Tag: acoustic survey

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Megan Woodward, July 5, 2009

NOAA Teacher at Sea
Megan Woodward 
Onboard NOAA Ship Oscar Dyson
July 1 – 18, 2009

Mission: Bering Sea Acoustic Trawl Survey
Geographical Area: Bering Sea/Dutch Harbor
Date: Tuesday, July 5, 2009

Weather/Location 
Position: N 58.37.239; W 171.05.968
Air Temp:  4.5-6.0 (deg C)
Water Temp:  4.94 (deg C)
Wind Speed: 16 knots
Weather: Overcast and rainy

This is the screen I use to get info about our ship’s location. The little white speck inside the red oval is our ship.
This is the screen I use to get info about our ship’s location. The little white speck inside the red oval is our ship.

Science and Technology Log 

We have been at sea now for almost five days in search of pollock. The fish had not been spotted on the lines we traveled on until today. We had the opportunity for our first pollock trawl around 02:00, and used the Methot net to bring in two zooplankton samples earlier in my shift. This was by far the most action yet.  I was eager and ready to see what the fishing process was all about. This log will focus on the zooplankton samples.

The Methot net was put in the water and lowered to the desired depth determined by watching the location of the acoustic return. After twenty minutes the net was brought back up and the catch was unloaded.  I was expecting a net full of euphausiids, but the critters were actually collected in a small container on the back end of the net.  The catch was brought into the fish lab and dumped into a bucket so we could separate the other organisms caught in the net (9 jellyfish and 23 tiny pollock in this case). Once the other fish had been removed, we took a sample (a ••• cup scoop) to weigh and count the euphausiids in the sample (sample is shown above). The rest of the catch was also weighed. 

There were 543 euphausiids in the scoop. The weight and number help estimate the amount of euphausiids in the entire catch. We repeated this process again a few hours later. The second sample had almost twice as many euphausiids, 13 jellyfish and fewer than 5 pollock.

The survey tech and skilled fishermen lower the Methot net into the water.
The survey tech and skilled fishermen lower the Methot net into the water.

Personal Log 

Until today, the fishing portion of this trip remained a mystery.  However, I was feeling a little sea sick, okay very sea sick, so it was probably a good thing. We encountered some VERY rough seas with sustained winds ranging from 30-40 knots and swells averaging 17 ft. Some of the swells were much larger; one was rumored to be almost 35 ft. high.  Apparently the rough seas are expected to return tonight and tomorrow. My sea legs are securely fastened, so I am ready to take on whatever the sea has to offer.

When we brought in the first haul of pollock last night, my eyes must have looked like they were going to roll out of my head.  I couldn’t believe how many fish were coming across the conveyor belt. This was what I had been waiting for, so I got on my rain gear and started sorting the fish.  Each species was placed into separate crates so a count of all fish caught could be taken.  Of course, pollock made up the majority of the catch.  In the next few weeks, I will become an expert member of the pollock survey team. Everyone on board, both scientists and crew, have been more than willing to answer my

A sample of zooplankton brought up in the Methot net. These are euphausiids, which are also referred to as krill.
A sample of zooplankton brought up in the Methot net. These are euphausiids, which are also referred to as krill.

Getting used to the 16:00-04:00 (4pm4am) shift has been trying.  Today’s shift was the first that didn’t require a nap.  Due to the odd shift hours, I’ve been waking up at 14:00 (2 pm) and going to bed around 05:00 (5 am).  This makes mealtime tricky.  Dinner is served first, then I eat some breakfast in the middle of the night. My body is thoroughly confused. The ship’s cooks are wonderful, and continually provide a stocked mess hall with loads of choices.  I swear the dessert bar is continually whispering my name. I couldn’t ask for a more kind, welcoming group of people to work questions. One part of this adventure I’m looking forward to is getting to know the wide range of characters who make this important research possible.

It was certainly a thrill to see the first whale of the trip. The pod was spotted just off the bow of the ship andlater seen in the distance.
It was certainly a thrill to see the first whale of the trip. The pod was spotted just off the bow of the ship andlater seen in the distance.

Animals Seen 

  • Fin Whale
  • Jelly Fish
  • Flathead Sole
  • Northern Flathead Sole
  • Arrow tooth Flounder
  • Pollock
  • Yellow Irish Lord
  • Euphausiids

New Vocabulary 

Zooplankton– A very small or microscopic animal organisms possessing little or no power of locomotion (can’t move themselves), leaving them to merely drift or float in the water.

Euphausiids (eu·phau·si·id) – A type of zooplankton, also known as krill, are tiny shrimp-like crustaceans that form an important part in the diet of many animals including whales, seals, fishes and birds. These are the main food source for pollock.

Methot Net  – Methot is the name of the man who designed the style of plankton net we used to catch the euphausiids.

