Unravelling growth trajectories from complicated otoliths-the case of Brazilian codling Urophycis brasiliensis.

Abstract

Uncertainty regarding the age determination of the Brazilian codling Urophycis brasiliensis has hampered its stock assessment. Transverse sections of otoliths displayed up to seven (in males) and 12 (in females) alternate opaque and translucent bands that could not be conclusively validated as annuli, resulting in unrealistically high ages of first maturity (A50 ) (A50male = 4·5years and A50female = 6years). Therefore, growth was described by the von Bertalanffy (VB) model using an alternative approach that combined microstructure data (daily growth increments) and a fixed asymptotic total length (L∞ ). This approach was supported by applying it to two other co-occurring species, the whitemouth croaker Micropogonias furnieri and the king weakfish Macrodon atricauda, for which daily and annual ring formation has previously been validated. The sensitivity to realistic errors associated with the choice of the L∞ and the daily increment readings was shown to be low. The results show that U. brasiliensis has a fast growth rate (Kmale = 1·19 year-1 , Kfemale = 0·71 year-1 ) and early maturation (A50male = 1·1-1·5years, A50female =1·6-1·8years); typical life-history traits for a sub-tropical coastal gadiform. This novel study offers an alternative approach for age and growth reconstruction for species with complex patterns of opaque and translucent bands provided that daily growth increments in the yearlings can be counted and L∞ reliably estimated.