OCS Study

BOEM 2013-0120

Coastal Marine Institute

U.S. Department of the Interior

Bureau of Ocean Energy Management

Gulf of Mexico OCS Region

Cooperative Agreement

Coastal Marine Institute

Louisiana State University

Platform Recruited Reef Fish Phase II: Do

Platforms Provide Habitat that Increases the

Survival of Reef Fishes?
 

OCS Study 

BOEM 2013-0120 

Coastal Marine Institute

Platform Recruited Reef Fish, Phase II: Do 

Platforms Provide Habitat that Increases 

the Survival of Reef Fishes? 

Authors: 

Michelle Zapp Sluis 

James H. Cowan, Jr. 

October 2013 

Prepared under BOEM Contract 

M08AX12679 

by 

The Department of Oceanography and Coastal Sciences 

School of the Coast and Environment 

Louisiana State University 

Baton Rouge, LA 70803-6513 

Published by 

U.S. Department of the Interior

Bureau of Ocean Energy Management 

Gulf of Mexico OCS Region 

New Orleans, Louisiana 

Coastal Marine Institute 

Louisiana State University 

Baton Rouge, Louisiana 
iii

DISCLAIMER

This report was prepared under contract between the Bureau of Ocean Energy Management 

(BOEM) and Louisiana State University. This report has been technically reviewed by BOEM, 

and it has been approved for publication. Approval does not necessarily signify that the contents 

reflect the views and policies of BOEM, nor does mention of trade names or commercial 

products constitute endorsement or recommendation for use.

REPORT AVAILABILITY

To download a PDF file of this Gulf of Mexico OCS Region report, go to the U.S. 

Department of the Interior, Bureau of Ocean Energy Management, Environmental Studies 

Program Information System website and search on OCS Study BOEM 2013-0120.

This report can be viewed at select Federal Depository Libraries. It can also be obtained 

from the National Technical Information Service; the contact information is below.

U.S. Department of Commerce

National Technical Information Service

5301 Shawnee Rd.

Springfield, Virginia 22312

Phone: (703) 605-6000, 1(800)553-6847

Fax: (703) 605-6900

Website: http://www.ntis.gov/

CITATION

Zapp Sluis, M. and J.H. Cowan, Jr. 2013. Platform recruited reef fish phase II: Do platforms 

provide habitat that increases the survival of reef fishes? U.S. Dept. of the Interior, Bureau of 

Ocean Energy Management, Gulf of Mexico OCS Region, New Orleans, LA. OCS Study 

BOEM 2013-0120 43 pp.

ABOUT THE COVER

On the cover is an image of platform “EI 346A” located in the Gulf of Mexico at Eugene 

Island Block 346. Image by Courtney Saari, Louisiana State University.
v

ACKNOWLEDGEMENTS

This project would not have been possible without funding by the Bureau of Ocean Energy 

Management (BOEM) through the Department of Oceanography and Coastal Sciences at 

Louisiana State University. We would like to thank Dave Nieland, Kirsten Simonsen, Melissa 

Hedges Monk, Kevin Boswell, Andy Fischer, Courtney Saari, Dannielle Kulaw, Shaye Sable, 

Steven Garner, Kim de Mutsert, Joris van der Ham, Brian Roth, Laura Heil, Elise Roche, Arie 

Roth Kaller, Michael McDonough, Shane Abeare, and Robert Ellis for help with field and 

laboratory work. We are indebted to Steve Tomeny Charters, Captain Mike Thierry Charters, 

Fisherman’s Wharf Deep Sea Fishing, NMFS Vertical Longline Surveys, the Dauphin Island 

Deep Sea Fishing Rodeo Jaycees, and several other charter boat captains and recreational fishers 

that graciously allowed us to sample their catch. Otolith, sediment and bivalve chemical analysis 

was performed through the guidance and expertise of Drs. Alan Shiller and Ilia Rodushkin. 

Finally, we would like to thank Dr. Maureen Mulino and anonymous reviewers from BOEM for 

their constructive criticism of this manuscript.
vii

ABSTRACT

Red snapper, Lutjanus campechanus, has been an economically important reef fish in the 

Gulf of Mexico (Gulf) for over 150 years; it is currently overfished. Catch statistics and 

demographic differences have led 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. During an initial pilot study, it was determined that Louisiana oil and gas platforms

impart detectable signatures in otoliths. Unique signatures were also detected for artificial reefs 

east and west of the Mississippi River. The objectives of this study were to determine if 

signatures based on trace metals associated with oil and gas platforms were geographically and 

temporally stable, and if the signatures could discriminate between region and habitat of origin to 

further examine population connectivity. Otoliths of red snapper (n = 1,778) collected from 

platforms and other habitats off Alabama, Louisiana, and Texas during the summers of 2007 and 

2008 were analyzed with sector field-inductively coupled plasma-mass spectrometry (SF-ICPMS) to determine if platforms impart detectable signatures based on seventeen trace metals.

Otolith chemical signatures were significantly different among regions and habitats (MANOVA, 

p < 0.001). Mean jackknifed classification accuracies from QDFAs indicated higher success for 

discriminating among regions (86%) than habitats (79%). These otolith chemical signatures were 

used as ‘baseline’ samples in maximum likelihood mixed-stock analyses to estimate region and 

habitat of origin of red snapper (n = 487) 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.
ix 

TABLE OF CONTENTS 

LIST OF FIGURES ..................................................................................................................................... xi

LIST OF TABLES ..................................................................................................................................... xiii

1. INTRODUCTION .................................................................................................................................. 1

1.1. Offshore Platforms .......................................................................................................................... 1

2. METHODS ............................................................................................................................................. 3

2.1. General ........................................................................................................................................ 3

2.2. Barnacle and Sediment Collection .............................................................................................. 5

2.3. Mixed Sample Collection ............................................................................................................ 5

2.4. Otolith Preparation and Analysis ................................................................................................ 6

2.5. Barnacle Preparation and Analysis ............................................................................................. 7

2.6. Sediment Preparation and Analysis ............................................................................................ 7

2.7. Statistical Analysis ...................................................................................................................... 8

3. RESULTS ............................................................................................................................................... 9

3.1. Baseline Red Snapper ................................................................................................................. 9

3.2. Mixed Red Snapper ................................................................................................................... 17

3.3 Barnacle and Sediment .............................................................................................................. 23

4. DISCUSSION ....................................................................................................................................... 25

LITERATURE CITED ............................................................................................................................... 33

APPENDIX: SUPPLEMENTARY CANONICAL DATA ....................................................................... 41
xi

LIST OF FIGURES

Figure 1. Sampling regions along the continental shelf of the northern Gulf of Mexico 

(Gulf) where adult red snapper, Lutjanus campechanus, were sampled on 

platform and non-platform habitats during the summers of 2007 and 2008. ............. 4

Figure 2. Sampling regions along the continental shelf of the northern Gulf of Mexico 

(Gulf) where adult red snapper, Lutjanus campechanus, were sampled on natural 

habitat during the summer of 2009............................................................................. 6

Figure 3. Jackknifed classification percentages of red snapper, Lutjanus campechanus, to 

six locations, three regions and two habitats in the Gulf of Mexico collected 

during the summers of 2007 and 2008. .................................................................... 13

Figure 4. Canonical plot scores derived from otolith chemical signatures of red snapper, 

Lutjanus campechanus, collected from six locations in the Gulf of Mexico 

during the summers of 2007 and 2008. .................................................................... 14

Figure 5. Canonical plot scores derived from otolith chemical signatures of red snapper, 

Lutjanus campechanus, collected from three regions in the Gulf of Mexico 

during the summers of 2007 and 2008. .................................................................... 15

Figure 6. Canonical plot scores derived from otolith chemical signatures of red snapper, 

Lutjanus campechanus, collected from two habitats in the Gulf of Mexico during 

the summers of 2007 and 2008................................................................................. 16

Figure 7. Bubbleplots of percent composition estimates derived from region-, habitat- and 

location-specific otolith chemistry-based discriminant function analysis indicate 

the origin of adult red snapper, Lutjanus campechanus, collected from four 

regions and two habitat types within the Gulf of Mexico during the summer of 

2009. ......................................................................................................................... 21

Figure 8. Bubbleplots of percent composition estimates derived from habitat-specific 

otolith chemistry-based discriminant function analysis using A.) all 17 elements 

or B.) only 11B, 138Ba, 120Sn, and 51V to indicate the habitat of origin of adult 

gray triggerfish, Balistes capriscus, collected from two regions representing two 

habitat types within the Gulf of Mexico during the summer of 2009.. .................... 22

Figure 9. Multidimensional scaling analysis (MDS) plot displaying variation in elemental 

concentrations of barnacles, red snapper otoliths and sediments collected from 

platforms off Louisiana during the summers of 2007 and 2008............................... 24
xiii

LIST OF TABLES

Table 1. Sample size and size range of red snapper, Lutjanus campechanus, collected 

from three regions across the Gulf of Mexico during the summers of 2007 and 

2008. AL = Alabama; LA = Louisiana; TX = Texas; P = platform habitat; NP = 

non-platform habitat. ................................................................................................ 10

Table 2. Summary of raw data for region and habitat otolith elemental concentrations (ppb) 

for red snapper (Lutjanus campechanus), collected from the Gulf of Mexico 

during the summers of 2007 and 2008. Values in bold represent significantly 

higher values. AL= Alabama; LA=Louisiana; TX= Texas; P=platform habitat; 

NP= non-platform habitat......................................................................................... 11

Table 3. Sample size and size range of red snapper, Lutjanus campechanus, and gray 

triggerfish, Balistes capriscus, collected from the Gulf of Mexico during the 

summer of 2009. DFL = Destin, Florida; TFL = Tampa, Florida; LA = 

Louisiana; TX = Texas. ............................................................................................ 18

Table 4. Summary of raw data of otolith elemental concentrations (ppb) for red snapper, 

Lutjanus campechanus, and gray triggerfish, Balistes capriscus, collected from 

the Gulf of Mexico during the summer of 2009. Bold numbers represent 

significantly higher concentrations in regions. DFL = Destin, Florida; TFL = 

Tampa, Florida; LA = Louisiana; TX = Texas......................................................... 19

Table 5. Summary of raw data for barnacle, red snapper (Lutjanus campechanus) otolith, and 

sediment elemental concentrations (ppb) collected from platforms off Louisiana 

during the summers of 2007 and 2008 ..................................................................... 24

Table A.1. Raw canonical coefficients for canonical discriminant analysis comparing 

location, region and habitat otolith chemical signatures of red snapper, Lutjanus 

campechanus, from three regions and two habitats in the Gulf of Mexico during 

the summers of 2007–2008....................................................................................... 42
1

1. INTRODUCTION

1.1. OFFSHORE PLATFORMS

In 1947, Kerr-McGee Oil Industries installed the first offshore oil well 70 km south of 

Morgan City, Louisiana (LA) in 5.6 m of water (Kasprzak, 1998). Today, according to estimates 

by the Bureau of Ocean Energy Management (BOEM), there are approximately 4,000 offshore 

oil and gas production platforms in the Gulf of Mexico (Gulf), with a majority located off the 

coast of Louisiana. The addition of production platforms to the northern Gulf has resulted in the 

largest unplanned artificial reef complex, perhaps in the world, which has increased reef habitat 

by 4.1% (10.4% for LA alone; Stanley and Wilson, 2003) to an ecosystem composed primarily 

of mud and sand substrate (Parker et al., 1983). While there has been support for artificial reef 

development, debates about their effectiveness still persist. Do artificial reefs produce new fish 

biomass or are fish simply attracted to them because of behavioral preferences? If artificial reefs 

are providing new habitat in a substrate-limited environment, they could potentially help increase 

fisheries production. However, if fish are aggregating to new, well-marked habitat (i.e.,

platforms) without producing new biomass, then unmanaged fishing could lead to a decline in 

reef-associated fish stocks. When overfishing becomes a problem, platforms are less likely to 

increase production, and instead make remaining fish populations more vulnerable to fishing 

pressures (Bohnsack, 1989).

Red snapper, Lutjanus campechanus, is a commercially important reef-associated fish in the 

Gulf; it is currently overfished due to high exploitation rates of directed and shrimp fisheries 

(GMFMC, 2010). Typical of reef-associated fish, red snapper tend to aggregate near structured 

environments on the sea floor, but are not dependent on such habitat to complete their life cycle.

Newly settled juveniles are attracted to low-profile reefs, relic-shell habitats and adjacent mudsand bottom habitats (Rooker et al., 2004; Szedlmayer and Howe, 1997; Wells et al., 2008a). As 

red snapper mature, a natural ontogentetic shift in habitat occurs, which results in movement to 

more complex natural and artificial reef habitats, including oil and gas platforms. Although it has 

been observed that red snapper recruit to platforms as early as age-1, platform populations are 

primarily dominated by age-2 and age-3 fish (Nieland and Wilson, 2003; Gitschlag et al., 2003).

