walleye pollock – Page 2 – NOAA Teacher at Sea Blog

August 9, 2013March 12, 2021

Julia Harvey: Calibration in Sea-Otterless Sea Otter Bay, August 7, 2013

NOAA Teacher at Sea
Julia Harvey
Aboard NOAA Ship Oscar Dyson (NOAA Ship Tracker)
July 22 – August 10, 2013

Mission: Walleye Pollock Survey
Geographical Area of Cruise: Gulf of Alaska
Date: 8/7/13

Weather Data from the Bridge (as of 21:00 Alaska Time):
Wind Speed: 10.42 knots
Temperature: 13.6 C
Humidity: 83%
Barometric Pressure: 1012.4 mb

Current Weather: A high pressure system is building in the east and the swells will increase to 8 ft tonight.

Science and Technology Log:

Before I begin, I must thank Paul for educating me on the calibration process. Because calibration occurred during the day shift, I was not awake for some of it.

The EK60 is a critical instrument for the pollock survey. The calculations from the acoustic backscatter are what determines when and where the scientists will fish. Also these measurements of backscatter are what are used, along with the estimates of size and species composition from the trawling, to estimate fish biomass in this survey. If the instruments are not calibrated then the data collected would possibly be unreliable.

Calibration of the transducers is done twice during the summer survey. It was done before leg one in June, which began out of Dutch Harbor, and again now near Yakutat as we end leg three and wrap up the 2013 survey.

As we entered Monti Bay last night, Paul observed lots of fish in the echosounder. This could pose a problem during calibrations. The backscatter from the fish would interfere with the returns from the spheres. Fortunately fish tend to migrate lower in the water column during the day when calibrations were scheduled.

This morning the Oscar Dyson moved from Monti Bay, where we stopped last night, into Sea Otter Bay and anchored up. The boat needs to be as still as possible for the calibrations to be successful.

Monti and Sea Otter Bays Map by GoogleEarth — Monti and Sea Otter Bays
Map by GoogleEarth

Calibration involves using small metal spheres made either of copper or tungsten carbide.

Chief Scientist Patrick Ressler with a tungsten carbide sphere

Copper sphere photo courtesy Richard Chewning (TAS) — Copper sphere
photo courtesy Richard Chewning (TAS)

The spheres are placed in the water under transducers. The sphere is attached to the boat in three places so that the sphere can be adjusted for depth and location. The sphere is moved throughout the beam area and pings are reflected. This backscatter (return) is recorded. The scientists know what the strength of the echo should be for this known metal. If there is a significant difference, then data will need to be processed for this difference.

The 38 khz transducer is the important one for identifying pollock. A tungsten carbide sphere was used for its calibration. Below shows the backscatter during calibration, an excellent backscatter plot.

The return for this sphere was expected to be -42.2 decibels at the temperature, salinity and depth of the calibration The actual return was -42.6 decibels. This was good news for the scientists. This difference was deemed to be insignificant.

Personal Log:

Calibration took all of the day and we finally departed at 4:30 pm. The views were breathtaking. My camera doesn’t do it justice. Paul and Darin got some truly magnificent shots.

As we left Yakutat Bay, I finally saw a handful of sea otters. They were never close enough for a good shot. They would also dive when we would get close. As we were leaving, we were able to approach Hubbard Glacier, another breathtaking sight. Despite the chill in the air, we stayed on top getting picture after picture. I think hundreds of photos were snapped this evening.

Location of Hubbard Glacier. Map from brentonwhite.com

Many came out in the cool air to check out Hubbard Glacier

Lots of ice from the glacier as we neared

Nearby Hubbard Glacier with no snow or ice — Near Hubbard Glacier

Did You Know?

According to the National Park Service, Hubbard Glacier is the largest tidewater glacier in North America. At the terminal face it is 600 feet tall. This terminal face that we saw was about 450 years old. Amazing!

