echosounder – NOAA Teacher at Sea Blog

August 15, 2023August 15, 2023

Germaine Thomas: What Does Acoustic Trawl Sampling Really Tell Us? August 13, 2023

NOAA Teacher at Sea

Germaine Thomas (she/her)

Aboard NOAA Ship Oscar Dyson

August 7 – August 21, 2023

Mission: Acoustic Trawl Survey (Leg 3 of 3)
Geographic Area of Cruise: Pacific Ocean/ Gulf of Alaska
Date: Sunday, August 13, 2023

Weather Data
Lat 59.12 N, Lon 150.11 W
Sky condition: Partly Cloudy
Wind Speed: 13 knots
Wind Direction: 330°
Air Temp: 14 °C

Science and Technology blog

The ocean is a really big place. We have really only mapped about 5% of the ocean bottom. How do we manage fisheries if we have to count fish in an area that is overwhelmingly large? This is where the genius of acoustics and trawl sampling complement each other. The scientists aboard NOAA Ship Oscar Dyson use the echo sounders to find fish or other animals lurking in the ocean and then they can extrapolate and upscale that data to a much larger area which is covered by their transects.

Wait! That is a lot of information using language that folks don’t really use at the dinner table. Could you please explain this in more basic terms? You bet, as a matter of fact in the last couple of days I have been swimming in a sea of new vocabulary, talking to really smart people and trying to keep up with the conversation that it almost makes my head explode. Don’t worry, I am safe. But it’s really impressive how scientists have developed ways to accurately know fish and marine organism populations in the ocean with out having to sample all of it.

Acoustics

Acoustics uses the echo-sounders a lot like a fish finder, but the ones on NOAA Ship Oscar Dyson are much more capable than the type you would find on your boat. The echo-sounders are attached to the bottom of a lowered centerboard—essentially a large keel—in the center of the boat, and they measure five different frequencies with different wavelengths.

A photo of a computer screen displaying five echograms (graphs of recorded echoes) in a row. Germaine has added annotation: a black arrow points at the top of the echogram with the label "Top of the ocean," and another points to a solid, dark red bar midway down the echogram with the label "bottom of the ocean." Dashed marks, angled up or down, are scattered across the echograms, concentrated in upper portions. Germaine has drawn a black circle around some of these, with the label "The colored marks in the oval indicate "backscatter," which could indicate fish or other marine organisms." At the top of each echogram, in its title, Germaine has circled the frequency measured, but they are difficult to read. — View of the 5 different frequencies measured by the echosounders, one in each frame. The darker marks on the screen could be fish, jellyfish, krill or other marine organisms, this is referred to as “backscatter.” The red circles show the different frequencies used to measure the backscatter.

So, if we can see the fish using acoustics, why do scientists need to sample using a trawl net? As you can see above, the marks in the backscatter can show the depth and the approximate shape of objects, but there is not enough detail to tell exactly what kind of organism is present. Most of the scientists on board have a pretty good idea what kind of fish or organisms are present, but the most definitive way to know is to take a trawl sample.

Trawl Sampling

The trawl net as seen in the picture below is being set off the aft deck.

A crewmember wearing a hard hat, life vest, and heavy work overalls stands off to the side as the trawl net is lowered off the aft deck from a large yellow A-frame. — The part that is in the air is called the codend. That is the section of the net where the specimens are ultimately collected.

view of two rollers - like large spools - containing rolled up fishing nets. the net on the right is orange. the net on the left is white and partially paid out. — The trawl is a about 172 meters long and it stored on these rollers on the back deck.

When the trawl is deployed to the depth that the scientists want to sample, the net will funnel fish and other organisms into it. This is called flying the net.

The screen above diagrams three different views of the net as it is pulled through the water. You can see that the trawl net was not directly behind the boat and went to a depth of 21.5 m.

photo of a computer screen displaying data about the position of the net, along with a more detailed diagram. Germaine has added arrows to label "The doors help open the net" and "the codend at the end of the net that collects the sample." We can see that the set length measures 457 meters. — In this image you can see the net and how far back it trails behind the *Oscar Dyson*.

I just have to include one more view of the trawl net from the bridge as it is pulled behind the boat.

