Net Tow – NOAA Teacher at Sea Blog

NOAA Teacher at sea
Bhavna Rawal
On Board the R/V Walton Smith
Aug 6 – 10, 2012

Mission: Bimonthly Regional Survey, South Florida
Geographic area: Gulf of Mexico
Date: August 8, 2012

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Weather Data from the Bridge:
Station: 21.5
Time: 1.43 GMT
Longitude: 21 23 933
Latitude: 24 29 057
Wind direction: East of South east
Wind speed: 18 knots
Sea wave height: 2-3 ft
Clouds: partial

Science and Technology Log:

Yesterday, I learned about the CTD and the vast ocean life. Today I learned about a new testing called net tow, and how it is necessary to do, and how it is done.

What is Net Tow? The scientist team in the ship uses a net to collect sargassum (a type of sea weed) which is towed alongside the ship at the surface of the predetermined station.

How did we perform the task? We dropped the net which is made of nylon mess, 335 microns which collects zooplanktons in the ocean. We left this net in the ocean for 30 minutes to float on the surface of the ocean and collects samples. During this time the ship drives in large circles. After 30 minutes, we (the science team) took the net out of the ocean. We separated sargassum species, sea weeds and other animals from the net. We washed them with water, then classified and measured the volume of it by water displacement. Once we measure the volume, we threw them back into the ocean.

Dropped the net which collects zooplanktons in the ocean

Measured the volume of it by water displacement

Types of Sargassum and Plankton: There are two types of sargassum; ones that float, and the other ones that attach themselves to the bottom of the ocean. There are two types of floating sargassum and many types attached to bottom of the ocean.

Also there are two types of plankton; Zooplankton and phytoplankton. As you all know phytoplankton are single celled organisms, or plants that make their own food (photosynthesis). They are the main pillar of the food chain. It can be collected in a coastal area where there is shallow and cloudy water along the coastal side. The phytoplankton net is small compared to the zooplankton and is about 64 microns (small mess).

Zooplanktons are more complex than phytoplankton, one level higher in their food chain. They are larva, fish, crabs etc. they eat the phytoplankton. The net that is made to catch zooplankton, is about 335 microns. Today, we used the net to collect zooplankton.

Why Net Tow is necessary: Net tow provides information about habitats because tons of animals live in the sargassum. It is a free floating ecosystem. Scientists are interested in the abundance of sargassum and the different kinds of animals, such as larva, fishes, crabs, etc. Many scientists are interested in the zooplankton community structures too.

Dive, Buoy and other data collection equipments: Two science team members prepared for diving; which means that they wore scuba masks, oxygen tanks and other equipment. They took a little boat out from the ship and went to the buoy station. They took the whole buoyancy and other data collection instruments with them. The two instruments were the Acoustic Doppler (ADCP) and the micro cat which was attached to the buoy. The micro cat measures salinity and temperature on profile of currents, and the ADCP measures currents of the ocean. Both instruments collect many data over the period. The reason for bringing them back, is to recover data in a Miami lab and the maintenance of the buoy.

The micro cat measures salinity and temperature on profile of currents

Acoustic Doppler (ADCP) measures currents of the ocean

Personal Log:

My first day on the ship was very exciting and nerve-racking at the same time. I had to take medicine to prevent me from being seasick. This medicine made me drowsy, which helped me to go to sleep throughout the night. The small bunk bed and the noise from the moving ship did not matter to me. I woke up in the morning, and got ready with my favorite ‘I love science’ t-shirt on. I took breakfast and immediately went to meet with my science team to help them out for the CTD and net tow stations. Today, I felt like a pro compared to yesterday. It was a bit confusing during the first day, but it was very easy today.

I started helping lowering the CTD in the ocean. Now I know when to use the lines for the CTD, water sampling for different kinds of testing, how to net tow and do the sargassum classification. I even know how to record the data.

When we have a station call from the bridge, then we work as a team and perform our daily CTD, water testing or net tow. But during the free time, we play card games and talk. Today was fun and definitely action packed. Two science team members dove into the ocean and brought the buoy back. I also saw a fire drill.

Nelson (the chief scientist) took me to see TGF or called the flow through station which is attached inside the bottom of the ship. This instrument measures temperature, salinity, chlorophyll, CDOM etc. Nelson explained the importance of this machine. I was very surprised by the precise measurements of this machine. Several hours later, I went to the captain’s chamber, also called the bridge. I learned how to steer the boat, and I was very excited and more than happy to sit on the captain’s chair and steer.

aug 8 048 — Excited to sit on the captain’s chair and steer the R/V Walton Smith

We have also seen groups of dolphins chasing our ship and making a show for us. We also saw flying fishes. In the evening, around 8 o’clock after dinner, I saw the beautiful colorful sunset from the ship. I took many videos and pictures and I can’t wait to process it and see my pictures.

aug 8 044 — Saw groups of dolphins ahead of ship

Around 10 o’clock in the night, it was net tow time again. We caught about 65 moon jelly fishes in the net and measured their volumes. Nelson also deployed a drifter in the ocean.

aug 6 104 — See moon jelly fish in my hand

Today was very fun and a great learning opportunity for me, and don’t forget the dolphins, they really made my day too!

