codend – Page 2 – NOAA Teacher at Sea Blog

August 6, 2012August 11, 2021

Johanna Mendillo: Nets, Northern Sea Nettles and More…, August 5, 2012

NOAA Teacher at Sea
Johanna Mendillo
Aboard NOAA ship Oscar Dyson
July 23 – August 10

Mission: Pollock research cruise
Geographical area of the cruise: Bering Sea
Date: Sunday, August 5, 2012

Location Data
Latitude: 61º 10′ N
Longitude: 179º 28’W
Ship speed: 4.3 knots ( 4.9 mph)

Weather Data from the Bridge
Air temperature: 11.1ºC (52ºF)
Surface water temperature: 8.1ºC (46.6ºF)
Wind speed: 5.4 knots ( 6.2 mph)
Wind direction: 270ºT
Barometric pressure: 1013 millibar ( 1.0 atm)

Science and Technology Log:

So far, you have learned a lot about the pollock research we conduct on board. You have learned:

How to age fish (with otoliths)
How to measure fish (with the Ichthystick)

and

How to identify fish gender (with your eyes!)

Now, we are going to backtrack a bit to the two big-picture topics that remain:

How do we CATCH the pollock (hint hint, that is today’s topics… NETS!)

and

How do we even find pollock in the Bering Sea (that is the next blog’s focus: acoustics!)

So, to begin, there are several types of nets we are carrying on board. Remember, when a net is dragged behind a ship in the water it is called trawling, and the net can be considered a trawl. The most-used is the Aleutian Wing Trawl, or AWT, which we use to sample the mid-water column (called a midwater trawl). We are also using a net called the 83-112, which is designed to be dragged along the ocean floor as a bottom trawl, but we are testing it for midwater fishing instead. In fact, sometimes during my shift we do one AWT trawl, and immediately turn around and go over the same area again with the 83-112 to see differences in the fish sizes we catch!

If the 83-112, which is a smaller net, proves to be adequate for midwater sampling, NOAA hopes it can be used off of smaller vessels for more frequent sampling, especially in the years the NOAA does not conduct the AWT (NOAA currently does AWT surveys biennially).

Now, for each type of net, there is some new vocabulary you should know:

The codend is the bottom of the net. A closed codend keeps the fish inside the net and an open cod end allows them to swim through. It may seem odd, but yes, sometimes scientists do keep the codend open on purpose! They do this with a camera attached to the net, and they simply record the numbers of fish traveling through a certain area in a certain time period, without actually collecting them! Here on the Dyson, the NOAA team is testing that exact type of technology with a new underwater camera called the Cam-Trawl, and you will learn about it in a later post.

The headrope is the top of the opening of the net.

The footrope is the bottom of the opening of the net.

(The 83-112 is called such because it has an 83 ft headrope and an 112 ft footrope.)

The trawl doors are in front of the headrope and help keep the net open. Water pressure against the trawl doors pushes them apart in the water column during both setting of the net and while trawling, and this helps spread out the net so it maintains a wide mouth opening to catch fish.

There are floats on the top of the net and there can be weights on the bottom of the net to also help keep it open.

Lastly, the mesh size of the net changes: the size at the mouth of the net is 3 meters (128in.), and it decreases to 64in., 32in., 16in.., 8in., etc. until it is only ½ inch by the time you are holding the codend!

Here is a diagram to put it all together:

awt-model-commented1 — Courtesy of Kresimir Williams, NOAA

If you think about the opening of the net in terms of school buses, it will help! It turns out that the AWT’s opening height, from footrope to headrope, is 25m, which is 2 school buses high! The AWT’s opening width, is 40m across, about 3.5 school buses across! Now, you can see why positioning and maneuvering the net takes so much care– and how we can catch a lot of pollock!

Here is a trawl returning back to the ship's deck! — Here is a trawl returning back to the ship’s deck!

Now, when the scientists decide it is “time to go fishing” (from acoustic data, which will be the topic of the next blog) they call the officers up on the Bridge, who orient the ship into its optimal position and slow it down for the upcoming trawl. Meanwhile, the deck crew is preparing the net. The scientists then move from their lab up to the Bridge to join the officers– and they work together to monitor the location and size of the nearby pollock population and oversee the release and retrieval of the net.

