Japanese Hatchery-based Stock Enhancement:
Lessons for the Chesapeake Bay Blue Crab

World Fisheries for Swimming Crabs

Worldwide fisheries for swimming crabs (Crustacea, Decapoda, Brachyura, Portunidae) are dominated by three species: Portunus trituberculatus (Japanese "gazami")(ca. 50%), P. pelagicus ("blue swimming crab")(ca. 25%), and Callinectes sapidus ("blue crab")(ca. 25%). In Japan and elsewhere, other portunid species are harvested and locally marketed, including several species exhibiting large adult size (e.g., Scylla serrata and S. tranquebarica in Japan and the Indo-west Pacific, several intermediate adult size Callinectes species in the Caribbean and Americas) and more diminutive species (e.g., Carcinus maenas in Spain, Charybdis spp. in Japan). The fisheries of the three dominant species appear to have grown over the past three decades, but harvests of the two Portunus species have increased at a more rapid pace than for C. sapidus (Figure 2). The reported world landings of P. trituberculatus are dominated by China (>90%), while Japan's catch represented less than 2% of the harvest during this period (Figure 3). Changes in reporting appear to account for some of the increase in landings for P. trituberculatus; the increase in 1987 is due to China, which had not reported landings prior to that year. In the mid 1990s the Chinese catch again suddenly doubled, and it is not clear whether this large increase resulted from a change in reporting methods as opposed to a real increase in landings. Watson and colleagues (Watson and Pauley 2001, Watson et al., 2001) concluded that reporting of nominal landings in China may be substantially inflated due to the motivation structure for local fisheries officials. Indeed, total coastal zone fisheries in China increased dramatically by four-fold during the period 1987-1999. During this same period, Chinese harvests of P. trituberculatus increased 2.5-fold from 108,000 to 270,000 metric tons (t) (FAO 2000). Dominant contributors to the world catch of P. pelagicus were China, Indonesia, the Philippines, and Thailand. The market for this species has expanded considerably with the importation of processed crab meat into the U.S. (Petrocci and Lipton 1993). Chesapeake Bay (Maryland and Virginia) continues to be the single largest producer of C. sapidus, but its contribution to world harvests has declined in recent years from 45% in 1990 to 27% in 1999. For the period 1990-1999, Chesapeake Bay landings of C. sapidus were 10-fold greater than the total Japanese production of P. trituberculatus, and 19-fold greater in comparison to the Seto Inland Sea, a comparably sized system in Japan but with substantially different geomorphology and ecology (Figure 1).

graph of swimming blue crab, gazami and blue crab landings from 1970 to 2000

Figure 2.World harvests of dominant swimming crab stocks (FAO 2000).