...Hold on. You can't possibly catch a bluefin tuna from the shore.
Most likely she got on a boat and...
A - Fished it out with a fishing tackle < would require serious arm strength and stamina to do
B - Fished it out with a net < ditto as above
C - Jumped in the water and speared it < not really probable since the tuna still struggled after it's "death" or capture
D - Jumped in the water and wrestled it bare-handed < absurd, seriously cool. However not really probably due to the reason above.
E - Jumped in the water and knocked it out with a punch or something < absurd and seriously cool. Most probable due to earlier info dropped.
Still, it's quite a shocker.