There are two ways to fix:
- run sudo chown <your_user_id> /dev/bpf* on command line before you start wireshark, you will need to do it again after reboot
- add a startup script to fix this permanently (see instructions that comes with wireshark, D&D Utilities/ChmodBPF directory in the installation package into /Library/StartupItems
. You can adjust the script for your needs as well, for details, see the documentation that comes with wireshare.