Julia Harvey: Here Fishy Fishy/Prince William Sound, August 1, 2013

NOAA Teacher at Sea
Julia Harvey
Aboard NOAA Ship Oscar Dyson (NOAA Ship Tracker)
July 22 – August 10, 2013

Mission: Walleye Pollock Survey
Geographical Area of Cruise: Gulf of Alaska
Date: 8/1/13

Weather Data from the Bridge (as of 00:00 Alaska Time):
Wind Speed: 12 knots
Temperature: 13 C
Humidity: 97 %
Barometric Pressure: 1021 mb

Science and Technology Log:

The main goal of Leg 3 of this mission is to use acoustics and trawling to survey the mid-water portion of the pollock population along the Gulf of Alaska starting near Kodiak to Yakutat Bay.

Pollock live in the an area between the middle of the water column and the seafloor. Sometimes we sample the mid-water and sometimes we will sample the bottom.

bump-food-web_600 — Location of Fish in Water Column

The Oscar Dyson carries three different types of trawling nets for capturing fish as part of the mid-water survey: the Aleutian Wing Trawl (AWT), a mid-water trawl net, the Poly Nor’Eastern (PNE), for bottom trawls and the Methot, which is for gathering samples of very small ocean creatures such as krill. I will focus on the AWT, although some of the video footage is from a bottom trawl.

Scale model of the Aleutian Wing Trawl (AWT) net courtesy of NOAA Scientist Kresimir Williams

When the net is deployed from the ship, the first part of the net to hit the water is called the codend. This is where most of the fish end up after the trawl. The mesh size of the net is smallest at the codend (about 1 cm) and gets larger as it approaches the doors (about 1 m).

A Cam Trawl goes in the water next. This is a pair of cameras that help scientists identify and measure the fish that are caught in the net. This technology can also be used to help scientists validate their biomass estimate from trawling sampling counts. This piece of equipment has to be clipped into loops on the trawl each time.

The trawl camera is attached to the net to monitor the fish entering the net.

The next piece of the net to hit the water is the “kite” which is secured to the head rope. Here, a series of sensors is attached to help the scientists gather data about the condition of the net including depth, size, and shape underwater. The major acoustic sensor, called the “turtle,” can tell if the fish are actually going into the net.

AWT Net — Close-up view of the AWT scale model to highlight the kite and the turtle that ride at the top of the net. The third wire holds the electrical wires that send data from the turtle to the bridge (courtesy of Teacher at Sea).

Once the kite is deployed, a pair of tom weights (each weighing 250 lbs), are attached to the bridal cables to help separate the head rope from the foot rope and ensure the mouth of the net will open. Then, after a good length of cable is let out, the crew transfers the net from the net reel to the two tuna towers and attach the doors. The doors create drag to ensure the net mouth opens wide.

The scientists use acoustic data to determine at what depth they should fish, then the OOD (Officer on Deck) uses a scope table to determine how much cable to let out in order to reach our target depth. Adjustments to the depth of the head rope can be made by adjusting speed and/or adjusting the length of cable released.

The scientists use the acoustic data sent from the “turtle” to determine when enough fish are caught to have a scientifically viable sample size, then the entire net is hauled in.

Once on board, the crew uses a crane to lift the cod end over to the lift-table. The lift-table then dumps the catch into the fish lab where the fish get sorted on a conveyor belt.

Personal Log:

The Oscar Dyson needed to pick up materials for a net repair so we headed into Prince William Sound towards Valdez. The area was spectacular.

Julia Harvey — Here I am in Prince William Sound

The sun was out and the skies were blue for most of the day. Although we have had very calm seas, we have been under clouds for most of the last few days.

Enjoying the Sun — A handful of people gathered at the bow of the ship to enjoy the sun and the sights.

The absolute highlight of the day was spotting Dall porpoises and filming them bow surfing.

Here are snapshots of the day. The area was so impressive that I have several hundred pictures. Here are just a few:

Click here to learn more about the Columbia glacier and to watch the changes to the glacier over time.

I am reminded of the Exxon Valdez oil spill devastation.

Did You Know?

The Exxon Valdez (oil tanker) ran aground on Bligh Reef in Prince William Sound, Alaska on March 24, 1989.

The amount of oil spilled into this pristine environment exceeded 11 million gallons of crude oil and affected over 1300 miles of shoreline. According to OCEANA, as many as 2,800 sea otters, 300 harbor seals, 900 bald eagles and 250,000 seabirds died in the days following the disaster.

