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

Discrimination of Juvenile Red Snapper Otolith Chemical Signatures from Gulf of Mexico Nursery Regions

Age-0 red snapper Lutjanus campechanus from the 2005-2007 year-classes were sampled in six regions across the Gulf of Mexico (Gulf) to develop nursery signatures from otolith element : Ca ratios (Ba:Ca, Mg:Ca, Mn:Ca, Sr:Ca, and Li:Ca) and stable isotope delta values (delta C-13 and delta O-18). Element : Ca ratios were analyzed with sector field inductively coupled plasma mass spectrometry on dissolved right sagittae; isotope ratio mass spectrometry was employed to analyze pulverized left otoliths for delta C-13 and delta O-18. Otolith chemical signatures were significantly different among regions in each year. Year-class-specific quadratic discriminant function analysis (QDFA) distinguished nursery regions with an accuracy of 82% for 2005, 70% for 2006, and 72% for 2007. However, samples were not obtained from all six study regions in 2005 and 2006. A QDFA of all year-classes combined produced an overall classification accuracy of 70%, thus indicating that region-specific otolith chemical signatures from adjacent sampling years could be used as surrogates for regions where samples were not obtained in a given year

Application of Otolith Chemical Signatures to Estimate Population Connectivity of Red Snapper In the Western Gulf of Mexico

Otolith chemical signatures of Red Snapper Lutjanus campechanus from six nursery regions were used to estimate the sources of recruits to four sampling regions in the western Gulf of Mexico (Gulf) and to estimate whether postsettlement mixing of Red Snapper occurs between the U.S. and Mexican portions of the western Gulf. In a previous study, region-specific otolith signatures (element : Ca ratios: Ba:Ca, Mg:Ca, Mn:Ca, Sr:Ca, and Li:Ca; stable isotope delta values: δ13C and δ18O) were developed based on age-0 Red Snapper (2005–2007 year-classes) sampled from the six nursery areas. In the present study, subadult and adult Red Snapper (ages 1–3) belonging to those same year-classes were collected from four sampling regions within the western Gulf (two regions in U.S. waters; two regions along the Mexican continental shelf) during summer in 2006–2008. Left sagittal otoliths were used to age subadults and adults to the corresponding nursery year-classes, and right sagittal otoliths were cored for chemical analysis. Off the southwestern U.S. coast, the sampled age-1–3 Red Snapper included locally derived recruits as well as recruits from the northwestern Gulf nursery region. However, analytical results were inconclusive with respect to estimating the connectivity between Red Snapper populations in U.S. and Mexican waters of the western Gulf

Platform Recruited Reef Fish Phase 2: Do Platforms Provide Habitat that Increases the Survival of Reef Fishes?

This is a study to find out if offshore platforms provide habitat for overfished species such as Red Snapper

Resource Partitioning of Sympatric Lutjanids in the Northern Gulf of Mexico Using Stable Isotope Analysis

Lutjanid snappers are ubiquitous at reef sites in the northern Gulf of Mexico (Gulf), but the degree of niche overlap and basal resource utilization is unknown for most species. Muscle tissue for stable isotope analysis was opportunistically sampled from red snapper (Lujanus campechanus), gray snapper (Lutjanus griseus), lane snapper (Lutjanus synagris), and vermilion snapper (Rhomboplites aurorubens) recreational catches across the northern Gulf. A Bayesian mixing model used to compare resource utilization indicated that Lutjanids occupy niches with varying degrees of overlap among regions but maintain a consistent hierarchy in isotopic composition. Scale shifts among regions were likely due to differences in riverine outflow, nitrogen fixation, and anoxic zones that alter prey abundance or isotopic d(15)N ratios. All four Lutjanid species had high percent contributions from particulate organic matter and benthic microalgae with little contribution by macroalgae to any species in any region. Ontogenetic shifts in stable isotope values were observed in most species indicating that size plays an important role in avoiding niche overlap due to intense competition for high-value prey items among congeners at isolated reef sites. Diet specialization is modest but likely plays an important role in avoiding complete niche overlap

