OCS Study 

•

MMS 2003-053 

Consequences of Alternative 

Decommissioning Options to Reef 

Fish Assemblages and Implications 

for Decommissioning Policy 

Final Technical Summary 

Final Study Report 

U.S. Department of the Interior 

Minerals Management Service

Pacific OCS Region 

Consequences of Alternative 

Decommissioning Options to Reef 

Fish Assemblages and Implications 

for Decommissioning Policy 

Final Technical Summary 

Final Study Report 

Authors 

Mark H. Carr 

Michael Vincent McGinnis 

Graham E. Forrester 

Jeffrey Harding 

Peter T. Raimondi 

Principal Investigators

Mark H. Carr 

Michael Vincent McGinnis 

Graham E. Forrester

Prepared under MMS Cooperative 

Agreement No. 14-35-0001-30758 

by 

Coastal Marine Institute 

Marine Science Institute 

University of California 

Santa Barbara, CA 93106 

U.S. Department of the Interior 

Minerals Management Service 

Pacific OCS Region

Camarillo

October 2003
Disclaimer 

This report has been reviewed by the Pacific Outer Continental Shelf Region, Minerals Management 

Service, U.S. Department of the Interior and approved for publication. The opinions, findings, 

conclusions, or recommendations in this report are those of the author, and do not necessarily reflect 

the views and policies of the Minerals Management Service. Mention of trade names or commercial 

products does not constitute an endorsement or recommendation for use. This report has not been 

edited for conformity with Minerals Management Service editorial standards. 

Availability of Report 

Extra copies of the report may be obtained from: 

U.S. Dept. of the Interior 

Minerals Management Service 

Pacific OCS Region 

770 Paseo Camarillo 

Camarillo, CA 93010 

Phone: 805-389-7621 

A PDF file of this report is available at: 

http://www.coastalresearchcenter.ucsb.edu/CMI 

Suggested Citation 

The suggested citation for this report is: 

Carr, Mark H., McGinnis, Michael Vincent, Forrester, Graham E., Harding, Jeffrey, and Peter T. 

Raimondi. Consequences of Alternative Decommissioning Options to Reef Fish Assemblages and 

Implications for Decommissioning Policy. MMS OCS Study 2003-053. Coastal Research Center, 

Marine Science Institute, University of California, Santa Barbara, California. MMS Cooperative 

Agreement Number 14-35-0001-30758. 104 pages. 
i

Table of Contents 

FINAL TECHNICAL SUMMARY....................................................................... 1 

FINAL STUDY REPORT...................................................................................... 9 

 Section One: Introduction............................................................................... 9 

 

 Background: Ecological Considerations of Artificial Reef Habitats ............ 9 

 Approach: Fish Assemblages on Natural Reefs and Production 

 Platforms ....................................................................................................... 14 

 Background: Ecological Information and Development of 

 Decommissioning Policy .............................................................................. 15 

 Approach: Characterization of the Role of Science and Values in 

 Decommissioning.......................................................................................... 16 

Section Two: Fish Assemblages on Natural Reefs and Production 

 Platforms............................................................................................................ 18 

 

 Methods......................................................................................................... 18 

 Fish Assemblages on Natural Reefs and Production Platforms.............. 18 

 Study Area......................................................................................... 18 

 Fish Assemblages on Shallow Portions of Platforms ....................... 19 

 Fish Assemblages on Shallow Natural Reefs ................................... 23 

 Fish Assemblages on Deep Portions of Platforms ............................ 24 

 Fish Assemblages on Deep Natural Reefs ........................................ 27 

 Analyses ............................................................................................ 27 

 Vertical Stratification of Fish Species and Life Stages on Platforms ..... 28 

 Comparison of Fish Density Estimates by ROV and Diver Surveys 29 

 Fish Movement Among Natural Reefs and Platforms ............................ 29 

 Relative Performance of Fishes on Platforms and Natural Reefs........... 31 

 Contribution of Platforms to the Abundance of Regional Reef 

 Structure .................................................................................................. 31 

 

 Results........................................................................................................... 32 

 

 Fish Assemblages on Natural Reefs and Production Platforms.............. 32 

 Vertical Stratification of Fish Species and Life Stages on Platforms ..... 51 

 Comparison of Fish Density Estimates by ROV and Diver Surveys 51 

 Fish Movement Among Natural Reefs and Platforms ............................ 54 

 Relative Performance of Fishes on Platforms and Natural Reefs........... 56 

 Contribution of Platforms to the Abundance of Regional Reef 

 Structure .................................................................................................. 56 

 
Final Technical Summary – Carr et al 

ii

 Discussion...................................................................................................... 56 

 

 Fish Assemblages on Natural Reefs and Production Platforms............... 57 

 Vertical Stratification of Fish Species and Life Stages on Platforms...... 59 

 Fish Movement Among Natural Reefs and Platforms............................. 60 

 Relative Performance of Fishes on Platforms and Natural Reefs............ 60 

 Contribution of Platforms to the Abundance of Regional Reef 

 Structure................................................................................................... 62 

 

 Future Recommendations .............................................................................. 62 

Section Three: Ecological Information and the Development of 

 Decommissioning Policy .................................................................................... 63 

 

 Methods.......................................................................................................... 63 

 

 Documentary Analysis............................................................................. 63 

 Analytical Framework: the “Revised Garbage Can” Model.................... 63 

 

 Results............................................................................................................ 64 

 

 Political Ecology of Decommissioning Policy Development in the 

 Gulf of Mexico......................................................................................... 64 

 The Problem Stream: The Perceived Lack of Reef Habitat............... 66 

 The Political Stream........................................................................... 68 

 The Policy Stream.............................................................................. 70 

 Political Ecology of Decommissioning Policy in the Southern 

 California Bight ....................................................................................... 74 

 California’s unique Political Ecology................................................ 76 

 

 Conclusions.................................................................................................... 80 

Acknowledgements ............................................................................................ 81 

References........................................................................................................... 82 

Appendices.......................................................................................................... 89 

 Appendix 1..................................................................................................... 89 

 Appendix 2..................................................................................................... 91 

 Appendix 3..................................................................................................... 93 

 Appendix 4..................................................................................................... 94 

 
iii

List of Tables 

Table 1. Structural Characteristics of Offshore Platforms Along California........ 13 

Table 2. Location and Depths of Natural Reefs Surveyed in this Study....................... 19 

Table 3. Sampling Frequency of Study Platforms and Natural Reefs .................. 20 

Table 4. Taxonomic Categories of Rockfish Species Used for Analyses............. 25 

Table 5. Date and Location of Fishes Tagged During the Movement Study........ 30 

Table 6. Distribution of Species Tagged During the Movement Study................ 31 

Table 7. Relationships Between Fish and Kelp Densities at Carpinteria Reef ..... 35 

Table 8. Summary of Fish Movement Patterns..................................................... 55 

List of Figures 

Figure 1. Location of Offshore Oil Production Platforms Along California.......... 12 

Figure 2. Illustration of Proposed Alternative Decommissioning Scenarios ......... 14 

Figure 3. Pattern of Sampling Conducted by Divers and ROV on Platforms........ 22 

Figure 4. Shallow Non-rockfish Species Densities: Platforms Versus Natural 

 Reefs........................................................................................................ 33 

