Palau's marine resources are rich and diverse. Subsistence fishing within the reef is a major activity and dominates market production. The total catch was 2,000 tons in 2000. Deep-sea fishing for pelagic species resulted in a tuna catch of 51 tons in 2000. Seasonal trochus harvesting for shell button manufacture is an important source of income for most fishermen. Other marine resources include pearls, shrimp, ornamental fish, seaweed (agar agar), and mollusks. Palau is known for having some of the best diving, snorkeling, and sport fishing areas in the world.