Relationship between elemental concentration and age from otoliths of adult snapper (Pagrus auratus, Sparidae): implications for movement and stock structure

The present study investigated the stock structure of snapper (Pagrus auratus) in South Australia, and the extent to which this is influenced by adult movement. Fish from the 9+ age class were sampled from six different regions, encompassing > 2000 km of coastline and different habitat types. The chemistry of transverse sections of otoliths was sampled using laser ablation inductively coupled plasma-mass spectrometry, providing elemental profiles that were related to age for the first nine years of the fish's lives. The age-related annual averages for both Sr-88 and Ba-138 differed significantly between regions. They were, however, similar for the first three years, then diverged considerably between the ages of three to five years, and then remained consistently different through to the age of nine years. This suggests that all fish, regardless of where captured, originated from only one or two nursery areas, but dispersed throughout the different regions between the ages of three to five years, before becoming resident to their new regions of occupancy. Thus, this population of snapper represents a single, large, stock where the individuals have a common origin, but through age-related emigration ultimately disperse and supplement the low abundance populations in regional State waters.