Figure 5. Surfperch Species Densities: Platforms Versus Natural Reefs............... 34 

Figure 6. Rockfish Species Complex Densities: Platforms Versus Natural Reefs. 36 

Figure 7. Shallow Benthic Rockfish Complex Species Densities: Platforms 

 Versus Natural Reefs............................................................................... 37 

Figure 8. Midwater Rockfish Complex Species Densities: Platforms Versus 

 Natural Reefs........................................................................................... 38 

Figure 9. Copper Rockfish Complex Species Densities: Platforms Versus 

 Natural Reefs........................................................................................... 39 

Figure 10. Relative Density of Rockfish Size Classes: Platforms Versus Natural 

 Reefs........................................................................................................ 41 

Figure 11. Relative Density of Non-rockfish Size Classes: Platforms Versus 

 Natural Reefs........................................................................................... 42 

Figure 12. Comparison of Shallow Fish Assemblages on Platforms and Natural 

 Reefs........................................................................................................ 44 

Figure 13. Comparison of Shallow Fish Assemblages Across Study Platforms...... 45 

Figure 14. Comparison of Deep Fish Assemblages on Platforms and Natural 

 Reefs........................................................................................................ 46 

Figure 15. Comparison of Deep Fish Assemblages Across Study Platforms .......... 47 

Figure 16. Comparison of Shallow Young-of-Year Fish Assemblages on 

 Platforms and Natural Reefs ................................................................... 49 

Figure 17. Comparison of Shallow Young-of-Year Fish Assemblages Across 

 Study Platforms....................................................................................... 50 

Figure 18. Comparison of Fish Assemblages Sampled by Divers and ROV on 

 Platforms ................................................................................................. 52 

Figure 19. Relative Depth Distribution of Rockfish Life Stages on Platforms........ 53 
Final Technical Summary – Carr et al 

iv

 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

1

FINAL TECHNICAL SUMMARY 

STUDY TITLE: Ecological Consequences of Alternative Abandonment Strategies for POCS 

Offshore Facilities and Implications for Policy Development 

REPORT TITLE: Consequences of Alternative Decommissioning Options to Reef Fish 

Assemblages and Implications for Decommissioning Policy 

CONTRACT NUMBER: 14-35-0001-30758 

SPONSORING OCS REGION: Pacific 

APPLICABLE PLANNING AREA: Southern California 

FISCAL YEAR(S) OF PROJECT FUNDING: FY 95, FY 96, FY 97 

COMPLETION DATE OF THE REPORT: May 2003 

COST(S): FY 95 - $101,586, FY 96 - $78,784, FY 97 - $75,325, FY 98 – no cost, FY 99 – no 

cost, FY 00 – no cost, FY 01 – no cost 

CUMULATIVE PROJECT COST: $255,695

PROJECT MANAGER: Russell J. Schmitt 

AFFILIATION: University of California, Santa Barbara 

ADDRESS: Coastal Research Center, Marine Science Institute, University of California, Santa 

Barbara, CA 93106-6150 

PRINCIPAL INVESTIGATORS: 1

Mark H. Carr, 2Michael Vincent McGinnis, and 3Graham 

E. Forrester 

ASSOCIATED AUTHORS: 4

Jeffrey Harding, 1Peter T. Raimondi 

ADDRESSES: 1

Department of Ecology and Evolutionary Biology, Long Marine Laboratory, 

100 Shaffer Rd, Santa Cruz, CA 95060 USA; 2

 Ocean and Coastal Policy Center, Marine Science 

Institute, University of California, Santa Barbara, CA 93106 USA; 3

 Department of Natural 

Resources Science, Coastal Institute in Kingston, University of Rhode Island, Kingston, RI 

02881 USA; 4

National Marine Fisheries Services, Southwest Fisheries Science Center, Santa 

Cruz Laboratory, 110 Shaffer Rd, Santa Cruz, CA 95060 USA 
Final Technical Summary – Carr et al 

2

KEY WORDS: California Outer Continental Shelf; Marine Ecology; Marine Policy; Rigs-toReefs; Gulf Outer Continental shelf; Artificial Reef Program; Temperate Reef Fishes; 

Decommissioning; Rockfishes; Garbage Can Model; Offshore Oil Platforms; Santa Barbara 

Channel; Sebastes; Macrocystis; Rocky Subtidal; Rocky Reefs; ROV; Diver Surveys; Fish 

Movement 

BACKGROUND: Critical to formulation of appropriate decommissioning policy is an 

understanding of the ecological, economic and social consequences of different 

decommissioning options and identification of the mechanisms by which such information is 

incorporated, or not, into legislation and public policy. One particularly important ecological 

consequence of abandoning production platforms along the West Coast is a potential change in 

the species composition and structure of regional fish populations and assemblages, which may 

in turn influence yields to fisheries. Hard substratum reefs represent a small fraction of the 

available offshore habitat in California, but are sites of high fish density and production 

(Greene1, Bond et al. 1999). However, prior to this study, only one study provided quantitative 

estimates of species composition and abundance of fishes at a single platform off southern 

California. Nor is it clear how and to what extent ecological information contributed past 

decommissioning decisions on the West Coast. 

OBJECTIVES: The two broad objectives of our study were to collect and provide information 

that would help ascertain (1) the ecological effects of total or partial removal of offshore 

structures, specifically with respect to their effects on regional fish population and assemblages, 

and (2) whether and how scientific information has influenced prior decommissioning policy, 

both along the coast of California and in the Gulf of Mexico. 

DESCRIPTION: Our approach to estimating the potential effects of decommissioning options 

on regional fish populations and assemblages included five primary components: (1) we 

compared the species composition, density and size distribution of reef fishes inhabiting vertical 

strata of six production platforms and five nearby natural reefs over a three-year period to 

determine what component of the regional fish assemblage occurred on platforms, (2) size 

distribution information provided insight into what life stages use platforms, which in turn 

suggests the resources provided by platforms and the fate of fishes using that habitat, (3) we 

estimated movement distances of fishes between natural reefs and platforms, again to determine 

how the presence of a platform influenced nearby natural populations, (4) we hoped to compare 

the relative density-specific performance (i.e. survival, growth and reproduction) of a model 

species between platforms and natural reefs, and (5) we hoped to use bottom maps of the Santa 

Barbara Channel to estimate the relative contribution of platforms to natural rocky reef habitat in 

that region. 

