© 2006 International Council for the Exploration of the Sea
Predicting juvenile Baltic cod (Gadus morhua) age from body and otolith size measurements
Department of Fisheries Oceanography and Marine Ecology, Sea Fisheries Institute ul. Ko
taja 1, 81-332 Gdynia, Poland
*Correspondence to D. P. Fey: tel: +48 58 7356130; fax: +48 58 7356110. e-mail: dfey{at}mir.gdynia.pl.
Six age-prediction models based on otolith size (weight, length, and width) and fish size (standard length, SL, and weight) were developed for juvenile Baltic cod Gadus morhua (SL, 40–153 mm; age, 90–230 d). Models were built based on stepwise selection and compared using the Akaike information criterion (AIC). Reference age was estimated by counting the growth increments in the transverse sections of sagittal otoliths (n = 310). Final comparison of the utility of the six models was based on the AIC. The best model included SL, fish weight, and sampling month as independent variables. Sampling month was added to account for differences in fish growth, after it was shown that otolith size at age was related to differences in somatic growth. The predicted age of all juveniles collected between 1991 and 1995 was used to estimate their hatch dates and growth rates. The average growth rate was 0.78 mm d–1 when estimated from predicted ages (1990–1995; n = 2036) and 0.73 mm d–1 when age based on direct increment enumeration was used (1990–1993; n = 310).
Keywords: age prediction, cod, daily increments, Gadus morhua, juveniles, otolith
Received 13 May 2005; accepted 30 March 2006.