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Midwater Trawls

Jul 12, 2011 | Gulf of Alaska Project | 0 comments

by Jamal Moss from the Northwest Explorer 


This morning we performed a mid-water trawl immediately after the first surface trawl of the day. Our goal was to sample a layer of acoustic targets at 200m. We have observed this layer consistently in the deeper portions of the survey. The included echogram shows 10 miles of our transect as the shelf drops off into the abyss. The ship’s acoustic sensors transmit sound energy and receive reflected energy from targets with a density difference from water. We sample what we see on our screen to find out what species compose the target. Several small targets close together could look like a larger target, so we measure what we catch in the net to give us an idea of how many targets we could be looking at on the sounder. We caught lanternfish (myctophids) of about 5cm and not much else in this tow.


https://www.nprb.org/assets/images/uploads/blog/lanternfish_n_chart.jpg

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