 

1

 Dr. Gary Greene, Moss Landing Marine Laboratories, personal communication. Dr. Greene 

has interpreted and categorized (by substratum type and relief) multibeam data collected by the 

Monterey Bay Aquarium Research Institute (MBARI) Mapping Team throughout the Santa 

Barbara Channel and Point Conception area: MBARI Santa Barbara Channel Multibeam 

Survey, Digital Data Series No. 4, 2001. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

3

Our diver and Remotely Operated Vehicle (ROV) surveys on six platforms and five natural reefs 

during 1995, 1996 and 1997 identified subsets of regional reef fish assemblages that occur on 

platforms and the nearby natural reefs. The primary differences in these assemblages were an 

under-representation of reef fishes that associate with macroalgae (e.g., the giant kelp, 

Macrocystis) or with limited larval dispersal (surfperches) on platforms, and a greater 

representation of many midwater and deeper-dwelling rockfishes (genus Sebastes). Both species 

and size classes exhibited vertical stratification along platforms, indicating differential use of 

vertical portions of the platforms. Species that inhabited the upper portions of platforms (< 20 m 

depth) were characteristic of species that inhabit shallow rocky reefs, and were predominantly 

planktivores. Species in the lower portion of the platforms were predominantly midwater and 

benthic rockfishes. Young stages of many species occurred only in the upper portion of 

platforms, whereas the young of other rockfishes occurred throughout the water column or on the 

bottom. The vertical stratification of juveniles and adults suggests that removal of the upper 

portion of platforms will reduce the abundance of some species directly, curtail recruitment of 

others and suggesting that removal might curtail recruitment of these species to these structures. 

Similarly, the young of some benthic rockfishes inhabited mounds of mussel shell litter beneath 

platforms. With removal of the upper portion of platforms and the source of mussel shell 

production, this habitat would also diminish in time. This implies that removal might curtail 

recruitment of these species to platform habitats. This vertical stratification of juveniles and 

adults of some, but not all species, suggests that removal of the upper portion of platforms will 

reduce the abundance of some species directly, curtail recruitment of others and alter the fish 

assemblage that inhabits otherwise intact platforms. 

Movement patterns were estimated by tagging over 450 fish, of which 50 were recaptured to 

provide some estimate on movement distance. Most fish were recaptured at the site of tagging, 

suggesting limited movement among habitat types. Patterns of the relative density of life stages 

between platforms and natural reefs reinforced this result for some species and contradicted it for 

others. Limited tagging of fishes on platforms made some of these patterns difficult to interpret. 

Because no one species co-occurred in large numbers on both the platforms and natural reefs we 

studied, we were unable to compare density-specific performance of fishes among the two 

habitat types. We also were unable to obtain appropriate bottom habitat maps to estimate the 

relative contribution of platforms to hard substratum habitat in the Santa Barbara Channel or the 

study area. These two constraints are highlighted as recommended issues to be addressed in 

future projects. 

Our approach to determining the role that ecological information has contributed to past 

decommissioning policy decisions required research on past decommissioning decisions in both 

the California and Gulf of Mexico regions. Section Three of this report describes our 

approaches, results and conclusions from this analysis. We use John Kingdon’s “revised garbage 

can model” analytical framework to show that there is a political ecology to decommissioning 

policymaking in the Gulf and California OCS regions. Decommissioning policy (including the 

development of the various “rigs-to-reefs” options) is shaped by the distinct ecological and 

political contexts of the Gulf and California. For background, this section describes briefly the 

ecological, political and historical context of California OCS oil and gas activity, the policy 

debate over decommissioning options in the State Legislature and development of 
Final Technical Summary – Carr et al 

4

decommissioning policy in the Gulf region. Our analysis identifies strong differences in the 

relative roles and effects of the ecology and scientific community in these two regions. 

SIGNIFICANT CONCLUSIONS: Fish assemblages on the production platforms and nearby 

natural reefs we studied differed in species composition and relative abundance. These 

differences stem from differences in the structural features of these two habitats (e.g., absence 

and presence of macroalgae), the surrounding landscape (platforms are located in deeper water 

further from shore and are isolated by deep water from natural reefs), and the unique vertical 

extension of platform structure from the bottom to the sea surface. Vertical stratification of 

different species and life stages indicate that decommissioning options that reduce the height of 

platforms will alter the abundance of species and the overall fish assemblage associated with 

such structures. Patterns of size structure and movement of some species strongly suggests that 

these species may recruit to natural reefs and migrate to platforms as older stages. Other species 

(e.g., surfperch) have such limited movement that they do not appear to migrate to platforms. 

Patterns of movement in the opposite direction may be substantial as well, however we were not 

able to conduct extensive tagging efforts on our study platforms. This is another research effort 

that would be useful to better understanding the role of platforms to regional fish populations. 

We show that state and federal decommissioning policymaking is based on economic and 

ecological factors that reflect particular regional and political settings. In the Gulf region, the 

rigs-to-reefs “idea” was less an invention and more a mutation of an old idea. The rigs-to-reefs 

idea represented the coupling of an already familiar activity of building artificial reefs in the Gulf 

to enhance commercial and recreational fisheries. The use of familiar ideas, such as the idea of 

artificial reef building in the Gulf, by policy entrepreneurs and experts is referred to as the “act of 

recombination”. The rigs-to-reef policy idea represented a recombination of an old solution (the 

reliance on artificial reefs to enhance fisheries) to a perceived new problem (the lack of natural 

habitat and potential economic impacts associated with complete removal of OCS oil and gas 

structures). The role of ecological research in the development of decommissioning policy in the 

Gulf region can be characterized as strongly supportive and directed at identifying the 

contribution of platforms to the enhancement of fisheries. 

In southern California, the political debate over the decommissioning of oil and gas structures 

involves the intermingling of ecological information, economic factors, preferences and interests 

associated with OCS oil and gas activity. The southern California context is much different from 

that of the Gulf experience. Gulf states are willing to accept the rigs-to-reefs alternative, and 

have developed state policy and programs. Gulf state rigs-to-reefs programs continue to serve 

the needs and interests of commercial and sports fishing industries. In California, state 

legislation that could lead to the creation of a state rigs-to-reefs program under the California 

Department of Fish and Game has been introduced repeatedly. That legislation has been rejected 

for several reasons, political reasons and an expression of scientific uncertainty and mixed 

conclusions among marine ecologists in that region. We describe the ecological, economic and 

historical factors that are part of the California rigs-to-reefs debate and the roles that ecological 

information appears to have influenced the development of decommissioning policy. 

STUDY RESULTS: In the case of the Gulf, an advocacy coalition that combined the interests 

of the oil industry, recreation and commercial fishing, scientists, and resource managers 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

5

supported the use of offshore platforms as artificial reefs. The development of oil and gas in the 

Gulf OCS led to an increase in commercial and sports fishing activity. Scientific reports and 

workshops spoke to the benefit of artificial reefs in the Gulf. States and local artificial reef 

programs had been established before the passage of the National Fisheries Enhancement Act 

(NFEA) of 1984. In passing the NFEA, the federal government granted discretionary authority 

to states to create their respective platforms to artificial reef program. Many of these programs 

were based on existing artificial reef programs. 

Despite the intent of the National Fisheries Enhancement Act of 1984, which fostered the 

development of Gulf state rigs-to-reefs programs, there remain a number of issues and concerns 

associated with the use of platforms as artificial reefs in California. The major issues and 

concerns that general public, the scientific community and policymakers are facing include the 

following: 

(1) The Liability Issue. Since the publication of the National Artificial Reef Plan, which 

recommended that the US Army Corps of Engineers develop specific permit standards and 

conditions, the issue of liability remains vague and unclear. The Corps has developed a policy 

requiring the permit holder of an artificial reef to prove adequate liability coverage. Gulf states 

with reefing programs have assumed the role of the permittee. This has necessitated a close 

review of the role of the states and localities in implementing the NFEA. Clarification of this 

issue would improve operational procedures and potentially reduce uncertainty about exposure 

on the part of state artificial reef managers. 

