Tag: Alaska

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Laura Guertin: Collecting Data: Icthysticks and Otoliths, June 21, 2023

dead fish laying on measurement board

NOAA Teacher at Sea

Laura Guertin

Aboard NOAA Ship Oscar Dyson

June 10 – June 22, 2023


Mission: 2023 Summer Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska

Geographic Area of Cruise: Islands of Four Mountains area, to Shumagin Islands area
Location (10:45AM (Alaska Time), June 21): 55o 29.7525′ N, 156o 44.7276′ W

Data from 10:45AM (Alaska Time), June 21, 2023
Air Temperature: 8.4 oC
Water Temperature (mid-hull): 8.2oC
Wind Speed: 8 knots
Wind Direction: 20 degrees
Course Over Ground (COG): 76 degrees
Speed Over Ground (SOG): 11 knots

Date: June 21, 2023

Once the echo sounder has shown us the position of an aggregation of Alaska walleye pollock (we hope they are pollock and not some other fish species), we lower the trawl net and see what we can catch. This is where the trawl sonar and CamTrawl (see previous blog post) come in handy to give us an idea of what is going into the net. It’s an amazing coordination of effort between the acoustics lab (who decides where to trawl), the bridge for navigation, and the deck crew for setting/retrieving the haul.

We aim for trawling at the mid-water level, where the pollock are typically found. Pacific Ocean perch (POP, or rockfish) can also be found in the mid-water level in the Gulf of Alaska, especially just off the shelf break. Bottom trawls can yield pollock and other fish (e.g., POP and other rockfish species, various species of flatfish).

Once the trawl net has been brought back on board, the catch is emptied into a bin called a table. There is a door on the side of the table that opens into the fish lab. Once the table door opens, the fish spill into the laboratory where they travel down a conveyor belt for the initial sorting. Our target species is the pollock. We weigh everything that ends up onto the sorting table, either in bulk (by species) or individually.

  • pollock moving along belt
    Pollock moving along the sorting belt
  • pile of dead rockfish
    Pile of Pacific Ocean perch (rockfish) after being hauled on the ship
  • dead squid on the deck of a ship
    Small squid that fell out of the trawl net on deck.

A subset of around 250 pollock are set aside to collect length data. The length of these of each individual pollock are measured on an Ichthystick. This is another invention by Rick Towler and Kresimir Williams (remember the CamTrawl? (see previous blog post)). As described in their article An inexpensive millimeter-accuracy electronic length measuring board, these NOAA scientists describe using magnetic measuring technology that, to millimeter resolution, takes a measurement when you placed a magnet on a sensor that runs the length of the board. For our pollock measurements, we were looking to record the fork length, and a quick placement of the red magnet along the fish tail sends the data to a computer program called CLAMS (Catch Logger for Acoustic Midwater Surveys).

  • green plastic bins containing dead pollock (fish)
    Bins of pollock waiting to be measured on the Ichthystick
  • A close-up view of the end of the measuring board shows the larger sizes on the scale (marked 75, 80, 85). The board's logo reads "Ichthystick" and includes a stylized illustration of a pollock.
    Ichthystick logo with a pollock sketch
  • computer screen with long measuring board
    Computer end of Ichthystick, which digitally shows the value of fish length and is written to CLAMS
  • illustration of a fish with lines showing the various lengths of measurement. Title: "Measuring Fish Length." labels: "Maximum Standard Length," "Fork Length," and "Maximum Total Length."
    Sketch showing what is measured for the fork length of a fish. From Corvallis Forestry Research Community.
  • dead fish laying on measurement board
    Pollock lying on Ichthystick getting its fork length being measured
  • two people in rain gear in a laboratory taking measurements of fish
    Two scientists measuring pollock fork length on Ichthystick

Another subset of approximately 50 pollock are set aside for additional data collection on individual specimens – length, weight, sex, maturity, and age. Otoliths (e.g., ear bones) are removed, and sometimes organs are removed and measured (ovaries for maturity development analyses, liver).

a black and white image showing pairs of otoliths from different fish species. Each otolith is white and gray in contrast with the solid black background; lighting reveals the ringed growth pattern
Otolith pairs (two per individual fish) from an assortment of Bering Sea fish species. Walleye pollock is located in the top left. Note: otolith sizes are not on a relative scale. Photo: NOAA Fisheries.

What are otoliths, and why remove them? Otoliths are ear stones, or ear bones, found in fish. To give you an idea of why we remove ear bones, let’s start by thinking about trees and corals… trees grow a new ring on their structure each year, and corals have differences in their skeletal density between the seasons (both trees and corals are also used to reconstruct past climate conditions (proxy data for paleoclimatology)). By counting the rings on trees and coral, we can calculate the age of that specimen. It turns out that fish also have a way to record their annual growth – and it occurs in their ear through Fish Otolith Chronologies.

