Monday, August 6, 2007

PS 14-154: Population characteristics of the mangrove crab Scylla serrata in Kosrae, Federated States of Micronesia: Effects of harvest and implications for management

Kimberly M. Bonine, Stanford University, Eric P. Bjorkstedt, Humboldt State University, Katherine C. Ewel, USDA Forest Service, and Moses Palik, Kosrae Island Resource Management Authority.

Recent appreciation of potential declines in the abundance of mangrove crabs (Scylla serrata) in Kosrae, Federated States of Micronesia, have prompted concern regarding the long-term persistence of this important cultural and economic resource. To support development of effective management strategies, we conducted a suite of studies to gather basic biological information for mangrove crabs in this part of the species’ range, to provide information on movement patterns, and to evaluate spatial variation in catch-per-unit-effort (CPUE) and population structure in the context of qualitative information on the intensity of human harvest. Various characteristics of the population of mangrove crabs on Kosrae, including estimated life span, ontogenetic shifts in habitat use, sex-specific allometric relationships, male-biased sex-ratios, and evidence for limited (< 2km) alongshore movement, are similar to those reported elsewhere in the species range, which suggests that lessons learned elsewhere might usefully inform management efforts on Kosrae. Application of a simple demographic model suggests that spatial variation in the size-structure of the population is driven by variable harvest pressure that reflects the distribution of the human population and the location of emerging commercial harvest operations. Based on these results, and corroborating information from estimates of CPUE, effective management of this important cultural and economic resource is likely to benefit from the application of size-based or sex-based restrictions on retention of mangrove crabs, and the species’ biology appears to be amenable to spatially explicit management approaches such as marine reserves. Development and implementation of effective management will necessarily depend on cultural as well as scientific information.

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