Just because you see shad on the fishfinder doesnt mean that fish is there at the time. Depending on how the shad show up should influence whether you fish or not. If the shad arent spread out then CHANCES are fish arent feeding on them. alot of times ive been with people fishing and they say find the shad find the fish... not always fish do go where the food goes but they may school up around 1 school of shad and follow, you may find a school of shad and catch 2 fish and sometimes thats just fish falling behind a school that take up with the school your fishing. Finding the shad is most critical when trolling open water and thats when you will catch your white crappie 14 foot deep in 50 ft of water, when they are feeding on shad the thermocline really affects the shad more than the fish (except gar and carp ) and the fish just follow suit and stay with the food. Green has alewives in it and they are quite different from gizzard shad hence your open water crappie. Between me and 3 of my buddies we caught almost 3000 keeper crappie last year ( meaning 9 inches) while trolling.