Megan Woodward

July 16, 2009April 5, 2021

Megan Woodward, July 16, 2009

NOAA Teacher at Sea
Megan Woodward
Onboard NOAA Ship Oscar Dyson
July 1 – 18, 2009

Mission: Bering Sea Acoustic Trawl Survey
Geographical Area: Bering Sea/Dutch Harbor
Date: Tuesday, July 16, 2009

All bony fish have otoliths (ear bones) that can be used for calculating the age of the fish.

Weather and Location
Position: N 58 13.617; W 171 25.832
Air Temp: 7.2 (deg C)
Water Temp: 6.54 (deg C)
Wind Speed: 15 knots
Weather: Overcast

Science and Technology Log

One of the most interesting things I’ve learned while participating in the pollock survey is the importance of otoliths. Otoliths are small bony structures situated in the head of all bony fish, and are often referred to as “ear stones.” For each haul we brought on board, 50 otoliths were taken from large fish (3+ years) and/or 5 from small fish (younger than 3 years old). The otolith holds the key to accurately calculating the age of a fish (scales and vertebrates can also be used, but are not as reliable). The average age of fish from the samples collected in the survey helps scientists estimate the strength of a year-class and size of the stock in the future.

Back in the lab, otolith samples are carefully catalogued.

The first step in taking an otolith is pictured above. An incision is made on the back of the pollock’s head, and an otolith is removed using tweezers. Once the otolith is removed, it is rinsed with water and placed in a glass vial containing a small amount of 50% ethanol solution for preservation purposes.

The otoliths are taken back to NOAA’s aging lab where ages are determined by reading rings similar to those on a tree trunk. A crosscut is made through each otolith revealing a pattern of rings. Scientists then count the rings to determine the age of the fish. Lightly burning or staining the otoliths makes the rings more visible.

New material is deposited on the surface of the otolith creating the rings as the fish grows. The translucent/light zones indicate the main growth that takes place in the summer months. The opaque/darker rings appear during the winter months when growth is slower. Because of the slower growth rate, new material is deposited on top of the old layers resulting in the dark ring. Each pair of light and dark zones marks one year. In fish younger than one year of age, rings can be identified for each day of life!

Personal Log

I was surprised to discover otoliths have been used for aging fish since the early 1900’s. While working in the fish lab I observed the scientist removing otoliths, however I did not remove any myself. The cracking sound heard when cutting the head open was like fingernails on a chalkboard to me. I spent most of my time in sorting and measuring fish, as well as assisting with the stomach collection project.

For the next two days we will be heading back to Dutch Harbor, and the likelihood of trawling for more fish is minimal. Our remaining work assignment is to give the fish lab a thorough cleaning. Everything in the lab is waterproof, so we’ll put on our Grunden’s (orange rubber coveralls) and boots and spray down the entire space. Working and living at sea for nearly 3 weeks has been an eye opening experience. My time aboard the Oscar Dyson has flown by. I have learned so much about fisheries research and life at sea. Dry land, however, will be warmly welcomed when we get back to Dutch Harbor. Would I do it again? Absolutely.

Animal Sightings

The whales have an incredible way of showing up when I don’t have my camera. Yesterday I spotted two orcas, but did not get a photograph. The seabirds continue to circle. I like the murres most. They look like small, flying penguins.

New Vocabulary

Otoliths- Small bony structures situated in the head of all bony fish. Often referred to as “ear stones.”

Stock- Refers to the number of fish available, supply.

*** Much of the information used for this log entry was found on the Centre for Environment, Fisheries & Aquaculture Science (Cefas) web site.

July 12, 2009April 5, 2021

Megan Woodward, July 12, 2009

NOAA Teacher at Sea
Megan Woodward
Onboard NOAA Ship Oscar Dyson
July 1 – 18, 2009

Mission: Bering Sea Acoustic Trawl Survey
Geographical Area: Bering Sea/Dutch Harbor
Date: Tuesday, July 12, 2009

Any bycatch in a haul has to be measured and weighed if there are more than 25 of the same species caught. — Any bycatch in a haul has to be measured and weighed if there are more than 25 of the same species.

