turbidity – NOAA Teacher at Sea Blog

July 11, 2026July 11, 2026

Amelia Black: We’re not in Kansas Anymore, July 8, 2026

NOAA Teacher at Sea

Amelia Black

Aboard NOAA Ship Oregon II

July 6-17, 2026

Mission: SEAMAP Summer Groundfish Survey
Geographic Area of Cruise: Gulf of America/Gulf of Mexico
Date: July 8, 2026

Weather Data from the Bridge:
Latitude: 28.41N
Longitude: 90.12W
Sea wave height: 1 ft
Wind Speed: 7 kt
Wind Direction: 180
Visibility: 10 miles
Sea Temperature: 88.34℉
Air Temperature: 85℉
Barometric Pressure: 30.03 inHg
Humidity: 70
Sky: Overcast

Science and Technology Log

“Toto, I’ve a feeling we’re not in Kansas anymore.” Judy Garland as Dorothy Gale in The Wizard of Oz

Amelia introduces Dorothy

Transcript: [Amelia]: And meet Dorothy! Dorothy is the CTD. And she’s named Dorothy II because we are on the Oregon II.

The entire instrument is called a rosette, but aboard Oregon II it is nicknamed Dorothy II. The rosette is the large circular frame that holds multiple bottles and scientific instruments. At the very bottom of the rosette is the CTD, affectionately known as Toto. CTD stands for Conductivity, Temperature, and Depth and it is one of the instruments scientists use to measure the health of the Gulf.

two images in a diagram. on the left is an photo of the entire rosette, seen against a white background. it is a circular white metal frame that contains a ring of tall, narrow water bottles mounted above an instrument in the base. the image on the right represents an enlarged view of just that bottom instrument. it is titled "CTD: Conductivity Temperature Depth." In this close-up view, arrows point to different labeled parts: transmissometer, conductivity sensor, temperature sensor, altimeter, pump, flourometer, oxygen sensors, pressure sensor (main unit) — Dorothy II (The Rosette on Oregon II)
_{Diagram created by Amelia Black, NOAA Teacher at Sea,
with input from NOAA Senior Survey Tech Stephanie Stable}

top-down closer view of just the conductivity, temperature, and depth sensor housed at the bottom of the rosette. we can see a label on the sensor reads TOTO. — Toto also known as the CTD

The first measurement the CTD collects is conductivity. Conductivity measures the salinity or how much salt is in the ocean. The higher the conductivity, the saltier the water (https://www.epa.gov/national-aquatic-resource-surveys/indicators-conductivity)

You may be wondering, how salty is the ocean? This depends on the temperature of the ocean water. The warmer the water, the more salt the water can hold. The Gulf’s average salinity is 36 parts per thousand or 3.6 percent. That’s roughly equivalent to a little under ½ a cup of salt dissolved in a gallon of water. Now that’s salty!

Next, the CTD measures the temperature of the water. Both temperature and conductivity are measured at different water depths. As the rosette approaches the seafloor, an altimeter uses sound waves to determine the distance to the bottom. An alert is sent to the scientists starting when the rosette is 100 meters from the ocean floor. The altimeter ensures that the rosette doesn’t run into the ground (bottom of the sea).

The next two sensors, the fluorometer and the transmissometer measure different particles within the water. According to NOAA Ocean Exploration page:

A fluorometer measures the amount of chlorophyll in the seawater by shining ultraviolet (UV) light through the water and measuring the amount of red light that is produced by the chlorophyll in response to the UV. (https://oceanexplorer.noaa.gov/expedition-feature/19gulfofalaska-logs-july26-2/)

Yes, chlorophyll, similar to the chlorophyll that plants use to change carbon dioxide into oxygen (photosynthesis). The fluorometer looks at fluorescents (types of chlorophyll and other compounds) that are in the water. This information helps the scientists to determine the overall productivity, or health, of the water. Similar to the fluorometer, the transmissometer uses a beam of light to measure the turbidity of the water. Turbidity is how clear the water is (https://www.epa.gov/system/files/documents/2021-07/parameter-factsheet_turbidity.pdf). The clearer the water, the farther the light travels. Think about the difference between a clear clean creek versus a muddy river. Which would you rather swim in?

Senior Survey Technician Stephanie Stabile explains final CTD checks as it is deployed into the water.

Transcript: [Stephanie]: We go over and we check to make sure all the bottles are open, none of the lanyards are stuck. These air vents at the top of the bottles? We want them closed. And then samples valves at the bottom, we want them pulled out all the way so all water stays in the bottle. We take the caps off the sensor: so there’s two red caps and then one white cap at the bottom as well. And then she’s ready to go!