Question of the Day:
How do you measure volume of solid (sea grass)?

New Word:
Sargassum

Something to Think About:
Why scientists use different instruments such as CTD as well as TFG to measuretemperature, salinity, chlorophyll, CDOM etc?

Challenge Yourself:
Why abundance of sargassum, types of animals and data collection is important in ocean?

Did you Know?
The two instruments were the Acoustic Doppler (ADCP) and the micro cat which was attached to the buoy. The micro cat measures salinity and temperature on profile of currents, which means it measures at surface of the ocean, middle of the ocean and bottom layer of the ocean too.

Animals Seen Today:
Five groups of dolphins
Seven flying fishes
Sixty five big moon jelly fishes
Two big crabs

NOAA Teacher at Sea
Lollie Garay
Onboard Research Vessel Hugh R. Sharp
May 9-20, 2009

Mission: Sea scallop survey
Geographical Area: North Atlantic
Date: May 10, 2009

The dredge is hoisted to the sorting table

Weather Data from the Bridge
Stationary front persists
West winds 10-20KT Seas 4-6 ft

Science and Technology Log

We began our shift today sampling in an area called Del Marva Closed Area, which is an area currently closed to scallop fishing. We conducted 8 dredge hauls last night in spite of the turbulent weather that pursued us. But today, we had calmer seas and beautiful blue skies.

The serious work of sorting and measuring the catch begins right after the dredge is brought up and secured. As it is coming up, someone on either side of the dredge uses a rake to shake the net which allows the catch to fall out. After the net is secured, readings are taken using from a sensor mounted to the dredge. The sensor is called an inclinometer; it measures the dredge angle during the 15minute tow. This allows the scientists to calculate the amount of time the dredge is on the bottom. Then I hop on the table to hold a whiteboard with the pertinent station information written on it next to the catch which is photographed for documentation. Then the frenzy begins! I leave and someone else gets on the sorting table to rake the catch towards waiting sorters who have several buckets and baskets ready.

The catch is a mixture of scallops, crabs, fish, lots of starfish, assorted other specimens and sometimes sand. We are primarily sorting out sea scallops and fish, but have had some stations that require us to sort out crabs as well. We work quickly to separate the catch which is then taken into the wet lab for measurement. I have been working with Larry Brady from NOAA Fisheries, learning how to measure scallops using the FSCS system. The FSCS is the Fisheries Scientific Computer System which is a collection of integrated electronic devices used to gather and store station and biological data. FSCS uses touchscreen monitors, motion compensation scales and electronic measuring boards. I feed Larry the scallops one after the other as he measures them using a magnetic wand. This information is automatically recorded into the data base. Last night we had a large number of scallops to process. However, today we have seen less and less; in fact we had one catch with none! The fish are not as plentiful either although we have seen various different specimens.

There are also special scallop samples that need to be processed. First, the scallops are cleaned with wire brushes. Then they are weighed in their shells. After this is recorded, they are opened to remove the meat and gonads, which are weighed separately. This information provides us with the gender of the scallop and can approximate their age. I dry the shells and number them. Then I put them into a cloth sack, tag them with identifying information and put them into the deep freeze.

The fish are also weighed and their species is recorded. Sometimes specimens need to be counted (I counted small crabs today). Once all the measurements are taken, everything is washed down! That includes the deck, the sorting table all the catch buckets, the FSCS measuring boards and the lab floors. We are then ready for the next dredge haul which follows approximately 20-30 minutes later. This pace continues throughout the shift, barring any mechanical or weather issues.

Personal Log

Lollie and Larry Brady scrub scallop shells for special samples.

I am very impressed by the precision of the work that the science team does. As I waited for the dredge to unload a catch this evening I reflected on how everyone does their job quickly and efficiently. It’s something I never fully appreciated – that there are people out on the seas doing this very thing all the time! Already in one full day, they have taught me so much about how the fisheries system works, and they have expanded my knowledge of different marine organisms. Even as we sort quickly through the catch, they are always identifying specimens to me and answering my questions.

One of the most amazing sights for me has been the incredible number of starfish that each catch brings up! I have never seen so many, and I am learning about the different types. I am also learning how to shuck scallops for the galley for dinner. So far this has not been strength of mine, but I am determined to master this skill! By the way, our lunch today was scallop soup! The beautiful sunset today gave way to the almost-full moon shining on the seas. My shift is over for tonight, I’d best get some sleep.

Animals Seen Today

Dolphins—made a quick but too brief appearance alongside the ship today. I caught a glimpse as they raced by. Polka dot Kuskeel; Baby Goosefish; Loligo Squid (pronounced Lollie go!) Snake Eel; and Clear Nose Skate.

Tag: Net Tow

Bhavna Rawal: Net Tow, Dive, Buoy Maintenance and Data Collection, August 8, 2012

Lollie Garay, May 10, 2009