(2) Scientific Uncertainty: Production versus Aggregation. Scientists and policymakers remain 

concerned about the production versus aggregation question. It remains unclear if platforms 

attract or produce fishes. Some scientists and policy makers contend that too much emphasis has 

been placed on adult fishery enhancement activity associated with offshore structures, and not 

enough resources have been spent on restoring essential coastal processes, such as estuarine 

habitats and wetland ecosystems (the “nurseries of the sea”). 

(3) Limited Funding. Since the passage of the NFEA, Gulf state and California artificial reef 

programs have not received adequate funding. State artificial reef programs maintain an average 

staff size of 1 full-time employee. Most funds are generated from either state appropriations or 

Wallop-Breaux funds, which refer to the 1984 Wallop-Breaux Amendment to the Federal Aid in 

Sport Fish Restoration Act (16 U.S.C. sec. 777 (1988)). Oil companies that “donate” structures 

are asked to contribute half of the disposal savings realized to the Fund. In addition, monitoring 

of existing artificial reefs and regulatory compliance issues remain important concerns of state 

artificial reef managers. 

STUDY PRODUCTS:

Publications: 

McGinnis, M.V. in press. The Political Ecology of the Offshore Oil Platform Rig-to-Reef Policy 

Debate. Proceedings of California and the World Ocean '02. California Resources 

Agency. 
Final Technical Summary – Carr et al 

6

Carr, Mark H., McGinnis, Michael Vincent, Forrester, Graham E., Harding, Jeffrey, and Peter T. 

Raimondi. Consequences of Alternative Decommissioning Options to Reef Fish 

Assemblages and Implications for Decommissioning Policy. MMS OCS Study 2003-

053. Coastal Research Center, Marine Science Institute, University of California, Santa 

Barbara, California. MMS Cooperative Agreement Number 14-35-0001-30758. 104 

pages. 

Carr, M. H. and G. E. Forrester. 2000. Ecological Consequences of Alternative 

Decommissioning Strategies for POCS Offshore Facilities: Preliminary Results. Pp. 499-

502 in Proceedings of the Fifth California Symposium, D.R. Brown, K. L. Mitchell, H. 

W. Chang, Eds. (Minerals Management Service Publication 99-0038), p. 379. 

Holbrook, S. J., Ambrose, R. F., Botsford, L., Carr, M. H., Raimondi, P. T., and M. J. Tegner. 

2000. Ecological Issues Related to Decommissioning of California’s Offshore 

Production Platforms. A Report to the University of California Marine Council by The 

Select Scientific Advisory Committee on Decommissioning, University of California. 

http://www.ucop.edu/research/ucmc_decommissioning/ 

McGinnis, M.V. 1998. An Analysis of the Role of Ecological Science in Offshore Continental 

Shelf Decommissioning Policy. In O.T. Magoon, H. Converse, B. Baird, and M. MillerHenson, eds. Taking a Look at California Ocean Resources: An Agenda for the Future. 

Reston, VA: American Society of Civil Engineers. Pp. 1384-1392. 

Databases and digital data: All databases generated from this study are available on CD and by 

request of Mark Carr (UC Santa Cruz). Underwater video footage collected by scuba 

divers and ROV during this project are available in both Hi-8 and S-VHS format. Video 

tapes currently reside in Dr. Carr’s lab (UC Santa Cruz) and available on request with 

permission of the MMS-POCS office. 

Presentations: 

Carr, M. Understanding the Ecological Consequences of Artificial Reefs in Coastal California. 

Invited Speaker to the California Coastal Commission. Los Angeles, CA, August, 1999. 

Carr, M., Forrester, G., and P. Raimondi. Ecological Consequences of Alternative 

Decommissioning Strategies for POCS Offshore Facilities: Preliminary Results. Channel 

Islands Symposium, Santa Barbara, CA, March 1999. 

Carr, M. Decommissioning of Offshore Oil and Gas Facilities: Contrasts Between Southern 

California and the Gulf of Mexico and Implications for Ecological Research. Invited 

Speaker. California and the World Ocean ’97, San Diego, California, March 1997. 

Carr, M. Ecological Aspects of the Decommissioning of Offshore Oil Facilities. Invited Speaker. 

Santa Barbara Chapter of the League of Women Voters. Santa Barbara, July 1997. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

7

Carr, M. Habitat Value: Summary of Research on the Ecological Role of Offshore Oil and Gas 

Production Facilities. Decommissioning and Removal of Oil and Gas Facilities Offshore 

California: Recent Experiences and Future Deepwater Challenges, Ventura, CA, 

September 1997. 

Carr, M. Summary and Recommendations on the Disposition of Offshore Oil and Gas Facilities 

Offshore California. Co-Chair of the Disposition Workgroup for the Decommissioning 

and Removal of Oil and Gas Facilities Offshore California: Recent Experiences and 

Future Deepwater Challenges, Ventura, CA, September 1997. 

Carr, M. Biological Research Applications of Remotely Operated Vehicles (ROV). Marine 

Technology Program, Santa Barbara City College, May 1996. 

Carr, M. and M. McGinnis. Contrasting Issues Relevant to Abandonment Policy and Regulation 

in Southern California and the Gulf of Mexico: Implications for Environmental 

Research. Invited Speaker, International Workshop on Offshore Lease Abandonment and 

Platform Disposal: Technology, Regulation and Environmental Effects, New Orleans, 

LA, April 1996. 

 
Final Technical Summary – Carr et al 

8
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

9

FINAL STUDY REPORT 

Section One: Introduction 

Background: Ecological Considerations of Artificial Reef Habitats 

The presence of man-made structures in the ocean has drawn great attention among scientists and 

resource managers both with concern for potential impacts to the natural environment caused by 

the presence of these structures and the communities of species that associate with them, and 

with interest for their possible role in enhancing species diversity, populations, and associated 

fisheries. Scientific assessments of the ecological consequences of man-made underwater 

structures (aka “artificial reefs”) have been the focus of a growing number of international 

conferences and scientific reports (e.g., volumes 44 and 55 of the Bulletin of Marine Science, 

volume 22 of Fisheries). One critical conceptual development in the consideration of ecological 

consequences of artificial reefs is the spatial scale of their influences. The importance of 

understanding ecological effects at a range of spatial scales stems from the complex life history 

of species typically associated with reef habitats and the implications for the spatial structure of 

their populations and communities. Most species of marine fishes and invertebrates have early 

life stages (i.e. spores, eggs, larvae) that can be dispersed great distances (in some cases up to 

hundreds of kilometers) to replenish populations elsewhere, but have adult stages that often 

remain in localized reef areas. As a result, populations and communities associated with a local 

reef habitat influence and are influenced by the dispersal of offspring and the movement of 

adults among populations. Thus, reef-associated populations are interdependent, and changes in 

habitat at any one location (a natural or artificial reef) should be viewed in the broader context of 

the regional set of local populations and communities. This necessitates examining the influence 

of structures to populations both in the close vicinity of the artificial reef as well as further away. 

