The Influence On Stock Assessment Advice Of Sampling Error In Research Survey And International Market Sampling Data For North Sea Cod (Gadus Morhua L.) And Plaice (Pleuronectes Platessa L.)

No abstracts are to be cited without prior reference to the author.

The influence of sampling error from both commercial and research vessel data on scientific advice are evaluated and compared for North Sea cod (Gadus morhua L.) and plaice (Pleuronectes platessa L.). Errors in the estimated numbers-at-age of the landed catch, obtained from market sampling, were investigated under the EU-funded study (EMAS - CFP Study Project 98/075) and previously reported (ICES 2001 CM/P:13 and ICES CM 2001/P:14); whilst sampling error in the indices of numbersat- age obtained from research vessel surveys were investigated under the EU-funded study (EVARES - FISH/2001/02 - Lot 1). The results of these studies were combined with XSA (Extended Survivors Analysis) stock assessment method through bootstrapping to evaluate the impact of sampling error on quantities used to provide scientific advice. These include estimates of current and historic SSB, recruitment and fishing mortality as well as biological reference points for fishing mortality, F0.1, (a proxy for FMSY) and biomass B* (a level below which recruitment is impaired). In addition a projection based upon the recommended precautionary level of fishing mortality, FPA, was performed to evaluate the sensitivity of estimates of the projected biomass and catch levels.