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

Conclusions

The current effort to assess the Japanese swimming crab industry and its relevance to the blue crab fishery in Chesapeake Bay was conducted within the context of a public debate that included many sectors of Maryland's research community, managers and the general public. The goal of this assessment was to bring back sufficient information to inform this debate and provide a better grounding for determining the feasibility of enhancing Callinectes sapidus populations by controlled releases of juvenile crabs. In many respects this debate mirrors those that have been taking place in a number of fisheries over many years. How one views a harvested species is of central importance and lies at the root of many of the controversies that have emerged nationwide. In a very simple sense, one might view a natural population as:

a stock that should be managed for harvest in a sustainable fashion,
an ecological unit, integral to ecosystem function on local to regional levels, or
a crop to be "cultivated" for beneficial uses, relative to either a or b.

These views tend not only to structure discourse but also prioritize research and management strategies. The conflicts between "fisheries management" and "stock enhancement" approaches have been well described for numerous species. The fact that in a number of cases, management strategies employing any one of these paradigms have not appeared to benefit a particular resource has proven particularly polarizing. The reality is that for Chesapeake Bay blue crabs, distinct aspects of all three of these overarching, albeit seemingly disparate views, are relevant. While the sense that Callinectes sapidus is both a stock and ecological unit is apparent, the widespread peeler industry is a reasonable example of how controlled "cultivation" is also at play in the region.

The intensive, long-term effort to cultivate and release Portunid crabs implemented in Japan provides important benchmarks -both in terms of the actual accomplishments and in terms of research and assessment technologies developed in Japan. The interpretation of these benchmarks cannot easily be separated from the lenses through which they are observed. The expression of these different perspectives in this report -leading to both consensus as well as disagreement -should be seen as a useful representation of these perspectives and finally as a strength of the overall effort.

There was strong consensus that information gleaned from the trip to Japan must be considered first within the context of the ongoing effort to develop new fisheries management regulations. Attaining a more stable and sustainable blue crab stock will depend upon proactive management activities like those underway through the Bi-State Blue Crab Advisory Committee (BBCAC) and other relevant scientific/management efforts. The impacts of any propagation effort -whether for enhancement or research purposes -will likely prove significant only over the long term. With this context in mind, multiple points of agreement emerged regarding what was observed in Japan and its potential relevance to Chesapeake Bay. Such efforts are now underway through BBCAC and other relevant scientific/management entities. The impacts of any propagation effort -whether for enhancement or research purposes -will likely prove significant only over the long term and a continuing emphasis on efforts to manage the fishery in Maryland and Virginia remains a priority. With this context in mind, multiple points of agreement emerged regarding what was observed in Japan and its potential relevance to Chesapeake Bay.

The Japanese Experience

It seems clear that fishing pressure, habitat degradation and possibly climatic shifts lie at the heart of the long-standing decline of the Portunid crab fishery in Japan. The close relationship between the fishing industry and Japanese government (at the national, prefectural, and fishing cooperative level) has fostered a 30-year collaboration leading to the development of exceptional cultivation technologies. These efforts are well integrated at the societal and fisheries levels in the coastal regions where they are employed. The close linkage between the fishing cooperatives and hatchery enhancement systems has been and remains a critical element in the overall implementation of the Japanese crab enhancement effort. Indeed, cultivation of Portunid crabs is but one part of a far more extensive program to artificially rear and release juveniles of a wide range of economically important species. This approach provides an important context within which the Japanese enhancement effort should be interpreted.

Based on examinations of available data and discussions with Japanese scientists, evidence exists that the net result of enhancement efforts are most apparent in small-scale systems. In these cases, controlled releases may be sustaining harvest levels in depressed fisheries, although evidence for improved fisheries is lacking. There is no clear evidence for enhancement of the fishery in the larger system studied by the research team and a measurable impact upon natural Portunid populations (stock enhancement) has not yet been demonstrated to date in Japan. Yet the carrying capacity of the larger systems is unknown and has probably declined due to habitat degradation at the same time as the hatchery release efforts.