A photo of a computer screen showing a 3-d rendering of the deployed trawl net and the following measurements: door depth port - 16.5 m. door depth starboard.- 15.7 m. door spread - 59.4 m. door pitch port - 4.7 degrees. door pitch starboard - 6.1 degrees. headrope horizontal range - 204 m. headrope true bearing - 326.0 degrees. depth - 21.0 m. change meters/minute - -0.2 m. — This image was taken when the crew was bringing the net back into the boat, so the depth is shallower.

The next image shows the path that the net was pulled through the water.

photo of a computer screen displaying an echogram (graph of recorded echoes.) This echogram shows the returns from a single frequency. Germaine has annotated it with arrows pointing to: Header rope or top of the trawl path, and Footer rope or bottom of the trawl path. Another arrow points to colored specks and reads: The echosounders show backscatter, which could be fish or other organisms. — The acoustics show the backscatter which the scientists make the trawl target. The next step is to process what is captured in the codend of the trawl and see exactly what is present.

Because the trawl is dragged through the water, it catches different organisms at different times. The scientists want to know when the different organisms were caught so they have cleverly attached a camera to the side of the net. Through the camera they can see which type of fish came into the trawl. Ultimately, this links the kind of acoustic backscatter viewed in the echograms recorded during the trawl to exactly the type of organism caught by the trawl.

view of a trapezoidal metal apparatus, containing underwater cameras and floats, attached to a blue trawl net, spread out on deck — The camtrawl: a camera that records the type of fish entering the net and when they enter.

Below is a picture of some fish as they enter the trawl net and move towards the codend.

a photo of a computer screen displaying a black-and-white underwater camera feed. a few fish (pollock) are visible swimming by the net. — The camera is looking across the net as the fish move past. The fish in the picture are pollock, the type of fish we are looking for on this leg of the cruise.

Transect Lines

So how do scientists take this information and extrapolate the data to a broader area? While the Oscar Dyson is out at sea they run transect lines while recording acoustic data. Transect lines are specific paths in the ocean. The picture below shows the transect lines that we plan to do and have done on this leg of the cruise.

a screenshot of an electronic nautical map of the Gulf of Alaska. straight lines extending toward and away from the coast are superimposed across the map. — The red lines are the transects we have done and the blue lines are the transects scientists plan to do in the remainder of this leg of the cruise. If you look closely there are pictures of fish symbols on the transect lines where the ship has made trawl samples.

Using the acoustic data that the echo-sounders provide and verifying the types of fish and other marine organisms through the trawl sampling allows the scientists to predict, with a high level of certainty, the amount and types of marine organisms that are present along the transect lines that were not trawl-sampled. Thus saving the taxpayers money, and allowing fisheries managers to use good data, keeping the fishery viable, and allowing commercial fishing boats to have reasonable catch limits.

Scientist in the Spotlight

Honestly it takes a team to make all of this happen. But, half of our team is sleeping at the moment, I have the night shift from 4pm to 4am, so I am going to introduce one fabulous expert in acoustics and fisheries:

Abigail, wearing a blue hoodie featuring a drawing of a salmon, sits back from a long computer desk with eight computer montiors mounted above and to the side. She smiles at the camera. — Abigail McCarthy in the Acoustics Lab

Abigail McCarthy has been working for MACE: Midwater Assessment and Conservation Engineering Program since 2007. She received her undergraduate degree in Biology from Wellesley College and then obtained a Masters in Fisheries from Oregon State University.

For fun, she surfs and enjoys long-distance prone paddle board races. She has recently found a new love with fly fishing.

Aboard the Ship Oscar Dyson, she is working as a specialist helping to run the acoustics lab.

I asked Abigail what she thought of about her educational experience? She immediately said, “I love learning! High school and college were both a lot of fun.”

What would be a good suggestion for a young aspiring high school student pursuing a degree related to ocean studies or science in general?

Her response was great: “Being curious and working hard is more important than being brilliant. Persistence and determination will get you where you want to be in the future.” Finally, “Learn to code! Become familiar with programing languages like Python and R.”

Hopefully, I answered your burning questions about the use of acoustic trawl sampling, and surveys. Yet, there is so much more to learn. Why not take a trip yourself? Check NOAA’s website out and just apply.

June 19, 2023June 19, 2023

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): 55^o 15.3391′ N, 160^o 17.8682′ W

Data from 2PM (Alaska Time), June 18, 2023
Air Temperature: 8.9 ^oC
Water Temperature (mid-hull): 7.7^oC
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.

