Determining age and growth of abalone using stable oxygen isotopes: a tool for fisheries management

Concerns of inaccuracy or bias associated with current techniques used to obtain age and growth data for abalone (age from shell layers, growth from tag-recapture, modal progression) have prompted consideration of alternative techniques to obtain data to ensure sustainable management of abalone fisheries. Stable oxygen isotopes have been used in many studies of molluscan age and growth, but to date this technique has not been applied to haliotids. Here we describe the procedure as applied to the blacklip abalone Haliotis rubra in south-east Tasmania. Stable oxygen isotope ratios of serial samples from calcium carbonate collected at approximately 1-4 mm intervals along the growth direction of the shell reflected the seasonal temperature cycle. From these oscillations, estimates of age and growth were obtained for two specimens, shell length 63.6 and 87.2 mm. We determined the age of these specimens to be 3.5 and 5 years. Growth rates ranged between 13 and 19 mm year−1. This study demonstrates the potential of stable oxygen isotopes to validate existing techniques used to determine age and growth of abalone, and could provide further insights into age and growth processes of haliotids.