Weather/Location
Position: N 60.35.172; W 174.08.187
Air Temp: 6.1 (deg C)
Water Temp: 5.24 (deg C)
Wind Speed: 25 knots
Weather: Overcast, rain

Science and Technology Log

How is all the data collected from a trawl and acoustic lab used? By collecting data about weight and length from a sample, scientists are able to connect the size of fish caught to the amount of return seen in the acoustic lab. The return is assigned a name (PK1, PK2, etc.) and all schools showing a similar acoustic pattern are given the same name. In the end, scientists can estimate the number of fish and their size for a given area based on the acoustic and fish lab data collected. This is repeated throughout the survey resulting in an estimate for the total number of fish in the survey area.

Both during and after the survey estimates of abundance in the same location over the past several years are compared. Scientists evaluate the data and determine if the pollock population in the survey area is increasing, declining or stable. Their conclusions are used to make a recommendation about pollock fishing limits for the upcoming year. In the past few years the pollock population has been lower than in previous years. Due to the decline, the fishing quota has been reduced. However, the 2006 year-class is proving to be strong. At 4 years of age pollock are considered mature and fishable. Therefore, the fishing quota is predicted to rise in the next year or two.

Personal Log

While discussing the acoustic survey project with the scientists on board, I was quite surprised to hear the pollock survey had been going since 1979. Acoustic technology has changed and improved, but in essence the project has remained the same. Modern computer technology has allowed collection and analysis of enormous data sets and greatly reduced the amount of paper work needed for the project’s success.

The concept of strong vs. weak year-class is also quite interesting. There doesn’t seem to be a direct connection between a year-class’ success and environmental factors. Environmental factors that are potentially influential are water temperature, available zooplankton, ice cover, storms and predators. The fish currently being caught by commercial fisherman are 5-7 years old. Can you figure out which year classes those fish are from?

We continue to spot plenty of seabirds and a few more minke whale pods. I was able to watch a group of Dall’s porpoises play in the wake of the bow for half an hour yesterday. There haven’t been any new animal sightings during the past few days.

Although we are out here working in the best interest of pollock, I have found it difficult to watch thousands of pollock come through the fish lab. I have to remind myself that sampling the fish is truly for the good of the order. In addition, after being measured the fish are sent back into the ocean where they become food for other organisms such as crab or birds. One of their natural predators is having a good meal, something that was likely to happen anyway.

Animal Sightings

Seabirds
Dall’s porpoises

New Vocabulary

Bycatch – Anytime something is caught during a trawl other than pollock it is labeled bycatch. Jellyfish has been the most common form of bycatch.

Year-class – All the fish born in a given year are members of that year-class. We have caught a lot fish from the 2008 year-class (1 year old fish).

July 10, 2009April 5, 2021

Megan Woodward, July 10, 2009

NOAA Teacher at Sea
Megan Woodward
Onboard NOAA Ship Oscar Dyson
July 1 – 18, 2009

Mission: Bering Sea Acoustic Trawl Survey
Geographical Area: Bering Sea/Dutch Harbor
Date: Tuesday, July 10, 2009

The pollock are carefully loaded onto the table.

Weather/Location
Position: N 56.30.202; W 172.34.37
Air Temp: 7.4 (deg C)
Water Temp: 7.4 (deg C)
Wind Speed: 19 knots
Weather: Overcast

Science and Technology

Once the fish are onboard a rigorous data collection process begins. All of the data collected are recorded via instruments linked to a computer network in the fish lab. Below is a series of photos showing the process used in the fish lab to collect valuable data.

Once the fish are on the table, we carefully look through the fish for any species other than pollock caught in the trawl. These non-pollock species are sorted into bins and accounted for. The fish are weighed one basket full at a time as they reach the end of the conveyor belt. Initially, we take a count of how many fish fill one basket. There is a scale connected to a computer program that records the basket’s weight.

The sorting begins. The pollock are sorted between male and female.

After weighing the pollock, we move on to sorting a sample of approximately 300 fish by sex. To find the sex of a fish we cut open its belly and look for either male or female reproductive organs. The sexed fish are then placed in the appropriate bin. Next, each pollock from the male/female sort is measured in centimeters. We use a measuring board linked to a computer that records the size of each fish. There is a small tool in my hand that gets placed at the “v” of the fish tail. Sensors on the board detect the placement of the measuring wand, and send a length measurement to the computer so it can be recorded. This program also keeps track of how many fish we measure, so we get an accurate sample count.

The stomach of a pollock is prepared for preservation.

