Northwest Fisheries Science Center

The Main Deck

Acoustic and trawl adventures in the Northeast Pacific

This portal tracks the research and sea-going activities of the Fisheries Engineering and Acoustic Technologies (FEAT) Team from NOAA¿s Northwest Fisheries Science Center.  Follow us as we use acoustics, trawling, and oceanographic sampling to learn about the Northeast Pacific Ocean.

Back deck of Bell M. Shimada
Acoustic echogram of hake
trawl catch
 

Watching while we fish

By Sandy Parker-Stetter
January 20, 2016


Cartoon image of a midwater trawl catching fish (Source: https://teacheratsea.files.wordpress.com/2012/08/trawl-net.jpg)

An important part of the winter survey sampling is our ability to verify that fish we see on the echograms are indeed Pacific hake. We do this using a “midwater trawl,” a large fishing net that the Shimada pulls through the water. Using a sonar system, we’re able to monitor how deep the net is below the surface and get a sense of whether a lot, or very few, fish are going in. We’re interested in the latter because we want a sample that is just large enough to collect the information we need.

Image from sonar used to monitor the net during fishing, showing the opening of the net and the sneaky fish below us! (Photo credit: Phil Manougian)

Before the midwater trawl reaches our “target depth,” it filters a lot of water, potentially catching other fish or invertebrates (like squid or jellyfish) on the way down.Critters can also be caught as the net is hauled back up to the ship. To give us a way to tell whether something unusual was caught in with our hake, or whether it came into the net on the way up or down, we strap a camera inside a waterproof housing and light system onto the net. Although we can’t see the video in real-time, we can replay it once the trawl is back on board.

A King-of-the-salmon caught during summer 2015 (Photo credit Sandy Parker-Stetter)

During a recent trawl, we caught a “King-of-the-salmon” (Trachipterus altivelis, http://www.fishbase.org/summary/3264). These “ribbonfish” can be found as deep as 900 m! Fish of the size in the photo can eat krill, squid, and small fishes – which might explain why we catch them deep down in the acoustic layer that contains small lanternfish.Watching the King-of-the-salmon swim in this video provides a rare glimpse of this fish in action.

Sandy

 

 

 

 

Video credit NWFSC/FRAM/FEAT

Tagged: Winter hake survey

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