Scientists are very interested in studying otoliths. When otolith data are combined with data on fish size, scientists are able to determine the growth rates of fish, which then combined with the survey work, helps inform annual fish stock assessment reports. We don’t do any of the otolith analyses on the ship, but we do collect the samples with a detailed label and all the corresponding data (fish length, sex, weight, location) that is sent back to the NOAA Fisheries Alaska Fisheries Science Center for analyses and entered into their Fish Otolith Collection Database.

  • Two otoliths in a person's hand
    Rockfish otoliths
  • close-up view of two otoliths in a person's hand; the growth rings are visible
    Zoom of rockfish otoliths
  • two gloved hands hold up a fish cut open to reveal the otoliths inside the head
    Otoliths still inside a pollock
  • person holding tweezers and placing object in glass vial
    Placing an otolith cleaned in freshwater into a vial for storage and shipment for analysis

Did you know… More than 30,000 otoliths are read annually by NOAA Fisheries Alaska Fisheries Science Center scientists. So far, the Science Center has collected more than 1.1 million fish otoliths for ageing. (from NOAA Fisheries)

To learn more about the fascinating studies of otoliths and what NOAA Fisheries is doing, check out these websites:

NOAA Fisheries Age and Growth – NOAA Fisheries scientists assess the age and growth rates of fish species and populations to better monitor, assess, and manage stocks. There is also a separate site for Age and Growth Research in Alaska.

NOAA Fisheries Age and Growth Homework: Determining How Old Fish Are

NOAA Fisheries Near-Infrared Technology Identifies Fish Species From Otoliths – NOAA Fisheries scientists are developing ways to use near-infrared spectroscopy (NIRS) analysis of otoliths (fish ear stones) to provide accurate information for sustainable fisheries management faster.

If you are really curious to explore some fish otolith data, check out the Alaska Age And Growth Data Map, an interactive map displays collected specimen information from recent age and growth studies from Alaska Fisheries Science Center.

Screenshot from the Alaska Age and Growth Data Map website. On the left is a map of Alaska with lots of orange, blue, and green circles marking sampling locations. To the right are two graphs plotting lengths (y-axis) against ages (x-axis) for walleye pollock sampled in 2021. Blue circles (or box-and-whisker plots) represent samples from the Western Bering Sea and green circles represent samples from the Eastern Bering Sea.
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Laura Guertin: Collecting data: Trawl Sonar and CamTrawl, June 20, 2023

rectangular frame with four orange round balls on top and two eyes on a metal cylinder in the middle

NOAA Teacher at Sea

Laura Guertin

Aboard NOAA Ship Oscar Dyson

June 10 – June 22, 2023


Mission: 2023 Summer Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska

Geographic Area of Cruise: Islands of Four Mountains area, to Shumagin Islands area
Location (2PM (Alaska Time), June 19): 55o 30.9384′ N, 159o 47.6478′ W

Data from 2PM (Alaska Time), June 19, 2023
Air Temperature: 8.2 oC
Water Temperature (mid-hull): 6.8oC
Wind Speed: 18 knots
Wind Direction: 62 degrees
Course Over Ground (COG): 30 degrees
Speed Over Ground (SOG): 11 knots

Date: June 20, 2023

To conduct a fisheries survey or any oceanographic research expedition, there’s an enormous checklist of items you need on a ship. Jokingly, those on board will tell you that food and internet access are at the top of the list. But there’s no doubt that technology and its function, application, durability, etc., are critical during the time at sea. For example, see NOAA’s explainers for Ocean Exploration Technology: How Robots Are Uncovering the Mysteries of the Deep and Collecting and Visualizing Deep-Sea Data. For a broader look at the technologies NOAA uses to explore the ocean (vessels and submersibles, observing systems and sensors, communication technologies, and diving technologies), see Exploration Tools.

Leg 2 of this Summer Survey will be bringing on board the DriX, an uncrewed surface vehicle (USV), to see if this technology can improve the efficiency of collecting acoustic and biological data to estimate pollock abundance when working alongside Oscar Dyson. To read more/see a video, check out NOAA’s article, Uncrewed Surface Vehicles Complement NOAA Vessels for More Efficient Fisheries Surveys.

