I think also if they are refrigerated and full of food, the food rots and gases off, keeping them afloat longer. Also, I recall something about certain containe

I think also if they are refrigerated and full of food, the food rots and gases off, keeping them afloat longer. Also, I recall something about certain containers (or maybe it was just an experiment?) having holes in them plugged with a material which dissolves after extended exposure to saltwater - so within a few hours they sink.