This Seeking Tech guide will explain how you can unlock the Spear Fishing trophy in Ghost of Yotei. In order to do so, check out the video and text guides below:
Step 1: Complete The Way of the Yari quest. By doing so, you will spear 4 fhis in addition to getting the Yari weapon.
Step 2: After the quest, go to any shallow river (like the Rumoi River).
Step 3: Run along the river until you see jumping fish.
Step 4: Equip your Yari and then attack the jumping fish. If you managed to spear it, then the trophy will unlock.