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Electrofishing, Fabrication

Electrofishing FabricationOur work often calls for quick thinking and adaptability. Last year, we ran into a situation where we had to come up with an electrofishing boat in a hurry (see How to fabricate an electrofishing boat in 24 hours). Luckily, our master fabricators were able to modify one of our smaller boats with the necessary components to get the job done. Since we are always looking for innovative ways to be more efficient and flexible, we recently came up with a system that will help us be just that. Rather than dedicating a boat or two to electrofishing only, we wanted to have an easy way retrofit any of our boats with an electrofishing system. Our solution was to build a lightweight electrofishing deck that can attach to the bow of a boat and be ready for action without much setup time.

Electrofishing BoatWe fabricated our electrofishing deck out of lightweight aluminum to make it portable enough for two people to lift into place and limit the effect on boat performance. The platform is complete with pole-mounted anodes, diodes, lights, safety rails and a non-slip floor. Once the deck is in place, a generator and the heart of the system, a Smith-Root GPP electrofisher, are placed at the stern of the boat. Thanks to the creativity and innovation of our master fabricators, we can now quickly adapt any of our boats for electrofishing and get back out on the water in a hurry.

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Commercial Fishery, Electrofishing, Fish Report, Marine

Traditional trawling methods

Traditional trawling methods (like those pictured above) have received considerable negative attention due to their adverse effects on the benthic ecosystem. Major concerns include destruction of the seabed and the high level of bycatch (“discards”) of fish and other benthic organisms. The bycatch is often discarded at sea because it is not considered marketable, and these organisms may experience high levels of mortality. A potential alternative fishing method is electrotrawling: instead of dragging a net with chains, ropes or beams along the seafloor, the net is fitted with electrodes that release electrical pulses, similar to an electrofishing boat. The electric pulses stimulate the nerves and muscles of benthic organisms, which respond by rising off the sea floor (either through a “startle reaction” or a “cramp reaction”) just as the net sweeps them up. The potential benefits of electrotrawling are reductions in damage to the seafloor, gear drag, fuel costs, and bycatch, since the electric pulses can be tuned to target different species and sizes. Researchers have been investigating the potential for electrotrawling for over 50 years, but much of the information was published in reports with limited distribution. A recent review article compiled these resources and produced a comprehensive overview of the opportunities and challenges of this alternative fishing method (Soetaert et al. 2013).

We have all been told that electricity and water don’t mix, so there are a few obvious technical challenges that electrotrawl developers face, including high power demand at sea, water resistance of the generators, electrode connections underwater, electrical material and efficiency, and, most importantly, crew safety. While some of these challenges have also been addressed in freshwater electrofishers, the distribution of the electric field in and around the fish is entirely different in seawater. The developers account for this by using reduced exposure times and voltage, and by using pulsed current instead of direct current to account for the high power demand needed at higher conductivity. Also, fluctuations in water temperature and salinity influence both the conductivity and the fishes’ behavioral response; thus, the trawl settings must be adaptable to varying conditions. Furthermore, little is known about the potential side effects (e.g., spinal injuries, cardiac arrest, hemorrhaging, or reduced growth) on marine organisms that are exposed to the current but not caught in the trawl or retained in the catch. Despite these challenges, the industry has slowly pressed forward in the development of electrotrawls, driven in part by high oil prices (which made traditional trawling less profitable) and international calls for more sustainable fishing practices.

Soetaert et al. (2013) described electrotrawls designed for flatfish, shrimp, and razor clams, all of which have demonstrated significant reductions in discards, and appear to have a reduced impact on the sea floor. A study of the flatfish pulse trawl reported a 30-50% reduction in discarded fish. Studies reported a decline in the catch of non-target fish and benthic organisms, as well as a reduction in catch of undersized individuals of target species. Clearly, electrotrawls are a promising alternative to traditional trawling with the potential to greatly reduce impacts on the marine ecosystem. However, additional research is necessary to investigate unwanted side effects on marine life and to acquire further reductions in discards.