Along the headrope, there are sensors to relay information to the Bridge, such as:

The depth of the net
The shape of the net
If the net is tangled or not
How far the net is off the bottom and
If fish are actually swimming into the net!

The fish and the net are tracked on this array of computer screens. As the officers and scientists view them, adjustments to the net and its depth can be made:

The start of the trawl is called “EQ” – Equilibrium and the end of the trawl is called “HB” – haul back. The net can be in the water anywhere from 5-60 minutes, depending on how many fish are in the area.

The AWT will get would up on this new reel — The AWT will get wound up on this reel

Now, sometimes an AWT catches so many fish that there are simply too many for us to measure and process in a timely fashion, so it is deemed a “splitter”! In a splitter, there’s an extra step between hauling in the net from the ocean and emptying it to be sorted and processed. The codend of the AWT is opened over a splitting crate, and half of the pollock go into a new net (that we will keep and sort through) and the rest of the pollock are returned to the water.

The net is back on board! Time to open up the codend and see what we have caught!

Personal Log:

Let’s continue our tour aboard the Oscar Dyson! Follow me, back to the bridge, where the OOD (Officer on Duty) is at the helm. As you already know, the first thing you notice on the bridge is the vast collection of computer screens at their disposal, ready to track information of all kinds. You will learn more about these in an upcoming blog.

Busy at work on the bridge... — Busy at work on the Bridge…

In addition to these high-tech instruments, I was very happy to see good old-fashioned plotting on a nautical chart. In class, students, you will have a special project where you get to track the changing position of the Oscar Dyson!

This chart is showing the northernmost point of three of our sampling transects- including the one closest to Russia!

Here is a sample of the hour-by-hour plotting, done by divider, triangle, and pencil:

I will end here with a sea specimen VERY different from pollock, but always a fan favorite— jellyfish! Interestingly, there are a large number of jellyfish in the Bering Sea- something I never would have assumed. The one that we catch in almost every net is the Northern Sea Nettle (Chrysaora melanaster). In one net, we collected 22 individuals!

When we collect non-pollock species such as these, we count, weigh, and record them in the computerized database and then release them back into the ocean. Here they are coming down the conveyor belt after the net has been emptied:

The so-called bell, or the medusa, can be quite large- some are the diameter of large dinner plates (45cm)! Their tentacles can extend to over 3m in length. They consume mostly zooplankton, small fish (including juvenile pollock), and other jellies. How so, exactly? Well, when the tentacles touch prey, the nematocysts (stinging cells) paralyze it. From there, the prey is moved to the mouth-arms and finally to the mouth, where it’s digested.

This same mechanism is used by sea nettle when it encounters danger like a large predator. It stings the predator with its nematocysts and injects its toxins into its flesh. In the case of smaller predators, this venom is strong enough to cause death. In larger animals, however, it usually produces a paralyzing effect, which gives the sea nettle enough time to escape.

Now in the case of me handling them… and other humans…their sting is considered moderate to severe. In most cases, it produces a rash, and in some cases, an allergic reaction. However, we wear gloves on board and none of the scientists have ever had an issue holding them. In fact, they offered to put one on my head and take a picture… but I declined! If a few students email me, begging for such a picture, maybe I will oblige…

July 28, 2011March 12, 2021

Cathrine Fox: Issue Six: Alaska, impossibly big and impossibly green

NOAA TEACHER AT SEA
CATHRINE PRENOT FOX
ONBOARD NOAA SHIP OSCAR DYSON
JULY 24 – AUGUST 14, 2011

Mission: Walleye Pollock Survey

Location: Kodiak, Alaska

Date: July 27, 2011

Weather Data from the Bridge

True Wind Speed: na

Air Temperature: 14° C dry/12° C wet

Air Pressure: na

Overcast

Latitude: 57.44° N, Longitude: 152.31° W

Ship heading: n/a

(Limited data, as ship is in port)

Scientific Log:

I’ve received an in-depth tour of the ship and labs, and I am starting to piece together how the “Acoustic Trawl Survey” works. Basically, NOAA is responsible for monitoring the populations of walleye pollock and accomplishes this task in several ways. The acoustic trawl survey is one part of how this is done.

