Effects of gizzard shad introductions on walleye growth and condition in northeastern South Dakota glacial lakes

Walleye (WAE) Sander vitreus abundance and growth increased following introductions of gizzard shad (GZD) Dorosoma cepedianum in western South Dakota (SD) reservoirs. The addition of an alternative prey source may also reduce predation on yellow perch Perca flavescens hence increasing perch recruitment.  The objective of this research was to compare WAE growth and condition before and after annual introductions of adult GZD in two northeastern SD glacial lakes.  Adult, pre-spawn GZD were stocked into two lakes (East Krause and Middle Lynn) in 2008 and 2009.  Walleye were collected seasonally from both treatment lakes and a control lake (Lardy) in 2007 (pre-shad) and 2008-2009 (post-shad).  Otoliths were used for aging and to back-calculate length at age.  Mean total length by age group was estimated and incremental growth analysis was conducted for all lakes pre- and post GZD introductions.  Mean relative weight by length group remained similar within both treatment lakes, but was slightly reduced in the control lake.  Our results illustrate the effect that GZD stockings may have on WAE growth and condition in SD glacial lakes and should also help determine if food resources are limiting for WAE in these treatment lakes.