They spawn in chilly spring water. I believe they scatter their eggs over rocky, gravelly areas. Try searching the Internet for yellow perch biology. It shouldn't take long to find more information than you need.
Lots of fish species develop eggs early, but they don't become 'ripe' until conditions are about right. I believe some will re-absorb eggs if conditions do not occur right.
Perch spawn in sand, last ice is the best for catching big perch after they spawn. I have found that if there are a lot of perch in the area you are fishing in the evening close to dark changing to glows the perch will hit till the walleye come in and then I will change too a russian spoon and jig just off the bottom 6" and when the line goes slack on down stroke pull one night i got 3 walleye in 3 drops of the line to the bottom.