Direct assessment of the regional effects of local habitat modification are problematic because of 

difficulties in (1) determining the spatial pattern of effects (determined by the movement of 

larvae and adults among reef habitat), (2) ascertaining the actual fate of young dispersed from a 

local population, and (3) detecting the small magnitude of effect (e.g., increased recruitment of 

young to adult populations) over the large area that individuals are dispersed. One approach to 

ascertaining regional effects is to monitor the state of a regional population before and after 

introduction of a structure within that regional population. This approach can be achieved by 

monitoring the state of both populations associated with the artificial structure and a 

representative subset of natural populations and employing various analytical methods (e.g., the 

Before-After-Control-Impact analysis; Osenberg et al. 2002)). Alternatively, ascertaining both 

the local and regional ecological effects of artificial reefs can be estimated indirectly by 

comparing how well individuals or populations perform (with respect to growth, survival, 

reproduction) on artificial structures relative to natural reefs (Alevizon and Gorham 1989, Beets 

and Hixon 1994, Carr and Hixon 1997). If species perform equivalently or better on artificial 

reefs than they do on natural reefs, it is most likely that presence of an artificial habitat will 

benefit the regional population of that species. If species perform more poorly, than any possible 
Final Study Report – Carr et al 

10

benefits are tenuous. For either assessment, comparison of demographic processes (e.g., 

mortality, reproduction) between artificial and natural reefs is mandatory. 

Along the West Coast of North America, as in many places in the world, the most substantial 

man-made structures are the offshore facilities created for the extraction of oil. At present, there 

are 27 “production platforms”, most of which are likely to end their period of oil extraction 

within the next two decades and at which time are required to be decommissioned. Four of these 

structures are in California State waters (Table 1). At the time that all 27 structures were 

installed, state and federal regulation required the complete removal of all structures and the 

return of the seafloor to pre-installation conditions at the end of their period of production 

(California Coastal Commission 1999). To date, only 7 smaller platforms have been 

decommissioned along the coast of California. The most recent decommissioning of four 

platforms (Hope, Heidi, Hazel and Hilda) in 1969, were removed as required by law. This 

activity raised interest in consideration of alternative decommissioning scenarios, particularly for 

decommissioning of structures at sea, to serve as artificial reef structures. This recent interest in 

alternative decommissioning scenarios has led to increased interest in exploring their ecological 

costs and benefits. 

Five decommissioning options for coastal platforms have been proposed, including (1) leaving 

the intact jacket and superstructure structure in place, (2) complete removal, (3) top portion of 

platform removed to 20 – 30 meters subsurface and remaining lower portion left standing in 

place (“topping”), (4) structure toppled over in the same location (“toppling”) and (5) structure 

moved to a new location and toppled (Figure 2). Two key attributes underpin the potential 

ecological consequences of these proposals. First is the consideration of leaving structures in 

place, or moving them to new locations. The ecological implication of this stems from the 

possible regional variation in ecological effects of structures where they currently exist or where 

they might be relocated. Therefore to better understand the potential local and regional 

ecological consequences of decommissioning at sea requires knowledge of spatial variation in 

the species assemblages and population attributes associated with structures in their present 

locations. The second, key feature of several decommissioning scenarios is the disappearance of 

the upper portion of platforms, either by their removal or the toppling of the structure. If the 

presence of the structure in the upper portion of the water column influences its ecological 

influence (e.g., algal and sessile invertebrate production, recruitment habitat for fishes), then 

understanding the ecological role of the upper portion of platforms is necessary for predicting the 

ecological consequences of these decommissioning scenarios. 

Perhaps the most important ecological consequence of decommissioning production platforms 

along the West Coast is likely to be a change in local and regional fish production (the biomass 

of fish accrued per year) and the structure (i.e. relative abundance) of the regional fish 

assemblage, both of which may in turn influence yields to fisheries. Hard substratum reefs 

represent a small fraction of the available offshore habitat in California, but are sites of 

extremely high fish production. Limited information suggests that these production platforms 

can support large numbers of fishes that associate with hard substrata, and may therefore 

function as sources of biomass and larval production (Carlisle et. al. 1964, Turner et. al. 1969, 

Bascom et. al. 1976, Mearns and Moore 1976, Love and Westphal 1990, Love et. al. 1994, 

2000). Indeed, throughout the Gulf of Mexico OCS region, where the amount of natural hard 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

11

substratum is more limited, oil platforms contribute substantially (ca. 28 %; Gallaway 1984) to 

local and regional abundance of “reef” habitat and the abundance of reef-associated fishes 

(Gallaway and Lewbel 1982, Continental Shelf Associates, Inc. 1982, Stanley and Wilson 1991, 

Scarborough Bull and Kendall 1994). There are, however, no quantitative estimates of the extent 

to which offshore production platforms contribute to the total amount of “reef” habitat in the 

Pacific OCS region. Prior to our study there was also very little quantitative data on the 

abundance and structure of fish populations and assemblages associated with production 

platforms, and no comparative studies of platforms and natural reefs. Also uncertain was whether 

the fish present around platforms are the result of increased production or simply reflect the 

attraction of fishes that would otherwise reside on natural reefs. Therefore, one key objective of 

our study was to describe quantitatively the fish populations and assemblages associated with 

production platforms and nearby natural reefs. To determine the extent to which fish 

assemblages associated with platforms possibly reflected the redistribution of fishes from natural 

reef habitat, we used a tagging study to estimate movement of fishes among natural reefs and 

platforms. 
Final Study Report – Carr et al 

12

Figure 1. Location of offshore oil production platforms along the coast of southern and central California. 

The six platforms studied in this project constitute the arc of platforms extending from shore in the eastern end 

of the Santa Barbara Channel (see inset). Latitude and Longitude values for the natural reefs are presented in 

Table 2. Values in parentheses are bottom depths of reefs and platforms.

Santa Rosa

Island Island

Santa Cruz

Carpinteria

1

2 3 4

5

6 8 7 10 9 11

4 km

Study Platforms Latitude and Longitude 

6= Hogan (50m) 34o20.27, 119o32.48 

7= Houchin (50m) 34o

20.10, 119o33.13

8= Henry (50m) 34o

20.00, 119o33.62

9= A (58m) 34o

19.92, 119o36.75 

10= B (58m) 34o19.93, 119o37.30 

11= C (58m) 34o

19.98, 119o37.85 

Natural reefs

1= 4-mile reef (36m)

2= Horseshoe reef (16m)

3= 3-Spot reef (11m)

4= Carpinteria reef (8m)

5= Crouch reef (34m)

Santa Rosa

Island Island

Santa Cruz

Carpinteria

1

2 3 4

5

6 8 7 10 9 11

4 km

Santa Rosa

Island Island

Santa Cruz

Carpinteria

1

2 3 4

5

6 8 7 10 9 11

4 km

Study Platforms Latitude and Longitude 

6= Hogan (50m) 34o20.27, 119o32.48 

7= Houchin (50m) 34o

20.10, 119o33.13

8= Henry (50m) 34o

20.00, 119o33.62

9= A (58m) 34o

19.92, 119o36.75 

10= B (58m) 34o19.93, 119o37.30 

11= C (58m) 34o

19.98, 119o37.85 

Natural reefs

1= 4-mile reef (36m)

2= Horseshoe reef (16m)

3= 3-Spot reef (11m)

4= Carpinteria reef (8m)

5= Crouch reef (34m)
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

13

Table 1. Structural characteristics of the 27 offshore platforms along the coast of California. Characteristics of the six 

platforms used in this study are indicated in bold font. Surface area estimates are based strictly on member dimensions and 

does not account for fouling organisms. 

