Assessing the Dispersal and Recruitment of Stocked Walleye Fry in a Northern Minnesota Chain of Lakes

Author

Joseph W. Amundson

Date of Award

10-2021

Document Type

Thesis

Department

Biology

First Advisor

Andrew Hafs

Abstract

As part of Minnesota's Walleye Sander vitreus egg take practice, 10% of eggs taken for hatchery purposes are stocked back into the donor lake. For Andrusia, part of the Cass Lake Chain of Lakes (Chain), this practice can result in elevated fry densities (mean: 17,000 fry/littoral hectare). However, if fry are able to disperse and use all available littoral hectares throughout the Chain, fry densities would be intermediate to typical stocking densities for Minnesota lakes (1,200 - 2,400 fry/littoral hectare). In 2016-2018, 3-3.5 million fry were mass-marked by immersion in oxytetracycline (OTC) prior to stocking into Andrusia to allow differentiation between these fish and those originating from natural reproduction or stocking of unmarked fry in other connected waters. Age-0 Walleyes were sampled throughout the Chain each fall (2016-2018) primarily by boat electrofishing. Each year, age-0 fish were widely distributed by late August. Combined mean marking rates (2016-2018) for each lake of the Chain ranged from 16 to 97% and cohort marking rates ranged from 71 to 78%. The ability of stocked fish to disperse throughout the Chain helped suppress density dependent effects, although, total length (mm) increased as catch-per-unit-effort (CPUE) decreased with distance from stocking site. In 2019, a chain-wide gill net assessment resulted in cohort (2016-2018) marking rates at ages 1 to 3 similar to their age-0 marking rates. The Chain was previously thought to be largely self-sustaining with put-back stocking considered a social aspect of management by compensating for the removal of eggs (i.e. potential recruits) rather than contributory to the Walleye population, but our results suggest that this stocking is substantially contributing to the population.

Recommended Citation

Amundson, Joseph W., "Assessing the Dispersal and Recruitment of Stocked Walleye Fry in a Northern Minnesota Chain of Lakes" (2021). Biology Graduate Theses. 10.
https://pines.bemidjistate.edu/thesis-biol/10