One of the port side downriggers
A weight that goes at the bottom of the filament to ensure the calibration sphere remains below the echo sounder
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

August 19, 2019August 19, 2019

Linda Kurtz: Hydrographic Surveys – Not your Mama’s Maps! August 17, 2019

NOAA Teacher at Sea

Linda Kurtz

Aboard NOAA Ship Fairweather

August 12-23, 2019

Mission: Cascadia Mapping Project

Geographic Area of Cruise: Northwest Pacific

Date: 8/17/2019

Weather Data from the Bridge

August 17^th 2019

Latitude & Longitude: 43◦ 53.055’ N 124◦ 47.003’W
Windspeed: 13 knots
Geographic Area: @10-15 miles off of the Oregon/California coast
Cruise Speed: 12 knots
Sea Temperature 20◦Celsius
Air Temperature 68◦Fahrenheit

Future hydrographer button — Is this you?

Navigation is how Fairweather knows its position and how the crew plans and follows a safe route. (Remember navigation from the last post?) But what “drives” where the ship goes is Hydrographic survey mission. There is a stunning amount of sea floor that remains unmapped, as well as seafloor that has not been mapped following a major geological event like an earthquake of underwater volcano.

Why is Hydrography important? As we talked about in the previous post, the data is used for nautical safety, creating detailed maps of the ocean floor, setting aside areas are likely abundant undersea wildlife as conservation areas, looking at the sea floor to determine if areas are good for wind turbine placement, and most importantly to the residents off the Pacific coast, locating fault lines — especially subduction zones which can generate the largest earthquakes and cause dangerous tsunamis.

In addition to generating the data needed to update nautical charts, hydrographic surveys support a variety of activities such as port and harbor maintenance (dredging), coastal engineering (beach erosion and replenishment studies), coastal zone management, and offshore resource development. Detailed depth information and seafloor characterization is also useful in determining fisheries habitat and understanding marine geologic processes.

The history of hydrographic surveys dates back to the days of Thomas Jefferson, who ordered a survey of our young nation’s coast. This began the practice and accompanying sciences of the coastal surveys. The practice of surveys birthed the science of Hydrography (which we are actively conducting now) and the accompanying science of Bathymetry (which we will go into on the next post.) This practice continues of providing nautical charts to the maritime community to ensure safe passage into American ports and safe marine travels along the 95,000 miles of U.S. Coastline.

Want to learn more about Hydrographic Survey history? Click on THIS LINK for the full history by the NOAA.

Scientists have tools or equipment that they use to successfully carry out their research. Let’s take a look at a few of the tools hydrographic survey techs use:

Want to learn more about the science of SONAR? Watch the video below.

ps://www.youtube.com/watch?v=8ijaPa-9MDs

On board Fairweather (actually underneath it) is the survey tool call a TRANSDUCER which sends out the sonar pulses.

The transducer on Fairweather is an EM 710- multibeam echo sounder which you can learn more about HERE.

The Transducer is located on the bottom of the ship and sends out 256 sonar beams at a time to the bottom of the ocean. The frequency of the 256 beams is determined by the depth from roughly 50 pings per second to 1 ping every 10 seconds. The active elements of the EM 710 transducers are based upon composite ceramics, a design which has several advantages, which include increased bandwidth and more precise measurements. The transducers are fully watertight units which should give many years of trouble-free operation. This comes in handy since the device in on the bottom of Fairweather’s hull!

Here is the transducer on one of the launches:

The 256 sonar beams are sent out by the transducer simultaneously to the ocean floor, and the rate of return is how the depth of the ocean floor is determined. The rate of pulses and width of the “swath” or sonar beam array is affected by the depth of the water. The deeper the water, the larger the “swath” or array of sonar beams because they travel a greater distance. The shallower the water, the “swath” or array of sonar beams becomes narrower due to lesser distance traveled by the sonar beams.

The minimum depth that this transducer can map the sea floor is less than 3 meters and the maximum depth is approximately 2000 meters (which is somewhat dependent upon array size). Across track coverage (swath width) is up to 5.5 times water depth, to a maximum of more than 2000 meters. This echo sounder is capable of reaching deeper depths because of the lower frequency array of beams.

The transmission beams from the EM 710 multibeam echo sonar are electronically stabilized for roll, pitch and yaw, while they receive beams are stabilized for movements. (The movement of the ship) What is roll, pitch, and yaw? See below – these are ways the Fairweather is constantly moving!

