Norm, I'm from SW Ontario, Canada ( a few miles north of Lake Erie) and I believe my BG spawn at least 1-2 times during the season if the right conditions are met. Early season warm weather to warm the shallow water early June and thus a later September spawn again. I noticed small BG along the shoreline the other day in the 1" range with the lake mostly still covered with ice. These small BG I believe are late spawned and most likely a second spawn with warm fall water temps. I hope this helps.

Rowly