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Determining Electrofishing Immobilization Thresholds of Smallmouth Bass, Blue Catfish and Flathead Catfish: A Critical Step to Develop a Standardized Sampling Protocol


July 2015 - June 2020


Management Issue: Improve the sampling accuracy and precision of population demographic parameters (e.g., catch per unit effort and length-frequency distributions) collected across sampling events via electrofishing so that more valid spatial and temporal comparisons and trend analysis of fish populations will be appropriate and useful to fisheries managers responsible for evaluating harvest regulations.

Initial Information Review: Standardization of electrofishing output will minimize bias, reduce variation in catch, and allow for more valid spatial and temporal comparisons of sample data (Bonar and Hubert 2002, Miranda 2009), regardless of the electrofishing control box used. Biologists need to know how conductivity of the water relates to the effective conductivity of Smallmouth Bass (SMB), Blue Catfish (BLC) and Flathead Catfish (FHC), hereafter referred to individually by the abbreviations or collectively as bass and catfish, in order to develop standardized electrofishing output goals that are species specific and maintain a desired capture-prone fish response (e.g., taxis or immobilization) across a range of water conductivities, water temperatures, and fish sizes.
The effective power (the product of current and voltage) transferred from the water to the fish during electrofishing is a critical electrical factor affecting fish response; power transfer depends on the ratio of fish conductivity to water conductivity (Kolz 1989, Kolz and Reynolds 1989, Reynolds and Kolz 2012). Effective fish conductivity is empirically derived based on the observed-behavioral response of live fish to electrical fields in tests across a range of water conductivity and is considered a constant for a given species (Kolz and Reynolds 1989, Dean and Temple 2011). Knowing the effective fish conductivity of a particular species would allow researchers to develop applied power, voltage, and amperage goal tables, standardized by power, for use by biologists when sampling targeted species. Standardizing electrofishing output by power as part of long-term sampling programs has been shown to reduce catch variance by up to 15% (Burkhardt and Gutreuter 1995), and would improve MDC’s ability to more accurately assess and monitor bass and catfish populations. With the exception of Asian carp and snakeheads, only general estimates of effective power goals exist, and these were derived from warmwater fish community information using a general value for effective fish conductivity (Burkhardt and Gutreuter 1995; Miranda 2009), and are not applicable to bass or catfish, two of the most important species groups to Missouri anglers.
To determine the most effective electrical waveform settings and develop target output goals for a particular species, experimental trials using a range of electrofisher settings at varying water conductivity levels and water temperatures are conducted in a controlled (i.e., aquaria) environment with a homogenous electric field to determine optimal settings that achieve a defined capture-prone fish response (e.g., immobilization). For example, using a fish conductivity value derived in a controlled laboratory setting, standardized power (and voltage) goal tables were recently developed to electrofish Asian carp and have resulted in improved catch rates of juvenile fish (K. Anderson, USGS, personal communication). The same process was recently conducted to identify optimal electrofisher settings successfully used in the field to collect snakeheads (A. Temple, USFWS, personal communication). To date, no work has focused specifically on SMB, and very little has focused on acceptable surrogate species such as Largemouth Bass (Dolan and Miranda 2003; Miranda and Dolan 2004; Miranda 2005). Even less work has been done on BLC and FHC (Bodine et al. 2013). Since past work has been carried out on different sized fish, across a limited range of electrofisher settings (due in part to electrofishing control box limitations), or as part of a warmwater fish community sample, it is difficult to confidently apply those findings to the specific species discussed in this proposal.

Who is requesting the new information: Fisheries Division and Resource Science Division Staff, specifically the MDC Sampling Protocol Subcommittee of the Smallmouth Bass Working Group along with the Big River and Truman Reservoir-Lake of the Ozarks Blue Catfish and Flathead Catfish Working Groups. Electrofishing experts who instruct the USFWS Principles and Techniques of Electrofishing Course and other electrofishing specialists along with agency biologists looking to develop (or refine) sampling protocols for these species in other states.

Why is the information needed: Black bass and catfish are popular sportfish in Missouri. Missouri’s 1.1 million anglers spend about 15 million days on the water each year, and about 77% of that time is spent pursuing bass or catfish species, making them the two most popular groups of fishes among Missouri anglers (U.S. Department of the Interior 2011).
The ability to accurately assess bass and catfish populations is needed to evaluate special regulations and monitor population trends and is critical to the credibility of MDC to make scientifically-sound management decisions. Combined with electrofishing training, this research will give biologists the tools and knowledge necessary to measure and adjust their electrofishing output applied in the field, allowing them to sample these species in a standardized, efficient, and safe manner. Any increase in sampling accuracy and precision (possibly as much as 15% [Burkhardt and Gutreuter 1995] or more) can provide higher confidence in making management decisions when changes in catch per unit effort (CPUE) occur. Further, standardization is critical for comparisons across lakes or rivers or when assessing long-term trends within a lake or river (Bonar and Hubert 2002, Miranda 2009). The knowledge gained from this work will also ensure consistency in data collection as biologists retire and new biologists are hired, which is critical for long-term evaluation of population trends (McClelland et al. 2013).
Additionally, BLC and FHC population assessments in the Missouri and Mississippi rivers are high priority information needs being addressed by the Big River Catfish Working Group. Missouri’s Catfish Management Plan (Dames et al. 2003) contains objectives to develop and refine standardized sampling techniques for both species in reservoirs and large rivers, respectively. Previous work reported high sample variation (e.g., CV > 50%) using existing boat electrofishing methods to sample FHC in the lower Missouri River (Travnichek 2011) and tributary rivers (Ford et al. 2011). Despite being the most commonly used gear, the unique behavioral response (i.e., surfacing ≥ 100 m from the electrofishing boat) of BLC and FHC to electrofishing is not well understood and it is unclear what level of electrofishing power (threshold power) or most efficient electrical waveform is necessary to consistently achieve a capture-prone response at varying water conductivities and water temperatures, and to collect a representative sample of all fish sizes (Bodine et al. 2013).

Immediacy of Information Need?
• Results will standardize current electrofishing protocols for SMB in Missouri streams and will be immediately incorporated. Future work on sampling protocols will also utilize this information.
• Results will help develop standardized electrofishing sampling protocols for BLC and FHC in the Missouri River and Mississippi River but also apply to sampling in streams and large reservoirs and will be immediately incorporated.


Current Staff

Federal Staff: 102

Masters Students: 247

Phd Students: 163

Post Docs: 55

University Staff: 266

5 Year Summary

Students graduated: 722

Scientific Publications: 1960

Presentations: 4355



Funding Agencies

  • Missouri Department of Conservation


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