Trawl Sonar

A sonar device (housed in a yellow hard plastic casing marked SIMRAD) sits on deck on a pile of coiled ropes
The Simrad FS70 on the back deck of Oscar Dyson (June 2023)

Trawl sonar units are used to provide a rough estimate of how many fish are going into the trawl net. The device (which we’ve been using on our expedition, a Simrad FS70 nicknamed “the turtle”) is a third wire system that in real time establishes communication between the submerged sonar head and the bridge. On this cruise, the trawl sonar unit is placed on the headrope of the trawl net (i.e., on the top of the mouth of the net). It communicates its depth back to the ship. It also scans the mouth of the net and relays any acoustic images of things going into the net back to the ship. These data allow the scientists and crew to adjust the depth of the net and length of time the trawl net remains in the water to collect samples. Our goal is to collect enough fish (approximately one ton) to have a representative sample of the various species and lengths of fishes in the water column.

Screenshot of the display returned by the FS70 during a trawl. The display is broken into three columns. The rightmost column is a list of settings.
Screenshot of the display returned by the FS70 during a trawl. The pink/yellow/blue line in the left column is where you see the bottom of the net. This is also represented in the middle column by the multi-colored horizontal line you see in the third circle from the center. (Screenshot from Leg 1 provided by Rick Towler).

The Simrad FS70 makes an appearance in the NOAA video Alaska’s Pollock Fishery: A Model of Sustainability. NOAA Ship Bell M. Shimada uses this FS70 trawl sonar unit for Pacific hake acoustic trawl surveys (see article).

CamTrawl

CamTrawl sits on the deck of NOAA Ship Oscar Dyson next to a blue trawl net that hangs down from a huge suspended spool. The CamTrawl consists of a metal frame housing cameras (not very visible) and buoys (more visible).

One fascinating piece of technology we’re using on this pollock survey is the CamTrawl. This article I found will give you everything you would want to know about CamTrawl in a non-technical summary:

–> Developing 3D Stereo Camera Technology to Support Sustainable Fisheries (from NOAA)

Introduced in 2012, the CamTrawl is a stereo camera system when attached to a trawl net, can provide data about fish without ever touching a fish. This 3D imagery records fish passing by the camera towards the codend (the closed end of the trawl net), which provides species and size composition data as well as how fish behave in the trawl net to be collected from within a midwater survey trawl. CamTrawl is used to verify the trawl catch and specimen data, and in some cases, can be used to determine where in the water column the species entered the net. These data help inform ecosystem-based fisheries management.

  • rectangular frame with four orange round balls on top and two eyes on a metal cylinder in the middle
    The CamTrawl on Oscar Dyson for 2023 Summer Survey. The orange balls are flotation devices, the two “eyes” in the middle are the stereo camera and computer system, with the battery power across/under the eyes. The four round devices in the corner are lights used during the image recording.
  • trapezoid frame with four orange balls across the top
    Top-down view of the CamTrawl. The front of the camera set-up is the wider side of the trapezoidal frame (top of image) which is then attached to the trawl net.
  • two sketches and a photo of the CamTrawl setup
    Figure 1 from Williams et al. (2016). CamTrawl system description.
  • CamTrawl device attached to a trawl net on the deck of a ship
    CamTrawl attached to trawl net about to be set off the back of Oscar Dyson.

The CamTrawl has uses and applications beyond our walleye pollock survey. It can go to depths of the ocean where it is not possible to lower a trawl net and capture data on other fish species like the bottom-dwelling rockfish. CamTrawl can explore and map deep-sea corals, and there is potential for collaborative research with the fishing industry.

Some CamTrawl footage from Leg 1 of 2023 Summer Survey.

The CamTrawl was developed by NOAA scientists  Kresimir Williams and Rick Towler (both of whom I’m sailing with on Oscar Dyson for Leg 1). I feel incredibly fortunate to have sailed with these two scientists and to hear how NOAA encourages their researchers to be creative and experiment with developing technologies to advance NOAA’s overall mission and expedition objectives.

people around a net removing equipment, while standing on the back of a ship at sea
CamTrawl being detached from a trawl net after a mid-water trawl (June 16, 2023, on Oscar Dyson)

Curious to see more? Check out this Salmon shark caught on CamTrawl underwater camera. Below is a picture of a salmon shark from the Shumagin Islands, Alaska area in February 2017 (photo provided by Sarah Stienessen).

shark seen by an underwater camera

Additional sources for exploration:

Using AI and 3D stereo cameras to support fisheries (National Fisherman, March 12, 2023)

Boldt et al. (2018). Development of stereo camera methodologies to improve pelagic fish biomass estimates and inform ecosystem management in marine waters. Fisheries Research, 198. https://doi.org/10.1016/j.fishres.2017.10.013

Williams et al. (2018). A method for computing volumetric fish density using stereo cameras. Journal of Experimental Marine Biology and Ecology, 508. https://doi.org/10.1016/j.jembe.2018.08.001

