They are definitely cracks - no question about that. If they were from an animal, the lines would be more parallel to each other - and rougher. I don't even think the cracks 'start' in the decal - it's just that the picture isn't showing everything. The counterpoint is that "the sticker isn't 'scratched' away up at the top". All that means is that the sticker, at the top, wasn't stretched by the crack enough, yet, to split the sticker.
From the pictures, I would lean towards thinking that the underlying glass is OK. The cracks don't look big/hard enough to have damaged the glass. The stern crack is probably easier to explain from an impact somewhere - it wouldn't have to necessarily have been a big impact - especially if the gelcoat had gotten laid in a little thicker in that corner.
The hull sides are harder to explain from those pictures. An impact, 99.9999% of the time will have an 'epicenter', of sorts. Those pictures don't show enough to offer an opinion on where they started, though. IfI had to guess, I would look at the rubrail area - an impact there could explain those types of cracks.
Also, an impact would NOT have to be recent for these to show up. It could have a while ago and the cracks just recently started to migrate.