Caitlin Thompson: Bottom Trawl, August 11, 2011


NOAA Teacher at Sea
Caitlin Thompson
Aboard NOAA Ship Bell M. Shimada
August 1 — 14, 2011

Mission: Pacific Hake Survey
Geographical Area: Pacific Ocean off the Oregon and Washington Coasts
Date: August 12, 2011

Weather Data from the Bridge

Lat. 48 degrees 07.0 N
Long. 125 degrees 13.7 W
Present weather: partly cloudy 6/8
Visibility: 10 n.m.
Wind direction: 335
Speed 10 kts
Sea wave height: 2-3 feet
Swell waves – direction: —
Swell waves – height: —
Sea water temperature: 15.0 degrees C
Sea level pressure: 1017.3 mb
Temperature – dry bulb: 15.8 degrees C
Temperature – wet bulb: 13.2 degrees C

Science and Technology Log

Third Wire FS70

The Third Wire FS70 provides an image of the net, shown as half circle, and the fish around it.

The big news is that we’re headed to port a day early. There was a electrical component failure in the engine system that converts the diesel power to electricity which powers the electrical motors that turn the propeller shaft. This reduced the Shimada to running on about half power. I can’t believe the cruise is ending!

Yesterday we did a bottom trawl, the first bottom trawl ever conducted on the Shimada. Using the sonars, the scientists on the sonar team saw an interesting aggregation of fish. They couldn’t use the usual mid-water net, which is relatively easy to damage, because the fish were very close to the bottom. Besides, the bottom appeared hard and rocky. I was excited when they decided to test the new net. Unlike the mid-water trawls, which usually bring up a mostly “clean” haul of hake, a bottom trawl tends to bring up a wide array of species. I wanted to learn some new names.

ITI

The ITI shows the distance of the bottom of the ocean from the net. Where the pink lines are highest, the net is lowest.

Deploying the bottom net proved educational. The mid-water net is sent down with the FS70 attached, which provides an image of the objects near and in the net. On the screen shot of the FS70 above and to the right, look for the half-circle, which shows the open net, the silver blue line under the net, which is the bottom of the ocean, and some dots inside the net that are most likely fish already caught in the net. The images are sent through a wire. It would be too easy to damage the wire in a bottom trawl, so the scientists use the ITI instead.

Larry was in charge of fishing today and was disatisfied with the image the ITI System produced of the bottom trawl. The ITI does not produce as good an image of the bottom trawl as the FS 70 did on the midwater trawl. This made it more difficult to decide how much was being caught and how long to fish. The scientists began planning how to get a better system for the ship.

The bottom trawl disappointed the scientists because it brought up fewer hake than they had hoped, but I was happy to see so many new kinds of fish, and to learn to identify many so that I could help sort. This is the list of everything we pulled up:

Ratfish

This spotted ratfish has a venomous spine on its dorsel fin!

Aspot prawn, full of eggs

A spot prawn, full of eggs

Rockfish

Larry, Alicia and I sort rockfish. Initially, the fish on the table looked the same to me, but I soon learned to identify ...

Rex sole

Rex sole

Arrowtooth flounder
Brown cat shark egg case
Cloud sponges
Darkblotched rockfish
Dover sole
Greenstriped rockfish
Hermit crab unident.
Lanternfish unident.
Long honred decorator crab
Longnose skate
Pacific hake
Pacific ocean perch
Pom pom anemonome
Redbanded rockfish
Rex sole
Rosethorn rockfish
Sablefish
Sea cucumber unident.
Sea urchins and sand dollars unident.
Sharpchin rockfish
Shortspine thornyhead
Skate egg case ulnident.
Slender sole
Snail unident.
Spot prawn
Spotted ratfish
Wattled eelpout

Personal Log

Last night, some of us went up to the fly bridge in hopes of seeing the Perseid Meteor Shower. The sky was miraculously clear but the nearly full moon and bright lights on the ship blocked out most of the stars. Still, we saw some truly magnificent shooting stars before the clouds rolled in. I had brought my sleeping bag for warmth and fell fast asleep to the soothing voices of my shipmates. When they woke me up, I dropped by the chemistry lab to see how the nighttime zooplankton sampling was going and discovered that a mallard had arrived on deck. Mallards are not sea birds and are not equipped to be so far out to sea, so we were highly surprised to see her some fifty nautical miles off land. We named her Myrtle. We gave Myrtle food and water and hoped she would stay with the ship until we were close to land, but after a long nap, she took off. I hope she makes it to land.

In cribbage news, I won the semi-finals but lost the championship game. I had such a great time playing.

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