One final piece of the CTD that is very crucial is the cable. This cable transmits (sends) data in real time back to the ship’s dry lab. Scientists receive the data and decide whether to close the rosette’s sampling bottles to collect water for further analysis. Common water samples are tested for chlorophyll, oxygen, and nutrient levels.

Back in the dry lab, scientists analyze the incoming data using multiple displays. There is an incredible amount of information flowing in before a single fish is ever caught!

a man sits at a desk with many computer monitors

photo of a computer screen displaying a table of data

NOAA Scientist Adam Pollack analyzing real-time data from the CTD

And all of this happens before the crew even deploys the otter trawl nets to collect the groundfish sample for SEAMAP.

Personal Log

I am really enjoying my time at sea. I’m not sure if it’s the beautiful ocean, getting to handle fascinating sea creatures, the delicious meals prepared by Chief Steward Missy, or simply the incredible people abroad Oregon II, but so far this has been an amazing experience!

Speaking of the great crew, I would like to introduce you to one of my coworkers, Senior Survey Technician Stephanie Stabile.

Stephanie works with NOAA as part of the relief pool. Rather than being permanently assigned to Oregon II, she gets the opportunity to work aboard many different NOAA ships and crew as relief help, similar to a substitute teacher.

Survey technicians are responsible for data acquisition. They oversee the collection and quality of the scientific data gathered by the ship. “Data is our ‘cargo’, it is why we are out here,” Stephanie explains.

portrait photo of a woman wearing a blue hard hat and an orange life vest, standing near a wooden railing of the ship at night. she has a pair of rubber yellow gloves clipped to her belt. — NOAA Senior Survey Technician Stephanie Stabile

Stephanie has worked for NOAA since 2015. The part of her job she enjoys most is being part of a team, accomplishing the mission, and spending time at sea.

“There are moments where I can’t believe that I get paid to be out at sea,” Stephanie says. “I look out at the horizon and see how vast the world is. It is very humbling.”

photo of sunset over the Gulf. the water is dark blue, and the sky has streaks of yellow, pink, and orange at the horizon beneath gray-blue clouds

“There are moments where I can’t believe that I get paid to be out at sea. I look out at the horizon and see how vast the world is. It is very humbling.”
–_{Stephanie Stabile}

view over the Gulf toward the horizon. the water is very calm, almost glassy in places, and gray. the sky is light blue with lots of white cloud cover. the water reflects the sky in places. — View of the horizon from Oregon II

Her advice for anyone unsure of their future career: “Whatever it is that you want to do, try to be around it as much as you can. Volunteer, work at an aquarium, get the experience.”

I absolutely love this advice! Sometimes the best way to discover whether something is the right path/career is simply to get involved and experience it firsthand.

Did You Know?

The ocean produces over half of the Earth’s oxygen! Check out this article from NOAA to learn more: https://oceanservice.noaa.gov/facts/ocean-oxygen.html

Don’t forget that you can follow along on my journey through the Gulf at https://www.windy.com/station/ship-wtdo?waves,27.501,-92.356,8,m:esbadxt

Be sure to check back for my next blog as I continue exploring life and science aboard Oregon II.

Adventure awaits!

Sources

July 8, 2018July 15, 2018

Pam Schaffer: Oceanographers Toolbox: What is a CTD? July 7,2018

NOAA Teacher at Sea

Pam Schaffer

Aboard NOAA Ship Bell M. Shimada

[July 2-10, 2018]

Mission: ACCESS Cruise

Geographic Area of Cruise: North Pacific: Greater Farallones National Marine Sanctuary, Cordell Bank National Marine Sanctuary

Weather Data from the Bridge

Date	July 7 2018
Time	1200 (noon)
Latitude	37° 58.3’ N
Longitude	123° 06.4’ W
Present Weather/ Sky	Cloudy
Visibility (nm)	10
Wind Direction (true)	341°
Wind Speed (kts)	18
Atmospheric Pressure (mb)	1018
Sea Wave Height (ft)	3-5
Swell Waves Direction (true)	330°
Swell Waves Height (ft)	3-5
Temperature Sea Water (C)	13.2°
Temperature Dry Bulb (C) Air Temperature	13.1°
Temp Wet Bulb (C )	12.1°

Science and Technology Log

Marine life is not evenly distributed throughout the World’s oceans. Some areas contain abundant and diverse life forms and support complex food webs whereas other areas are considered a desert. This variation is due to environmental factors like temperature, salinity, nutrients, amount of light, underlying currents, oxygen levels and pH. Some of these variables, such as temperature, oxygen levels, and pH, are experiencing more variability as a result of climate change. In order to understand the health of marine environments, scientists explore the chemical and physical properties of seawater using a set of electronic instruments on a device called a CTD. CTD stands for conductivity, temperature and depth and is the standard set of instruments used to measure variables in the water column.

