Effects of sample size and ageing error on estimates of sustained yield

Abstract

A Monte Carlo simulation model of an exploited age-structured fish population was constructed, to evaluate the effects of sampling and ageing the catch on estimates of population parameters from catch-age analysis with auxiliary information and resultant estimates of sustained yield. A factorial experimental design was used where input parameters were varied among: small (100), medium (300) and large (900) catch sample sizes; high and low levels of ageing precision; and a range of ageing biases. Ageing bias and precision had dramatic effects on estimated sustained yield: positive ageing bias and ageing imprecision generally caused under-estimation of sustained yield, while negative ageing bias caused over-estimation of sustained yield. The multiple reader/reading ageing scenarios designed to mitigate ageing error were able to reduce the affects of ageing imprecision, but were unable to alleviate the problems associated with ageing bias. The simulation model can be modified for a variety of recreational fish populations; a diskette and user manual are available.