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New Gear for Darters , Chubs and YOYO's

Started by Guest_netmaker_* , Dec 23 2009 11:46 AM

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#1 Guest_netmaker_*

Guests

Posted 23 December 2009 - 11:46 AM

I thought I would break up the winter doldrums with a sneak peek at something new ......

This summer, I was asked about taking fish, especially darters, out of small cobble and rock. Looking back over some older designs from BITD ,I found a beam net gear that we had made for Pacific sole and flounder. We tweaked it, scaled it down and sent it to a crew of USFWS field guys.

The Chain Maile Net system gently dislodges the cobble and stirs the detritus without digging and dredging. It spooks the 1-4 cm fish up and out of the pebbles and into the net. The design uses the curved rings to stir and not dig the cobble. Equipped with a Live Catch codend, the net handles the fish softly and reduces mortality. We are looking to reduce the need for shocking as well as NOT dredge and damage as much of the bottom sediment in extricating these little critters from their rocky lairs. It may never be at a 100% efficiency level for this purpose, but everything in the research net design business is a compromise.
Only the next set of field trials will tell if we have accomplished that goal.

*If large rocks become a problem we can add a Rock Skirt similar to one we installed on the Penn State Mini-Missouri trawl used in their electro-fishing project.*

A crew will field test Model 2 in about 6 weeks. It has several improvements in the net geometry and fishing circle that are expected to produce better catches and less "trash" in the net. Model 1 (shown here) worked well enough and caught target species......I just saw something I didn't like so we tweaked the design a little more in Model 2.

Basically, I just want a gear for use in cobble, that catches everything on bottom .......without catching the bottom.

Any and all comments are welcomed.

Bon Noel,

Greg

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#2 Guest_natureman187_*

Guests

Posted 23 December 2009 - 03:00 PM

Now that is cool. Keep us posted how it works!

#3 Michael Wolfe

Board of Directors

North Georgia, Oconee River Drainage

Posted 23 December 2009 - 03:07 PM

Equipped with a Live Catch codend, the net handles the fish softly and reduces mortality. We are looking to reduce the need for shocking as well as NOT dredge and damage as much of the bottom sediment in extricating these little critters from their rocky lairs.

Greg... I don't think I know what this means... codend?... also how "tall" is this net? In the picture it look like there is a lot of net, but that the floats are pretty close to teh rings, is that right or an artifact of 2D photography?

Either write something worth reading or do something worth writing. - Benjamin Franklin

#4 Guest_netmaker_*

Guests

Posted 23 December 2009 - 04:34 PM

The Codend is the catch hold area. Its the last section in the very back of the net where everything that comes into the net collects. Most nets have a tubular codend that holds everything but most of the time kills the catch due to the swirling action. In really big commercial gears the codend can be split into a Siamese Tail Bag where 20cm shrimp are separated from 60cm fish. However, in these research nets, its more like separating 1-5cm fish from EVERYTHING ELSE.
In some cases like the gear Dave Herzog of M.D.C. developed, there are two concentric codends, one inside the other . This stops the big critters from crushing the ity bitty critters.

The Live Catch codend is shaped such that it dispells the internal pressure wave (IPW) and lets the critters move about a little more freely away from larger detritus. It also holds bottom better.
Its one of the reasons I warn folks NOT to use shrimp trawls for research work involving delicate critters.

FYI.
This system will work on several trawl designs. The one shown here is a Combination USFWS PUSH TRAWL. It can be used with a set of otter boards or a beam frame.

This particular net has a catenary (lift) of about 30" dead center of the Head Rope ( floats) and 12" at each Breastline (wing). The photograph is of a net laying down and 'peeled' back to show the footrope (bottom of the net). Model 2 has a different curvature to the rings and its attached differently.

This system will work on several other nets that are in use by researchers if the field trials show what I am expecting to see. Nothing is 100% perfect, but enough researchers asked for something that could work in cobble and yet not tear up too much bottom or cost too much to get started (like a shock system).

Anyway, its just another tool in the fisheries box of goodies.

sa va,
Greg