Intercalibration of age readings of ling (Molva molva L.) blue ling (Molva dipterygia Pennant, 1784) and tusk (Brosme brosme L.)

Abstract

To facilitate intercalibration of the age readings of ling, blue ling and tusk, series of otoliths were exchanged among the fisheries laboratories in Iceland, the Faroes and Norway. For ling and tusk, the precision was significantly improved by the exchange exercises, but remained relatively low. Many large specimens could not be aged with confidence, and for tusk of all sizes a rather high proportion of the otoliths were unreadable. For blue ling, some progress was made using otolith sections of juvenile fish, but it remained difficult to decide what patterns should be accepted as annuli. The age readings from otoliths of 1-2 group tusk and blue ling corresponded well with assumed ages based on modes in the length-frequency distributions from Icelandic groundfish surveys.