ACCESS NUMBER: 30951-18181 

STUDY TITLE: Platform Recruited Reef Fish, Phase 1: Do Platforms Provide Habitat 

That Increase the Survival of Juvenile Reef Fishes? 

REPORT TITLE: Proof of Concept for Platform Recruited Reef Fish, Phase 1: Do 

Platforms Provide Habitat for Subadult Red Snapper? 

CONTRACT NUMBER: 1435-01-99-CA-30951-18181 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA: Central 

FISCAL YEARS OF PROJECT FUNDING: 2001-2005 

COMPLETION DATE OF REPORT: February 2010 

COSTS: $239,743 

PROJECT MANAGER: Richard F. Shaw, PhD 

AFFILIATION: Louisiana State University, Coastal Marine Institute 

ADDRESS: Coastal Studies Institute, Louisiana State University, Baton Rouge, LA 

PRINCIPAL INVESTIGATORS: Richard F. Shaw, James H. Cowan, Jr., and Lauren K. 

Nowling 

KEY WORDS: red snapper, Essential Fish Habitat, site fidelity, artificial reefs, Gulf of 

Mexico oil and gas platforms, drilling muds, otolith microchemistry, trace element 

isotope ratio fingerprints, Inductively Coupled Plasma-Mass Spectrometry 

BACKGROUND: The 1996 reauthorization of the Magnuson-Stevens Fisheries 

Management and Conservation Act contains language calling for understanding and 

conservation of Essential Fish Habitat (EFH) for federally managed marine finfish and 

shellfish. One of the most pressing federal fisheries management concerns in the Gulf 

of Mexico region is the overfished status of the red snapper, Lutjanus campechanus. 

Most evidence suggests that bycatch of juvenile red snapper by shrimp trawling is the 

primary cause of overfishing. Juvenile red snapper are very abundant in specific 

locations that are presumed to be EFH. These habitats include naturally-occurring, 

open-sand bottom and low-relief shell rubble reefs, as well as oil and gas platforms and 

other artificial reefs (or at least in their proximity). The ways in which different life 

stages of red snapper utilize these various habitats as they grow, e.g. for feeding, 

protection or both, once they settle from the plankton as small juveniles, is poorly 

known. Moreover, some researchers question whether or not artificial reefs (of any 

type) are a positive influence on reef fish stock dynamics because of doubts about 

whether they produce or attract fish. Artificial reefs may be useful tools if they increase 

production; however, if they simply attract fish, they may be promoting overfishing. 

Consequently, resolution of this question is essential to the management of reef fish 
ACCESS NUMBER: 30951-18181 

stocks because current knowledge of artificial reefs as EFH is not adequate for 

managers to consider them as a viable management tools in all situations. 

While it has been demonstrated that juvenile red snapper have a strong preference for 

habitats with some vertical relief, it has been hypothesized that oil and gas platforms 

and their adjacent footprints or ‘shadows’ provide exceptionally high quality habitat, 

such that fishes located there have a survival advantage over conspecifics located in 

other artificial and natural environments. Increased habitat on, or immediately around, 

oil and gas platforms is believed to be derived from increased in situ food production 

associated with encrustation by fouling organisms, and by increased physical habitat via 

structures that extend from the bottom to the surface of the water column. 

OBJECTIVES: The main objective of this project was to test the hypothesis that 

association with oil and gas platforms during early life imparts a detectable ‘trace 

element isotope ratio fingerprint’ in the otoliths of juvenile red snapper, i.e., prespawning 

adults (age 2 to 4). It was hypothesized that the elemental fingerprint specific to 

platforms would depend upon the specific drilling muds discharged by the platform 

during its working years. This success of this phase of the project is set the stage for 

ongoing work (Phase II) that is testing whether adult fishes containing the ‘platform 

fingerprint’ in their otoliths contribute disproportionately to adult stocks on nearby natural 

and artificial reefs. The rationale for the choice of red snapper as a surrogate for reefassociated fish in Phase I of the project is due to their site fidelity, as well as their 

recreational and commercial importance. Although there are differing conclusions on 

red snapper site fidelity, we believe that they exhibit the appropriate model life history to 

prove the concept of this study. Red snapper have been shown to have high site fidelity 

(70%) during their first years as recruits on offshore habitats, with site fidelity decreasing 

as fish get older. Based on this work, we have shown that red snapper remain at oil 

and gas platforms long enough to incorporate a signal into their otoliths. If this signal 

proves to be temporally and geographically stable in Phase II, determination of the 

relative value of oil and gas platforms as red snapper EFH will be an important tool for 

fisheries managers and may help to restore stock size. The determination of the 

impacts of artificial reefs (of any type) on the demographics of reef-associated fishes is 

a necessary step in moving towards final resolution of the production vs. attraction 

debate. 

