acoustics – Page 16 – NOAA Teacher at Sea Blog

June 1, 2009April 5, 2021

Susan Smith, June 1, 2009

NOAA Teacher at Sea
Susan Smith
Onboard NOAA Ship Rainier
June 1-12, 2009

Mission: Hydrographic survey
Geographical area of cruise: Trocadero Bay, Alaska; 55°20.990’ N, 33°00.677’ W
Date: June 1, 2009

Weather Data from the Bridge
Sea Temperature: 10.0 C (50 F)
Visibility: Clear, 10+ nautical miles

Science and Technology Log

What a way to start the day- learning how to deploy launches and all that goes into that process. Each new person onboard the ship who was going to be taking a launch, or responsible for their deployment, was required to attend this training meeting. Safety is of utmost importance on the NOAA ships and the smallest things when not done properly can result in disaster.

I learned a great deal of new vocabulary this morning, mostly pertaining to launch equipment, rope terms, and parts of the launch. It was stressed that in order for us all to have a positive experience we had to learn these terms and their procedures as quickly as possible.

Vocabulary: davit, lizard line, frapping line, bitter end, bite of line.

Three launches were deployed this afternoon to various areas around the Trocadero Bay. Using a Conductivity, Temperature and Depth(CTD) cast three times, we were able to determine salinity, depth of water, and temperature, all measurements used to calculate speed of sound. We set off to finish collecting data from areas missed, called “getting the holiday”. These are generally very small white areas on the screen which need to be surveyed. The wide pink line on the screen to the right indicates the section being surveyed. The pink section is actually made of many tiny lines as the sonar pings back to the launch.

Beautiful screen showing sonar return, most likely a rocky bottom. There are no breaks in the line, or acoustic shadows. The surveyors and techs really like this display of information.

This display is not so beautiful. The bottom was most likely mud or other soft bottom type, preventing a strong sonar return. The line with orange and yellow dots under the bright green line is very weak and blurry. There are blank sections called acoustic shadows, or locations the sonar does not reach.

Animals Sighted: Red jellyfish, blue jellyfish, deer on the coastline

Personal Log

Brown Kelp often deceives the sonar as it may appear as rocks.

What a grand time to be on a NOAA ship in Alaska! The weather has been fantastic, the scenery quite beautiful, and wonderful people who enjoy their jobs. Upon my arrival I was assigned “The PIT”, A C desk sleeping berth areas. It is below the laundry room, but very dark and surprisingly quiet considering its proximity to other mechanical areas of the ship. The suggested ear plugs were certainly a welcome item in the event I just couldn’t get to sleep.

Once I got my bearings, most of the areas I had to be in were easy to find. I was a little apprehensive that the onboard drills would be stressful, especially if I happened to be on the bridge or in the plot room. Going down three sets of steps, getting my survival suit, climbing back up one set of steps, and making it to my muster station as quickly as possible was not my idea of fun. However it was not as I imagined, as there were plenty of other new people who had to maneuver themselves around as well. Plus, we did not have to don the suits…this time!

Here I am working the sonar on a launch. Computer screens showing a vast array of data being collected and the charts used to record the data.

As for the food…it is wonderful, as our cooks know what really drives the ship—a hunger-satisfied crew. And we get service with a smile, something not found in most public restaurants in this day and time. After my dinner Tuesday night I was able to go kayaking in the Trocadero Bay, located inside the Tongass National Forest. Never having done this activity before, I was quite excited to get going. Four of us took to the water for about two hours, kayaking around a large island. While sitting as still as the current would allow I was able to see quite a few seals pop their heads up, look around, then dive under again. Maybe we were infringing upon their recreation area!

The view was spectacular, the water was calm, and I finally got to view a few eagles close enough to actually see the white feathers on their necks. Bird calls were also abundant. Such a nice way to end the day at sea.

