Reproduction, sex ratio and rate of natural mortality of Cape hakes Merluccius capensis Cast. and M. paradoxus Franca in the Cape of Good Hope area

Abstract

Reproductive patterns of Cape hake off the Cape of Good Hope are described. Females of both species tend to mature at a greater length and age than their male counterparts, 50-per-cent maturity being achieved at some 470–480 mm and 360–380 mm (∼ 4.8 and ∼ 3.8 years) respectively. For both species, females undoubtedly and males probably shed all sexual products at each spawning, but there is evidence from the long spawning season of serial spawning or of spawning of different batches offish at different times. It is concluded that Cape hakes in the study area spawn in a double wave, the first wave in November/December sustained by both species and the second one in February/March mainly by Merluccius paradoxus. Females dominate the sex ratios by 1,5: 1 and 1,7: 1 for M. capensis and M. paradoxus respectively. In mature, larger fish, the dominance is even greater, particularly so in M. paradoxus, of which species males were scarce. The rate of instantaneous natural mortality M was calculated from age at maturity. M for males was higher (0,42–0,44) than for females (0,33–0,34) and an unweighted mean value of 0,4 was calculated for Cape hake in the study area.