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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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Schematic representations of the Deep Vision frame and trawl section.
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pone-0112304-g001: Schematic representations of the Deep Vision frame and trawl section.

Mentions: Deep Vision observations were carried out during standard sampling hauls on the BESS inside the Isfjord and Billefjord areas at Svalbard in August 2012 with RV “Johan Hjort”. The trawl was towed at three depths (with the headline at 0, 20 and 40 m) for 0.5 nautical miles each, at a speed over ground of 3 knots [6]. The survey uses a pelagic standard sampling trawl for young-of-the-year fish [Harstad sampling trawl; 8]. The four panel trawl consists of seven sections with mesh sizes ranging from 200 mm in the front of the trawl to 8 mm in the codend [13]. The Deep Vision section was attached to the trawl between the extension and the codend (Fig. 1). The trawl dimensions (i.e. vertical opening of the net mouth, wing spread and depth of the headline) were measured with acoustic trawl instrumentations (SCANMAR AS, Åsgårdstrand, Norway). The catch was measured using the BESS standard biological sampling procedure [14]. Images from Deep Vision were analysed post-cruise.


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 representations of the Deep Vision frame and trawl section.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0112304-g001: Schematic representations of the Deep Vision frame and trawl section.
Mentions: Deep Vision observations were carried out during standard sampling hauls on the BESS inside the Isfjord and Billefjord areas at Svalbard in August 2012 with RV “Johan Hjort”. The trawl was towed at three depths (with the headline at 0, 20 and 40 m) for 0.5 nautical miles each, at a speed over ground of 3 knots [6]. The survey uses a pelagic standard sampling trawl for young-of-the-year fish [Harstad sampling trawl; 8]. The four panel trawl consists of seven sections with mesh sizes ranging from 200 mm in the front of the trawl to 8 mm in the codend [13]. The Deep Vision section was attached to the trawl between the extension and the codend (Fig. 1). The trawl dimensions (i.e. vertical opening of the net mouth, wing spread and depth of the headline) were measured with acoustic trawl instrumentations (SCANMAR AS, Åsgårdstrand, Norway). The catch was measured using the BESS standard biological sampling procedure [14]. Images from Deep Vision were analysed post-cruise.

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