Tuesday, February 03, 2009

Drift Net In Action At Estill Fork On Saturday

Saturday's trip went well for the primary objective of collecting a decent number of telescope shiners for gut content examination, length/weight data and probably some brain analysis. But we also had a chance to test a drift net I've had for a few years that I built myself (with help from my wife in sewing the bag). The purpose of such a net is to collect passively drifting small animals and maybe algaes. The net is staked into the bottom of the stream so that water is flowing through it, and then wait some period of time before collecting what might have been trapped. Mine is 12" x 18", with a PVC pipe frame holding a bag made from organza silk, which has a very fine mesh. The challenge is how to stake it to the bottom. I've had metal tent stakes in the past that worked, but I lost them in our building move a year ago. So we tried bamboo poles. Unfortunately I couldn't force them into the streambed, so I talked Taito and Brittany into holding the net in place for about 15 minutes as a field test. And it worked!

Below is a photo looking downstream to the area we netted for telescope shiners. The flowing pool gives way to about 100 m of deep riffles with some scourholes in dense packed cobble and gravel.

Here are Taito and Brittany holding the net in place. The top of the net is just above the water level so that (hopefully) water is flowing into the bag, and not being blocked by any kind of turbidity right in front of the net.

Here's a closer view of the bag in action. Water was indeed flowing through it. We quickly saw leaves, sticks and few insects trapped inside the bag. And some protein foam started to build up at the top of the bag.

So I'm happy with the net's results. We also trapped a surprising amount of sand that seemed to be entrained in the current. I didn't keep the collection for further examination, since I think it's still too early for truly interesting drift such as ichthyoplankton to be present. But maybe next trip in early March, especially if I have the wit to go get some decent metal stakes so we can stake it out and take a break for an hour or so before checking the catch.

0 Comments:

Post a Comment

<< Home