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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

Species distribution and abundance throughout haul 04.Species include polar cod (Boreogadus saida), shanny family (Stichaeidae), Northeast Arctic cod (Gadus morhua) and krill (Thysanoessa spp.).
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pone-0112304-g005: Species distribution and abundance throughout haul 04.Species include polar cod (Boreogadus saida), shanny family (Stichaeidae), Northeast Arctic cod (Gadus morhua) and krill (Thysanoessa spp.).

Mentions: Individuals were observed at all the depth layers during the standard 30-minute towing time, with most species increasing in number down to 30 m and then decreasing at greater depths (Fig. 4). However, numbers of Northeast Arctic cod and krill continued to increase as the depth increased. Species were observed to enter the codend in patches and with other species during haul 04 (Fig. 5). Polar cod and shannies were observed together at all depths throughout haul 04. A large number of polar cod and Greenland halibut were observed to pass the camera when the trawl was at the surface during heaving with up to 35% of polar cod and 80% of Greenland halibut passing outside of the designated 30-minute trawling time (Fig. 6). During heaving, when the trawl was already at the surface, more than 280 polar cod per second passed the Deep Vision system, with individuals moving ahead (towards the trawl entrance) in patches for short periods of time before re-entering the field of view. This made it difficult to quantify young-of-the-year fish during heaving when high densities and turbulent flow were observed. Counts from the images may therefore be underestimates. Individuals of all species were observed entering the codend in groups during heaving (at the surface) and some were seen to have damaged opercula.


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)

Species distribution and abundance throughout haul 04.Species include polar cod (Boreogadus saida), shanny family (Stichaeidae), Northeast Arctic cod (Gadus morhua) and krill (Thysanoessa spp.).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0112304-g005: Species distribution and abundance throughout haul 04.Species include polar cod (Boreogadus saida), shanny family (Stichaeidae), Northeast Arctic cod (Gadus morhua) and krill (Thysanoessa spp.).
Mentions: Individuals were observed at all the depth layers during the standard 30-minute towing time, with most species increasing in number down to 30 m and then decreasing at greater depths (Fig. 4). However, numbers of Northeast Arctic cod and krill continued to increase as the depth increased. Species were observed to enter the codend in patches and with other species during haul 04 (Fig. 5). Polar cod and shannies were observed together at all depths throughout haul 04. A large number of polar cod and Greenland halibut were observed to pass the camera when the trawl was at the surface during heaving with up to 35% of polar cod and 80% of Greenland halibut passing outside of the designated 30-minute trawling time (Fig. 6). During heaving, when the trawl was already at the surface, more than 280 polar cod per second passed the Deep Vision system, with individuals moving ahead (towards the trawl entrance) in patches for short periods of time before re-entering the field of view. This made it difficult to quantify young-of-the-year fish during heaving when high densities and turbulent flow were observed. Counts from the images may therefore be underestimates. Individuals of all species were observed entering the codend in groups during heaving (at the surface) and some were seen to have damaged opercula.

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