It is unclear if this recruitment pattern is attributable to attraction or production. The decrease in 

individuals older than age-3 on platforms may be caused by emigration, low site fidelity, or 

reduced recruitment of older fish. However, by age-2 and age-3 red snapper enter the directed 

fishery and high fishing pressure at platforms may result in fewer older individuals at these 

habitats (Nieland and Wilson, 2003; Patterson, 2007). Therefore, further research to examine 

recruitment and movement patterns associated with platforms could prove beneficial to red 

snapper management strategies. 

According to Bohnsack (1989), the attraction compared with the production debate is not that 

simple, but instead involves a continuum of factors, including site fidelity, habitat availability, 

recruitment limitation, and fishing pressure. Artificial reefs are likely to increase production if 

fish are habitat-limited rather than recruitment-limited, not experiencing overfishing, and exhibit 

high site fidelity. Red snapper production in the Gulf does not appear to be limited by habitat, 

especially when considering that natural habitats supported the population before it was heavily 

exploited (Cowan et al., 1999; Lindberg, 1997). The association of red snapper with artificial 

reefs may actually make them more vulnerable to fishing pressure by concentrating them to wellmarked areas more accessible to commercial and recreational fishers (Bohnsack, 1989; Cowan et 
2

al., 2010). Furthermore, red snapper annual site fidelity is estimated to range between 25–60% 

for fish associated with artificial reefs off the Alabama (AL) coast (Patterson and Cowan, 2003; 

Schroepfer and Szedlmayer, 2006; Strelcheck et al., 2007). Nonetheless, data suggest that as red 

snapper recover from overfishing, populations are also showing signs of recovery on the west 

Florida (FL) and south Texas (TX) continental shelf (SEDAR, 2009). It is unknown if population 

expansions off west FL and south TX are caused by self recruitment in response to stricter 

management strategies, or if regions with higher abundance are supplying recruitment subsidies, 

as conventional tagging studies suggest (Patterson et al., 2001a; Addis et al., 2008). If other 

regions are supplying recruits, it is unknown if artificial reefs contributed production.

Problems associated with conventional tagging (Patterson, 2007) can cause red snapper 

movement to be underestimated. For this reason, among fishery scientists the use of otolith (ear 

stone) microchemistry to develop natural tags has become an effective tool for examining

movement patterns of adult stocks (Gillanders and Kingsford, 1996; Thorrold et al., 2001; 

Rooker et al., 2008). To achieve this, nursery signatures are developed by analyzing elemental 

and stable isotope concentrations accreted onto juvenile fish otoliths from surrounding waters.

Since the otolith precipitates as the fish grows and is metabolically inert (Campana, 1999), the 

juvenile portion, or core, of an otolith can be used to identify the nursery of origin of an adult 

fish and thus be used to examine movement patterns. However, nursery signatures in otoliths 

based on the usual suite of elements examined (Ba, Li, Mg, Mn, Sr) can differ among years, due 

to temporal variability in temperature, salinity and water mass characteristics (Gillanders and 

Kingsford, 2000; Rooker et al., 2001), requiring cohort specific signatures to be identified.

Spencer et al. (2000) determined that lead isotopes based on anthropogenic sources could be 

detected in otoliths and used to reconstruct the nursery of origin in Hawaiian estuaries. Thus, it 

may be possible to avoid chemical concentration variations of elements in otoliths by 

establishing signatures based on a known anthropogenic source in a particular area. 

Oil spills, drilling fluids and cuttings, produced water, protective antifouling paints and 

sacrificial anodes associated with oil and gas platforms all have the potential to release toxic 

chemicals into the surrounding water column and sediments. Several trace metals found in 

drilling fluids and produced waters (Ag, Ba, Be, Cd, Cr, Cu, Fe, Ni, Pb and Zn) have been 

detected at significantly higher levels than natural marine sediments and seawater (Neff et al.,

1987). In a pilot study, Nowling et al. (2011) tested whether oil and gas platforms impart a 

detectable signature in the otoliths of adult red snapper. That study proved successful in 

identifying unique otolith chemical signatures for oil and gas platforms off the LA coast, as well 

as unique signatures for artificial reefs east and west of the Mississippi River. Using such 

signatures can help examine population connectivity of older red snapper in the northern Gulf.

Furthermore, if a platform signature is evident in otoliths of fish collected in areas devoid of 

platforms, such as FL, it may indicate some contribution of platform-reared recruits.

Red snapper annual site fidelity is estimated to range between 25–60% for fish associated 

with artificial reefs off the AL coast (Patterson and Cowan, 2003; Schroepfer and Szedlmayer,

2006; Strelcheck et al., 2007). The relatively low site fidelity of red snapper (Patterson and 

Cowan, 2003), along with close proximity of other habitat types within the study region 

(McDonough, 2009; Westmeyer et al., 2007), may result in low classification success when 

developing habitat signatures. Gray triggerfish (Balistes capriscus) is another reef-associated fish 

that is known to display high site fidelity with limited dispersion from reefs (63–87%) per year 

for AL artificial reefs (Ingram, 2001). Based on these traits, Ingram and Patterson (2001) 

concluded that gray triggerfish would benefit more from artificial habitat established within 
3

marine protected areas than would red snapper. Additionally, higher site fidelity of gray 

triggerfish would make it a better candidate for testing the accuracy of the platform otolith 

signature.

The two main objectives of this study were to (1) determine if oil and gas platforms impart 

detectable chemical signatures in red snapper otoliths collected from a broader geographical 

range over two years, and (2) to apply these otolith chemical signatures to estimate region and 

habitat of origin for adult red snapper collected from areas devoid of platforms. Specifically, 

natural tags derived from otolith trace metal concentrations were used to examine temporal and 

geographical stability of platform signatures among three regions and two habitats on the 

continental shelf of the northern Gulf. Region- and habitat-specific chemical signatures were 

developed to determine if discriminant classifications were strong enough to validate the use of 

platform signatures to estimate the percent contribution of platform-reared recruits to regions 

devoid of platforms. 

At this time, barnacle and sediment samples were collected from and near platform piles to 

determine the pathway of incorporation of the platform elemental fingerprint into red snapper 

otoliths. If otolith signatures were similar to elemental signatures of barnacle shells, then the 

source of incorporation may be derived from the water column. If otolith signatures resemble 

elemental signatures of sediments, then the source of incorporation may be derived from 

bioavailable metals in the sediment. Natural tags derived from otolith trace metal concentrations 

of red snapper collected from platform and non-platform habitats from three regions in the Gulf 

were compared to otolith concentrations of adult red snapper collected from natural habitats in 

the western Gulf and from areas devoid of oil and gas development in the eastern Gulf. Otolith 

trace metal concentrations of gray triggerfish collected from platform and non-platform habitats 

were also analyzed to test the accuracy of the platform otolith signature. The goal was to use 

regional signatures to further examine red snapper population connectivity among Gulf regions, 

and use platform signatures to estimate the contribution of platform-reared recruits to regions 

devoid of platforms.

2. METHODS

2.1. GENERAL

Red snapper were collected during the summers 2007 and 2008 off the coasts of Port Aransas 

and Galveston, TX, Port Fourchon, LA, and Dauphin Island, AL (Figure 1). Within LA, samples 

were collected in the Ship Shoal (SS), South Timbalier (ST) and Grand Isle (GI) federal (BOEM) 

mineral leasing areas. The objective was to collect 1,000 red snapper each year, with 300 from 

TX, 500 from LA and 200 from AL. Fish were collected from two habitat types within each 

region: oil and gas platforms (both standing and toppled) and non-platform habitats (natural 

bottom, artificial cement reefs, and wrecks). It is important to note that decommissioned oil and 

gas platforms that had been toppled to serve as artificial reefs were still categorized as platform 

because potential contaminants would remain in the area. Fish collected within 50 m of oil and 

gas platforms were also categorized as being collected from platforms. Red snapper samples 

were collected from recreational landings, the Dauphin Island Deep Sea Fishing Rodeo, 

sampling trips aboard the R/V Acadiana, and the National Marine Fisheries Service’s (NMFS) 

Vertical Longline Survey.

Due to large sample sizes, red snapper otolith extraction occurred in the field. These otoliths 

will be used to develop regional and platform chemical signatures, and are thus referred to as 
4

“baseline” samples. Both sagittae were extracted, rinsed free of associated tissue with deionized 

(DI) water, and stored in individual paper coin envelopes until further laboratory analysis. Fish 

total lengths (TL) were measured to the nearest mm; however, measurements were not obtained 

for 451 individuals (23% of all individuals sampled). Estimated fish length was calculated based 

on power relationships between TL and otolith weight (mg; Pawson, 1990). Total length was 

strongly correlated with otolith weight in red snapper (y = 16.487x0.530, r

2 = 0.947) and this 

relationship was used to approximate TL of the individuals that were not directly measured in the 

field. Red snapper with a TL between 250 – 650 mm were targeted to obtain a majority of fish

between ages two through six years (Fischer et al. 2004; Saari, 2011) between ages two through 

six years (Fischer et al., 2004; Saari, 2011).

Figure 1. Sampling regions along the continental shelf of the northern Gulf of Mexico (Gulf) 

where adult red snapper, Lutjanus campechanus, were sampled on platform and 

non-platform habitats during the summers of 2007 and 2008.
5

2.2. BARNACLE AND SEDIMENT COLLECTION

During the summers of 2007 and 2008, 50 barnacle samples and 50 sediment samples were 

collected from LA oil and gas platforms each year. Barnacle samples were dislodged from 

platform piles (legs) using a boat hook and rubber landing net. Sediment samples were collected 

near platform piles using a Teflon®-coated ponar grab. A plastic scoop was used to collect 

sediment samples from the center of the ponar grab sample to minimize contamination risks.

Once barnacle and sediment samples were collected, they were placed in WhirlPak® bags and 

stored on ice until arrival to the laboratory where they were stored in an ultra-low freezer at 80oC 

until processed.

2.3. MIXED SAMPLE COLLECTION

Adult red snapper were collected during the summer of 2009 off the coasts of South Padre 

Island, TX; Port Fourchon, LA; Destin, FL (DFL); and Tampa, FL (TFL; Figure 2). The 

objective was to collect 500 red snapper total with 100 coming from TX, 100 from LA and 300 

combined from the two FL regions. Red snapper were collected from recreational landings and 

sampling trips aboard a research vessel. To test the effectiveness of regional and platform 

signatures developed from red snapper otolith (baseline) samples collected in 2007 and 2008, 

adult red snapper (mixed) samples collected in 2009 were targeted on natural habitat or other 

habitats in areas devoid of oil and gas platforms. Red snapper in TX were collected on natural 

rock outcrops, LA samples were collected on shelf edge banks (Alderdice Bank, Bouma Bank 

and Jakkula Bank), DFL samples were collected on natural habitat, artificial reefs and wrecks, 

and TFL samples were collected on the FL middle grounds. Both red snapper sagittae were 

extracted in the field, rinsed free of associated tissue with deionized (DI) water and stored in 

individual plastic coin envelopes until further laboratory analysis. Fish total lengths (TL) were 

measured to the nearest mm. In attempt to collect older individuals that are more likely to have 

migrated away from platforms, red snapper with a TL greater than 500 mm were targeted to 

obtain a majority of fish that were older than age-5 (Fischer et al. 2004; Saari 2011).
6

Figure 2. Sampling regions along the continental shelf of the northern Gulf of Mexico 

(Gulf) where adult red snapper, Lutjanus campechanus, were sampled on 

natural habitat during the summer of 2009.

Gray triggerfish also were collected during the summer of 2009 off the coasts of Port 

Fourchon, LA and DFL. To determine if the platform signature was valid for other species, gray 

triggerfish were targeted on platforms (Eugene Island mineral leasing area; LA) and natural 

habitat (DFL). Gray triggerfish were collected from recreational landings and sampling trips 

aboard a research vessel. Fish TLs were measured in the field to the nearest mm. Heads were 

removed in the field and frozen until further laboratory processing. In the laboratory, both 

sagittae were extracted, rinsed free of associated tissue with deionized (DI) water, and stored in 

cell trays until further analysis.

2.4. OTOLITH PREPARATION AND ANALYSIS

In the laboratory, all sagittae were cleaned with a synthetic bristle brush to remove any 

adhering tissue, rinsed with DI water, and placed in polyethylene vials to air-dry under a class100 clean hood. The rest of the procedures occurred in a class-100 clean room under laminar 

flow using acid-washed supplies. Materials and solution blanks were tested before sample 

preparation to ensure there were no sources of contamination. Right sagittae were selected for 

trace elemental analysis for the following elements: 107Ag, 109Ag, 27Al, 11B, 138Ba, 209Bi, 111Cd, 

114Cd, 59Co, 63Cu, 65Cu, 56Fe, 7

Li, 55Mn, 98Mo, 60Ni, 206Pb, 123Sb, 120Sn, 205Tl, 238U, 51V, 64Zn, 

66Zn. Before and after cleaning, dry otoliths were weighed to the nearest 0.01 mg. Whole otoliths 

were immersed in 1% ultra-pure nitric acid (HNO3) for 5 minutes to remove surface 

contamination. The otolith was then rinsed with double deionized water (ultra-pure 18 MΩ cm-1 

water; DDIH2O) to remove any remaining acid and dried under a class-100 clean hood for 24 

hours. Otoliths remained in acid-leached polystyrene Falcon® tubes during the entire cleaning 

process. Once otoliths were dried and reweighed, the tubes were capped and placed in double 

Ziploc® bags. Otolith samples, along with blanks prepared from 1% ultra-pure HNO3 and 
7

processed through the same stages of sample preparation, were sent to the Scandinavia ALS 

Laboratory Group in Luleå, Sweden for total digestion and trace elemental analysis. 

