Pewaukee Lake Walleye Stocking Evaluation

Pewaukee Chapter of Walleyes for Tomorrow

Wisconsin Department of Natural Resources

Prepared by; Benjamin Heussner – WDNR Fisheries Biologist

Introduction

Pewaukee Lake has an extensive stocking history including walleye, northern pike and muskellunge. In recent years, WDNR comprehensive survey results have revealed a decline in adult walleye abundance. Both stocking and natural reproductive failure has occurred in recent years with the last significant year class documented in 1998. The 2012 portion of the comprehensive survey confirmed the lack of younger year classes of female walleyes with a RSD-20 of 100%, (79 out of 79 females were greater than 20 inches). Fall electrofishing catch rates from 2010 & 2012 revealed an average YOY per mile of zero. Small fingerling walleyes averaging 1.25 inches were stocked during this evaluation period concluding that small fingerling stocking success has been very poor in recent years.

In 2014, two new stocking efforts were added to Pewaukee including annual fry stocking from the Pewaukee Chapter of Walleyes for Tomorrow and alternate year stocking of large fingerlings as a part of the WDNR Wisconsin Walleye Initiative. In 2015 fall catch rates of juvenile walleyes were the highest since the 1998 year class at 16.8 per mile and averaging 9.7 inches. Results of the fall 2015 electrofishing survey have clearly shown excellent 2014 year class strength resulting in the need to further evaluate the stocking source. Tissue samples were sampled at three different stages including the following;

1) brood stock prior to egg take at Delavan Lake in 2014 2) fall fingerlings during stocking in 2014 3) fall electrofishing yearling tissue samples taken in 2015

Assuming no significant natural reproduction had occurred, we will be able to determine the proportion of fish stocked as large fingerlings versus stocked as fry. This information will help make science based management decisions for future stocking efforts on Pewaukee Lake.

This draft document is intended to explain techniques for evaluating recent stocking success on Pewaukee Lake and will be continually updated as new information becomes available.

Background Information

The 1999 comprehensive fisheries survey report revealed a strong year class in 1998. 1998 fall YOY catch rate was 6.5 per mile

1999 fall 1+ catch rate was 29.9 per mile 1999 fall walleye average size was 9.9 inches.

Fall catch rates during 2010 and 2012 small fingerling walleye stocking evaluations were zero fish per mile. The results of the small fingerling stocking evaluations resulted in a management recommendation to switch WDNR stocking strategies to utilizing large fingerlings to improve survival.

The 2011-2012 comprehensive survey report revealed limited stocking success from stocking efforts in 2000 – 2011. 86% of the adult walleyes found in the sample were estimated to be between ages 6 to 9. This group correlates to the 264,917 small fingerling walleyes stocked in 2002, 2004 and 2006.

In 2015, fall walleye catch rates were highest recorded since the 1999 evaluation. The average length of the juvenile walleye captured was 9.7 inches ranging from 8 to 12.6 and having a mode of 9.3 inches. Assuming the results of the genetic tissue testing will result in the majority being comprised of 2014 large fingerling stocked fish, large fingerlings would prove to be an effective stocking technique. Any fish aged as YOY would indicate 2015 fry stocking success, assuming no natural reproduction had occurred. Relative contribution of WFT fry stocks in non-large fingerling stocked years may prove to be an effective supplemental stocking technique.

More information is needed to determine the reason for the recent recruitment success in order to help make informed decisions on stocking efforts in the future. Genetic testing of the tissue samples taken from the 2015 fall juvenile walleye will help determine the origin of these fish. It is estimated that the cost per tissue sample is $17 dollars per sample. We have collected 100 samples and will need $1700 to pay the University of Wisconsin Stevens Point genetics laboratory. WDNR fisheries staff will complete aging of 2015 fall walleye subsamples; perform data entry and analysis, analyze length at age data and summarize information for continued development of this evaluation.