Williams et al. (2016). Automated measurements of fish within a trawl using stereo images from a Camera-Trawl device (CamTrawl). Methods in Oceanography, 17. https://doi.org/10.1016/j.mio.2016.09.008

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Laura Guertin: Collecting Data: Acoustic Survey, June 19, 2023

What looks like a long fishing rod attached to a ship's rail on the ocean

NOAA Teacher at Sea

Laura Guertin

Aboard NOAA Ship Oscar Dyson

June 10 – June 22, 2023


Mission: 2023 Summer Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska

Geographic Area of Cruise: Islands of Four Mountains area, to Shumagin Islands area
Location (2PM (Alaska Time), June 18): 55o 15.3391′ N, 160o 17.8682′ W

Data from 2PM (Alaska Time), June 18, 2023
Air Temperature: 8.9 oC
Water Temperature (mid-hull): 7.7oC
Wind Speed: 4 knots
Wind Direction: 182 degrees
Course Over Ground (COG): 356 degrees
Speed Over Ground (SOG): 12 knots

Date: June 19, 2023

Acoustic fisheries surveys seek to estimate the abundance and distribution of fish in a particular area of the ocean. In my case, this Summer Survey is looking at walleye pollock in the Gulf of Alaska. How is this accomplished? Well, it’s not through this method:

The Alaska walleye pollock is widely distributed in the North Pacific Ocean with the largest concentrations in the eastern Bering Sea. For this expedition, Oscar Dyson is traveling to specific regions in the Gulf of Alaska and running transects perpendicular to the bathymetry/contours (which are not always perpendicular to the shore) to take measurements using acoustics and targeted trawling to determine the abundance and distribution of walleye pollock which informs stock assessment and management models. For this blog post, let’s focus on how and why we can use acoustics to locate fish.

A map of the distribution of walleye pollock in the waters around Alaska. Alaska is centered in this map, but not disconnected from adjacent portions of Canada, and portions of Russia are visible to the east. Colors representing topography are visible, emphasized on the land of Alaska and depicted faintly on Canada and Russia. The ocean is depicted as a solid blue. We see latitude and longitude lines at ten degree intervals. We can see labels for the Beaufort Sea (north of Alaska), Chukchi Sea (northwest), Bering Sea (west), Bristol Bay (southwest), Gulf of Alaska (south and southeast.) The polygon representing the distribution of pollock is shaded with diagonal red lines. It starts in the Chukchi Sea, extends southwest out to the Bering Sea, and curves around the Aleutian Islands, hugging the coastline around the Gulf of Alaska.
Walleye pollock (Gadus chalcogrammus) are distributed broadly in the North Pacific Ocean and eastern and western Bering Sea. In the Gulf of Alaska, pollock are considered as a single stock separate from those in the Bering Sea and Aleutian Islands.  Image from Alaska Department of Fish and Game.
A screenshot of an electronic nautical chart of the area around the Alaska Peninsula. Overlain on the chart are straight blue lines connecting blue points in a boxy meandering path in and out from the coastline, west to east. A few segments are red instead of blue.
An snapshot of a nautical chart with transects plotted. The first transect was run during Leg 1 on June 14 at the furthest location to the west, then the ship worked its way back east with approximately 40 nautical miles between transects. Once Oscar Dyson reached the Shumagin Islands, survey work shifted into this area..

Our story starts with the fish itself. Alaska walleye pollock have a swim bladder. The swim bladder is an internal organ filled with gas that allows a fish to maintain its buoyancy and stability at depth.

One interesting effect of the swim bladder is that it also functions as a resonating chamber that can produce and receive sound through sonar technology. This connection was first discovered in the 1970s, when low-frequency sound waves in the ocean come in contact with swim bladders and they resonated much like a tuning fork and return a strong echo (see WHOI’s Listening for Telltale Echoes from Fish).

illlustrated diagram of the internal anatomy of a boney fish. The swim bladder is located in the middle of the fish, beneath the long, skinny kidney and behind the stomach.
Internal anatomy of a boney fish. From Wikipedia (CC BY-SA 3.0).
Illustration of a survey ship on the ocean surface, with the ocean cutaway so that we can see a cone of sound pulses extending out from the ship's hull to the ocean floor. A school of fish is depicted in the middle of the water column, in the cone of sound.
The sound pulses travel down into the water column, illustrated by the white cones here, and bounce back when encountering resistance. (from NOAA Fisheries)

NOAA Fisheries uses echo sounding, which works by emitting vertical pulses of sound (often referred to as pings), and measuring the return strength and recording the time for the signal to leave and then return. Anything having a different density from the surrounding water (in our case – fish, plankton, air bubbles, the seafloor) can return a signal, or “echo”.

