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OCS Study 

MMS 2003-009 

 

Coastal Marine Institute 

Rigs and Reefs: A Comparison 

of the Fish Communities at Two Artificial 

Reefs, a Production Platform, and a 

Natural Reef in the Northern Gulf of Mexico 

Final Report 

Cooperative Agreement

Coastal Marine Institute 

Louisiana State University 

U.S. Department of the Interior

Minerals Management Service 

Gulf of Mexico OCS Region 
U.S. Department of the Interior Cooperative Agreement 

Minerals Management Service Coastal Marine Institute 

Gulf of Mexico OCS Region Louisiana State University 

OCS Study 

 MMS 2003-009 

 

Coastal Marine Institute 

Rigs and Reefs: A Comparison 

of the Fish Communities at Two Artificial 

Reefs, a Production Platform, and a 

Natural Reef in the Northern Gulf of Mexico 

Final Report 

Editors 

Charles A. Wilson 

Aaron Pierce 

Mark W. Miller 

August 2003 

Prepared under MMS Contract 

14-35-0001-30660-19960 

by 

Coastal Fisheries Institute 

School of the Coast and Environment 

Louisiana State University 

Baton Rouge, Louisiana 70803 

Published by 
iii

DISCLAIMER

This report was prepared under contract between the Minerals Management Service (MMS) and

Coastal Fisheries Institute, Louisiana State University (LSU). This report has been technically

reviewed by the MMS, LSU, and it has been approved for publication. Approval does not

signify that the contents necessarily reflect the views and policies of LSU or the MMS, nor does

mention of trade names or commercial products constitute endorsement or recommendation for

use. It is, however, exempt from review and compliance with the MMS editorial standard.

REPORT AVAILABILITY

Extra copies of the report may be obtained from the Public Information Office (Mail Stop 5034)

at the following address:

U.S. Department of the Interior

Mineral Management Service

Gulf of Mexico OCS Region

Attn: Public Information Office (MS 5034)

1201 Elmwood Park Boulevard

New Orleans, Louisiana 70123-2394

Telephone: (504) 736-2519 or

1-800-200-GULF

CITATION

Suggested citation:

Wilson, C.A., A. Pierce, and M.W. Miller. 2003. Rigs and Reefs: a Comparison of the Fish

Communities at Two Artificial Reefs, a Production Platform, and a Natural Reef in the

Northern Gulf of Mexico. Prepared by the Coastal Fisheries Institute, School of the

Coast and Environment. Louisiana State University. U.S. Dept. of the Interior,

Minerals Mgmt. Service, Gulf of Mexico OCS Region, New Orleans, LA. OCS Study

MMS 2003-009. 95 pp.
v

ACKNOWLEDGMENTS

The authors wish to thank Mr. Greg Boland in the Environmental Studies Section of the

Minerals Management Service, New Orleans for his guidance during this project and help with

information concerning the Flower Gardens. We also recognize the pioneering efforts of Dr.

Dave Stanley for establishing the use of hydroacoustics to study fish around platforms and for

playing an integral role in the original project design. We extend our appreciation to Louisiana

Department of Wildlife and Fisheries (LDWF) for helping fund this and other projects related to

the work our group has conducted around oil and gas platforms and resultant artificial reefs. We

extend special thanks to Rick Kasprzak, Coordinator of the Louisiana Artificial Reef Program at

LDWF for his help in identifying study sites, assistance in survey design, and assistance in

reviewing earlier versions of this report. We thank Jan Culbertson of Texas Parks and Wildlife

for providing information about reef sites off of Texas. We extend out deepest appreciation to

Shell Oil Company who provided logistical support for our work on High Island 350A. Many

LSU graduate and undergraduate students and research associates deserve recognition for their

work in and/or research leading up to this project including, but not limited to Jeff Render,

Yvonne Allen, Dave Nieland, Joe Nunn, Jim Tolan, Wes Heath, Alex Grenier, Jim Boland,

Lyndy Donnelson, Joel Chalky, Dave Harmon, and Eddie Weeks. Many thanks to Dr. Jay

Geaghan of LSU for his assistance with statistical analysis.
vii

EXECUTIVE SUMMARY

The proximity of the two Rigs to Reefs projects and an operating oil and gas platform to

the natural coral formations of the Flower Gardens (WFGB) afforded us the opportunity to not

only compare several platform configurations, but also to compare the fish communities at

“artificial reefs” to that of a neighboring natural system. It was therefore the purpose of this

study to compare the fish communities associated with an operating oil and gas platform, two

artificial reef configurations, and the WFGB. Reef configurations included a production

platform toppled in place as a deep water artificial reef (West Cameron 617A), a nearby partially

removed platform (High Island A355), and an operating production platform (High Island

A350). We sought to identify species composition at each site; to estimate the fish

biomass/density associated with each site; to determine the effects of side, depth, and distance

from each site on fish biomass. Comparisons were then made between these sites and to other

sites that had been surveyed.

Dual beam hydroacoustic surveys were used to estimate fish density and biomass at all

sites. Survey design consisted of a stationary array of four transducers at the standing platform

and mobile surveys at the remaining sites. The mobile survey of the two reefs sites consisted of

multiple vessel passes over each structure and the mobile survey of WFGB consisted of

twenty-seven transects spaced 300 meters apart running along the long axis of the WFGB, from

northeast to southwest. Visual surveys were conducted with a Deep Ocean Engineering Phantom

HD2 ROV with standard visual census techniques recorded onto S-VHS video tape.

Overall, we found that fish biomass and density and around the standing oil and gas

platform was higher than the artificial reefs or natural reef. Comparison of the mean biomass

(Sv) found at the standing platform and over and immediately around the two reef sites and the

WFGB terraces clearly indicate an order of magnitude difference in fish biomass between the

standing platform and other sites, suggesting that standing platforms support greater fish

biomass. Our results are in support of previous findings that when a platform is converted into a

artificial reef by toppling in place or by partial removal, it loses a significant portion of the fish

community. Fish biomass at the artificial reef sites was similar to the upper terrace of the

nearby natural reef. In each habitat, we tended to find higher fish densities in habitats with more

vertical structure. 

This research continues to support the working hypothesis that platforms do make useful

artificial reefs since they tend to support a population of fish that can be 10 to over 1000 times

greater in density than the adjacent sand and mud bottom habitats, and are equal to or even

exceed that of natural coral reef habitat like the WFGB. The species associated with the

artificial reefs (including standing platforms) do however, differ from those found on natural reef

habitats. Future research efforts might be directed toward determining the reasons for this

difference. Integration of these types of study results into a comprehensive spatial database will

go far to improving management of these resources. 
ix

TABLE OF CONTENTS

 Page

List of Figures......................................................................................................... xi

List of Tables.......................................................................................................... xv

List of Abbreviations.............................................................................................. xvii

1.0 Introduction............................................................................................... 1

1.1 Past Research...................................................................................... 2

1.2 Goals of This Study ............................................................................ 4

2.0 Materials and Methods................................................................................ 7

2.1 Site Descriptions.................................................................................. 7

2.1.1 High Island A350 (standing platform).................................... 7

2.1.2 West Cameron 617A (toppled platform)................................ 7

2.1.3 High Island A355 (partially removed platform)..................... 7

2.1.4 West Flower Garden Bank (WFGB)...................................... 7

2.2 Survey Designs.................................................................................... 10

2.2.1 High Island A350................................................................... 10

2.2.2 West Cameron 617A and High Island A355.......................... 10

2.2.3 West Flower Garden Bank..................................................... 12

2.3 Acoustic Data Collection and Processing.............................................. 12

2.4 Data Analysis....................................................................................... 16

2.4.1 Statistical Analysis................................................................ 16

2.4.2 Randomized Block Design (RBD) ANOVA's........................ 17

2.4.3 Logistic Regression............................................................... 17

2.4.4 Fish Abundance Estimation.................................................... 18

2.5 Visual Surveys..................................................................................... 18

3.0 Results............................................................................................................. 21

3.1 High Island A350 (standing platform) Results...................................... 21
x

TABLE OF CONTENTS (CONTINUED)

 Page

3.1.1 Fish Energy (from Sv)............................................................ 21

3.1.2 Density Estimates.................................................................. 21

3.1.3 Target Strength..................................................................... 21

3.1.4 Species Composition and Abundance..................................... 31

3.2 West Cameron 617A and High Island A355 Results........................ 31

3.2.1 West Cameron 617A Results................................................. 38

3.2.1.1 Fish Energy ............................................................ 38

3.2.1.2 Target Strength....................................................... 38

3.2.1.3 Density Estimates.................................................... 49

3.2.1.4 Species Composition and Abundance...................... 49

3.2.2 High Island A355 (partially removed platform) Results......... 49

3.2.2.1 Fish Energy............................................................. 49

3.2.2.2 Target Strength....................................................... 56

3.2.2.3 Density Estimates.................................................... 56

3.2.2.4 Species Composition and Abundance.................... 56

3.3 West Flower Garden Bank Results.................................................. 59

 3.3.1 Fish Energy............................................................................ 59

3.3.2 Density Estimates.................................................................. 66

3.3.3 Target Strength..................................................................... 66

3.3.4 Species Composition and Abundance..................................... 66

4.0 Discussion........................................................................................................ 75

5.0 References........................................................................................................ 87

Appendix A. Images from ROV Surveys Conducted in June 1999 and June 2000 of High 

Island A 355, and West Cameron 617A........................................... 93
xi

LIST OF FIGURES

Figure Page

1 Map of the sites surveyed in June 1999 and 2000 8

2 Configuration of downward-facing transducers at HI A350. 11

3 Survey design for the mobile surveys of the artificial reef sites. 13

4 Intended vessel track lines for the WFGB hydroacoustic survey conducted in 14

June 2000.

5 Sample color echogram showing structure as viewed in Visual 15

Analyzer v 4.02.

6 Mean fish energy/m3

 (antilog of volume backscattering) by depth 25

stratum for HI A350.

7 Mean fish energy/m3

 (antilog of volume backscatter) at TOD 26

for HI A350. 

8 Estimated mean fish density (#/m3) at depth for HI A350. 27

9 Estimated mean fish density (#/m3) at TOD for HI A350. 28

10 Estimated mean target strength (dB) by depth stratum around 29

HI A350.

11 Estimated mean target strength (dB) by TOD around HI A350. 30

12 Line drawings of WC 617A (toppled platform) and HI A355 32

(partially removed platform with a small 4-leg section to the 

southwest).

13 Plot of vessel track (dotted lines) over WC 617A (A) and 33

HI A355 (B) for surveys conducted June 1999 and June 2000. 
xii

LIST OF FIGURES (CONTINUED)

14 Acoustic depth profiles of WC 617A and HI A355 based on a 34

geo-referenced plot of depth from the hydroacoustic survey 

conducted in June 1999 and 2000.

15 Color enhanced echograms of WC 617A (A) and HI A355 (B) 35

from BioSonics Visual Analyzer (v4.02) analysis viewer.

16 Change in probability of finding a fish with consecutive transect 36

number for WC 617A (A) and HI A355 (B) during 1999 

referenced to the final transect.

17 Estimated mean fish energy /m3

 (antilog of volume backscatter) 41

at distance from reef site for WC 617A (A) and HI A355 (B).

18 Estimated mean fish energy /m3

 (antilog of volume backscatter) 42

at orientation for WC 617A (A) and HI A355 (B).

19 Estimated mean fish energy /m3

 (antilog of volume backscatter) 43

at depth stratum for WC 617 (A) and HI A355 (B).

20 Estimated mean fish energy /m3 (antilog of volume backscatter) 44

by TOD for WC 617A (A) and HI A355 (B).

21 Estimated mean target strength (Love 1971) by orientation for WC 617A 45

(A) and HI A355 (B).

22 Estimated mean target strength (Love 1971) at distance from reef site for 46

WC 617A (A) and HI A355 (B).

23 Estimated mean target strength (dB) at depth stratum for WC 617A (A) 47

and HI A355 (B).

24 Estimated mean target strength (dB) at time of day for 48

WC 617A (A) and HI A355 (B).

25 Estimated mean fish density (fish/m3

) at distance for the reef site 50

for WC 617A (A) and HI A355 (B).

26 Estimated mean fish density (fish/m3) by orientation for 51

WC 617A (A) and HI A355 (B).
xiii

LIST OF FIGURES (CONTINUED)

27 Estimated mean fish density (fish/m3) by depth stratum for 52

WC 617A (A) and HI A355 (B).

28 Estimated mean fish density (fish/m3) by TOD for 53

WC 617A (A) and HI A355 (B).

29 Actual track lines of the WFGB hydroacoustic survey 61

conducted in June 2000.

30 Echogram of WFGB survey conducted June 2000. 62

31 Echograms from June 2000 hydroacoustic survey of the WFGB. 63

32 A color enhanced image of the relative horizontal acoustic 64

reflectance over a bathymetry outline of the WFGB.

33 A color enhanced image of the relative horizontal acoustic 65

reflectance over a bathymetry outline of the WFGB

34 Mean fish energy (from volume backscatter) by Terrace over 67

the West Flower Garden Bank based on a dual beam 

hydroacoustic survey conducted in June 2000.

35 Mean fish energy (from volume backscatter) by time of day 68

over the West Flower Garden Bank based on a dual beam 

hydroacoustic survey conducted in June 2000.

36 Mean target strength (dB) by Terrace over the West Flower 69

Garden Bank based on a dual beam hydroacoustic survey 

conducted in June 2000.

37 Estimated density of fish (fish/m3

)

 over the West Flower Garden 70

Bank based on a dual beam hydroacoustic survey conducted in 

June 2000.

38 A color enhanced image of the estimated density of fish (#/m3

) 71

over a bathymetry outline of the WFGB. 
xiv

LIST OF FIGURES (CONTINUED)

39 Comparison of the mean fish energy observed over and immediately 77

around the standing (HI 350A), partially removed (WC 617A), and 

Toppled (HI A355) platforms and the upper, middle, and lower 

terraces of the WFGB.

40 Estimated fish density at depth for all sample locations. 77

41 Proportion of fish by depth at each survey site (platforms) based 79

on ROV surveys.

42 Average number of fish found at platforms and platforms used as 82

artificial reefs as determined with dual beam hydroacoustics 

(Jan 1992-Jan 2002). 

A1 A school of greater amberjack swims by a severed leg of 95

HI 355 A.

A2 Closeup of a creolefish in the wellbay of HI A350. 95

A3 A collection of mixed reef fish along one of the well bay 95

of HI A350.

A4 A scamp swims towards the toppled WC 617A platform. 95

A5 A red snapper swims down through the water column of 95

HI 355 A.

A6 A warsaw grouper swims through the piling of WC 617A 95

size is estimate ~ 1 meter.
xv

LIST OF TABLES

Table Page

1 General information about the oil and gas structures surveyed 9

in June 1999 and 2000 with stationary or mobile dual beam 

hydroacoustics.

2 RBD ANOVA (block on side) results (significant) of fish energy 22

(arithmetic form of volume backscatter) with platform side 

(Ornt), depth stratum (Stratum), TOD, and selected

interactions at High Island A350.

3 RBD ANOVA (block on side) results (significant) of 23

log10 (fish density) with platform side (Ornt), depth stratum 

(Stratum), TOD, and selected interactions at High Island A350.

4 RBD ANOVA (block on side) results (significant) of target 24

strength with, depth stratum (Stratum), TOD, and selected 

interactions at High Island A350.

5 Species common names and scientific names, numbers of 37

individuals by stratum, totals, and percent composition from visual 

point counts using video from a remotely operated vehicle (ROV) 

from High Island A350, June 1999.

6 Logistic regression analysis results of fish energy (antilog of 39

volume backscatter) with platform side (Ornt), depth stratum 

(Stratum), and TOD at West Cameron 617A.

7 RBD ANOVA (block on side) results of target strength with 40

platform side, depth stratum, distance away from the platform,

TOD, and selected interactions at West Cameron 617A.

