Results of the anchovy (Engraulis encrasicholus, L.) otolith exchange programme

The  1995  Working  Group  on  the  Assessment  of  Mackerel,  Horse  Mackerel,  Sardine  and  Anchovy agreed to carry out an anchovy otolith exchange programme in order to compare otolith age readings made by the scientists of the different countries, which fish anchovies.
In total, 650  pairs  of  otoliths  were exchanged, of  which 200 were from ICES  Division  VIIIab,  250 were from ICES Division VIIIc and 200 were from ICES  Sub-division IXa North, and three readers from  the  two  countries  (France  and  Spain)  took  part  in  the  exchange.  The  comparison  of  otolith readings of the three areas was carried out separately.
Taking into account the few ages read, due to the anchovy being a species with a short life-span, the average  general  agreement  between  readers  was unsatisfactory in Division  VIIIab (71%)  and VIIIc (80%). In Division IXa North agreement was greater than in the other two areas (96%) owing to the sample  of  otoliths consisting  of  specimens  of  one  single  age. Agreement  between  readers  varied between 59% and 88% for the Division VIIIab, between 77% and 82% for Division VIIIc and between 94% and 97% for Sub-division IXa North.
Standard deviations by age groups increase from age 2 for the Division VIIIab and VIIIc area sample. In Division VIIIc the standard deviations also increase in age 0.
The  age  bias  plots  of  each  reader  against  the  modal  age  show    variability  in  the  samples from Divisions VIIIab and VIIIc. The age bias plots for all readers combined show that bias increases with age, and that those from age 2 tend to be underestimated in Division VIIIab and that those of age 0 tend to be overestimated in Division VIIIc. In Division IXa North the level of bias is very low.
Considering the importance of  age readings in  assessment, new investigations are needed to increase agreement, and to standardize ageings.