Once samples arrived at the ALS laboratory, otoliths were transferred to individual acid 

washed Teflon vessels and 2 ml of concentrated ultrapure HNO3 was added. When dissolution 

was completed (30–45 minutes), a second 2 ml aliquot of HNO3 was added. After one hour, 6 ml 

of DDIH2O was added to the vessels and digested solutions were transferred to acid washed 15 

ml polypropylene tubes. Samples were not manipulated for the next 24 hours, at which point 

digested solutions were further diluted using 1.4 M HNO3 in DDIH2O to obtain a final dilution 

factor of 1,000 to 1,500-fold. All sample preparation was performed in a clean laboratory with a 

constant supply of HEPA-filtrated air. Diluted digests were analyzed with a Thermoscientific 

Element2 sector field-inductively coupled plasma-mass spectrometer (SF-ICP-MS) using an AllTeflon introduction system, self-aspiration and methane addition to plasma. Both low resolution 

(LR) and medium mass resolution (MR) acquisition modes were used. At least two preparation 

blanks were analyzed concurrently with each batch of 56 otolith sample solutions to estimate 

instrument limits of detection (LOD), which were estimated as three standard deviations of mean 

blank values. The combination of external calibrations (synthetic blanks and standards prepared 

in 1.4 M HNO3) and internal standardization (In and Lu added to all solutions at 200 ppt level) 

was employed for quantification. Detection and quantification capabilities were evaluated with 

results from preparation blanks.

2.5. BARNACLE PREPARATION AND ANALYSIS

Barnacle shell sections removed from “clusters” were rinsed with DI water and cleaned with 

a synthetic bristle brush to remove any adhering tissue. The barnacle shell fragments were then 

placed in polyethylene vials to air-dry under a class-100 clean hood for 24 hours. The rest of the 

procedures occurred in a class-100 clean room under laminar flow using acid-washed supplies.

Barnacle shell sections were cleaned and analyzed following the exact same procedures as 

otolith samples.

2.6. SEDIMENT PREPARATION AND ANALYSIS

In the laboratory, 5 g (wet weight) of each sediment sample were dried in a drying oven 

(Yamato, Orangeburg, New York; Model DX 600) at 105o

C for 24 hours. To homogenize the 

sample, the dry sediment was pulverized with an agate mortar and pestle. Next, 1g of dry 

sediment was added to 20 mL of 1M HCl, and placed on a hotplate stirrer at 30o

C for 1 hour. The 

sample was then centrifuged at 3500 rpm for 5 minutes. The supernatant was filtered through 

0.45μm polypropylene syringe filters. Finally, 1 mL of the filtered supernatant was stored in 

clear, acid-washed microcentrifuge tubes, packaged in double Ziploc® bags, and sent to the 

University of Southern Mississippi for high resolution-inductively coupled plasma-mass 

spectrometry (HR-ICP-MS) analysis. Sediment samples were analyzed for the following 

elements: 107Ag, 109Ag, 110Cd, 111Cd, 114Cd, 59Co, 63Cu, 65Cu, 60Ni, 62Ni, 206Pb, 207Pb, 208Pb, 238U, 

51V, 64Zn, 66Zn. Note: the University of Southern Mississippi was the initial laboratory of choice 

to analyze all of the samples. Although the sediment samples were able to be processed there, 

multiple mechanical failures and approaching deadlines resulted in the need to find a new 

laboratory (ALS) to process the samples. This also explains the slight variation in elements 

analyzed between sediment and otolith/barnacle samples. Sediment samples were analyzed by 

diluting 20x in 1% ultrapure HNO3. Blanks were prepared from 1% ultrapure HNO3 and 

processed through the same stages of sample preparation as sample solutions. Blanks were 
8

analyzed concurrently with sediment sample solutions to estimate instrument limits of detection 

(LOD), which were estimated as three standard deviations of mean blank values.

2.7. STATISTICAL ANALYSIS

To meet parametric assumptions, all data were ln transformed prior to statistical analysis.

Because a variety of ages was being examined simultaneously, residual values were analyzed in 

order to compensate for mass differences and ontogenetic shifts within otoliths of fish of varying 

ages (Pattersont and Patterson, 2010). Year-specific residual values were computed by 

subtracting mean elemental concentrations from each respective sample concentration.

For the baseline red snapper data set, multivariate analysis of variance (MANOVA) was used 

to test for differences in otolith elemental signatures among years, regions, and habitats, with 

Pillai trace (V) as the test statistic because it is the most robust to violations of homogeneity of 

variance (Wilkinson et al. 1996). No significant year differences were detected (MANOVA, F17, 

1755 = 0.12, p < 1.00); therefore, subsequent models were blocked by year. An analysis of 

variance (ANOVA) was used to test elemental concentrations individually to determine a source 

of variance among regions and between habitats. ANOVA’s were performed to examine 

significant effects of independent variables (region, habitat and their interaction), and were also 

used to assess significant levels of chemical signatures for each region and/or habitat. Reported 

values are based on least square (LS) means.

To determine which elements are the most significant in discriminating between regions, 

habitats and habitats within regions (from now on referred to as “location”), a stepwise 

discriminant analysis (SDA) was used. An SDA was used to find a set of the original quantitative 

variables that best discriminate among sites or groups. To distinguish regions, habitats and 

locations with otolith chemical signatures, discriminant function analyses were performed. As 

variance-covariance matrices of elemental and stable isotope variables were dissimilar between 

red snapper otolith samples from each region, habitat or location, a quadratic discriminant 

function analysis (QDFA) was used along with jackknifed cross validation classifications to 

quantify classification success to respective locations, regions, and habitats. A canonical 

discriminant analysis (CDA) was used to compare otolith chemical concentrations of each 

region, habitat and location. The CDA determines the best linear combination of quantitative 

variables where the means of the groups are most different and whether this difference varies by 

year class.

For the mixed red snapper data set, multivariate analysis of variance (MANOVA) was used 

to determine if differences existed in red snapper otolith elemental signatures between DFL and 

TFL, with Pillai trace (V) as the test statistic because it is the most robust to violations of 

homogeneity of variance (Wilkinson et al. 1996). This was done to determine if the regions 

needed to be analyzed separately or as a combined FL region. An analysis of variance (ANOVA) 

was used to test elemental concentrations individually to determine the source of variance among 

regions. Reported values are based upon least square (LS) means. All analyses were performed 

with the Statistical Analysis System (SAS Institute, 2006) with a significance level of p = 0.05.

A maximum likelihood -stock analysis “HISEA” developed by Millar (1990) was used to 

estimate the region, habitat, or location of origin of adult red snapper in areas devoid of 

platforms. The baseline data set consisted of residual values of red snapper otolith region, habitat 

and location signatures that are reported for samples collected in 2007 and 2008. The 2009 adult 

red snapper otolith data were classified as unknowns, or mixed data, against the baseline data to 

determine their presumed origin based on maximum likelihood estimates (MLE) of mixed-stock 
9

proportions. Mixed data for each region was classified individually into region-, habitat-, and 

location-specific baseline data. Direct MLE and standard deviations were developed in HISEA 

by bootstrapping with 1000 resampled baselines.

Multivariate analysis of variance (MANOVA) was used to determine if differences existed in 

gray triggerfish otolith elemental signatures between habitats, again using Pillai trace (V) as the 

test statistic. An analysis of variance (ANOVA) was used to test elemental concentrations 

individually, to determine the source of variance between habitats. Reported values are based on 

least square (LS) means. The HISEA model was used to determine if gray triggerfish otolith 

samples could be accurately classified to the habitat in which they were collected. The gray 

triggerfish otolith data were classified as mixed data against the red snapper otolith habitat 

signature baseline data to determine their presumed origin based on MLE of mixed-stock 

proportions. Mixed data for each habitat was classified individually into the habitat-specific 

baseline data in HISEA by bootstrapping with 1,000 resampled baselines.

Variation in trace metal concentrations between red snapper otoliths, barnacles, and 

sediments was compared using non-parametric methods available in the PRIMER multivariate 

data analysis package. Procedures were computed using a Bray-Curtis similarity matrix after 

log(x+1) transforming the elemental data. A multidimensional scaling analysis (MDS) was used 

to graphically represent differences in elemental concentrations between sample types. Samples 

spaced closer together have more similar elemental concentrations than samples spaced farther 

apart (Clarke and Warwick, 2001). An analysis of similarity (ANOSIM) was used to investigate

elemental concentrations among sample types. Finally, a similarity percentages (SIMPER) 

procedure was computed to determine which elements contribute to the similarity and 

dissimilarity among sample types. These tests were used to investigate possible sources of metal 

incorporation into the otolith.

3. RESULTS

3.1. BASELINE RED SNAPPER 

A total of 1,964 red snapper otolith samples collected from three regions across the Gulf was 

processed for otolith chemical analysis. However, due to poor sample quality or inadequate 

detection limits only 1,778 samples were used to determine otolith chemical signatures (Table 1).

Seven of the 24 elements (107Ag, 109Ag, 27Al, 114Cd, 60Ni, 123Sb, 238U) were below LOD and were 

discarded. The remaining 17 elements (11B, 138Ba, 209Bi, 111Cd, 59Co, 63Cu, 65Cu, 56Fe, 7Li, 55Mn, 

98Mo, 206Pb, 120Sn, 205Tl, 51V, 64Zn, 66Zn) were present in red snapper otoliths above LODs. The 

chemical signatures were significantly different among regions (MANOVA, F34, 3512 = 74.69, p < 

0.001), habitats (MANOVA, F17, 1755 = 21.52, p < 0.001), and locations (MANOVA, F34, 3512 = 

11.82, p < 0.001). 
10

Table 1.

Sample size and size range of red snapper, Lutjanus campechanus, collected from three regions across 

the Gulf of Mexico during the summers of 2007 and 2008. AL = Alabama; LA = Louisiana; TX = Texas; P 

= platform habitat; NP = non-platform habitat.

Sample Year Region Habitat Samples 

Collected

Samples 

Analyzed

Size Range 

(mm TL)

2007 AL P 92 86 251–613

NP 108 103 402–615

LA P 340 292 268–599

NP 160 144 248–611

TX P 238 218 286–596

NP 62 57 266–530

2008 AL P 82 77 281–625

NP 115 111 293–647

LA P 328 298 253–650

NP 139 119 326–642

TX P 267 243 284–513

NP 33 30 299–523

Mean concentrations of elements varied across regions and habitats (Table 2). Although all 

elemental concentrations differed significantly (ANOVA, p ≤ 0.05) among locations and regions 

overall, some elemental concentrations were not significantly different between two regions. For 

instance, red snapper otoliths collected from AL and LA did not significantly differ in 59Co (p = 

0.1834), 206Pb (p = 0.2979) and 205Tl (p = 0.4907) concentrations, otoliths collected from AL and 

TX had non-significant differences in 63Cu (p = 0.9467), 65Cu (p = 0.4985) and 56Fe (p = 0.9806) 

concentrations, and otoliths collected from LA and TX had non-significant differences in 59Co (p 

= 0.1531), 120Sn (p = 0.9353), 64Zn (p = 0.3905) and 66Zn (p = 0.0838) concentrations.
11

Table 2.

Summary of raw data for region and habitat otolith elemental concentrations (ppb) for red snapper (Lutjanus campechanus), collected from the 

Gulf of Mexico during the summers of 2007 and 2008. Values in bold represent significantly higher values. AL= Alabama; LA=Louisiana; TX=

Texas; P=platform habitat; NP= non-platform habitat.
12

Red snapper otoliths collected from AL had higher concentrations of 111Cd, 7Li, 98Mo 

and 120Sn, otoliths collected from LA had higher concentrations of 11B and 138Ba, and 

otoliths collected from TX had higher concentrations of 206Pb and 205Tl. Almost all 

elemental concentrations differed significantly among habitats, with the exceptions of 111Cd 

and 98Mo (ANOVA, p = 0.9059 and p = 0.1213, respectively). Otoliths from red snapper 

collected at platform habitats had higher concentrations of 138Ba, 59Co, 63Cu, 65Cu, 56Fe, 

55Mn, 206Pb, 51V, 64Zn and 66Zn, and samples collected at non-platform habitats had higher 

concentrations of 11B, 209Bi, 7

Li, 120Sn and 205Tl.

