Raceway Requirements

Scientists at the University of Maryland’s Center for Marine Biotechnology believe the maximum density in which adult blue crabs can survive is somewhere in the neighborhood of 6-9 crabs per cubic yard, or 300 crabs per hectare. According to COMB’s Odi Zmora, the ideal depth for these ponds or raceways is somewhere around 1 yard. As blue crabs are a molting species, there is no need for antibiotics, and disease is rare. Given that the raceway system recirculates water through an inline filtration system, the ponds will not need to be emptied more often than once at the end of every growth cycle (4 times/yr). This will ensure that all adult crabs are removed from the system and that the water is fully remediated in the wetland before it is pumped back into the raceway for reuse with a new crop of crabs. If an adult crab were to remain in the system, he would systematically eat all smaller crabs over the course of the next growth cycle. As crabs are a cannibalistic species, the amount of defensible space is proportional to the rates of survival. Given the proper raceway landscaping, it is thought that ponds/raceways could produce survival rates of somewhere in the neighborhood of 20% - 30% (fig. 31).
Figure 31 – Spatial Requirements. Author illustration.

One of the biggest challenges for the enclosed raceway system is the issue of rainwater. Since the concentration of salts and other trace elements are actively monitored and maintained, the irregular introduction of rainwater into the raceway system could dramatically affect a precarious electrolytic balance. Thus, it is believed that rainwater should be entirely diverted from the raceway system. This requirement determined the need for onsite water detention and retention ponds, and in many ways shaped the final outcome of the landscape strategies.
[22] Interview with and Odi Zmora, COMB Master Nutritionist, conducted 02.12.09.
[23] Interview with Dr. Yonathan Zohar, COMB Director, and Odi Zmora, COMB Master Nutritionist, conducted 02.12.09.