Chemical signatures in the otoliths of a coastal marine fish, Menidia menidia, from the northeastern United States: spatial and temporal differences

Knowledge of population structure in marine systems is fundamental to effective management and conservation. The geochemical signature of otoliths may provide a promising natural tag for quantifying population structure in marine fishes. However, the spatial scale at which chemical signatures differ among species from different environments and with different life histories is not yet clear. We examined chemical signatures in the otoliths of juvenile Menidia menidia, a ubiquitous nearshore marine species found along the east coast of North America that undergoes offshore winter migration. Specimens were collected from 16 locations in 2003 and from 9 locations in 2004 between New Jersey and Maine. Otolith geochemistry was analyzed using laser ablation inductively coupled plasma-mass spectrometry and isotope ratio mass spectrometry. Juvenile fish showed significant site-specific differences and were assigned to natal sites with 70% (2003) and 77% (2004) average cross-validated classification accuracies based on elemental (Mg, Mn, Sr, Ba, Cu, and Pb relative to Ca) and isotope (delta C-13, delta O-18) ratios using quadratic discriminant function analysis. Geochemical signatures showed significant interannual variation, suggesting natural tags are year-class specific. Results suggest enough heterogeneity exists in marine chemical signatures to track movements and determine whether M menidia return to their natal, nearshore location upon return from winter migration. Because M menidia show evidence of local adaptation, knowledge of this winter migration will have evolutionary and ecological implications. Geochemical signatures of otoliths will likely serve as a useful tool in species with similar life histories.