Several scientists have asked us to collect pollock for various research projects. One project, designed to study the diet of pollock, requires us to sex, measure, weigh and take the stomach of 20 pollock from each haul. A label with all of the information is placed in a bag with the stomach. They are placed in a freezer for preservation purposes.

Here I am using the measuring board. The stomach of a pollock is prepared for preservation. — Here I am using the measuring board.

We also use a similar process for scientists examining one-year-old pollock. This study asks for the entire fish to be preserved, not a specific organ. In one 12-hour shift there is a maximum of 3 trawls if fish sign is identified in the acoustics lab. Each trawl takes 2 to 3 hours to process. It’s possible another trawl could happen while finishing up the data collection from the previous haul. This makes for a very busy, fish filled shift.

Personal Log

Working in the fish lab has provided for a tremendous amount of new learning to take place. I’ve learned to identify species of fish that mix in with pollock (capelin, flatfish, skate and cod), and have seen several crustaceans and jellyfish, too. All of the measuring technology has been straight forward and user friendly. Sexing the fish has been the most difficult job, but has become easier with practice. Examining the innards to identify male or female reproductive organs seems nearly impossible in the young fish, and it’s not always clear in the older fish.

Today I was in charge of weighing the fish as they came down the conveyor belt. I was certainly mistaken when I thought it would be a simple task. First off, I had to count the fish as they dropped into the basket at a speed faster than I could count. At the same time I had to control the speed of the belt and open the gate so more fish would move down the line. When the basket was full, I stopped the belt and placed the full (semi-accurately counted) basket on the scale and waited for the scale’s “steady” signal to come on. Since the boat is constantly in motion the steady light rapidly blinks on and off. It took me three tries before I managed to get the basket weighed. Meanwhile the rest of the team patiently waited. Maybe I’ll give it another try tomorrow.

This average sized skate was flapping his wings making him difficult to hold. Look closely at the fish on the conveyor belt and you will see hermit crabs and seastars.

Basketstars were brought up in a bottom trawl. Hermit crabs and snails were also caught in the bottom trawl. — Basketstars were brought up in a bottom trawl.

Hermit crabs and snails were also caught in the bottom trawl. — Hermit crabs and snails were also caught in the trawl.

Animals Seen

Minke Whale
Skate
Pacific Cod
Tanner Crab
Snow Crab
Basketstar
Sturgeon Poacher
Snails
Hermit Crabs
Arrow Tooth Flounder

July 7, 2009April 5, 2021

Megan Woodward, July 7, 2009

NOAA Teacher at Sea
Megan Woodward
Onboard NOAA Ship Oscar Dyson
July 1 – 18, 2009

Mission: Bering Sea Acoustic Trawl Survey
Geographical Area: Bering Sea/Dutch Harbor
Date: Tuesday, July 7, 2009

This map depicts the path the Miller Freeman will take on our cruise. — This map depicts the path the Miller Freeman will
take on our cruise.

Weather/Location
Position: N 56.18.292; W 171.46372
Air Temp: 7.3 (deg C)
Water Temp: 6.9 (deg C)
Wind Speed: 17 knots
Weather: Overcast

Science and Technology Log

We are traveling on designated lines in the north/south direction looking for pollock (travel lines are illustrated above). The samples we pull in are compared to the amount of fish found in the same location over 20+ years. The process used to “go fishing” is not as easy as one might think. Several things need to align for a successful trawl to take place. As of today, I have been a part of three successful trawls. Below is an explanation of the fishing process.

The Fisheries Research Biologist and his team recognize a series of acoustic returns as potential pollock schools while sitting in the acoustics lab. Then they decide if the amount of fish being seen is enough to fish on. If yes, go to step 2.
Next the team questions if the weather conditions are calm enough, are the fish far enough off the bottom of the sea floor, and have we traveled at least 30 miles from our last fishing point. If conditions are aligned, move to step 3.
The team contacts the bridge to prepare the crew for fishing. The bridge receives the exact location (longitude/latitude) the nets should enter the water for the best possible fishing. By now we have traveled over the top of the fish we saw on the acoustic screen. A decision must be made about the best direction to travel so the nets work properly: Do we flip a u-turn and fish up the line, or do we circle back to where we saw fish and retrace our path on the line? The water’s current and prevailing winds impact how the nets will function, which are some of the deciding factors in choosing the direction we will tow the nets. Fishing in motion, continue to step 4.
Up to the wheelhouse. Here the lead fisherman, the ship’s Officer of the Deck (person in charge of driving the ship) and the fisheries team can work together to create the best fishing scenario. The same acoustic information can be viewed in the wheelhouse as in the acoustic lab. Based on the depth of the acoustic return, the fisheries team can inform the fisherman how far to lower the nets in the water. Keep going to step 5. We almost have fish…we hope!
Once the net is in the water, there are two acoustic screens closely watched. These are pictured below with the explanation of the information received. The net is continually raised or lowered based on the depth of the return. A trawl lasts for 20 minutes and covers 1 mile on average. The fisheries team is aiming for 300 fish per trawl. They are careful to not over fish. Almost done, bring the fish aboard.
The final step is bringing the nets back in and unloading the fish. If all went as planned, the next few hours will be spent in the fish lab collecting information about the sample. Unfortunately the system is not perfect. It’s possible to bring in a water haul or a stuffed sausage. Neither one is good news.

