The rules are clear. Page 10 of the rulebook:
When it’s your turn to pile animals you always have to do it in the following order:
1. First roll the die.
2. Then stack an animal. . .
3. . . .[then] turn the rotating disk. . .
So you must stack on every turn. If the fin comes up, you stack, turn fin around and rotate. Anything else comes up, you stack first then rotate.
I see how you could interpret it that way, but the rules make it far from clear. Especially what it says for when you roll the Two buoys versus The arrow or The shark fin.
For the arrow it specifically says to stack one of your animals and then fulfill the rest of the action. The arrow and shark fin make no mention of stacking. So why do the rules refer to doing so specifically when rolling the two buoys? I read the rules in German and they are worded just as unclearly.
I know it's a kids game and you can just make up whatever house rule your want, but I'm disappointed a bit with this Haba because of the unclear rules.