Report of the Workshop on Age Reading on Roundnose Grenadier (WKARRG)
Knowledge of the biology and stock structure of the North Atlantic Roundnose grenadier were reviewed and discussed. There is no direct validation of the age estimation for Roundnose grenadier. Nevertheless, Gordon and Swan carried out an indirect validation with marginal increment analysis for the young fish.
France presented national sampling, processing and age determination methods. Ifremer determines ages from the sectioning method because all samples are old adults of more than 30 years old.
Results from an exchange experiment were presented. Altogether 66 fish of sectioned otoliths had been read on the slides and on images by 7 persons. All images were annotated. The overall agreement for sectioned otoliths agreement was very low with 30.2 % (CV=10.4%).
After extensive discussions, a re-reading of 40 sectioned samples from the exchange programme was done. The percentage agreement was higher in the re-reading compared to the original readings in both sets of otoliths (38.1% compared to 30.2%). Results indicate a higher consistency among readers than obtained prior to the workshop.
A first draft of an international manual for age determination of Roundnose grenadier was discussed during the meeting. It was agreed that the objective of the manual is to provide quality assurance among and within national laboratories.
It was recommended that sectioning of otoliths should be used for the age determination of Roundnose grenadier. It is recognized that among readers random differences with respect to interpretations and age estimate errors will always exist. The occurrence of such differences may only be reduced through frequent otolith exchanges and comparative readings.
Published under the auspices of the following ICES Steering Group or Committee