Assessment of the natural stocks of Gelidiella acerosa (Forssk.) Feld. et Hamel in Mantigue Is., Camiguin, Southern Philippines
1993
Fortes, M.D. (Philippines Univ., Diliman, Quezon City (Philippines). Marine Science Inst.)
Natural stocks of Gelidiella acerosa on the reef flat of Mantigue Is., Camiguin, Southern Philippines, were assessed in terms of their distribution, abundance, growth and mortality rates, and harvest yield from Aug 1989 to Dec 1990. This was supplemented by bimonthly monitoring of water movement (diffusion index factor), temperature (minimum-maximum), and salinity (refractive index). The seaweed stocks total at least 0.31 sq km, comprising about 20 percent of the total reef area. Mean biomass of the seaweed was 13.5 gdw/sq m. In general, rapid growth as well as high mortality were manifest in all but the last five upper size classes of the plants in both unharvested and harvested sites. Comparatively, highest value for growth rate in the latter plots was twice smaller than that in the former. Mean yield of the seaweed at the former site was 0.125 g, while at the latter, it was 0.154 g. The unharvested site could support only 18 plants to reach Class 13 (131-140 mm) per sq m area or the reef, while the harvested site could support 39 plants per square meter. There was a consistent relationship between CPUE and the duration of the harvest-shortest when CPUE was highest and longest when CPUE was lowest. There was an apparent localized depletion of the harvestable resource when the number of harvesters was largest. In order to reach the grand mean daily harvest of 3.4 kg, the number of harvesters from the maximum of 69 (in Aug) should be reduced by at least 50-60 percent in order to reach the grandmean CPUE of 0.57 kg/ha
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