Jodi, who works the night shift with me, grew up in Cordova, Alaska and as a child remembers the smell of the disaster and the fears in her town (many were fishermen).

Has the area recovered? Part of the settlement with Exxon established a fund to support research. Read more.

July 31, 2013March 12, 2021

Julia Harvey: Listening to Fish/How I Spent My Shift, July 28, 2013

NOAA Teacher at Sea
Julia Harvey
Aboard NOAA Ship Oscar Dyson (NOAA Ship Tracker)
July 22 – August 10, 2013

Mission: Walleye Pollock Survey
Geographical Area of Cruise: Gulf of Alaska
Date: 7/28/13

Weather Data from the Bridge (as of 18:00 Alaska Time):
Wind Speed: 15.61 knots
Temperature: 13.71 C
Humidity: 91%
Barometric Pressure: 1023 mb

Science and Technology Log:

How do scientists use acoustics to locate pollock and other organisms?

Scientists aboard the NOAA Research Vessel Oscar Dyson use acoustics, to locate schools of fish before trawling. The Oscar Dyson has powerful, extremely sensitive, carefully calibrated, scientific acoustic instruments or “fish finders” including the five SIMRAD EK60 transducers located on the bottom of the centerboard.

Trnasducer — Scientists are using the EK60 to listen to the fish.

This “fish-finder” technology works when transducers emit a sound wave at a particular frequency and detect the sound wave bouncing back (the echo) at the same frequency. When the sound waves return from a school of fish, the strength of the returning echo helps determine how many fish are at that particular site.

The transducer sends out a signal and waits for the return echo... — The transducer sends out a signal and waits for the return echo…

Sound waves bounce or reflect off of fish and other creatures in the sea differently. Most fish reflect sound energy sent from the transducers because of their swim bladder<s, organs that fish use to stay buoyant in the water column.

The above picture shows the location of the swim bladder. (Photo courtesy of greatneck.k12.ny.us)

Click on this picture to see how sound travels from various ocean creatures through water. (Photo from sciencelearn.org)

These reflections of sound (echoes) are sent to computers which display the information in echograms. The reflections showing up on the computer screen are called backscatter. The backscatter is how we determine how dense the fish are in a particular school. Scientists take the backscatter that we measure from the transducers and divide that by the target strength for an individual and that gives the number of individuals that must be there to produce that amount of backscatter. For example, a hundred fish produce 100x more echo than a single fish. This information can be used to estimate the pollock population in the Gulf of Alaska.

The trawl data provide a sample from each school and allow the NOAA scientists to take a closer look by age, gender and species distribution. Basically, the trawl data verifies and validates the acoustics data. The acoustics data, combined with the validating biological data from the numerous individual trawls give scientists a very good estimate for the entire walleye pollock population in this location.

echogram for krill — These echograms are similar to the ones produced when we trawled for krill. Krill have a significant backscatter with the higher frequencies (bottom right screens)

Personal Log:

How I spent my shift on Saturday, July 27^th?

When I arrived at work at 4 pm, a decision was made to trawl for krill. A methot trawl is used to collect krill.

Then we set to work processing the catch. First we have to suit up in slime gear because the lab will get messy. My previous blog mentioned not wanting to count all of the krill in the Gulf of Alaska. But in this case we needed to count the krill and other species that were collected by the methot trawl.

Counting krill — I needed my reading glasses to count these small krill.

How many krill do you think we collected?

Krill Sample — This is the total krill from the first methot trawl of the night.
How many are here?

Patrick, the lead scientist, put a few specimens under the microscope so we could see the different types of krill.

The collection of krill was preserved in formaldehyde and sea water. It will be sent to Poland for further species diagnosis.

preserving krill — Scientist Darin Jones preserves the krill for shipment to Poland.

As the ship continued back on transect, I wandered in to see what Jodi and Darin were doing with the data collected last night. Jodi was processing data from the multibeam sonar and Darin was surveying the images from the drop camera. Jodi was very patient explaining what the data means. I will write more about that later. But I did feel quite accomplished as I realized my understanding was increasing.

multibeam data — These images are what Jodi was processing.

