A Comparison between Conventional Boat Electrofishing and the Electrified Dozer Trawl for Capturing Silver Carp in Tributaries of the Missouri River, Missouri

Silver Carp Hypophthalmichthys molitrix are elusive fish that can be difficult to capture with conventional management tools. New tools must be developed to help increase the capture of Silver Carp, thereby improving the understanding and management of the species. An electrified dozer trawl was developed in an attempt to increase the capture of Silver Carp while reducing the amount of sampling effort needed to successfully assess a population and inform management actions. We compared Silver Carp catch rates, sample run time, and Silver Carp length frequency distributions from the electrified dozer trawl with those from conventional boat electrofishing. Silver Carp capture was greater and sample time was shorter for the electrified dozer trawl compared to conventional boat electrofishing. Length frequency distributions were similar between gears. The electrified dozer trawl can shorten sample run times and potentially improve Silver Carp capture, thus facilitating management. Use of the electrified dozer trawl should be expanded beyond Missouri River tributaries to further understand the gear's potential for sampling Silver Carp in a diverse array of environments. Proper management actions for a fishery require agencies to accurately and successfully capture targeted species. This can be difficult when targeting highly elusive species, such as the Silver Carp Hypophthalmichthys molitrix (Conover et al. 2007; Klumb 2007; Hayer et al. 2014). Silver Carp pose a major threat to the native biota found in river basins (Kolar et al. 2007; Phelps et al. 2017) and also threaten the biodiversity of the Laurentian Great Lakes. The ability to capture invasive species like the Silver Carp is essential for understanding their distribution, life history characteristics, biology, and population dynamics (i.e., recruitment, growth, and mortality) and ultimately for effectively monitoring, managing, and eradicating these fish. Conventional boat electrofishing has proven effective at capturing multiple fish species in a variety of habitats (Reynolds and Kolz 2012); however, it has been difficult to capture Silver Carp due to their elusive behavior (Bouska et al. 2017). Environmental factors, like water clarity, can have a negative influence on the ability of netters to capture fish (Pygott et al. 1990; Zalewski and Cowx 1990; Hayes et al. 1996; Bayley and Austen 2002; Reynolds and Kolz 2012; Lyon et al. 2014). Furthermore, conventional boat electrofishing has a bias toward large‐bodied fish and may overrepresent larger fish while underrepresenting smaller‐sized fish (Chick et al. 1999; Dolan and Miranda 2003; Ruetz et al. 2007). The combination of a low success rate due to low visibility in water, a bias toward large fish, and the elusiveness of Silver Carp can lead to high variability in abundance estimates and misrepresentation of size structure. These inaccuracies make it difficult to understand current Silver Carp population assessments and could lead to the mismanagement of the population. Nevertheless, monitoring efforts for Silver Carp typically use conventional boat electrofishing methods. Improving catch rates over a large size range with an effective method would provide crucial information to managers for population status and trend assessments. *Corresponding author: jeremy_hammen@fws.gov Received October 30, 2018; accepted April 15, 2019 North American Journal of Fisheries Management 39:582–588, 2019 Published 2019. This article is a U.S. Government work and is in the public domain in the USA ISSN: 0275-5947 print / 1548-8675 online DOI: 10.1002/nafm.10297