Could be simple timing. Cooler water might account for less activity, especially if you had been catching them during a spawn or prespawn feeding binge. Also, did you harvest those fish or release them? Any chance others are fishing your pond without your knowledge?

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.