Since the sonar is sent through water, the variable of the water that the sonar beams are sent through must be taken into account in the data.

Some of the variables of salt water include: conductivity (or salinity) temperature, depth, and density.

Hydrographic scientists must use tools to measure these factors in sea water, other tools are built into the hydrographic survey computer programs.

One of the tools used by the hydrographic techs is the XBT or Expendable Bathy Thermograph that takes a measurement of temperature and depth. The salinity of the area being tested is retrieved from the World Ocean Atlas which is data base of world oceanographic data. All of this data is transmitted back to a laptop for the hydrographers. The XBT is an external device that is launched off of the ship to take immediate readings of the water.

Launching the XBT: There is a launcher which has electrodes on it, then you plug the XBT probe to the launcher and then XBT is launched into the ocean off of the back of the ship. The electrodes transmit data through the probe via the 750-meter copper wire. The information then passes through the copper wire, through the electrodes, along the black wire, straight to the computer where the data is collected. This data is then loaded onto a USB then taken and loaded into the Hydrographic data processing software. Then the data collected by the XBT is used to generate the sound speed profile, which is sent to the sonar to correct for the sound speed changes through the water column that the sonar pulses are sent through. The water column is all of the water between the surface and seafloor. Hydrographers must understand how the sound moves through the water columns which may have different densities that will bend the sound waves. By taking the casts, you are getting a cross section “view” of the water column on how sound waves will behave at different densities, the REFRACTION (or bending of the sound waves) effects the data.

See how the XBT is launched and data is collected below!

Hydrotech Bekah Gossett preparing to cast
The XBT probe
The XBT launcher

I got to do a cast-
thanks Bekah!
Instant readings from the XBT
Bekah downloading data from the XBT

Videos coming soon!

The other tool is the MVP or moving vessel profiler which takes measurements of conductivity, temperature, and depth. These are all calculated to determine the density of the water. This is a constant fixture on the aft deck (the back of the ship) and is towed behind the Fairweather and constantly transmits data to determine the speed of sound through water. (Since sonar waves are sound waves.)

MVP and launching wench — MVP (left) and the launching wench (right)

The sonar software uses this data to adjust the calculation of the depth, correcting for the speed of sound through water due to the changes in the density of the ocean. The final product? A detailed 3d model of the seafloor!

Our current survey area! (Thanks Charles for the image!)

All of this data is run through the survey software. See screen shots below of all the screens the hydrographers utilize in the course of their work with explanations. (Thanks Sam!) It’s a lot of information to take in, but hydrographic survey techs get it done 24 hours a day while we are at sea. Amazing! See below:

ACQ software screenshot — Hydrographic Survey “Mission Control”

Did You Know? An interesting fact about sonar: When the depth is deeper, a lower frequency of sonar is utilized. In shallower depths, a higher sonar frequency. (Up to 900 meters, then this rule changes.)

Question of the Day: Interested in becoming a hydrographic survey tech? See the job description HERE.

Challenge yourself — see if you can learn and apply the new terms and phrases below and add new terms from this blog or from your research to the list!

New Terms/Phrases:

Multibeam sonar

Sound speed

Conductivity

Salinity

Sonar

Sound waves

Refraction

Water column

Roll, Pitch, and Yaw

Animals seen today:

Humpback Whale

Bathymetry and USGS friends coming soon!

Plot room — Hydro-technician Sam Candio (right) collaborating with USGS Research Geologist James Conrad and Physical Scientist Peter Dartnell.

August 6, 2017August 6, 2017

Brad Rhew: The Sounds of the Sea, July 31, 2017

NOAA Teacher at Sea

Brad Rhew

Aboard NOAA Ship Bell M. Shimada

July 23 – August 7, 2017

Mission: Hake Fish Survey

Geographic Area of Cruise: Northwest Pacific Ocean, off of the coast of Oregon

Date: July 31, 2017

Weather Data from the Bridge

Latitude: 44 49.160 N
Longitude 124 26.512

Temperature: 59^oF
Sunny
No precipitation
Winds at 25.45 knots
Waves at 4-5ft

Science and Technology Log

TAS Rhew 7-31 acoustics lab2 — Inside the acoustics lab

The scientists on the Hake survey project are constantly trying to find new methods to collect data on the fish. One method used is acoustics. Scientists Larry Hufnagle and Dezhang Chu are leading this project on the Shimada. They are using acoustics at a frequency of 38 kHz to detect Pacific Hake. Density differences between air in the swimbladder, fish tissue, and the surrounding water allows scientists to detect fish acoustically.

