Preliminary estimation of optimal sample size for assessing the recruitment of Mesodesma donacium (Lamarck, 1818) on beaches of central-north Chile: Application of the power analysis

Abstract

This work presents a preliminary study to estimate the optimal sample size for the assessment of recruitment of Mesodesma donacium, an important bivalve that supports an intensive fishery in the most important bays of northern Chile. The specific objective was to assess the influence of the cusps (bays and horns) on the abundance of early recruits (< 15 mm shell length) of M. donacium and to include this effect on the sampling program. The bays and horns produced a difference (noise) of ca 20% in the density estimation, which was supported by the low statistical power calculated (0.20, 0.25 and 0.30 for November, December and March, respectively). Based on these results, we suggest that the assessment of the recruitment of M. donacium requires a sampling which comprises both bays and horns in intermediate beaches of northern Chile. Based on the effect size estimated of ca 0.41 for the three study periods, 80 corers must be taken from bays as well as from horns as a preliminary sample size strategy. The a priori statistical power analysis is one of the most useful strategies for the estimation of optimum sample size when the goal is to assess any working hypothesis.