The stepwise discriminant analysis retained all otolith elements for the location model, 

retained all elements except 66Zn for the region model, and retained all elements except 63Cu 

for the habitat model. However, removal of these elements resulted in insignificant changes 

to the QDFA models, so all elements were retained in all of the models. Mean jackknifed 

classification accuracies of the QDFA models were 72.7% for location, 85.8% for region, 

and 79.4% for habitat (Figure 3). The low classification success among locations was due 

primarily to misclassifications within regions. In fact, the lowest classification success was 

for TX non-platform samples (60.9%); 31% of those samples were misclassified as having 

been collected from TX platform habitats. Therefore, regions alone were analyzed and this 

resulted in the highest classification successes. The largest misclassification among regions 

was 12.7% of LA red snapper that were misclassified as having been collected from TX.

Habitats analyzed separately also had higher classification success than locations; higher 

classification success occurred for red snapper collected from platforms (84.3%) than from 

non-platform (74.6%) habitats.

The canonical variable plot for locations further shows significant separation of regions,

with major overlap of habitats within regions (Figure 4; also see the appendix). Thus, 

locations again were disregarded, and a plot for regions alone were developed (Figure 5; 

also see the appendix). Based on the analyses of the elemental variables, AL red snapper 

otolith signatures appear to be correlated with 111Cd, 7

Li, 98Mo and 120Sn, LA otolith 

signatures appear to be correlated with 11B and 138Ba, and TX otolith signatures appear to be 

correlated with 206Pb and 205Tl. These results coincide with mean elemental concentrations 

for each region (Table 2). Although the plot shows that LA red snapper otolith signatures 

may also be correlated with 59Co, these concentrations did not differ significantly from the 

other two regions. Thus, 59Co was not considered a substantial element to the development 

of LA otolith signatures. A canonical variable plot for habitats further confirms platform 

otolith signatures to be correlated with 138Ba, 59Co, 56Fe, 55Mn, 206Pb, and 51V, and nonplatform signatures to be correlated with 11B, 209Bi, 7

Li, 120Sn and 205Tl (Figure 6; see also 

Appendix). Although 63Cu, 65Cu, 64Zn and 66Zn mean concentrations were higher for 

platform samples, these elements appear divided among habitat types in Figure 6.
13

Figure 3. Jackknifed classification percentages of red snapper, Lutjanus 

campechanus, to six locations, three regions and two habitats in 

the Gulf of Mexico collected during the summers of 2007 and 

2008. Percentages were estimated with quadratic discriminant 

function analyses (QDFA) of otolith chemical signatures. AL = 

Alabama; LA = Louisiana; TX = Texas; P = platform habitat; NP 

= non-platform habitat.
14

Figure 4. Canonical plot scores derived from otolith chemical signatures of red snapper, 

Lutjanus campechanus, collected from six locations in the Gulf of Mexico during the 

summers of 2007 and 2008. AL = Alabama; LA = Louisiana; TX = Texas; P = platform 

habitat; NP = non-platform habitat.
15

Figure 5. Canonical plot scores derived from otolith chemical signatures of red snapper, 

Lutjanus campechanus, collected from three regions in the Gulf of Mexico 

during the summers of 2007 and 2008. Ellipses indicate 95% confidence 

levels. AL = Alabama; LA = Louisiana; TX = Texas.
16

Figure 6. Canonical plot scores derived from otolith chemical signatures of red snapper, 

Lutjanus campechanus, collected from two habitats in the Gulf of Mexico during 

the summers of 2007 and 2008. Ellipses indicate 95% confidence levels. P = 

platform habitat; NP = non-platform habitat.
17

3.2. MIXED RED SNAPPER 

A total of 500 adult red snapper otolith samples collected from four regions across the 

Gulf was processed for otolith chemical analysis. However, due to either poor sample 

quality or inadequate detection limits, only 487 otolith samples were compared to baseline 

otolith signatures to determine region and habitat origin (Table 3). All 17 elements (11B, 138Ba, 209Bi, 111Cd, 59Co, 63Cu, 65Cu, 56Fe, 7

Li, 55Mn, 98Mo, 206Pb, 120Sn, 205Tl, 51V, 64Zn, 

66Zn) were present in adult red snapper otoliths above LODs. Trace metal concentrations 

were significantly different between DFL and TFL (MANOVA, F17, 275 = 40.71, p < 0.001); 

therefore these two regions were analyzed separately.

Mean concentrations of elements differed among regions (Table 4), and all elemental 

concentrations differed significantly (ANOVA, p ≤ 0.05) among regions overall. As 

reported for baseline data, red snapper mixed sample otoliths collected from LA and TX 

continued to not differ significantly in 59Co (p = 0.8496), 120Sn (p = 0.1692), 64Zn (p = 

0.9569) and 66Zn (p = 0.9976) concentrations. Additionally, these samples had similar 11B (p 

= 2534), 111Cd (p = 0.9448), 98Mo (p = 0.9974), and 51V (p = 1.000). The only elements not 

significantly different between red snapper otoliths collected from DFL and TFL were 209Bi 

(p = 0.0785), 98Mo (p = 0.2798), 120Sn (p = 0.7193) and 64Zn (p = 0.8965). Red snapper 

otoliths collected from LA and DFL did not differ significantly in 111Cd (p = 0.2022) and 

206Pb (p = 0.1253) concentrations, whereas LA and TFL had non-significant differences in 

11B (p = 0.0638), 111Cd (p = 0.6956), 56Fe (p = 0.9715), and 205Tl (p = 0.8604) 

concentrations. More similarities existed in elemental concentrations of red snapper otoliths 

collected from TX and the FL regions. For instance, TX and DFL red snapper otoliths had 

non-significant differences in 111Cd (p = 0.5242), 63Cu (p = 0.5166), 65Cu (p = 0.1063), 56Fe 

(p = 0.7014), and 55Mn (p = 0.1730) concentrations, while TX and TFL otoliths had nonsignificant differences in 11B (p = 0.9621), 209Bi (p = 0.3210), 111Cd (p = 0.3229), 63Cu (p = 

0.880), 65Cu (p = 0.7428), and 7

Li (p = 0.9232) concentrations. Red snapper otoliths 

collected from DFL had significantly higher concentrations of 11B, 138Ba, 59Co, 7Li, 205Tl, 

and 51V compared to the other regions (Table 4). As was also observed for baseline data, TX 

red snapper otoliths continued to have the highest concentrations of 206Pb.
18

Table 3.

Sample size and size range of red snapper, Lutjanus campechanus, and gray triggerfish, 

Balistes capriscus, collected from the Gulf of Mexico during the summer of 2009. DFL = Destin, 

Florida; TFL = Tampa, Florida; LA = Louisiana; TX = Texas.

Species Region Samples 

Collected

Samples 

Analyzed

Size Range 

(mm TL)

Red snapper DFL 155 153 447–747

TFL 145 140 452–764

LA 100 96 458–735

TX 100 98 517–708

Gray triggerfish DFL 15 15 409–548

LA 39 15 254–587
19

Table 4.

Summary of raw data of otolith elemental concentrations (ppb) for red snapper, Lutjanus campechanus, and gray triggerfish, Balistes capriscus, 

collected from the Gulf of Mexico during the summer of 2009. Bold numbers represent significantly higher concentrations in regions. DFL = 

Destin, Florida; TFL = Tampa, Florida; LA = Louisiana; TX = Texas.
20

Direct MLE based on region-specific baseline data indicates that red snapper collected from 

DFL were estimated to originate predominately from LA (82.1%) and secondarily from AL 

(16.1%; Figure 7). Red snapper collected from TFL were also estimated as originating from LA 

(53.6%) with more influence from AL (37.8%). However, the original objective of this study was 

to test the validity of platform signatures collected from regions where platforms were evident; 

hence baseline DFL and TFL data were not collected. Surprisingly, the suite of elements 

believed to be associated with platforms and other artificial habitats performed better for 

discriminating among Gulf regions than between habitats, and were applied here to further 

examine population connectivity among red snapper Gulf regions. Thus, evaluating MLE based 

on regional signatures for DFL and TFL should be interpreted with caution because baseline 

samples for these regions were not collected, and this causes biased results. LA red snapper 

consisted mainly of locally derived recruits (66.2%) with small contributions from AL and TX 

(16.2% and 17.6%, respectively). Texas red snapper were largely locally derived (85.7%). Direct 

MLE based on habitat-specific ‘baseline’ data indicated that red snapper collected from DFL, 

LA, and TX were derived from platform habitats (79.3%, 98%, and 100%, respectively). Only 

red snapper collected from TFL were classified as originated from non-platform habitats 

(97.6%). Although classification success was the lowest for location-specific ‘baseline’ data, 

direct MLE based on location-specific baseline data mimics the overall trends displayed in 

region- and habitat-specific MLE results (Figure 7).

A total of 54 adult gray triggerfish otoliths was collected from DFL and LA to test the 

validity of the platform signature described in Chapter 3 on other reef-associated species. Only 

30 samples were processed for otolith chemical analysis to allow even numbers to be processed 

from both regions/habitats (Table 3). Each LA gray triggerfish was collected from platform 

habitats and each DFL gray triggerfish was collected from non-platform habitats. However, trace 

metal concentrations were not significantly different among regions or habitats (MANOVA, F17, 

12 = 2,48, p < 0.0576). Only 11B (p = 0.0145), 138Ba (p = 0.0055), 120Sn (p = 0.0068) and 51V (p = 

0.0005) concentrations were significantly different in gray triggerfish otoliths collected from 

these two regions (Table 4). Direct MLE based on habitat-specific baseline data using all 17 

elements indicate that 60.8% of DFL gray triggerfish were collected at non-platform habitats and 

78.4% of LA gray triggerfish were collected from platform habitats (Figure 8A). Yet, direct 

MLE based on habitat-specific baseline data using only the 4 significant elements better reflects 

actual collection sites, with 99.9% of DFL gray triggerfish classified collected from non-platform 

habitats and 98.8% of LA gray triggerfish classified collected from platform habitats (Figure 

8B).
21

Figure 7. Bubbleplots of percent composition estimates derived from region-, habitat- and locationspecific otolith chemistry-based discriminant function analysis indicate the origin of adult 

red snapper, Lutjanus campechanus, collected from four regions and two habitat types 

within the Gulf of Mexico during the summer of 2009. Bubbles are scaled by diameter. DFL 

= Destin, Florida; TFL = Tampa, Florida; LA = Louisiana; TX = Texas; AL = Alabama; P = 

platform habitat; NP = non-platform habitat
22

Figure 8. Bubbleplots of percent composition estimates derived from 

habitat-specific otolith chemistry-based discriminant function 

analysis using A.) all 17 elements or B.) only 11B, 138Ba, 

120Sn, and 51V to indicate the habitat of origin of adult gray 

triggerfish, Balistes capriscus, collected from two regions 

representing two habitat types within the Gulf of Mexico 

during the summer of 2009. All DFL gray triggerfish were 

collected on non-platform habitats and all LA gray triggerfish 

were collected on platform habitats. Bubbles are scaled by 

diameter; DFL = Destin, Florida; LA = Louisiana; P = 

platform habitat; NP = non-platform habitat.
23

3.3 BARNACLE AND SEDIMENT 

A total of 100 barnacle samples, 114 sediment samples, and 668 fish samples collected from 

platform habitats off LA was processed for chemical analysis. All 17 elements analyzed in 

sediment samples were above LODs. However, due to differences in elements analyzed among 

sample types, and low LODs for some elements in otolith samples, only 8 elements (111Cd, 59Co, 

63Cu, 65Cu, 206Pb, 51V, 64Zn, 66Zn) were used to compare elemental concentration among otolith, 

barnacle, and sediment samples. Mean concentrations of elements varied across sample types

(Table 5).

The MDS plot displayed strong separation of the three sample types; same sample types 

clumped together. Also, barnacle and sediment sample groupings were spaced closer together, 

and red snapper otolith samples were spaced farther apart (Figure 9). This agrees with the 

ANOSIM results that confirmed significant differences (p = 0.001) among the sample types; a 

global R value of 0.998 indicated more similarities within groups than between groups. Based on 

SIMPER results, the mean similarities within groups was 91.82% for barnacles, 95.75% for red 

snapper otoliths, and 93.18% for sediments. The dissimilarity between barnacle and otolith 

sample elemental concentrations was 27.3%; a majority (60%) of the difference was due to V, 

Cd, and Pb. The dissimilarity between barnacle and sediment samples was 15.75%; most (60%) 

of the difference was due to Pb, Co, and Cd. Finally, the dissimilarity between otolith and 

sediment sample elemental concentrations was 36.71%; a majority (67%) of the difference was 

due to V, Pb, and Co.