8 Species common and scientific names along with numbers of individuals 54

by stratum, totals, and percent composition from visual point

counts using video from a remotely operated vehicle (ROV) from

a toppled platform (West Cameron 617A) June 1999.

9 Logistic analysis results of fish energy (antilog of volume 55

backscatter) with class variables platform side (Ornt), depth stratum 

(Stratum), and time of day at High Island A355.
xvi

LIST OF TABLES (CONTINUED)

10 RBD ANOVA (block on side) results of target strength with 57

platform side (Side), depth stratum (Stratum), distance away 

from the platform (Away), time of day, and selected interactions 

at High Island A355.

11 Species common and scientific names along with numbers of individuals 58

by stratum, totals, and percent composition from visual point counts 

using video from a remotely operated vehicle (ROV) from a partially 

removed platform (High Island A355) June 1999 and 2000.

12 Logistic analysis results of fish energy (antilog of volume 60

backscatter) with class variables terrace level (Terrace), depth 

stratum (Stratum), and time of day (TOD) at WFGB.

13 RBD ANOVA (block on Terrace) results (significant) of target 72

strength with stratum (Strata), and time of day and selected 

interactions at WFGB.

14 Species common and scientific names along with numbers of individuals by 73

stratum, totals, and percent composition from visual point counts

using video from a remotely operated vehicle survey (ROV) from the West 

Flower Garden Bank, June 2000.

15 Estimated numbers of fish over the West Flower Garden Bank based 74

on a dual beam hydroacoustics survey conducted in June 2000. 

16 Percent species composition at the standing platform (HI 350A), 80

partially removed (HI A355) and toppled platform (WC 617A), 

based on ROV surveys.
xvii

LIST OF ABBREVIATIONS

ANCOVA analysis of covariance

ANOVA analysis of variance

GOM Gulf of Mexico

HI High Island

kts knots

RBD randomized block design

RTR rigs to reefs

S sigma

TOD time of day

TS target strength

WC West Cameron

WFGB West Flower Garden Bank
1

1.0 INTRODUCTION

Most of the natural substrate in the northern Gulf of Mexico (GOM) from Destin, Florida

to Brownsville, Texas is silty with approximately 2800 km2 of naturally occurring hard bottom

(Parker et al. 1983). In the last 60 years, the area of hard substrate in this region has increased

through the development of infrastructure for a thriving oil and gas industry. Currently, there are

4,046 oil and gas platforms operating in state and federal waters of the northern GOM

(http://www.gomr.mms.gov/homepg/pubinfo/freeasci/platform/freeplat.html), creating the

largest de facto artificial reef system in the world. Combined, these platforms only increase the

surface area of hard substrate available in the northern GOM by 4% (Stanley and Wilson 1990,

1991, 1997), but they arguably have a substantial impact on regional fisheries. Off the coast of

Louisiana in particular, the Mississippi River deposits vast amounts of clay and other finegrained sediment and oil and gas platforms provide a large percentage of hard-bottom area for

reef-dwelling fishes. In coastal waters off Louisiana, Stanley and Wilson (1996, 1997, 1998,

2000a), determined that each standing platform seasonally provides habitat for 10,000-20,000

fishes, many of which are of great recreational and commercial importance. By adding

substantially to the amount of reef available, petroleum platforms have doubtless affected many

regional ecosystem processes such as energy (food) availability, habitat, recruitment, 

competition, and predation (Menge and Sutherland 1987; Doherty and Williams 1988; Bohnsack

et al. 1991; Stanley and Wilson 2000a).

In response to both the federally mandated removal of obsolete platforms, and to the

popularity of petroleum platforms as fishing destinations, Louisiana, Texas, and other states

along the northern GOM now convert retired oil and gas platforms into artificial reefs (NRC

1996). The Louisiana Artificial Reef Program (LARP) was established in 1986 and is currently

administered by the Louisiana Department of Wildlife and Fisheries. The Texas Parks and

Wildlife Department established a rigs-to-reef program in 1988. To date, these states have

established over 150 artificial reefs from converted oil and gas platforms.

The concept of using oil and gas platforms as artificial reefs i.e. “Rigs to Reefs” (RTR) is

strongly supported by recreational and commercial fishers and their respective organizations

such as the Coastal Conservation Association. The scientific community, however, still

questions the real ecological value of artificial reefs in general, and the particular effectiveness

of petroleum platforms as artificial reefs. Specifically, do artificial reefs primarily increase reef

fish production or do they attract reef fishes away from natural substrates. How do species

composition and density of artificial reef fish communities compare to those found on natural

substrates? (Seaman and Jensen 2001). 

Beyond purely scientific concerns, there are also many management questions

concerning the effect of water depth, geographic location, and general reef configuration on fish

production at both standing platforms and artificial reefs. For example, under current RTR

projects, oil and gas platforms are typically converted into reefs by laying a platform on its side

either by toppling in place or by moving a toppled platform to a new location. More recently,

the Louisiana Artificial Reef Program has followed the Texas Artificial Reef Program by
2

removing the top portion of a standing platform to a depth (typically 85 feet below surface)

sufficient to comply with Coast Guard regulations. This practice is referred to as partial

removal. Stanley and Wilson (1997) proposed that vertical profile is important in maintaining

the fish density resident at standing platforms. There is a great difference in the vertical profile

of standing, toppled and partially removed platforms, and we therefore may expect fish density

and species composition to be different among these three different artificial reef configurations. 

1.1 Past Research

There have been several surveys of fish communities conducted around oil and gas

platforms in the GOM. The extent of this work was reviewed by Stanley and Wilson (2000a)

and is summarized below. Scientific investigations of fish assemblages at petroleum platforms

did not start until the mid 1970's. They consisted of visual surveys performed by SCUBA divers,

with remotely operated underwater vehicles (ROV), and with stationary cameras. The majority

of these projects were short term, even one time studies (Sonnier et al. 1976; Gallaway et al.

1981; Continental Shelf Associates 1982; Gallaway and Lewbel 1982; Putt 1982). The results of

this early research described the fish density and species composition found at each platform,

and how they varied amongst platforms, water depth, and time of year. The results are, however,

difficult to compare due to sampling problems associated with limited visibility, gear bias, and

diver avoidance by fish, including lack of standardized survey methodology. Although visual

surveys are the method of choice to survey natural and artificial reefs (Bortone and Kimmel

1991), the presence of SCUBA divers affects the density and possibly species composition of

fishes at the site (Sale and Douglas 1981; Brock 1982; Bohnsack and Bannerot 1986; Stanley

and Wilson 1995). 

In response to the difficulty in assessing these fisheries resources, several investigators

evaluated and established guidelines for using acoustics to survey platform communities.

Gerlotto et al. (1989) demonstrated that towed hydroacoustics could be used to measure fish

densities near petroleum platforms off Cameroon. Scientists at Louisiana State University’s

Coastal Fisheries Institute combined visual surveys and quantitative dual beam hydroacoustics to

document the assemblage of fishes associated with four petroleum platforms in the northern Gulf

of Mexico (Wilson and Stanley 1991; Stanley and Wilson 1995, 1996, 1997, 2000a). 

 

Regardless of methodologies, investigators have reported that platforms harbor a large

numbers of fishes, and that abundances and species compositions vary greatly both spatially and

temporally (Sonnier et al. 1976; Continental Shelf Associates 1982; Gallaway and Lewbel 1982;

Putt 1982; Stanley and Wilson 1996, 1997, 2000a). Gerlotto et al. (1989) reported that fish

densities were 5 to 50 times higher immediately adjacent to a platform than 50 m away. Stanley

and Wilson (1996, 1997) reported that fish densities were 3-25 times higher within 16m of the a

standing platform on the GOM continental shelf. At 30m, they found that fish densities were

comparable to open waters of the northern GOM. Long-term studies have also reported that fish

populations at petroleum platforms are highly variable over time. Putt (1982) reported that

density varied by a factor of two from month to month, while Stanley and Wilson (1996, 1997,

2000b) reported that spatial, monthly, and seasonal abundances varied by up to a factor of five. 
3

The importance of standing platforms in holding significant reef fish communities has

been well established. There are, however, little data to determine whether currently popular

RTR configurations are as productive as standing platforms. And further, there is little research

comparing fish community characteristics on artificial and natural reefs. Although Wilson and

Stanley (1998) suggested that both toppled and partially removed platforms may not be as

productive as either standing platforms or natural reef systems, the impact of various RTR

conversions on the resulting reef community needs further investigation.

The largest natural reef in the northern GOM is the Flower Garden Banks (Flower

Gardens). Although fishermen have known about the Flower Gardens since the late 1800's, it

was not until 1936 that the banks were officially discovered by the U.S. Coast and Geodetic

Survey during surveys in the GOM to map pinnacles. In 1961, Dr. Thomas E. Pulley

documented that the Flower Gardens were viable coral communities (Elvers and Hill 1985). 

After nearly two decades of effort, the Flower Gardens were designated a marine sanctuary in

1992 (Gittings and Hickerson 1998). Although several fisheries surveys have been conducted

around these geological features, few scientific investigations have considered a holistic account

of the fish population and fish density beyond the cryptic reef fishes.

To date, the most extensive survey of fish assemblages on the Flower Gardens was

conducted by LGL Ecological Research Associates during a period from 1980 to 1982. The

report (Boland, et. al. 1983), funded by the Environmental Protection Agency through the

National Marine Fisheries Service, was based on 357 hours of video data processed in 1 minute

intervals and determined the standing stock/density estimates of 16 primary reef fish taxa. A

total of 141 fish taxa were reported from 12 cruises to the East and West Flower Garden Banks. 

The investigators reported characteristic fish assemblages zoned primarily by depth and/or

habitat types. Habitat types included: upper coral reef, algal-nodule sponge zone, shallow

drowned reef, deep drowned reef, and soft bottom. The investigators also estimated species

abundance. For example, they estimated that the population size for creole-fish Paranthias

furcifer ranged from 400,000 to 993,948, red snapper Lutjanus campechanus from 4,000 to

20,000, and groupers Mycteroperca spp. from 20,000 to 47,000 at the East Flower Garden Bank.

Biotic zonation of the West Flower Garden Bank (WFGB) was described by Bright et. al.

(1974). They reported on the major biotic elements of the bank and provided a quantitative

baseline assessment of the reef community. They used divers, towed video systems and manned

submersibles to collect seventy days of data during 17 cruises between July 1970 and December

1972. Their report included a thorough catalog of fauna. Bright and Cashman (1974) reported

that 101 fish species at the WFGB.

Three distinct reef fish assemblages were reported at the WFGB (Dennis and Bright

1988) in association with three major biotic zones (coral reef, algal-sponge, and drowned reef). 

Species composition is similar to outer slope Carribean reefs, but the WFGB exhibits a much

lower diversity (253 primary species reported at Caribbean reefs versus 84 found at the WFGB). 

Cluster analysis of fish assemblages yielded three depth zonations with a distinct species
4

composition in each of the three zones. Twenty-eight species were observed in the upper zone

(<45m), 45 species were observed in the middle zone (45-85m), and 20 species were observed in

the lower zone (>85m). These depth ranges are consistent with the known epifaunal zones for

this area

Rooker, et. al. (1997) found marked differences when they compared fish species

richness at the WFGB to a nearby oil platform (High Island A389A). They reported 54 species

and 39 species, respectively, at the WFGB and HI A389A. They also reported that midwater

pelagics such as carangids and scombrids accounted for over 50% of all taxa enumerated at the

platform while 50% of the observed total fish population at the WFGB was species from the

family Pomacentridae.

1.2 Goals of This Study

The close geographic proximity of several RTR projects to a standing platform (HI

A355) and the natural coral formations of the Flower Gardens afforded us the unique opportunity

compare the fish communities associated with these different habitats using hydroacoustics and

ROV. RTR configurations included a production platform toppled in place as a deep water

Louisiana artificial reef (WC 617A), and a nearby platform (HI A355) partially removed as a

Texas artificial reef. 

While several qualitative studies have documented the colonization and relative

abundance of organisms associated with standing production platforms, no one has attempted to

compare the fish communities of these platforms to those found associated with different

artificial reef configurations and natural reefs. This research project was designed to assist

MMS, the National Marine Fisheries Service, and the artificial reef programs of Louisiana and

Texas in decisions regarding the deployment and siting of platforms as artificial reefs, especially

with respect to deep water artificial reefs.

The goals of this study were therefore to : 1) identify species composition at each

artificial reef site, 2) estimate fish density and biomass associated with each site, 3) determine

the effects of orientation, depth, and distance away from each site on fish biomass, and 4)

determine the relative importance of reef configuration on the each of these measures. During

the course of the study, we expanded our efforts to include an analysis of the abundance and

distribution of fish populations at the WFGB reef system, and determine how these metrics

compare to those found at artificial reefs. Comparisons were also made to results from

previously published studies.

This report is presented in four sections. The following Materials and Methods (Section

2) gives detailed site descriptions, explains the equipment, site specific sampling design, and

acoustic and statistical analysis. The Results section (Section 3) is separated into the results for
5

 the standing platform (HI A350) and the two artificial reef sites (HI A355, and WC 617A) and

the WFGB. A common Discussion (Section 4) section is used to compare and synthesize the

results.
7

2.0 MATERIALS AND METHODS

2.1 Site Descriptions

This research project was designed to effectively sample and compare the fish resources

associated with a standing platform, two artificial reefs and natural reef system located in a

similar geographic region in the northern GOM off the Texas/Louisiana border (Figure 1 and

Table 1). 

2.1.1 High Island A350 (standing platform)

The standing platform, HI A350, owned by Shell Corporation, is located at 28o 1.130'

north latitude and 93o 27.512' west longitude. This large 8 pile structure was installed in 1976

(Table 1) in 90 m of water. The vertical profile of this standing platform goes from the bottom to

the surface of the 90m in water column and occupies a footprint of 68m x 40m at its base.

2.1.2 West Cameron 617A (toppled platform)

The toppled platform, WC 617A, owned by Mobil Corporation, is located at 28o 3.664'

north latitude and 93o 18.805' west longitude at a depth of 98 m. It was installed as an eight pile

structure in 1976. In July 1992, the upper deck was removed then the jacket was severed below

the mudline with explosives, then the remaining structure was toppled in place. This toppled

platform has a vertical profile of 31m in the 98m water column and occupies a footprint of 84 m

x 20 m. 

2.1.3 High Island A355 (partially removed platform)

The partially removed platform, HI A355, owned by Occidental Petroleum, is located at

28o 2.491' north latitude and 93o 42.551' west longitude in 90 m water depth. It was installed as

a large eight pile structure in 1978. In January 1996, it was partially removed by mechanically

cutting it at -27.5 m. The upper jacket was split vertically, and a four pile portion was set to the

southeast side of the main structure. The remainder was returned to shore. This partially

removed platform has a vertical profile of 68m in the 90m water column and occupies a footprint

of 60m x 40m. The four pile section on the south side has a vertical profile of 32 m and occupies

a footprint of 24m x 18m. 

2.1.4 West Flower Garden Bank (WFGB) 

 

The WFGB is located about 172 km southeast of Galveston, Texas, on the edge of the

outer continental shelf at 27/ 52.4' north latitude and 93/ 48.8' west longitude. The WFGB was

created by the uplift of a salt dome of Jurassic, Louann origin (Rezak 1981, as in Dokken et 
HI A 355

Partially Removed WC 617

Platform oppled Platform

* H1A350

West Flower Standing Platform

Garden Banks

8

Figure 1 . Map of the sites surveyed in June 1999 and 2000
9

Table 1. 

General information about the oil and gas structures surveyed in June 1999 and 2000 with stationary or m

hydroacoustics.