Source: ACCESS www.ACCESSoceans .org — Source: ACCESS http://www.ACCESSoceans .org

The CTD is the bread and butter of oceanography research. It is primarily used to profile and assess salinity and temperature differences at varying depths in a water column. But the device can also carry instruments used to calculate turbidity, fluorescence (a way to measure the amount of phytoplankton in the water), oxygen levels, and pH. Conductivity is a way of determining the salinity of water. It measures how easily an electric current passes through a liquid. Electric currents pass much more easily through seawater than fresh water. A small electrical current is passed between two electrodes and the resulting measurement is interpreted to measure the amount of salt and other inorganic compounds in a water sample. Dissolved salt increases the density of water, and the density of water also increases as temperature decreases. Deeper water is colder and denser. Density is also affected by water pressure. Since water pressure increases with increasing depth, the density of seawater also increases as depth increases.

Optical sensors are used to measure the amount of turbidity, fluorescence, and dissolved oxygen at various depths in the water column. Dissolved oxygen levels fluctuate with temperature, salinity and pressure changes and is a key indicator of water quality. Dissolved oxygen is essential for the survival of fish and other marine organisms. Oxygen gets into the water as gas exchange with the atmosphere and as a by-product of plant photosynthesis (algae, kelp etc.).

Photo Credit: Julie Chase/ACCESS/NOAA/Point Blue

Typically, CTD instruments are attached to a large circular metal frame called a Rosette, which contains water-sampling bottles that are remotely opened and closed at different depths to collect water samples for later analysis. Using the information and samples collected, scientists can make inferences about the occurrence of certain chemical properties to better understand the distribution and abundance of life in particular areas of the ocean.

Scientist Carina Fish collects samples from CTD

On our mission, scientists deploy the CTD to a depth of 500 meters at most stations. On the shelf break, the researchers deployed the CTD to 1200 meters (more than 3/4 of a mile below the surface) to collect samples. The pressure is so great at this depth that a 1 foot by 1 foot square of Styrofoam is crushed to a quarter of its size(3″x 3″).

Personal Log

Around 01:30 last night we lost our Tucker Trawl net as it was being re-positioned. The winds had picked up to around 20 knots and the sea height was around 5-8 feet according to the bridge log. The sea state complicated the retrieval and as best we can conclude the wind and seas pushed the net bridle into a prop blade which swiftly and effortlessly cut the 1/3” thick metal wire cable and separated the net from its tether. Mishaps at sea are part and parcel of working in a harsh and variable environments. Even the very best and most experienced captain and crew encounter unforeseen issues from time to time. Dr. Jaime Jahncke quickly stepped into action and made contact with onshore colleagues to arrange for another net for the next research cruise. In the meantime, we plan to use the hoop net to collect krill samples, weather permitting.

Did You Know?

According to NOAA scientists, only about 5% of the Earth’s oceans have been explored.

May 28, 2015August 21, 2021

DJ Kast, Interview with Megan Switzer and the Basics of the CTD/ Rosette, May 28, 2015

NOAA Teacher at Sea
Dieuwertje “DJ” Kast
Aboard NOAA Ship Henry B. Bigelow
May 19 – June 3, 2015

Mission: Ecosystem Monitoring Survey
Geographical area of cruise: Gulf of Maine
Date: May 28, 2015, Day 11 of Voyage

Interview with Student Megan Switzer

Chief Scientists Jerry Prezioso and graduate oceanography student Megan Switzer — Chief Scientist Jerry Prezioso and graduate oceanography student Megan Switzer

Megan Switzer is a Masters student at the University of Maine in Orono. She works in Dave Townsend’s lab in the oceanography department. Her research focuses on interannual nutrient dynamics in the Gulf of Maine. On this research cruise, she is collecting water samples from Gulf of Maine, as well as from Georges Bank, Southern New England (SNE), and the Mid Atlantic Bight (MAB). She is examining the relationship between dissolved nutrients (like nitrate and silicate) and phytoplankton blooms. This is Megan’s first research cruise!

In the generic ocean food chain, phytoplankton are the primary producers because they photosynthesize. They equate to plants on land. Zooplankton are the primary consumers because they eat the phytoplankton. There are so many of both kinds in the ocean. Megan is focusing on a particular phytoplankton called a diatom; it is the most common type of phytoplankton found in our oceans and is estimated to contribute up to 45% of the total oceanic primary production (Yool & Tyrrel 2003). Diatoms are unicellular for the most part, and a unique feature of diatom cells is that they are enclosed within a cell wall made of silica called a frustule.