This is the acoustics lab. The top screens are displayed in the bottom monitors as needed. The top two left monitors show the acoustic return from the 5 frequencies (pings) sent out.

Personal Log

Now that I have participated in three trawls, I’m feeling much more comfortable with the whole fishing process. Rather than looking at the acoustic screens with a puzzled look, I’m able to recognize what the return from a school of pollock looks like. Jellyfish show up on the screen as blue-green clusters, and have been present in the top 40 meters of water the majority of time we’ve been at sea. I can only imagine how many of those creatures are down there.

There seems to be a bit of humor in all we do at sea. There are two awards given out based on the hauls we bring in: The water haul and the stuffed sausage awards. You really don’t want to be the recipient of either one. The water haul award goes to the team that brings in the haul with the least fish (mostly water). This happened yesterday when we attempted to catch pollock close to the surface. There wasn’t but a single pollock in the net. Of course there were numerous jellyfish.

This is an acoustic screen showing a return typical of pollock. The several clusters with the trail of return on the left are showing a good fishing opportunity. The dark red across the middle of the screen is the sea floor. — This is an acoustic screen showing a return typical
of pollock. The several clusters with the trail of
return on the left are showing a good fishing
opportunity. The dark red across the middle of the screen is the sea floor.

The stuffed sausage is just the opposite of a water haul. As you may have guessed, the stuffed sausage award goes to the team that brings in the most over-stuffed net. If we were looking to make money off of our catch, this would be considered a success. However, we really only want a sample of about 300 fish. A stuffed sausage means too many fish were brought in. It is possible to be the “winner” of both awards.

Animals Seen

Red-legged kittiwake
Blacklegged kittiwake
Albatross
Fulmar
Fur Seal
Capelin (they smell like cucumber)

This screen shows the return from a signal that sweeps left to right like a pendulum. The bottom of the net is the ½ circle shape. During a trawl you can see if a school of fish enters the net. — This screen shows the return that sweeps left to right like a pendulum. The bottom of the net is the ½ circle shape. During a trawl you can see if a school of fish enters the net.

When the net is in the water, there is return from the top and bottom of the net. This screen shows a vertical return. We can see we are at the correct depth, but maybe we are too far to the left or right. — There is return from the top and bottom of the net. This screen shows a vertical return. We can see we are at the correct depth, but maybe too far to the side.

New Vocabulary

Acoustic Lab: AKA “The Cave” because there are no windows. This is where the Fisheries Research Biologist and his team watch the acoustic return monitors.

Bridge/Wheelhouse: This is where the officer on duty drives the ship using several navigational tools. Named the wheelhouse because the ship’s steering wheel is found here. The bridge is located on the top level of the ship. The Methot and trawl nets are also operated from the bridge.

Haul: This is how the fish are referred to when they are caught in the net. One might ask, “How was the haul?” “It was a (big haul, small haul, water haul, stuffed sausage).”

Water Haul: A net lacking fish following a trawl.

Stuffed Sausage: An overstuffed net, too many fish caught.

This fur seal followed the boat for about 30 minutes while we were trawling for pollock. He was hoping for a free dinner. — This fur seal followed the boat for 30 minutes while we were trawling. He was hoping for a free dinner.

The center bird is a blacklegged kittiwake, identified by the black wing tips, white underwing and the light gray color on its back.

