Browsing by Author "Walton, Mark E."
Baseline assessment of fisheries for three species of mud crabs (Scylla spp.) in the mangroves of Ibajay, Aklan, Philippines MJHL Lebata, L Le Vay, JH Primavera, ME Walton & JB Biñas -
Bulletin of Marine Science, 2007 - University of Miami, Rosenstiel School of Marine and Atmospheric ScienceStock enhancement through habitat restoration and habitat release have both been considered as approaches to the management of declining Scylla spp. Prior to stock enhancement trials, the present study was conducted to monitor recruitment and yields of three Scylla spp. in ∼70 ha of natural mangroves in Aklan, Panay, Philippines. Results showed that Scylla olivacea (Herbst, 1796) was the most abundant mud crab species, comprising 95% of the catches over the 4 yr sampling period. Size distribution for this species indicated year-round recruitment with peaks in the numbers of smaller, immature crabs during the summer months. The decreasing mean size at capture, yield and CPUE in terms of weight throughout the 4-yr sampling period is an indication that the area has been subjected to heavy fishing pressure. The constant CPUE in terms of numbers of crabs suggests that recruitment is constant, though this is likely to be lower than in other mangrove areas due to the topography of the site with limited access to the open sea, resulting in relatively low crab abundance and yields. Combined with the fidelity of S. olivacea to the mangrove habitat, this indicates a suitable population for investigation of the effectiveness of a hatchery-release program.
ArticleMJH Lebata, ME Walton, JB Biñas, JH Primavera & L Le Vay -
Aquatic Conservation: Marine and Freshwater Ecosystems, 2012 - Wiley
- 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.
- 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.
- 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.
- Von Bertalanffy and Gompertz growth models yielded estimates for L∞ (carapace width) of 117.3 ± 14.7 and 110.6 ± 2.1 mm and for k of 2.16 ± 0.74 and 3.25 ± 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.
- 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.