Diatom Frustules. Photo by: 3-diatom-assortment-sems-steve-gschmeissner — Diatom Frustules. Photo by: Steve Schmeissner

Diatoms! PHOTO BY: — Diatoms! Photo by: Micrographia

The frustules are almost bilaterally symmetrical which is why they are called di (2)-atoms. Diatoms are microscopic and they are approximately 2 microns to about 500 microns (0.5 mm) in length, or about the width of a human hair. The most common species of diatoms are: Pseudonitzchia, Chaetocerous, Rhizosolenia, Thalassiosira, Coschinodiscus and Navicula.

Pseudonitzchia. Photo by National Ocean Service

Thalassiosira. Photo by: Department of Energy Joint Genome Institute

Photo of Coscinodiscus by: — Photo of Coscinodiscus

Diatoms also have ranges and tolerances for environmental variables, including nutrient concentration, suspended sediment, and flow regime. As a result, diatoms are used extensively in environmental assessment and monitoring. Furthermore, because the silica cell walls are inorganic substances that take a long time to dissolve, diatoms in marine and lake sediments can be used to interpret conditions in the past.

In the Gulf of Maine, the seafloor sediment is constantly being re-suspended by tidal currents, bottom trawling, and storm events, and throughout most of the region there is a layer of re-suspended sediment at the bottom called the Bottom Nepheloid Layer. This layer is approximately 5-30 meters thick, and this can be identified with light attenuation and turbidity data. Megan uses a transmissometer, which is an instrument that tells her how clear the water is by measuring how much light can pass through it. Light attenuation, or the degree to which a beam of light is absorbed by stuff in the water, sharply increases within the bottom nepheloid layer since there are a lot more particles there to block the path of the light. She also takes a water sample from the Benthic Nepheloid Layer to take back to the lab.

Marine Silica Cycle by Sarmiento and Gruber 2006

Megan also uses a fluorometer to measure the turbidity at various depths. Turbidity is a measure of how cloudy the water is. The water gets cloudy when sediment gets stirred up into it. A fluorometer measures the degree to which light is reflected and scattered by suspended particles in the water. Taken together, the data from the fluorometer and the transmissometer will help Megan determine the amount of suspended particulate material at each station. She also takes a water sample from the Benthic Nepheloid layer to take back to the lab. There, she can analyze the suspended particles and determine how many of them are made out of the silica based frustules of sinking diatoms.

This instrument is a Fluorometer and is used to measure the turbidity at various depths. Photo by: DJ Kast

She collects water at depth on each of the CTD/ Rosette casts.

Rosette with the 12 Niskin Bottles and the CTD. Photo by DJ Kast

Up close shot of the water sampling. Photo by DJ Kast

CTD, Rosette, and Niskin Bottle basics.

The CTD or (conductivity, temperature, and depth) is an instrument that contains a cluster of sensors, which measure conductivity, temperature, and pressure/ depth.

Here is a video of a CTD being retrieved.

Depth measurements are derived from measurement of hydrostatic pressure, and salinity is measured from electrical conductivity. Sensors are arranged inside a metal housing, the metal used for the housing determining the depth to which the CTD can be lowered. Other sensors may be added to the cluster, including some that measure chemical or biological parameters, such as dissolved oxygen and chlorophyll fluorescence. Chlorophyll fluorescence measures how many microscopic photosynthetic organisms (phytoplankton) are in the water. The most commonly used water sampler is known as a rosette. It is a framework with 12 to 36 sampling Niskin bottles (typically ranging from 1.7- to 30-liter capacity) clustered around a central cylinder, where a CTD or other sensor package can be attached. The Niskin bottle is actually a tube, which is usually plastic to minimize contamination of the sample, and open to the water at both ends. It has a vent knob that can be opened to drain the water sample from a spigot on the bottom of the tube to remove the water sample. The scientists all rinse their bottles three times and wear nitrile or nitrogen free gloves to prevent contamination to the samples.

On NOAA ship Henry B. Bigelow the rosette is deployed from the starboard deck, from a section called the side sampling station of this research vessel.

The instrument is lowered into the water with a winch operated by either Adrian (Chief Boatswain- in charge of deck department) or John (Lead Fishermen- second in command of deck department). When the CTD/Rosette is lowered into the water it is called the downcast and it will travel to a determined depth or to a few meters above the ocean floor. There is a conducting wire cable is attached to the CTD frame connecting the CTD to an on board computer in the dry lab, and it allows instantaneous uploading and real time visualization of the collected data on the computer screen.

CTD data on the computer screen. Photo by: DJ Kast

The water column profile of the downcast is used to determine the depths at which the rosette will be stopped on its way back to the surface (the upcast) to collect the water samples using the attached bottles.

Niskin Bottles:

Messenger- The manual way to trigger the bottle is with a weight called a messenger. This is sent down a wire to a bottle at depth and hits a trigger button. The trigger is connected to two lanyards attached to caps on both ends of the bottle. When the messenger hits the trigger, elastic tubing inside the bottle closes it at the specified depth.