 

Number Name State / Federal 

Waters 

Region Depth (m) Footprint 

(m2

) 

Surface 

Area (m2) 

Volume 

(m3) 

1 Irene Federal Pt. Conception 73 2633 192,793 

2 Hildago Federal Pt. Conception 130 4154 564,086 

3 Harvest Federal Pt. Conception 205 5859 444,720 

4 Hermosa Federal Pt. Conception 184 5142 944,097 

5 Heritage Federal West SB Channel 326 nd nd 

6 Harmony Federal West SB Channel 363 10606 nd 

7 Hondo Federal West SB Channel 255 4649 nd 

8 Holly State West SB Channel 66 nd 21,515 

9 A Federal East SB Channel 58 1930 16,111 80,541 

10 B Federal East SB Channel 58 1930 16,111 80,541 

11 C Federal East SB Channel 58 1930 16,111 80,541 

12 Hillhouse Federal East SB Channel 58 nd nd 

13 Henry Federal East SB Channel 52 1505 8,577 50,403 

14 Houchin Federal East SB Channel 49 1435 8,190 68,350 

15 Hogan Federal East SB Channel 47 1435 8,190 68,350 

16 Habitat Federal East SB Channel 88 2284 nd 

17 Grace Federal East SB Channel 96 3090 244,196 

18 Gilda Federal East SB Channel 62 2342 132,800 

19 Gail Federal East SB Channel 224 5327 1198,176 

20 Gina Federal East SB Channel 29 561 16,414 

21 Edith Federal Orange County 49 2879 nd 

22 Elly Federal Orange County 80 2949 nd 

23 Ellen Federal Orange County 80 2511 nd 

24 Eureka Federal Orange County 212 4635 nd 

25 Emy State Orange County 

26 Eva State Orange County 

27 Esther State Orange County 
Final Study Report – Carr et al 

14

Figure 2. Illustration of the five proposed alternative decommissioning scenarios. 1= leaving entire structure in 

place, 2= removing entire structure to shore, 3= removing upper 20 m of structure in place, 4= removing upper 30 m 

and toppling structure in place, 5= same as 4 but relocating structure elsewhere at sea. 

Approach: Fish Assemblages on Natural Reefs and Production Platforms 

Our approach to ascertaining the potential effects of decommissioning options on regional fish 

populations and assemblages included three components. First, we compared the species 

composition, density and size distribution of reef fishes inhabiting vertical strata of six 

production platforms and five nearby natural reefs over a three-year period to determine what 

component of the regional reef fish fauna occurred on platforms and natural reefs during that 

period. Such information is required to determine what species and life stages might be 

influenced by the various decommissioning options. Do fish recruit to each habitat type from the 

plankton (as larvae) or migrate onto one habitat type from the other as older stages (benthic 

juveniles and adults)? Comparison of fishes between platforms and natural reefs provides 

information on what stages use the two habitat types. Patterns of fish sizes over time can also 

provide information on how long fishes associate with each habitat type and how well they grow 

and survive. Such information is critical to understanding the relative value of natural reefs and 

platforms as fish habitat. 

Also fundamental to understanding the net contribution of local populations to regional 

production is information on the size-specific rate of migration of fishes among local, reefassociated populations. In the context of platform decommissioning, knowledge of the net 

direction and rate of transfer of individuals between platforms and natural reefs is crucial. For 

example if fish recruit to natural reefs and eventually migrate to platforms, accumulation of fish 

biomass on platforms would be incorrectly attributed to production at the platform habitat. 

1 2 3 4 5
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

15

Conversely, if platforms provide recruitment habitat for fish that eventually migrate to natural 

reefs, the contribution of platforms to regional production may be grossly underestimated by 

simply measuring production in the two habitats. Movement information is also important to 

determine whether the loss of fish at a site is due to emigration rather than mortality. Therefore, 

we conducted a tagging study to patterns of movement in the vicinity of platforms and nearby 

natural reefs. 

Finally, for reasons mentioned above, we hoped to compare the relative performance (i.e. growth 

and survival) of a model species between platforms and natural reefs. We were particularly 

interested in species of economic importance, such as the kelp bass and kelp rockfish for the 

recreational and commercial fishery, respectively. 

Background: Ecological Information and Development of Decommissioning Policy 

The transition from exploration and development to decommissioning of offshore production 

platforms and associated structures marks a fundamental change in the history of oil and gas 

activity along the West Coast. The National Research Council (1985) estimated that the 

cumulative costs for removal of all platforms in the offshore continental shelf (OCS) could total 

$2.9 billion by 2005 and $9.9 billion by 2020. The Governmental Account Office (GAO 1994) 

reviewed offshore structure removal operations and concluded that better understanding of the 

risk of ecosystem damage posed by certain decommissioning practices, such as the use of 

explosives as a removal technique is needed. Government agencies, scientists and special 

interest groups have proposed alternatives to complete removal of offshore platforms. While 

states on the Gulf of Mexico have developed and implemented “rigs-to-reefs” (i.e. 

decommissioning structures at sea) policies and programs, the different ecological setting, 

political culture, and the role played by the marine scientific community in California have all 

contributed to greater opposition in the development of similar policies here (McGinnis et al. 

2001). The policy debate is trans-scientific -- it involves the intermingling of both values and 

facts including important perceptual, value-based and ethical issues (Shrader-Frechette and 

McCoy 1994). The politics of integrating scientific information into the platform 

decommissioning debate is a highly charged and contentious intergovernmental process that 

involves participants who may not share the same values about offshore oil and gas activities or 

the role of artificial reefs in the broader context of “enhancement” and conservation of the 

nearshore marine environment. Historically, OCS oil and gas activity is a political process that 

includes litigation (Lester 1991). Moreover, given scientific uncertainties associated with marine 

ecosystems, “good” scientific information is that which supports one’s position in the decisionmaking situation (McGinnis 1998). 

Implementation of decommissioning practices for the West Coast other than complete removal 

will require development of new policy and legislation. The relevance of our ecological research 

to decommissioning decision-making and policy development assumes that knowledge of the 

ecological roles of oil platforms might contribute to such policy development. However, 

formulation of alternative decommissioning policies must also consider their political, social, 

and economic consequences. The extent to which ecological research will contribute to decision 

making will depend on at least two issues: (1) how strong of an effect the presence of offshore 

structures has on regional populations and communities of marine organisms, and (2) how 
Final Study Report – Carr et al 

16

important such ecological effects are relative to social and economic consequences of alternative 

decommissioning policies. A first approximation of the potential effects of ecological 

information on policy making along the West Coast can be gleaned from its role in the 

development of the current policy on decommissioning. 

We explore the diverse historical, ecological, and political settings that have shaped the 

policymaking process associated with the development of decommissioning alternatives to 

complete removal of platforms on the West Coast and in the Gulf of Mexico. We conducted a 

comprehensive documentary analysis to investigate whether and how ecological information has 

contributed to the historical development of California’s present decommissioning policies. 

