Aug 30, 2016

So How Bout Them Walleye 

By: Adam Walton

When it comes to maintaining great walleye fisheries throughout Wisconsin, some systems are natural fish factories and others need a guiding hand, usually provided through stocking and/or stricter harvest regulations.  On waters that require a little help, efforts made by the DNR, numerous fishing clubs and other private organizations often go unnoticed…until things turn for the worse, that is.  Usually when things turn poor, DNR regulations are first to take the blame, but it goes much deeper than that. 

Take the Lake Koshkonong / Rock River system for example.  This system is open to fishing year round and gets plenty of pressure from anglers.  The current daily limit here is five walleye or saugers, which both must be a minimum of 15” to harvest.  The walleye population here can fluctuate, with large fish present for a few seasons and then suddenly the only walleye that seem to bite are “short” fish that don’t hit the magic 15” mark.  Many anglers find themselves asking how one year can be a banner season and the next is a bust.  Some point to over harvest when things were good, others blame a lack of a slot limit, and yet others see it as an ongoing up and down cycle caused by conditions such as weather, natural spawn, stocking, and water levels, etc…  

Looking at the entire situation, all of the things mentioned above may be contributing factors, but it’s hard to point to just one.  If stocking and natural spawn produce huge numbers of walleye year after year, fish will continually replace each other and over harvest is hard to blame.  However, if there is a poor spawn year and stocking efforts are also affected, lack of new fish coming into a system, along with excessive harvest of legal fish, can unquestionably cause problems.  If these spawning problems occur in consecutive seasons, it can cause a potential long term dilemma.  Since it is unrealistic to change DNR harvest regulations seasonally in order to adjust for a poor spawn/stocking year, it makes for a difficult line to walk.   

Slot limits are also a tricky subject.  Generally speaking, a common example of an imposed slot limit allows walleye between 15 to 18 inches to be harvested, while walleyes between 18 to 25 inches are protected and must be released.  Once fish grow out of the protected slot sizes and reach over 25 inches, they are allowed be harvested again.  Since females don’t typically mature and spawn until they grow to 18 inches, this slot limit concept protects the main spawning classes of walleye.  In some systems the concept of protecting 18 to 25 inches fish thrives, but in other systems it can set up a fishery for future failure.  For example, in lakes that are heavily pressured and have consistent poor natural spawning occur, a slot limit can cause potential long term problems.  DNR studies have shown a majority of smaller legal walleye tend to get plucked before they reach the protected slot sizes. This leaves a low number of fish that would have eventually replaced the large fish currently protected in the slot size.  Slot limits may initially work to protect bigger fish, but years down the road, a lack of “replacements” can cause a complete collapse of the large fish population. 

To get a better understanding of what it takes to manage a fishery, I recently had the opportunity to sit down with DNR fish biologist, Laura Stremick-Thompson, retired DNR fish biologist, Don Bush, and DNR fishery technician, Doug Lubke, whom all have fish management experience on numerous systems throughout Wisconsin.  Although much of the following information below applies to many DNR managed systems, we took data compiled from years of tracking the Lake Koshkonong/Rock River system. 

The first thing Stremick-Thompson, Bush and Lubke suggested was to understand three important driving factors of system management; Recruitment, Growth and Mortality.  These three factors are the foundation of how a system is managed and show where success has occurred or where improvement is needed.  

Recruitment 

When it comes to the term “Recruitment,” we’re talking about both natural spawn and stocking efforts that produce walleye fry.  It should be noted, the Lake Koshkonong/Rock River system does not have a great natural spawn compared to other systems and requires assistance from the Bark River Fish Hatchery/DNR stocking program.  The recruitment factor is a little tricky for a few reasons.   Again, looking at the Lake Koshkonong system specifically, Lubke stated that over the past several years natural spawning locations have changed, making it difficult to estimate how productive a season was.  Changing spawning locations also makes it difficult to locate females needed for egg harvesting used in stocking.  Stremick-Thompson noted, the Bark and Crawfish Rivers, which are tributaries to the Rock River, allow walleye to travel large areas.  With such a large amount of water available, walleye can be hard to track and net with limited DNR staffing.   

Other factors, such as weather, can also play a key role in “Recruitment.”  For example, the 2016 spring was anything but.  Walleye generally spawn in 44 to 48 degree water, but weather here seemed to drastically change between winter and summer, causing a roller coaster in water temperature.  This factor alone made for not only a poor natural spawn, but it also caused an unsuccessful DNR netting operation used to harvest female eggs for stocking.  Although females were netted and some had spawned out, many of their eggs were not ready to harvest and likely did not drop this season.  These eggs would simply be reabsorbed, which is not a very common occurrence seen in big groups of walleye.  