Todd with the manually operated Niskin Bottle. Photo by: DJ Kast — Todd holding a messenger to trigger the manually operated Niskin Bottle. Photo by: DJ Kast

Manual CTD fully cocked and ready to deploy. Photo by DJ Kast

Here is a video of how the manual niskin bottle closes: https://www.youtube.com/watch?v=qrqXWtbUc74

The other way to trigger Niskin bottles is electronically. The same mechanism is in place but an electronic signal is sent down the wire through insulated and conductive sea cables (to prevent salt from interfering with conductivity) to trigger the mechanism.

Here is a video of how it closes electronically: https://www.youtube.com/watch?v=YJF1QVe6AK8

Conductive Wire to CTD. Photo by DJ Kast

Photo of the top of the CTD. Photo by DJ Kast — Photo of the top of the CTD showing the trigger mechanism in the center. Photo by DJ Kast

Top of the Niskin Bottles to show how the white wires are connected to the top. — Top of the Niskin Bottles shows how the lanyards are connected to the top. Photo by DJ Kast

The pin on the bottom is activated when an electronic signal is sent through the conductive sea cables. Photo by DJ Kast

Using the Niskin bottles, Megan collects water samples at various depths. She then filters water samples for her small bottles with a syringe and a filter and the filter takes out the phytoplankton, zooplankton and any particulate matter. She does this so that there is nothing living in the water sample, because if there is there will be respiration and it will change the nutrient content of the water sample.

Filtering out only the water using a syringe filter. Photo by DJ Kast

Syringe with a filter on it. Photo by: DJ Kast

This is part of the reason why we freeze the sample in the -80 C fridge right after they have been processed so that bacteria decomposing can’t change the nutrient content either.

Diatoms dominate the spring phytoplankton bloom in the Gulf of Maine. They take up nitrate and silicate in roughly equal proportions, but both nutrients vary in concentrations from year to year. Silicate is almost always the limiting nutrient for diatom production in this region (Townsend et. al., 2010). Diatoms cannot grow without silicate, so when this nutrient is used up, diatom production comes to a halt. The deep offshore waters that supply the greatest source of dissolved nutrients to the Gulf of Maine are richer in nitrate than silicate, which means that silicate will be used up first by the diatoms with some nitrate left over. The amount of nitrate left over each year will affect the species composition of the other kinds of phytoplankton in the area (Townsend et. al., 2010).

The silica in the frustules of the diatom are hard to breakdown and consequently these structures are likely to sink out of the euphotic zone and down to the seafloor before dissolving. If they get buried on the seafloor, then the silicate is taken out of the system. If they dissolve, then the dissolved silicate here might be a source of silicate to new production if it fluxes back to the top of the water column where the phytoplankton grow.

Below are five images called depth slices. These indicate the silicate concentration (rainbow gradient) over a geographical area (Gulf of Maine) with depth (in meters) latitude and longitude on the x and y axis.

Depth slices of nitrate and silicate. Photo by: This is the type of data Megan is hoping to process from this cruise. — Depth slices of nitrate and silicate. Photo by: GOMTOX at the University of Maine
This is the type of data Megan is hoping to process from this cruise.

June 22, 2012August 11, 2021

Lesley Urasky: Smile and say, “Squid!”, June 20, 2012

NOAA Teacher at Sea
Lesley Urasky
Aboard the NOAA ship Pisces
June 16 – June 29, 2012

Mission: SEAMAP Caribbean Reef Fish Survey
Geographical area of cruise: St. Croix, U.S. Virgin Islands
Date: June 20, 2012

Location:
Latitude: 18.1937
Longitude: -64.7737

Weather Data from the Bridge:

Air Temperature: 28°C (83°F)
Wind Speed: 19 knots (22 mph), Beaufort scale: 5
Wind Direction: from N
Relative Humidity: 80%
Barometric Pressure: 1,014.90 mb
Surface Water Temperature: 28°C (83°F)

Science and Technology Log

The cameras are a very important aspect of the abundance survey the cruise is conducting. Since catching fish is an iffy prospect (you may catch some, you may not) the cameras are extremely important in determining the abundance and variety of reef fish. At every site sampled during daylight hours, we deploy the camera array. The cameras can only be utilized during the daytime because there are no lights – video relies on the ambient light filtering down from the surface.

