Bluefin Tuna fishing is available by charter only
The season spans from Aug 15th until the end of October
You can find a few charters here, but there are more options:
https://www.tripadvisor.com/Attractions-g154971-Activities-c61-t217-Antigonish_Nova_Scotia.html
https://www.facebook.com/Bluefin.Tuna.Charters/
https://www.facebook.com/macdougallbluefintunacharters/
Capt. Josh Temple – Prime Time Adventures: 1-250-266-1987 | captjosh@mac.com