For all elements, except Cd, sediment samples had the highest mean concentrations, followed 

by barnacle samples and then otolith samples. While otolith elemental concentrations were more 

similar to barnacle elemental concentrations compared to sediment elemental concentrations, this 

most likely reflects the mean concentrations between sample types. It is not surprising that 

sediment samples had higher elemental concentrations, because it is the one sample type that is 

not physiologically regulated. Trace metals incorporated into barnacle shells can substitute for 

Ca of the calcium carbonate material, and concentrations are affected by skeletal mineralogy, 

temperature, and salinity (Watson et al. 1995). Trace metals incorporated into otoliths can also 

substitute for Ca in the calcium carbonate matrix, and can be affected by temperature and salinity 

(Campana 1999). Furthermore, elemental concentrations can differ among fish species because 

of differences in life history parameters, otolith accretion, and metabolic rates (Patterson et al.,

2010; Hamer and Jenkins, 2007). Watson et al. (1995) found that barnacle shells would not be 

good biomonitoring indicators because changes in trace metal concentrations in the shell can 

occur during rapid shell growth, concentrations are correlated with shell weight, and 

intrapopulation variability in metal concentrations can occur. Thus, again it is not surprising that 

large differences occur between barnacle and red snapper otolith trace metal concentrations due 

to physiological differences between species. Though red snapper feed mostly on the benthos 

(McCawley and Cowan, 2007; Wells et al., 2008b), and may incorporate metals through the diet 

from the sediment, further work is needed to determine the pathway of platform metal 

incorporation into the otolith.
24

Table 5.

Summary of raw data for barnacle, red snapper (Lutjanus campechanus) otolith, and sediment elemental 

concentrations (ppb) collected from platforms off Louisiana during the summers of 2007 and 2008

Element

Barnacle Red Snapper Sediment

Mean Std Err Mean Std Err Mean Std Err

111Cd 23.08 2.15 0.13 0.00 4.82 0.40

59Co 12.55 1.72 0.14 0.01 184.64 10.33

63Cu 180.45 50.90 43.62 0.33 388.61 31.83

65Cu 174.78 49.80 41.70 0.33 386.54 31.67

206Pb 44.42 19.61 1.88 0.22 760.21 62.34

51V 150.56 13.75 0.16 0.01 408.95 24.62

64Zn 1460.06 109.86 456.42 6.51 2193.60 365.44

66Zn 1411.06 109.32 392.28 6.33 2191.64 365.76

Figure 9. Multidimensional scaling analysis (MDS) plot displaying variation in 

elemental concentrations of barnacles, red snapper otoliths and 

sediments collected from platforms off Louisiana during the summers of 

2007 and 2008.
25

4. DISCUSSION

Otolith trace metal concentrations were temporally stable for red snapper collected in the 

northern Gulf over the two-year baseline study period. When developing natural tags, interannual stability of chemical signatures is desired to avoid the need to produce annual baseline 

data and further validate the effectiveness of the tag. The temporal stability of otolith chemical 

signatures can vary within months, between two consecutive years, or show negligible 

differences over a two-year period with drastic changes occurring after 4–13 years (Patterson et 

al., 1999; Campana et al., 2000; Gillanders, 2002). Thus, while the temporal stability of otolith 

trace metal concentrations in this study is significant, it should be noted that there is potential for 

concentrations to change in the future.

Natural tags derived from baseline red snapper otolith trace metal concentrations 

demonstrated significant spatial differences. Classification success was high for regions and 

habitats when analyzed separately, whereas locations had a much lower classification success.

The high classification error of locations is attributed to misclassification among habitats within 

the same region. Although red snapper aggregate near platforms, they tend to periodically move 

away from platforms possibly for foraging purposes (Bortone et al., 1998; McDonough, 2009).

Platforms are occasionally placed only a few hundred meters apart from other platforms, 

artificial reefs or natural habitats, allowing red snapper to encounter new habitat while foraging 

away from these structures. In fact, acoustic studies have revealed that red snapper do move 

between closely spaced platforms and surrounding habitats (Westmeyer et al., 2007). Patterson 

and Cowan (2003) reported that red snapper site fidelity to artificial reefs was low, with 

substantial dispersion. However, a consistent pattern seen in red snapper tagging studies is that 

most fish only move short distances and slowly diffuse away from tagging sites (<10 km; 

Patterson, 2007), with larger fish more likely to travel greater distances than smaller fish 

(Patterson et al., 2001a). Therefore, localized movement within regions, along with different

habitat types close to one another, may explain the low classification success of locations and 

high regional classification success in this study.

Otoliths of baseline red snapper collected from AL had significantly higher concentrations of 

111Cd, 7

Li, 98Mo, and 120Sn. These results differed from Nowling et al. (2011), in which higher 

concentrations of 59Co and 62Ni were found in otoliths of red snapper collected east of the 

Mississippi River, which they attributed to discharge from Mobile Bay. Although temporal 

variations in ambient water elemental concentrations could be a factor, differences between these 

studies may be caused by variations in analytical procedures and sample sizes (Nowling, 2005).

Cd, Li, Mo, and Sn can all be associated with anthropogenic materials used to construct artificial 

reefs. Though few platforms exist east of the Mississippi River, approximately 20,000 artificial 

reefs have been deployed in a 3,100 km2 designated area, beginning in the early 1950s (Minton 

& Heath, 1998; Patterson et al., 2001a). These artificial reefs are constructed from a variety of 

objects, including car bodies, liberty ships, shrimp boats, barges, concrete, military tanks, and 

small planes. During the 1950s, Cd was used primarily as a protective coating on iron and steel 

parts associated with tanks, automobiles, ships, and aircrafts (Lansche, 1958), but because of 

environmental concerns, the use of Cd coating has gradually decreased(Tolcin, 2011).

Molybdenum has principally been used as an alloying agent in iron and steel products to enhance 

durability and protect against corrosion (Polyak 2011). Before the introduction of the Li battery, 

Li compounds were used mainly in ceramics, glass and aluminum (Jaskula, 2011). Tributyltin 

(TBT)-based antifouling paints were used on ship hauls because of the durable (5 years) 

protection it provided; it was banned in 2003 because of environmental concerns (Hayman et al.,
26

2000). Tributyltin degrades slowly in marine environments until it becomes inorganic Sn 

(MacLeod et al., 2004) and gradually less toxic. Though the ban resulted in lower water column 

levels, TBT and associated degradation products are still retained in marine sediments of affected 

areas (Antizar-Ladislao, 2008). The various objects used to construct artificial reefs are properly 

cleaned until they are deemed environmentally safe before they are disposed in the ocean.

However, over time these items will corrode due to natural processes. Thus, the higher 

concentrations of 111Cd, 7Li, 98Mo and 120Sn in red snapper otoliths collected from AL may 

reflect the unique materials used to create the region’s artificial reef system. Future research 

should determine if water and sediment samples around these artificial reefs also show high 

levels of these metals.

Before 2002, red snapper collected from LA waters accounted for more than 50% of 

commercial landings in the Gulf. The majority of red snapper are harvested around artificial 

structures, including the large number of oil and gas platforms in the area, because natural hard 

substrate is limited on the LA continental shelf. In fact, a survey of recreational fishers 

determined that 70% preferred to fish on LA platforms (Stanley & Scarborough-Bull, 2003). In 

this study, baseline red snapper otoliths collected from LA had higher concentrations of 11B and 

138Ba, both of which are associated with platform production processes. Elevated concentrations 

of B have been associated with oilfield brines (Collins, 1975) and Ba as barite is a main 

component in drill muds (Kennicutt et al., 1996). Although higher concentrations of 138Ba were 

associated with platform habitats in this study, the opposite is true for 11B, which was associated 

with non-platform habitats. The main source of B input into the oceans seems to originate from 

continental discharge (Lemarchand et al., 2002). Weathering of natural rocks and mineral 

deposits as a result of riverine processes has been a significant source of metals to estuaries 

(Summers et al., 1996). The Mississippi River system drains 41% of the conterminous United 

States (Turner & Rabalais, 1991) and its plume has been known to extend well offshore.

Furthermore, Ba is deposited into the otolith in proportion to ambient water conditions (Bath et 

al., 2000) and follows a nutrient-type profile with higher concentrations in riverine and nearcoastal waters (Thorrold et al., 1997). Thus, higher concentrations of 11B and 138Ba in LA red 

snapper otoliths may actually be attributed to influences of the Mississippi River discharge, 

rather than platform production processes. Again, these results differed from Nowling et al. 

(2011), in which higher concentrations of 114Cd, 65Cu, 238U, 107Ag and 109Ag were found in 

otoliths of red snapper collected west of the Mississippi River. Several of these elements were 

below detection limits in the current study.

Concentrations of 206Pb and 205Tl were higher in baseline red snapper otoliths collected from 

TX. Lead has been detected in drilling muds resulting from trace impurities in barite and in 

produced waters from drilling operations (Neff et al., 1987). Studies have shown that Pb and Ba 

are not highly correlated in sediments collected around Gulf platforms (Kennicutt et al., 1996), 

and at times Pb in marine sediments can be equal to or higher than levels in drilling muds (Neff 

et al., 1987). Therefore, other sources are likely responsible for high Pb levels; these include 

produced water, welding operations, lubricants, and corrosion of galvanized structures associated 

with offshore oil development. Lead concentrations in otoliths reflect ambient water conditions 

and can serve as an environmental monitor (Geffen et al., 1998; Ranaldi & Gagnon, 2010). In the 

current study, platform samples had higher concentrations of 206Pb and, with the majority of TX 

red snapper having been collected at platforms, these associations may explain the correlation of 

206Pb with TX otolith signatures. Conversely, high Tl concentrations were not associated with 

platform samples. Thallium occurs naturally in trace concentrations in the earth’s crust within 
27

sulfide ores of Zn, Cu and Pb (Peter and Viraraghavan, 2005). Higher concentrations of Tl can 

be found in sulfide deposits (i.e., pyrite) and released into the water column through weathering 

of Tl-rich sulfides (Xiao et al., 2003). Interestingly, recent work based on a subset of samples 

collected during this study (Zapp Sluis et al., 2013) showed that sulfur isotopes were more 

enriched in red snapper tissue samples collected from TX compared to the other two regions.

Further research is needed to determine if high Tl levels are correlated with high levels of sulfur 

in sediment samples from this region.

Otolith concentrations of 11B, 209Bi, 7

Li, 120Sn, and 205Tl were significantly higher in baseline 

red snapper otoliths collected from non-platform habitats compared with platform habitats. Each 

of these elements, except Bi, was presented above as being linked to a region in a way not 

associated with platforms. It may be possible that each of these elements were correlated to nonplatform habitats in their respective regions and combining regions has grouped them together to 

form the non-platform signature, which may also explain the lower classification success of 

habitats compared to regions. The dominant source of Bi to the ocean is through aeolian inputs 

that originate from volcano processes and European-Asian arid land regions (Lee et al., 1986, 

Bertine et al., 1996). As such, it would be assumed that 209Bi concentrations should be uniform 

across the Gulf, or at least between habitats within regions. In the United States, Bi is used 

primarily by the chemical and pharmaceutical industries, and for additives used in casting and 

galvanizing (Carlin, 2010). Red snapper otoliths from AL and LA had higher concentrations of 

209Bi compared to TX samples; thus it could be possible that Bi enriched chemicals and 

pharmaceuticals were leaked into the ocean through riverine input. However, again, both habitat 

types should be affected equally. Though it is unknown at this time as to why 209Bi is higher in 

non-platform compared with platform otolith samples, it most likely is not a strong contributing 

factor to non-platform otolith signatures.

An important concern facing future offshore oil and gas platform development is the longterm biological and environmental effects they might create. Drilling fluids and produced water 

associated with oil production processes, and the corrosion of the rig structures, antifouling 

paints, and sacrificial anodes can all be responsible for leaching metals into the water column 

and sediments around platforms. In the current study, baseline red snapper otoliths collected 

from platform habitats had higher concentrations of 138Ba, 59Co, 56Fe, 55Mn, 206Pb, and 51V. Each 

of these metals has been detected in drilling fluids, produced water and crude oil (Neff et al. 

1987; Bezerra et al., 2007; Kennicutt et al., 1996). Tillery et al., 1981, as cited in Neff, 1987) 

analyzed sediments, invertebrates, and fish for common metals (Ba, Cd, Cr, Cu, Fe, Ni, Pb, V, 

and Zn) associated with oil and gas platforms. Concentrations of Ba, Cr, Cu, Pb, and Zn were 

elevated in sediments within 100 m of the platform, but there was no indication of metal 

bioaccumulation in tissues of marine fauna associated with platforms. Fast turnover rates may 

prevent high levels of metal from accumulating in tissues of marine fauna, but the inert property 

of otoliths will allow metal concentrations to continuously increase the longer the fish resides on 

a platform. Accordingly, analyzing whole otoliths may show stronger platform signatures 

because they represent the metal accumulation for the entire duration of time spent on a platform, 

which could be multiple years. Furthermore, Kennicutt et al. (1996) confirmed that metal 

contamination levels due to drilling and discharge effects at deeper water sites (>80 m) remain 

stable in sediments for several years, possibly decades (except Pb which increased over time).

Thus, it may be possible for otolith platform signatures to remain temporally stable for longer 

than the two-year period of this study. Nowling et al. (2011) also observed higher concentrations 
28

of 206Pb and 51V in otoliths collected from platform habitats; however, they did not test for 138Ba, 

56Fe, and 55Mn.