The strength or loudness of the echo is affected by how strongly different ocean elements reflect sound and how far away the source of the element is. The seafloor usually makes the strongest echo because it is composed of rock which has a density different than the density of water. In fish, the swim bladder provides a contrast from the water. In addition, each fish species has a unique target strength or amount of sound reflected to the receiver. The size and shape of the swim bladder influence the target strength. There is a different target strength to length relationship for each species of fish – the larger the fish, the greater the strength of the returning echo.

It’s important to note that echo sounders cannot identify fish species, directly or indirectly. The only way we know which fish species is causing a signal is based on trawl catch composition. There is nothing within the acoustic data that lets us identify fish species, even with the catch data. This is a subtle, but important, distinction. Acoustic data, particularly calibrated acoustic data, in tandem with the information from the trawl, definitely allows us to count fish.

Where is the echo sounder on Oscar Dyson? Look at the figure in the next section of this post – it’s a sketch of NOAA Ship Rainier, but the placement of the echo sounder is the same for Dyson. You can see a rectangular “board” that is extended down from the center of the ship. This is called – what else – the center board! Attached to the bottom of the center board are the echo sounders. When lowered, the echo sounders sit at 9 meters below the level of the sea (~4 meters below the bottom hull of the ship).

Did you know… Southern Resident killer whales use their own echolocation clicks to recognize the size and orientation of a Chinook’s swim bladder? Researchers report that the echo structure of the swim bladders from similar length but different species of salmon were different and probably recognizable by foraging killer whales. (reported in Au et al., 2010)

It starts with a calibration

Typical setup of the standard target and weight beneath the echo sounder. (from NOAA Fisheries)

Before we can begin collecting data, we need to calibrate the echo sounder. The calibration involves a standard target (a tungsten carbide sphere) with a known target strength. The calibration needs to be completed in waters that are calm and without significant marine life for the best results.

The sphere is suspended below the ship’s hull using monofilament lines fed through downriggers attached to ship railings. One downrigger is in line with the echo sounder on the starboard side, and the other two on the port side. This creates a triangle that suspends the sphere in the center of the echo sounder’s sound beam. By tightening and loosening the lines, the sphere can be positioned under the center of the sound beam and can also be moved throughout the beam. By doing an equipment calibration at the beginning and end of a survey, we can ensure the accuracy of our data.

  • What looks like a long fishing rod attached to a ship's rail on the ocean
    One of the port side downriggers
  • Two people holding a ball on string on a ship
    A weight that goes at the bottom of the filament to ensure the calibration sphere remains below the echo sounder
  • Shiny ball being lowered over side of ship
    The tungsten carbide sphere attached to the line, being lowered over the side

For further exploration

NOAA Ocean Service – Ocean Facts – How do scientists locate schools of fish?

Discovery of Sound in the Sea – How is sound used to locate fish?

NOAA Fisheries – Acoustic Echosounders–Essential Survey Equipment and Acoustic Hake Survey Methods on the West Coast

NOAA Ocean Service – Ocean Facts – What is sonar?

Science – Sounds like my favorite fish – killer whales differentiate salmon species by their sonar echoes

NOAA Fisheries – Sound Strategy: Hunting with the Southern Residents, Part 2

The Pew Charitable Trusts – Advanced Sonar Technology Helps NOAA Count Anchovy

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Laura Guertin: NOAA Fisheries Surveys, Highlighting Acoustic Trawling, June 16, 2023

pollock moving along belt

NOAA Teacher at Sea

Laura Guertin

Aboard NOAA Ship Oscar Dyson

June 10 – June 22, 2023


Mission: 2023 Summer Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska

Geographic Area of Cruise: Islands of Four Mountains area, Western Gulf of Alaska
Location (2PM (Alaska Time), June 15): 53o 38.9534′ N, 166o 10.9927′ W

Data from 2PM (Alaska Time), June 15, 2023
Air Temperature: 8.74 oC
Water Temperature (mid-hull): 6.2oC
Wind Speed: 3.55 knots
Wind Direction: 310.61 degrees
Course Over Ground (COG): 64.09 degrees
Speed Over Ground (SOG): 11.61 knots

Date: June 16, 2023

One of the nine key focus areas for NOAA is research (https://research.noaa.gov/). Additional summaries about NOAA’s research activities can be found at NOAA Ocean Today. There are also numerous articles that describe the impact of NOAA’s research activities, such as Five ways NOAA’s research improves hurricane forecasts and other articles listed under Latest News and Features.

