Spatial Differences in Gulf of Mexico Red Snapper Otolith Microchemistry

Red snapper (Lutjanus campechanus; n = 1,778) were sampled from Alabama, Louisiana and Texas during the summers of 2007 and 2008 from oil and gas platforms and a variety of other habitats to determine if platforms impart detectable elemental signatures in otoliths.  Seventeen elements were analyzed with inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) on dissolved sagittal otoliths.  Otolith chemical signatures were significantly different among regions and habitats (MANOVA, p < 0.001).  Mean jackknifed classification accuracies from quadratic discriminant function analyses were highest for state alone compared to habitat and habitat within state separation.  These otolith chemical signatures were used as baseline samples in maximum likelihood mixed-stock analyses to determine if signatures were detectable in additional red snapper samples (n = 487) collected from Florida, Louisiana and Texas natural habitats during the summer of 2009.  Results indicated that platform signatures were evident in otolith samples collected from Florida, a region devoid of oil and gas platforms, alluding to the possibility that platforms contribute to red snapper biomass.  Preliminary results also suggest that the western Gulf of Mexico may be contributing to the eastern Gulf of Mexico stock, further confirming a metapopulation structure for red snapper.