This paper compares the influence of otolith selection for age reading, from observer collected samples, on the estimation of the biological productivity parameters, maturity at age and expected length at age, for Patagonian toothfish (Dissostichus eleginoides) in Subarea 48.3 between 2011 and 2020.
Age-length key datasets have been produced by two otolith selection methods which have been applied in CCAMLR: random and stratified selection. Historically, in Subarea 48.3, otoliths were sampled randomly which led to low sample numbers from length-classes that are proportionally less frequent in the catch, predominately, larger (older) individuals. Following a review of the sampling, a random stratified otolith sampling approach has been initiated to ensure a more even selection of otoliths for aging across the catch length-classes. During 2021/22, unread otoliths from the UK library samples from 2012 to 2016 have been re-selected for reading using the stratified approach applied since 2017. Any additional otoliths have then been included in analyses to evaluate the effect of these additional samples on estimates of maturity and growth.
For the time periods considered in this study, the change to the otolith sampling regime to provide coverage of the full length-class distribution of the catch had no influence of the estimation of maturity at age. However, the revised stratified random otolith sampling procedure led to substantial changes in the estimated expected growth parameters.
Further re-sampling and reading of historic otolith samples for length and age classes that are currently under-represented in the age dataset will be carried out to allow the comparison of parameter estimates across a longer time-series. These outputs, as well as the influence of these updated estimates in the assessment, will be presented at WG-FSA-22.