Report of the workshop on age estimation of sprat
There are difficulties in following strong and weak cohorts of sprat in the North Sea and Div IIIa (ICES 1998, 2000, 2003). It is assumed that this is mainly caused by problems in age determinations. Exchanges of sprat otoliths and Work Shops have been performed regularly since 1994 in order to solve some of the ageing problems (Torstensen 1994, 1996, 2002). The last exchange performed in 2001-2002 revealed that estimation of sprat ages was inconsistent, with an overall CV of 28%.
The ICES Planning Group on Commercial Catch, Discards and Biological Sampling (PGCCDBS), recommended at its March 2003-meeting (ICES 2003), that an age reading workshop for sprat should be organised by Norway in 2004.
An otolith exchange was organised prior to the workshop to clarify current problems in the age estimations. Samples of otoliths were circulated from May to December and the report of the exchange is presented in Annex 1. Otoliths are here equivalent to the largest of the three pair of otoliths in fish, the sagittae.
The WS took place at the Institute of Marine Research (IMR), Flødevigen, Arendal, 14-17 December 2004. Digital images of otoliths used in the analyses were made and prepared by IFREMER and Øystein Paulsen, IMR- Flødevigen.
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