Over 1500 individuals were used for age estimation. Scales from around 50 individuals were removed monthly from September 2000 to August 2001 (n = 600) for validating the periodicity of growth mark formation.
Additional scales were removed from 900 individuals in January 2001 (set as month of birth for sardine, see below) and age-length keys were constructed based on observed lengths at age.
Scales (6-8 from each fish) were extracted from the left flank, washed, placed between slides and were viewed using an image processing system fitted on a microscope.