Natural trace elemental markers for adult red rock lobsters Jasus edwardsii vary among replicate distinct water masses

In order to determine the potential utility of trace elemental natural tags to resolve fine-scale stock structure and residency patterns in adult crustaceans, we investigated whether concentrations of trace elements in exoskeleton could be used to resolve capture sites of red rock lobsters Jasus edwardsii. Using inductively coupled plasma mass spectrometry, we measured ratios of Li, Mg, Mn, Ba and Sr to Ca in samples of exoskeleton from 4 pairs of inner fjord and outer coast sites in Fiordland on New Zealand’s southwest coast. Water column salinity structure was characterised at these 8 sites from a 12 yr series of conductivity, temperature and depth casts. Information on capture site, sex, carapace length and moult stage was used in an information theoretic framework to assess the degree to which capture site could be statistically discriminated using trace element signatures of exoskeleton. Using a permutational multivariate analysis of variance, we found significant differences in trace elemental signatures of exoskeleton at the scale of 10 to 20 km for 2 of the 4 fjords. In these same 2 fjords, we found persistent differences in water column salinity structure between sites. A multivariate permutational assignment test (canonical analysis of principal coordinates) successfully reclassified individuals from all 4 pairs of sites better than chance. These results indicate that trace elements can effectively be used to discriminate capture sites of adult rock lobsters between regions with different water mass characteristics. Within these limits, trace elements of exoskeleton may prove effective as natural tags to provide valuable information on fine-scale stock structure and residency patterns for rock lobsters.