APPLICATION OF THE OTOLITH WEIGHT - AGE RELATIONSHIP FOR THE PILCHARD, SARDINOPS-SAGAX NEOPILCHARDUS

Adult pilchard (Sardinops sagax neopilchardus) from southwestern Austr alia held in fish cages for 1 year showed minimal increase in mean len gth but a steady increase in mean otolith weight (1.61-1.83 mg); this increase (0.22 mg) closely parallels the previously calculated mean di fference between adjacent age classes (0.24 mg). Modes in otolith weig ht frequency distributions of fishery-caught pilchards, previously sug gested as corresponding with separate year classes, generally persiste d and progressed through subsequent samples. By contrast, fish length frequency distributions of these samples showed no consistent modal pr ogression. The average weight of otoliths for year classes 2-8 were us ed to calculate growth rates: following sexual maturity, at age 2, mal es grew to a significantly smaller maximum size than females (L(infini ty) = 162 and 172 mm respectively). The otolith weight - age relations hip, validated by following a cohort of unusually low abundance as it moved through the fishery, indicated that recruitment to the fishery g enerally began at age 2 but was not complete until age 4. These data h ave been successfully used in forecasting the catch rate of the fisher y up to 2 years in advance and providing an estimate of the rate for n atural mortality of 0.43.