A decision was made to do another methot trawl. This time we had a huge sample.

In an approximately 50 gram sample we counted 602 individual krill. Compare this to the 1728 individuals in a 50 gram sample from the first trawl. They were much bigger this time. The total weight of the entire sample of krill was 3.584 kilograms.

How many individuals were collected in the second trawl? (Check your answer at the end of the blog)

Around midnight, Paul decided to verify an echogram by trawling.

trawl net haul — Emptying out the trawl net right next to the fish lab.

We collected data from the trawl net and the pocket net.

This trawl had a variety of specimen including Pacific Ocean perch, salmon, squid, eulachon, shrimp and pollock.

The pocket net catches the smaller organisms that escape through the trawl net.

pocket trawl — These were caught in the pocket net.

It was after 2 am by the time we had processed catch and washed down the lab. The internet was not available for the rest of my shift due to the ship’s position so I organized my growing collection of videos and pictures.

I wasn’t sure how I would handle my night shift (4 pm to 4 am) after I dozed off during the first night. Now that I have adjusted, I really enjoy the night shift. The night science team of Paul, Darin and Jodi are awesome.

Did You Know?

People who are on the Oscar Dyson live throughout the United States. They fly to meet the boat when they are assigned a cruise. Jodi is from Juneau, Alaska. Paul is from Seattle, Washington. And Darin is from Seattle/North Carolina. There are a number who are based out of Newport, Oregon.

Something to Think About:

When we are fishing, a number of birds gather behind the boat. What different sea birds are observable this time of the year in our survey area?

July 31, 2013March 12, 2021

Julia Harvey: Determining Population Size/A Day in My Life Cruising, July 27, 2013

NOAA Teacher at Sea
Julia Harvey
Aboard NOAA Ship Oscar Dyson (NOAA Ship Tracker)
July 22 – August 10, 2013

Mission: Walleye Pollock Survey
Geographical Area of Cruise: Gulf of Alaska
Date: 7/27/13

Weather Data from the Bridge (at 1:00 am Alaskan time):

Wind Speed = 3.52 knots
Air Temperature = 13.6 C
Humidity = 94%
Barometric Pressure = 1025.5 mb

Science and Technology Log:

How can you determine the population size of species?

You could count every member of the population. This would be the most accurate but what if the population moves around a lot? What if the population is enormous and requires too much time to count each and every one? Would you want to count all of the krill in the Gulf of Alaska?

You could mark and recapture. In this method you catch individuals from the population and tag them. Data are compiled from the recaptures and the population is mathematically calculated. Halibut and many other populations are monitored this way and require fishermen to report any recaptures.

Tagged Halibut
photo courtesy of Greenland Institute of Natural Resources

Another method is sampling. The organisms in a small area are counted and then the overall population in the entire area is calculated.

line_transect — Using a transect to sample a population.
Photo courtesy of http://www.kscience.co.uk/as/module5/succession/fieldwork.htm

This picture above illustrates the use of a transect line. On various increments along the transect line, samples of populations are taken. Imagine the Oscar Dyson’s path as the measuring tape and the trawl net as the sampling square.

The overall survey area of the pollock study this summer is the northern Gulf of Alaska between the shore and the continental break. Within this area transect lines were established. These are pathways that the Oscar Dyson will travel along and periodically take samples of the fish.

Transect Plan — The pollock summer survey is broken into three legs. I am part of leg 3.
Photo courtesy of NOAA

The current set of transects are 25 nautical miles (1 nautical mile is equal to 1 minute of latitude) apart and are parallel but transects in other areas may be 2 or 5 miles apart. Transects that we are following now are located on the shelf and are perpendicular to the coastline. Transects in inlets and bays may run differently and may even zigzag.

OD Current Cruise — Leg 3 left from Kodiak and is moving eastward for the survey.
Photo courtesy of NOAA

If fish are located through acoustics, the ship will break transect (a mark is made on the map) and the ship will circle around and a sample of the population is taken by trawling. The population of pollock can then be mathematical calculated. After trawling, the ship will return to the break and continue along the transect line.

