Amanda Peretich: Trawling for Fish, July 4, 2012


NOAA Teacher at Sea
Amanda Peretich
Aboard Oscar Dyson
June 30, 2012 – July 18 2012

Mission: Pollock Survey
Geographical area of cruise:
Bering Sea
Date:
July 4, 2012

Location Data
Latitude: 56ºN
Longitude: 170ºW
Ship speed: 12.5 knots (14.4 mph)

Weather Data from the Bridge
Air temperature: 7.3ºC (45.1ºF)
Surface water temperature: 5.8ºC (42.4ºF)
Wind speed: 7 knots (8.1 mph)
Wind direction: 280.8ºT
Barometric pressure: 1011.5 millibar (1.0 atm, 758.6 mmHg)

Science and Technology Log
For those that know me, I like to press snooze on my alarm clock. A lot. So this whole being in the acoustics lab at 0400 has been pretty hard for me, but I haven’t been late yet (knock on wood). On July 3rd, I was a little snooze-happy and didn’t climb out of bed until 0355. Now, I could have showered and been a little late down to the lab, but I’m so glad I decided to forgo smelling good in order to not be late. The night shift was processing our first trawl to catch fish and I was lucky enough to catch the “tail” end of it. We had three more fish trawls during my shift yesterday, too!

Stern View

View of the stern (back) of the Oscar Dyson, showing both trawl nets: midwater trawl on right, bottom trawl on left

So what exactly is a trawl? Trawling is used in fishing when you pull a net in the water behind a ship, with the net itself being called the trawl. There are two main types of trawling, based on where the net is located in the water column:
* bottom (or benthic) trawling – the net is towed along the ocean floor
* midwater (or pelagic) trawling – the net is towed above the benthic zone

Bottom trawling can have various negative impacts on the environment, most notably the fact that the trawl disturbs seabed habitats. It can also remix sediments with the water column so if there were any pollutants (like DDT) that had settled to the bottom, they could make their way back into the food chain and into the food we eat. However, there are also many positive things to be learned from bottom trawling, and it is necessary in scientific investigations. Some of the scientific research in this field involves adjusting various factors on the trawl to minimize habitat disturbance.

On the Oscar Dyson, the ship is large enough to have reels for both a bottom and a midwater net. The bottom net is called the 83-112 (83 ft headrope and 112 ft footrope) and the midwater net is called the AWT (Aleutian Wing Trawl). One of the side research projects that has been going on here: adjustments on a bottom trawl to allow for midwater fishing.

A basic trawl net looks like this:

Trawl Net

This is what a trawl net looks like!

The trawl doors help keep the net open at the front when the net is in the water and there are floats on the top of the net along with the headline and there can be weights on the bottom of the net along with the foot rope. There are other things attached to the net to collect data, such as something that knows how deep the fishing occurred and at what temperature and another device that measures the amount of light.

The chief scientist will be watching various things on the computer screens in the acoustic lab (more on this later) to know when they should put the net in the water. He will relay this information to the people on the bridge that will then have the deck crew get ready to fish. There has to be plenty of good communication onboard, that’s for sure! The chief scientist then goes up to the bridge and analyzes more screens to determine when he thinks we have caught enough fish to reel in the net and begin processing.

There are 7 main objectives for the Oscar Dyson DY1207 cruise, which is also how scientific research works – there is more than one “project” going on at a time to maximize productivity. These objectives are:

1. collect acoustic data and trawl data necessary to determine the distribution, biomass, and biological composition of walleye Pollock and other scatterers
2. calibrate the ER60 and ME70 acoustic systems
3. collect target strength data using hull-mounted transducers or a lowered transducer for use in scaling echo integration data to estimates of absolute abundance
4. collect physical oceanographic data (temperature, salinity, fluorescence, and oxygen profiles with associated water samples), and continuously collect sea surface temperature, salinity, fluorescence, and oxygen data with associated water samples
5. collect data on fish distributions and school characteristics using ME70 multi-beam echosounder
6. collect light intensity and penetration data
7. conduct midwater trawl and bottom trawl comparisons

When we go “fishing” we are working on the first objective most of the time. Why is this pollock survey even important? The data from this survey allows managers to adjust the amount of Alaskan pollock (or other types of fish from other surveys) that commercial fisherman can harvest without overfishing. This helps ensure the viability of pollock fishing for future generations. Check out this great article as NOAA scientists kick off surveys to collect data vital to success of Alaska’s fisheries!

Here’s a little video to walk through what happens in the fish lab to process the fish and collect data:

Personal Log

Rare sunny day in the Bering Sea

It’s a rare beautiful sunny day in the Bering Sea for the Fourth of July

I am lucky enough to be able to say I’m spending Fourth of July in the middle of the Bering Sea with some pretty great people! Last night was probably the roughest seas we’ve had so far, and lucky for me, I had taken some Dramamine right before heading to sleep because I still wasn’t feeling 100% myself. I was sliding around all over my bed and at one point thought we had gone headfirst into the water. Apparently this isn’t even really bad weather, so I’m definitely glad that I’m on a summer cruise with calmer waters.

Today the sun finally came out (I haven’t seen it since we were back in Dutch Harbor), and I was able to get a nice “Alaskan tan” (and a quick nap) on my face and hands up on the flying bridge with ENS Chelsea Frate for a little bit.

Flying Bridge Naptime

Enjoying a quick nap in the rare sunshine on the flying bridge of the Oscar Dyson

So far there are some things I’ve found challenging on board:
* showering (those handles are in there for a reason!)
* passing up on any of the delicious food (making the following thing difficult as well)
* using the treadmill (elliptical – ok, bike – ok, stair stepper – ok, treadmill – are you kidding me?!)
* staying awake during movies in the lounge off shift – those couches are just so comfy!

Animal Love
We caught a few extra critters in our fish trawl this morning, so here they are:
* Rock sole (Lepidopsetta bilineata), normally found in the benthic zone

Rock sole

This is a rock sole fish, which is a type of flatfish.

* Yellow Irish lord (Hemilepidotus jordani)

Yellow Irish lord

This is a Yellow Irish lord fish

* Pacific herring (Clupea pallasii)

Pacific herring

This is a Pacific herring

3 responses to “Amanda Peretich: Trawling for Fish, July 4, 2012

  1. I know how handy those handles are. Use them. That yellow fish is quite interesting, but i love the sole . Take care Terri

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