While advances in cultivation technology for P. trituberculatus have been truly remarkable, similar progress in the development and implementation of appropriate tools to assess impacts of enhancement efforts is -despite the 30-year history -lacking. Such efforts are now underway in Japan -facilitated by many of the same technological advances that have led to a detailed understanding of Portunid biology and reproduction and that have served as the foundation for cultivation efforts there.

Implications for Chesapeake Bay

The results of the fact-finding mission to Japan strongly suggest that a broad, Bay-wide effort to enhance the Chesapeake Bay blue crab fishery through hatchery efforts would face significant barriers to success. While the team diverged in their opinion about whether enhancement might be possible in a more limited context, they agreed that there were compelling reasons to develop a local capability to rear significant numbers of blue crabs. Hence there was strong concurrence that state of the art rearing facilities, capable of producing on the order of 100,000 to 1,000,000 juvenile (releasable) crabs per year would be an important (if not essential) contribution to gaining new insights into blue crab biology, while also improving our technological capabilities. They agreed that such facilities would provide tangible opportunities to advance our understanding of the reproduction, life cycle and ecology of this species. These insights and technological advances were seen as essential steps to the development of better tools for the management of the natural fishery. In addition, development of technologies directed towards economical, controlled production of very high value, soft-shell crabs was seen as an immediate benefit of such an investment in a hatchery. Key to overall success of these efforts will be a conscious attempt to integrate approaches that cross traditional boundaries and scientific disciplines -from the molecular to ecosystem scales.

While the results of the decades-long Japanese cultivation efforts were apparent, contributions made with regard to enhancement of swimming crab populations have remained clouded by an apparent lack of systematic assessment of impacts. With respect to the Chesapeake Bay blue crab, the team concurred that any and all efforts must be grounded in testable hypotheses and integrated assessment programs that include cost-benefit analyses. The team clearly diverged on the implications of scale, the importance of localized blue crab populations and the significance of temporal and spatial dispersal patterns. Thus the feasibility of enhancement emerged in very different contexts, depending upon the assumptions made and the intended outcomes for such efforts. According to one view, hatchery technology could be aimed at enhancing reproductive stocks in location-specific refuges. The other view holds that based upon the life cycle of Chesapeake Bay blue crabs, there is no practical means to enhance reproduction through localized releases. Enhancement of the stock is most efficiently accomplished through fisheries and habitat management. The divergence of opinion expressed in this regard suggests that experiments to assess scaling issues are key, and that they should be designed in a manner that leads not only to new information but to new tools.

Of the many questions that were posed during this effort, a central one was whether or not Chesapeake Bay is fundamentally different from the sites in Japan. Actually, there are a number of important similarities between the ecosystems. In both cases, there have been significant declines in natural fisheries concurrent with substantial degradation of habitat. Crab fisheries in both cases are complex and prone to high variability. Complications imposed by these factors present true challenges in the context of enhancement issues, as well as to more traditional fisheries management strategies. Of particular note, however, are the societal and management contexts in both cases. Management and engineering of coastal ecosystems and their associated fisheries are clearly more pervasive in Japan than in Chesapeake Bay. Aquaculture of many different species in Japan is extremely well integrated as is targeted stocking conducted with close coordination of producers and fishers. The model applied in Chesapeake Bay is quite different. Efforts like those of the Bi-State Blue Crab Advisory Committee suggest that the near-term approach must be grounded in consensus building and clear guidance from the scientific community. As we learn more about the suite of issues that regulate natural populations in Chesapeake Bay and as we develop a better understanding of the fundamental properties of Callinectes sapidus, very likely a greater set of options for maintaining a sustainable fishery will become apparent. Learning from examples like those studied in Japan will unquestionably prove an essential step in that direction.