Age and Growth of Jack Mackerel, Trachurus declivis (Jenyns), from South-eastern Australian Waters

Abstract

Jack mackerel data were collected between October 1973 and February 1976 from south-eastern Australian waters. Otoliths were read using reflected light on (1) the surface of the whole otolith and (2) the broken and burnt transverse sections of the same otolith. Growth rings were read to 13 years in the first method and to 16 years in the second.

Otolith radius (R, nucleus to posterior margin) measured along the concave surface was related to fish length (L) in a curvilinear form: R = 2.39L^0.6635. Otolith intermediate radii (rn) plotted against fish length for ages 1 to 10 years indicated a regular deposition of growth rings.

Growth according to the von Bertalanffy equation was slow (L_∞ = 46.3, K = 0.23). No significant difference between the mean lengths was apparent between sexes at most ages.

The geometric mean regressions of length on weight indicated differences between fish in spawning and non-spawning condition.