Age comparisons of capelin otoliths by Norwegian and Russian age readers 1999-2003 : a review

Abstract

Experts from the two labs IMR in Bergen and PINRO in Murmansk met for the first time in 1984 to discuss age determination of capelin. It was concluded that no systematic differences existed between the labs (Gjoesaeter, 1985). Analyses during the following years showed that during the joint autumn surveys there were, seemingly, small differences between the age readings on the different participating vessels. Up to 1993, the reported catch statistics by age group also showed no sign of bias in age reading. On the other hand, judged from catch-at-age data reported to the ICES Northern Pelagic and Blue Whiting Working Group from the winter capelin fishery in the years following the fishing moratorium 1994-1998 and from scientific surveys during the winter-spring period, large discrepancies were found, which could not be attributed to differences in length. Normally, PINRO reported higher ages than IMR. To check the presence of systematic differences between the otolith readers at the two laboratories and to study the reasons for such differences, a capelin otolith workshop was organized and hosted by PINRO in autumn 1999 (Gjoesaeter and Ushakov, 2000). During that workshop it was decided to start an otolith exchange program and to organize biannual workshops. The second workshop was hosted by PINRO in November 2001 (Gjoesaeter et al. 2002), and the third in October 2003. The present report sums up the results and conclusions so far, both from the otolith exchange program and the three workshops.