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
 

All stop - what is that?

By Sandy Parker-Stetter, NWFSC
Posted on February 8, 2017


Sometimes, even after surveying thousands of nautical miles of the ocean (on this trip, and over the years), we see something that piques our curiosity. If weather cooperates, and we have time, we stop and check it out. 

echogram
Echogram of shallow layer on (L to R) 18, 38, and 120 kHz. From 0-500 m below surface is shown (vertical) and a distance of 9 nmi (horizontal)

This morning, offshore of San Diego, was one of those times. The shallow layer was thick from the surface down to 100 m. What caught our interest (especially that of Chelsea and Chu) was the pattern across the frequencies – it was almost absent on the 18 kHz, very strong at 38 kHz, and then much weaker at 120 kHz. 

bongo samplelarval fish
Top: Sample from 333um bongo net. There are a lot of little eyes!
Bottom: Close up of larval fish from bongo net.
Both photos credit Parker-Stetter, NWFSC

We guessed that the layer was not fish given the frequency pattern, so opted to deploy the bongo net. This net has two 60-cm rings and 333 um (i.e. micrometers) mesh, so it’s good at catching small things. The bongo is lowered into the water and then towed toward the surface at a 45° angle. 

When the bongo tow on our mystery layer was done, we looked into the jar and saw lots of little eyes looking back – larval fish! Given their size, these fish likely hatched from eggs less than two weeks ago. In the close-up photo you can see the distinct dark band on the tail and fins and the dark pigment near the eyes. We’re pretty sure these are larval hake, but need to get confirmation from an ichthyoplankton (i.e. larval fish) specialist. 

The big question for us – if these are larval hake, where are the adults? 


Tagged: Hake, Acoustics, Winter hake research, FEAT, FRAM, Oceanography, Ecosystem, California Current Large Marine Ecosystem, CCLME, El Niño, La Niña, Climate

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See more blog entries:

July 2017
June 2017
February 2017
January 2017
February 2016
January 2016