Concentrations of 63Cu, 65Cu, 64Zn, and 66Zn were significantly higher in baseline otoliths of 

red snapper collected from platforms. Both of these metals are associated with oil production 

processes and have been found in higher concentrations in sediments near platforms (Tillery et 

al., 1981, as cited in Neff,1987). However, concentrations of Cu and Zn in otoliths may not be 

proxies of ambient water conditions because they are both influenced by physiological 

regulations (Campana, 1999). Zinc is absorbed primarily through the intestines and dietary 

exposure is responsible for most of the Zn assimilation in teleosts. Since otolith formation 

requires a large amount of Zn, it is unlikely that Zn concentrations in otoliths accurately 

represent ambient water concentrations (Miller et al., 2006). In fact, it is not uncommon for high 

concentrations of Zn to be present in otoliths, and these increased levels most likely represent 

diet or metabolism influences (Friedrich & Halden, 2010). For the same reasons, Cu 

concentrations in otoliths will not reflect ambient waters unless extreme conditions occur in 

which Cu levels are high enough to stress the fish and the liver can no longer remove Cu 

adequately (Milton & Chenery, 2001). However, because whole otoliths were analyzed, higher 

concentrations of Cu and Zn in red snapper otoliths may reflect accumulation of these elements 

over several years without harmful health affects being detected in fish. Furthermore, red 

snapper feed mostly on the benthos (McCawley and Cowan, 2007; Wells et al., 2008b), which 

possibly causes increased Cu and Zn concentrations in platform sediments to be assimilated 

through the food web. Significantly higher concentrations of Zn were observed for baseline red 

snapper collected off LA and TX compared to fish collected off AL. Thus, increased levels of 

these elements can be useful for distinguishing among red snapper populations as demographic 

differences in physiological regulation and metabolic influences may exist between regions.

Once otolith microchemical signatures were established from baseline red snapper samples, 

the next objective of this study was to determine if oil and gas platform otolith signatures were 

evident in red snapper collected from regions devoid of platforms, including the west FL shelf.

Based on MLE results using habitat-specific signatures, the platform marker was apparent in red 

snapper otoliths collected from FL, but primarily for fish collected from the DFL region. Also, 

all red snapper collected from natural habitats in LA and TX exhibited the platform marker. A 

natural ontogenetic shift in habitat is known to occur in red snapper as juveniles move from lowprofile reefs, relic-shell, and mud habitats to more complex habitats with increasing vertical 

dimension (Patterson, 2007). As red snapper continue to mature, larger individuals are less 

dependent upon structures, including platforms, and can be found on outer shelf-edge reefs 

(Render, 1995; Mitchell et al., 2004). The dominance of age-2 and age-3 red snapper on 

platforms has been attributed to this ontogenetic shift in habitat, and to intense fishing pressure 

associated with platforms (Nieland and Wilson, 2003; Patterson, 2007). While this study cannot 

rule out fishing pressure as a cause for the reduction of older individuals on platforms, the fact 

that red snapper collected from natural habitat and shelf-edge banks exhibited the platform 

marker implies an ontogenetic shift from platform habitats to natural, lower relief habitats. 

Low site fidelity of red snapper, along with localized movement between habitat types within 

regions, likely contributed to the lower classification success of habitats compared to regions as 

discussed previously. To minimize the effect of movement between habitats and the 

accumulation of additional platform elements, ‘mixed’ red snapper samples from LA and TX 

were collected on shelf-edge banks and rock formations away from platforms. This proved more 

difficult for the LA region due to the abundance of platforms in the area (Figure 9), which may 
29

have caused the platform signature to be continually evident in ‘mixed’ red snapper otoliths from 

this region as a result of the close proximity of habitats. However, mean otolith elemental 

concentrations for LA ‘mixed’ red snapper were lower than the mean concentrations for the LA 

region and platform habitat reported in ‘baseline’ samples. Red snapper on the outer shelf-edge 

banks are exposed to fewer platforms and are farther removed from the influence of the 

Mississippi River plume.

Therefore, new material that is incorporated onto the otolith while the fish resides on the 

shelf-edge bank will likely have lower elemental concentrations than in fish collected further 

inshore and on platform habitats. Because whole otoliths were analyzed, if a red snapper resided 

on a platform at one time during its life, the platform signature would still be present within the 

otolith, due to the inert property of the otolith. However, the elemental concentration of the 

signature may be diluted by additional material accumulated on the otolith after the fish migrated 

away from the platform. Gray triggerfish otoliths were analyzed to further examine the 

effectiveness of the platform signature in a reef-associated fish with higher site fidelity. The 

MLE revealed the platform signature was able to accurately predict the habitat of origin for gray 

triggerfish. However, for the signature to be highly accurate, elements had to be removed based 

on significance levels between regions examined. Patterson et al. (2010) discovered differences 

in otolith chemical signatures between age-0 lane snapper (Lutjanus synagris) and red snapper of 

similar sizes. Unlike red snapper, lane snapper may recruit to estuaries before migrating offshore, 

which may contribute to the observed differences. Furthermore, some of the elements (i.e., Cu 

and Zn) contained in the platform signature are physiologically regulated, as previously 

discussed. Thus, differences in life history parameters and physiological regulation among fish 

species may cause variability in the levels of metal incorporation into otoliths, making it 

necessary to alter signatures based on species and regions being analyzed.

It may also be speculated that the estimates of habitat origin is confounded by region,

because all gray triggerfish platform samples were collected off LA and all non-platform 

samples were collected off DFL. Otoliths from gray triggerfish collected at platforms had 

significantly higher concentrations of Ba and V. While high concentrations of Ba likely can be 

attributed to the Mississippi River discharge (see above), Ba as barite is also the main component 

in drilling muds associated with oil production processes (Kennicutt et al., 1996). Further, 

average Ba concentrations in gray triggerfish otoliths were six times greater than average Ba 

concentrations of baseline red snapper collected from LA or platforms. Average V 

concentrations were also greater in gray triggerfish otoliths compared to concentrations in

baseline red snapper otoliths collected from LA or platforms. Vanadium is present at significant 

levels in crude oil (Kennicutt et al., 1996). Thus, the higher site fidelity of gray triggerfish may 

result in elevated otolith concentrations of Ba and V for samples collected at platforms.

Additionally, gray triggerfish collected from non-platform habitats had significantly higher 

concentrations of Sn, a metal associated with anti-fouling paints. Several of the gray triggerfish 

collected off DFL were from shipwrecks. Again, average Sn otolith concentrations of gray 

triggerfish were greater than average Sn otolith concentrations of baseline red snapper collected 

from non-platform habitats. Therefore, the estimates of gray triggerfish origins may in fact be the 

result of habitat differences between regions.

Despite AL’s small coastline, red snapper caught there represent nearly 40% of the total 

recreational landings in the Gulf. Fishery scientists have debated whether the artificial reef 

system off AL has increased production of red snapper or if it merely serves as a sink for stockspecific production (Szedlmayer and Shipp, 1994; Shipp, 1999; Cowan et al., 1999; Patterson et 
30

al., 2001b; Shipp and Bortone, 2009; Cowan et al., 2010). Red snapper collected off AL and LA 

have similar growth rates and size distributions (Patterson et al. 2001b; Fischer et al., 2004; 

Saari, 2011). Although both regions have unique artificial habitat, age distribution in the eastern 

Gulf is truncated compared to that in the western Gulf and the eastern substock is projected to 

have lower productivity than the western substock (SEDAR, 2009). Region-specific MLE results 

showed little contribution from AL red snapper to the 2009 sampling regions. The largest 

estimated contribution of AL red snapper was to the TFL region. This result is biased because no 

FL baseline samples were collected. However, it does confirm conventional tagging data in 

which fish tagged off AL and the FL panhandle were shown to move east and southeast, with red 

snapper recaptured as far south as TFL, but only one fish tagged off AL has been recaptured west 

of the Mississippi River (Patterson et al., 2001a; Addis et al., 2008). Also, the low contribution 

of AL red snapper to neighboring regions could imply that the AL artificial reef system is not 

highly productive and high fishing morality in the area may actually cause the artificial reef 

system to serve as a net sink for the Gulf-wide population. 

By the late 1960s, the majority of commercial landings for red snapper was in the western 

Gulf. In fact, a significant portion of red snapper landed at ports in the eastern Gulf was off the 

coast of LA (Goodyear, 1995). The genetic effective population size of LA red snapper is 

estimated to be ten-fold greater than red snapper originating from AL and TX (Gold and Saillant,

2007). Furthermore, the recent increase in red snapper spawning potential ratio (SPR) has been 

attributed to the western Gulf (SEDAR, 2009). Thus, it is not surprising that MLE results of this 

study estimate a large contribution of LA red snapper to the FL regions. Again, these results are 

biased as FL baseline samples were not collected for comparison. However, the platform marker 

was evident in red snapper collected from DFL, and with LA red snapper being highly correlated 

with the platform signal, this may imply a western substock contribution to the area. The results 

of Sluis (2011) indicate that LA was an important source of recruits for the western red snapper 

substock and results from Patterson et al. (2010) revealed that LA may potentially be a source of 

recruits to the west FL shelf as well. Though data were insufficient to determine the stock 

structure of FL red snapper, observed MLE based on regional and habitat otolith signatures, 

along with the results of Sluis (2011) and Patterson et al. (2010), suggest LA may be a 

potentially important source of red snapper recruits for the entire northern Gulf.

Based on MLE results using cohort specific signatures, TX red snapper appear to be locally 

derived with a relatively small contribution from LA. Further, TX red snapper appear to 

contribute little to the other Gulf regions sampled. These results are supported by results 

described in Sluis (2011), in which TX juvenile red snapper were primarily locally derived and 

LA was a secondary important source of recruits depending on the year class examined. 

Diamond et al. (2007) reported small-scale movement of tagged red snapper along the TX coast, 

supporting an isolated stock theory. They concluded that an isolated stock could explain the 

smaller sizes of TX red snapper compared to LA and AL, and supported the notion of a separate 

demographic TX substock. Kritzer and Sale (2004) define a metapopulation as “a system of 

discrete local populations, each of which determines its own internal dynamics to a large extent, 

but with a degree of identifiable and nontrivial demographic influence from other local 

populations through dispersal of individuals.” The idea of managing red snapper as a 

metapopulation is not new (Pruett et al., 2005; Gold and Saillant, 2007; Patterson, 2007; Saillant 

et al., 2010). The microchemical otolith results of the western Gulf red snapper in this study 

demonstrated discrete regional populations with some dispersal from neighboring regions, 

further supporting the notion of a metapopulation. 
31

Previous studies have determined that trace metals based on known anthropogenic sources 

could be detected in otoliths and used to discriminate the nursery or location of origin (Dove and 

Kingsford, 1998; Spencer et al., 2000). While otolith trace metal analysis is not a novel idea, this 

study is novel in terms of the large suite of trace metals analyzed and the intent of trying to use 

these metals to distinguish between habitat types that co-occur in the open ocean. Otolith 

chemical signatures based on trace metals associated with oil and gas production platforms were 

able to discriminate among three red snapper collection regions, and, to a lesser extent, between 

habitats, in the Gulf. Furthermore, this study can provide baseline data for future projects 

examining the effects of oil and gas production in the Gulf. On April 20, 2009 the Deepwater

Horizon oil well blowout near the Mississippi River delta resulted in the largest oil spill in U.S. 

history. Morales-Nin et al., (2007) found that some elements associated with the oil of a sunken 

oil tanker were incorporated into turbot (Scophthalmus maximus) otoliths through a diet 

laboratory study. Thus, three years of “pre-spill” otolith trace metal concentrations are present in 

this study that could be compared to otolith concentrations of red snapper collected “post-spill” 

to see if a spike in elements associated with crude oil (i.e., Cu, Ni, V) occurred. If so, it may infer 

that crude oil was assimilated into the diet of red snapper collected from areas affected by the oil 

spill. 

Numerous studies have shown that oil and gas platforms are used by red snapper, but 

whether these unique habitats are beneficial is still debatable. The results of this study indicate 

that trace metals associated with platforms can be used to develop otolith chemical signatures to 

differentiate among regions, and, to a lesser extent, habitats, in the Gulf. Although the overall 

goal was to develop oil and gas platform otolith signatures based on a suite of trace metals, this 

combination of trace metals proved to work best for discriminating among regions because of 

unique features, e.g., the Mississippi River, that differentially affect each area. Furthermore, 

whole otolith analysis has proven useful for distinguishing among fish stocks or among fish 

inhabiting different niches for some period of time (Campana et al., 1994; Patterson et al., 1999; 

Elsdon and Gillanders, 2003). However, whole otolith analysis incorporates the entire life of the 

fish, and it is not possible to determine when geographic separation occurred. Future work 

should use laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) to 

analyze specific loci along a transverse section of the otolith to determine an approximate age at 

which red snapper migrate away from platforms. If this age coincides with the disappearance of 

older red snapper from platforms, it would further demonstrate that a natural ontogenetic shift in 

habitat does occur, which may be more prominent to the disappearance of older fish from 

platforms than fishing pressure. Moreover, evidence of the platform signature in regions devoid 

of platforms may not indicate that platforms enhance the production of red snapper, but instead 

reflect a possible western contribution to the eastern Gulf. Additional analysis, including the 

collection of FL baseline samples, is needed to determine mixing dynamics and stock separation 

in the eastern Gulf. 
33

LITERATURE CITED

Addis, D.T., W.F. Patterson, III, and M.A. Dance. 2008. Site fidelity and movement of reef 

fishes tagged at unreported artificial reef sites off northwest Florida. Proceedings of the Gulf 

and Caribbean Fisheries Institute 60:297-304.

