First one depends on the bowling ball. Most alleys have balls ranging from 7lb to 16lb, all the same volume, and the crossover point where they’d sink is 11.6lb.
If it was a floating bowling ball, the lake water level would stay the same when you toss it from a boat. If it were a sinking one, it would decrease.
I think you're counting the overall sphere as the volume, but water would leak in through the finger holes so only their actual material counts. I suspect different weight bowling balls generally have different volumes.
If it was a floating bowling ball, the lake water level would stay the same when you toss it from a boat. If it were a sinking one, it would decrease.