July 23, 2007April 1, 2021

Roy Arezzo, July 23, 2007

NOAA Teacher at Sea
Roy Arezzo
Onboard NOAA Ship Oscar Dyson
July 11 – 29, 2007

Mission: Summer Pollock Survey
Geographical Area: North Pacific, Alaska
Date: July 23, 2007

Weather Data from Bridge
Visibility: <1 nm (nautical miles)
Wind direction: 220° (SW)
Wind speed: 8 knots
Sea wave height: <1 foot
Swell wave height: 0 feet
Seawater temperature: 9.8 °C
Sea level pressure: 1006.7 mb (millibars)
Air Temperature: 10°C
Cloud cover: 8/8, fog

Roy and Tamara get excited about birding on the bridge of the OSCAR DYSON

Science and Technology Log

Consumers became very aware of the issue of by-catch when the media reported the canned-tuna industry was killing dolphins in their nets nearly a decade ago. The industry responded by changing some of their fishing methods and marketing “dolphin-safe tuna”. NOAA monitors and sets catch limits for commercial fishing, regulating by-catch, among other things. The Coast Guard assists by also enforcing these fishing regulations. Some of the scientists working here on the pollock survey have worked as fishery observers on commercial vessels, monitoring by-catch in the Alaska fleets. The by-catch regulations vary based on the region, species and season. For example, on the Bering Sea none of the finfish outfits are allowed to keep any crab, they need a special permit to keep halibut and they need to keep cod if they are fishing for pollock. Commercial trawling for pollock results in typically low by-catch. Some environmental groups have listed pollock as a sustainable fish food compared to other seafood in that the harvest does not seem to significantly harm the environment or severely deplete fish stocks. The Marine Stewardship Council, an independent global nonprofit organization, has certified Alaskan pollock as a sustainable fishery.

NOAA Scientist Abby separates out Chrysaora melanaster, common name Lions Mane. — NOAA Scientist Abby separates out a Chrysaora melanaster jellyfish.

Although we are not dealing with by-catch directly, I find the connection between by-catch, sustainability and fish stocks very interesting. The Echo Integration Trawl Survey uses acoustic data to estimate pollock populations. When we put out our nets we do so to obtain a sample of fish, detected by our acoustic instruments. Since we are conducting mid-water trawls we bring up mostly pollock. The non-pollock species that occasionally get caught in the net are important in verifying the acoustic data and to know what is in the water column with the target species. As a science teacher, the diversity makes for interesting fishing and I have been able to observe a few organisms that spend most of their time in deep water. I have shared some of my images of the unusual species below, all of which I had never seen before this trip. Many of the organisms we bring up go back into the water after we record the data but some of our catch makes it to the galley to be served up for meals.

More Invertebrates

Flathead Sole (Hippoglossoides elassodon). Flatfish tend to swim higher in the water column in the evening following the plankton

Greenland Turbot (aka Greenland Halibut)

Great Sculpin (Myoxocephalus polyacanthocephalus)

Smooth lumpsucker (Aptocyclus ventricosus)

Kier, Chef and Assistant to the Chief Steward, makes a serious shrimp bisque.

Catch of the day: Chief Steward Rick cooks up Pollock Fish and Chips

Bird of the Day: Turns out, there is no such thing as a seagull. This was passionately explained to me by birder who will remain nameless. You ask, why no seagulls? Simply the term is not used in the scientific community. There are seabirds and of this general group there are well over 100 species of gulls. Some gulls are found well inland. Some species of land-based gulls have become popularized due to their opportunistic feeding around humans. Many of the pelagic gulls I have seen this trip are not as well trained as the ones in NYC and stick to wild foods, not even accepting the occasional fish scraps I have tempted them with off the back deck. I had reported in a previous log seeing Kittiwake’s and some immature Herring Gulls. Today we saw a Slaty-back Gull. It is a handsome gull with striking contrasts of black, dark grey and white. They seem to turn up more each time we reach the northern end of a transect line (above 60° latitude). I also learned that the red spot on the beak is a sign of maturity in many adult gulls. I have a renewed appreciation for gulls and look forward to identifying the species back home.

