Analysis of annuli in otoliths, age distribution and growth rates of the Namibian hake (Merluccius capensis)

Dissertação mest., Gestão da Água e da Costa, Universidade do Algarve, 2007

Age and growth estimates of Cape hake (Merluccius capensis), in the waters off Namibia were described from 804 specimens collected during January and February 2003. Each specimen was aged twice using whole otoliths. Otolith growth measurements was taken and used in back-calculated length-at-age data of M. capensis. Direct average otolith growth measurements have shown that up to three false rings formed prior to the first annulus. Ogives demonstrated the differences in otolith diameter, location frequency between the annuli and false rings. A power fish length-otolith diameter relationship used for back-calculation is: (L = 1.39 * OD). The average back-calculated lengths for the first four years of life were 19.3, 25.6, 31.8 and 38.2 cm total fish length. Age composition, estimated from an age length key, indicated that juveniles and young fish predominate in survey and commercial catches. The von Bertalanffy growth parameters was (growth coefficient, K = 0.07; asymptotic length, = 123.13; = -1.5). Sexual maturity was reached at age 1.67 years. The high correlation between otolith weight and age permits the use of otolith weight as a substitute for future age assessments. 1717.1∞L0t Key