Been a long time since I targetted cats early spring on a resevoir. Spent my early days fishing spring runoffs in creeks and small rivers feeding the lakes. Later yrs were spent chasing walleye and wipers during the spring. The first severals yrs after I started fishing from small boats,I done well picking channels up in the southern most coves. Can't remember what month,but the water was just warming up in the calm shallows. I think the cats were in there feeding on crappie eggs. I'd pitch shinners hanging below slip bobbers at weeds edge,using 6-8 lb test on ultralites. Sometimes you'd see the weeds parting,and pitch in front of them. Caught a lot of 4-10 lb channels on those lite rigs. Lost a bunch too,but much fun! Know you can find them up in the flats at ice-off picking up winter kill,but that's really before what I'd call spring.