Deployment of the array at a site begins once the Bridge verifies we are over the sampling site. The camera array is turned on and is raised over the rail of the ship and lowered to the water’s surface on a line from a winch that has a ‘quick release’ attached to the array. Once over the surface, a deck hand pulls on the line to the quick release allowing the array to free fall to the bottom of the ocean. Attached to the array is enough line with buoys attached. The buoys mark the array at the surface and give the deck hands something to aim for with the grappling hook when it is time for the array to be retrieved. Once the buoys are on deck, a hydraulic pot hauler is used to raise the array from the sea floor to the side of the ship. From there, another winch is used to bring the array on board.

Deploying camera array — Vic, Jordan, Joey, and Joe deploying the camera array.

When the array is deployed, a scientist starts a computer program that collects the time, position and depth the array was dropped at. The array is allowed to “soak” on the bottom for about 38 minutes. The initial 3-5 minutes are for the cameras to power up and allow any sediment or debris on the bottom to settle after the array displaces it. The cameras are only actually recording for 25 of those minutes. The final 3-5 minutes are when the computers are powering down. At one point in time, the cameras on the array were actual video cameras sealed in waterproof, seawater-rated cases. With this system, after each deployment, every individual case had to be physically removed from the array, opened up, and the DV tape switched out. With the new system, there are a series of four digital cameras that communicate wirelessly with the computers inside the dry lab.

We did have a short-lived problem with one of the digital cameras — it quit working and the electronics technician that takes care of the cameras, Kenny Wilkinson, took a couple of nights to trouble shoot and repair it. During this time period, we reverted back to the original standard video camera. Throughout the cruise, Kenny uploads the videos taken during the day and repairs the cameras at night so they will be ready for the next day’s deployments.

squid bait — Squid (before being cut into pieces) used for bait on the camera array

Besides the structure of the camera array which is designed to attract reef fish, the array is baited with squid. A bag of frozen, cut squid hangs down near the middle. The squid is replaced at every site.

In addition to the bait bag, a Temperature Depth Recorder (TDR) is attached near the center, hanging downward near the bottom third of the array. The purpose of the TDR is to measure the temperature of the water at various depths. It is also used to verify that the depth where the camera comes to rest on the ocean bottom and is roughly equivalent to what the acoustic sounding reports at the site. This is important because the camera generally doesn’t settle directly beneath the ship. Its location is ultimately determined by the drift as it falls through the water column and current. The actual TDR instrument is very small and is attached to the array near the bait bag. After retrieving the array at each site, the TDR is removed from the array and brought inside to download the information. To download, there is a small magnet that is used to tap the instrument (once) and then a stylus attached to the computer is used to read a flash of light emitted by an LED. The magnet is then tapped four times on the instrument to clear the previous run’s data. The data actually records the pressure exerted by the overlying water column in pounds per square inch (psi) which is then converted to a depth.

TDR data — Computer screen showing the data downloaded from the TDR.

The video from each day is uploaded to the computer system during the night shift. The following day, Kevin Rademacher (chief scientist), views the videos and quickly annotates the “highlights”. The following things are noted: visual clarity (turbidity [cloudiness due to suspended materials], what the lighting is like [backlit], and possible focusing issues), substrate (what the bottom is made of), commercially viable fish, fish with specific management plans, presence of lionfish (an invasive species), and fish behavior. Of the four cameras, the one with the best available image is noted for later viewing.

Computer data entry form for camera array image logs

Once back at the lab, the videos are more completely analyzed. A typical 20-minute video will take anywhere from 30 minutes to three days to complete. This is highly dependent upon density and diversity of fish species seen; the greater the density and diversity, the longer or more viewing events it will take. The experience of the reader is also an important factor. Depending upon the level of expertise, a review system is in place to “back read” or verify species identification. The resulting data is entered into a database which is then used to assign yearly data points for trend analysis. The final database is submitted to the various management councils. From there, management or fisheries rebuilding plans are developed and hopefully, implemented.

Spotted moray eel viewed from the camera array. He’s well camouflaged; can you find him?

Coney with a parasitic isopod attached below its eye.

Two Lionfish - an invasive species — Two Lionfish – an invasive species

Personal Log

Today, we are off the coast of St. Thomas and St. John in the U.S. Virgin Islands. We traveled from the southern coast of St. Croix, went around the western tip of the island and across the straight. When I woke up I could see not only St. Thomas and St. John, but a host of smaller islands located off their coastline.

Map of the Virgin Islands. St. Croix and St. Thomas are separated by 35 miles of ocean. It took us about 3 hours to cross to our next set of sampling sites.

Around dinner time last night we had an interesting event happen on board. They announced over the radio system that there was a leak in the water line and asked us not to use the heads (toilets). A while later, they announced no unnecessary use of water (showers, etc.); following that they shut off all water. It didn’t take long for the repairs to occur, and soon the water was returned. However, when I went to dinner, I discovered that the stateroom I’m sharing with Kelly Schill, the Ops Officer, had flooded. Fortunately, the effects of the flooding were not nearly as bad as I had feared. Only a small portion of the room had been affected. The crew did a great job of rapidly assessing the problem and fixing it in a timely manner. After this, I have absolutely no fear about any problems on board because I know the crew will react swiftly, maintain safety, and be professional all the while.

