It’s hard enough to catch a pallid sturgeon once, but twice?!

 

USGS employees Beau Griffith (left) and Becky Welly (right) hold a telemetered pallid sturgeon they recaptured in a trammel net. The wooden object with 2 white buoys to the right of Welly is called a "Buck" or a "Mule" and is used to pull the net along in the current.

Any fisherman will tell you that just knowing where a fish is located is not enough to catch it.  If it were, we would call it “catching” instead of “fishing.”   Recapturing telemetry tagged pallid sturgeon takes skill, experience, hard work, and a little bit of luck. 

Telemetered pallid sturgeon are targeted for recapture in the spring after spawning, in the fall of the year before the next spawning season, and at any time our database tells us that the transmitter battery is nearing the end of its life.  Examining the same pallid sturgeon before and after the spawning season allows scientists to determine whether or not a sturgeon was in reproductive condition and if it spawned successfully.  Knowing this important information helps us to understand each fish’s motivation and more accurately interpret the behavior of the fish we are tracking.  Comparing the behavior and physiology of fish that successfully spawn to those that do not provides important insight into how environmental conditions in different years may influence the location, timing, and success of spawning.

The chosen gear for recapturing telemetry tagged pallid sturgeon is a drifted trammel net.  The trammel net is 120 feet long and 6 feet deep with three layers of net hung between a “float” line and a “lead” line.  The buoyant float line lifts the top of the net towards the surface of the water while the heavy lead line sinks to the bottom of the river.  The middle net has 3 to 4 inches square mesh while the two outer nets have 16 inches square mesh.  The inner net is deeper than the outer layers of large mesh, allowing more of the finer, inner net to fish along the bottom where sturgeon can become entangled in it.  The larger, outer mesh is made of heavier twine which holds the trammel net together when it becomes caught, or snagged, on rocks and logs.  Trammel nets fished this way for sturgeon perform more like reinforced, or tied down, gill nets than typical trammel nets.

 

It's not uncommon to become snagged while drifting a trammel net in the Lower Missouri River. This stump was hauled in during efforts to recapture a telemetry tagged sturgeon.

Once a telemetered pallid sturgeon in need of recapture is identified and located, the habitat is evaluated for safety.  Sometimes the water is too deep or too swift to attempt fishing for the tagged pallid sturgeon.  Rock dikes, submerged trees, navigation buoys, and commercial boat traffic in the area may further complicate or terminate the effort.  However, if no hazards are near, crews begin recapture efforts.

 

Once the area is declared safe for fishing, the trammel net is deployed from the front of a reversing boat. The "buck" which is thrown out first, can be seen floating in the river.

 

Moving upstream of the targeted fish, the trammel net is let out into the water in a shallow u-shaped arc.  One end of the float line is tied to a special float called a “buck” or a “mule” that catches the current and pulls the net downstream.  The other end of the float line is held at the bow of the boat.  Heavy weights are added to the lead line to sink it quickly and to ensure it fishes as close to the bottom as possible.  The net and boat drift downstream with the current until the net drifts past the location of the targeted fish or snags the bottom.  If the fish is captured, there is celebration.  If not, it is lather, rinse, repeat – drifting over the fish’s location until it moves to another location, the net becomes too damaged to continue, or the day is over. 

 

Pallid sturgeon can be very good at avoiding nets. It is necessary to locate telemetered pallid sturgeon between capture attempts because they move if harassed by repeated drifts of the net. The trammel net and buck sit on the deck of the boat waiting for the next attempt.

 

 Completed with contributions by Aaron DeLonay.

 

About Emily Pherigo

Emily is no longer with the Comprehensive Sturgeon Research Project. When she was here, she was a biologist contracted to the Comprehensive Sturgeon Research Project. Most of her time was spent at a computer performing QA/QC on data or updating figures and graphs most used by Aaron DeLonay. However, she occasionally made it to the river, where she enjoyed seeing pallid sturgeon and was reminded why she entered the natural resources field.
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