July 5, 2009April 5, 2021

Megan Woodward, July 5, 2009

NOAA Teacher at Sea
Megan Woodward
Onboard NOAA Ship Oscar Dyson
July 1 – 18, 2009

Mission: Bering Sea Acoustic Trawl Survey
Geographical Area: Bering Sea/Dutch Harbor
Date: Tuesday, July 5, 2009

Weather/Location
Position: N 58.37.239; W 171.05.968
Air Temp: 4.5-6.0 (deg C)
Water Temp: 4.94 (deg C)
Wind Speed: 16 knots
Weather: Overcast and rainy

This is the screen I use to get info about our ship’s location. The little white speck inside the red oval is our ship.

Science and Technology Log

We have been at sea now for almost five days in search of pollock. The fish had not been spotted on the lines we traveled on until today. We had the opportunity for our first pollock trawl around 02:00, and used the Methot net to bring in two zooplankton samples earlier in my shift. This was by far the most action yet. I was eager and ready to see what the fishing process was all about. This log will focus on the zooplankton samples.

The Methot net was put in the water and lowered to the desired depth determined by watching the location of the acoustic return. After twenty minutes the net was brought back up and the catch was unloaded. I was expecting a net full of euphausiids, but the critters were actually collected in a small container on the back end of the net. The catch was brought into the fish lab and dumped into a bucket so we could separate the other organisms caught in the net (9 jellyfish and 23 tiny pollock in this case). Once the other fish had been removed, we took a sample (a ••• cup scoop) to weigh and count the euphausiids in the sample (sample is shown above). The rest of the catch was also weighed.

There were 543 euphausiids in the scoop. The weight and number help estimate the amount of euphausiids in the entire catch. We repeated this process again a few hours later. The second sample had almost twice as many euphausiids, 13 jellyfish and fewer than 5 pollock.

The survey tech and skilled fishermen lower the Methot net into the water.

Personal Log

Until today, the fishing portion of this trip remained a mystery. However, I was feeling a little sea sick, okay very sea sick, so it was probably a good thing. We encountered some VERY rough seas with sustained winds ranging from 30-40 knots and swells averaging 17 ft. Some of the swells were much larger; one was rumored to be almost 35 ft. high. Apparently the rough seas are expected to return tonight and tomorrow. My sea legs are securely fastened, so I am ready to take on whatever the sea has to offer.

When we brought in the first haul of pollock last night, my eyes must have looked like they were going to roll out of my head. I couldn’t believe how many fish were coming across the conveyor belt. This was what I had been waiting for, so I got on my rain gear and started sorting the fish. Each species was placed into separate crates so a count of all fish caught could be taken. Of course, pollock made up the majority of the catch. In the next few weeks, I will become an expert member of the pollock survey team. Everyone on board, both scientists and crew, have been more than willing to answer my

A sample of zooplankton brought up in the Methot net. These are euphausiids, which are also referred to as krill.

Getting used to the 16:00-04:00 (4pm4am) shift has been trying. Today’s shift was the first that didn’t require a nap. Due to the odd shift hours, I’ve been waking up at 14:00 (2 pm) and going to bed around 05:00 (5 am). This makes mealtime tricky. Dinner is served first, then I eat some breakfast in the middle of the night. My body is thoroughly confused. The ship’s cooks are wonderful, and continually provide a stocked mess hall with loads of choices. I swear the dessert bar is continually whispering my name. I couldn’t ask for a more kind, welcoming group of people to work questions. One part of this adventure I’m looking forward to is getting to know the wide range of characters who make this important research possible.

It was certainly a thrill to see the first whale of the trip. The pod was spotted just off the bow of the ship andlater seen in the distance.

Animals Seen

Fin Whale
Jelly Fish
Flathead Sole
Northern Flathead Sole
Arrow tooth Flounder
Pollock
Yellow Irish Lord
Euphausiids

New Vocabulary

Zooplankton– A very small or microscopic animal organisms possessing little or no power of locomotion (can’t move themselves), leaving them to merely drift or float in the water.

Euphausiids (eu·phau·si·id) – A type of zooplankton, also known as krill, are tiny shrimp-like crustaceans that form an important part in the diet of many animals including whales, seals, fishes and birds. These are the main food source for pollock.

Methot Net – Methot is the name of the man who designed the style of plankton net we used to catch the euphausiids.

