Tags and Trawls: Tracking Walleye and Sauger Movement and Entrainment in Lewis and Clark Lake.

William J. Radigan, PhD Candidate, University of Nebraska-Lincoln. Lincoln, NE.

Christopher Longhenry, Senior Fisheries Biologist, South Dakota Department of Game, Fish, and Parks. Chamberlain, SD.

Lewis and Clark Lake was formed with the completion of Gavins Point Dam in 1957, and the reservoir has undergone several changes since its construction. Lewis and Clark Lake has experienced droughts and floods, with notable floods occurring in 2011 and 2019. These floods resulted in significant entrainment, or washing, of larval and adult walleye and sauger through Fort Randall and Gavins Point Dams. For instance, Andrew Carson (South Dakota State University graduate student) found approximately 30-43% of adult walleye in Lewis and Clark Lake were hatched in reservoirs above Fort Randall Dam and subsequently entrained through the dam during the 2011 flood. However, baseline non-flood entrainment rates of both larval and adult walleye and sauger in Lewis and Clark Lake were unknown until a recent survey was conducted. 

South Dakota Game, Fish, and Parks, the Nebraska Game and Parks Commission, and the University of Nebraska-Lincoln teamed up to research larval and adult walleye and sauger entrainment through Fort Randall and Gavins Point Dams and examine adult movement patterns of walleye and sauger. Entrainment of larval fish was assessed using nets dropped into various depths in the water column below each dam at randomly generated times each week from May to August, or May to September during low-flow or average-flow years (2021-2023). Acoustic telemetry was used to assess adult walleye and sauger entrainment and movement patterns. 

Larval sampling annual entrainment estimates of 24,174–148,722 larval fish of all species through Fort Randall Dam, and 710,000–1,400,000 larval fish of all species through Gavins Point Dam. Generally, over 90% of the larval fish entrained through both dams are freshwater drum, a prey item for adult walleye and sauger. Between 305-772 larval walleye and sauger are entrained annually through Fort Randall Dam, and between 906-4,155 larval walleye and sauger are entrained annually through Gavins Point Dam. Generally, for every larval walleye or sauger that is entrained through Fort Randall Dam, two to five larval walleye or sauger are entrained through Gavins Point Dam in a given year. 

Further, our investigation looked at adult walleye and sauger entrainment rates and movement patterns using acoustic telemetry. Acoustic telemetry is conducted using transmitters inserted into the body cavities of fish that transmit a signal to a receiver. These receivers, or “listening stations,” can be anchored on the river bottom, affixed to structures such as bridges or the shoreline, or moored in the water column. We implanted 132 adult walleye and 76 adult sauger with transmitters and detected their movements year-round using receivers stationed approximately every 5 miles in Lewis and Clark Lake. We found that 5% or less of adult walleye and sauger implanted with transmitters were entrained through Gavins Point Dam each year in years with either below-average or average flows. Acoustic telemetry also allowed us to assess how many fish were being harvested by anglers. We found that 12-19% of tagged walleye were harvested each year, while 10-15% of tagged sauger were harvested annually. These harvest rates are similar to other systems like Lake Oahe. 

Acoustic telemetry also allowed us to examine fish movement patterns. We found walleye or sauger movement patterns varied based on what part of Lewis and Clark Lake the fish was tagged at, the sex of the fish, and which species. For instance, we found a portion of the walleye tagged below Fort Randall Dam make annual migrations in the fall to near Gavins Point Dam, where they overwinter, before making spring-time migrations back up to Fort Randall Dam (presumably for spawning). We found a spawning aggregation of walleye forms in the spring near Santee, Nebraska, as well. Most sauger tagged in the delta below Fort Randall Dam never left the delta over the study duration. Sauger seem to spawn in the delta, and it may be that there is adequate food and habitat for saugers in the delta that makes movement out of the delta unnecessary. Approximately 37-49% of all walleye and sauger were site residents, moving less than 6 miles from their tagging location over the study duration. Non-site resident male and female sauger utilized 27-29 miles of the reservoir’s 69-mile expanse. Female walleye utilized more of the reservoir (36 miles) than male walleye (28 miles). Walleye tagged near Fort Randall Dam utilized more of the reservoir (approximately 44 miles) than walleye tagged elsewhere (29 miles).

So, what does this all mean for Lewis and Clark Lake’s walleye and sauger fishery? It seems that harvest rates are not depleting the reservoir’s walleye and sauger populations, suggesting current harvest regulations set by South Dakota Game, Fish, and Parks and the Nebraska Game and Parks Commission are appropriate. However, larval and adult entrainment are considerable sources of loss for larval and adult walleye and sauger. Losses of larval and adult fish due to entrainment are strongly tied to flows. In years with decreased flow, fewer larval and adult walleye and sauger will be lost to the Lewis and Clark Lake fishery due to entrainment through Gavins Point Dam. Decreased fish losses in low-flow years will likely result in increased abundances of walleye and sauger in Lewis and Clark, at least until the next flood comes along! 

For more information, please contact Will Radigan at wradigan2@huskers.unl.edu or Chris Longhenry at Chris.Longhenry@state.sd.us. 

 

 An acoustic receiver secured to a frame and affixed to an anchor.

Author (Will Radigan) and a jaw-tagged walleye implanted with an acoustic transmitter.