**ABSTRACT NOT FOR CITATION WITHOUT AUTHOR PERMISSION. The title, authors, and abstract for this completion report are provided below. For a copy of the full completion report, please contact the author via e-mail at mboogaard@usgs.gov. Questions? Contact the GLFC via email at slrp@glfc.org or via telephone at 734-662-3018.**

Comparison of Continuous and Interrupted Lampricide Block Toxicity

to Sea Lamprey and Lake Sturgeon

Stephen R. Lantz^2,3, Cheryl Kaye², Lori Criger², Timothy Sullivan⁴, Brian Stephens⁵,

Michael Boogaard³, Terrance D. Hubert³

^{2 U.S. Fish and Wildlife Service Marquette Biological Station 3090 Wright Street Marquette, MI 49855}

^{3 U.S. Geological Survey Upper Midwest Environmental Sciences Center 2630 Fanta Reed Road La Crosse, WI 54602}

^{4 U.S. Fish and Wildlife Service Ludington Biological Station 229 South Jebavy Drive Ludington, MI 49855}

^{5 Fisheries and Oceans Canada Sea Lamprey Control Centre 1219 Queen Street East Sault Ste Marie, ON P6A 2E5}

July 2019

ABSTRACT:

Lake Sturgeon (Acipenser fulvescens, LST) is a state, provincial, and tribal species of special concern that is sensitive to lampricides used in sea lamprey control. As such, there is significant interest in the Great Lakes fisheries community to develop alternative sea lamprey (Petromyzon marinus, SL) control approaches to minimize impacts on LST for applicable LST-producing streams. Currently, lampricides are applied continuously to streams for 10 to 14 hours to achieve at least a 9-hour lampricide block at or above the SL minimum lethal concentration (MLC). Once the application of lampricides are initiated it usually takes 1-4 hours for the lampricide concentration to build to the target concentration during treatments depending on the flow dynamics of the stream. An interrupted lampricide block, wherein the treatment consists of two lampricide blocks (cumulative MLC of at least 9 hours) with a break in the middle, has been shown to decrease burrowing mayfly (Hexagenia limbata) mortality and resulted in no change to MLC when interruptions were up to 12 hours in duration. This study compared mortality of LST and SL during continuous and interrupted lampricide blocks with the goal of establishing whether an interrupted lampricide block treatment could be used to protect LST while maintaining treatment efficacy. Results show that there was no difference in toxicity to larval SL or LST between the interrupted block and continuous exposures. No differences were detected among calculated LC25s and LC50s for LST in the interrupted block tests compared to the continuous block tests during laboratory and streamside bioassays. An interrupted block field trial on Eliza Creek resulted in high mortality among caged larval SL (99.5%); however, posttreatment surveys estimated the treatment kill at 83.5% compared to >99% from the two previous continuous block treatments (2007, 2001). This suggests a substantial decrease in treatment effectiveness when using the interrupted block approach. The lack of separation in toxicity between LST and SL under continuous and interrupted block treatment and the reduced efficacy of the interrupted treatment block combine to make the interrupted treatment block approach a less desirable option.