement results in some ambiguities and fundamental inconsistencies. Further, when considered in a Lagrangian frame of reference, we have that the theorems of Helmholtz, Kelvin and others require that a given Lagrangian point always represents the same identifiable material "particle", i.e. that the Jacobian is constant and equals 1. Hence, there is also reason to question the common assumption of irrotational (potential) flow in motions generated by conservative (potential) forces only, since this requirement is based on a material (Lagrangian) interpretation of the theorems on vortex motion. The weaker requirement of zero curl of the acceleration in such flows still applies, irrespective of the behaviour of the Jacobian. The Lagrangian wave theories of Gerstner and Miehe are presented, pertammg to regular waves in deep and intermediate water, respectively. These wave theories represent closed orbital particle motion, i.e. without any net transport of mass. They also contain vorticity (rotationality) at second order, and are therefore traditionally considered invalid beyond first order. The classical solution for surface waves is Stokes 211d order wave theory. The difference between this theory and the two above is Stokes drift; a second order forward transport of mass. Stokes waves and Stokes drift are here also studied from a Lagrangian point of view. It is found that Stokes waves violate continuity and cause a vorticity at second order within less than one wave period, even for waves of small amplitude. Stokes waves are therefore theoretically inconsistent in the Lagrangian frame of reference, which in turn questions the arguments rendering Gerstner's (and Miche's) theory invalid, i.e. the above-mentioned assumption of irrotational motion. The wave theories of Gerstner and Miehe are concluded to be applicable basic solutions for regular waves in the limit of negligible viscosity. Irregular waves are here modelled as a sum of linear regular Gerstner or Miehe waves, superposed in the Lagrangian frame of reference. The Lagrangian approach is better suited to show the physics of the wave motions than the Eulerian approach, and the linear Lagrangian model of irregular waves automatically includes what are known as nonlinear interactions from an Eulerian point of view. The irregular approach presented here is still only a solution of the linearized Lagrangian problem; it is not a model for nonlinear irregular waves in a mathematical sense. Iterative methods have been developed that determine which water particle occupies a specific spatial (Eulerian) position at a specific instant in time. This means that also Eulerian quantities can be calculated, in a practical manner, based on the Lagrangian solutions. The iteration methods apply to regular as well as broad-banded irregulm· waves, and yield theoretically consistent values everywhere, also in the splash zone. Since the models of irregular waves presented in this thesis are based on the linear (first order) parts of the regular solutions only, they are not affected by the above questions regarding continuity, vorticity and mass transport at second order. The Lagrangian theories and models are compared with laboratory wave data for both regular and irregular wave cases. The wave data include measurements of the surface elevation and LDV-measurements of water particle velocities at different vertical positions, also above the still water level. The mean horizontal velocity in a vertical cross-section has been studied closely, and the instantaneous horizontal velocity in a vertical cross-section beneath individual crests and troughs has also been considered. The analysis of the experimental data show that distinct transitions in the mean horizontal velocity in the flume take place after a relatively short period of time. These analysis, along with visual observations, also indicate that water particles actually move in more or less closed orbits, i.e. similar to Gerstner and Miehe waves, which is fundamentally different from the commonly assumed Stokes drift and associated return current. Again, this supports the above questioning of Stokes waves, Stokes drift and irrotational motion. For regular waves, the wave theories of Gerstner and Miehe are found to compare exceptionally well with the measurements after the transitions have taken place and a relatively steady mean velocity profile has been established. For irregular waves, the Lagrangian models also compare well with the measurements, although these results are more subject to uncertainties. In particular, the horizontal velocity beneath crests and troughs predicted by the Lagrangian approach is compared with calculations according to the widely used Wheeler's method. The Lagrangian approach is generally found to compare better with the measurements than Wheeler's method does, and it accounts for the discrepancies typically observed when Wheeler's method is compared with wave flume measurements. It should be noted that Wheeler's "ad hoe" method does not satisfy the basic equations of motion, while the Lagrangian approach presented here does satisfy the basic equations consistently, even in the splash zone. Hence, this study raises some fundamental theoretical questions with respect to continuity, vorticity and mass transport. For waves, it is of the utmost importance to resolve the issues of non-uniform mass transport when higher order solutions are sought. Caution should be taken when analyzing wave flume measurements, in particular for irregular wave cases. Such measurements may not be satisfactorily suited for comparisons with, or verification of, theoretical models of irregular ocean waves. Anyhow, the Lagrangian approach presented herein should be of great practical and theoretical value, very well suited for simulations and design purposes. The potential for further development seems considerable, and may e.g. open for theoretically consistent superposition of nonlinear Lagrangian components and detailed modelling of wave-wave interactions and wave-current interactions

MultiSEPT – Initial model scale tests of traditional and alternative trawl ground gears

This report describes initial model scale experiments with lighter ground gear in bottom trawls in the MultiSEPT project. This includes tests with traditional rockhopper gear, skirt, modified skirts, modified plate gears and a new bottom gear made with semi-circular profiles. In some cases the different types of gear are combined, i.e. with one type of gear in the side sections and another type in the center section. Tension in lower sweeps, headline, fishing line and gear chain was measured, including measurements of the maximum tension as the gear encountered a bottom obstacle. The results indicated that the towing resistance for a scaled (1:4) bottom trawl in the flume tank (i.e. with low bottom friction and excluding doors and warps) was reduced by approximately 15 % by replacing the rockhopper with a skirt, and that an elastic skirt can be advantageous with regard to passing bottom obstacles compared to a traditional skirt. The proposed semi-circular spreading gear also showed promising features.publishedVersio

Oppsummering og konklusjoner fra workshop. FHF prosjekt 900789.

