Report of the Workshop on Age Reading of European and American Eel (WKAREA2)

The workshop commenced with the analysis of the results of the experienced reader inter calibration exercise that had been carried out several months previous the meeting. This intercalibration exercise was based on image exchange for both species. The readings  had  been  performed  on  a  web  platform  device  allowing  the  positioning  of  age  checks  on  the  pictures  and  recording  the  number  of  checks  identified  by  each  reader.  A  total  of  21  readers  participated  to  the  exchange.  A  collection  of  117  European  eel  pictures  and  44  American  eel  otolith  pictures  were  used  for  the  exchange.  The overall agreement rate of the readings with the modal age ranged from 66.2% to 13.2%.  The  results  showed  that  more  agreement  would  have  been  obtained  if  the  reading rules had been applied more consistently. Some readers discarded some “difficult”  otoliths.  The  absence  of  metadata  such  as  the  location,  date  of  capture  and  habitat  type  of  the  otolith  was  also  identified  as  a  source  of  misinterpretation  of  growth  patterns.  It  was  recognized  for  future  readings  that  metadata  should  be  included and that all otoliths would be read, with the addition of a reading confidence parameter.  A  reference  collection  composed  of  38  A.  Anguilla  and  19  A.  rostrata  known  age  otolith  pictures  was  set  up,  with  one  blind  file  and  one  fully  annotated  file. The manual was updated with more precisions included for the different preparation protocols. A protocol for age reading and training age reading and routine age reading was proposed, including the use of the reference collection.

Includes Annex 5: Manual for the ageing of Atlantic Eel, produced by the Workshop participants.