A stylized graphic design representing NOAA Research, this is a blue circle containing icons of a chemistry beaker, a pie chart, and a bar graph. The adjacent text contains the description of NOAA Research found here: https://www.noaa.gov/research

And now, it’s time for some science and surveying! Before I dive into the specifics of the methods we are carrying out on Oscar Dyson, I’m sharing this incredibly helpful NOAA Fisheries page that summarizes their Research Surveys, where “Our scientists and partners collect data on the water, from aircrafts, and from shore to understand the abundance, distribution, and health of marine life and habitats. That data forms the scientific foundation for our management and conservation work.”

There is also an informative podcast episode, Learn About NOAA Fisheries Surveys (transcript available at link). This podcast covers the need for sustainable fisheries, the 2013-2016 North Pacific Blob, how surveys were done historically, how surveys are using new technology, the impact of the pandemic, and the concept of being in a “stationary” versus “non-stationary” world. Such a fascinating listen!

First episode of “Dive In with NOAA Fisheries,” titled Learn About NOAA Fisheries Surveys

There is another podcast episode from the same series that is an excellent follow-on from the episode available above. Surveying Alaska’s Waters (transcript available at link) shares how surveys are a tools that allow NOAA to reach its mission, whether those measurement techniques come from satellites, autonomous vehicles, buoys, ships, drones, etc. Although these tools assist NOAA scientists in collecting data, climate change is playing an even bigger role in making ecosystem management a moving target. Again – worth a listen!

Third episode of “Dive In with NOAA Fisheries,” titled Surveying Alaska’s Waters

Surveys in the Gulf of Alaska

Trawl surveys have been conducted by Alaska Fisheries Science Center (AFSC) beginning in 1984 to assess the abundance of groundfish in the Gulf of Alaska (2021 Stock Assessment Report, p. 9). Starting in 2001, the survey frequency was increased from once every three years to once every two years on odd-numbered years. This is a flyer that describes the biennial bottom trawl survey in the Gulf of Alaska 2023.

The website Alaska Fish Research Surveys includes field season research briefs going back to 2021. The 2023 field season includes a link to my current expedition, Summer Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska.

The strategy of combining trawl and acoustic surveys was developed by AFSC and the University of Washington. They published a paper in the Canadian Journal of Fisheries and Aquatic Sciences (Kotwicki et al., 2018) that discusses the need to perform acoustic-trawl (AT) and bottom-trawl (BT) surveys to accurately estimate the abundance of fish populations along with their spatial distribution. I’ve provided below part of a news release from the University of Washington describing the content of the publication:

Many species of fish spend some of the time on the ocean bottom, and some of their time far off the bottom, which makes them hard to survey. Acoustic surveys (that bounce sound off fish schools), can estimate the midwater component of so-called “semipelagic” fish, while trawl surveys can measure the portion on the bottom. Now a new method has been developed that combines data from both types of surveys into a single estimate using information about the environment (bottom light, temperature, sand type, and fish size). The new method has been used to assess the status of walleye pollock, which sustains the largest fishery in the United States.

This image from Kotwicki et al., 2018, does an excellent job of showing the two types of survey methods, acoustic and bottom trawling.

Illustration of conceptual model of walleye pollock sampling by an echo sounder and a bottom trawl. At the top right is an illustration of a fishing vessel sailing left. Two blue lines extend out the back of the vessel diagonally downward toward the seafloor and connect to two points on an illustration of a bottom trawl net. To the left of the net (in front of the opening) is drawn a school of fish; more fish are drawn directly below the ship. Two other blue lines extend diagonally down from the center of the ship's hull to form a triangle representing the acoustic swath. Blue boxes indicate the areas of the water column missed by either the bottom trawl net (that is, the entire pelagic zone) or the acoustic sampling (a narrow benthic zone right off the seafloor.)
Fig. 1. Illustration of conceptual model of walleye pollock sampling by an echo sounder and a bottom trawl. Note that acoustic data are collected directly under the survey vessel, while the bottom trawl catches walleye pollock some distance behind the vessel. Diving occurs in the time between the vessel passing over the school of walleye pollock and the trawl catching the same school. Source: Kotwicki et al. 2018.

What is different for my current expedition is that we are not doing any bottom trawling. We are doing the acoustic piece of the survey and trawling off the bottom. Separate surveys and ships are collecting the bottom data, and then will be combined with our data to provide a more accurate snapshot for the water column for the annual Stock Assessment Report for Walleye Pollock. AT and BT surveys get NOAA to their research objective: informing fish stock assessment models and catch allocation. NOAA publishes an annual 100+page Assessment of the Walleye Pollock Stock in the Gulf of Alaska from the surveys conducted each year (see reports from 2019, 2020, 2021).

