Growth variability in Atlantic mackerel (Scomber scombrus) and Spanish mackerel (Scomber japonicus) off Portugal

Year-class effects may be very important when analysing fish growth. This work aims to compare growth in weight and in length between year classes of Atlantic and Spanish mackerel found off the Portuguese coast. The analysis included Atlantic mackerel data from year classes 1986-1993 and Spanish mackerel data from year classes 1988-1995. The analyses indicated significant differences between year classes in terms of mean weight-at-length and mean length-at-age. Atlantic mackerel year classes also showed significant differences in mean weight-at-length between males and females, and Spanish mackerel year classes showed significant differences between sexes for mean length-at-age. No significant effects were found for the two-way interaction between year class and sex. Growth variability may be linked with variability in environmental factors as well as density-dependence.