I am betting Northern Pike have a larger impact than climate change. I have met some of the DNR scientists here in Michigan, not impressed.
Northern Pike are getting bigger and more numerous at the same time as Walleye population decreasing. Coincidence?
I look at Lake Mille lacs here in MN the Walleye population is at an all time low yet big northern and muskie slots are still narrow for keepers. Big Pike and Muskie are becoming more numerous and their small off-spring are veracious eaters.
We had a very big decrease in Walleye population at Leech Lake about 7 years ago. The primary culprit was believed to be too a cormorant population. I believe about 10,000 cormorant were culled. The Walleye population has returned. This may not have been exclusively due to cormorants but it certainly seemed to help.