Stock discrimination of school mackerel, Scomberomorus queenslandicus, and spotted mackerel, Scomberomorus munroi, in coastal waters of eastern Australia by analysis of minor and trace elements in whole otoliths

Abstract

The concentrations of 11 elements in individual whole sagittal otoliths from school mackerel (Scomberomorus queenslandicus) and spotted mackerel (Scomberomorus munroi) collected in east coast waters of Queensland, Australia (16°S to 28°S) were determined by using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Spatial and ontogenetic variation in otolith elemental composition was examined to make inferences about the stock structure of these species. Stepwise canonical discriminant analyses of the concentrations of barium, potassium, magnesium, manganese, sodium, phosphorus, sulphur, and strontium were used to differentiate groups of fish. These analyses identified an optimum grouping of at least two stocks of school mackerel and a single stock of spotted mackerel in the study region, although our results showed that the most informative comparisons were made among fish of the same year class. The age of fish in collected samples produced strongly significant effects on mean elemental composition of otoliths. These patterns offered independent support for hypotheses about stock structure from previous tagging, catch monitoring, ageing, and reproductive studies. Discrimination between school and spotted mackerel stocks will enable the species to be managed on the basis of stock structure throughout their east coast distribution.