Last night was the first sunset I’ve seen since I’ve been on board. Up until this point, it has been too hazy and cloudy. The current haze is caused by dust/sand storms in the Sahara Desert blowing minute particles across the Atlantic Ocean.

Today has been a slow day with almost nary a fish caught. We did catch one fish, but by default. It was near the surface and hooked onto our bait. We immediately reeled in the line and extracted it. It was necessary to remove it because it would have skewed our data since it was caught at the surface and not near the reef. This fish was a really exciting one for me to see, because it was a Shark Sucker (Echeneis naucrates). These are the fish you may have seen that hang on to sharks waiting for tasty tidbits to float by. They are always on the lookout for a free meal.

One of the most interesting aspects of the shark sucker is that they have a suction device called laminae on top of their heads that looks a little like a grooved Venetian blind system. In order to attach to the shark (or other organism), they “open the blinds” and then close them creating a suction-like connection.

The "sucker" structure on the Shark Sucker — The “sucker” structure on the Shark Sucker. Don’t they look like Venetian blinds?

I got to not only see and feel this structure on the fish, but also let it attach itself to my arm! It was the neatest feeling ever! The laminae are actually a modified dorsal spines; these spines are needed because of the roughness of shark’s skin. When the shark sucker detached itself from me, it left a red, slightly irritated mark on my arm that disappeared after a couple of hours.

Look, Ma, No Hands! Shark sucker attached to my arm.

Tomorrow we’ll be helping place a buoy in between St. Croix and St. Thomas. It will be interesting to see the process and how the anchor is attached.

With all the weird and wonderful animals we’re retrieving, I can’t wait to see what another day of fishing brings.

July 13, 2011April 28, 2021

Kathleen Harrison: Shumagin Islands, July 9, 2011

NOAA Teacher at Sea
Kathleen Harrison
Aboard NOAA Ship Oscar Dyson
July 4 — 22, 2011

Location: Gulf of Alaska
Mission: Walleye Pollock Survey
Date: July 9, 2011

Weather Data from the Bridge
True wind direction: 59.9°, True wind speed: 11.44 knots
Sea Temperature: 9°C
Air Temperature: 8.9°C
Air pressure: 1009.74 mb
Foggy with 1 mile visibility
Ship heading: 88°, ship speed: 11 knots

Science and Technology Log

The Shumagin Islands are a group of about 20 islands in the Gulf of Alaska, southwest of Kodiak Island. They were named for Nikita Shumagin, a sailor on Vitus Bering’s Arctic voyage in 1741. They are volcanic in origin, composed mostly of basalt.

Several islands even exhibit hexagonal basaltic columns. There are about 1000 people who reside in the islands, mostly in the town of Sand Point, on Popof Island. According to the United States Coast Pilot (a book published by NOAA with extensive descriptions about coastlines for ship navigation), the islands extend out 60 miles from the Alaskan Peninsula. They are bold and mountainous.

The shores are broken in many places by inlets that afford good anchorages. The shores are rockbound close to. Fishing stations and camps are scattered throughout the group, and good fishing banks are off the islands. Fox and cattle raising are carried on to some extent.

long range view of SI, Alaskan Peninsula — Shumigan Islands to the left, snow covered peaks of Alaskan Peninsula in background. An amazing sight on a rare sunny day in the Gulf of Alaska.

Sea water quality is very important to the scientists on the Oscar Dyson. So important, that it is monitored 24 hours a day. This is called the Underway System. The sea water comes through an intake valve on the keel of the bow, and is pumped up and aft to the chem lab. There, it goes through 4 instruments: the fluorometer, the dissolved Oxygen unit, the Thermosalinograph (TSG), and the ISUS (nitrate concentration).

The fluorometer measures the amount of chlorophyll and turbidity in the sea water once every second. A light is passed through the water, and a sensor measures how much fluorescence (reflected light) the water has. The amount of chlorophyll is then calculated. The measurement was 6.97 µg/L when I observed the instrument. The amount of phytoplankton in the water can be interpreted from the amount of chlorophyll. Another sensor measures how much light passes through the water, which gives an indication of turbidity. Twice a day, a sample of water is filtered, and the chlorophyll is removed. The filter with the chlorophyll is preserved and sent to one of the NOAA labs on land for examination.

Here are all of the water quality instruments, they are mounted to the wall in the chem lab. Each one has a separate line of sea water.

