Temporal and Spatial Variability in Juvenile Red Snapper Otolith Elemental Signatures in the Northern Gulf of Mexico WILLIAM F. PATTERSON III* Department of Biology, University of West Florida, 11000 University Parkway, Pensacola, Florida 32514, USA JAMES H. COWAN,JR. AND CHARLES A. WILSON Coastal Fisheries Institute, School of the Coast and Environment, Louisiana State University, 2179 Energy, Coast, and Environment Building, Baton Rouge, Louisiana 70803, USA ZHONGXING CHEN 1 Department of Marine Science, University of Southern Mississippi, 1020 Balch Boulevard, Stennis Space Center, Mississippi 39529, USA Abstract.—We examined otolith chemistry of age-0 red snapper Lutjanus campechanus in U.S. waters of the northern Gulf of Mexico (GOM) to determine if otolith elemental signatures could be employed as natural tags to estimate postsettlement population connectivity. Fish (n ¼ 755) belonging to five successive year- classes (1996–2000) were sampled from three GOM regions. Solution-based analysis of otolith chemistry was accomplished with sector field-inductively coupled plasma-mass spectrometry (Ba, Mg, Mn, and Sr) and inductively coupled plasma-optical emissions spectrometry (Ca). Several regional trends observed for individual elements were consistent among year-classes, yet elemental signatures were significantly different among years as well as among regions (multivariate analysis of variance [MANOVA]; p , 0.001). Jackknifed classification accuracies from linear discriminant function analysis approached 80% (mean ¼ 78.4%) in all years except 1998 (62.4%). Overall, these results indicate otolith elemental signatures may serve as effective region-specific natural tags of GOM red snapper. Significant differences in otolith chemistry among year- classes indicates year-class-specific analysis is required to derive natural tags. Furthermore, regional differences in elemental signatures may be insufficient in some years to be employed as accurate natural tags. Red snapper Lutjanus campechanus is among the most economically and ecologically important reef fishes in the U.S. Gulf of Mexico (GOM). Significant bycatch mortality caused by shrimp trawling in juvenile snapper habitats on the continental shelf, as well as high exploitation rates by directed recreational and commercial fisheries, have resulted in an estimated 90% reduction in red snapper biomass since the 1970s (Goodyear and Phares 1990). Despite increasingly restrictive fishing regulations since the early 1990s, GOM red snapper have been estimated to be significantly overfished for well over a decade (SEDAR7 2004; Porch 2007). Significant research has been directed in recent years at examining red snapper population ecology to enhance fishery conser- vation efforts. In particular, studies examining popula- tion structure and population dynamics have greatly increased knowledge of red snapper ecology. Red snapper have been managed historically as a single unit stock in the GOM. That approach was supported by results of early genetics studies that employed a variety of markers to examine population structure. Several authors reported that differences in mitochondrial (mt)DNA allele distributions among GOM regions were insufficient to reject the null hypothesis of panmixia (Camper et al. 1993; Gold et al. 1994; Garber et al. 2004). Gold et al. (2001) reported similar findings based on nuclear DNA microsatellite distributions. Saillant and Gold (2006) examined spatial and temporal variability in microsatellites among three GOM regions and two red snapper cohorts and found little evidence of significant spatial heterogeneity among regions. However, they also reported that significant differences in genetic effective population size existed among regions, which they inferred to indicate the existence of different ‘‘demo- graphic stocks’’ in the northern GOM. Pruett et al. (2005) stated that the current spatial distribution of mtDNA alleles in the northern GOM indicated a complex history of isolation and dispersal. They * Corresponding author: wpatterson@uwf.edu 1 Present address: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge Massachusetts 02138, USA. Received November 29, 2006; accepted September 9, 2007 Published online April 3, 2008 521 Transactions of the American Fisheries Society 137:521–532, 2008 Ó Copyright by the American Fisheries Society 2008 DOI: 10.1577/T06-264.1 [Article]