Description of the subareas of Ragay Gulf, Philippines, and their fish assemblages by exploratory data analysis

Abstract

Exploratory data analysis using four different techniques of classification and ordination was applied to the catch data from a 15-month demersal trawl survey in Ragay Gulf, Philippines, in order to characterize the area. The four techniques yield almost identical results and therefore lend confidence to the three subareas identified: shallow, coralline and deep. Species characteristic of the subareas were also identified. The observed pattern remained consistent during the study period, suggesting that seasonal variability is not pronounced.

This study provides further empirical evidence of the zonation of fish communities by depth. Preliminary comparison of the results of this study with those of studies of demersal fish community assemblages in the Samar Sea shows that boundary depths defining zonation are different in the two areas because of their different depth ranges and spatial scales. This comparison leads to the question of whether the boundary depths as identified via classification and ordination methods could be a function of the shape of the depth distribution of the samples. The use of a bootstrapping method to investigate this question is suggested. The importance of applying exploratory data analysis to the catch data from a demersal trawl survey done to assess fish stocks is also discussed.