"I don't care, fine me. I'm rich!"

[Durian Fiend]

What difference does it make what animal he threw the rock at?  Throwing a rock at any animal is a mean and stupid thing to do. But there's no law against mean and stupid people, unfortunately, for the poor animals they abuse. 

I think there are circumstances where throwing a rock at an animal is justifiable, especially when your life or other lives are in danger. In this case, it's pretty clear that isn't going to be a good defense.

I have thrown rocks at dogs charging me in the past.  Now I carry a bamboo club and wouldn't hesitate to take a hearty swing at a dog or , much less likely, a pig attacking me.

In this case, I agree that his defense isn't solid if his actual intention was to "protect" turtles.  However, it could result in a lesser penalty.