Generally, walleye “Recruitment” is best measured by tracking year classes well after the spawn.  For example, there is currently an abundance of 12 to 14-inch walleye in the Lake Koshkonong system, which indicates that the combination of natural spawn and stocking during the 2012 – 2014 seasons was successful.  In contrast, with the poor natural spawn and stocking effort seen this season, the 2016 class of walleye will be very small.  Anglers however, won’t typically see this effect until several seasons later. 

Growth 

The second driving factor in fishery management is “Growth.”  This factor is much more constant and easier to follow.  Let’s start at the beginning and look at fry growth.  Stremick-Thompson first pointed out that abnormal cold spring weather can cause a poor supply of zooplankton, a food source walleye fry depend on.  With limited zooplankton, fry may die or grow slower than normal.  Once walleye grow larger, their main forage in the Lake Koshkonong / Rock River system changes to river shiners, small white bass, perch and small sheepshead.  Of course seasonal occurrences such as mayfly and bug hatches also come into play.  This forage base sets the stage on how fast walleye develop.  Since the forage base remains fairly constant here, walleye growth can be charted fairly accurately.  From data collected in past surveys, two important sizes are noted.  We first look at 15 inches, because this is the minimum legal limit to harvest and 18 inches, because this is the size a female walleye fully matures and is able to spawn.  Growth rates indicate a 15-inch walleye is roughly 4 years old while an 18-inch walleye is roughly 6 years old.  After a walleye hits the magic 18-inch mark, gender will play a larger factor in growth rate.  Females will grow faster and bigger than males.  For comparison purpose, the length of numerous 7 year-old males and 7 year-old females were averaged out and females were 1.1” larger. Data also shows male walleye generally topping out around 20 inches while females can exceed 27 inches, if allowed to by anglers.   However, once a female grows to 25”, her growth rate will slow tremendously.  Data shows 9 year old females averaging 25.6 inches, while 12 year-old females average 26.7 inches.  With a fluctuating slow growth rate of fish above 27 inches, their estimated age can be anywhere between 13 to 18+ years old.  

Mortality 

The third and most controversial driving factor in fishery management is “Mortality.”  With natural mortality low, the main cause of walleye death is anglers.  Stremick-Thompson and Lubke both agreed this is where things can get really complicated.  On the Lake Koshkonong system, walleye fishing is open year round and it’s heavily pressured.  Some anglers are pushing for a slot limit, but enacting that regulation will only move the problem Stremick-Thompson stated.  If 18 to 25 inch fish are protected like on other systems, data has shown there is a huge drop in the 15 to 17.5 inch walleye population, due to harvest.  With smaller fish being taken out of the system, there are few fish left that actually grow up into the protected slot.  If a minimum 18 inch size limit regulation is enacted, fish will grow to that size, but are no longer protected after that.  A change in size limit from 15” to 18” would allow females to grow into maturity and may possibly improve natural spawning.  However, studies have shown in waters with an 18 inch minimum size limit, there is still a significant drop in large walleyes[Text Box]over 18 inches due to angler harvesting. 

Although certain regulation changes may help some, Stremick-Thompson, Bush, and Lubke all agreed, the most important way to help a fishery succeed is for anglers to change their fishing habits.  Bush made a great comparison between walleye fishing and deer hunting.  Many hunters practice deer management and allow small bucks to develop into trophy size animals before harvesting them.  However, when it comes to walleye fishing, the majority of anglers do not practice this theory and harvest a large amount of legal, but immature fish.  Bush stated the Lake Koshkonong system can easily hold a large population of trophy walleye, but most fish are harvested before they grow to trophy size.  With that said, harvesting a large number of big mature breeding fish can hurt the natural spawn and stocking efforts as well.  Maintaining a healthy balance of both size and quantity of fish in any given system is truly up to anglers.   

There is no shame in keeping a few walleye for the freezer, but anglers must realize there is a lot involved maintaining a true successful fishery.  As the owner of a fishing guide service, we try to help by practicing selective harvest.  On the Lake Koshkonong system for example, walleye over 18 inches on get released and only a handful of legal fish below 18 inches are harvested by our clients.  We call it “Release breeders, keep a few eaters.”  This is a principal I have believed in since understanding how fisheries operate.  So what is important to you?  Are you happy with your current walleye fishery or would you like to see it improve?  The choice is yours.   

Good luck on the water this season and stay safe.  

Captain Adam Walton 
Pike Pole Fishing Guide Service 
www.pikepolefishing.com