Bottom trawls, conducted on the previous leg of this study, tend to have more diversity in the sample

Personal Log

We are approaching the northwestern edge of our transect field and the water is deeper and colder and we are finding less fish. I am lucky to find more time to spend on the bridge and witness the communication with Russian fishing vessels, jumping salmon and occasional marine mammal sightings. I have a little camera envy. Some of the folks aboard have the right lens and the right camera to catch the action out at sea. My little 4X zoom digital is looking mighty bleak on the deck and thus I need to rely on the serious photographers for images of some of these exciting finds; their generosity in sharing their images is most appreciated.

Question of the Day

Today’s question: How does one become a Golden Dragon?

Previous Question: Why do pollock rise in the water column at night?

Much of the food eaten by pollock fluctuates in their vertical migration depending on light penetration. During the daylight hours many of the euphausiids (krill) can be found lower in the water column. It seems that by staying lower in the darker portions of the water column during the day, zooplankton may be more protected from their major predators. Near the surface, the phytoplankton (algae) uses the sun’s energy to produce food all day. As the light fades the zooplankton rise, feeding on algae, and the pollock follow their food source.

Krill from one of our nighttime raids with the Methot Trawl

Krill (pollock food): Partially digested from inside the stomach of a pollock

Pollock gill rakers screen food from leaving the oral cavity as the water passes out of the gill slits, oxygenating the gills

July 19, 2007April 1, 2021

Roy Arezzo, July 19, 2007

NOAA Teacher at Sea
Roy Arezzo
Onboard NOAA Ship Oscar Dyson
July 11 – 29, 2007

Mission: Summer Pollock Survey
Geographical Area: North Pacific, Alaska
Date: July 19, 2007

Weather Data from Bridge
Visibility: 10+ nm (nautical miles)
Wind direction: 270° (SW)
Wind speed: 11 knots
Sea wave height: 5 foot
Swell wave height: 5feet
Seawater temperature: 8.1°C
Sea level pressure: 1004.4 mb (millibars)
Air Temperature: 9.7°C
Cloud cover: 6/8, stratus

NOAA’s Lieutenant Commander D. ZezulaReading the chart of the North Bering Sea — NOAA Lieutenant Commander D. Zezula reading the chart of the North Bering Sea

Science and Technology Log:

I would like to thank David J. Zezula, Lieutenant Commander for NOAA and Alaska Region’s Navigation Manager, who spent over an hour showing me charts and resources for my school. David is serving as a relief officer of the deck aboard the OSCAR DYSON. Around our second Transect this leg we needed to break off from our line momentarily to avoid some shallow pinnacles listed on the chart. Of the three, one pinnacle is charted in deep water and the tall thin pinnacle seems an unlikely seafloor feature. I was surprised to learn that the information on the printed chart was different from the digital GLOBE program the scientists use to assess the bottom. It was indicated on the printed chart that these shallow regions were charted back before we started making seafloor maps using multi-beam sonar technology. The actual depth in that region is thus questionable and rather than sail over what seemed like deep enough water we cruised around it for safety precautions. Our draft is about 29 feet and all of sensors are located on the centerboard that extends down below the hull’s lowest point. As a research vessel we care very much about our sensors.

Long-tail Jaeger photographed off the bow of OSCAR DYSON by Tamara K. Mills

I asked David about this and he went to his files and was able to show me more information about the dates and background on that specific chart. Some of the archives he has access to were actually scanned from hand written charts created with lead lines back at the turn of the century. One of the main parts of his job back on land is to help prioritize what regions of Alaskan waters are to be updated with modern technology as part of NOAA’s Office of Coast Survey (the hydrographic and nautical charting division of NOAA). Obviously they focus on key ports and channels first but there is much water out there to chart and verify.

