Investigations into the distribution of sample sizes for determining age composition of multiple species

Abstract

Collecting age-composi-tion data is a critical aspect of stock assessment; however, there are no biological or statistical investigations that support optimization of the distribution of sample size across species. Sample sizes for both collection and age-reading are often set by using ad hoc or historical values. Investigations into quantifying the trade-offs when allocating sample sizes across species are needed because resources for age determination are always limited. In this study we performed analyses to investigate the distribution of sample sizes to determine ages across multiple species by using methods derived from sampling theory and simulation testing of stock assessment models. We found that, in terms of methods based on sampling theory, distribution of sample size under 2-stage sampling could be significantly related to the life-history characteristics of the species. Results from simulation analysis illustrated that the influence of sample sizes required to determine age composition of fish on uncertainty in stock assessment models was related to uncertainty in a survey index and recruitment variability of the species being assessed. The simulation analysis highlighted cases in which larger age-composi-tion sample size did not appreciably decrease uncertainty in the stock assessment model, in particular, for species with lower recruitment variability and larger survey index uncertainty.