The purpose of the swim bladder in a fish is to help with the fish’s buoyancy. Fish can regulate the amount of gas in the swim bladder to help them stay at a certain depth in the ocean. This in return decreases the amount of energy they use swimming.

TAS Rhew 7-31 echosounder — The screen shows the data collected by the echosounder at different frequency levels.

Larry and Chu are looking at the acoustic returns (echoes) from 3 frequencies and determining which are Hake. When the echosounder receives echoes from fish, the data is collected and visually displayed. The scientists can see the intensity and patterns of the echosounder return and determine if Hake are present.

The scientists survey from sunrise to sunset looking at the intensity of the return and appearances of schools of fish to make the decisions if this is an area to fish.

TAS Rhew 7-31 scientists Larry and Chu — Scientists Larry Hufnagle (left) and Dezhang Chu (right) monitor the nets and echosounder while fishing for hake.

The ultimate goal is to use this data collected from the echosounder to determine the fish biomass. The biomass determined by the survey is used by stock assessment scientist and managers to manage the fish stock.

Personal Log

Everyday aboard the Shimada is a different experience. It has been amazing to be able to go between the different research labs to learn about how each group of scientists’ projects are contributing to our knowing more about Hake and marine ecosystems. My favorite part so far has been helping with the sampling of Hake. Some people might find dissecting fish after fish to determine length, sex, age, and maturity to be too much. However, this gives me an even better understanding and respect for what scientists do on a daily basis so we can have a better understanding of the world around us. We have also caught other fascinating organisms that has helped me explore other marine species and learn even more about their role in the ocean.

Even though the wind is a little strong and the temperatures are a little chilly for my southern body I wouldn’t trade this experience for anything…especially these amazing sunsets…

TAS Rhew 7-31 sunset — View of sunset over the Pacific Ocean from NOAA Ship Bell M. Shimada

Did You Know?

Before every fishing operation on the boat we must first do a marine mammal watch. Scientists and other crew members go up to the bridge of the boat to see if any mammals (whales, seals, dolphins) are present near the boat. This is to help prevent these animals from being harmed as we collect fish as well as making sure we are not running a risk of these mammals getting caught in the fishing nets.

Fascinating Catch of the Day!

Today’s fun catch in the net was a Brown Catshark! These creatures are normally found in the deeper parts of the Pacific Ocean. They are typically a darker brown color with their eyes on the side of their head. Their skin is very soft and flabby which can easily lead to them being harmed. They have two dorsal fins and their nostrils and mouth on the underside of their body. One of the sharks we caught was just recently pregnant.

Two brown catsharks

Catsharks have two dorsal fins (on their backs)

Catsharks’ nostrils and mouths are on the undersides of their bodies

Catshark egg sacks

Notice to yellow curly substance coming out of the shark? That is from the egg sac. Sharks only produce one egg sac at a time. It normally takes up to a full year before a baby shark to form!

June 23, 2017June 23, 2017

Marsha Lenz: Celebrating Science and the Solstice, June 21, 2017

NOAA Teacher at Sea

Marsha Lenz

Aboard Oscar Dyson

June 8-28, 2017

Mission: MACE Pollock Survey

Geographic Area of Cruise: Gulf of Alaska

Date: June 21, 2017

Weather Data from the Bridge

Latitude: 55 15.0 N

Longitude: 160 06.7 W

Time: 1300

Visibility: 10 Nautical Miles

Wind Direction: VAR

Wind Speed: LT

Sea Wave Height: <1 foot

Barometric Pressure: 1003.4 Millibars

Sea Water Temperature: 9.8°C

Air Temperature: 7.0°C

Science and Technology Log

We have been surveying transect lines (sometimes we fish, sometimes we don’t). During the times that we aren’t fishing, I find myself looking out at the ocean A LOT! During these quiet times on the ship, I am reminded of how large the oceans are. I found a quiet window to sit by in the Chem Lab and enjoy watching as the waves dance off of the side of the ship.