The science team identifies particular transect areas in the Gulf of Alaska. The ship travels to that area, then transmits acoustic signals about once per second as it travels along each transect. The returning echo gives scientists an initial measurement of the abundance of organisms in the water below the ship. Just “listening,” however, is not enough. We also have to sample populations physically to determine the ages, sizes, and species of the organisms. The ship trawls for these additional data.

A trawl is a large net towed behind the ship to catch fish and other organisms. The individuals (of all species) in the catch are identified and counted. Cameras (three) are mounted inside the back of the trawl (codend) to collect images as they pass through the trawl. From this larger catch, a sample of the walleye pollock (about 300 individuals) are dissected to determine sex, diet, measured (length and weight) for size and aged by looking at (yes) their ear bones or otoliths. I’ll cover all of this in depth once I have been able to do it and see it in action, but that is the gist.

Personal Log:

I think first impressions are important. Alaska? Alaska is impossibly big and impossibly green. Too big, perhaps to describe with common adjectives. It took me about two days of travel from the 4-Corners to make my way up here: a Beechcraft 1900 from Cortez to Denver, then flights from Denver to Seattle and Seattle to Anchorage. I spent the night in Anchorage and wandered the city at midnight… …not that you can tell that it was so late from the pictures.

The next morning I took off from Anchorage and met up with the crew and scientific party onboard the Oscar Dyson in Kodiak, an island the size of Connecticut in the Gulf of Alaska

As for how ‘impossibly green’ Alaska is, I was thinking about the reasons Georgia O’Keeffe gave for moving from New York City to New Mexico in 1949. She said (and I paraphrase) that she wanted to use more vibrant colors in her palette of paints than just green. Ms. O’Keeffe would have it rough here in Alaska: greens, greys and blues abound. Adventures in a Blue World Issue 6 may not convince you of the colors of Alaska, but I hope it gives you a grasp of its size.

I’ve already settled in to the ship and my stateroom. My stateroom is small but comfortable, and I share it with a woman who is part of the scientific NOAA team. Interestingly, she worked for the same professor at the Rocky Mountain Biological Laboratory in Gothic, Colorado as an undergraduate that I did. Very Small World.

We are docked in Kodiak for a few more days than anticipated: we are awaiting the arrival of another deck-hand, and there are a few repairs that need to be made to the ship. Once we get started, I will be working the 4am-4pm shift, and taking part in whatever science is taking place. In the meantime, I get to ‘nose around’ Kodiak, go for hikes and runs, check out museums (see below), and eat as many salmonberries as I can stuff into my mouth.

Until our next adventure,
Cat

July 22, 2010March 12, 2021

Story Miller, July 22, 2010

NOAA Teacher at Sea: Story Miller
NOAA Ship: Oscar Dyson

Mission: Summer Pollock III

Geographical Area: Bering Sea

Date: July 22, 2010

Time: 0754 AKST
Latitude: 58°31N
Longitude:175°45W
Wind: 13-20 knots (approx. 14.96 – 23.02 mph)
Direction: 239° (SW)
Sea Temperature: 8.28°C (approx. 46.9°F)
Air Temperature: 8.03°C (approx. 46.5°F)
Barometric Pressure (mb): 1017
Wave Height: 4 feet
Sea Swells: 6 feet
Combined Wave Height: 10 – 12 feet

Scientific Log

This afternoon, we conducted a test with a drogue which is like a large sea anchor. Sea anchors allow a boat that is simply sitting in the water to not drift so far with the waves. This drogue will stabilize the camera of an experimental trawl net device, called a Cam-Trawl, and prevent it from fluttering when it is photographing the fish. The Cam-Trawl was designed by Kresimir Williams. Currently the objective of this new device is to observe the fish we see in the backscatter which are the animals we can see in the echosounder

(See Figure 1).

