Sometimes, things just don’t work as expected. You go to a new sampling site, determine ambient water conductivity, estimate a good starting point for standardizing by power and conduct a quick pretrial to fine tune the voltage, current or power levels for successful fishing. But, either the starting point is incorrect, or the sampling begins successfully and then something changes to reduce effectiveness. Below are three examples of unusual circumstances in electrofishing. Two of these were my direct experiences; the other was reported to me.Continue Reading..
Jim Reynolds and I just taught a boat electrofishing course in Redding, California at Whiskeytown Lake. That provided some threshold fishing data for voltage, current and power for each of four electrofishing boats. One can standardize by power using any of the three parameters. Which parameter is less variable among a fleet of boats?
Fisheries biologists are knowledgeable about fish, their habitat and about ways to collect fish using a variety of gear and techniques. Many are less familiar with the electrical terms which are used in fish capture using electricity. This blog is meant to explain electrical terms which are used in electrofishing classes and in the literature.
Electrical fields around electrofishing anodes are critical to fish capture effectiveness. The size, shape and intensity of those electrical fields are determined by the anode design and deployment in the water as well as by the electricity applied to them. There were two main questions to answer in this little study: (1) Could accurate electrical measurements be made from approximately ¼ scale model electrodes in a small body of water, and (2) Would those measurements provide useful information about the effect of anode ring size on their electrical fields?
Modern electrofishing pulsator (control box) manufacturers as a whole produce a variety of direct current pulse shapes. Which of these are more effective or more efficient for fish capture? We have noticed some differences in fish reaction thresholds and overall behavior when exposed to different pulse. For years, I have wanted to compare various pulses under controlled laboratory conditions. The challenge has been acquiring a suitable power supply that can produce the desired pulse shapes. That opportunity recently became available.
Fisheries biologists have known for a long time that many factors affect fishing success. The most important environmental factor is the conductivity of the water, i.e. its ability to conduct an electrical current due to the concentration of ions in the water. Water conductivity has been used as independent variables in multiple regression equations or as covariates to estimate catch per unit effort or some measure of capture efficiency. For decades, biologists made equipment adjustments to compensate for varying water conductivity in an ad hoc fashion without a guiding principle.
Alan Temple wrote a blog, Setting Doses for Lab Experiments, which I followed with Setup for Lab Experiments in Tanks. That was followed by a short one, Size Matters, on the effect of fish size on the threshold voltage gradient and power density for immobilization or other responses. This blog discusses some aspects of how a tank study is conducted. Specifically mentioned are the fish themselves, the desired response to be assessed, how that response is to be evaluated, and two primary approaches for quantifying the results.
Yes, size matters…and that includes fish size when electrofishing. Large fish are immobilized with less field intensity or power density than are small fish. Large fish sustain a higher total dose of electrical energy than do small fish; this is sometimes referred to as whole body voltage. An excellent paper on this topic is Dolan, C.R. and L.E. Miranda. 2003. Immobilization thresholds of electrofishing relative to fish size. Transactions of the American Fisheries Society 132:969-976. This short blog provides results of a simple study with various sizes of alligator gar.
Dr. Alan Temple posted a blog on December 9, 2015 entitled “Setting Doses for Lab Experiments.” He suggested that I submit a blog on other aspects of lab studies in tanks. This blog covers the setup of tank studies for electrofishing research, and I plan to submit a companion blog on procedures for tank studies. Important aspects to consider for lab studies are the test tank, the electrodes, the power supply and the electrical field.