Carterville FWCO Continues Use of Multiple SONAR Tools to Evaluate Fish Behavior and Abundance at an Electric Fish Barrier
BY AARON PARKER, CARTERVILLE FWCO
deployed into the CSSC. Credit USFWS
Since I began working at the Carterville Fish and Wildlife Conservation Office (FWCO) last year, my job has mainly consisted of running various wires through boats and analyzing fish images on a computer screen, as opposed to deploying nets and actually holding real fish. That’s because our office has been tasked with evaluating the behavior and abundances of feral fish that are currently present at the World’s largest electrical fish barrier.
This electrical fish barrier is located in the Chicago Sanitary and Ship Canal (CSSC), near Romeoville, Illinois. The primary purpose of this barrier is to prevent the upstream movement of bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) (collectively referred to as Asian carp) from entering Lake Michigan. By evaluating the behavior and abundances of feral fish that are presently near the barrier system (mostly common carp [Cyprinus carpio] and gizzard shad [Dorosoma cepedianum] based on field sampling). Inferences can be made about how Asian carp may react to the barrier if they encounter it.
To assess the behavior and abundances of fish throughout the barrier system, we have used both direct and indirect methods of evaluation. Our indirect methodology consists of using 2 200 khz SONAR transducers and 1 1200 khz side-scan SONAR unit to perform three scans before a brief barrier maintenance shutdown, and three scans after a shutdown. Once the before-and-after scans are completed, we post-process the raw SONAR echograms back at the office and compare the number of fish above the barrier both before and after the maintenance event. By comparing these numbers, we can indirectly assess the behavior of the fish that were immediately below the barrier to see if they opportunistically moved upstream.
ensonifying the entire width of the strongest
barrier. Credit USFWS
Now for the direct observations of fish behavior within the barrier, this was definitely a harder nut to crack! Last year, we spent some time positioning a boat over the strongest part of the barrier and observed fish using a one dual-frequency identification SONAR (DIDSON) unit. While the data that we obtained were useful, we also decided that we really needed to use two separate DIDSON units and that we also needed to mount them onto something that was stable, unlike the boat, which we had to constantly try to maintain position in.
Luckily I work with a pretty smart group of people who are no strangers to unconventional fisheries work (see past entries about our fish-barge interaction work!). After many discussions and meetings with partners, the day finally came where, using a contracted telescopic boom lift, we were able to deploy two separate DIDSON units into the strongest part of the barrier from the shore. By using the two different units we were able to view the entire width of the barrier, and by not using a boat anymore, the images were rock solid. The first deployment off of the boom lift was a success and future work using the lift again is being planned.