Honestly, I'm not really sure. But I can speak into a strategy for tackling the prehatch. As the water temps begin to rise in the spring (55-65 degrees, and probably even a bit before this), wigglers (the nymph stage of the mayfly) begin to move.
Interestingly enough, we see wigglers in the stomachs of walleyes almost all year long on Lake Leelanau. We are starting to believe that many walleyes in Lake Leelanau and probably other lakes, make wigglers their primary forage. Why? Because wigglers are easy to catch. The walleye doesn't have to exert much energy to consume a stomach full of these invertebrates. What does that mean to the fisherman? I have a couple of working theories...
1. Walleyes aren't always excited about bigger and faster presentations on some lakes. For example, the Rapala rippin rap didn't catch a walleye on my boat this spring. On some lakes, a 5" jerkbait takes fish while on other lakes, the jerkbait isn't as effective for 'eyes.
2. The Charlie Brewer 3" Slider Grub shines in the middle of fish feeding on wigglers, especially in pumpkin black flake and green pumpkin and green pumpkin black tail. The way the fish hit these jigs is what we describe as "grabbing them." There isn't a pronounced thump. As you lift the bait, you feel what I describe as something that feels "spongy." As you lift, the fish often gets hooked in the top of the mouth (but not real deep).
Key in this scenario is to do what a friend of mine turned me onto years ago - fish Fluorocarbon instead of braid. Fluoro like the Gamma Edge Fluoro in 8lb test has just a little "give" to it that allows you to hook a walleye when they are just "grabbing" the bait.
3. You want a rod with a little give in it. I just recently tested the 6'10" light Summit FavoriteUSA spinning rod and loved it work this application. Paired with an 1/8oz jighead from Old Fart Lures and you're set.
4. You're heard the phrase "hook sets are free"? If you feel anything, give the rod a quick lift and then start reeling.
5. Lastly, fish areas where you think the water is warming more quickly or where you suspect wigglers to be hatching and active. We had some really cool experiences this past couple of weeks where we found walleyes very shallow. Many times we caught fish in 2-5 feet of water. You have to train yourself to look shallow for fish, especially if wind is blowing into a spot or if the water has a little color or has been stirred up.
We love the learning aspect of fishing...make it your goal to learn something new everytime you are out. Try something different. Experiment. Hope my theories will help you put more fish in the boat!