For a small requiem shark such as Bonnethead or Sharpnose - a 12' diameter pond isn't large enough.
Small coastal requiems sharks are very active species - so they need a pond that is at least 6 times their maximum length(a bare minimum of 25-26' in diameter).
Small coastal requiems sharks are very active species - so they need a pond that is at least 6 times their maximum length(a bare minimum of 25-26' in diameter).