Document: KIM-3-78-6

Ecological relationships of Scylla serrata in the Federated States of Micronesia: Modeling strategies for mangrove resource management.

BONINE, K.M.* ¹, K.C.EWEL ², R.L.NAYLOR ¹ and R.D.HAUFF ³

Stanford University, Stanford, CA 94305 USA ¹
USDA Forest Service, Honolulu, HI USA ²
Kosrae Division of Forestry and Wildlife, Kosrae, F.S.M. ³

Abstract:
Mangrove crabs (Scylla serrata) comprise an important local fishery in the Federated States of Micronesia. On the easternmost island of Kosrae, approximately 40% of households collect crabs worth an estimated $500,000 per year. Population growth and decreased employment subsidies have placed more pressure on subsistence activities on the island, and as a result mangrove crabs are under threat from increased harvesting rates and mangrove degradation. We have developed a mangrove resource use model integrating ecological and economic factors to evaluate potential management policies. Using belt transects in the mangrove forests on Kosrae, we obtained baseline data on crab density, distribution, and habitat requirements. We found significantly higher crab burrow density (p<0.05) in interior (0.39/100m²) and riverine (0.50/100m²) zones than in the fringe zone (0.00/100m²), and we estimate a range of 45,000135,000 crabs for the mangrove area of Kosrae. We also conducted household interviews on Kosrae to obtain demographic and resource use information to estimate current harvest rates and economic drivers of resource consumption. Survey results indicate an annual harvest rate of 97,000 crabs, with relatively more harvesting by unemployed subsistence households. A logistic growth model incorporating harvesting, mangrove area, and upper estimates for crab density indicates that a doubling of current harvest rates might push crab populations on Kosrae to the edge of sustainability. A natural human population growth rate of over 2% and continued decline in real incomes on Kosrae may necessitate active management measures such as harvesting size limits, harvest-free mangrove reserves, and export restrictions.

Keywords: Scylla serrata, mangrove crabs, mangrove habitat, sustainable resource management

This abstract is being presented at: 1:30 PM in session:
Oral Session #18: Mangrove Ecology.