This post featured in our weekly e-newsletter, the Fish Report. You can subscribe to the Fish Report here.

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Electrofishing, Field Crew, Field Notes

checking-conditions

Hanging off the back of our North River jet boat offers a bit of a window into our work. This maneuverable 16-foot boat is ideal for sidewinding our way through small tributaries and backwater areas, letting us edge up close to the banks. Such dexterity is particularly helpful when surveying floodplain habitats like this one. Part of our process includes checking the quality of the water, including its temperature and dissolved oxygen content. Measuring dissolved oxygen can be an involved procedure when we want to be very precise (see Essence of life), but this handheld YSI sensor can give us a quick read on the conditions. We also survey the habitat for fish using the backpack electro-fisher you can see in the background (see Walk the line). With the help of portable equipment like this, we can jump right in to a variety of different environments at the ready.

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Electrofishing, Field Crew, Other Fish Species

Sacramento Pikeminnow

What more fitting place to catch a Sacramento pikeminnow than on the Sacramento River, a short swim from the Sacramento Airport. We scooped up this massive native minnow (Ptychocheilus grandis) during an electrofishing survey as part of our project to monitor repaired levee sites on the Sacramento River. We’re especially interested in the abundance of this ravenous fish because it predates heavily on juvenile salmonids (see Survival of the biggest). Although hefty, this particular specimen is far from record breaking: Sacramento pikeminnow can grow to more than 1 m (3.3 feet) in length. We’ve seen a few other mega-sized pikeminnows in our day – with mouths to match (see Hotlips).

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Electrofishing

 

 What do you do when your electrofishing boat breaks down in the middle of a time sensitive research project and it’s going to take a week to get the parts needed for repairs? Build a replacement. That’s exactly what we did. With a little technical help from our friends at Smith-Root, we retrofitted one of our smaller boats with a Streambank Generator Powered Pulsator. Working well beyond normal hours, our master fabricators were able to construct a guardrail, mount fiberglass poles to suspend the electrode arrays, install floodlights, and wire-up all the electronics that make an electrofishing boat operate. Thanks to a dedicated team of people we were back on the water in less than 24 hours, catching the fish needed to complete our study.

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Electrofishing

Last week we conducted electrofishing in New Bullards Bar Reservoir as part of a Federal Energy Regulatory Commission (FERC) relicensing assessment. FERC is the government agency that regulates and monitors hydroelectric projects and fisheries research is often required during relicensing of hydropower projects. The purpose of the study was to provide information concerning the distribution, occurrence, and condition of fishes in the reservoir. In this case, we conducted the electrofishing at night since it yielded a greater diversity of species and number of fish, and also reduced impacts of the project on recreational users. Another perk of conducting our sampling at night is that it left the day free for taking in the local sights.

New Bullards Bar Dam, which stands 645 ft. above the canyon floor, is touted as the 2nd tallest dam in California and the 5th tallest in the United States (Oroville Dam is the tallest at 770 ft.). It is quite an impressive site to look over the side of the concrete monolith into the canyon that once held the full force of the North Fork Yuba River. Some water is released at the base of the dam to support the fishery below, but the majority of the water now travels 4.7 miles through an underground tunnel to the New Colgate Powerhouse. New Bullards Bar Dam was constructed by the Yuba County Water Agency as a flood control reservoir in response to the flood of 1955. The dam was completed in 1969 and provides 170,000 acre feet of flood control storage space. Unlike many similar dams, people are still allowed to travel across this structure and gain an appreciation for its massive scale.

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Electrofishing, Monitoring

Armed with a half-dozen backpack electrofishers, a crew of “netters” and “shockers” waded through the Lower Kings River last week in search of rainbow trout. FISHBIO assisted with multi-pass depletion electrofishing efforts as part of the Kings River Conservation District’s (KRCD) annual rainbow trout population study in the Kings River below Pine Flat Dam in California’s Central Valley. The annual monitoring is preformed to assess the response of the trout population to habitat enhancements conducted over the past decade, as required by the Federal Energy Regulatory Commission (FERC). The Kings River Fisheries Management Program (KRFMP) has implemented extensive gravel augmentation, boulder placement, side channel enhancement, and riparian planting. The KRFMP is a partnership between the Kings River Water Association (KRWA), California Department of Fish and Game (CDFG) and the KRCD working to enhance and maintain a sustainable trout fishery on the lower Kings River.

