Richard Chewning, June 17th, 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 17, 2010

Weather Data from the Bridge

Position: north of Dutch Harbor
Time: 0830
Latitude: N 54 58.080
Longitude: W 165 58.080
Cloud Cover: cloudy with fog
Wind: 20 knots from SW
Temperature: 6.9 C
Barometric Pressure: 1007.9 mbar

Science and Technology Log

In addition to the Tucker trawl, fish biologists onboard the Dyson also utilize the Methot trawl to catch zooplankton in their study of pollock. The Methot is a single net with a large square mouth (the opening of the net) that is deployed from the stern and towed behind the Dyson. The Methot uses fine mesh with openings slightly larger than the Tucker trawl. This larger mesh size allows the net to be towed at higher speeds. A torpedo looking instrument called a flowmeter is suspended in the mouth of net to measure the flow of water moving through the net. The flowmeter allows the researchers to calculate how much zooplankton is found in a certain volume of water. With its larger mouth and faster speed through the water, the Methot is able to catch the larger zooplankton such as euphausiids the Tucker trawl might miss. Pollock seem to love euphausiids as I have seen firsthand stomachs of pollock caught during Aleutian wing trawls that have had stomachs stuffed with euphausiids.

Deploying the Methot trawl

Recovering the Methot trawl

After the Methot is return onboard, the sample is rinsed and poured through a strainer to separate the zooplankton from smaller algae and phytoplankton. After being weighed, a small subsample is removed and preserved for later identification. The number of euphausiids in a second subsample is counted to calculate the total number in the catch. Several individual euphausiids are also frozen so they can later be analyzed for age and development by examining their eye stalks. In addition to catching the small zooplankton pollock eat, the Methot will also catch some of the largest zooplankton in the ocean: jellyfish. Almost all the Dyson’s trawls have yielded large number of Chrysaora melanaster jellyfish. After being removed from the sample, these jellyfish are also weighed and measured. These jellyfish produce only a mild sting but can be quite frustrating to process in large numbers.

The flowmeter

The Dyson has also been routinely deploying a piece of equipment known as a CTD (conductivity-temperature-depth recorder). This instrument package allows scientists to measure temperature, depth, dissolved oxygen, chlorophyll, light intensity and conductivity. By measuring conductivity (the amount of electricity carried by seawater), salinity can also be calculated, and from temperature and salinity, density can be calculated. The CTD is deployed once every night before dawn and during selected locations during the day. The CTD is attached to a metal frame called a carousel along with other pieces of scientific equipment. Niskin bottles can be attached to the carousel allowing the recovery of water samples from different depths. The Niskin bottle is a vertical plastic tube that is initially deployed with both ends open allowing seawater to flow through. Once the CTD is lowered to the desired depth, the bottle is ‘fired’. Firing signals the bottle to close the openings, sealing the water sample inside. This water can be brought to the surface and filtered to measure the amount of chlorophyll it contains. By better understanding how the properties of seawater such as temperature and chlorophyll concentration relate to the various biological organisms that form the foundation of the Bering Sea ecosystem, researchers can better understand pollock distribution and abundance.

Recovering the CTD

Personal Log

After getting to know the crew over the last week and a half, I have noticed most have a passion for the great outdoors and enjoy a wide range of physical activities such as hiking and skiing when not at sea. Most enjoy hunting and fishing and several enjoy competitive events such as running and cycling. You would think staying active while sharing a platform only 208.6 feet long and 49.2 feet wide with up to 40 people might seem like a daunting task, but this is surprisingly not the case. I have noticed most of crew members from the CO (the commanding officer) to the guest scientists have dedicated time in their schedule to keeping physically fit.

The deck crew has an upper hand in this endeavor as their work often involves moving heavy lines, chains, and gear. Their labor is aided however by powerful hydraulic winches that can lift even the heaviest objects with ease. The Dyson’s acting XO (executive officer) Lieutenant Sarah Duncan was also willing to suit up in her foul weather gear and life vest to give the deck crew an extra set of hands with two late night pollock trawls. Besides the physical workout of retrieving the gear, she told me that working down on deck gives her better appreciation for how the deck crew is affected by the ship’s movements and weather conditions when deploying and retrieving gear. This is very valuable information for Sarah for when she is high in the bridge working hard to direct the ship’s movement so the deck crew can work efficiently and safely in different weather conditions and sea states.

Maintaining one’s physically fitness benefits every member of the crew regardless of station as rough seas can wear the body down physically and mentally in a very short period of time. The rowing machine seems to be the first choice among the crew although the stationary bike and elliptical machine are also popular. The treadmill is the most challenging workout as you are constantly being thrown off balance. I can’t help but wonder what prisoners chained to the oars of wooden ships of old would think knowing that mariners today use large mechanical engines to power the ship and use stationary rowing machines for exercise!

Measuring Chrysaora melanaster jellyfish

Holding Chrysaora melanaster jellylfish

Did you know? The word ‘plankton’ and ‘planet’ come from the same root word? Both names come from the Greek word planktos that means ‘wander’. Plankton is any plant or animal not strong enough to swim against water currents. Examples include diatoms, dinoflagellates, copepods, and euphausiids. Planets were named because they were observed by early astronomers to drift or wander among the stars. Stars appear to maintain the same spatial relationships with each other as they rotate across the sky because they are located so far away. Although they are actually moving, their position in relation to each other appears to be unchanging. This is the reason why the same constellations (pattern of stars in the sky) have been identified throughout human history. Planets on the other hand move through the star field as they are very close in comparison and are orbiting the sun. Thus planets appear to wander among the stars just like plankton drift among the currents of the ocean.

Saving a euphausiid sample

Aurelia labiata

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