During some of these times when we are not collecting data from fish, identifying species from the DropCam, or preparing for the next haul, I find myself reading, which is a luxury all in itself. A friend of mine lent me to book to read and as I was reading the other day, the author quoted Jules Verne, author of 20,000 Leagues Under the Sea. Verne said, “Science, my lad, is made up of mistakes, but they are mistakes which it is useful to make, because they lead little by little to the truth.” I found this to be fitting for what I am doing on this survey, for the three weeks that I am a Teacher At Sea. Though I am surrounded by trained and educated professionals, I have realized that mistakes still happen and are something to be expected. They happen regularly. Often, actually. And, it’s a good thing that they do. They are important for learning. When humans make mistakes, hopefully, we can adjust our actions/behaviors to reduce the chances of that same “mistake” from happening again. When applied to science, the same idea is also true. When we can collect data from something that we are studying, we learn about the ways that it interacts with its surroundings. Through these findings, we not only learn more about what we are studying, but then take measures to protect its survival.

We had a real experience like this happen just the other day. For days, the “backscatter” was picking up images of fish that the scientists didn’t think were pollock on the bottom of the ocean. Backscatter is what the scientists use to “see” different groups of fish and quantify how many are in the water. The ship uses various echosounders. Several times, the science team decided to collect fish samples from these areas. Every time that they decided to “go fishing”, we pulled up pollock. The team was baffled. They had a hypothesis as to why they were not catching what they thought they saw on the backscatter. They thought that it was rockfish that were hanging around rocks, but the pollock were being caught as the net went down and came back up. Finally, after several attempts of not catching anything but pollock, they decided to put down the DropCam and actually try to see what was going on down there.

At that point, the Chem lab was filled with scientists. Everyone wanted to see what was going to show up on the monitor. The NOAA Corps Commanding Officer even came to see what was going to show up on the monitor. The room will filled with excitement.

Abigail steers the DropCam and watches the monitor simultaneously.

We see rockfish!

It was just as they predicted! The rockfish were hanging out in the rocks. It was a moment of great satisfaction for the scientists. They were able to identify some of the fish on the backscatter that was causing them so much confusion! Yay, science!

19433465_10211635923631739_1269694918_n — This is a pollock!

Later in the day, we went fishing and collected the usual data (sex, length, weight, etc.) from the pollock. There are usually 4 of us at a time in the Fish lab. We are getting into a routine in the lab and I am getting more familiar with my responsibilities and duties. I start by controlling the door release, which controls the amount of fish released onto the conveyor belt. After all of the fish have been weighed, I separate the females and males. Once that has been done, I take the lengths of a sample of the fish that we caught. When I finish, I assist Ethan and Abigail in removing and collecting the otoliths from a selected fish sample. Then, its clean-up time. Though we all have appropriate gear on, I somehow still end up having fish scales all over me. Imagine that!

Every time that we “go fishing”, a “pocket net” is also deployed. This is a net that has finer mesh and is designed to catch much smaller marine life. On this haul, we caught squid, age “zero” pollock, and isopods.

We also found some young Magister Armhook squid.

Age “Zero” pollock under under the age of 1.

Parasitic isopods attach themselves to the pollock and suck their blood.

We record the mass and length of everything caught.

We also caught a larval flatfish and an Age “Zero” pollock.

In the evening, we headed towards Morzhovoi Bay. There, we were greeted by a pod of Pacific white-sided dolphins. They spent some time swimming next to us. When they discovered that we were not that interesting, they swam off. They did leave us though with a great sense of awe and appreciation (and a few great pictures!).

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Personal Log

Happy Summer Solstice! Today is the longest day of the year! We have had some spectacular days. We were all excited as we got up this morning to welcome the rising of the sun. We woke up and were holding position in front of Mt. Pavlof. We saw the sunrise and went up to the Flying Bridge to do some morning yoga. After a wonderful breakfast of a bagel with cream cheese, salmon, Larrupin sauce, and Slug Slime, I went back up to the Bridge to get a full 360 degree view of the bay. There I saw a humpback whale swimming around. This will definitely be a summer solstice to remember!

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Did You Know?

A humpback whale is about the size of a school bus and weighs about 40 tons! They also communicate with each other with songs under the water.

sidenote: I know I wrote in my last blog that I was going to discuss the fishing process today, but there were so many other amazing things that happened that it is going to have to wait until next time. Sorry!