Identifying mangrove areas for fisheries enhancement; population assessment in a patchy habitat

摘要

1. Small-scale fisheries are an important element of the ecosystem goods and services that mangrove habitats provide, especially to poorer coastal communities that rely most on natural resources, and have similar values to payments for ecosystem services (PES) under carbon-trading schemes. 2. In advance of fishery-enhancement trials for the mud crab Scylla olivacea, a mark-recapture study was conducted to estimate population size and turnover in 50 ha of isolated mangrove on Panay Island, Philippines. A total of 811 crabs were released in six sessions with an overall recapture rate of 41.5 ±3.6%. Population size ranged from 607-1637 individuals. 3. There was a high degree of site-fidelity, with 45.5% of recaptures in the same sampling areas as releases. Total mortality was 0.79 month"1, with fishing mortality accounting for 95% of overall mortality. 4. Von Bertalanffy and Gompertz growth models yielded estimates for (carapace width) of 117.3 ± 14.7 and 110.6 ±2.1 mm and for k of 2.16 ±0.74 and3.25 ±0.81, respectively. Crab densities of 12-33 individuals ha"1 in the study area were lower than in other mangrove systems owing to intermittent recruitment, while growth rates indicated no limitation in terms of food supply. 5. The study demonstrates that in specific mangrove habitats that are below carrying capacity, there is potential for fisheries enhancement to sustain or increase direct economic benefits from mangrove ecosystems and hence promote community engagement in broader conservation and PES initiatives.