The comparison of selected sampling methods for determining the age distribution of fish in the catches

Jan Horbowy

doi:10.3750/aip1999.29.1.05

Abstract

Computer simulations were employed to determine the efficiency of selected sampling methods used to determine the age composition of the catches. Both proportional (PROP) and stratified sampling schemes were analysed. In the stratified sampling, the efficiency of drawing a constant number of fish from the stratum (S_CON) as well as drawing a number of fish proportional to the product of the fish numbers and the standard deviation of age in the stratum (S_PROP*SD) were investigated. The S_PROP*SD sampling method was proven to be the most effective. The proportional sampling was shown to be the best when taking into consideration the sampling efficiency and the practical possibilities of implementation of a given drawing scheme.

Highlights

The application ofthe majority of mathematical models for the assessment of the state of fish stocks requires data concerning the age composition of the catches
Comparing various fish sampling methods for investigations of the age composition of the catches and determining the best method from among those analyzed were based on computer simulations
The results obtained indicate that the lowest total variance was usually obtained when samples of fish for age investigations were collected at random (PROP) or by the stratified method, when the size ofsub-sample in the stratum is proportional to the product of the number offish in the stratum and the standard deviation ofthe age distribution in the stratum (S_PROP*SD)

Summary

Introduction

The application ofthe majority of mathematical models for the assessment of the state of fish stocks requires data concerning the age composition of the catches. This is deter mined using fish samples from which otoliths or scales are collected in order to determine fish age. The calculations are carried out using the so-called age-length key, which was first introduced by Fridrikson (1934, after Kimura 1977).

Methods

Results

Conclusion