Variability in red snapper otolith microchemistry among Gulf of Mexico regions
Red snapper, Lutjanus campechanus, has been an economically important reef fish in the Gulf of Mexico (Gulf) for over 150 years and is currently overfished. Catch statistics and demographic differences have lead to the population being categorized into eastern and western substocks divided by the Mississippi River, but data is recombined to set a Gulf-wide annual catch limit. The two objectives of this study were to apply otolith nursery chemical signatures to estimate red snapper mixing dynamics in the western Gulf, and to determine if signatures based upon trace metals associated with oil and gas platforms could discriminate between region and habitat of origin to further examine population connectivity. Nursery otolith signatures were developed from age-0 red snapper belonging to the 2005 - 2007 year classes and collected from six nursery regions in the Gulf (Florida, Alabama, Louisiana, Texas, Veracruz, and Campeche Banks). Year class-specific quadratic discriminant function analyses (QDFAs) distinguished nursery regions with 71 – 84% accuracy. Maximum likelihood analyses identified sources of sub-adult and adult red snapper sampled during the summer of 2006 - 2008 from the western Gulf and Mexico regions based on year class-specific otolith core chemical concentrations. Locally derived and Louisiana recruits were apparent among red snapper collected off Texas, but data were inconclusive to estimate connectivity between the western Gulf and Mexico regions. Otoliths of red snapper collected from platforms and other habitats off Alabama, Louisiana and Texas during the summer of 2007 and 2008 were analyzed to determine if platforms impart detectable signatures based on seventeen trace metals. Mean jackknifed classification accuracies from QDFAs indicated higher success for discriminating among regions (86%) than habitats (79%). Maximum likelihood analyses estimated region and habitat of origin of red snapper collected from natural habitats off Florida, Louisiana and Texas during the summer of 2009. Platform signatures were evident in otoliths from red snapper collected off Florida, a region devoid of platforms, possibly reflecting a western Gulf contribution to the eastern substock. The microchemical otolith signatures of western Gulf red snapper in this study demonstrated discrete regional populations with some interpopulation mixing, further supporting a metapopulation structure.
red snapper, otolith microchemistry, Gulf of Mexico, connectivity, habitat
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