DESCRIPTION: Red snapper were collected from artificial reefs (anything other than 

oil and gas platforms – controls) in Alabama south of the Hugh Swingle permit area and 

Louisiana south of Port Fourchon in the South Timbalier Lease Block. Experimental fish 

collected from oil and gas platforms were fished from platforms in the Grand Isle Lease 

Block. All fish were collected during the two year period from 2002 to 2004 using hook 

and line. Fish were measured and their heads removed, frozen and sent to LSU for 

otolith removal. Otoliths were removed and sent to the University of Hawaii at Manoa 

where they were analyzed for fifteen (15) isotopes by Inductively Coupled Plasma-Mass 

Spectrometry. These isotopes, chosen because of their potential presence in drilling 

muds and platform operations, included Vanadium 51, Cobalt 59, Nickel 62, Zinc 64, 

Copper 65, Zinc 66, Silver 107, Cadmium 100, Cadmium 114, Lead 206, Lead 207, 

Lead 208, and Uranium 238. Data were analyzed statistically using stepwise and 
ACCESS NUMBER: 30951-18181 

canonical discriminant function analyses to compare red snapper otolith fingerprints 

from on and off platforms and from east and west of the Mississippi River. 

SIGNIFICANT CONCLUSIONS: This method was successful; otolith microchemistry 

can be used to determine the trace element signature of oil and gas platforms in otoliths 

of red snapper. 

Vanadium 51, Lead 206, Lead 207, and Lead 208 may be dissolution products 

incorporated into red snapper otoliths from oil and gas platform operations and their 

prior drilling operations. 

These result allowed us to move forward (in Phase II funded by MMS) with expanding 

the geographical and temporal coverage of samples of subadult red snapper (Gulfwide), and with micromilling a sub-sample of either otolith cores, or increments that are 

deposited with age progressively out from the core of adult fish, to determine if the new 

recruits that are now expanding into the eastern Gulf were associated with oil and gas 

platforms during some portion of their early life, and to determine age-specific habitat 

affinity. 

Phase II results should allow us to determine if there are a disproportionate number of 

adult red snapper in the eastern Gulf and elsewhere that have acquired this ‘oil and gas 

platform signature’ in their otoliths, sometime during their early life history. If this is true, 

oil and gas platforms may constitute red snapper essential fish habitat and, as such, 

should be considered as viable tools in management of red snapper.

STUDY RESULTS: The objective of this study was to determine if a trace element 

isotope ratio fingerprint could be detected and described as unique to red snapper 

inhabiting the platforms. Stepwise and canonical discriminant function analyses were 

used to compare red snapper otolith fingerprints from on and off platforms, and from 

east and west of the Mississippi River. Classification accuracies based on the 

probability of an individual fish being correctly classified into the habitat from which it 

was sampled were over 90% for each of the two main comparisons. When comparing 

the elemental composition of red snapper otoliths from Louisiana oil and gas structures 

and Louisiana artificial reefs, the classification accuracy was 93.75%. When comparing 

the elemental composition of red snapper otoliths from Louisiana artificial reefs and 

Alabama artificial reefs, the classification accuracy was 91.06%. Vanadium 51, Lead 

206, Lead 207, and Lead 208 all appear to be linked with oil and gas structures or their 

prior drilling operations, as the concentrations of these four elements or isotopes were 

significantly higher in otoliths sampled from platforms in Louisiana than in otoliths 

sampled from artificial reefs in either Louisiana or Alabama. These platform isotopic 

fingerprint results indicate that it may be possible to sub-sample from otoliths of adult 

fish in Phase II of our study to determine age-specific habitat affinity, and to determine if 

the new recruits now expanding into the eastern Gulf as the red snapper population 

rebuilds were associated with oil and gas platforms during some portion of their early 

life. 
STUDY PRODUCT: Nowling, L.K., J.H. Cowan, Jr., and R.F. Shaw. 2010. Proof of 

concept for platform recruited reef fish, Phase 1: Do platforms provide habitat for 

subadult red snapper? U.S. Dept. of the Interior, Minerals Management Service, Gulf of 

Mexico OCS Region, New Orleans, LA. OCS Study MMS 2010-002. 80 pp.