The next instrument that the water passes through will measure the amount of dissolved oxygen every 20 seconds. Oxygen is important, because aquatic organisms take in oxygen for cellular respiration. From plankton to white sharks, the method of underwater “breathing” varies, but the result is the same – oxygen into the body. The oxygen in the water is produced by aquatic plants and phytoplankton as they do photosynthesis, and the amount directly affects how much aquatic life can be supported.

The TSG will measure temperature, and conductivity (how much electricity passes through) every second, and from these 2 measurements, salinity (how much salt is in the water) can be calculated. The day that I observed the TSG temperature was 8.0° C, and the salinity was 31.85 psu (practical salinity units). Average sea water salinity is 35. The intense study of melting sea ice and glaciers involves sea water temperature measurements all over the world. A global data set can be accumulated and examined in order to understand changing temperature patterns.

instrument to measure — This instrument measures the amount of nitrate in the sea water. It is called the ISUS.

The last instrument measures nitrate concentration in the sea water every couple of minutes. It is called ISUS, which stands for In Situ Ultraviolet Spectrophotometer. Nitrate comes from organic waste material, and tends to be low at the surface, since the wastes normally sink to the bottom. The normal value is .05 mg/L, at the surface, at 8°C. Values within the range of 0.00 to 25 mg/L are acceptable, although anything above 5 is reason for concern.

All of the data from these instruments is fed into a ship’s computer, and displayed as a graph on a monitor. The Survey Technician monitors the data, and the instruments, to make sure everything is working properly.

New Species Seen today:

Whale (unknown, but probably grey or humpback)

Horned Puffin

Dall’s Porpoise

Krill

Chum Salmon

Eulachon

monitor shows current data — The current water quality data is shown on this computer screen beside the instruments.

Personal Log

Living on a ship is quite different from living at home. For one thing, every item on the ship is bolted, strapped, taped, or hooked to the bulkhead (wall), or deck (floor). Most hatches (doors) have a hook behind them to keep them open(this reminds me of when I put hooks behind my doors at home to keep little children from slamming them and crushing fingers). Some hatches (around ladderways (stairwells)) are magnetically controlled, and stay open most of the time. They close automatically when there is a fire or abandon ship situation or drill. Every drawer and cabinet door clicks shut and requires moving a latch or lever to open it. For some cabinet doors that you want to stay open while you are working in the cabinet, there is a hook from the bulkhead to keep it open.

bracket holds copier — The copier machine is held in place by a 4 post bracket that is bolted to the floor.

On every desk is a cup holder, wider on the bottom than the top, designed to hold a regular glass or a cup of coffee. If one of those is not handy, a roll of duct tape works well for a regular glass. All shelves and counters have a lip on the front, and book shelves have an extra bar to hold the books in. Trash cans and boxes are lashed to the bulkhead with an adjustable strap, and even the new copier machine has a special brace that is bolted to the deck to hold it in one place (I heard that the old copier fell over one time when there was a particularly huge wave). There are lots of great pictures on the bulkheads of the Oscar Dyson, and each one is fastened to the bulkhead with at least 4 screws, or velcro. There are hand rails everywhere – on the bulkhead in the passageway (hallway) (reminds me of Mom’s nursing home), and on the consoles of the bridge.

hallway hand rails — This view down the hall shows the hand rail. It comes in handy during rough weather.

Desk chairs can be secured by a bungee cord, and the chairs in the mess (dining room) can be hooked to the deck.

Another thing that is different from home is the fact that the Oscar Dyson operates 24-7 (well, in my home, there could easily be someone awake any hour of the night, but the only thing they might operate is the TV). The lights in the passageways and mess are always on. The acoustics and water quality equipment are always collecting data. Different people work different shifts, so during any one hour, there is usually someone asleep. Most staterooms have 2 people, and they will probably be on opposite shifts. One might work 4 am to 4 pm, and the other would work 4 pm to 4 am. That way, only one person is in the room at a time (there is not really room for more than one). There is always someone on the bridge – at least the Officer of the Deck (OOD) – to monitor and steer the ship. During the day, there is usually a look out as well.

binoculars on the bridge — These binoculars are used by the look out to scan the surrounding area for anything in the water - whales, boats, islands, kelp, or anything else in proximity to the ship.

His job is to, well, look out – look for floating items in the water, whales, rocks, and other ships (called contacts or targets). This helps the OOD, because he or she can’t always keep their eyes on the horizon.

I have thoroughly enjoyed living on the Oscar Dyson (we have had calm seas so far), and talking with the NOAA staff and crew. They are ordinary people, who have chosen an extraordinary life – aboard a ship. It has challenges, but also great rewards – seeing the land from a different perspective, being up close to sea life, and forging close relationships with shipmates, as well as participating in the science that helps us understand the world’s oceans.