Trawling for Krill

NOAA Teacher at Sea:  Tammy Orilio

NOAA Ship Oscar Dyson

Mission:  Pollock Survey

Geographical Area of Cruise:  Gulf of Alaska

Date:  29 June 2011

Weather Data from the Bridge:

Latitude:  58.01 N

Longitude: -152.50 W

Wind: 23.95 knots

Surface Water Temperature:  9.4 degrees C

Air Temperature: 10.8 degrees C

Relative Humidity: 71%

Depth: 177.72 m

Science & Technology Log:
What are krill, you ask?  They're animals in the Phylum Arthropoda, which means they're related to insects, spiders, crabs, lobsters, etc.  They have jointed legs and an exoskeleton, are usually a couple centimeters in length, and are reddish/orange-ish in color.  They can often be found in dense schools near the surface of the water, and play an important role in the ecosystem as a source of food for lots of larger animals (like fish, whales, & penguins).
I've mentioned the two types of trawl gear that we use to catch fish, but if we want to catch smaller things like plankton, the mesh on those nets is way too small.  Therefore, we use a third type of trawl called the Methot which has very fine mesh to corral the plankton down into a collection container at the end of the net.  In addition to having a hard container at the end- as opposed to just a bag/codend that you see in the fish trawls- the Methot trawl also has a large metal frame at the beginning of the net.  Check out the photos below.

The Methot trawl being taken out of the water.  Note the square frame. 

The container that collects all of the plankton in the net.

After the net is brought back on deck, one of the fishermen or deckhands brings the container of krill into the fish lab.  The first thing we do is dump the container into a sieve or a bucket and start picking out everything that isn't krill.  The two most common things that are collected (besides krill) are gelatinous animals (like jellyfish & salps) and larval fish.  The fish get weighed (as one big unit, not individually) and then frozen for someone to look at later on.

The larval fish that we separated from one plankton tow. 

After sorting the catch, we're left with a big pile of krill, which gets weighed.  We then take a small subsample from the big pile of krill (it's a totally random amount- depends on how much we scoop out!) and then weigh the subsample. Then the fun begins, as I'm the one that does this job- I get to count every single individual krill in the subsample.  Tedious work.  All of the data is then entered into the computer system, and the krill and anything else that we've caught (besides the larval fish) are thrown back into the water.

Sorting through the big pile of krill.

How many individual krill are in this picture?  You get a prize if you're the closest without going over :)

Personal Log:
I mentioned that once we're done with the krill, we throw it back into the water- that was until I came aboard!  My eel (Ms. Oreelio for those of you that don't know!) eats dried krill, and I'm going to run out soon, so I figured I'd take these krill home with me!  I got a gallon-size baggie from the galley (kitchen) and filled it up with krill, and holy cow, it's a lot!!  I stuck it in our freezer- which is at -22 degrees C (or 7.6 degrees F) so now I have a big frozen block of krill to take back home with me.  What a great souvenir.