Check out this website if you are curious to see images from Bottom Trawl Surveys in Alaska. NOAA’s Groundfish Assessment Program regularly conducts bottom trawl surveys to assess the condition of groundfish and shellfish stocks in Alaskan marine waters).

1883 International Fisheries Exhibition

To prepare to sail on Leg 1 of the Summer Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska, I did a lot of reading and preparation so I could better understand what I would be learning, and how I could then connect the material with my students and additional audiences I see post-expedition. These two books in the image below helped give me a much better picture of not only walleye pollock but the fisheries industry, policy, and practices over time and space.

Photo of two books - one titled Billion-Dollar Fish, by Kevin Bailey, and other titled World Without Fish, by Mark Kurlansky

Each of these books provides some fascinating insight into the history, thought, and even debates, about the nature of ocean resources.

The title of Chapter 4 in Kurlansky’s book gives a hint for how to respond to my questions: “Being The Myth of Nature’s Bounty And How Scientists Got It Wrong For Many Years.” Early in the chapter, Kurlansky states:

“In the 1800s, when the study of fish and oceans was a relatively new science, it was the fishermen who were afraid that fish populations could be destroyed by catching too many fish, especially small fish. Scientists at the time believed that it was impossible to catch too many fish because fish produced so many eggs.” — World Without Fish, p. 53

One of the causes of concern for fishermen was the new technology developing – specifically, engine power, that allowed for even more fish to be caught.

There was a great historical debate on fisheries, too! London was the site of the Great International Fisheries Exhibition of 1883, where a debate about the ocean took place between British scientists Thomas Huxley and Edwin “Ray” Lankester. Huxley gave the inaugural address of the exposition – you can read it in its entirety online. Here are excerpts:

“I believe that it may be affirmed with confidence that, in relation to our present modes of fishing, a number of the most important sea fisheries… are inexhaustible… and probably all the great sea-fisheries, are inexhaustible; that is to say that nothing we do seriously affects the number of fish. And any attempt to regulate these fisheries seems consequently… to be useless.” (*feel free to dive into Huxley’s speech to see his reasoning – the multitudes of fish available, and the destruction is minimal)

Then Lankester gave the final summary speech of the Exhibition – a rebuttal to Huxley. Lankester made the point that the fish in the sea are not unlimited, and captured fish are not readily replaced by others that exist further offshore from the fishing location. He raised the concern that the removal of the parents by fishing was going to impact the production of the young.

Although at the time many gave Huxley the victory in this debate, Huxley did not take into account the new development that I mentioned above – the modern trawl and the steam trawler to pull it, resulting in larger nets and catches. It’s interesting to note that eventually, Huxley studied the impact from engine-driven net draggers and changed his story. Huxley eventually agreed that overfishing was not only possible, but that it was happening.

Now to circle back to why we survey fisheries… it ultimately comes down to ecosystem management. As described in the two audio files at the top of this blog post and in my other posts, as well as the title to Chapter 8 in Kurlansky’s book, “The Best Solution To Overfishing: Sustainable Fishing.” And to engage in sustainable fishing, you need the data to make that happen – hence, fisheries surveys!

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Laura Guertin: Alaska Pollock and Sustainable Fisheries 101, June 15, 2023

NOAA Teacher at Sea

Laura Guertin

Aboard NOAA Ship Oscar Dyson

June 10 – June 22, 2023


Mission: 2023 Summer Acoustic-Trawl Survey of Walleye Pollock in the Gulf of Alaska

Geographic Area of Cruise: Islands of Four Mountains area, Western Gulf of Alaska
Location (2PM (Alaska Time), June 14): 52o 30.9860′ N, 169o 08.0942′ W

Data from 2PM (Alaska Time), June 14, 2023
Air Temperature: 8.11 oC
Water Temperature (mid-hull): 8.0oC
Wind Speed: 8.27 knots
Wind Direction: 243.96 degrees
Course Over Ground (COG): 239.25 degrees
Speed Over Ground (SOG): 13.05 knots

Date: June 15, 2023

I’m trained as a geologist and oceanographer. My teaching and research has focused on the physical sciences, which is why I’m so excited to have the opportunity to work with scientists in the life sciences. But before I start with the acoustic-trawl survey of walleye pollock, I had to do my homework – namely, learn something about this fish!

There is a wealth of resources on NOAA’s website that are providing me the introductory overview or “101” on pollock and the overall mission of maintaining sustainable fisheries. I started by viewing this NOAA video on Alaska’s Pollock Fishery: A Model of Sustainability.

