Spring Assessments

SPRING ASSESSMENT WORK

Reports of ice cover melting off of local lakes are among the many signs of spring Resource Management Division staff look forward to each year.  For walleye, the increasing day length and warming water temperatures triggers their impulse to spawn, or breed.  For us, that means the start of a very busy few weeks as we begin our assessments of spawning walleye populations. 

An electrofishing boat is utilized to conduct these surveys.  Electrofishing is done at night when walleyes congregate in shallow, rocky areas of lakes to spawn.  The survey crew slowly maneuvers the shocking boat along the shoreline, temporarily stunning the fish. The walleye are then scooped up with a dipnet and placed in an onboard tank to recover.  When a sampling station has been completed, shocking operations cease and the crew begins to collect data.  Each walleye’s sex is determined, lengths are recorded, and spines are collected so we can later determine age and growth rates for the fish.  The walleyes are then released.  On subsequent nights (usually 3-5 consecutive nights per lake) the crew repeats the sampling procedures until at least a third of the fish captured in any given night are recaptures (as shown by the absence of a dorsal spine).  We then are able to utilize a relatively simple mathematical procedure to estimate how many walleyes are present in those areas for spawning. 

These surveys are also important and quick ways to identify critical walleye spawning habitat in area lakes.  The first night that we are on any lake, we try to run all of the available shoreline and are able to quickly determine which areas are suitable spawning habitat.  This is particularly useful information in situations where shoreline residents may be interested in altering the shoreline or nearshore areas to enhance their utilization of the lake.  In areas where walleye spawning is likely to occur, care must be taken not to alter the characteristics of the shoreline that make it attractive to walleyes.