I'm just speculating, but I wouldn't be surprised if the liklihood of a supplemental spawn might jump a little when Wr's are good. If an adult fish can expend a little energy toward spawning without damaging it's own individual chances of surviving the winter, then this might give the species a better chance at propogating, in particular a year with poor spring recruitment.
If bluegill populations work like some other animals that have been studied, then in years with low numbers of spring YOY survival, the breeding size adult fish would have less competition for invertebrates, thereby increasing Wr's. This would in turn encourage a late summer/fall spawn to supplement the depressed YOY numbers.
It's a virtual certainty that late summer/fall recruits would have a lower winter survival rate than their spring counterparts. Good evidence to support this thinking has been collected by studying walleye winter survival. There is a "cutoff" size that does quite well in winter survival, with those individuals below this size and Wr doing much more poorly in following spring samplings.