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Electrofishing, Monitoring

Backpack electrofishing has been a common tool for sampling salmonids for decades. Similar to the snorkel surveys we use in deeper rivers, backpack electrofishing is often used to estimate the abundance of fish in a shallow river or stream. During this process, there are teams composed of a “shocker,” the person operating the electrofishing unit, and at least one “netter” to quickly scoop up the momentarily stunned fish. The number of teams depends on the width of the stream, since the teams form a line and move together upstream as they shock. The goal of staying in line is to ensure uniform sampling effort across the width of the stream and to prevent fish from slipping back downstream behind the shockers. There are several assumptions associated with this abundance estimation method (Temple and Pearsons 2007), including the important assumption that the fish are in a “closed population.” Essentially, we assume that as the teams pass upstream and sample, the fish are not eluding capture by moving further upstream. To avoid this, we place a block net at the top and bottom of the stream segment, temporarily trapping the fish. Of course, there are always some fish that elude capture the during the first pass upstream; thus, a common method is to use three or four passes in each stream segment to account for this, a technique called “depletion” or “multiple-pass” electrofishing.

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Electrofishing

If you’ve been following our blog posts over the years then you know we have done our share of electrofishing. With the right study design and procedures electrofishing can be an effective means of evaluating fish composition and abundance. For example, sampling equipment such as traps and seine nets are designed to capture a certain size or type of fish, and sampling with these gear will only provide data on part of the fish community. By employing standardized assessment methodology such as grid point or continuous electrofishing, fish in the sampling area will generally have a similar chance of being captured and the data will be more robust. We are currently utilizing electrofishing, as well as other methods, to evaluate fish abundance and community structure on the lower Sacramento River at sites where the U.S. Army Corps of Engineers has repaired levees. A key objective in the study is to identify features of levee repair sites that maximize fish use and provide the greatest value to listed species.

We are excited to announce the addition of Dr. Michael (Mike) Holliman, Senior Research Biologist and internationally recognized electrofishing expert to our team. Mike is perhaps the only scientist in North America with a PhD in electrofishing theory and principles, and has extensive experience using electromagnetic resonance imaging and x-ray technology for assessing potential fish injuries from electric fields during electrofishing surveys. He brings advanced quantitative expertise, electofishing theory and management skills to our growing staff.

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Electrofishing

First off, these aren’t Ghostbusters exterminating ghosts, this field crew is all decked out for a mission to rescue fish. Our previous experiences with fish rescue at the Tehama-Colusa Canal Authority Fish Passage Improvement Project in Red Bluff have taught us to always expect the unexpected. In December, we found ourselves electrofishing from a boat inside a cofferdam (Water + Steel + Electricity = ?); and in January, we slogged through waist-deep mud (A Muddy Situation). Last week, we knew we were in for another adventure when they warned us that we would be receiving ‘Confined Spaces’ training prior to conducting the rescue. We arrived at the site to find that the roughly 400 foot-long cement siphon tunnels under construction were flooded during the recent high flows. As the water receded, fish, mud, and some debris were trapped in the tunnels. After receiving training on how to safely operate in a confined space, we entered the tunnels armed with our safety gear and our atmosphere monitor that would alert us of potentially hazardous changes in the air we were breathing. We used a backpack electroshocker, a seine net, and hand nets to corral and capture the fish, which was definitely easier said than done. The quicksand-like mud that hampered our last rescue operation was still present, and we had the additional challenge of working in the dark. Once the fish were captured, they were hauled in buckets over the 30 foot cofferdam walls and released into the Sacramento River. There’s no telling what we might encounter on our next trip.

Photo source: FISHBIO