Accurate classification of juvenile weakfish Cynoscion regalis to estuarine nursery areas based on chemical signatures in otoliths

We investigated the ability of trace element and isotopic signatures in otoliths to record the nursery areas of juvenile (young-of-the-year) weakfish Cynoscion regalis from the east coast of the USA. Juvenile C. regalis were captured with otter trawls at multiple sites in Doboy Sound (Georgia), Panllico Sound (North Carolina), Chesapeake Bay (Virginia), Delaware Bay (Delaware) and Peconic Bay (New York), from July to September 1996. One sagittal otolith from each specimen was assayed for Mg/Ca, Mn/Ca, Sr/Ca and Ba/Ca ratios uslng inductively coupled plasma mass spectrometry (ICP-MS), while 6I3C and 6180 values from the other sagittal otohth in the pair were determined using lsotope ratio mass spectrometry (IR-MS). A multivanate analysis of variance determined that there were significant differences in trace element signatures among locations. Bootstrapped 95% confidence ellipses on canonical variates indicated that all 5 locations were significantly isolated in discriminant space. On the basis of these differences, linear &scrirninant function analysis (LDFA) and artificial neural network (ANN) models were used to classify inbvidual fish to their natal estuary with an overall error rate of 37 % for LDFA and 29.6% for ANN. Addtion of 6I3C and 6180 values to the LDFA and ANN models derived from the trace element data resulted in overall error around 10%. We d, therefore, be able to use chemical signatures from the juvenile portion of adult C, reyalis otoliths to accurately classify these fish to their natal estuary.