One of several jellyfish brought up in the nets. This guy is slimy and heavy, but not a stinger
One of several jellyfish brought up in the nets. This guy is slimy and heavy, but not a stinger 
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Megan Woodward, July 1, 2009

NOAA Teacher at Sea
Megan Woodward 
Onboard NOAA Ship Oscar Dyson
July 1 – 18, 2009

Mission: Bering Sea Acoustic Trawl Survey
Geographical Area: Bering Sea/Dutch Harbor
Date: Tuesday, July 1, 2009

Science and Technology Log 

What is this trip all about?  Well, NOAA is working to collect a range of pollock fish samples from across the Bering Sea.  The samples collected will help set fishing regulations based on the estimated pollock fish population.  The fish are looked at to assess the male to female ratio, size and age.

Pollock, a member of the cod family, are mainly found in the Bering Sea. They are typically found between 328 to 984 feet depths. Pollock lives up to 17 years, and reach maturity around age 4. The maximum size of the pollock is slightly larger then 3 feet long.

The colors in the picture at right indicate the amount of return received from the 3 spheres seen towards the top. The other mass of colors at the bottom and surrounding the lines are fish, which are interfering with the read.
The colors in the picture at right indicate the amount of return from the 3 spheres seen towards the top. The other mass of colors at the bottom and surrounding the lines are fish, which are interfering with the read.

We are currently preparing to set sail.  Departure time is set for 15:00 (3:00 pm).  Our first anchoring will take place just a few hundred feet from where we are docked in Dutch Harbor.  At that time, the Chief Scientist and other members of the science team will calibrate (check the accuracy) the echo sound system used during the course of the survey.  Once the calibration is complete and the data is collected, we will continue to sail in search of pollock fish.

The echo sound system is used to measure the amount of return or “back scatter” from a ping (term to describe the sound sent down into the ocean).  Depending on the size of the return, the scientists are able to determine if they are detecting fish.  Pollock are known to give a return within a specific range, which provides the scientists with one of the clues that help them make an educated guess about the type of fish being detected.

In order to calibrate the echo sound system, three metal spheres that have an expected return level are lowered into the sea.  A ping is sent into the open sea, and the scientists are able to watch the amount of return from the spheres through their computer.  The amount of return can be seen using a color-coded scale. Red shows the highest level of return, and gray is the color indicating very little return. The scientists can then see if each sphere is giving the expected return. If a sphere is giving off more or less than the expected return, the scientists then know how to adjust the level of return they are getting from fish throughout the project.

Eagle or seagull? This guy sits and waits for a food meal on top of the hotel dumpster.
Eagle or seagull? This guy sits and waits for a food meal on top of the hotel dumpster.

Personal Log 

After a day and a half in Dutch Harbor, I’m glad to finally be getting under way.  Dutch Harbor is a small, small town.  There are a few restaurants, one hotel and a Safeway.  All of the other businesses are linked to the fishing industry in one-way or another. Flying into the island was an incredible experience. The plane hummed through the air between multiple tiny landforms.  The airport runway stretches out to the edge of the sea, allowing the passengers to think, for just one moment, they are making a water landing. The plane touched down just beyond the shore.

Since my arrival, I have been welcomed with warmth from all of the NOAA scientists and deck crew. Everyone has been more than wiling to answer even the most ridiculous of questions I’ve had. My time the past two evenings were spent getting to know several of the Oscar Dyson officers and crew members.  

A good chunk of Monday was spent hiking Ballyhoo with two of the officers from the ship.  Ballyhoo is a steep hill behind the airport (approx 1400 ft. elevation). The hill was littered with WWII shelters.  As we tromped up the hill, the wind began to pick up. By the time we were nearing the top, the wind was practically knocking me sideways.  The gusts were sustained and powerful. Certainly some of the windiest conditions I’ve encountered. The wildflowers growing on the hillside were reminiscent of the summer blooms found on Mount Rainier. The views from the top were breathtaking.  Several bald eagles swooped past the emerald hills, and the sun started to peak out as we made our way back to sea level.

Animals Seen in Dutch Harbor 

  • Ground Squirrel
  • Jelly Fish
  • Bald Eagles
  • Variety of Seabirds
  • Arctic Fox
  • Guard dog
This little ground squirrel wasn’t bothered as we walked by.
This little ground squirrel wasn’t bothered as we walked by.

New Vocabulary 

Echo Sound System – A tool used to measure the return or “back scatter” from a ping.  The amount of return helps determine what is hiding under the sea.

Ping – The name of the sound that is sent into the water to create an echo/return for the scientists to read. The ping is a constant, repeated sound wave.  Several different frequencies are used to detect objects.

Return  – AKA back scatter, is the amount of acoustic sound waves/echo bouncing back off an object beneath the water.

Trawl – The phrase used when talking about catching fish using a large net