SITE COMPANY LATITUDE LONGITUDE DEPTH PILES INSTALLED REMOV

HI A350

(standing)

SHELL 28.01884N 93.4585W 89 8 1976

HI A355

(partially

removed)

OXY USA 28.04152N 93.70919W 88.4 8 1978 1/15/19

WC617A

(toppled)

MOBIL 28.06107N 93.31342W 97.5 8 1976 7/16/19
al. 1999). It is the largest charted calcareous bank in the northwestern GOM (Bright

et al. 1985 as in Dokken et al. 1999) and the northern-most coral reef on the continental shelf of

North America (Bright et al. 1984 as in Dokken et al. 1999). The coral cap varies in depth from

approximately 18 to 36 meters. (Rezak et al. 1985 as n Dokken et al. 1999). The major features

of the 137 km2 WFGB are three crests aligned along an east-west axis. The middle, most

prominent crest rises from a surrounding depth of 100 –150 meters to within 18 meters of the

surface and supports a coral reef community. (Rezak et al. 1985 as in Dokken et al. 1999).

2.2 Survey Designs

At the standing platform, stationary dual beam hydroacoustic surveys (Stanley and

Wilson 1997) were conducted using an array of four transducers. At the remaining sites, mobile

acoustic surveys were done using a single transducer mounted on a v-fin tow body (towfish). 

The original plan was to conduct stationary acoustic sampling at each of the two RTR sites,

however, the research vessels were unable to anchor effectively due to high currents

2.2.1 High Island A350 

The standing platform was surveyed in June 1999 with stationary dual beam

hydroacoustic equipment and sampling design developed during previous research efforts

(Wilson and Stanley 1991; Stanley and Wilson 1995, 1996, 1997,1998, 1999). The stationary

transducer array (Figure 2) was designed to measure in situ target strength distribution and

density of fishes immediately adjacent to each side of the platform. Three downward-oriented

transducers (120 kHz) were placed approximately 3 m below the surface, one on each side of the

platform. The fourth transducer on the west side could not be used due to equipment failure. 

Vertical acoustic sampling consisted of two hour time blocks over a 24 hour interval

encompassing four periods (dawn, noon, dusk and midnight). Hydroacoustic data were collected

sequentially from each transducer in five minute intervals.

2.2.2 West Cameron 617A and High Island A355 

For the mobile acoustic surveys at the RTR sites, a 120 kHz downward oriented

transducer was towed from the starboard hip of the research vessel R/V Pelican (June 1999) or

the M/V Epic Mariner (June 2000). The towfish was flown 5 m from the side of the hull with a

telescoping mast and 3 m below the surface at approximately 4 kts. Navigational data were

collected with a Garmin GPS III global positioning system (GPS) with a Garmin GB 21

differential beacon receiver. The antenna for the GPS was mounted directly above the tow body.

The navigation data stream, updated once per second, was incorporated into the acoustic data

string and then saved onto a laptop computer. The towed transducer provided acoustic coverage

from a depth of 10 m to within approximately 5 m of the bottom depending upon site.

10 
Figure 2. Configuration of downward-facing transducers at HI A350.

11 
Survey transects over the RTR sites were alternating east-west then north-south passes

over the target area (Figure 3). In June 1999 a total of 100 transects (50 east-west and 50

north-south) were run over each site. In the June 2000 survey, efforts were reduced to a total of

40 transects (20 east-west and 20 north-south) which gave the same statistical power as the 1999

survey. Transects were extended out to a distance of 100 m from each side of the target area for

a total transect distance of approximately 300 m.

2.2.3 West Flower Garden Bank

 The mobile survey of WFGB consisted of twenty-seven transects spaced 300 meters

apart running along the long axis of the WFGB, from northeast to southwest (Figure 4). 

Transect lines were planned to begin and end near the outer boundaries of the Marine Sanctuary

along the 100 m depth curve. This design allowed an open water control sample to be collected

at the beginning and ending of every transect line. The lines varied in length from 2.5 kilometers

to 13.5 kilometers. Data were collected along these transects continuously over a 29 hour period

from 21-23 June 2000. For analysis purposes, the data collected at the WFGB were separated

into three “terraces” based on water depth and specified as upper (20-50 meters), middle (80-

100 meters), and lower (> 100 meters) (Bright and Boland 1985). A high resolution multi-beam

side scan survey assisted the determination of the terraces (Gardner et al. 1998). These

geological terraces have also been related to distinct biological zonations (Dennis and Bright

1998). 

2.3 Acoustic Data Collection and Processing 

Acoustic data were collected with a BioSonics model DT5000 scientific

echosounder/multiplexer. All data were collected with 120 kHz transducers which had been

factory calibrated to a - 42 dB tungsten sphere. Source levels were 223 dB / Pa at 1 m. 

Sampling rate was 5 pings /sec with a pulse width of 0.4 ms. Received signals were adjusted for

spreading loss by applying a 40 log R time varied gain, digitized and recorded on the computer

hard drive and later transferred to CD digital media. The data collection threshold was -55 dB,

corresponding to a minimum detection of a 2.5 cm fish (Love 1971).

Digitized hydroacoustic data were processed with a BioSonics' Visual Analyzer 4.02.

Recent advances in the software allowed simultaneous estimates of sigma (target strength) and

mean volume backscatter (reflected acoustic energy) for each depth strata. These parameters are

used to estimate fish density/m3

 and fish size. Data were aggregated into ten meter depth strata

for each site. For the mobile surveys, data were processed through Visual Analyzer with the

bottom tracking feature turned on; the bottom was then manually inspected and adjusted to

insure that neither the bottom nor the platform were included in the analyzer window (Figure 5). 

Interactive bottom correction was not necessary for the standing platform as the transducers were

fixed.

12 
200m

 

Figure 3. Survey design for the mobile surveys of the artificial sites. The arrows indicate

the vessel direction.

13 
Ni -4

C 01C Ni -I

0 01Ni Ni -.4 (51 a Ni -40 (SI Ni Ni -1

0 0

Figure 4. Intended vessel track lines of the WFGB hydroacoustic survey conducted 

in June 2000.

14 
Ylnoal Analyzee- 08095894.DT4

File Vierz Display Zooming Analyze Configure Windosi Help IIlII lIlQ] 1S19101 I II I 08095894.0T4 - ChannelS Narrow Beam Echogram

Ping: 60, Depth: 3.76 Waters 06/22/00 13:13:05 I 200 2.3970 N 930 12.5730W

ITVG: 0 IThresh:-55.0 dB lAbs: 0.0353 dB/rs ICel: 0.000dB

Figure 5. Sample color echogram showing structure as viewed in Visual Analyzer v 4.02. 

The bottom limit of the processed data was set just above the structure as shown

by small boxes.

15 
The standing platform data were analyzed in 5 minute blocks for each side as in previous

studies (Stanley and Wilson 1997). Visual Analyzer outputs for the standing platform included

volume backscatter/m3, fish density/m3, and mean target strength/m3. A Visual Basic program

was used to extract the data of interest from analysis outputs and to compile the results into a site

specific database for statistical analysis.

Mobile transects were analyzed at one second resolution (2 meters linear distance) to

determine the volume backscatter and target strength/m3 within each depth stratum along the

transect. Analysis of each one second block of data provided geographic position and mean

volume back scatter. Individual target strength information was acquired by extracting ping

specific data, which could be selectively output as a text file. A Visual Basic program was used

to calculate an average target strength for each target, by strata, and location.

2.4 Data Analysis 

Processing of acoustic data yields several parameters of interest. Fish density is

calculated based on the volume backscatter (reflected acoustic energy) per volume of water

divided by the average target strength (reported as sigma) from that same volume of water.

Density is reported as number/m3

 in this study. Density estimates are dependent upon accurate

estimates of the mean sigma of the targets within that same volume of water. Analysis of

standing platform data with Visual Analyzer version 4.02 produced useful density estimates;

however, analysis of the mobile data required refinement for more accurate density comparisons. 

The accuracy of sigma increases with repeated acoustic hits on the same target (Jim Dawson -

pers com .Biosonics Inc. 4027 Leary Way NW Seattle Wa 98107- . Given that research

operations were from a vessel moving at 4 knots and transmitting acoustic pulses (pings) at a rate

of 4-5 pings per second, the chance of hitting a target multiple times was very low. In many

cases, data processing resulted in a volume backscatter, but no sigma for that same volume of

water. In estimating fish densities for mobile surveys, a mean sigma (proxy sigma) was

calculated for a 30 m linear distance by stratum, and used as a proxy for target strength to

calculate density. The assumption in this case, was that fish size was similar in the same stratum

for 30 linear meters for the artificial reef sites and WFGB. If sigma was missing, but a volume

backscatter volume was available, the proxy sigma was substituted to estimate density. 

2.4.1 Statistical Analysis

Statistical analysis of these data included the reported reflected acoustic energy as

volume backscatter (Sv), a proxy for fish biomass, as a dependent variable in our analysis. Sv is

an exponential number provided by the BioSonics Visual Analyzer and is a per ping average of

energy/m3

. For regression analysis and calculation of means, Sv is converted into a “arithmetic

form”, called “Fish Energy”, with the relationship,

 Fish Energy = 10 sv/10, (Equation 1)

where sv is volume backscatter (reflected acoustic energy) per cubic meter of water.“Fish

Energy” should be considered to be an acoustic measurement of fish biomass as it is reported on

16 
the average acoustic reflectance/m3 in decibels. The second dependent variable in our analysis

was density/m3

, which was generated from Visual Analyzer for HI A350 and calculated for the

mobile surveys of two reef sites at the WFGB with the equation, 

10 Sv/10 /10 S/10 = fish/m3 (Equation 2)

where Sv is the volume backscatter/m3

 and S is the observed sigma (or the proxy sigma

discussed above). 

10s/10 (Equation 3)

is also the formual used to calculate Target strength (TS).

A randomized block analysis of variance was used to examine the main effects at HI

A350 and TS at all sites as described by Stanley and Wilson (1997). Due to the larger number of

zero values in the mobile survey, logistic regression (Trexler and Travis 2001) was used to

analyze the mobile data. 

2.4.2 Randomized Block Design (RBD) ANOVA’s 

Randomized block design ANOVA’s (SAS Institute Incorporated 2000) were performed

on the data from HI A350 with transformations as log 10 (fish density + 1). Class variables

included time of day (TOD; dawn, noon, dusk, midnight), platform side (north, south, east, west)

ten meter depth strata (strata), and their interactions. 

ANOVA’s were used to analyze TS at all sites. Class variables for HI A350 include

TOD, stratum, platform side, and all two-way interactions. Class variable for WC 617A and HI

A355 include time of day (TOD), depth bin (stratum), reef side, horizontal 10 meter distance

intervals away from the reef structure (away), and all two-way interactions. Class variables for

WFGB included depth or terrace, stratum, TOD, transect number, and all two-way interactions. 

Tukey's standardized range tests (Ott 1982) were used to compare the means of significant

variables. Statistical tests were reported as significant at the alpha < 0.01 level.

2.4.3 Logistic Regression

Traditional parametric analysis was not used for analysis of mobile acoustic data given

the large number of zero values and the problem of autocorrelation that occurs in mobile

acoustic data. A binomial logistic regression model was constructed for each site using the

presence or absence of "fish energy" to evaluate the probability, or chance, of finding fish. This

analysis was performed on the primary output of acoustic data analysis which was reported in 1

second intervals. Class variables for the artificial reef sites included orientation (over the

platform, and north, south, east, and west sides), 10 m depth bin (stratum), distance away from

the ref structure (away), Time of day (TOD), year (1999 or 2000), site (standing or toppled) and

17 
transect (ordinal number). Class variables for the WFGB were depth b in (stratum), terrace, and

TOD. 

The use of logistic regression in ecological sampling was described by Trexler and Travis

(2001). It has been shown to be useful with data that have a large proportion of zero values

when error is usually not normally distributed. In most cases, analysis consists of converting the

dependent variable into a discrete form (e.g. presence/absent, agree/disagree, etc). The

regression model then assumes a binomial distribution of errors (Trexler and Travis 2001,

Garrison et al 2000). 

The Statistical Analysis System (SAS Institute Incorporated 2000) includes a program

called Proc Logistic that uses logistic analysis . When run with the intercept option, it produces

a Type III analysis of main effects, which provides an estimate of the significance of class

variables, based on a maximum likelihood test (Chi Square test of significance p=0.01) that is

used for comparing within class variables. When run without an intercept, Proc Logistic

provides an odds ratio estimate; in our use it is the probability of finding fish in a given class

variable cell compared to another cell. Output also includes percent concordance, which is the

percent of the time that the model correctly predicts the outcome. 

2.4.4 Fish Abundance Estimation 

Total fish abundance estimates at each site were calculated by determining a 20m

near-field area of influence of each reef site or platform, then multiplying estimated fish density

for each stratum and side (number of fish/m3) by the volume of water on each side of or over the

platform (Stanley and Wilson 1998). Fish density within the center of each platform was not

measured with acoustics due to interference by structural members and was assumed to be the

average of the density estimates of the four sides of the platform. Fish abundance in the center

of the platform was calculated by multiplying the estimated fish density of the center by the

volume of water in the center of the platform. Fish abundance estimates of the WFGB were

based on the average density by stratum, within terrace times the area of each terrace and

summed over all strata. 

2.5 Visual Surveys

Visual surveys were conducted with a Deep Ocean Engineering Phantom HD2 ROV with

standard visual census techniques and recording video on S-VHS tape (Bohnsack and Bannerot

1986). ROV based S-VHS recordings were made by flying the ROV on the down current side of

each structure, along major legs, the ROV was paused at 10 m intervals from the surface to the

bottom. Cryptic fishes were not included in the video surveys results since they could not be

assessed in the acoustic surveys. Point counts were made from the S-VHS recordings and

individual fish were identified to the lowest taxonomic level possible. Results and data were

expressed as percent species composition by stratum at each site. Species abundances were

estimated by multiplying the percent composition of a given species by the total number of fish

estimated to be at that site (after Stanley and Wilson 1997).

18 
During mobile surveys, the ROV was deployed from the M/V Epic Mariner or R/V

Pelican. The vessel was anchored near each artificial reef site, and the ROV deployed to dive

and capture video images over the toppled and partially-removed platforms. During the survey

of the partially removed platform (HI A355), the ROV was flown from the top of the structure

down to the bottom, stopping every 10 m for approximately 1 minute. During the survey of the

toppled platform (WC 617A), the ROV was flown down to the top of the structure and then run

along the south side, east side, and over the top of the toppled platform. Video surveys of the

standing platform (HI A350), were conducted directly from the standing platform. The ROV

was flown from the surface to the bottom, stopping every 10 m for approximately 5 minutes. 

Video data from the WFGB were collected along random transects designed to represent the

three major terrace regions and geologic features located throughout the WFGB. The ROV was

flown just above the bottom where it traveled at a speed of 1 knot for 45 minutes along a transect

through each of the three major terraces. 

19 
3.0 RESULTS

3.1 High Island A350 (standing platform) Results

The stationary hydroacoustic survey of HI A350 was conducted in June 1999. A five-day

trip was made to the platform where acoustic data and ROV data were collected.

3.1.1 Fish Energy (from Sv)

Volume Backscatter (Sv), the measure of the amount of reflected acoustic energy, or fish

biomass /m3 was converted to Fish Energy using Equation 1 in the Materials and Methods. Fish

Energy ranged from 0.0 to 2.2 x 10-4 /m3; the mean value at HI A350 was 1.2 x 10-6 /m3. Based

on ANOVAs, Fish Energy was affected by depth, time of day, and the interactions of side and

depth (Table 2). Fish Energy was highest at the surface and lowest near the bottom. The upper

two strata ( 10 and 20m) were significantly different from one another and both were

significantly higher than the remaining deeper strata (30 - 80m) (Figure 6). Fish Energy also

varied significantly with time of day (TOD) and was highest at dusk followed by noon, morning,

and midnight (Figure 7). 

