In the long run, some firms will respond by, (Producing more tuna and earning positive profit, producing more tuna and running at a loss, entering the industry, producing less tuna and running at a loss, producing less tuna and earning positive profit, exiting the industry) until (tuna populations grow large enough to support more firms, new technologies are discovered that lower cost, each firm in the industry is once again earning zero profit, consumer demand returns to its original level)
The new equilibrium price and quanity suggest that the shape of the long-run supply curve in this industry is (horizontal, vertical, upward sloping, downward sloping)