Figure 1: Image of the echo sounder in the acoustics lab. The image on the top in the blue is representing a swarm of jellyfish. Jellyfish tend to be best seen using the 18 kHz transducer.

In short, the ship’s hull has transducers that send pings of sound energy down through the ocean and when they hit some object, such as the bottom of the ocean or a fish, some of the energy in the sound ping is returned to the ship and received by our echo sounding system in the acoustics lab of the ship.

When we locate a group of fish we want to study with the echo sounder, we have two primary methods of collecting data from the fish. The device we use the most is the AWT(Aleutian Wing Trawl) net and the other is an 83-112 bottom trawl net. The AWT is used for catching fish located at midwater depths and the other, as stated in the name, trawls the sea floor. To imagine the shape of these devices in the water, imagine a large funnel with a catch sack on the end. The beginning portion of these nets, nearest to the boat, has large meshes and its primary function is to funnel the fish toward the catch sack. As fish move farther down the net, the meshes get smaller until they reach the catch sack, which we call the codend, and once in there, the fish cannot escape. We then pull them to the surface and begin collecting data, such as size and species. The largest drawback to these methods is that the fish caught in the net will most likely die. To understand why, think of a diver in the deep ocean. If the diver comes up too fast, the body cannot adjust to the pressure fast enough as air expands, potentially causing lungs to rupture. For the fish, bringing them up too quickly causes their swim bladders to rupture. Rockfish tend to have their stomachs inverted out of their mouth. While killing the fish for research is unfortunate, it is one of the few ways we can learn about their patterns of behavior, health, and diversity.

Chris Wilson in the process of attaching buoys to stabilize the Cam-Trawl

The Cam-Trawl is an innovative experimental design that may help reduce the killing of fish and allow us to collect data from endangered or nearly extinct fish species. For example, many Rockfish species off the west coasts of California, Washington and Oregon are endangered and as a result, we do not want to catch them in our nets because we would most likely kill them. The Cam-Trawl would remedy that and would allow us to receive continuous data at each depth along its path. The other trawls catch all the fish in their path which means the collection of fish is mixed and we cannot tell the depth at which they were originally swimming or which species was at what depth. To picture how the Cam-Trawl works underwater, imagine a funnel again, except this time, there is no codend attached. At the end of the funnel, the stereocamera is positioned to photograph the fish that pass through the funnel. The resolution of the fish photos is much more advanced than what we have ever had before. This sampling technique is supposed to give us a better resolution of what we are able to “see” using acoustics (echo sounder) than the traditional midwater (AWT) and bottom trawls (83-112).

Personal Log:

Sleeping at sea was a new experience for me. The seas were only four to eight feet high which are marginal compared to the conditions this ship experiences in the winter months. Overall, I enjoyed being rocked to sleep but my 0330h alarm was not as pleasant. My room is located four flights of stairs below the bridge deck and I’ve been told it is one of the better places to be because the rocking of the boat is not as intense. The rooms are pretty cozy as space is limited but there is room for a desk, two closets and a bathroom (called a head on a ship) that reminds me of the sizes found in European hotels. I have the top bunk and each has a curtain that wraps around the entire bed so that if your roommate has a different shift than you, the light to the main room won’t be a disturbance. Of course, since I have lived in Alaska for two years, I have become accustomed to sleeping in bright conditions.

Something the non-boating community may not realize is that on a ship, it is very important that there is a night crew and a day crew operating. On the bridge where the main controls of the ship are located, there must always be a NOAA Corps Officer, with qualifications to drive the ship, on watch 24/7. However, all crews, with the exception of the kitchen, on the ship are operating around the clock. For example, there are always engineers operating in case there is some type of mechanical issue and scientists operate because there are still fish in the ocean and their behavior needs to be observed at all times.