Tirsdag 5.juni ble det arrangert en workshop med en kombinasjon av innlegg/foredrag og gruppearbeid for å belyse problemstillinger knyttet til arealbruk og forankring av flytende oppdrettsanlegg. Basert på presentasjoner og resultat fra gruppearbeid er det rimelig å konkludere med at det er mulig å ta til sikker forankring av oppdrettsanlegg med mindre beslag av bunnareal. Løsninger, teknologi og kunnskap eksisterer og er kjent og anvendes blant annet innen olje og gassindustrien. Derimot finnes det ikke spesifikke produkter og leverandører for slike løsninger rettet mot forankring av oppdrettsanlegg. Ut i fra presentasjonene og tilbakemeldinger fra gruppearbeidet er det ikke åpenbart i hvilken grad redusert beslag av areal fra forankring av oppdrettsanlegg vil redusere utfordringer knyttet til tilstedeværelse av oppdrettsanlegg i forbindelse med fiskeri. En del av utfordringen knyttet til plassering av oppdrettsanlegg i forhold til fiskeriinteresser ligger i selve tilstedeværelsen av anlegget, like mye som arealbeslag av fortøyning.Fiskeri- og havbruksnæringens forskningsfondpublishedVersio

Sikre og mindre arealkrevende fortøyningssystem for havbruksanlegg

Tirsdag 5.juni ble det arrangert en workshop med en kombinasjon av innlegg/foredrag og gruppearbeid for å belyse problemstillinger knyttet til arealbruk og forankring av flytende oppdrettsanlegg. Basert på presentasjoner og resultat fra gruppearbeid er det rimelig å konkludere med at det er mulig å ta til sikker forankring av oppdrettsanlegg med mindre beslag av bunnareal. Løsninger, teknologi og kunnskap eksisterer og er kjent og anvendes blant annet innen olje og gassindustrien. Derimot finnes det ikke spesifikke produkter og leverandører for slike løsninger rettet mot forankring av oppdrettsanlegg. Ut i fra presentasjonene og tilbakemeldinger fra gruppearbeidet er det ikke åpenbart i hvilken grad redusert beslag av areal fra forankring av oppdrettsanlegg vil redusere utfordringer knyttet til tilstedeværelse av oppdrettsanlegg i forbindelse med fiskeri. En del av utfordringen knyttet til plassering av oppdrettsanlegg i forhold til fiskeriinteresser ligger i selve tilstedeværelsen av anlegget, like mye som arealbeslag av fortøyning

Flotasjon av lakselus

På bakgrunn av henvendelser fra næringsaktører kontaktet FHF SINTEF Fiskeri og havbruk for en innledende studie av hvorvidt flotasjon av frittsvømmende stadier av lakselus (luselarver) kan redusere sannsynligheten for at de slipper inn lakseanlegg. Målsetningen med prosjektet var å gjennomføre kvalitative studier og observasjoner av flotasjon av luselarver i laboratorieforsøk, altså å undersøke hvorvidt små luftbobler fester seg til luselarver og løfter dem mot overflaten ved hjelp av oppdrift. Forsøkene ble gjennomført i SINTEF Sealab's laboratorier, i en kolonnetank med tverrsnitt 29,5 x 29,5cm, 100cm høy. En keramisk diffusor og trykkluft ble benyttet til å generere mikroboblene. Speilreflekskamera med makroobjektiver ble benyttet til billedtaking. Det ble tatt mer enn 450 bilder med lus eller skall fra lus i synsfeltet til kamera, der flere av bildene inneholder mer enn en luselarve. Av disse observasjonene var det ingen bobler som festet seg til lus eller skall. Potensielt ville en fungerende metode for flotasjon av lakselus kunne bidra til å konsentrere luselarvene i de øverste deler av vannsøyla, og på den måten lede disse vekk fra laksen.FHFpublishedVersio

Field demonstration of a novel towed, area bubble-plume zooplankton (Calanus sp.) harvesting approach

This paper presents field experiment results of using a new technology to harvest copepods (Calanus sp.) in the ocean by bubble upwelling. Two largo-scale bubble rafts, a 21 m2 and a flexible 75 m2 bubble raft with tow parallel and perpendicular sparger elements, respectively, were field tested in areas with high, upper 25-m water column Calanus densities. Measured bubble-driven upwelling velocities (Vup) at different air flows (Q) and depths (z0), found Vup-(f21 under stratified marine conditions, in agreement with other results for stratified conditions. Bubble trawls significantly enhanced Calanus concentrations in the upper water column, as much as 1416% integrated over the upper 2·m, with the best results for the tow-transverse raft, which also was tested under unstratified seas. Bubble trawl perfonnance aJso was related to stratification with the highest enhancement for the lowest stratification. Catch species analysis showed reduced bycatch. Thus, this new harvesting technology showed a potential to develop an economically robust, environmentally benign, and sustainable fishery on a renewable resource at lower trophic levels in the food web, within the context of ecosystem-based managementpublishedVersio