Interspecific variation in juvenile snapper otolith chemical signatures in the northern Gulf of Mexico

The objective of this study was to evaluate whether age-0 lane snapper Lutjanus synagris otolith chemical signatures could serve as accurate proxies for those of its congener, red snapper L. campechanus, among northern Gulf of Mexico (GOM) nursery regions. Red (n = 90) and lane (n = 53) snappers were sampled from 3 regions of the northern GOM in fall 2005, and their otolith chemistry was analyzed with sector field-inductively coupled plasma-mass spectrometry (Ba:Ca, Mg:Ca, Mn:Ca, Sr:Ca, Li:Ca) or stable isotope ratio-mass spectrometry (δ13C and δ18O). Chemical signatures were significantly different among regions (MANOVA, p < 0.001) and between species (MANOVA, p = 0.029), with the species effect being driven by significant differences in 4 of the 7 constituents analyzed (ANOVA, p < 0.036). The significant region effect persisted (MANOVA, p < 0.001), but the species effect was non-significant (MANOVA, p = 0.964) when constituent values were normalized to species-specific means. Mean regional classification accuracies from linear discriminant functions computed with otolith constituent data were 84% for lane snapper and 80% for red snapper whether data were normalized or not. Maximum likelihood models parameterized with normalized lane snapper otolith chemistry data estimated red snapper regional composition reasonably well among mixed-region samples (mean error = 9.7% among models). Therefore, it appears age-0 lane snapper otolith chemical signatures can serve as accurate proxies for those of red snapper in the northern GOM. These results have broader implications for deriving natural tags based on otolith chemistry for fishes that may have low abundance in parts of their range

Interspecific Variation In Juvenile Snapper Otolith Chemical Signatures In the Northern Gulf of Mexico

The objective of this study was to evaluate whether age-0 lane snapper Lutjanus synagris otolith chemical signatures could serve as accurate proxies for those of its congener, red snapper L. campechanus, among northern Gulf of Mexico (GOM) nursery regions. Red (n = 90) and lane (n = 53) snappers were sampled from 3 regions of the northern GOM in fall 2005, and their otolith chemistry was analyzed with sector field-inductively coupled plasma-mass spectrometry (Ba:Ca, Mg:Ca, Mn:Ca, Sr:Ca, Li:Ca) or stable isotope ratio-mass spectrometry (δ13C and δ18O). Chemical signatures were significantly different among regions (MANOVA, p \u3c 0.001) and between species (MANOVA, p = 0.029), with the species effect being driven by significant differences in 4 of the 7 constituents analyzed (ANOVA, p \u3c 0.036). The significant region effect persisted (MANOVA, p \u3c 0.001), but the species effect was non-significant (MANOVA, p = 0.964) when constituent values were normalized to species-specific means. Mean regional classification accuracies from linear discriminant functions computed with otolith constituent data were 84% for lane snapper and 80% for red snapper whether data were normalized or not. Maximum likelihood models parameterized with normalized lane snapper otolith chemistry data estimated red snapper regional composition reasonably well among mixed-region samples (mean error = 9.7% among models). Therefore, it appears age-0 lane snapper otolith chemical signatures can serve as accurate proxies for those of red snapper in the northern GOM. These results have broader implications for deriving natural tags based on otolith chemistry for fishes that may have low abundance in parts of their range

Taxonomic composition, abundance and habitat associations of squid paralarvae in the northern Gulf of Mexico