Such information can provide a better understanding of how ecological, and scientific 

information in general, is incorporated into policy development and how that process might be 

enhanced. The history of decommissioning policy is far more developed in the Gulf of Mexico 

region. Because the perceived importance of ecological information differs markedly among 

communities and within communities through time, we compared our results from California 

with the role of ecological information in the development of decommissioning policies adopted 

in the Gulf of Mexico. Such a comparison will increase our understanding of the potential role 

of ecological information in future developments of decommissioning policy in general. 

 

We also intended to use this initial study to develop and motivate a subsequent proposal for more 

extensive analysis of the influence of ecological processes (e.g., climatic and oceanographic 

variability) and existing institutional structures (e.g., California Department of Fish and Game’s 

Artificial Reef program) on the development of decommissioning policy on the West Coast. 

This effort culminated in a subsequent MMS study and report (see McGinnis et al. 2001). 

Approach: Characterization of the Role of Science and Values in Decommissioning 

Our approach to determining the role that ecological information has contributed to past 

decommissioning policy decisions involved research on past decommissioning decisions in both 

the California and Gulf of Mexico regions. The choice for a decommissioning option is 

influenced by the ecology of the marine environment, the quantity and quality of scientific 

information available for that environment, and the political context that is associated with 

offshore oil and gas activity. The focus of this study is on both the science (and scientific 

communities) and politics that have influenced the choice for a particular decommissioning 

option. For background, this section describes briefly the ecological, political and historical 

context of California OCS oil and gas activity, the policy debate over decommissioning options 

in the State Legislature and development of decommissioning policy in the Gulf region. 

It is important to note that scientific investigation does not take place in a political vacuum, but 

involves important perceptual, value-based and ethical issues (Shrader-Frechette and McCoy 

1994). The politics of integrating scientific information in the platform decommissioning is a 

highly charged and contentious intergovernmental process that involves participants who may 

not share the same values about offshore oil and gas activity. Historically, OCS oil and gas 

activity is political process that includes litigation (Lester 1991). Moreover, given scientific 

uncertainties associated with marine ecosystems, “good” scientific information is that which 

supports one’s position in the decision-making situation (McGinnis 1998). 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

17

Shrader-Frechette (a philosopher) and McCoy (an ecologist) received funding from the National 

Science Foundation to evaluate the role of ecological theory and information in policy making. 

Their findings are also relevant to the politics of decommissioning policymaking (McGinnis 

1998). Shrader-Frechette and McCoy (1994) show the following: 1) Ecologists do not agree on 

what the basic principles or ecological laws (“community” and “stability”) are; 2) All scientific 

facts are laden with epistemic or cognitive values. Values can be divided into three types: bias 

values, contextual values, and methodological values; 3) Ecology cannot dictate ends or goals 

(but can act as a guide to good environmental policy); 4) Ecologists and laypersons do not share 

the same uncontroversial and unambiguous goals; 5) Ecology cannot tell us what is “natural”; 6) 

Ecological applications arise when and because scientists have a great deal of knowledge about 

the (qualitative and quantitative) natural history of a specific organism or place (which is not the 

case in this policy area). 

Given scientific uncertainty, participants in the policymaking process will act out of their 

perceptual and value-based understandings of the world (Stone 1985). With respect to marine 

ecological information, science and the scientific community cannot provide policy makers with 

goals or values for policies, but can guide policy makers regarding the means to attain or the 

reasons to not to pursue particular policy ends or goals (Shrader-Frechette and McCoy 1994). 

In platform decommissioning, values matter. The scientific community that is associated with 

the Gulf and Mexico and southern California played different roles in the political process 

(McGinnis et al. 2001). One reason is that the role of the marine scientific community plays in 

the policymaking process is predicated on the particular political setting of the decision-making 

situation. The biophysical characteristics of particular marine ecosystems are “interpreted” by 

the scientific community, and these interpretations have influenced the political debate over the 

future of offshore oil platforms. In short, the political debate over particular platform 

decommissioning options is shaped by the particular ecological setting of the region, and the 

specific marine scientific community associated with the place. 

John Kingdon’s (1995) “revised garbage can model” will be used as an analytical framework to 

describe the role of scientists and science in the political debate over the future of offshore oil 

platforms and the rigs-to-reefs option. We show that state and federal decommissioning 

policymaking is based on political and ecological factors that reflect particular marine ecological 

and political settings. In the Gulf OCS region, the platforms to reefs “idea” was less an 

invention and more a mutation of an old idea. The platforms to reefs idea represented the 

coupling of an already familiar activity of building artificial reefs in the Gulf to enhance 

commercial and recreational fisheries. The use of familiar ideas, such as the idea of artificial 

reef building in the Gulf, by policy entrepreneurs and experts is referred to as the “act of 

recombination” (Kingdon 1995). The platforms to reef policy idea represented a recombination 

of an old solution (the reliance on artificial reefs to enhance recreational and commercial fishing 

industries) to a perceived new problem (the lack of natural habitat in the Gulf of Mexico and 

potential economic impacts associated with complete removal of OCS oil and gas structures). 

We then consider whether and how this approach applies to the development of 

decommissioning policy on the West Coast. 

For clarity, the remainder of this report presents separately the methods, results, discussion and 

recommendations for the ecological and policy research. 
Final Study Report – Carr et al 

18

Section Two: Fish Assemblages on Natural Reefs and Production Platforms 

Methods 

Fish Assemblages on Natural Reefs and Production Platforms 

Study Area 

We measured attributes of fish populations and assemblages at six production platforms (A, B, 

C, Hogan, Houchin and Henry) in the eastern portion of the Santa Barbara Channel (Figure-Map) 

and five nearby natural rocky reefs. Structural features and depths of the six study platforms are 

summarized in Table 1 along with other platforms along the West Coast for comparison. The 

underwater structure of offshore platforms is characterized by a matrix of vertical, diagonal and 

horizontal pipes of varying diameter. These are referred to collectively as the “jacket”. 

Platforms typically consist of 6 to 8 large (1 to 5 meter diameter) vertical legs with a matrix of 

horizontal and diagonal members of smaller (0.25 to 1 meter) diameter that extend between the 

legs at varying depths along the entire length of the legs. The six study platforms were both 

shallower (50-57 m depth) and smaller than the majority of the 27 platforms off California. We 

selected these platforms for study for four reasons. Firstly, owners of these platforms allowed 

access of both diving and ROV operations. Secondly, the close proximity to the Santa Barbara 

Harbor allowed frequent access by small vessels for sampling. Thirdly, the shallow depth and 

smaller size of these platforms allowed for a greater portion of the platforms to be sampled by 

scuba divers. A fourth reason for selecting these platforms was their location within an 

oceanographic transition area that experiences marked variation in oceanographic conditions. 

The eastern portion of the Channel is characterized as a transition area between the warm waters 

typical of further south in the Southern California Bight, and the cooler waters toward Point 

Conception at the western end of the Channel intermittently bathed by the colder California 

Current that flows south from central California (Hickey 1993, Harms and Winant 1998). 

