My previous answer was entirely based on my own understanding and without any Scriptures to support it.
Now,here is a completely revised answer that is based on Scriptures:
When one's life is in danger, he can kill a Brahmana, Vysya, Kshatriya or a Shoodra or even a cow, horse or any other animal, to
protect his life from them. This will not earn him any sin. ...The
king, for the sake of the gods and the Brahmanas, should kill harmful
animals such as the lion, tiger etc. In times of distress, the king
may kill and eat an animal, that is fit to be consumed. He should
never indulge in this act, in any other circumstance, except for the
sake of gods and Brahmanas.
The above passage is from Brahmanda Purana,Uttara Khanda.
The words are those of Brihaspati(Deva Guru) and the conversation is between him and Deva Raja Indra.
According to Vishnu Smriti:
Protecting (one attacked by robbers, or by tigers, or otherwise in
danger) is more meritorious than any (other) gift.
By doing so he obtains that place of abode (after death) which he
188. He who kills (in his own defence a tiger or other) animal with sharp nails and claws, or a (goat or other) horned animal (excepting
cows), or a (boar or other) animal with sharp teeth, or an assassin,
or an elephant, or a horse, or any other (ferocious animal by whom he
has been attacked), commits no crime.(Chapter V)
So,it seems,killing a potentially dangerous animal is not a sin provided you are being attacked by it.