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.
Alan Temple and I taught an electrofishing course in Ft. Collins, Colorado last October. The course was unusual in that there were only backpack electrofishers, so that allowed us to have two field trips, in different habitats, using only backpacks. That permitted us to examine two questions – one pertinent to electrofishing in general, and one more specific to backpack units. This blog examines both questions and what we found.
How much electricity does it take to kill a fish egg, or unhatched embryo? We have mentioned that in classes but have only discussed it in generalities. The purpose of this blog is to look more closely at the question and to quantify it as best we can with the limited information available. It makes sense to look at this from the perspective of egg, or embryo, diameter. Bohl et al. (2010), Electroshock-induced mortality in freshwater fish embryos increases with embryo diameter: a model based on results from 10 species, Journal of Fish Biology 76:975-986 is the source of information for this investigation.
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.
In early 2016, I published a paper, “Spheres, rings and rods in electrofishing: Their effects on system resistance and electrical fields” (Transactions of the American Fisheries Society 145:239-248, 2016). My aim was to elucidate the relative importance of size and shape of common electrodes in determining electrical resistance of electrofishing systems and the intensity and size of the electrical fields they produce. In that paper, I did not cover the relationship of electrode surface area to resistance; instead, I am reporting that information in this blog.
On behalf of a fish biologist who wishes to remain anonymous, we are publishing this blog. The biologist has an implanted heart pacemaker and faced concerns about participation in electrofishing operations. The text has been authored in first person and lightly edited by us with approval by the author. We believe that this factual investigation will provide useful information to employees and supervisors alike.
~Colleen Caldwell, New Mexico Cooperative Fish and Wildlife Research Unit and Jim Reynolds, Alaska Cooperative Fish and Wildlife Research Unit (retired)
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.
This blog is being presented it two parts. Part A involves the lab trials to determine Grass Carp effective conductivity, Cf, and power density at match, Dm. Refer to prior blogs at this site on the power transfer theory and on lab experiments for more information about terms, setup and procedures.