Me trying on my “Gumby” Suit during the fire drill

The entire crew participated in a fire drill and abandon ship drill yesterday so that all hands on the ship knew where to muster for a head count and to learn how to operate the life rafts in case the ship was sinking. Additionally we needed to learn how to get into our survival suits (Gumby Suits). My first experience putting on the suit was during a field trip onto this vessel with my seventh and eighth grade students in May so I was aware of the cozy fit! Fire and abandon ship drills are practiced once a week when the ship is underway, which is very important as the crew onboard are not just NOAA employees but also in charge of fighting fires and responding to any onboard emergencies. So, if you want to be a fireman and a scientist and cannot choose, perhaps serving aboard a NOAA ship would be right up your alley!
To end my day (remember bedtime for me is early as my alarm is set for 0330) I had a “late” supper of sushi, spring rolls, meatloaf, and for dessert a fabulous set of s’mores! Who says you can’t have them on the ship?

Animals Observed:
Northern Fulmar
Crested Auklets
Tufted Puffin
Black-legged Kittiwake
Orcas

Something to Ponder:
When we are asked, “What do you want to be when you grow up?” usually we say one occupation – firefighter, actor, scientist, teacher, soldier, waitress. However, most jobs require many skills. For example, the scientists on board put a variety of skills into practice and as mentioned in the Scientific Log, scientist Kresimir Williams engineered the Cam-Trawl which employed his knowledge of the biological sciences (fish/oceanography), physical science (how to deploy the device without it breaking), and photography! So for my students, what do you want to be when you grow up?

June 18, 2010March 12, 2021

Richard Chewning, June 18th, 2010

NOAA Teacher at Sea
Richard Chewning
Onboard NOAA Ship Oscar Dyson
June 4 – 24, 2010

NOAA Ship Oscar Dyson
Mission: Pollock Survey
Geographical area of cruise: Gulf of Alaska (Kodiak) to eastern Bering Sea (Dutch Harbor)
Date: June 18, 2010

Weather Data from the Bridge

Position: Bering Sea, north of Dutch Harbor
Time: 1600 hours
Latitude: N 55 06.120
Longitude: W 166 33.450
Cloud Cover: Mostly cloudy
Wind: 10 knots from the west
Temperature: 7.1 C
Barometric Pressure: 1010.8

Science and Technology Log

In order to manage a public resource such as pollock, fisheries managers must develop a stock assessment. A stock assessment is a big picture overview of a certain population of fish. Fisheries managers use stock assessments to determine opening and closing dates for fishing seasons, catch limits (the number of fish that can be caught by a particular fisherman or boat), and the total allowable catch for the season. Stock assessments are developed from a combination of fishery dependant and independent data. Fishery dependant data includes catch records from commercial fishing boats and reports from processors dockside that prepare and package the fish for market. Combined with this information is fishery independent data. This information is gathered from sources not involved with commercial fishing.

chewning_log8_img_1 — Cod end filled with pollock

chewning_log8_img_3 — Unsorted catch entering wet lab

The Dyson’s acoustic trawl survey is one of the primary sources of fishery independent data for the pollock stock assessment. The Dyson’s transducers provide a wealth of acoustic data from each transect. These acoustic returns must first be identified or deciphered before being used in the stock assessment. Just like you need a key to decode the symbols on a road map or need a scale to interpret the colors on a weather map, the acoustic returns also need to be referenced with actual pollock specimens collected by trawling. By matching up the characteristics of the fish caught in the trawl with their acoustic returns, researchers can interpret all the acoustic data from the entire survey area.

chewning_log8_img_4 — My what sharp teeth you have! Arrowtooth flounder

Pollock specimens are collected with Aleutian wing trawls, or AWTs for short. An Aleutian wing trawl is a single large net deployed off the stern of the Dyson. Large metal fishbuster doors are used to open the mouth of the net in the water. The catch is collected in a bag located at the end of the net called the cod end. The cod end’s mesh size prevents anything larger than 0.5 inches from escaping. Once the net is hauled back on deck, the cod end is emptied in the wet lab, and the entire catch is sorted. Fish are identified, counted, weighed, and measured. The gender and maturity of a subsample of pollock are also recorded. Stomachs are collected to determine what the pollock are eating. Finally, otoliths, the ear bones of fish, are collected. Just like counting the rings of a tree, researchers will count the number of rings in the otolith to determine the age of the pollock. Notable bycatch (fish that were not targeted) include eulachon, arrowtooth flounder, Pacific cod, sturgeon poacher, and yellowfin sole. Misha told me Russians used to dry out eulachon whole and use them as candles because of their high oil content. In fact I learned that one of common names in the US for eulachon is candlefish!