Antizar-Ladislao, B. 2008. Environmental levels, toxicity and human exposure to tributyltin 

(TBT)-contaminated marine environment. A review. Environmental International 34:292-

308.

Barnett, B. and W.F. Patterson III. 2010. The effect of coring and pulverizing juvenile red 

snapper, Lutjanus campechanus, otoliths on their chemical signatures. Environmental 

Biology of Fishes 89:463-471.

Bath, G.E., S.R. Thorrold, C.M. Jones, S.E. Campana, J.W. McLaren, and J.W.H. Lam. 2000.

Strontium and barium uptake in aragonitic otoliths of marine fish. Geochimica et 

Cosmochimica Acta 64:1705-1714.

Bertine, K.K., M. Koide, and E.D. Goldberg. 1996. Comparative marine chemistries of some 

trivalent metals-bismuth, rhodium and rare earth elements. Marine Chemistry 53:89-100.

Bezerra, M.A., S.M.N. Maeda, E.P. Oliveira, M.F.B. Carvalho, and R.E. Santelli. 2007. Internal 

standardization for the determination of cadmiolm, cobalt, chromium and manganese in 

saline produced water from petroleum industry by inductively coupled plasma optical 

emission spectrometry after cloud point extraction. Spectrochimica Acta Part B 62:985-991.

Bohnsack, J.A. 1989. Are high densities of fishes at artificial reefs the result of habitat limitation 

or behavioral preference? Bulletin of Marine Science 44:631-645.

Bortone, S.A., R.P. Cody, R.K. Turpin, and C.M. Bundrick. 1998. The impact of artificial-reef 

fish assemblages on their potential forage area. Italian Journal of Zoology 65:265-267.

Campana, S.E., A.J. Fowler, and C.M. Jones. 1994. Otolith elemental fingerprinting for stock 

identification of Atlantic cod (Gadus morhua) using laser ablation ICPMS. Canadian Journal 

of Fisheries and Aquatic Sciences 51:1942-1950.

Campana, S.E. 1999. Chemistry and composition of fish otoliths: pathways, mechanisms and 

applications. Marine Ecology Progress Series 188: 263-297.

Campana, S.E., G.A. Chouinard, J.M. Hanson, A, Frechet, and J. Brattey. 2000. Otolith 

elemental fingerprints as biological tracers of fish stocks. Fisheries Research 46:343-357.

Carlin, J.F., Jr. 2010. Minerals Yearbook 2009: Bismuth. United States Geological Survey. 

Clarke, K.R. and R.M. Warwick. 2001. Change in Marine Communities: An Approach to 

Statistical Analysis and Interpretation, 2nd edition. PRIMER-E: Plymouth.
34

Collins, A.G. 1975. Geochemistry of Oilfield Waters. Elsevier, New York.

Cowan, J.H., Jr., W. Ingram, J. McCawley, B. Sauls, A. Strelcheck, and M. Woods. 1999. The 

attraction vs. production debate: Does it really matter from the management perspective? A 

response to the commentary by R. L. Shipp. Gulf of Mexico Science 17:137-138.

Cowan, J.H., Jr, C.B. Grimes, W.F. Patterson, III, C.J. Walters, A.C. Jones, W.J. Lindberg, D.J. 

Sheehy, W.E. Pine, III, J.E. Powers, M.D. Campbell, K.C. Lindeman, S.L. Diamond, R. 

Hilborn, H.T. Gibson and K.A. Rose. 2010. Red Snapper Management in the Gulf of 

Mexico: Science- or Faith-Based? Reviews in Fish Biology and Fisheries 21:187-204.

Diamond, S.L., M.D. Campbell, D. Olson, and Y. Wang. 2007. Movers and stayers: Individual 

variability in site fidelity and movements of red snapper off Texas. Pages 163-187 in W.F. 

Patterson, III, J.H. Cowan, Jr., G.R. Fitzhugh, and D.L. Nieland, editors. Red snapper 

ecology and fisheries in the U.S. Gulf of Mexico. American Fisheries Society Symposium 

60, Bethesda, Maryland.

Dove, S.G. and M.J. Kingsford. 1998. Use of otoliths and eye lenses for measuring trace-metal 

incorporation in fishes: a biogeographic study. Marine Biology 130:377-387.

Elsdon, T.S. and B.M. Gillanders. 2003. Reconstructing migratory patterns of fish based on 

environmental influences on otolith chemistry. Reviews in Fish Biology and Fisheries 

13:219-235.

Fischer, A.J., M.S. Baker, Jr., and C.A. Wilson. 2004. Red snapper (Lutjanus campechanus) 

demographic structure in the northern Gulf of Mexico based on spatial patterns in growth 

rates and morphometrics. Fisheries Bulletin 102:593-603.

Friedrich, L.A. and N.M. Halden. 2010. Determining exposure history of northern pike and 

walleye to tailings effluence using trace metal uptake in otoliths. Environmental Science and 

Technology 44:1551-1558.

Geffen, A.J., N.J. Pearce, and W.T. Perkins. 1998. Metal concentrations in fish otoliths in 

relation to body composition after laboratory exposure to mercury and lead. Marine Ecology 

Progress Series 165:235–245.

Gillanders, B.M., and M.J. Kingsford. 1996. Elements in otoliths may elucidate the contribution 

of estuarine recruitment to sustaining coastal reef populations of a temperate reef fish. 

Marine Ecology Progress Series 141:13-20.

Gillanders, B.M., and M.J. Kingsford. 2000. Elemental fingerprints of otoliths of fish may

distinguish estuarine “nursery” habitats. Marine Ecology Progress Series 201:273-286.

Gillanders, B.M. 2002. Temporal and spatial variability in elemental composition of otoliths: 

implications for determining stock identity and connectivity of populations. Canadian Journal 

of Fisheries and Aquatic Sciences 59:669-679.
35

Gitschlag, G.R., M.J. Schirripa, and J.E. Powers. 2003. Impacts of red snapper mortality 

associated with the explosive removal of oil and gas structures on stock assessments of red 

snapper in the Gulf of Mexico. Pages 83-94 in D.R. Stanley and A. Scarborough-Bull, 

editors. Fisheries, reefs, and offshore development. American Fisheries Society Symposium 

36, Bethesda, Maryland. 

GMFMC. 2010. Final Regulatory Amendment to the Reef Fish Fishery Management Plan to Set 

Total Allowable Catch for Red Snapper. Gulf of Mexico Fishery Management Council, 

Tampa, FL. 261 pp.

Gold, J.R. and E. Saillant. 2007. Population structure of red snapper in the northern Gulf of 

Mexico. Pages 201-216 in W.F. Patterson, III, J.H. Cowan, Jr., G.R. Fitzhugh, and D.L. 

Nieland, editors. Red snapper ecology and fisheries in the U.S. Gulf of Mexico. American 

Fisheries Society Symposium 60, Bethesda, Maryland.

Goodyear, C.P. 1995. Red snapper in U.S. waters of the Gulf of Mexico. Stock assessment report 

MIA-95/96-05. Miami Laboratory, Southeast Fisheries Science Center, Miami, FL.

Hamer, P.A. and G.P. Jenkins. 2007. Comparison of spatial variation in otolith chemistry of two 

fish species and relationships with water chemistry and otolith growth. Journal of Fish 

Biology 71:1035-1055.

Hayman, B., M. Dogliani, I. Kvale, A.M. Fet. 2000. Technologies for reduced environmental 

impact from ships—Ship building, maintenance and dismantling aspects. ENSUS-2000, 

Newcastle upon Tyne, United Kingdom.

Ingram, G.W. 2001. Stock structure of gray triggerfish on multiple spatial scales. PhD 

dissertation, University of South Alabama, Mobile, Alabama.

Ingram, G.W. and W.F. Patterson, III. 2001. Movement patterns of red snapper (Lutjanus 

campechanus), greater amberjack (Seriola dumerili), and gray triggerfish (Balistes capriscus) 

in the Gulf of Mexico and the utility of marine reserves as management tools. Proceedings of 

the Gulf and Caribbean Fisheries Institute 52:686- 699.

Jaskula, B.W. 2011. Minerals Yearbook 2009: Lithium. United States Geological Survey.

Kasprzak, R.A. 1998. Use of oil and gas platforms as habitat in Louisiana’s artificial reef 

program. Gulf of Mexico Science 1:37-45.

Kennicutt, M.C., II, P.N. Boothe, T.L. Wade, S.T. Sweet, R. Rezak, F.J. Kelly, J.M. Brooks, B.J. 

Presley, and D.A. Wiesenburg. 1996. Geochemical patterns in sediments near offshore 

production platforms. Canadian Journal of Fisheries and Aquatic Sciences 53:2554-2566.

Kritzer, J.P. and P.F. Sale. 2004. Metapopulation ecology in the sea: from Levins’ model to 

marine ecology and fisheries science. Fish and Fisheries 5:131-140.

Lansche, A.M. 1958. Minerals Yearbook 1956: Cadmium. United States Geological Survey.
36

Lee, D.S., J.M. Edmond, and K.W. Bruland. 1986. Bismuth in the Atlantic and North Pacific: a 

natural analogue to plutonium and lead? Earth and Planetary Science Letters 76:254–262.

Lemarchand, D., J. Gaillardet, E. Lewin, and C.J. Allegre. 2002. Boron isotope systematics in 

large rivers: implications for the marine boron budget and paleo-pH reconstruction over the 

Cenozoic. Chemical Geology 190:123-140.

Lindberg, W.J. 1997. Can science resolve the attraction-production issue? Fisheries 22:10-13.

MacLeod, I., P. Morison, V. Richards, and N.West. 2004. Corrosion monitoring and the 

environmental impacts of decommissioned naval vessels as artificial reefs. Pages 53-74 in J. 

Ashton and D. Haallam, editors. Metal 04: Proceedings of the International Conference on 

Metals Conservation. National Museum of Australia, Canberra. 

McCawley J. and J.H. Cowan, Jr. 2007. Seasonal and size specific diet and prey demand of red 

snapper on Alabama artificial reefs: Implications for management. Pages 77-104 in W.F. 

Patterson, III, J.H. Cowan, Jr., G.R. Fitzhugh, and D.L. Nieland, editors. Red snapper 

ecology and fisheries in the U.S. Gulf of Mexico. American Fisheries Society Symposium 

60, Bethesda, Maryland.

McDonough, M. 2009. Oil platforms and red snapper movement and behavior. MS thesis, 

Louisiana State University, Baton Rouge, LA.

Millar, R.B. 1990. Comparison of methods for estimation of mixed stock fishery composition. 

Canadian Journal of Fisheries and Aquatic Sciences. 47:2235-2241.

Miller, M.B., A.M. Clough, J.N. Batson, and R.W. Vachet. 2006. Transition metal binding to cod 

otolith proteins. Journal of Experimental Marine Biology and Ecology 329:135-143.

Milton, D.A. and S.R. Chenery. 2001. Sources and uptake of trace metals in otoliths of juvenile 

barramundi (Lates calcarifer). Journal of Experimental Marine Biology and Ecology 264:47-

65.

Minton, R.V. and S.R. Heath. 1998. Alabama’s artificial reef program: Building oasis in the 

desert. Gulf of Mexico Science 1:105-106. 

Mitchell, K.M., T. Henwood, G.R. Fitzhugh, and R.J. Allman. 2004. Distribution, abundance, 

and age structure of red snapper (Lutjanus campechanus) caught on research longlines in US 

Gulf of Mexico. Gulf of Mexico Science 22:164–172.

Morales-Nin, B., A.J. Geffen, F. Cardona, C. Kruber, and F. Saborido-Rey. 2007. The effect of 

Prestige oil ingestion on the growth and chemical composition of trubot otoliths. Marine 

Pollution Bulletin 54:1732-1741.

Neff, J.M. 1987. Biological effects of drilling fluids, drill cuttings, and produced waters. Pages 

469-538 in D.F. Boesch and N.N. Rabalais, editors. Long-term environmental effects of 

offshore oil and gas development. Elsevier Applied Science Publishers, London.
37

Neff, J.M., N.N Rabalais, and D.F. Boesch. 1987. Offshore oil and gas development activities 

potentially causing long-term environmental effects. Pages 149-173 in D.F. Boesch and N.N. 

Rabalais, editors. Long-term environmental effects of offshore oil and gas development.

Elsevier Applied Science Publishers, London.

Nieland, D.L. and C.A. Wilson. 2003. Red snapper recruitment to and disappearance from oil 

and gas platforms in the northern Gulf of Mexico. Pages 73-81 in D.R. Stanley and A. 

Scarborough-Bull, editors. Fisheries, reefs, and offshore development. American Fisheries 

Society Symposium 36, Bethesda, Maryland.

