You are right about the spawn. The majority are not interested in taking flies at that time.
That is when the chum comes out.
I may get abuse for being pro-chum but I only use it when the long term pattern shows a lack of success with naturals alone.
Bread works great in the spring because they are often on top sunning anyway.
I am usually too lazy and impatient to chum though so I only use it when absolutely needed. I usually have faster luck with sight fishing to already feeding fish.