3.1.2 Density Estimates 

Estimates of fish density were based on Sv divided by the average sigma for fish in the

same volume of water (See Equation 2) and in general followed Fish Energy patterns. Estimated

fish densities ranged from 0.0 to 0.7 fish/m3; the mean fish density at HI A350 was 0.015 ± .003

(mean ± std error) fish/m3. Based on RBD ANOVAs, density was affected by depth, TOD and

their interactions. Densities were highest in the upper part of the water column and generally

decreased with depth (Figure 8). Density also varied with TOD and was highest at dusk and

lowest at midnight (Figure 9). The results of the ANOVA are shown in Table 3.

3.1.3 Target Strength

Target strength (TS) is an acoustic measure of fish size which was used as a dependent

variable to test for relationships between fish size with TOD, orientation, and depth and their

interactions. TS ranged from -52.46 to -30.75 dB; the average TS at HI A350 was - 40.73 dB

which is equivalent to a 12.5 cm fish. No singel targets were identified in the 10m or 80m strata. 

Based on the RBD ANOVAs, TS at the standing platform was affected by depth and time of day 

(Table 4). Targets ranged from -39.2 to -36.4 dB in the upper three strata (20, 30, and 40m),

peaked at -32.5 dB at 50m, and dropped to near -45 dB in the 60 and 70m strata (Figure 10). 

Targets were also significantly larger in the morning than at noon, dusk, and midnight (Figure

11).

21 
Table 2. 

RBD ANOVA (block on side) results (significant) of fish energy (arithmetic form of volume

backscatter) with platform side (Ornt), depth stratum (Stratum), TOD, and selected interactions

at High Island A350.

Source DF SS MS F Prob > F

Model 95 0.00000001 0 12.56 0.0001

Error 573 0 0

Corrected Total 668 0.00000001

RSquaredC.V. Root MSE Energy

Mean

0.67 131.735 0.00000212 0.00000161

Variables DF Type III SS Mean

Square

F Value Pr > F

Stratum 7 0 0 61.53 0.0001

Time of day 3 0 0 5.73 0.0007

Ornt*Time of

day

6 0 0 4.69 0.0001

Stratum*Time

of day

21 0 0 7.59 0.0001

22 
Table 3. 

RBD ANOVA (block on side) results (significant) of log10 (fish density) with platform side

(Ornt), depth stratum (Stratum), TOD, and selected interactions at High Island A350.

Source DF SS MS F Prob > F

Model 95 0.071 0.000755 4086 0.0001

Error 432 0.067 0.00015541

Corrected

Total

527 0.13

RSquaredC.V. Root MSE LogDEN

Mean

0.51 319.73 0.012 0.0038

Variables DF Type III SS Mean Square F Value Pr > F

Stratum 7 0.039109 0.000558 35.95 0.0001

Time of day 3 0.00167 0.0005583 3.59 0.0137

Ornt*Stratum 14 0.00824 0.0005889 3.79 0.0001

Stratum*Time

of day

21 0.01283 0.000611 3.93 0.0001

23 
Table 4. 

RBD ANOVA (block on side) results (significant) of target strength with, depth stratum

(Stratum), TOD, and selected interactions at High Island A350.

Source DF SS MS F Prob > F

Model 33 0.071 0.0008 4086 0.0001

Error 55 0.067 0.00016

Corrected Total 88 0.13

RSquaredC.V. Root MSE LogDEN

Mean

.55 319.73 0.012 0.0038

Variables DF Type III SS Mean Square F

Value

Pr > F

Stratum 6 0.039 0.0005 35.95 0.0001

Time of day 3 0.001 0.0005 3.59 0.0137

Ornt*Stratum 14 0.008 0.0005 3.79 0.0001

Stratum*Time of

day

21 0.012 0.0006 3.93 0.0001

24 
-2.00E-06

0.00E+00

2.00E-06

4.00E-06

6.00E-06

8.00E-06

0 10 20 30 40 50 60 70 80 90

Depth (m)

Fish Energy

Figure 6. Mean fish energy/m3 (antilog of volume backscatter) by depth stratum for HI 

A350. Error bars are 95% confidence intervals.

25 
1.00E-07

1.10E-06

2.10E-06

3.10E-06

Dawn Noon Dusk Midnight

Time of Day

Fish Energy

Figure 7. Mean fish energy/m3 (antilog of volume backscatter) at TOD for HI A350. Error

bars are 95% confidence intervals.

26 
Fish Density: HI 350

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 10 20 30 40 50 60 70 80 90

Depth (m)

Fish Density

Figure 8. Estimated mean fish density (#/m3) at depth for HI A350. Error bars are 95%

confidence intervals.

27 
0

0.01

0.02

0.03

0.04

Dawn Noon Dusk Midnight

Time of Day

Fish Density 

Figure 9. Estimated mean fish density (#/m3) at TOD for HI A350. Error bars are 95% 

 confidence intervals.

28 
-48

-45

-42

-39

-36

-33

-30

0 10 20 30 40 50 60 70 80

Depth Stratum (m)

dB

Figure 10. Estimated mean target strength (dB) (Love 1971) by depth stratum around HI A350. 

 Error bars are 95% confidence intervals.

29 
-48

-45

-42

-39

-36

-33

-30

D a w n N o o n D u s k M id n ig h t

T im e o f D a y

dB

Figure 11. Estimated mean target strength (dB) (Love 1971) by TOD around HI A350. 

 Error bars are 95% confidence intervals.

30 
3.1.4 Species Composition and Abundance 

The fish community observed by ROV at HI A350 was very similar to previous studies and 

consisted of pelagic planktivores near the surface and reef-associated species near the bottom

(Appendix). Bermuda chub and blue runner were the most abundant species making up more

than 50 percent of the fish observed on the ROV survey; they were most common near the

surface. Creole-fish, scamp, and red snapper were also fairly abundant and made up

approximately one-third of the species present. Red snapper and scamp were most numerous at

40-50m and creole-fish were most abundant at mid-depth (30m). Species composition at HI

A350 is shown in Table 5. 

We estimate that there were 7,100 fish at HI A350 within a 20 m radius. Based on a

combination of ROV data and acoustic data, there were approximately 2,100 blue runner, 1,000

Bermuda chub, 1,000 creole fish, 500 scamp, and 400 red snapper. 

3.2 West Cameron 617A and High Island A355 Results

Schematic diagrams of both WC 617A (toppled platform) and HI A355 (partially removed

platform) are shown in Figure 12, and depict the orientations and configurations of the platforms

at the times of conversion into reef sites. Bottom depth was extracted from our acoustic surveys

and a plot of the vessel track lines and extracted bottom contours is shown in Figure 13. Figure

14 shows a three-dimensional representation of the current configuration and bathymetry at each

RTR site. 

Sample color enhanced echograms of transects are shown in Figure 15. These echograms

represent several seconds of data taken over each site. The images clearly illustrate the outlines

of each structure and the acoustic comparison of structure and bottom hardness. Figure 15A is

an echogram of the toppled platform with several fish located above the structure. Cross

members and legs appear in bright red indicating that the platform is much harder (and more

reflective) than the bottom. Figure15B is from the partially removed platform and shows a

distinct water mass at 50-60 m that populated by scattered small targets. Several fish can be seen

near the top in Figure 15B. 

Acoustic data were used to determine fish presence based on volume backscatter, to estimate

density /m3

, and to estimate fish size above, around, and away from the reef sites. One concern

was that transect number might lead to a decrease in fish density as multiple passes of the vessel

over each site might scare away fish. Including transect number (n=100) as a class variable in

the logistic regression for the 1999 data at both sites indicated a significant effect; however,

there was no pattern indicating a predictable decrease or increase in the probability of finding

fish with consecutive transects or TOD (Figure 16). We therefore combined all transects for

further analysis. Results of our analysis are discussed below by site.

31 
S

-L

JQtd iUma

N S N

Oriv'r'I Ic] >Lj,i

A.

B.

Figure 12. Line drawings of WC 617A (toppled platform) and HI A355 (partially removed 

 platform with a small 4-leg section to the southwest).

32 
WC , Bottom Relief and ship track

-g3,307 3oea Q33066 -3.3OS4 -O3O2 ..3Oe 43,3O8 43,3O6 -03,3054 -03.3003 -03,305 -0330.45 -03.3045 '03.3044

HI 355, Bottom Rellof and Track

23040443.7104 43.7194 43J1C+2 43.71 aiooe -fl&1006 43.7094 -93.7042 43.709 43.7046 -93.7046 433084 -93.70

26.0426

2$

23041$ 23041; 21041

2SO412 21011- 28+ 230404

A. 

B.

Figure 13. Plot of vessel track (dotted lines) over WC 617A (A) and HI A355 (B) for surveys 

 conducted June 1999 and June 2000. Bathymetry contour show depths at each reef 

 site and indicate the platforms. North is up in both figures. 

33 
WC 617 Bottom Relief

HI 355 Bottom Relief

A.

B.

Figure 14. Acoustic

depth profiles of WC 617A and HI A355 based on a geo-referenced plot of depth

from the hydroacoustic survey conducted in June 1999 and 2000. Outlines of both

structures are evident based on bottom depth.

34 
N

N>N

- ii' Jv. iT

T ç! 'A:. 'h

I ::

.

: IIIIb1I!IIII ITT1

File y,e- DiscS Zo .ze Conligure Window Help

ILCIJ IJTh Til HWHG] [jj

-10.01

Pingl 632, Depth: 40.00 meters 08/27/98 10:27:11 28e 7.160 N 91e 20.380W

Zoom in on Selected Area.Zoom It TVG: 40 Thresh: -55.0dB Ahs: 0.00234 dB/m Call 10.000dB

Qvisual Analyze.- 10224451.DT4 MU

A.

B.

Figure 15. Color enhanced echograms of WC 617A (A) and HI A355 (B) from BioSonics 

Visual Analyzer (v4.02) analysis viewer. Arrows point toward fish. Acoustic

Scattering Layer (ASL) in B is likely due to plankton.

35 
0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90 100

Transect Number

Probability

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 10 20 30 40 50 60 70 80 90 100

Transect Number

Probability

A.

B.

Figure 16. Change in probability of finding a fish with consecutive transect number for WC

617A (A) and HI A355 (B) during 1999 referenced to the final transect.

36 
37

Table 5. 

Species common names and scientific names, numbers of individuals by stratum, totals, and percent compositi

counts using video from a remotely operated vehicle (ROV) from High Island A350, June 19

High Island A350 June 1999Common Name Scientific Name 0 m 10 m 20 m 30 m 40 m 50 m 60 m 70 m TAlmaco jack Seriola rivoliana 5 1 22 9 - 1 - - 3

Bermuda chub Kyphosus sectatrix 280 - - - - - - - 2

Bar jack Caranx ruber 1 - - - - - - - 1 

Great barracuda Sphyraena barracuda 6 10 2 - - - - - 1

Blue angelfish Holacanthus bermudensis - 6 10 5 - - - - 2

Blue runner Caranx crysos 92 33 182 - - - - - 3

Blue tang Acanthurus coeruleus - 2 4 1 - - - - 7 

Creole-fish Paranthias furcifer - - 94 53 - - - - 1

Crevalle jack Caranx hippos - 9 - - - - - - 9 

French angelfish Pomacanthus paru - - 4 3 - - - - 7 

Gag Mycteroperca microlepis - - 1 - - 1 - - 2 

Greater amberjack Seriola dumerili - 2 4 4 2 8 1 - 2

Gray triggerfish Balistes capriscus 1 - 1 2 4 - - - 8 

Rainbow runner Elagatis bipinnulata - - 11 - - - - - 1

Red snapper Lutjanus campechanus - - - - 11 50 - - 6

Rock beauty Holacanthus tricolor - - - 1 - - - - 1 

Reef butterflyfish Chaetodon sedentarius - - - - 1 - - - 1 

Scamp Mycteroperca phenax - - 2 17 7 37 10 - 7

Sergeant major Abudefduf saxatilis 6 1 7 - - - - - 1

Spanish hogfish Bodianus rufus - - 9 1 1 - - - 1

Squirrelfish Holocentrus adscensionis - - 3 - - - - - 8 
3.2.1 West Cameron 617A Results

3.2.1.1 Fish Energy

A binomial logistic regression model was constructed to analyze WC 617A acoustic data

with presence/absence of Sv (Fish Energy) in 1 second intervals as the dependent variable with

class variables, orientation, stratum, away, TOD, and year and all two way interactions. All

class variables were significant indicating their influence on the probability of fish occurring

(Table 6). Two-way interactions were evaluated and found to be either insignificant or of no

biological meaning, so they were removed from the model as they confounded the class variables

interpretation.

Odds ratio estimates produced in Proc Logistic without an intercept provided insight into

how the probability of finding fish varied within each class variable. Analysis outputs indicated

that there was a difference between years as the chance of finding a fish in 1999 was

approximately 2.5 times that in 2000. In addition, there was a higher probability of finding a fish

over than any of the four sides or away from the platform . Not only was the probability of

finding fish higher over the platform, but also there was higher mean biomass (measured as Fish

Energy) over the platform than on the sides. Hence when fish were present, higher biomass was

found over the reef site than on any of its sides. Logistic regression analysis also indicated that

fish were more likely to occur near the bottom.

Mean Fish Energy was highest over the platform and declined with distance (Figure

17A). Fish Energy also varied by side (orientation), but was lower on all sides compared to over

the platform (Figure 18A). Beyond 30 m away from WC 617 Fish Energy was similar to open

water levels. We therefore assigned a 20 meter area of influence of this site. Mean Fish Energy

also varied with depth and time of day, tending to be higher near the bottom (Figure 19A) and

higher at midnight (Figure 20A).

3.2.1.2 Target Strength 

The relationship between TS and associated class variables was modeled with RBD

ANOVAs. TS was affected by side, depth stratum, and TOD and all interactions (Table 7). Fish

were, on average, larger over the platform (Figure 21A) and decreased with increased distance

from the site (Figure 22A). Fish size also varied with depth and targets tended to be larger

immediately above the structure and near the surface (Figure 23A). Average acoustic size at WC

617A was - 46 dB (8.6 cm) and ranged from -62 to -26 dB (1.2 to 96 cm) (Love 1971). Target

size changed with TOD, and fish were larger at dawn followed by midnight, dusk, and noon

(Figure 24A).

38 
 Table 6. 

Logistic regression analysis results of fish energy (antilog of volume backscatter) with platform

side (Ornt), depth stratum (Stratum), and TOD at WC 617A.

Type III Analysis of Effects

Effect DF WaldChi-Square Pr > ChiSq

ORNT 4 115.50 <.0001

Stratum 6 5102.70 <.0001

Time of day 3 871.32 <.0001

YEAR 1 1073.04 <.0001

away 7 80.46 <.0001

Analysis of Maximum Likelihood Estimates

Parameter DF Estimate Standard Error Chi-Square Pr > ChiSq

Intercept 1 -1.10 0.03 1027.14 <.0001

ORNT 1 1 -0.47 0.07 41.97 <.0001

ORNT 2 1 -0.63 0.07 76.85 <.0001

ORNT 3 1 -0.44 0.07 35.87 <.0001

ORNT 4 1 -0.30 0.07 16.25 <.0001

Stratum 1 1 -1.08 0.04 713.04 <.0001

Stratum 2 1 -1.00 0.04 654.75 <.0001

Stratum 3 1 -0.31 0.03 98.96 <.0001

Stratum 4 1 0.01 0.03 0.06 0.81

Stratum 5 1 0.02 0.03 0.75 0.39

Stratum 6 1 1.25 0.02 2856.71 <.0001

Time of day 1 1 0.33 0.03 137.86 <.0001

Time of day 2 1 -0.33 0.03 140.19 <.0001

Time of day 3 1 -0.51 0.02 546.49 <.0001

YEAR 1999 1 -0.52 0.02 1073.04 <.0001

away 0 1 -2.36 0.30 60.11 <.0001

away 10 1 0.31 0.06 32.11 <.0001

away 20 1 0.39 0.06 47.52 <.0001

away 30 1 0.37 0.06 42.67 <.0001

away 40 1 0.27 0.06 21.43 <.0001

away 50 1 0.26 0.06 19.94 <.0001

away 60 1 0.29 0.06 24.25 <.0001

away 70 0 0.29 . .