This afternoon, we were working smaller transect lines near Amatuli Trench that were 6 miles apart. It is an area that has had good pollock catches. Just when we were going to fish, a pod of fin whales was spotted in the area. So we moved to another area and hauled in quite the catch of Pacific Ocean perch.

POP Haul — After fish are caught they are processed in the fish lab. Here we are processing the Pacific Ocean perch.

It is hopeful that the Oscar Dyson will finish a transect line by nightfall and then the ship can be at the next transect by sunrise. This maximizes the time looking for fish and trawling.

Personal Log:

I am settling into life on the Oscar Dyson and have established a routine that will support my night shift (4 pm to 4 am). So how do I spend 24 hours on the ship?

I wake up around 11:45 in the morning to be able to eat lunch that is served only between 11:00 and 12:00. Because of the shift schedules, some people are bound to miss one or more of the meals. I miss breakfast because I am sleeping. We are able to request a plate of food be saved for later.

Between the end of lunch and the start of my shift, there are several things that I can do. The weather has been very nice and so I often go on deck to soak up the sun and whale watch.

Whale watching — Can you spot the fin whales?

I may need to do laundry as my clothes start to smell fishy.

Laundry Room — We are lucky to have a laundry room on board. It meant I did not have to bring many clothes.

I will also workout in one of the two gyms. The gym at the back of the boat can’t be used when trawling because of the high noise level. There is a rower, two exercise bikes, two treadmills, a cross trainer, mats and weights. I got lucky and someone installed a makeshift pull up bar.

Front exercise room — This is the exercise room towards the bow of the ship.

Back Exercise Room — This is the exercise room toward the stern of the ship.

There is also a lounge where I can read or watch DVDs. Some of the movies are still in theaters.

An hour before my shift starts, I read and take a short nap. Then, I grab a cup of coffee at 4 pm as my shift starts. I listen as the day shift fills in the evening shift about the happenings of the last 12 hours.

During my shift, there are several things that I may do. If we have fished, there will be pollock and other organisms to process.

Processing pollock — Here Jodi, Kirsten and I are processing the pollock by determining their sex. Then, they will be measuresd weighed and their otoliths removed.

After processing, we need to clean up the fish lab which involves spraying down everything include ourselves with water to remove scales and slime.

I also keep an eye on the acoustic monitors, to see what I can recognize. Paul and Darin are always willing to answer my questions (even the ones I already asked).

Acoustics Screens — The four screens of acoustic data. From these screens, Paul will determine whether to fish.

I may look at trawl camera footage or observe camera drops. Drop Camera

I also have time to work on my blog.

Work Space — I have set myself up an area in the “Cave” to write my blog.

Dinner is served at 5 pm but the mess is always open and is filled with snacks such as sandwich fixings, ice cream, yoghurt, a salad bar and pop tarts.

Whenever I get hungry at night, I just head for the mess. It is a time that I am able to chat with the crew and NOAA Corps as they come in for snacks too.

At 4 am, I make it a point to head directly to my stateroom and go to sleep. The room has a window but I can close the curtains on the portlight (window) and around my bed.

There are no weekends out here. Everyone works 7 days a week for the duration of the cruise.

Did You Know?

Usually fin whales show only their back as they surface for air. Check out my video clip and see if you can spot the whale. It wasn’t too close.

July 24, 2013March 12, 2021

Julia Harvey: Yakutat or Bust, July 23, 2013

NOAA Teacher at Sea
Julia Harvey
Aboard NOAA Ship Oscar Dyson (NOAA Ship Tracker)
July 22 – August 10, 2013

Mission: Walleye Pollock Survey
Geographical Area of Cruise: Gulf of Alaska
Date: July 22, 2013

Weather Data from the Bridge: (7/23/13 at 11 pm)
Wind Speed = 13 knots
Air Temperature = 12.7 C
Humidity = 93%
Barometric Pressure = 1017 mb

Science and Technology Log:

There is a great deal of hope to complete the survey, which is supposed to end near Yakutat in the southeast of Alaska. It began near the islands of Four Mountains during leg 1. We are on leg 3, the final leg this summer. Leg 3 began in Kodiak. Three Legs of the Survey

Gulf of Alaska Map — Kodiak Island is the green marker and Yakutat Bay is the red.

