Thursday, May 9, 2013

Nets on Nets on Nets

Sub-surface Neuston Net
Nueston net.
We use three nets to catch plankton. The first is the sub-surface Neuston, a 1 meter by 2 meter frame with a long conical net attached to it. The plankton collects in a plastic tube at the end called the "cod end." With the help of the winch operator, we do a few dips with the net to 10 meters (~30 feet). So far, this is the most effective method for finding tuna, and often the plankton from these tows is sorted right on the boat by one of us.

The second net, called the Mini-Bongo (it looks just like its name) is made up of two connected PVC pipes that each have a net and cod end attached to them. One net has a mesh that captures the small stuff; the other has larger mesh that keeps in the bigger plankton. These samples will be used to examine what tuna are eating and to create a food web from stable isotope values of nitrogen. 

The last net is the MOCNESS (also known affectionately as the MOCNESS Monster or the Franken-MOCNESS). This net can be really useful, as it has a unique system where plankton samples from different depths can be taken on a single tow by opening and closing various nets. It's taken us many hours to set it up and the system is very heavy, complicated, and had some set-up issues in the beginning, but in the last few days we've finally gotten it working and have done several successful MOC tows. If you're interested in learning more about the MOCNESS, visit WHOI's page.

And in case you're wondering (I bet you are!), MOCNESS stands for Multiple Opening and Closing Net Environmental Sensing System.

Mini bongo
Mini-bongo, with two nets attached to
the "bongo" portion.

Diagram of the MOCNESS as it flies in the water
Plankton in a Sieve
Plankton collected in a sieve after a
subsurface neuston tow

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