Association of Predicted Probabilities and Observed Responses 

Percent Concordant 73.4 Somers' D 0.479

Percent Discordant 25.5 Gamma 0.484

Percent Tied 1.2 Tau-a 0.148

Pairs 528577500 c 0.739

39 
Table 7. 

RBD ANOVA (block on side) results of target strength with platform side (Side), depth stratum

(Stratum), distance away from the platform (Away) and TOD (Time of day), and selected

interactions at WC 617A.

Source DF SS MS F Prob > F

Model 89 107215.16 1204.66 66.75 0.0001

Error 9910 178858.04 18.048

Corrected Total 9999 286073.2

R-Squared C.V. Root MSE TS Mean

0.37 -9.35 4024832 -45.42

Variables DF Type III SS Mean

Square

F Value Pr > F

Ornt 3 3318.04 1106.01 61.28 0.0001

Stratum 6 7213.15 1202.19 66.61 0.0001

Time of day 3 649.24 216.41 11.99 0.0001

Ornt*Away 3 852.43 284.14 15.72 0.0001

Ornt*Stratum 18 4043.77 224.65 12.45 0.0001

Ornt*Time of day 9 1633.80 181.53 10.06 0.0001

Stratum*Away 6 1311.37 218.56 12.11 0.0001

Stratum*Time of day 18 12305.13 683.61 37.88 0.0001

Away*Time of day 3 383.450 127.81 7.08 0.0001

Ornt*Away*Time of

day

9 737.99 81.99 4.54 0.0001

40 
0.00E+00

1.00E-07

2.00E-07

3.00E-07

0 10 20 30 40 50 60 70 80 90

Distance Form Artificial Reef (m)

Fish Energy

0.00E+00

1.00E-07

2.00E-07

3.00E-07

0 10 20 30 40 50 60 70 80 90

Distance from Artificial Reef

Fish Energy

A.

B.

Figure 17. Estimated mean fish energy /m3

 (antilog of volume backscatter) at distance from reef 

 site for WC 617A (A) and HI A355 (B). Error bars are 95% confidence intervals.

41 
0.00E+00

1.00E-07

2.00E-07

North South East West Over

Orientation

Fish Energy

0.00E+00

1.00E-07

2.00E-07

North South East West Over

Orientation

Fish Energy

A.

B.

Figure 18. Estimated mean fish energy /m3

 (antilog of volume backscatter) at orientation for WC 

 617A (A) and HI A355 (B). Error bars are 95% confidence intervals.

42 
0.00E+00

1.00E-07

2.00E-07

3.00E-07

0 10 20 30 40 50 60 70 80

Depth Stratum (m)

Fish Energy

0.00E+00

1.00E-07

2.00E-07

3.00E-07

0 10 20 30 40 50 60 70 80

Depth Stratum (m)

Fish Energy

A.

B.

Figure 19. Estimated mean fish energy /m3

 (antilog of volume backscatter) at depth stratum for 

 WC 617 (A) and HI A355 (B). Error bars are 95% confidence intervals.

43 
0.00E+00

1.00E-07

2.00E-07

Dawn Noon Dusk Midnight

Time of Day

Fish Energy

0.00E+00

1.00E-07

2.00E-07

Dawn Noon Dusk Midnight

Time of Day

Fish Energy

A.

B.

Figure 20. Estimated mean fish energy /m3

 (antilog of volume backscatter) by TOD for WC 

 617A (A) and HI A355 (B). Error bars are 95% confidence intervals.

44 
-52

-50

-48

-46

-44

-42

-40

North South East West Over

Orientation 

dB

-52

-50

-48

-46

-44

-42

-40

North South East West Over

Orientation

dB

A.

B.

Figure 21. Estimated mean target strength by orientation for WC 617A (A) and HI A355 (B). 

 Error bars are 95% confidence intervals.

45 
-52

-50

-48

-46

-44

-42

-40

0 10 20 30 40 50 60 70 80 90

Distance from Platform (m)

dB

-52

-50

-48

-46

-44

-42

-40

0 10 20 30 40 50 60 70 80 90

Distance from Platform (m)

dB

A.

B.

Figure 22. Estimated mean target strength at distance from reef site for WC 617A (A) and HI 

 A355 (B). Error bars are 95% confidence intervals.

46 
-52

-50

-48

-46

-44

-42

-40

10 20 30 40 50 60 70 80

Depth Stratum (m)

dB

-52

-50

-48

-46

-44

-42

-40

10 20 30 40 50 60 70 80

Depth Stratum (m)

dB

A.

B.

Figure 23. Estimated mean target strength (dB) at depth stratum for WC 617A (A) and HI A355 

 (B). Error bars are 95% confidence intervals.

47 
-52

-50

-48

-46

-44

-42

-40

Dawn Noon Dusk Midnight

Time of Day

dB

-52

-50

-48

-46

-44

-42

-40

Dawn Dusk Midnight Noon

Time of Day

dB

A.

B.

Figure 24. Estimated mean target strength (dB) at time of day for WC 617A (A) and HI A355 

 (B). Error bars are 95% confidence intervals.

48 
3.2.1.3 Density Estimates

Fish density was calculated based on acoustic volume backscatter and TS (mean target

strength/m3

 or its proxy described in Materials and Methods). Plots of the mean density values

provide actual density estimates for comparison to earlier studies. Density over and away from

WC 617A ranged from 0 to 0.5 fish/m3 and the overall mean density of the site within 20 m was

0.0015 fish/m3. Mean density decreased slightly beyond 30 meters (Figure 25A) and did not

vary greatly. Mean density was slightly higher over the platform compared to the east, west,

north and south sides (Figure 26A). Density also varied with depth and was highest at the

surface and immediately above the bottom (Figure 27A). Density varied with time of day and

was highest during midnight followed by dusk, noon and morning (Figure 28A). Although

density did not vary greatly, it should be noted that Fish Energy was higher over WC 617A

where the fish were also larger.

3.2.1.4 Species Composition and Abundance 

Species present at WC 617A were to the reef-associated communities tht we have seen

around platforms in the past (Stanley and Wilson 1997). Based on ROV surveys, seven species

made up 90% of the community (Table 8). Red snapper were the most abundant and made up

over 45% of the population followed by greater amberjack, Spanish hogfish, gray triggerfish,

and creole-fish.

Total fish abundance at WC 617A within a 20 m area of influence was estimated at

2,700. Combining this acoustic density estimate with the relative proportions of species observed

in ROV surveys (Table 8), there were approximately 1,220 red snapper, and 405 amberjack,

followed by 270 Spanish hogfish and 216 gray triggerfish.

3.2.2 HI A355 (Partially Removed Platform) Results 

3.2.2.1 Fish Energy

A binomial logistic regression model was constructed for HI A355 with presence/absence

of Sv (hence fish) over 1 second intervals as the dependent variable with class variables:

orientation, depth stratum, away, time of day, year and all two-way interactions. Significant

effects were found with orientation, away, time of day, and year. (Table 9). Two way

interactions were evaluated and determined to be either insignificant or of no biological

significance, so they were removed from the model as they confounded the class variables

interpretation.

49 
0

0.001

0.002

0.003

0.004

0.005

0 10 20 30 40 50 60 70 80 90

Distance from Artificial Reef (m)

Fish Densit

y

0

0.001

0.002

0.003

0.004

0.005

0 10 20 30 40 50 60 70 80 90

Distance from Artifical Reef (m)

Fish Density 

A.

B.

Figure 25. Estimated mean fish density (fish/m3

) at distance for the reef site for WC 617A (A) 

 and HI A355 (B). Error bars are 95% confidence intervals.

50 
0

0.001

0.002

0.003

0.004

0.005

North South East West Over

Orientation

Fish Density 

0

0.001

0.002

0.003

0.004

0.005

North South East West Over

Orientation

Fish Density 

A.

B.

Figur

e 26. Estimated mean fish density (fish/m3

) by orientation for WC 617A (A) and HI 

 A355 (B). Error bars are 95% confidence intervals.

51 
0

0.001

0.002

0.003

0.004

0.005

0.006

0 10 20 30 40 50 60 70 80

Depth Stratum (m)

Fish Density 

0

0.001

0.002

0.003

0.004

0.005

0.006

0 10 20 30 40 50 60 70 80

Depth Stratum (m)

Fish Densit

y

A.

B.

Figure 27. Estimated mean fish density (fish/m3

) by depth stratum for WC 617A (A) and HI 

 A355 (B). Error bars are 95% confidence intervals.

A.

52 
0

0.001

0.002

0.003

0.004

Dawn Noon Dusk Midnight

Time of Day

Fish Density

0

0.001

0.002

0.003

0.004

Dawn Noon Dusk Midnight

Time of Day

Fish Density

B.

Figure

28. 

Estima

ted mean fish density (fish/m3

) by TOD for WC 617A (A) and HI A355 (B). 

Error bars are 95% confidence intervals.

53 
54

Table 8. 

Species common names and scientific names along with numbers of individuals by stratum, totals, and percen

visual point counts using video from a remotely operated vehicle (ROV) from a toppled platform (West Camer

Common Name Scientific Name 0m 10m 20m 30m 40m 50m 60m 70m Almaco jack Seriola rivoliana - - - - 1 9 4 - Creole-fish Paranthias furcifer - - - - - - 9 - Gag Mycteroperca microlepis - - - - - - 3 - Greater amberjack Seriola dumerili - - - - 2 25 2 - Gray triggerfish Balistes capriscus - - - - - 8 7 - Red snapper Lutjanus campechanus - - - - 7 32 46 - Reef butterflyfish Chaetodon sedentarius - - - - - - - 1 Scamp Mycteroperca phenax -- - -- 6 6 - Spanish hogfish Bodianus rufus -- - -- 6 14 - 
Table 9. 

 Logistic analysis results of fish energy (antilog of volume backscatter) with class variables

platform side (Ornt), depth stratum (Stratum), and time of day at High Island A355.

Type III Analysis of Effects

Effect DF Wald Chi-Square Pr > ChiSq

ORNT 4 74.02 <.0001

Stratum 6 9422.52 <.0001

Time of day 3 626.95 <.0001

YEAR 1 133.74 <.0001

AWAY 7 18.17 0.0112

Analysis of Maximum Likelihood Estimates

Parameter DF Estimate Standard Error Chi-Square Pr > ChiSq

Intercept 1 -0.79 0.03 546.82 <.0001

ORNT 1 1 0.37 0.07 25.71 <.0001

ORNT 2 1 0.32 0.07 18.85 <.0001

ORNT 3 1 0.13 0.07 3.05 0.08

ORNT 4 1 0.40 0.07 29.12 <.0001

Stratum 1 1 -2.17 0.05 1949.78 <.0001

Stratum 2 1 -1.64 0.04 1650.81 <.0001

Stratum 3 1 -0.07 0.03 6.42 0.01

Stratum 4 1 0.82 0.03 1033.99 <.0001

Stratum 5 1 1.88 0.03 4733.73 <.0001

Stratum 6 1 1.56 0.03 3524.16 <.0001

Time of day 1 1 0.55 0.02 518.06 <.0001

Time of day 2 1 -0.18 0.02 92.00 <.0001

Time of day 3 1 -0.17 0.03 46.86 <.0001

YEAR 1999 1 -0.18 0.02 133.74 <.0001

Association of Predicted Probabilities and Observed Responses 

Percent Concordant 83.1 Somers' D 0.67

Percent Discordant 16.4 Gamma 0.67

Percent Tied 0.5 Tau-a 0.30

Pairs 5.32E+08 c 0.83

55 
Odds ratio estimates from Proc Logistic run without an intercept provided insight into

how the probability of finding fish varied within each class variable. Analysis outputs indicated

that there was a difference between years as the chance of finding a fish in 1999 was 1.3 times

higher than that in 2000. A difference in orientation was also found with the probability of a fish

presence was highest on the south side. There was a slightly greater chance of finding fish

within 30 m rather than immediately over the reef (Table 9). Analysis also indicated that the

probabilty of fish occurring was higher near the bottom and closer to the reef. 

The biological significance of these differences was best appreciated by plotting mean

fish energy and estimated fish density (with 95% confidence intervals) for each class variable. 

The mean fish energy values plotted on these graphs is greatly influenced by the larger number

of zero values, but they allow for comparisons. Mean fish energy was highest over HI A355 and

reached a minimum beyond 30 meters away from the reef so we assigned a 20 meter area of

influence to this site. Mean fish energy was highest over the reef and declined with distance

from the reef (Figure 17B, 18B). Mean fish energy also varied with depth and time of day,

tending to be higher near the surface of the water column (Figure 19B) and higher in the morning

(Figure 20B).

3.2.2.2 Target Strength

The relationship between TS and associated class variables was modeled with RBD

ANOVAs. TS was affected by orientation, depth, TOD and all two way interactions (Table 10). 

Fish were, on average, larger over the reef and smallest on the south side (Figure 21B). Mean

TS within 20 meters of HI A355 was -48 dB (equivalent to a 6.7 cm fish); TS ranged from -62

to -25 dB (1.2 to 108 cm) (Love 1971). Fish size decreased with increased distance from the site

(Figure 22B). Size also varied with depth as targets tended to be larger near the surface and

decreased in size toward the bottom. (Figure 23B). Target size changed with TOD and was

greatest in the morning followed by midnight, dusk, and noon (Figure 24B).

3.2.2.3 Density Estimates

Fish density was calculated based on acoustic volume backscatter and sigma (or its proxy

value described in Materials and Methods). The results of the density estimates showed similar

trends to the analysis of Fish Energy presented in the previous section. Density over and away

from HI A355 ranged from 0 to 0.55 fish per cubic meter and averaged 0.002 fish per cubic

meter within 20 meters of the reef. However, mean density varied little with distance (Figure

25B). Mean density was slightly higher on the west side of the reef than the other sides, but

there was little difference in mean density among its four sides (Figure 26B). Density also

varied with depth and was highest 10 to 20 m above the bottom (Figure 27B). Highest density

occurred at dusk, although there was little difference among times of day (Figure 28B).

3.2.2.4 Species Composition and Abundance

Species compositions in June 1999 and June 2000 are given in Table 11 and some sample

images are included in the Appendix. During both surveys greater amberjack were the most 

56
Table 10. 

 RBD ANOVA (block on side) results of target strength with platform side (Side), depth stratum

(Stratum), distance away from the platform (Away), time of day, and selected interactions at

High Island A355.

Source DF SS MS F Prob > F

Model 89 73368.6688 824.367 48.14 0.0001

Error 10825 185377.4073 17.1249337

Corrected Total 10914 258746.0762

R-Squared C.V. Root MSE TS Mean

0.28 -8.544507 4.12822 -48.43

Variables DF Type III SS Mean Square F Value Pr > F

Ornt 3 122.9 41 2.39 0.0665

Stratum 6 187572.6 3095.4 180.76 0.0001

Away 1 615.8 615.8 35.96 0.0001

Time of day 3 367.5 122.5 7.15 0.0001

Ornt*Stratum 18 288.7 158 9.23 0.0001

Ornt*Time of

day

9 809.6 90 5.25 0.0001

Stratum*Away 6 556.9 93.8 5.42 0.0001

Stratum*Time

of day

18 6160.9 342.3 19.99 0.0001

Away*Time of

day

3 229.6 76.5 4.47 0.0038

57
58

Table 11. 

 Species common and scientific names, along with numbers of individuals by stratum, totals, and percent comp

point counts using video from a remotely operated vehicle (ROV) from a partially removed platform (High Isla

and 2000.