Why gather so much information on a single species of fish like pollock? Fisheries managers are responsible for the sustainable use of public resources. Without careful monitoring, fishing pressure, natural predation, and disease might remove pollock from the population faster than they can replace themselves. There is great demand for pollock both commercially and in the Bering Sea ecosystem. Walleye pollock is the largest US fishery by volume and third largest by value. Annual US catches can average 2.5 billion pounds. Pollock is also an important food source for Stellar sea lion, other marine mammals, birds, and other fish.

chewning_log8_img_8 — The Dyson in Dutch Harbor

Personal Log

On Thursday, I had the pleasure of joining two members of the deck crew, Joel Kellogg and Glen Whitney, to pick up a new addition of the science party in Dutch Harbor. Mike Sigler, a fish biologist with NOAA, is a project leader and principal investigator with the North Pacific Research Board’s Bering Sea Integrated Ecosystem Research Program (BSIERP). He is joining the Dyson for the last week of our survey. BSIERP is a six year long collaborative study with the National Science Foundation’s Bering Ecosystem Study (BEST). More than a hundred scientists from these two groups are investigating the organisms and physical forces that make up and influence life in the Bering Sea ecosystem.

chewning_log8_img_9 — Recovering the Peggy D.

To pick up Mike, the Dyson launched the Peggy D. Named for wife of Oscar Dyson, the Peggy D. is a small power boat used to ferry people to and from shore. Peggy Dyson is a famous Alaskan in her own right, serving as a National Weather Service ship to shore weather broadcaster. Her voice brought vital information and reassurance to Alaskan fisherman. She diligently performed these duties twice a day, seven days a week for 25 years. I really enjoyed having the opportunity to see the Dyson from the water as my only vantage point for the last two weeks has been from the Dyson looking out. I was surprised how quickly the Dyson shrunk on the horizon as we sped away and traveled into Dutch Harbor. Dutch Harbor felt like a true frontier town. The vehicles seemed to reflect the character of the town. While looking rough and weathered on the outside, the beat-up cars and trucks of Dutch Harbor revealed a resilience and gritty determination to keep moving forward and press on against an unforgiving environment. I loved hearing the cry of the bald eagles that were spotted everywhere you looked. While I enjoyed having solid ground under my feet for a few short minutes, I appreciated the sense of familiarity and belonging I felt upon returning to the Dyson.

chewning_log8_img_7 — Scute visits the Bering Sea

Scute, the Georgia Sea Turtle Center Mascot, was spotted visiting the Bering Sea today! Scute, a loggerhead sea turtle, travels the world promoting awareness of sea turtles. We know Scute was only visiting the Bering Sea as these waters are too cold for loggerhead sea turtles. Loggerhead sea turtles are the most abundant sea turtles in US coastal waters. Scute’s home is the Georgia Sea Turtle Center (GSTC) located on Jekyll Island, Georgia. The GSTC is a research, rehabilitation, and education center dedicated to helping sea turtles along the GA coast and around the world. Sea turtles released from the GSTC will often have a satellite transmitter attached to their shell just like Scute. The transmitters allow researchers to track their movements at sea. Only one of the seven species of sea turtles found worldwide can survive this far north – the leatherback sea turtle. The leatherback sea turtle is the largest species of sea turtle reaching six and a half feet in length and weighing as much as 2000 pounds! Leatherbacks have several adaptations such as high oil content in their large bodies that help them tolerate the cold waters of the southern Bering Sea. Leatherback sea turtles feed on jellyfish and can dive to great depths because the protection provided by their leathery shell (a hard shell would crack under the high pressure of the water). For more information about Scute and sea turtles, check out the GSTC website at http://www.georgiaseaturtlecenter.org !