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.
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.
|Course Title:||Backpack Electrofishing: Principles and Practices|
|Course ID:||BIO 407|
|Date(s):||June 7, 2016: 8:30am – 4:30pm
June 8, 2016: 8:30am – 4:30pm
June 9, 2016: 8:30am – 4:30pm
|Location:||William Jack Hernandez Sport Fish Hatchery
N Reeve Blvd
|Instructor:||Dr. James B. Reynolds|
|Tuition:||$945 / $895*|
|$845 / $795* (Before May 7, 2016)|
|Course Title:||Boat Electrofishing: Principles and Practices|
|Date(s):||May 10, 2016: 8:30am – 4:30pm
May 11, 2016: 8:30am – 4:30pm
May 12, 2016: 8:30am – 4:30pm
|Location:||Red Lion Inn
1830 Hilltop Dr,
|Instructor:||Dr. James B. Reynolds|
|Tuition:||$995 / $945*|
|$895 / $845* (Before April 9, 2016)|
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..
Testing equipment, particularly current clamps and scopemeters, have a substantial role to play in electrofishing sampling programs. I was first introduced to this notion years ago by A. Lawrence (“Larry”) Kolz and Jim Reynolds, two people that made substantial advances in the conceptual basis for electrofishing. Since then, Jan Dean and I have used test equipment in a number of situations, built Excel-based programs to utilize collected information, and have worked on identifying inexpensive yet accurate meter alternatives.
In this blog, I will attempt to describe purposes of testing equipment, some approaches and considerations regarding their use, share a few of our test results, and provide a list of suggested models.
Experimental set-up for small fish. Picture by Dr. Jan Dean
Lab or tank experiments on fish have been around for decades, beginning with studies of fish behavior in electric fields. Presently, tank experiments are used for evaluating the effectiveness of candidate waveforms, estimating thresholds for various reactions that assist capture, guidance, and electrosedation, and determining probability of trauma. While insights gained by lab work, in combination with field trials, can and have improved fisheries sampling and provided insights for risk analysis, there are pitfalls that can sink the ship. A couple problems that often occur are the rationale for setting dose levels and the actual description of dose levels. These issues can lead to misinterpretations, inappropriate management decisions, and constrain application of experimental results. In fact, dose setting is becoming a big issue in electrofishing experimentation. I have seen studies lately that have used incredibly high doses, in fact extreme overdoses, preventing a connection from the lab to application in the field. I think the results of those studies are relatively meaningless. And, most of the disconnect is due to a poor understanding of electric fields generated by common sampling gears and typical exposure times while electrofishing.
Overall resistance of an electrofishing system is determined by the combination of ambient water conductivity and the electrodes. The electrode shape, number, length or size, diameter of stock material, configuration and spacing affect both their overall resistance and the profile of the electrical field in the water around the electrodes. Rarely are there data available for assessing the effects of electrode changes on resistance or on fish catch. This blog presents some empirical results from field measurements of electrode resistance before and after some electrode changes.