A primary aim of electrofishing is to produce an electrical field in the water of sufficient intensity to enable the capture of fish within the field. The field intensity is highest near the electrodes and decreases with distance from the electrodes. Miranda and Kratochvil (2008; TAFS 137:1358-1362) used a floating grid around the anode arrays of an electrofishing boat to measure field intensity, or voltage gradient (V/cm), in x,y coordinates so that a map of the field intensity could be constructed. This blog includes graphs which show the effect on the field of changing the distance between the anode arrays. What is new from the article is the use of color graphs made using R code for spline interpolation.
Electrofishing thresholds are the minimum settings (volts, watts, amps) needed for successful fishing. We teach biologists to aim for thresholds so that they can acquire the samples they need for research or for management and yet avoid negative impacts on the fish or other aquatic organisms which could be affected. Normally, we help develop conservative goal settings for a given situation and ask biologists to begin there and to make minor changes while fishing so as to determine those thresholds. But is there another way to estimate such thresholds? This blog explores an attempt at estimating electrofishing thresholds using electrical measurements made at the boat ramp.
While attending the Annual Meeting of the American Fisheries Society in Kansas City in August, I visited the vendors, especially the electrofisher manufacturers. It is good to visit with those I know and to see new products. I don’t attend a lot of such meetings, but this was the first time for me to see a booth by ETS Electrofishing Systems LLC. Burke O’Neal of ETS Electrofishing retired and sold the company to his sons. Mark O’Neal now operates the company, which had a slight name change, and moved it to Madison Wisconsin. Burke and I never met, though we had corresponded by email and had talked on the phone over the years. We even collaborated on some testing of voltage gradient probes and of backpack electrofisher anodes. In August, it was my privilege to meet Mark.
ETS now manufacturers an 82 peak amp, high-conductivity version called the MBS-82. It is an upgrade from their former 72-amp high-conductivity version and also has a larger internal circuit breaker. The 82-amp version has been their standard high-conductivity model since August 2015. The new development is a high-voltage version for use in lower conductivity water. This new version, which was in beta format for the AFS meeting, has three voltage ranges – 1000, 600 and 300 volts – to cover a very wide range of water conductivity. The expected current outputs were reported as 30, 40 and 82 peak amps for the 1000, 600 and 300 volt ranges, respectively. While advertised performance is somewhat informative, I wanted to see actual performance data. So, I talked Mark into doing some extensive testing of his new unit over a wide range of resistance to simulate a wide range of water conductivity. This blog shows those results.
A scale model is a physical representation of an object which maintains general relationships between its constituent aspects. Alternately, it is “a small copy of something” or “a miniature representation of something.” This blog describes electrical measurements made on a scale model, yet functional, electrofishing boat and how to scale those up or down to a full size boat. Warning, this will be a long blog, and it may contain errors of logic or calculation. You can use the MythBusters TV show approach and determine if you believe the assumptions are confirmed, plausible or busted.
In Part A of this blog, it was calculated from a lab study that the effective conductivity of Grass Carp was 62 uS/cm. In Part B, let me show you a simple way of using that information in the field to improve the capture success of Grass Carp based on those results. You may want to download the Electrofishing Tool or App from the Tool section of this site.
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?
Here’s a few pics of electrofishing porn from the American Fisheries Society meeting in Portland, OR, 2015. Lots of new goodies. Enjoy!
Most boat electrofishing pulsators (control boxes) are powered with portable generators that provide 240-V, single-phase AC. These generators are available from common commercial sources such as hardware stores or electrical supply houses. (Note: a notable exception is the GPP pulsator made by Smith-Root, Inc., that requires a specially-constructed generator; it will not be discussed further here.) This short blog explains the electrical outlet of a generator, how to test for the safety of a generator if used for boat electrofishing, and what to do if the test indicates that a generator is not safe for electrofishing.
Electrofishing is a primary sampling method for near-shore fish species in lakes and rivers, and for fish species and assemblages in streams. We must admit, however, that it is a sampling technique with inherent risks. People, water and electricity are in close proximity. This blog describes the potential for human injury or death if someone falls into water having an electrical field. It specifically involves boat electrofishing, but the same idea can be used for tow/push barges, shore-based units and backpack electrofishing.Continue Reading..