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Deep vision: an in-trawl stereo camera makes a step forward in monitoring the pelagic community.

Underwood MJ, Rosen S, Engås A, Eriksen E - PLoS ONE (2014)

Bottom Line: The system showed potential for measuring the length of small organisms and also recorded the vertical and horizontal positions where individuals were imaged.Young-of-the-year fish were difficult to identify when passing the camera at maximum range and to quantify during high densities.This study suggests modifications to the Deep Vision and the trawl to increase our understanding of the population dynamics.

View Article: PubMed Central - PubMed

Affiliation: Institute of Marine Research, Bergen, Norway; Department of Biology, University of Bergen, Bergen, Norway.

ABSTRACT
Ecosystem surveys are carried out annually in the Barents Sea by Russia and Norway to monitor the spatial distribution of ecosystem components and to study population dynamics. One component of the survey is mapping the upper pelagic zone using a trawl towed at several depths. However, the current technique with a single codend does not provide fine-scale spatial data needed to directly study species overlaps. An in-trawl camera system, Deep Vision, was mounted in front of the codend in order to acquire continuous images of all organisms passing. It was possible to identify and quantify of most young-of-the-year fish (e.g. Gadus morhua, Boreogadus saida and Reinhardtius hippoglossoides) and zooplankton, including Ctenophora, which are usually damaged in the codend. The system showed potential for measuring the length of small organisms and also recorded the vertical and horizontal positions where individuals were imaged. Young-of-the-year fish were difficult to identify when passing the camera at maximum range and to quantify during high densities. In addition, a large number of fish with damaged opercula were observed passing the Deep Vision camera during heaving; suggesting individuals had become entangled in meshes farther forward in the trawl. This indicates that unknown numbers of fish are probably lost in forward sections of the trawl and that the heaving procedure may influence the number of fish entering the codend, with implications for abundance indices and understanding population dynamics. This study suggests modifications to the Deep Vision and the trawl to increase our understanding of the population dynamics.

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Related in: MedlinePlus

Schematic representation of the (A) net mouth geometry and (B) headline depth.The black line indicates the headline depth for haul 04, while the grey line indicates the headline depth for haul 06. The dashed line shows the stepwise protocol for BESS. The shaded areas under the dashed line indicate the height of the trawl mouth opening and the depths surveyed.
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pone-0112304-g003: Schematic representation of the (A) net mouth geometry and (B) headline depth.The black line indicates the headline depth for haul 04, while the grey line indicates the headline depth for haul 06. The dashed line shows the stepwise protocol for BESS. The shaded areas under the dashed line indicate the height of the trawl mouth opening and the depths surveyed.

Mentions: The depth sensor showed that the path of the trawl in the water column deviated from the survey protocol (Fig. 3). Measurements of the trawl geometry also showed that the vertical opening and wing spread changed with depth. The vertical opening of the trawl diminished from approximately 16 to 10 m with the headline at 0 m and 40 m respectively, while the corresponding wingspread measurements increased from approximately 25 to 29 m.


Deep vision: an in-trawl stereo camera makes a step forward in monitoring the pelagic community.

Underwood MJ, Rosen S, Engås A, Eriksen E - PLoS ONE (2014)

Schematic representation of the (A) net mouth geometry and (B) headline depth.The black line indicates the headline depth for haul 04, while the grey line indicates the headline depth for haul 06. The dashed line shows the stepwise protocol for BESS. The shaded areas under the dashed line indicate the height of the trawl mouth opening and the depths surveyed.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230979&req=5

pone-0112304-g003: Schematic representation of the (A) net mouth geometry and (B) headline depth.The black line indicates the headline depth for haul 04, while the grey line indicates the headline depth for haul 06. The dashed line shows the stepwise protocol for BESS. The shaded areas under the dashed line indicate the height of the trawl mouth opening and the depths surveyed.
Mentions: The depth sensor showed that the path of the trawl in the water column deviated from the survey protocol (Fig. 3). Measurements of the trawl geometry also showed that the vertical opening and wing spread changed with depth. The vertical opening of the trawl diminished from approximately 16 to 10 m with the headline at 0 m and 40 m respectively, while the corresponding wingspread measurements increased from approximately 25 to 29 m.

Bottom Line: The system showed potential for measuring the length of small organisms and also recorded the vertical and horizontal positions where individuals were imaged.Young-of-the-year fish were difficult to identify when passing the camera at maximum range and to quantify during high densities.This study suggests modifications to the Deep Vision and the trawl to increase our understanding of the population dynamics.

View Article: PubMed Central - PubMed

Affiliation: Institute of Marine Research, Bergen, Norway; Department of Biology, University of Bergen, Bergen, Norway.

ABSTRACT
Ecosystem surveys are carried out annually in the Barents Sea by Russia and Norway to monitor the spatial distribution of ecosystem components and to study population dynamics. One component of the survey is mapping the upper pelagic zone using a trawl towed at several depths. However, the current technique with a single codend does not provide fine-scale spatial data needed to directly study species overlaps. An in-trawl camera system, Deep Vision, was mounted in front of the codend in order to acquire continuous images of all organisms passing. It was possible to identify and quantify of most young-of-the-year fish (e.g. Gadus morhua, Boreogadus saida and Reinhardtius hippoglossoides) and zooplankton, including Ctenophora, which are usually damaged in the codend. The system showed potential for measuring the length of small organisms and also recorded the vertical and horizontal positions where individuals were imaged. Young-of-the-year fish were difficult to identify when passing the camera at maximum range and to quantify during high densities. In addition, a large number of fish with damaged opercula were observed passing the Deep Vision camera during heaving; suggesting individuals had become entangled in meshes farther forward in the trawl. This indicates that unknown numbers of fish are probably lost in forward sections of the trawl and that the heaving procedure may influence the number of fish entering the codend, with implications for abundance indices and understanding population dynamics. This study suggests modifications to the Deep Vision and the trawl to increase our understanding of the population dynamics.

Show MeSH
Related in: MedlinePlus