Bird of the Day: Today I was fortunate to see yet another “new to me” species. The Long-tail Jaeger (Stercorarius, longicaudus) is a pelagic seabird that rules the air. Although it probably eats some fish near the surface it is famous for its aerial piracy. It is a very muscular bird that is capable of upending flying birds forcing them to regurgitate their stomach contents to obtain a meal. This is currently their breeding time so it is early in the season for them to be found this far out at sea but soon mature adults and their grown offspring will be out on the Bering looking for food before their winter migration to the south. I keep missing the albatross sightings and hope that it will be my next bird of the day. Information provided courtesy of Mark Rauzon, birder, author, educator and friend.

Personal Log

Land! It was very exciting to see land for many reasons. First, the sun was out, a rare treat on the Bering. Many of the weather entries above will list the cloud cover as 8/8, which means out of 8 parts of sky all of it is covered by clouds. Also the visibility was good and the seas, which turned up with some high winds last night, had calmed down considerably. Lastly we were looking at Russia, many of us for the first time, which made sense since we were in the north part of our third transect line in Russian waters. It was also the first time we have seen land since we left Dutch Harbor. Cape Otvesnyy, at 860 meters high was visible from about 63 miles away. We all went outside the bridge to take photos and celebrate.

Question of the Day

Today’s question: Why do pollock rise in the water column at night?

Previous Question: How is the field of acoustics used in science?

OSCAR DYSON’S deck crew attaches an acoustic device (yellow) to the fishing gear

Acoustics is a huge area of technology that ranges from how we design theaters to the use of sonograms to view unborn children. Much of the acoustic technology used in science has to do with creating alternative ways to observe different environments. Light does not travel through water as far as sound (vibrations). Sound waves are the key to looking deep into water. Marine mammals know this and can find prey with echolocation, reading reflected sound waves they send out to locate food and communicate.

On OSCAR DSYON we use several types of acoustic instruments

The Simrad EK60 is our main fish counting instrument and it uses about a 7º beam to send out sound waves of different frequencies and receive echoes from organisms and objects of different sizes. It is mounted on the centerboard and reads information from 5 frequencies ranging from 18 to 200 KHz. As we run along our transect line the data that is received is used to estimate the fish density. The scientists onboard spend a fair amount of time checking to see that the echoes actually represent pollock.

The ME70 Multi-beam is mounted to the ship’s hull and is a powerful tool in creating a wide swath three-dimensional image of what is below the ship. This is especially useful in hydrographic work that involves charting and mapping the seafloor bottom but it may be used for the fish survey in the future. The Acoustic Doppler Current Profiler (ADCP) is also connected to the centerboard and uses the Doppler Effect (the change in frequency and wavelength of a sound pulse as perceived by an observer moving relative to the source of the sound) to estimate current and fish speed.

We place a Net Sounder (FS70, affectionately known as the turtle) on to our fishing n each time we trawl. Like scientists, commercial fishermen often use this instrument to monitor the shape of the net opening and the amount of fish entering the net. It does this by sending a 200 kHz frequency beam across the opening of the net and transmits data along a cable for the team to see on our monitors. Along with the turtle we send down a Simrad ITI, which is smaller and wireless but a lower resolution net sounder that is used as backup in the event we have trouble with our cable.

The DIDSON (Dual Frequency Identification Sonar) is an instrument that has been developed for divers in low visibility water and has many industrial applications. It creates an image typical to the one seen on sonogram tests. It uses a high frequency beam (up to 1.8 MHz) to achieve a short-range image (up to 50 meters). It has been applied to salmon return rate studies and has well enough resolution to make out the shape of a moving fish. The pollock survey team has been experimenting with it as a way to monitor fish escapement from the net and how fish behave within the net.

In our survey work most of our mid-water trawls occur between 17 and 700 meters. The acoustic technology is vital to verify fish at these depths.