The purpose of this cruise is to survey the walleye pollock (Theragra chalcogramma) in the Gulf of Alaska. Pollock is a significant fishery in the United States as well as the world. Pollock is processed into fish sticks, fish patties and imitation crab. Last year, about 3 million tons of pollock were caught in North Pacific. The scientists on board will collect data to determine the pollock biomass and age structure. These data are used with results from other independent surveys to establish the total allowable pollock catch.

According to the Alaska Fisheries Science Center, pollock can grow to about 3 ½ feet and weigh about 13 lbs. More typically the pollock are approximately 50 cm (20 in) and weigh .75 kg (1.7 lbs). They live in the water column and feed on krill, zooplankton and other crustaceans. As they age they will eat juvenile pollock and other small fishes such as capelin, eulachon and herring as well. Sexual maturity is reached around age 4. Spawning and fertilization occurs in the water column in early spring. The eggs stay in the water column and once hatched are part of the zooplankton until they are free swimming.

The general process used to catch the pollock involves multiple parts. I will break down those steps in a series of blogs. But basically, acoustics are used to locate fish in the water column. Once the scientists have located the fish along the transect (transects are the paths that the ship will travel on so the scientists can collect data), the Oscar Dyson sets out a trawl equipped with a camera. The trawl is brought in and data from the catch is documented. And then the ship continues on.

Trawling is usually completed only during daylight hours. Fortunately the sun does not set here in Alaska right now until after 10 pm. When it is dark, work aboard the Oscar Dyson continues. Jodi is documenting the sea floor with a drop camera. She is looking at life that is there as well as potential threats to the trawl nets for the bottom trawl surveys.

Questions:

How do scientists use acoustics to locate pollock?
How are the transects locations determined?
How are pollock and the rest of the catch processed?
What information is retrieved from the trawl camera?
What is a bottom trawl and how is it different from a mid-water trawl?

Personal Log:

We left Kodiak at 1 pm on July 22 heading southwest.

We had 8 hours of travel time before we would reach our first transect. But before we got too far away from Kodiak, we needed to practice the three drills for the safety of everyone. The fire drill and man overboard drill required me to report to the conference room and meet up with the rest of the science team. Patrick, the lead scientist, then reported that we were all accounted for. The crew had more complex tasks of deploying a small boat and retrieving “the man overboard”.

The other drill was the abandon ship drill. We are assigned to a lifeboat and I reported to my muster on the portside of the trawl deck with my survival suit, long sleeve shirt, hat and life preserver. We will have drills weekly at anytime.

For the last two days I have been becoming oriented to the ship and to my responsibilities to the science team. Jodi, a post doctorate from Juneau gave us a tour of the boat on the first day we arrived in Kodiak. I then practiced finding all of the key parts of the ship I will need to access. I now am confident that I can find my stateroom, the mess, laundry room, both exercise spaces, acoustics lab, and fish lab. For other sites, I wander around for a while until I locate it.

A Door — Many doors on the the Oscar Dyson are water tight. They must be latched after passing through them.

My first shift began at 4 pm on Monday. There are two shifts for scientists. Some work 4 am to 4 pm and the others work 4 pm to 4 am. I work the night shift. I never drink coffee but today I realized that I needed it. My shift includes scientists Paul, Jodi and Darin as well as a survey tech named Vince. We all share staterooms with people who work the opposite shift.

Science Team in Cave — The night shift science team includes Paul, Darin and Jodi (left to right). They monitor the fish in the acoustics lab also known as “The Cave”.

The ocean is very calm but most of us took Bonine (a seasickness medication) anyway to acclimate to the movement. Hopefully we will be adjusted to the motion before the seas get very rough if it does. The rocking of the boat does make one very sleepy.

Cruising the Gulf of Alaska — The sea have been very calm for us.

Did You Know?

The requirements for joining the NOAA Corps include a bachelor’s degree in science, math or engineering and a 5 month program at the US Coast Guard Academy in New London, CT. This is Abby’s second cruise with the NOAA Corps. She has a bachelor’s degree in chemistry and just completed her NOAA officer basic training.

Something to Think About:

What is a day in the life aboard the Oscar Dyson like?