Uncertainties in sampling procedures for age composition of hake and sardine in Iberian Atlantic waters

Abstract

Estimates of the age composition of hake (demersal) and sardine (pelagic) in Iberian Atlantic waters in 1999 are analysed, paying specific attention to sampling variability. Two methods are applied, one based on an analytical approach and the other on simulation using a non-parametric bootstrap technique. The methods were used to estimate the catch at age by numbers per species for 1999, and the associated variability. They provide a useful means of analysing the precision of the estimates, of assessing data quality, and of optimising different sampling schemes. The estimates are precise for the reference ages used in assessment (CV < 13% for both species). The bootstrap method is considered better owing to its non-parametric nature, despite its more complicated implementation and greater need of computational resources.

Keywords

• age composition
• hake
• sampling variance
• sardine