Characteristics of Scylla spp. (Decapoda: Portunidae) and Their Mangrove Forest Habitat in Ngaremeduu Bay, Republic of Palau.

v. ill. 23 cm.QuarterlyThree species of mangrove crabs (Scylla spp.) were captured in live traps in Ngaremeduu Bay on the island of Babeldaob, Republic of Palau. Most were S. serrata, but one individual each of S. olivacea and S. paramamosain was also trapped, establishing existence of a biogeographic gradient in mangrove crab species diversity across the Micronesian archipelago. Species composition of mangrove trees along transects around the bay and along the three major tributaries was similar to that of other Micronesian islands, although trees are smaller in Palau. For 17 months in 1999–2000, crabs were trapped in the bay and captured by hand along the transects; they were trapped again for 1 month in 2004. Characteristics of the crabs and of burrows encountered along the transects suggested that only S. serrata was captured in 1999–2000 and that population density of this species was 40 crabs ha_1. Carapace widths for the 159 crabs captured during the entire study did not differ significantly over the 4-yr span, and averaged 153 mm for males and 137 mm for females. However, average carapace widths for the largest quartile of crabs declined significantly from 174 mm to 171 mm across the study period. Catch per unit effort was 0.28 crab per trap night in 1999–2000 and 0.45 in 2004. Although large crabs are still available in Ngaremeduu Bay, current regulations may not be sufficient to keep populations from decreasing gradually in size, especially in the face of increasing harvest pressure on the island of Babeldaob

Population Characteristics of the Mangrove Crab Scylla serrata (Decapoda: Portunidae) in Kosrae, Federated States of Micronesia: Effects of Harvest and Implications for Management.

v. ill. 23 cm.QuarterlyApparent declines in abundance of mangrove crabs Scylla serrata (Forsska°l, 1755) in Kosrae, Federated States of Micronesia, have prompted concern regarding long-term persistence of this important cultural and economic resource. To support development of effective management strategies, we gathered basic biological information about mangrove crabs on this island, where S. serrata is the only mangrove crab species present. In particular, we were interested in understanding movement patterns and evaluating spatial variation in population structure. Many population characteristics, including estimated life span, ontogenetic shifts in habitat use, sex-specific allometric relationships, male-biased sex ratios, and evidence for limited (<2 km) alongshore movement, are similar to those reported elsewhere in the range of the species. Therefore, insights from S. serrata populations elsewhere might usefully inform management of the species on Kosrae. Moreover, information reported in this study, for which there is no ambiguity about species identification, has broader relevance. Spatial variation in size structure of the population appears to be driven by variable harvest pressure that reflects distribution of the human population and location of emerging commercial harvest operations. Effective management of mangrove crabs is therefore likely to benefit from application of size-based or sex-based restrictions on harvest and might usefully incorporate spatially explicit strategies, such as partial or complete reserves. Development and implementation of effective management will necessarily depend on cultural as well as scientific information