Nowling, L.K. 2005. Platform recruited reef fish, Phase I: Do platforms provide habitat that 

increase the survival of juvenile reef fishes? M.S. Thesis, Louisiana State University, Baton 

Rouge, LA.

Nowling, L., R.W. Gauldie, J.H. Cowan, Jr., and E. De Carlo. 2011. Successful discrimination 

using otolith microchemistry among samples of red snapper Lutjanus campechanus from 

artificial reefs and samples of L. campechanus taken from 

Patterson, H.M., S.R. Thorrold, and J.M. Shenker. 1999. Analysis of otolith chemistry in Nassau 

grouper (Epinephelus striatus) from the Bahamas and Belize using solution-based ICP-MS. 

Coral Reefs 18:171-178.

Patterson, W.F., III, J.C. Watterson, R.L. Shipp, and J.H. Cowan, Jr. 2001a. Movement of tagged 

red snapper in the northern Gulf of Mexico. Transactions of the American Fisheries Society 

130:533-545.

Patterson, W.F., III, J.H. Cowan, Jr., C.A. Wilson, and R.L. Shipp. 2001b. Age and growth of 

red snapper, Lutjanus campechanus, from an artificial reef off Alabama in the northern Gulf 

of Mexico. Fisheries Bulletin 99:617-627.

Patterson, W.F., III and J.H. Cowan, Jr. 2003. Site fidelity and dispersion of red snapper 

associated with artificial reefs in the northern Gulf of Mexico. Pages 181-193 in D.R. Stanley 

and A. Scarborough-Bull, editors. Fisheries, reefs, and offshore development. American 

Fisheries Society Symposium 36, Bethesda, Maryland.

Patterson, W.F., III. 2007. A review of Gulf of Mexico red snapper movement studies: 

Implications for population structure. Pages 221-236 in W.F. Patterson, III, J.H. Cowan, Jr., 

G.R. Fitzhugh, and D.L. Nieland, editors. Red snapper ecology and fisheries in the U.S. Gulf 

of Mexico. American Fisheries Society Symposium 60, Bethesda, Maryland.

Patterson, W.F., III, J.H. Cowan, Jr., B.K. Barnett, and M. Zapp Sluis. 2010. MaRFIN Final 

Report (NA05NMF4331072): Estimation of the source of red snapper recruits to west Florida 

and south Texas with otolith chemistry: implications for stock structure and management. 46 

pp.

Pawson, M.G. 1990. Using otolith weight to age fish. Journal of Fish Biology 36:521-531.
38

Peter, A.L.J. and T. Viraraghavan. 2005. Thallium: a review of public health and environmental 

concerns. Environment International 31:493-501.

Polyak, D.E. 2011. Minerals Yearbook 2009: Molybdenum. United States Geological Survey.

Pruett, C.L., E. Saillant, and J.R. Gold. 2005. Historical population demography of red snapper 

(Lutjanus campechanus) from the northern Gulf of Mexico based on analysis of sequences of 

mitochondrial DNA. Marine Biology 147:593–602.

Ranaldi, M.M. and M.M. Gagnon. 2010. Trace metal incorporation in otoliths of pink snapper 

(Pagrus auratus) as an environmental monitor. Comparative Biochemistry and Physiology 

152:248-255.

Render, J.H. 1995. The life history (age, growth, and reproduction) of red snapper (Lutjanus 

campechanus) and its affinity for oil and gas platforms. Doctoral dissertation, Louisiana State 

University, Baton Rouge, Louisiana.

Rooker, J.R., D.H. Secor, V.S. Zdanowicz, and T. Itoh. 2001. Discrimination of northern bluefin 

tuna from nursery areas in the Pacific Ocean using otolith chemistry. Marine Ecology 

Progress Series 218:275-282.

Rooker, J.R., A.M. Landry, Jr., B.W. Geary, and J.A. Harper. 2004. Assessment of a shell bank 

and associated substrates as nursery habitat of postsettlement red snapper. Estuarine, Coastal 

and Shelf Science 59:653-661.

Rooker, J.R., D.H. Secor, G. DeMetrio, A.J. Kaufman, A.B. Rios, and A. Ticina. 2008. Evidence 

of trans-Atlantic movement and natal homing of bluefin tuna from stable isotopes in otoliths. 

Marine Ecology Progress Series 368:231-239.

Saari, C.R. 2011. Comparison of the age and growth of red snapper (Lutjanus campechanus) 

amongst habitats and regions. M.S. Thesis: Louisiana State University, Baton Rouge, LA.

Saillant, E., S.C. Bradfield, and J.R. Gold. 2010. Genetic variation and spatial autocorrelation 

among young-of-the-year red snapper (Lutjanus campechanus) in the northern Gulf of 

Mexico. ICES Journal of Marine Science 67:1240–1250.

SAS Institute. 2006. Statistics, version 9.1. SAS Institute, Cary, North Carolina.

Schroepfer, R.L. and S.T. Szedlmayer. 2006. Estimates of residence and site fidelity for red 

snapper Lutjanus campechanus on artificial reefs in the northeastern Gulf of Mexico. 

Bulletin of Marine Science 78:93-101.

SEDAR. 2009. Southeast Data, Assessment, and Review Update Assessment of Red Snapper in 

the Gulf of Mexico. 279 pp.

Shipp, R.L. 1999. The artificial reef debate: Are we asking the wrong questions? Gulf of Mexico 

Science 17:51-55.
39

Shipp, R.L. and S.A. Bortone. 2009. A prospective of the importance of artificial habitat on the 

management of red snapper in the Gulf of Mexico. Reviews in Fisheries Science 17:41-47.

Sluis, M.Z. 2011. Variability in red snapper otolith microchemistry among Gulf of Mexico 

regions. PhD Dissertation: Louisiana State University, Baton Rouge, LA.

Spencer, K., D.J. Shafer, R.W. Gauldie, and E.H. DeCarlo. 2000. Stable lead isotope ratios from 

distinct anthropogenic sources in fish otoliths: a potential nursery ground stock marker. 

Comparative Biochemistry and Physiology 127:273-284.

Stanley, D.R. and A. Scarborough-Bull, editors. 2003. Fisheries, reefs, and offshore 

development. American Fisheries Society Symposium 36, Bethesda, Maryland. 

Stanley, D.R. and C.A. Wilson. 2003. Seasonal and spatial variation in the biomass and size 

frequency distribution of fish associated with oil and gas platforms in the northern Gulf of 

Mexico. Pages 123-153 in D.R. Stanley and A. Scarborough-Bull, editors. Fisheries, reefs, 

and offshore development. American Fisheries Society Symposium 36, Bethesda, Maryland.

Strelcheck, A.J., J.H. Cowan, Jr., and W.F. Patterson, III. 2007. Site fidelity, movement, and 

growth of red snapper: implications for artificial reef management. Pages 135-148 in W.F. 

Patterson, III, J.H. Cowan, Jr., G.R. Fitzhugh, and D.L. Nieland, editors. Red snapper 

ecology and fisheries in the U.S. Gulf of Mexico. American Fisheries Society Symposium 

60, Bethesda, Maryland.

Summers, J.K., T.L. Wade, and V.D. Engle. 1996. Normalization of metal concentrations in 

estuarine sediments from the Gulf of Mexico. Estuaries 19:581-594.

Szedlmayer, S.T. and R.L. Shipp. 1994. Movement and growth of red snapper, Lutjanus 

campechanus, from an artificial reef area in the northeastern Gulf of Mexico. Bulletin of 

Marine Science 55:887-896.

Szedlmayer, S.T. and J.C. Howe. 1997. Substrate preference in age-0 red snapper, Lutjanus 

campechanus. Environmental Biology of Fishes 50:203-207.

Tolcin, A.C. 2011. Minerals Yearbook 2009: Cadmium. United States Geological Survey.

Thorrold, S.R., C.M. Jones, and S.E. Campana. 1997. Response of otolith microchemistry to 

environmental variations experienced by larval and juvenile Atlantic croaker (Micropogonias 

undulatus). Limnology Oceanography 42:102-111.

Thorrold, S.R., C. Latkoczy, P.K. Swart, and C.M. Jones. 2001. Natal homing in a marine fish 

metapopulation. Science 291:297-299.

Tillery, J.B., R.E. Thomas, and H.L. Windom. 1981. Part 4. Trace metals studies in sediments 

and fauna. Pages 1-122 in C.A. Bedinger, Jr, editor. Ecological investigations of petroleum 

production platforms in the central Gulf of Mexico. Volume 1. Pollutant fate and effects 

studies. Research Institute, San Antonio, Texas.
40

Turner, R.E. and N.N. Rabalais. 1991. Changes in Mississippi River water this century. 

BioScience 41:140-147.

Watson, D., P. Foster, and G. Walker. 1995. Barnacle shells as biomonitoring material. Marine 

Pollution Bulletin 31:111-115.

Wells, R.J.D., J.H. Cowan, Jr., W.F. Patterson, III, and C.J. Walters. 2008a. Effect of trawling on 

juvenile red snapper (Lutjanus campechanus) habitat selection and life history parameters. 

Canadian Journal of Fisheries and Aquatic Sciences 65:2399-2411.

Wells, R.J.D., J.H. Cowan, Jr., and B. Fry. 2008b. Feeding ecology of red snapper, Lutjanus 

campechanus, in the northern Gulf of Mexico. Marine Ecology Progress Series 361:213-225.

Westmeyer, M.P., C.A. Wilson, III, and D.L. Nieland. 2007. Fidelity of red snapper to petroleum 

platforms in the northern Gulf of Mexico. Pages 105-121 in W.F. Patterson, III, J.H. Cowan, 

Jr., G.R. Fitzhugh, and D.L. Nieland, editors. Red snapper ecology and fisheries in the U.S. 

Gulf of Mexico. American Fisheries Society Symposium 60, Bethesda, Maryland.

Wilkinson, L., G. Blank, and C. Gruber. 1996. Desktop data analysis with SYSTAT. Prentice 

Hall, Upper Saddle River, NJ.

Xiao, T., D. Boyle, J. Guha, A. Rouleau, Y. Hong, and B. Zheng. 2003. Groundwater-related 

thallium transfer processes and their impacts on the ecosystem: southwest Guizhou Province, 

China. Applied Geochemistry 18:675-691.

Zapp Sluis, M., K.M. Boswell, M.M. Chumchal, R.J.D. Wells, B. Soulen, and J.H. Cowan, Jr. 

2013. Regional variation in mercury and stable isotopes of red snapper (Lutjanus 

campechanus) in the northern Gulf of Mexico, USA. Environmental Toxicology and 

Chemistry 32:434-441.
APPENDIX

SUPPLEMENTARY CANONICAL DATA
42

Table A.1.

Raw canonical coefficients for canonical discriminant analysis comparing location, region and habitat 

otolith chemical signatures of red snapper, Lutjanus campechanus, from three regions and two habitats in 

the Gulf of Mexico during the summers of 2007–2008.

Element

Location Region Habitat

Can 1 Can 2 Can 1 Can 2 Can 1 Can 2

11B -0.251 -3.079 0.391 -3.016 -0.275 0.343

138Ba -0.797 -0.934 -0.755 -0.946 0.530 0.872

209Bi -0.302 0.075 -0.313 0.024 -0.216 0.140

111Cd -0.195 0.561 -0.274 0.525 -0.184 -0.084

59Co -0.182 -0.202 -0.261 -0.232 0.316 0.202

63Cu -0.188 2.471 -0.749 2.276 -0.296 -4.546

65Cu 1.273 -1.184 1.518 -0.941 0.809 4.745

56Fe 0.029 0.207 -0.034 0.213 0.158 -0.211

7

Li -2.093 1.774 -1.981 1.641 -1.805 -0.598

55Mn 0.418 1.039 0.020 1.034 0.889 -0.991

98Mo -0.105 0.386 -0.352 0.312 0.356 0.405

206Pb 0.514 -0.016 0.544 0.056 0.188 -0.289

120Sn -0.240 0.557 -0.159 0.578 -0.481 -0.077

205Tl 1.931 0.244 2.162 0.452 -0.344 0.256

51V 0.216 0.220 0.201 0.262 0.120 0.283

64Zn 0.443 -1.975 0.826 -1.858 0.256 -9.053

66Zn 0.203 0.446 -0.002 0.468 0.613 8.086
The Department of the Interior Mission

As the Nation’s principal conservation agency, the Department of the Interior 

has responsibility for most of our nationally owned public lands and natural 

resources. This includes fostering the sound use of our land and water 

resources; protecting our fish, wildlife, and biological diversity; preserving the 

environmental and cultural values of our national parks and historical places; 

and providing for the enjoyment of life through outdoor recreation. The 

Department assesses our energy and mineral resources and works to ensure 

that their development is in the best interests of all our people by encouraging 

stewardship and citizen participation in their care. The Department also has a 

major responsibility for American Indian reservation communities and for 

people who live in island communities. 

The Bureau of Ocean Energy Management Mission 

The Bureau of Ocean Energy Management (BOEM) promotes energy 

independence, environmental protection, and economic development through 

responsible, science-based management of offshore conventional and 

renewable energy.