NOAA Teacher at Sea
Anne Mortimer
Onboard NOAA Ship Oscar Dyson
July 4 — 22, 2011
Mission: Pollock Survey
Geographical area of cruise: Gulf of Alaska
Date: July 7, 2011
Weather Data from the Bridge
Air temperature: 9.53 C, Foggy
Sea temperature: 8.19 C
Wind direction: 145
Wind Speed: 18.73 knots
Barometric pressure: 1013.22 mbar
Science and Technology Log
Last night, we attempted a bottom trawl for walleye pollock. The way scientists know that fish are present is by using acoustic sampling. The centerboard of the ship is set-up with sound emitting and recording devices. When a sound wave is emitted toward the bottom, it will eventually be returned when it hits a fish or the ocean bottom. This is called echo-sounding and has been used by sport & commercial fisherman and researchers for many decades. The sound waves are sent down in pulses every 1.35 seconds and each returned wave is recorded. Each data point shows up in one pixel of color that is dependent on the density of the object hit. So a tightly packed group of fish will show as a red or red & yellow blob on the screen. When scientists see this, they fish!
The scientists use this acoustic technology to identify when to put the net in the water, so they can collect data from the fish that are caught. The researchers that I am working with are specifically looking at pollock, a mid-water fish. The entire catch will be weighed, and then each species will be weighed separately. The pollock will all be individually weighed, measured, sexed, and the otolith removed to determine the age of the fish. Similar to the rings on a tree, the otolith can show the age of a fish, as well as the species.
These scientists aren’t the only ones that rely on technology, the ships navigation systems is computerized and always monitored by the ship’s crew. For scientific survey’s like these, there are designated routes the ship must follow called transects.
Personal Log
I think that I must have good sea legs. So far, I haven’t felt sick at all, although it is very challenging to walk straight most times! I’ve enjoyed talking with lots of different folks working on the ship, of all ages and from all different places. Without all of the crew on board, the scientists couldn’t do their research. I’ve been working the night shift and although we’ve completed a bottom trawl and Methot trawl, we haven’t had a lot of fish to sort through. My biggest challenge is staying awake until 3 or 4 am!
Did you know?
That nautical charts show depths in fathoms. A fathom is a unit of measurement that originated from the distance from tip to tip of a man’s outstretched arms. A fathom is 2 yards, or 6 feet.
Species list for today:
Humpback Whale
Northern Fulmar
Tufted Puffin
Stormy Petrel
In the Methot net:
Multiple crab species including tanner crabs
Multiple sea star species, including rose star
Sanddollars
Juvenile fish
Brittle stars
Sponge
Multiple shrimp species including candy striped shrimp
