Evaluation of Walleye Minimum Length Limits with Changing Water Regimes in the Great Plains

Abstract

AbstractAbove‐normal precipitation in the 1990s resulted in new waters and Walleye Sander vitreus fisheries across northeastern South Dakota. Concerns with overharvest led to the implementation of a Walleye minimum length limit (MLL) on many new fisheries, but over time most of the MLLs were removed. We were interested in knowing why the MLLs failed. We compared Walleye gill‐net data and angler creel data under rising and declining water regimes and between periods with and without an MLL regulation in two new waters (Bitter Lake and Waubay Lake). We also assessed Walleye annual recruitment and growth patterns and examined if water regimes, MLLs, or Walleye recruitment were potential drivers of Walleye relative abundance, growth, and size structure. Few differences were found across water regimes and between periods with and without an MLL. At Bitter Lake, significant differences were identified across water regimes for the number of age‐3 Walleyes per gill net, Walleye proportional size distribution of preferred length (PSD‐P), angling pressure, and angler catch rates of Walleyes. Walleye relative weight and PSD‐P significantly differed between water regimes at Waubay Lake. Mean length at capture for age‐3 Walleyes and proportional size distribution were significantly different between periods having an MLL and no MLL at Bitter Lake. At Waubay Lake, Walleye gill‐net CPUE (number/gill net) and PSD‐P significantly differed between periods with and without an MLL. Water regimes, MLL, and Walleye recruitment were not identified as strong drivers of Walleye population characteristics. Recruitment was variable in each lake (Bitter Lake age‐3 CPUE CV = 148%, Waubay Lake age‐3 CPUE CV = 166%), with occasional strong cohorts recruiting. We believe recruitment dynamics influenced Walleye abundance and growth, which led to the removal of MLLs from each lake. Knowledge concerning Walleye population recruitment dynamics and growth is important when implementing MLLs and evaluating their effectiveness.