In-game icon
Spearfishing is an action that appears after successfully using the poke action.
While
Fishing Spots use the poke action, when the action is completed successfully, the notice that appears shows that the action is actually spearfishing and uses the same icon as poking.
Mechanics[]
The mechanics of spearfishing are actually the mechanics of poking.
Only two tools can be used for spear fishing: a
stick or a
sharpened stick.
Once successful with spearfishing, 
strip the tool with an empty hand to remove the caught creature.