High Island A355 June 1999Common Name Scientific Name 0 m 10 m 20 m 30 m 40 m 50 m 60 m 70 m TAlmaco jack Seriola rivoliana - - - - - 17 - - 1

Blue angelfish Holacanthus bermudensis - - - - - 7 - - 7 

Creole-fish Paranthias furcifer - - - - - 2 - - 2 

Greater amberjack Seriola dumerili - - - - - 78 - - 7

Gray triggerfish Balistes capriscus - - - - - 3 - - 3 

Red snapper Lutjanus campechanus - - - - - 17 - - 1

Scamp Mycteroperca phenax - - - - - 5 - - 5 

Spanish hogfish Bodianus rufus - - - - - 3 - - 3 

High Island A355 June 2000Common Name Scientific Name 0 m 10 m 20 m 30 m 40 m 50 m 60 m 70 m TAlmaco jack Seriola rivoliana - - 2 7 2 - 2 - 1

Blackfin tuna Thunnus atlanticus - - 9 - - - - - 9 

Blue angelfish Holacanthus bermudensis - - - 2 5 1 2 1 1

Creole-fish Paranthias furcifer - - - 11 7 - - - 1

Crevalle jack Caranx hippos - - 2 1 - - - - 3 

Greater amberjack Seriola dumerili - - - 1 6 22 17 10 5

Gray triggerfish Balistes capriscus - - - - - - 3 - 3 

Ocean surgeon Acanthurus bahianus - - - 2 - - - - 2 

Red snapper Lutjanus campechanus - - - - 3 12 28 7 5

Spanish hogfish Bodianus rufus - - - - 18 3 - - 2

Warsaw grouper Epinephelus nigritus - - - - - - 1 - 1 

1
59

abundant species. In 1999, greater amberjack made up almost 60% of the fish community

compared to 30% in 2000. Red snapper were the second most abundant species both years and

ranged from 13% in 1999 to 27% in 2000 (Table 11).

Total fish abundance at HI A355 within a 20 m area of influence was estimate at 2,850

individuals. The most abundant fishes at HI A355 were greater amberjack and red snapper. 

Averaging percent species compositions for both years, we estimate there were approximately

1,200 greater amberjack and 500 red snapper followed by 250 Spanish hogfish and 225 creolefish.

3.3 West Flower Garden Bank Results

Intended track lines for the June 2000 of the WFGB survey are shown in Figure 4. 

Individual survey lines covered a linear distance from 2.5 to13.5 km with a line spacing of 300

m. The survey took 29 hours to cover approximately 160 km of survey lines. The actual survey

lines are shown in Figure 29. Transducer cable problems prevented data collection over a

portion of the upper terrace. 

Analysis of the acoustic data produced some very interesting results reflecting

topography, fish biomass, and general geology. The three terraces were very obvious based on

bottom depth; each terrace had different reflectance patterns indicative of different benthic

communities. Figure 30A shows a transition from the middle to the upper terrace. Figure 30B

is an enlargement of the area indicated in 30A showing a dense fish community just above the

bottom. The acoustic system, not only provided quantification of the fish community and insight

into geological properties of the bottom (Figure 31-A), but also location of natural gas seeps

(Figure 31 B).

3.3.1 Fish Energy

For analysis purposes, we divided WFGB into three terraces: upper = 20 – 50 m, middle

= 51 – 80 m, lower = 81 – 100 m based on description by Dennis and Bright (1998). We

considered depths greater than 100 m to be open water in our analysis. 

A binomial logistic regression with the presence/absence of Sv as the dependent variable

was used to model the relationship between fish presence and class variables: terrace, time of

day, and stratum (Table 12). All class variables were significant. 

Proc Logistic run without an intercept provided insight into the relative differences

within the class variables. The chance of encountering a fish was highest over the upper terrace

and lowest over open water. Illustrations of the change in acoustic energy with depth can be

seen in Figures 32 and 33, which show horizontal volume backscatter (sum of mean Sv)

throughout the water column. Figure 32 shows that the horizontal backscatter (HSV) is highest

over the upper 
60

Table 12. 

Logistic analysis results of fish energy (antilog of volume backscatter) with class variables

terrace level (Terrace), depth stratum (Stratum), and time of day (TOD) at WFGB.

Type III Analysis of Effects 

Effect DF Wald Chi-Square Pr >

ChiSq

TERRACE 3 5778 <.0001

Stratum 9 4852 <.0001

TOD 3 122 <.0001

Stratum*TOD 27 9329 <.0001

Analysis of Maximum Likelihood Estimates

Parameter DF Estimate Standard Error Chi-Square Pr > ChiSq

Intercept 1 -3.82 1.49 6.56 0.0104

TERRACE 1 1 0.39 0.01 1313.54 <.0001

TERRACE 2 1 0.66 0.01 3116.01 <.0001

TERRACE 3 1 0.18 0.01 273.18 <.0001

Association of Predicted Probabilities and Observed Responses 

Percent Concordant 80.6 Somers' D 0.62

Percent Discordant 17.8 Gamma 0.63

Percent Tied 1.6 Tau-a 0.17

Pairs 5.5E+10 c 0.81
C) C'.) U) C) c.-J

0 U) U) U)

N N- (N (N (N (N

0 U) U) IC) 0 N

N N- (N (N (N

61

Figure 29. Actual track lines of the WFGB hydroacoustic survey conducted in June 2000.
_23441 I l6.DT4CHANHCL7 NARROWB(&1 ECHOORMI

'Jricj Ii. Depth: 6434 meters Louise en selected orea2eom In w

TVG:40 Thresh: SSfldB .Abs:OD49 dB/n, CeI:O. dB

Ping 7429, Depth 906 meters or hide the status has 05/23/00 00'24'25 27052 0640 N 939 495990' W

'Pu'G' 40 Thresh-55 0 dO Abs 0 0350 dO/a Ca[ 0000 dO

62

Fish

A.

B.

Figure 30. Echogram of WFGB survey conducted June 2000. (A). Screen image includes dB 

color scale on left and depth on the right side; red box highlights an area of high

acoustic reflectance presumed to be fish and plankton. (B). Magnified image of a 

gentle slope onto the upper Terrace (@40m); arrows highlight fish targets.
S920 5930 S940 S9S0

Ping: 5957, Depth: 72.OI soeters

Displeythe csrrentfile dinpipy end threshnid nettinqs

5990 S970 S980 5990 6000 6010 6020 6030 6040 60S0 6060 6070 6000 6090 111111 IllIllIlIllIl I

06/23/00 07:30:11

tITVG: 10 Thresh: -55.0 dE tI.Abs: 0.01353 d6/ro lCd: 0.000dB

40.00

50.00

60.00

I 270 53.1510' N 939 18.9990' W

63

Gas Seeps

A.

B.

Figu

re 31. Echograms from June 2000 hydroacoustic survey of the WFGB. (A) Linear

changes in reflectance illustrate the value of hydroacoustics in characterizing

bottom type. (B) Large areas of low reflectance on the bottom are thought to be

gas seeps.
-93.88 -93.87 -93.88 -93.85 -93.84

WFGB HSV

-93.83 -93.82 -93.81 -93.8 -93.79 -93.78

-64

-66

.88

7Q

-72

-74

-76

-78

8O

.82

-84

-86

-88

-90 42

64

Figure 32. A color enhanced image of the relative horizontal acoustic reflectance over a 

bathymetry outline of the WFGB. Yellow areas are highest acoustic energy and

white are the lowest as indicated on the scale to the right. These data are not

corrected for depth as HSV is the sum of energy from the surface to the bottom.
27.9

27.92

27.91

27

27.8 p. FWFGB HSV weighted by depth

I I I I I I I I I I I -93.88 -93.87 -93.86 -83.88 -93.84 -93.83 -93.82 -93.81 -93.8 -93.79 -8378

-92.00

-84.00

-96.00

-98.00

-100.00

-102.00

-104.00

-106.00

-108.00

-110.00

-112.00

-114.00

-116.00

-118.00

-120.00

-122.00

-124.00

65

Figure 33. A color enhanced image of the relative horizontal acoustic reflectance over a 

bathymetry outline of the WFGB. Yellow areas are highest acoustic energy 

and white are the lowest as indicated on the scale to the right. Data are corrected 

for depth (HSV/depth in meters).
66

terrace and middle terrace areas. When corrected for depth, (HSV/water depth) as in Figure 33,

it is clear that the highest fish biomass occurs in the shallower areas. Based on logistic

regression (without intercept), there was a 35 and 100 times greater chance of finding fish over

the upper terrace compared to the middle and lower terraces. 

We generated several plots to visualize significant variables in the logistic model. Mean

fish energy was an order of magnitude higher over the upper terrace compared to the middle and

lower terrace and over open water (Figure 34). Fish energy also varied with TOD as energy over

the WFGB was an order of magnitude lower at noon that at other times of day (Figure 35). 

3.3.2 Density Estimates

Estimated fish density ranged from 0 to 0.005 fish/m3

 over the WFGB. When broken down

by terrace, fish densities were highest over the upper terrace just above the bottom at about 30

meters and just above the bottom of the middle terrace at about 70 meters (Figure 37). Similarly,

densities on the lower terrace peaked just above the bottom at 90 meters but were almost an

order of magnitude less than the highest densities observed on the upper terrace. Figure 38 is a

color enhanced illustration of the variation in fish density over different portions of WFGB.

3.3.3 Target Strength

Using RBD ANOVA to model the effect of class variables on fish size, fish size varied with

terrace and depth and their interactions (Table 13). Fish were significantly larger over the upper

terrace and near the surface (Figure 36). Mean fish size over the WFGB was - 47dB (6.7 cm),

and ranged from -65 to -25 dB (1 to 108 cm) (Love 1971).

3.3.4 Species Composition and Abundance

The fish community at the WFGB was very diverse and reflected that of a typical coral reef

community. Creole-fish and Bermuda chub were the most abundant species present followed by

great barracuda and black durgon (Table 14). The ROV survey results likely represent only a

small cross-section of the total species present as we did not include cryptic species in the visual

survey.

Fish abundance at the WFGB was estimated at 2,500,000 (Table 15). The most abundant

fishes at the WFGB were Bermuda chub and creole-fish and, as observed at the standing

platform, these fish were most commonly observed in the upper depth strata. Combining

acoustic density estimates and ROV species composition results, there were roughly 630,000

bermuda chub and 485,000 creole-fish followed by 261,000 great barracuda 130,000 and black

durgon.
1.00E-09

1.01E-072.01E-07

Upper Middle Lower 

Terrace

Fish Energy

67

Figure 34. Mean fish energy (from volume backscatter) by Terrace over the West Flower Garden Bank based on 

 hydroacoustic survey conducted in June 2000.
0.00E+00

5.00E-091.00E-081.50E-082.00E-08

Dawn Noon Dusk M

Terrace

Fish Energy

68

Figure 35. Mean fish energy (from volume backscatter) by time of day over the West Flower Garden Bank base

 hydroacoustic survey conducted in June 2000. Error bars are 95% confidence intervals
-52

-50-48-46-44-42-40

Upper Middle Lower 

Terrace

dB

69

Figure 36. Mean target strength (dB) by Terrace over the West Flower Garden Bank based on a dual beam h

 conducted in June 2000. Error bars are 95% confidence intervals.
0.000

0.0010.0020.0030.0040.0050.0060.0070.0080.0090.010

0 2 4 6 8 10

Depth (x10m)

Fish Density

OpenLowerMiddleUpper

70

Figure 37. Estimated density of fish (fish/m3) over the West Flower Garden Bank based on a dual beam hydr

conducted in June 2000. Error bars are 95 % confidence intervals.
27.93-

27.92-J

27.91-

27,9-

27.89-

27.68-

27.S7-

27.86-

27. 85-

27.84

27.83-

I I I T

-93.88 -93.87 -93.86 -93.85 -93.84 -93,83 -93.82 -93.81 -93.9 -93.79 -93 78

L._L Q

o ooe 0.0055

o Dos

0.0045

0 004

0.0035

0.003

0 0025

0.002

00015

0.001

0.0005

71

Figure 38. A color enhanced image of the estimated density of fish (#/m3) over a bathymetry 

outline of the WFGB. Yellow areas are highest density and white areas are the 

lowest density as indicated on the scale to the right. 
72

Table 13. 

RBD ANOVA (block on Terrace) results (significant) of target strength with, stratum (Strata),

and time of day and selected interactions at WFGB.

Source DF SS MS F Prob > F

Model 42 79751 1898 95.8 0.0001

Error 30874 611741 19

Corrected Total 30916 691493

R-Squared C.V. Root MSE TS Mean

.12 -9.4 4.45 -47.4

Variables DF Type III SS Mean Square F Value Pr > F

Terrace 3 1436 478 24.2 0.0001

Strata 9 11543 1282 64.73 0.0001

Diel 3 245 82 4.13 0.0062

Terrace*Strata 20 10234 512 25.83 0.0001

Terrace*Diel 7 12122 1731 87.4 0.0001
73

Table 14. 

Species common names and scientific names along with numbers of individuals by stratum, totals, and percen

visual point counts using video from a remotely operated vehicle (ROV) from the West Flower Garden Ba

West Flower Garden Banks June 2000Common Name Scientific Name 0 m 10 m 20 m 30 m 40 m 50 m 60 m 70 m 80m 90 Almaco jack Seriola rivoliana - - - - - - 2 - - - 

Bermuda chub Kyphosus sectatrix - 56 1 - - - - - - - Bar jack Caranx ruber - 1 1 - - - - - - - Great Barracuda Sphyraena barracuda - 22 - - - - - - - - Black durgon Melichthys niger - - 11 - - - - - - - Black jack Caranx lugubris - 1 - - - - - - - - Bluehead Thalassoma bifasciatum - - 1 - - - - - - - Blue runner Caranx crysos - - - 8 - - - - - - Blue tang Acanthurus coeruleus - - - 4 - - - - - - Cocoa damselfish Pomacentrus variabilis - - 3 - - - - - 1 - 

Creole-fish Paranthias furcifer - - 38 - - - - - - 3 

Dog snapper Lutjanus jocu - - 1 - - - - - - - French angelfish Pomacanthus paru - - - - 2 - - - - - Grey triggerfish Balistes capriscus - - - - 1 - - - - - King mackerel Scomberomorus cavalla - - - - - - - - 1 - Knobbed porgy Calamus nodosus - - - - 1 - - - - - Ocean triggerfish Balistes vetula - 1 - - - - - - - - Bank butterflyfish Chaetodon aya - - - - - - - - - 6 Scamp Mycteroperca phenax - - - - - - 2 - - - Short bigeye Pristigenys alta - - - - - - - - 1 4 Spanish hogfish Bodianus rufus - - - 1 - - - - - - Squirrelfish Holocentrus adscensionis - - - - - - - - - 2 Trumpetfish Aulostomus maculatus - - - - 1 - - - - - 
74

Table 15. 

Estimated numbers of fish over the West Flower Garden Bank based on a dual beam hydroacoustics survey con

Depth refers to a 10 m depth stratum and Area is the spatial extent of the WFGB that falls within that depth r

number of fish estimated to be within each depth range summed across all 10m stratum. Upper Terrace = 10-50

50-80m, and Lower Terrace = 80-100m. Population size is the sum of the total number of fish by T

Depth area (m2) Stratum

1

Stratum

2

Stratum

3

Stratum

4

Stratum

5

Stratum

6

Stratum

7

Stratum

8

Stratum

9

S

10-20 144,800 724 3,910 20-30 200,000 1,000 5,400 15,200 30-40 195,800 979 5,287 14,881 4,699 40-50 1,668,700 8,344 45,055 126,821 40,049 41,718 50-60 1,752,200 4,030 2,804 4,030 9,988 19,274 42,438 60-70 2,215,800 5,096 3,545 5,096 12,630 24,374 53,667 67,139 70-80 8,290,900 19,069 13,265 19,069 47,258 91,200 200,806 251,214 215,563 80-90 16,403,700 10,466 2,264 9,662 18,700 39,369 57,413 124,668 96,782 162,397 

90-100 15,653,200 9,987 2,160 9,220 17,845 37,568 54,786 118,964 92,354 154,967 

Terrace Population size Mean density (#/m2)

Upper 314,065 0.1422Middle 1,111,556 0.0907Lower 1,093,140 0.0341Total 2,518,761 0.0541
75

4.0 DISCUSSION

This project demonstrates the advantages of dual beam hydroacoustics coupled with

visual survey techniques to characterize, quantify, and compare fish communities associated

with standing platforms, artificial reefs, and natural reefs. The close geographical proximity of

the four study sites allowed us to run coincident surveys and compare fish community

characteristics at each of these unique sites without the confounding effects of season, depth, and

large spatial separation. Inclusion of the WFGB in this study afforded us the first direct acoustic

and visual comparison of fish communities between natural reefs and artificial reefs in the same

geographic region. 

