Is a catheter needed for gallbladder surgery?

No. It depends on how big is the stones and if its obstructing the duct.
It depends. Whether a urinary catheter is needed depends on the length of the operation as well as surgeon preference. Sometimes a catheter is placed for the operation only and removed before a patient wakes up from anesthesia. If the operation is uncomplicated and only involves taking out the gallbladder, then this is usually short enough to not need a catheter.