Summer plankton surveys were conducted in 2015–2017 to characterize the distribution and abundance of squid paralarvae in epipelagic waters of the northern Gulf of Mexico (Gulf). Paralarvae present at stations sampled were from 12 families, with the most abundant being Ommastrephidae (flying squids), Enoploteuthidae (armed squids) and Onychoteuthidae (hooked squids). Mean density and percent frequency of occurrence for squid paralarvae across all surveys was 8.8 paralarvae 1000 m−3 and 76%, respectively. Julian day, salinity, sea surface height (SSH) and time of day were identified as influential environmental variables in generalized additive models (GAMs). Paralarval densities peaked during early morning and late evening sampling times, which is in accord with diel vertical migration patterns. Densities increased in early July, in areas with low SSH and lower salinity (28–35 psu), indicating upwelling areas and proximity to inflow from the Mississippi River represent productive early life habitats for squid. Results suggest that oceanic squid spawn in the northern Gulf in the summer exploiting the position of mesoscale oceanographic features and the extension of freshwater discharges from the Mississippi River

Spatial distribution and movement of Atlantic tarpon (Megalops atlanticus) in the northern Gulf of Mexico

Atlantic tarpon (Megalops atlanticus) are capable of long-distance migrations (hundreds of kilometers) but also exhibit resident behaviors in estuarine and coastal habitats. The aim of this study was to characterize the spatial distribution of juvenile tarpon and identify migration pathways of adult tarpon in the northern Gulf of Mexico. Spatial distribution of juvenile tarpon was investigated using gillnet data collected by Texas Parks and Wildlife Department (TPWD) over the past four decades. Generalized additive models (GAMs) indicated that salinity and water temperature played a significant role in tarpon presence, with tarpon occurrences peaking in the fall and increasing over the past four decades in this region. Adult tarpon caught off Texas (n = 40) and Louisiana (n = 4) were tagged with acoustic transmitters to characterize spatial and temporal trends in their movements and migrations. Of the 44 acoustic transmitters deployed, 18 of the individuals were detected (n = 16 west of the Mississippi River Delta and n = 2 east of the Mississippi River Delta). Tarpon tagged west of the Mississippi River Delta off Texas migrated south in the fall and winter into areas of south Texas and potentially into Mexico, while individuals tagged east of the delta migrated into Florida during the same time period, suggesting the presence of two unique migratory contingents or subpopulations in this region. An improved understanding of the habitat requirements and migratory patterns of tarpon inhabiting the Gulf of Mexico is critically needed by resource managers to assess the vulnerability of each contingent to fishing pressure, and this information will guide multi-state and multi-national conservation efforts to rebuild and sustain tarpon populations

Spatial distribution and movement of Atlantic tarpon (Megalops atlanticus) in the northern Gulf of Mexico.

Atlantic tarpon (Megalops atlanticus) are capable of long-distance migrations (hundreds of kilometers) but also exhibit resident behaviors in estuarine and coastal habitats. The aim of this study was to characterize the spatial distribution of juvenile tarpon and identify migration pathways of adult tarpon in the northern Gulf of Mexico. Spatial distribution of juvenile tarpon was investigated using gillnet data collected by Texas Parks and Wildlife Department (TPWD) over the past four decades. Generalized additive models (GAMs) indicated that salinity and water temperature played a significant role in tarpon presence, with tarpon occurrences peaking in the fall and increasing over the past four decades in this region. Adult tarpon caught off Texas (n = 40) and Louisiana (n = 4) were tagged with acoustic transmitters to characterize spatial and temporal trends in their movements and migrations. Of the 44 acoustic transmitters deployed, 18 of the individuals were detected (n = 16 west of the Mississippi River Delta and n = 2 east of the Mississippi River Delta). Tarpon tagged west of the Mississippi River Delta off Texas migrated south in the fall and winter into areas of south Texas and potentially into Mexico, while individuals tagged east of the delta migrated into Florida during the same time period, suggesting the presence of two unique migratory contingents or subpopulations in this region. An improved understanding of the habitat requirements and migratory patterns of tarpon inhabiting the Gulf of Mexico is critically needed by resource managers to assess the vulnerability of each contingent to fishing pressure, and this information will guide multi-state and multi-national conservation efforts to rebuild and sustain tarpon populations