In this study we used two modes of data collection and statistical analysis. At High

Island A350, we used stationary transducers that resample the same volume of space at synoptic

intervals. Using log transformed data, we could analyze the data set with ANOVAs to determine

if factors such as platform side, depth, or time of day significantly affected fish biomass (after

Stanley and Wilson 1996). Significant effects were then graphed as appropriate for comparison. 

The mobile acoustic surveys covered the WFGB, the toppled platform (WC617A) , and the

partially removed platform (HI A355). In this design, the transducer was towed a 2m/sec so it

did not sample the same volume of water, however we achieved repeated measures by running

multiple transects in the case of the reef sites. We were concerned about vessel effect, however,

we did not observe a change in fish biomass with repeated passes over the same site (Figure 15). 

These data were analyzed using logistic regression to determine if factors such as side, depth,

time of day, or distance from the site significantly affected fish biomass. Since the acoustic data

are averaged on a per ping basis, data collected in five-minute blocks at HI350 and previous

studies by Stanley and Wilson (2000a, 2000b) and Stanley (1994) are comparable to the mobile

acoustic data collected in 1 sec blocks reported in this study.

Traditional parametric analyses were not used for analysis of mobile acoustic data, given

the large number of zero values and the problem of autocorrelation that occurs in mobile

surveys. The use of logistic regression in ecological sampling was described by Trexler and

Travis (2001) as a nonlinear way of expressing ecological data. Logistic regression has been

shown to be useful with data sets that have a large number of zero values which are usually not

normally distributed. For regression analysis, the dependent variable was converted into a

binomial array of presence/absence of acoustic reflectance (fish measured as acoustic energy)/m3

to evaluate the probability or chance of finding a fish in a given cell. A cell was a one second

block (@2m linear distance) of time divided into 10 m depth strata. The presence/absence of

volume backscatter (Sv) was used as a dependent variable in performing logistic regression

because Sv is the mean measured amount of acoustic energy returned from each acoustic ping,

scaled for a cubic meter of water. 

Stanley and Wilson (1997) used fish density (#/m3) as the dependent variable, but this

value is very sensitive to cross-sectional backscatter (sigma) of individual targets which is used

to estimate fish size (fish size). Sigma accuracy increases with the number of times a single

target is pinged. In our mobile survey, the vessel traveled at 2 m/sec, therefore the chance of
76

hitting a single target, numerous times, was low. Due to the uncertainty of the accuracy of TS,

the accuracy of density becomes uncertain. We therefore used Sv as a proxy for fish presence,

hence the dependent variable in our models. If there was a statistically significant effect by a

class variable indicated in the logistic regression analysis, then the procedure was re-run using a

no intercept option. The resultant Odds Ratio Estimates provide a comparison of probabilities of

fish occurring within each class variable. Significant class variables were visualized and

compared within and between sites by plotting Sv and estimated fish density by significant class

variables.

Overall, we found that fish biomass and density and around the standing oil and gas

platform were higher than the artificial reefs or natural reef. Comparison of the mean Sv found

at the standing platform and over and immediately around the two reef sites and the WFGB

terraces clearly indicate an order of magnitude difference in fish biomass between the standing

platform and other sites (Figure 39), suggesting that standing platforms support greater fish

biomass. Our results are in support of the findings reported by Stanley and Wilson (2000a), that

when a platform is converted into a artificial reef by toppling in place or by partial removal, it

loses a significant portion of the fish community. Fish biomass at the artificial reef sites were

similar to the upper terrace of the nearby natural reef. In each habitat, we tended to find higher

fish densities in habitats with more vertical structure. 

We found significant effects of orientation, distance, and depth with both artificial reefs.

The probability of finding a fish at WC 617A was highest over the toppled platform and within

30 m of the reef, which is similar to the survey of EI 313 done by Stanley and Wilson (1999). 

This is also similar to a reported 16 m area of influence by Stanley (1994) at platforms from 50-

100m depths. Platforms appear to have a finite reef effect that does not extend beyond visual

range of the associated species. The probability of finding a fish at HI A355 was highest around

the sides of the partially removed platform and within 30 m of the structure, although fish

biomass was highest directly over the reef site. Stanley and Wilson (1999) reported higher

numbers of fish directly over another artificial reef (EI 313), and reported the same high fish

densities within 30 m of the artificial reef. The significant effect of orientation (north, south,

east, and west) at HI A355 could be related to a section of the jacket being placed roughly 30m

away from the partially removed platform on the southeast side. Stanley and Wilson (1997) also

reported differences in density between platform side and suggested that these differences may

be due to platform configuration as higher densities tended to be associated with the conductor

bays. Fish biomass near the bottom was approximately the same for the standing platform and

artificial reef sites suggesting that the artificial reef sites retain the community found at the lower

portion of the standing platform. 

Density patterns were basically the same as fish energy. Fish density at the standing

platform was an order of magnitude greater than those found at the RTR sites or the WFGB

(Figure 40). Density at the two artificial reef sites ranged from 0 to 0.7 fish/m3 and the partially

removed platform had a slightly higher fish density than the toppled platform with overall mean

values (within 20m of each site) of 0.002 vs. 0.0015, respectively. Both sites had highest fish 
1.6x1O

1 4x1O

4OxlO

1OxlO -

0.0

VVFGB

Standing

L

Partal Toppled Upper Middle Lower Open

Habitat

0.005-

0 004 -

0.003 -

0 002 -

0.001 -

0.000

* 7'

30

V \

40 50 60 70 80

Depth Stratum (m)

-.- Standing

-A-- Toppled

y Partially Removed

--WFGB (Upper)

0.07- . 0,06

0.006-

77

Figure 39. Comparison of the mean fish energy observed over and immediately around the

standing (HI 350A), partially removed (WC 617A), and Toppled (HI A355)

platforms and the upper, middle, and lower terraces of the WFGB.

Figure 40. Estimated fish density at depth for all sample locations. Note axis shift for the

standing platform.
78

densities below 50m, which is opposite the pattern observed at the standing platform. However,

the partially removed platform, HI A355, also had elevated estimated densities closer to the

surface than WC 617A resembling fish distribution at the standing platform. Time of day and

depth stratum had an effect on fish density as had been reported previously (Stanley and Wilson

2000a), however the density patterns exhibited at different times of day do not follow a

predictable pattern and are likely site-specific. In addition, the short duration of this study make

comparison to the longer term studies of Stanley and Wilson (various) inappropriate. We

continue to see fish density and size being greater near the surface than the bottom and of

standing oil and gas platforms. 

We conclude that fish density around a standing platform and the resultant artificial reef

configurations of toppled in place or partially removed, are greater than that nearby WFGB

habitat on a per unit area basis. The highest densities at the WFGB were found over the upper

terrace where they were two to three orders of magnitude greater than the middle or lower

terraces and similar to artificial reef sites. Densities associated with the upper terrace were

similar to the artificial reef sites. While densities associated with the remaining terraces were

more similar to those found away from the 30m area of influence surrounding RTR structures. 

Target strength data were not only used in estimating fish density at each site, but also

shed some light on the change in community structure between sites as target strength data

reveals information about fish size distribution. In general, slightly larger fish were associated

with the standing platform, particularly in the middle and upper water column, compared to the

partially removed or toppled platforms, where they are larger over the reef sites. Mean target

strengths observed at the standing platform ranged from 39 to -33 dB, or fish sizes of 20 - 41 cm

(Love 1971). The larger species were shown to be pelagic planktivores and piscivores by

Stanley and Wilson (1997). These species appear to be lost when a platform is converted into an

artificial reef. Target strengths around the lower portion of the standing platform were similar to

the same depths at both reef sites. Fish around the standing platform and reef sites, were in

general larger than those found over the WFGB. Within the WFGB complex, fish size was

largest over the upper terrace and smallest over the open water areas.

Species composition at the standing platform and two reef sites were fairly similar at

depth, but both were different than the WFGB. In general, the greater percentage of fish

observed with the ROV were found associated with vertical profile (Figure 41). The most

obvious difference between the standing platform and reef sites was that pelagic planktivores

such as blue runner and Bermuda chub were present in the upper part of the water column at HI

350A, but not at the reef sites. The species composition around both reef sites was basically the

same and were similar to the lower portion (>50 m) of HI 350A (Table 16). ROV surveys of HI

A355 in June 1999 and in June 2000 indicated that red snapper and amberjack were the two most

abundant species both years, and together they made up over 70 percent of the fish community. 

Similarly, the survey of WC 617A, conducted in June 1999 only, indicated that amberjack,

almaco jack, and red snapper were the most abundant species (Table 16). The standing platform,

and the two reef sites were inhabited by the same type of depth-specific fish community that 
79

 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Depth Statum (m)

 Standing

 Partially Removed

 Toppled

Figure 41. Proportion of fish by depth at each survey site (platforms) based on 

ROV surveys.
80

Table 16. 

Percent species composition at the standing platform (HI 350A), partially removed (HI A355)

and toppled platform ( WC 617A), based on ROV surveys.

Standing Partial Toppled

Almaco Jack 3.83% 8.50% 8.38%

Amberjack 2.11% 36.60% 17.37%

Bermuda Chub 28.20%

Bar Jack 0.10%

Barracuda 1.81%

Bluerunner 30.92%

Creole fish 14.80% 11.76%

Crevalle jack 0.91% 1.96% 5.39%

Gag Grouper 0.20% 1.80%

Rainbow Runner 1.11%

Red Snapper 6.14% 32.68% 50.90%

Scamp 7.35% 7.19%

Triggerfish 0.81% 1.96% 8.98%

Blackfin Tuna 5.88%

Warsaw Grouper 0.65%
81

Stanley and Wilson (1997, 2000a) reported for other structures in similar water depths. These

included important to recreational and commercial species such as amberjack, red snapper,

creole fish, trigger fish, and almaco jack. Stanley and Wilson (2000a) referred to this suite of

species as reef- associated.

Since densities were highest in the upper strata of the standing platform, and ROV

surveys indicated that these communities were dominated by pelagic planktivores, we believe

that vertical profile plays an important role in the attracting/maintaining blue runner and chub in

upper depths. By design, both RTR structures had much lower vertical profile to avoid hazard to

navigation. We found very few fish in the shallower open waters above the RTR structure

(Figure 41). We presume most of pelagic planktivores such as blue runner and Bermuda chub

are “lost” following creation of reef sites. However, creation of a reef site using a platform does

not seem to reduce production at lower strata as the number of species such as red snapper,

grouper, creole fish, etc were similar. Red snapper, amberjack, and scamp were the dominant

species between 40-60m at all platform sites. They made up 94% of fish species observed with

the ROV at 40-60m near the standing platform and 67% and 76% of fish observed at WC617A

and HIA355, respectively, in 1999. These data suggest that the fish community in the lower

depth strata may be uncoupled from the community found in the upper strata. Fish at these

lower depths may instead be relying more heavily upon benthic or open water prey production. 

This observation warrants further detailed investigation because red snapper and amberjack tend

to be most heavily targeted by recreational and commercial fishers. 

Species composition at the WFGB was quite different than the standing platform and reef

sites. We found 23 species of fish at the WFGB compared to 7 and 8 at the two reef sites and 13

at the standing platform. The WFGB community was dominated by Bermuda chub and

barracuda over the upper terrace and creole fish closer to the bottom. We also found a much

greater proportion of reef-dependent species (Stanley and Wilson 20021a) at the WFGB than the

standing platform or reef sites. There is a possibility that vessel or ROV avoidance may have

been an issue, but it was not apparent in the acoustic survey. The most extensive historical study

of the fish community and WFGB was conducted by Boland et al. (1983). Boland et al. (1983)

used video surveys to document species composition at the both Flower Garden Banks. Most of

their efforts were focused on reef species with a few meters of the bottom. Boland et al. (1983)

identified more than twice the number of species that we found, including many cryptic reef

species that live close to or within the reef structure. We found eight of the 16 primary species

reported by Boland et al. (1983) from the WFGB, of these 16, seven were cryptic and not

targeted in our study. The difference in species composition and density between the WFGB and

the platform sites is evidence that oil and gas platforms serve as a different type of habitat than a

natural reef; the fish communities are different.

One of our main goals was to estimate and compare the total number of fish associated

with each site. This number is dependent upon density and “area of influence” of a reef site. We

found that both reef sites had an area of influence of 30 m as densities beyond 30 were basically

the same as open water, particularly at WC 617A. Based on the reports by Stanley and Wilson 
82

0

5000

10000

15000

20000

25000

30000

22m24m40m60m

HI 350A (89m)

110m140m220m

Partial EI 313

Toppled EI 366

Partial HI A355

Toppled WC 617A

Number of Fish

Figure 42. Average number of fish found at platforms and platforms used as artificial reefs 

as determined with dual beam hydroacoustics (Jan 1992 - Jan 2002). Depths indicate 

the depth of standing platforms.
83

(various) we used a 20 m area of influence for the standing platform. We estimate that total fish

numbers at WC617 and HIA355 were 2,850 and 2,700, respectively. We also estimated that

there were approximately 12,000 fish around HI A350. These “total community” estimates

along with those of Stanley and Wilson (various) illustrate the change in fish biomass that occurs

when a platform is converted into an artificial reef. As mentioned previously, however, the

majority of these changes occur with the loss of pelagic planktivores and piscivores in the upper

depth strata. There were approximately 2,000 fish below 40 m at HI A350 which was similar to

the number of fish around both reef sites. The number of fish at HI A350 is consistent with the

estimates of fish communities reported by Stanley and Wilson (2000b, 1997) for platforms in

similar water depths. They reported 10,000 to 20,000 fish inhabited each of the four oil and gas

platforms they had studied (Figure 42).

 Similarly, fish density estimates for each terrace at the WFGB and the spatial extent of

each terrace were used to estimate that there were approximately 2,500,000 fish associated with

the WFGB. This estimate is on the same order of magnitude as reported in Boland et al. (1983)

who assigned estimates to the abundance of individual species. For example, Boland et. al.

(1983) reported from 400,000 - 900,000 creole-fish on the WFGB. We estimate that 23% of

2,500,000, or 575,000 creole-fish were present at the time of our survey. Note that these studies

were nearly 20 years apart.

Acoustic surveys have been conducted at several artificial reef sites. As mentioned

previously, Stanley and Wilson (1999) conducted a mobile acoustic survey of the Penrod drilling

rig at EI 313. Although their data were not published, they found approximately 7,000 fish

around the Penrod drilling rig in EI 313 (Wilson and Stanley 1999). The Penrod drilling rig was

located in shallower water than these sites reported herein and the drilling rig had a more

complex inner-structure of decking and cross-member material; this more complex structure

combined with vertical relief likely influenced fish populations. In a survey of the Tenneco II

artificial reef off southern Florida, Seaman et al. (1989), found that the solid deck portion of the

platform did not contain the diversity and abundance of fishes found on the grated surface

section of the platform deployed 30m away. They postulated that the grating likely afforded

more hiding places for small fishes, thereby increasing diversity of small species and also food

supply for predatory species. Openings in the grated surface would also permit access to the

upper surface for animals living in protected areas under the deck (Seaman et al. 1989). It is

likely that the greater number of fish around the Penrod drilling rig was due to the different type

of material such as decking and shallower water depths. Studies suggest that optimal artificial

reef configurations exist, but vary, depending on the target species (Stanley and Wilson 1990).

