Stratis Gavaris

Improving the Precision of Abundance Estimates of Eastern Scotian Shelf Atlantic Cod from Bottom Trawl Surveys

Abstract Abundance estimates from bottom trawl surveys are important elements in the evaluation of stock status. The reliability of stock assessment results are greatly influenced by the precision of the survey abundance estimates. In this study, a new stratified random design, based upon historical spatial distribution, for estimating the abundance of ages 5–12 Atlantic cod Gadus morhua on the eastern Scotian Shelf off Nova Scotia was evaluated. Gains in precision from the new design, relative to simple random sampling, were mainly due to the improved allocation of trawl sets to strata, whereas the gains solely due to the new stratification scheme were minimal. We conclude that any reasonable stratification scheme that is flexible enough to allow for the optimization of the allocation of sets to strata should perform well. In our study, the allocation scheme was based upon the historical spatial distribution of abundances. Although annual changes in spatial distribution would require revision of the allo...