Association for Tropical Biology 2010

Take home message:Explore, don`t Ignore, the Zeroes

Estimation of fish abundance in a seagrass marine protected area in Central Philippines using Delta-Type Two-Steps model

Abstract

Fish abundance estimates serve as a useful indicator on the status of the fishery and hence is important for fisheries management. To understand the status of parrotfish, we investigated its abundance in Jagoliao, central Philippines from underwater visual census data. However, data from underwater visual census are typically highly skewed and contains many zeroes. The objective of this paper is to estimate abundance of parrotfishes in Jagoliao using Delta-Type Two-Step model which take into account the zero-inflated characteristics of the data. Our result shows that the presence of parrotfish is a function of season and period of MPA implementation; different from those that affects its non-zero abundance which was a function of the site covariate. Given similar season and period, the over-all mean abundance of parrotfishes in Jagoliao was similar in both the reserve and non-reserve sites. Our estimates suggest that the number of fish per 250 square meters ranges from a low of 2.41 (95% CI: 0.89 – 7.22) in the current reserve site before the MPA was implemented in the wet season, to a high of 36.48 (95% CI: 18.78 - 69.18) in the non-reserve site during the implementation of MPA in the dry season.