This video shared so much but also generated so many more questions! I decided to take a step back and do a deeper dive into some of these topics, starting with the fish…

Alaska (walleye) pollock

Photo of dead Alaska pollock on a flat surface
Alaska pollock (Gadus chalcogrammus) on the sorting table, from NOAA Photo Library

NOAA Fisheries is doing an incredible volume of work in the Alaska region – including a focus on the Alaska pollock.

A member of the cod family, Alaska pollock (Gadus chalcogrammus) is also referred to as pollock, walleye pollock, and Pacific pollock. The NOAA Fisheries Species Directory for Alaska pollock states that Alaska pollock typically grow between 12 and 20 inches and weigh between 1 to 3 pounds. Their speckled coloring allows them to blend in with the seafloor to avoid predators such as Stellar sea lions, fish, seabirds – even older pollock will feed on juvenile pollock! Humans feed on pollock in products from fillets to fish sticks to surimi.

Alaska pollock are found throughout the North Pacific Ocean but are most common in the Bering Sea. Pollock migrate inshore to shallow water to breed and feed in the spring, then move back to warmer, deeper waters in the winter.

Sustainable fisheries

I always like to start by ensuring I’m using the terminology correctly. The NOAA web page for Understanding Fisheries Management in the United States defines fishery as the following:

The word “fishery” is used in many ways. It can refer to the occupation, industry, or season for catching fish. It can also refer to the area of ocean where fish are caught, or the business of catching the fish. U.S. fisheries include commercial (catching/marketing fish and shellfish for profit), recreational (fishing for sport/pleasure), and subsistence (fishing for personal/family/community consumption or sharing.

Next, what is meant by sustainable fisheries? NOAA defines this in the following video and in the quote below:

“U.S. fisheries are big business, providing jobs and recreation and keeping our coastal communities vibrant. In fact, the United States is a global leader in responsibly managed fisheries and sustainable seafood. Working closely with commercial, recreational, and small-scale tribal fishermen, we have rebuilt numerous fish stocks and managed to create some of the most sustainably managed fisheries in the world. U.S. fisheries are scientifically monitored, regionally managed, and legally enforced under 10 national standards of sustainability. Managing sustainable fisheries is a dynamic process that requires constant and routine attention to new scientific information that can guide management actions.” — from NOAA Fisheries – Sustainable Fisheries

[*Note – To help my students with ocean definitions, I also like to show video clips from the Pew/Jim Toomey (cartoonist behind “Sherman’s Lagoon”) Visual Glossary of Ocean Terminology, such as the videos for What Is U.S. Fisheries Management? and What Is Ecosystem-Based Fishery Management? ]

NOAA’s FishWatch website is a great place to find the most up-to-date information on popular seafood harvested or farmed in the United States. This helps each of us as consumers to make smart choices! Check out the page for the Alaska pollock to see the details available for this fish, currently classified as a smart seafood choice because it is “sustainably managed and responsibly harvested under U.S. regulations.” This is so important to note, as according to FishWatch, the Alaska pollock fishery is one of the most valuable in the world, with commercial landings of Alaska pollock from the Bering Sea and Gulf of Alaska in 2020 totaling more than 3.23 billion pounds and were valued at approximately $420 million.

Alaska pollock library of articles

Several articles on NOAA’s website were helpful in not only providing me more background information to prepare for my time on Oscar Dyson, but the content really showed me the context of what NOAA is doing for fisheries research/management and why it matters. My students probably recognize this as a list of articles I would give them to develop their current event literacy, as these are recent dates of publication and from a credible source (NOAA, of course!) – and of course, contribute to advancing their ocean literacy.

If you wish to learn more about the current state of Alaska pollock research with NOAA, I highly recommend these recent articles from NOAA Fisheries News & Announcements:

For podcast fans, this 2013 NOAA Fisheries podcast episode titled Keeping an Eye on Pollock is an excellent overview of how “scientists and fishermen work together to understand how walleye pollock respond to a changing environment” (transcript available online).

NOAA Fisheries podcast, Keeping an Eye on Pollock

In reviewing these articles and the podcast, it is clear that NOAA is focused on advancing the technology to survey Alaska pollock with new tools such as saildrones. There is also an interest in closely monitoring the impact climate change is having on the juvenile and adult populations of pollock (see the NOAA Fisheries site on Climate Change). This video, released January 2022, is a great snapshot of how NOAA Fisheries is preparing and responding to the impacts of climate change (link to web page that supports the video).

OK, I’m feeling good about my background on the “what” and “why” of Alaska pollock, and I hope you are, too! Next, it’s time to share the activities of the science team that is applying science knowledge and technology tools to studying pollock on Oscar Dyson!