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6 results on '"Stockhausen, Hans Hagen"'

3. A unifying hypothesis for the spawning migrations of temperate anguillid eels.

Author

Durif, Caroline M. F., Stockhausen, Hans Hagen, Skiftesvik, Anne Berit, Cresci, Alessandro, Nyqvist, Daniel, and Browman, Howard I.

Subjects
*EELS, *GEOMAGNETISM
Abstract

Anguillid eels grow in freshwater but spawn in the open ocean. The cues that guide eels over long distances to the spawning area are unknown. The Earth's magnetic field can provide directional and positional information and is likely used by catadromous eels during their spawning migration; as magnetosensitivity and compass orientation have been reported in eels. To test whether this is theoretically possible, we compared the migratory routes of five species of temperate eels that undertake long migrations with the geomagnetic field of their distribution/spawning areas. We found that, regardless of the species and although routes are different between life stages, larvae of those species always drift along paths of increasing magnetic inclination and intensity, while adults follow reverse gradients. This is consistent with an imprinting/retracing hypothesis. We propose a general navigation mechanism based on larvae imprinting on a target magnetic intensity (or inclination) at the hatching area and on the intensity (or inclination) gradient during larval drift. Years later, adults retrace the magnetic route by following the gradient of decreasing total intensity (or inclination) values that occurs towards lower latitudes. As they reach the target value, adults switch to compass orientation to stay on the target isoline and reach the spawning area. The proposed mechanism fits for all temperate eels examined. Knowledge about navigational strategies of eels is important to evaluate the effectiveness of management strategies that involve stocking of juveniles displaced from one area to another to rebuild local populations. [ABSTRACT FROM AUTHOR]

Published
2022
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4. Effekter av fiskeri og havbruk på bunn og bunnfauna: Oppfølging og forslag til nye forvaltningstiltak

Author

Buhl-Mortensen, Lene, Aglen, Asgeir, Breen, Michael, Buhl-Mortensen, Pål, Ervik, Arne, Husa, Vivian, Løkkeborg, Svein, Røttingen, Ingolf, and Stockhausen, Hans Hagen

Subjects
VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Aquaculture: 922, aquaculture, VDP::Mathematics and natural science: 400::Geosciences: 450::Sedimentology: 456, VDP::Mathematics and natural science: 400::Geosciences: 450::Oceanography: 452, akvakultur, trawling, havbruk, mariculture, fiskeredskaper, tråling, fishing gear, VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Resource biology: 921
Abstract

Rapporten gir en beskrivelse av fiskeredskaper brukt i norske fiskerier som berører bunn. Berørte områder og grad av eksponering beskrives i rapporten. Bunntrål etter fisk og reker er den redskapstypen som har størst effekt på bunnsubstrater, habitater og bunndyr. Vi har i rapporten også lagt vekt på å beskrive modifiserte fangstteknikker som kan bidra til at bunnpåvirkningen reduseres. Rapporten skisserer tiltak som kan bidra til redusert påvirkning på havbunn og bunnfauna ved trålfiske.

Published
2013

6. Orientation of homing salmon (Salmo salar L.) mapped in relation to geomagnietic field

Author

Sturlaugsson, Johannes, Gudbjornsson, Sigmar, and Stockhausen, Hans Hagen

Subjects
atlantic salmon, migration patterns, atlantisk laks, vandringsmønster, VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Resource biology: 921
Abstract

A migration study on the homing of Atlantic salmon was carried out in waters off SW – Iceland. Data was sampled on the salmon behaviour and environment during spawning migration in sea. New type of data storage tag was used to measure the earth‘s magnetic field and the tilt (in 3 directions) and paired information on fish depth (pressure) and correspondingly the temperature experienced. By taking advantage of this new research tool we have managed in this study to bring forward new information on salmon orientation. The study involves new approach in mapping information on behaviour and positioning of free ranging fish. Information already available from the study is showing that salmon migration behaviour changes when moving from offshore to inshore waters. We conclude that this stands for changes in the orientation behaviour of the salmon due to the increased use of olfactory sense in the inshore area. Based on that we recommend to divide the spawning migration in sea into three phases in relation to the different migration (orientation) behaviour in different sea area (offshore; inshore; estuary). Parallel to this finding is the fact that the directional geomagnetic recordings sampled during the migration of the salmon from release offshore to entry to their home river showed that fixed direction all the way from offshore to the home fjord area or home estuary could not explain their migration. Therefore we make that assumption that shoreline orientation is important in finding the way once the shore has been approached. The study setup has brought to shore many interesting recordings of new parameters on behaviour and environmental patterns that will be examined further later. Keywords: Atlantic salmon, migration, homing, orientation, navigation, data storage tags

Published
2009

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