One of several jellyfish brought up in the nets. This guy is slimy and heavy, but not a stinger

July 1, 2009April 5, 2021

Megan Woodward, July 1, 2009

NOAA Teacher at Sea
Megan Woodward
Onboard NOAA Ship Oscar Dyson
July 1 – 18, 2009

Mission: Bering Sea Acoustic Trawl Survey
Geographical Area: Bering Sea/Dutch Harbor
Date: Tuesday, July 1, 2009

Science and Technology Log

What is this trip all about? Well, NOAA is working to collect a range of pollock fish samples from across the Bering Sea. The samples collected will help set fishing regulations based on the estimated pollock fish population. The fish are looked at to assess the male to female ratio, size and age.

Pollock, a member of the cod family, are mainly found in the Bering Sea. They are typically found between 328 to 984 feet depths. Pollock lives up to 17 years, and reach maturity around age 4. The maximum size of the pollock is slightly larger then 3 feet long.

The colors in the picture at right indicate the amount of return received from the 3 spheres seen towards the top. The other mass of colors at the bottom and surrounding the lines are fish, which are interfering with the read. — The colors in the picture at right indicate the amount of return from the 3 spheres seen towards the top. The other mass of colors at the bottom and surrounding the lines are fish, which are interfering with the read.

We are currently preparing to set sail. Departure time is set for 15:00 (3:00 pm). Our first anchoring will take place just a few hundred feet from where we are docked in Dutch Harbor. At that time, the Chief Scientist and other members of the science team will calibrate (check the accuracy) the echo sound system used during the course of the survey. Once the calibration is complete and the data is collected, we will continue to sail in search of pollock fish.

The echo sound system is used to measure the amount of return or “back scatter” from a ping (term to describe the sound sent down into the ocean). Depending on the size of the return, the scientists are able to determine if they are detecting fish. Pollock are known to give a return within a specific range, which provides the scientists with one of the clues that help them make an educated guess about the type of fish being detected.

In order to calibrate the echo sound system, three metal spheres that have an expected return level are lowered into the sea. A ping is sent into the open sea, and the scientists are able to watch the amount of return from the spheres through their computer. The amount of return can be seen using a color-coded scale. Red shows the highest level of return, and gray is the color indicating very little return. The scientists can then see if each sphere is giving the expected return. If a sphere is giving off more or less than the expected return, the scientists then know how to adjust the level of return they are getting from fish throughout the project.

Eagle or seagull? This guy sits and waits for a food meal on top of the hotel dumpster.

Personal Log

After a day and a half in Dutch Harbor, I’m glad to finally be getting under way. Dutch Harbor is a small, small town. There are a few restaurants, one hotel and a Safeway. All of the other businesses are linked to the fishing industry in one-way or another. Flying into the island was an incredible experience. The plane hummed through the air between multiple tiny landforms. The airport runway stretches out to the edge of the sea, allowing the passengers to think, for just one moment, they are making a water landing. The plane touched down just beyond the shore.

Since my arrival, I have been welcomed with warmth from all of the NOAA scientists and deck crew. Everyone has been more than wiling to answer even the most ridiculous of questions I’ve had. My time the past two evenings were spent getting to know several of the Oscar Dyson officers and crew members.

A good chunk of Monday was spent hiking Ballyhoo with two of the officers from the ship. Ballyhoo is a steep hill behind the airport (approx 1400 ft. elevation). The hill was littered with WWII shelters. As we tromped up the hill, the wind began to pick up. By the time we were nearing the top, the wind was practically knocking me sideways. The gusts were sustained and powerful. Certainly some of the windiest conditions I’ve encountered. The wildflowers growing on the hillside were reminiscent of the summer blooms found on Mount Rainier. The views from the top were breathtaking. Several bald eagles swooped past the emerald hills, and the sun started to peak out as we made our way back to sea level.

Animals Seen in Dutch Harbor

Ground Squirrel
Jelly Fish
Bald Eagles
Variety of Seabirds
Arctic Fox
Guard dog

This little ground squirrel wasn’t bothered as we walked by.

New Vocabulary

Echo Sound System – A tool used to measure the return or “back scatter” from a ping. The amount of return helps determine what is hiding under the sea.

Ping – The name of the sound that is sent into the water to create an echo/return for the scientists to read. The ping is a constant, repeated sound wave. Several different frequencies are used to detect objects.

Return – AKA back scatter, is the amount of acoustic sound waves/echo bouncing back off an object beneath the water.

Trawl – The phrase used when talking about catching fish using a large net