Reef configuration (toppled vs partially removed) appeared to have no discernable

impact on fish production. Taken over the entire water column, mean fish density within 20m of

the partially removed platform (0.0020 fish/m3 2,850 fish) was only slightly higher than

observed at the toppled platform (0.0015 fish/m3, 2,700 fish) and is likely insignificant. 

However, partial removal would be the preferred option as it can avoid the use of explosives

which has been shown to kill many of the resident species and poses a general hazard to human

safety.
84

Red snapper and amberjack populations at the two reef sites were similar in number to

the populations estimated to be at the standing platform in similar water depths. These artificial

reef sites, like their platform predecessors, have significant fishing value since the majority of

species associated with these reef sites are targeted by commercial and recreational fishers. 

When a standing platform is converted into an artificial reef site, it appears that the pelagic

planktivores make up the greatest biomass that is lost, and the more desirable recreational

species are retained. According to survey results from HI A355 and WC 617A, we estimate a

loss of approximately 50-80 percent of the fish population when a standing platform is converted

(toppled or partially removed) into an artificial reef site in 100 m of water. Each artificial reef

site harbored approximately 2,500 fish compared to 12,000 fish around the HI A350 and the

10,000- 20,000 reported by Stanley and Wilson (1998). This decline of fish numbers was also

observed during a pre- and post- toppling survey of EI 367 (Wilson and Stanley 1998). 

We recognize some that the absolute estimates of fish numbers are likely skewed due to

the uncertainty of target strength estimates. However, these data do provide a basis for

comparisons between the different habitat types. The WFGB, for example, supports well over 2

million fish that can be detected by acoustics. This fish biomass is comparable to the combined

fish populations of 150 standing platforms and or 1000 “reefed” platforms in similar water

depths (ranging from 100 to 500 m) . Future refinements in the approach to stationary and

mobile acoustic studies will lead to even more accurate assessments of fish habitat. Integration

of these types of study results into a comprehensive spatial database will go far to improving

management of these resources.

This research continues to support the working hypothesis that platforms do make useful

artificial reefs since they tend to support a population of fish that can be 10 to over 1000 times

greater in density than the adjacent sand and mud bottom habitats, and are equal to or even

exceed that of natural coral reef habitat like the WFGB. The species associated with the

artificial reefs (including standing platforms) do however, differ from those found on natural reef

habitats. Future research efforts might be directed toward determining the reasons for this

difference. 

Completion of this research has provided quantitative data on the effect of vertical profile

on fish abundance, assessed the effectiveness of retired platforms sited as artificial reefs,

provided comparison to a natural reef, and presented the differences in abundance and species

composition among sites. Since the reef sites are of similar age and size, and are located within

a radius of 48 km, comparison of the production platform and the partial removal with the

toppled platform has provided valuable insight into the effect of platform configuration on the

assemblage of fishes while minimizing confounding effects.

To date over 150 retired petroleum platforms from Texas to the Atlantic coast of Florida

have been converted to artificial reefs. A variety of removal techniques and placement

configurations have been employed in siting these reefs. While numerous qualitative studies

documenting the colonization and relative abundance of organisms associated with production

platform have been undertaken, it has proven difficult to conduct quantitative studies at artificial
85

reefs. Consequently, very little could be said about how different reef configurations impacted

fish abundances and, further, how these abundances compared to abundances at natural reefs. 

Development of artificial reefs has been advocated by government and the Gulf of Mexico

Fishery Management Council (GMFMC 1989). They identified several research needs and

goals, including general information on the effects of artificial reefs, improving the quantitative

assessment techniques used to describe artificial reef communities, monitoring biological

changes at reef sites, assessing the importance of fish attraction versus fish production, and

quantifying the relationships between reef fish production and habitat. This research provides

information critical in fulfilling these goals. 
87

5.0 REFERENCES

Bohnsack, J.A. and S.P. Bannerot. 1986. A stationary visual census technique for quantitatively

assessing community structure of coral reef fishes. NOAA Technical Report NMFS 41.

15 pp.

Bohnsack, J.A., D.L. Johnson, and R.F. Ambrose. 1991. Artificial habitats for marine and

freshwater fisheries. Ecology of Artificial Reef Habitats. Academic Press. New York,

New York. Pp. 61-108. 

Boland, G.S., B.J. Gallaway, J.S. Baker, and G.S. Lewbel. 1983. Ecological effects of energy

development on reef fish of the Flower Garden Banks. Ecological Research Associates,

Inc., Bryan, Texas. 466 pp.

Bortone, S.A. and J.J. Kimmel. 1991. Environmental assessments and monitoring of artificial

habitats. Artificial Habitats for Marine and Freshwater Fisheries. New York: Academic

Press. Pp. 177-236.

Bright, T.J., J.W. Tunnell, L.H. Pequegnat, T.E. Burke, C.W. Cashman, D.A. Cropper, J.P. Ray,

R.C. Tresslar, J. Teerling, and J.B. Wills. 1974. Biotic zonation on the West Flower

Garden Bank. Texas A&M University, University of Southwestern Louisiana and

University of Houston. Pp. 1-54.

Bright, T.J. and C.W. Cashman. 1974. Fishes. Biotic zonation on the West Flower Garden Bank.

Texas A&M University, University of Southwestern Louisiana and University of

Houston. Pp. 340-409.

Bright, T.J. and G.S. Boland. 1985. Biotic zonation, East and West Flower Garden Banks. In:

The Flower Gardens: A compendium of information. U.S. Department of the Interior,

Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, Louisiana.

OCS Study MMS 85-0024. Pp 53-90.

Brock, R.E. 1982. A critique of the visual census method for assessing coral reef fish

populations. Bulletin of Marine Science. 32:269-276.

Continental Shelf Associates. 1982. Study of the effects of oil and gas activities on reef fish

populations in the Gulf of Mexico OCS area. U.S. Department of the Interior, Minerals

Management Service, Gulf of Mexico OCS Region, New Orleans, Louisiana. OCS

Report MMS 82-10.

Dennis, G.D. and T.J. Bright. 1988. Reef fish assemblages on hard banks in the northwestern

Gulf of Mexico. Bulletin of Marine Science. 43(2):280-307.
88

Doherty, P.J. and D. McB. Williams. 1988. The replenishment of coral reef fish populations. 

Oceanography and Marine Biology. 26:487-551.

Dokken, Q.R., I.R. MacDonald, J.W. Tunnell, C.R. Beaver, G.S. Boland, and D.K. Hagman.

1999. Long- Term Monitoring at the East and West Flower Garden Banks,1996-1997.

U.S. Department of the Interior, Minerals Management Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. OCS Study MMS 99-0005. Pp. 1-7.

Elvers, D.J. and C.W. Hill, Jr. 1985. History of activities at the Flower Garden Banks. In: The

Flower Gardens: A compendium of information. U.S. Department of the Interior,

Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, Louisiana.

OCS Study MMS 85-0024. Pp. 3-10.

Gallaway, B.J. and G.S. Lewbel. 1982. The ecology of petroleum platforms in the northwestern

Gulf of Mexico: A community profile. USFWS Office of Biology Services, Washington,

D.C. FWS 10BS-82/27. Open File Report. Pp. 82-103.

Gallaway, B.J., L.R. Martin, R.L. Howard, G.S. Boland, and G.D. Dennis. 1981. Effects on

artificial reefs and demersal fish and macrocrustacean communities. Marine Science.

14:237-299.

Gardner, J.V., L.A. Mayer, J.E. Hughes Clarke, and A. Kleiner. 1998. High-resolution

multibeam bathemetry of East and West Flower Gardens and Stetson Banks, Gulf of

Mexico. Gulf of Mexico Science. 16(2):131-143.

Garrison, L.P., W. Michaels, J.S. Link, and M.J. Fogarty. 2000. Predation risk on larval gadids

by pelagic fish in the Georges Bank ecosystem. I. Spatial overlap associated with

hydrographic features. Canadian Journal of Fisheries and Aquatic Sciences. 57:2455-

2469.

Gerlotto, F., C. Bercy, and B. Bordeau. 1989. Echo Integration Survey Around O ffshore Oil

Extraction Platforms off Cameroon: Observations of the Repulsive Effect on Fish of

Some Artificially Emitted Sounds. Proceedings of the Institute of Acoustics. (19):79-88.

GMFMC (Gulf of Mexico Fisheries Management Fisheries Council). 1989. Amendment 1 of the

Reef Fisheries Management Plan for the Fisheries Resources of the Gulf of Mexico. 

GMFMC. Tampa FL. 420 pp.

Gittings, S.R. and E.L. Hickerson. 1998. Introduction. Gulf of Mexico Science. 16(2):128.

Love, R.H. 1971. Dorsal aspect target strength of an individual fish. Journal of Acoustic

Society of America. 62:1,397-1,403.
89

Menge, B.A. and J.P. Sutherland. 1987. Community regulation: Variation in disturbance

competition and predation in relation to environmental stress and recruitment. American

Naturalist. 130:730-757.

NRC (National Research Council). 1996. An assessment of techniques for removing offshore

structures. Washington, DC: National Academy Press.

Ott, L. 1982. An introduction to statistical methods and data analysis. 2nd Edition. Duxbury

Press. Boston, Mass. 774 pp.

Parker, Jr., R.O., D.R. Colby, and T.P. Willis. 1983. Estimated amount of reef habitat on a

portion of the U.S. South Atlantic and Gulf of Mexico Continental Shelf. Bulletin of

Marine Science. 33:935-940.

Putt, Jr., R.E. 1982. A quantitative study of fish populations associated with a platform within

Buccaneer oil field, northwestern Gulf of Mexico. M.Sc. Thesis. Texas A&M

University. College Station, Texas.

Rooker, J.R., Q.R. Dokken, C.V. Pattengill, and G.J. Holt. 1997. Fish assemblages on artificial

and natural reefs in the Flower Garden Banks National Marine Sanctuary, USA. Coral

Reefs. 16:83-92.

Sale, P.F. 1990. Recruitment of marine species: Is the bandwagon rolling in the right direction? 

Trends in Evolutionary Ecology. 5:25-27.

Sale, P.F. 1991. Reef fish communities: Open nonequilibrial systems. In: Sale, P.F. editor. The

ecology of fishes on coral reefs. New York: Academic Press. Pp. 564-600.

Sale, P.F. and W.A. Douglas. 1981. Precision and accuracy of visual census technique for fish

assemblages on coral patch reefs. Environmental Biology of Fish. 6:333-339.

SAS Institute Incorporated. 2000. SAS user's guide: Statistics. Version 8. SAS Institute. Cary,

NC. 1,290 pp. 

Seaman, Jr., W.J. Lindberg, C.R. Gilbert and T.K. Frazer. 1989. Fish habitat provided by

obsolete petroleum platforms off Southern Florida. Bulletin of Marine Science.

44(2):1014-1022.

Seaman Jr., W.J. and A. Jensen 2001. Purposes and practice of artificial reef evaluation. In:

Seaman, W.A., editor. Artificial Reef Evaluation. CRC Press. Pp. 1-20.

Sonnier, F., J. Teerling, and H.D. Hoese. 1976. Observations on the offshore reef and platform

fish fauna of Louisiana. Copeia. No. 1.
90

Stanley, D.R. 1994. Seasonal and spatial abundances and size distribution associated with a

petroleum platform in the Northern Gulf of Mexico. Dissertation. Louisiana State

University.

Stanley, D.R. and C.A. Wilson. 1990. A fishery-dependent based study of fish species

composition and associated catch rates around oil and gas structure off Louisiana.

Fishery Bulletin. 88(4):719-730.

Stanley, D.R. and C.A. Wilson. 1991. Factors affecting the abundance of selected fishes near oil

and gas platforms in the northern Gulf of Mexico. Fishery Bulletin. 89(1):149-159. 

Stanley, D.R. and C.A. Wilson. 1995. Detection of the effect of scuba divers on fish density and

target strength utilizing dual-beam hydroacoustics. American Fisheries Society.

124:946-949.

Stanley, D.R. and C.A. Wilson. 1996. Abundance of fishes associated with a petroleum platform

as measured with dual-beam hydroacoustics. ICES Journal of Marine Science. 53: 473-

475.

Stanley, D.R. and C.A. Wilson. 1997. Seasonal and spatial variation in abundance and size

distribution of fishes associated with a petroleum platform in the northern Gulf of

Mexico. Canadian Journal of Fisheries and Aquatic Sciences. 54:1166-1176.

Stanley, D.R. and C.A. Wilson. 1998. Spatial variation in fish density at three petroleum

platforms as measured with dual-beam hydroacoustics. Gulf of Mexico Science.

1998(1):73-82.

Stanley, D.R., and C.A. Wilson. 1999. Survey of the fisheries resources at the toppled jackup

drilling rig in Eugene Island 313. A report to Texaco Inc. 

Stanley, D.R. and C.A. Wilson. 2000a. 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. A final report for the U.S. Department of Interior, Minerals Management

Service Gulf of Mexico OCS Region, Gulf of Mexico OCS Region, New Orleans,

Louisiana. OCS Study MMS 2000-005.

Stanley, D.R. and C.A. Wilson. 2000b. Variation in the density and species composition of fishes

associated with three petroleum platforms using dual beam hydroacoustics. Fisheries.

47:161-172.

Trexler, J.C. and J. Travis. 2001. Nontraditional regression analysis. Ecology. 74(6):1629-1637.
91

Wilson, C.A. and D.R. Stanley. 1991. Technology for assessing the abundance of fish around

oil and gas structures. In: Nakamura, M., R.S. Grove, and C.J. Sonu, editors. Recent

advances in aquatic habitat technology. Southern California Edison Company. 

Environmental Research Report Series 91-RD-19. Pp. 115-119. 

Wilson, C.A. and D.R. Stanley. 1998. The Louisiana Artificial Reef Research Program Annual

Report. Louisiana Department of Wildlife and Fisheries. 
93

Appendix A

Images from ROV Surveys 

Conducted in June 1999 and June 2000 

of High Island A350, High Island 355A, 

and West Cameron 617A. 
Figure A1. A school of greater amberjack

swims by a severed leg of HI 355 A.

95

Figure A2. Closeup of a creolefish in thewellbay of HI A350.

Figure A4. A scamp swims towards thetoppled WC 617A platform.

Figure A5. A red snapper swims down through

the water column of HI 355 A.

Figure A6. A warsaw 

through the piling of Westimated ~ 1 meter. Nposterior of the right e

Figure A3. A collec

along one of the well 
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 

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 territories under U.S. administration. 

The Minerals Management Service Mission 

As a bureau of the Department of the Interior, the Minerals Management Service's (MMS) 

primary responsibilities are to manage the mineral resources located on the Nation's Outer 

Continental Shelf (OCS), collect revenue from the Federal OCS and onshore Federal and Indian 

lands, and distribute those revenues. 

Moreover, in working to meet its responsibilities, the Offshore Minerals Management Program 

administers the OCS competitive leasing program and oversees the safe and environmentally 

sound exploration and production of our Nation's offshore natural gas, oil and other mineral 

resources. The MMS Minerals Revenue Management meets its responsibilities by ensuring the 

efficient, timely and accurate collection and disbursement of revenue from mineral leasing and 

production due to Indian tribes and allottees, States and the U.S. Treasury. 

The MMS strives to fulfill its responsibilities through the general guiding principles of: (1) being 

responsive to the public's concerns and interests by maintaining a dialogue with all potentially 

affected parties and (2) carrying out its programs with an emphasis on working to enhance the 

quality of life for all Americans by lending MMS assistance and expertise to economic 

development and environmental protection.