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Research Papers: Ocean Space Utilization

Effects of a Shielding Skirt for Prevention of Sea Lice on the Flow Past Stocked Salmon Fish Cages

[+] Author and Article Information
K. Frank

SINTEF Fisheries and Aquaculture,
Trondheim 7465, Norway
e-mail: Kevin.Frank@sintef.no

L. C. Gansel

SINTEF Fisheries and Aquaculture,
Trondheim 7465, Norway
e-mail: Lars.Gansel@sintef.no

A. M. Lien

SINTEF Fisheries and Aquaculture,
Trondheim 7465, Norway
e-mail: Andreas.M.Lien@sintef.no

J. Birkevold

SINTEF Fisheries and Aquaculture,
Trondheim 7465, Norway
e-mail: Jens.Birkevold@sintef.no

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received June 26, 2013; final manuscript received August 7, 2014; published online October 3, 2014. Assoc. Editor: Elzbieta Maria Bitner-Gregersen.

J. Offshore Mech. Arct. Eng 137(1), 011201 (Oct 03, 2014) (6 pages) Paper No: OMAE-13-1062; doi: 10.1115/1.4028260 History: Received June 26, 2013; Revised August 07, 2014

The effect of a shielding skirt, a tarpaulin mounted from the surface down to 5 m depth around a net cage, on the flow pattern at a commercially stocked salmon cage was investigated. Dye was used as a tracer for water movement and the dye spreading was monitored using aerial images. Current meters were employed to investigate the flow close to the net inside and outside the cage. Tests were conducted with and without the shielding skirt. The focus was on the effectiveness of the shielding skirt to deflect water around the cage. This study shows that a shielding skirt can reduce horizontal flow components significantly inside a cage, which is related to a reduction of water exchange. The flow toward a cage is divided by a shielding skirt, i.e., some of the water is transported around the cage, while some is passing underneath the shielding skirt. Some water entering the fish cage from underneath the tarpaulin is transported toward the surface inside the cage. The use of a shielding skirt might not prevent interaction of the upper water layers inside and outside of a fish cage completely, but it has the potential to reduce the inflow of surface water into the cage, if deployed properly.

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Figures

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Fig. 1

Position of the fish farm in Norway, overview of the surrounding islands, and an aerial image of the farm

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Fig. 2

Sketch of a shielding skirt mounted around a circular gravity net pen fish cage

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Fig. 3

Placement of the velocity meters (NORTEK vector) inside the cage in the west (IW) and east (IE) as well as outside of the cage in the west (OW) and east (OE)

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Fig. 4

Fish-eye lens image series of case Ref with indicated time steps in min; white arrows indicate line from the steady location the pictures were taken toward the cage center, red dotted line observed environmental current direction

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Fig. 5

Case A—Time series of dye transport. The numbers indicate time in minutes and the upper image is a qualitative summary of flow patterns deducted from the time series. The ropes crossing the cage are on the north–south axis (∼5 deg N).

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Fig. 6

Case B—Time series of dye transport. The numbers indicate time in minutes and the upper image is a qualitative summary of flow patterns deducted from the time series. The ropes crossing the cage are on the north–south axis (∼5 deg N).

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Fig. 7

Case C—Time series of dye transport. The numbers indicate time in minutes and the upper image is a qualitative summary of flow patterns deducted from the time series. The ropes crossing the cage are on the north–south axis (∼5 deg N).

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