Oceanographic conditions vary seasonally, among years due to El Nino-Southern Oscillation 

events, and during decade-long regime shifts. Because of the location of the six study reefs 

within this transition area, fish assemblages appear to be particularly susceptible to these longterm dynamics. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

19

The abundance of rocky reef habitat in the Santa Barbara Channel appears to be intermediate to 

levels to the north (Pt. Conception) and south of the Channel. We identified five natural reefs in 

proximity to the six production platforms for comparison of fish assemblages. Three of these 

reefs (Carpinteria, Three-spot, Horseshoe) were at depth less than 30 m, allowing diver surveys 

and comparison with the shallow portion of platforms (Table 2). The other two natural reefs 

(Four-mile, Crouch) were the closest to the bottom depths of the study platforms that we could 

find in the study area (Table 1 versus Table 2). The substratum at Carpinteria reef was 

characterized by sandstone ridges (≤ 3m vertical relief), low-relief bedrock shelf, and sand 

intrusions. Giant kelp, Macrocystis, was present on Carpinteria reef in all three years of study. 

The substratum at 3-spot reef was characterized by boulders (to 2m diameter) on low-relief 

bedrock shelf. Giant kelp was present at 3-Spot reef only in the first 1.5 years of the study. The 

substratum at Horseshoe reef consisted primarily of boulders (to 1m diameter). No macroalgae 

was present on Horseshoe reef. The substratum at 4-mile reef was comprised of a pronounced 

sandstone ridge (≤ 4m vertical relief), boulders (to 1m diameter), and no macroalgae. The 

substratum at Crouch reef was characterized as a sandstone ridge (≤ 2m vertical relief), boulders 

(to 1m diameter), and no macroalgae. 

Fish Assemblages on Shallow Portions of Platforms 

Sampling schedule--The fish assemblages associated with shallow (< 33m) portions of the six 

production (Hogan, Houchin, Henry, A, B, and C) were sampled in June, August, and October 

1995 and February 1996 using visual scuba diver surveys (Table 3). Platforms were sampled by 

scuba divers a total of 16 times (three surveys in 1995, seven in 1996, and six in 1997). In 1995, 

the sampling interval was approximately once every two months (June, August, and October). 

Sampling was conducted monthly between June and October of 1996 and 1997, with the addition 

of one winter sample (February, 1996). 

Density estimates--Surveys conducted by divers on production platforms involved estimates of 

the density and size of individuals of each species along 2 m wide x 2 m tall belt transects at 

predetermined locations and depths. Transect location and depth corresponded with vertical legs 

Table 2. Description of the location and depths of natural reefs surveyed in this study. 

Reef Latitude Longitude Survey 

method 

Sampling 

depth 

average 

(meters) 

Sampling 

depth 

range 

(meters) 

Distance 

to shore 

(nautical 

miles) 

Distance to 

nearest 

platform 

(nautical 

miles) 

Carpinteria 34o 23.52 119 o 32.72 Diver 8 5-10 0.3 3.2 to Hogan 

3-Spot 34o 23.66 119 o 33.70 Diver 11 9-12 0.9 3.5 to Hogan 

Horseshoe 34o 23.71 119 o 34.70 Diver 16 14-20 1.0 3.9 to Henry 

4-mile 34o 21.29 119 o 38.17 ROV 36 32-43 3.7 1.3 to C 

Crouch 34o 21.49 119 o 32.76 ROV 36 30-38 2.3 1.2 to Hogan 
Final Study Report – Carr et al 

20

and horizontal cross members. Transects varied in length corresponding to the length of the 

crossbeam where the transect was located. Crossbeam lengths were determined from schematic 

diagrams provided by the platform operators. Thus, a known volume of water was sampled for 

each transect. For comparisons among platforms or depths, the concentration of fish (number of 

individuals per volume), rather than absolute abundance, was analyzed. Divers used waterproof 

data sheets and plastic slates to count and record all fish encountered on transects during the 

dive. Fish were identified to species, or occasionally to broader groups consisting of two or 

more species. 

Table 3. Sampling frequency of study platforms and natural reefs with divers (D) and ROV (R). Carp = 

Carpinteria Reef, Horse= Horseshoe Reef. 

 Platforms Natural Reefs 

Year Month Henry Hogan Houchin A B C Carp 3-Spot Horse 4-Mile Crouch

1995 6 D,R D,R D,R D,R D,R D,R D D 

 8 D,R D,R D,R D,R D,R D,R D D D,D R R 

 9 D D D,D 

 10 D,R D,R D,R D,R D,R D R R 

1996 2 D D D D D D D D D,D 

 5 D D D D D D D D 

 6 D,R D,R D,R D,R D,R D,R D D D,D R R 

 7 D D D D D D D D D,D 

 8 D,R D,R D,R D,R D,R D,R D D D,D R R 

 9 D D D D D D D D D,D 

 10 D,R D,R D,R D,R D,R D,R D D D,D R R 

1997 5 D D D D D D D D D,D 

 6 D,R D,R D,R D,R D,R D,R D D D,D R R 

 7 D D D D D D D D D,D 

 8 D D D D D D D D D,D 

 9 D D D D,R D,R D,R D D D,D 

 10 D D D D D D D D D,D 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

21

Sampling design--Divers worked in teams of two and followed a standard swim pattern when 

sampling each of the six platforms (Figure-diver path). From the surface, they descended 

directly along one of the corner legs to the third main set of horizontal crossbeams (30 – 39 m, 

depending on platform). At this depth, they sampled a portion of the platform’s perimeter and 

interior by swimming (at a moderate and constant speed) just above the horizontal crossbeams. 

From here they ascended to the next shallower set of crossbeams and repeated the 

perimeter/interior swim loop. A total of three depth levels were sampled at each platform, plus 

the vertical transects along the corner legs during the descent and ascent between levels. Across 

all study platforms and sampling dates, a total of 379,613 m3

 was sampled over the course of the 

study. 

Two dives, one after the other, on opposite sides of the platform were conducted on each 

sampling date. The total sample incorporated all four-corner legs as well as most of the major 

horizontal crossbeams of the jacket and a substantial portion of the interior. Each dive required 

about 30 minutes, and individual divers made a maximum of two platform dives per day. All 

dives were conducted within no-decompression dive limits (using dive computers). In most 

cases, all six platforms were sampled in two consecutive days by six divers. 

Size distribution--Size estimates (total length) were made for individual fish (to the nearest 1 cm 

for fishes less than 15 cm TL, and to the nearest 5 cm for fishes greater than 15 cm TL). When 

groups or schools of fish were encountered, a range of sizes was recorded. All divers 

performing visual counts had previous training in size estimation. In addition to the first diver’s 

visual size estimates, direct in-situ laser measurements of fish size were recorded on video. One 

member of each dive team (the diver not responsible for visual counts) used a video camera 

(Sony Hi-8, TR700) in an underwater housing (Light and Motion) to film fishes on and adjacent 

to the sampled transects. Two parallel-mounted red lasers (Quarton, 5mW) attached to the 

housing projected beams through the camera’s center of view. The distance between the beams 

was fixed (at 25mm), and they were clearly visible in the videotape image as points of bright 

light on objects up to 4 m from the camera (depending on water clarity). The objective was to 

strike the fish with the beams perpendicular to the main body axis. 

In the laboratory, size estimates (TL) were made by measuring (with a ruler or calipers) the beam 

separation and fish length directly from the video monitor. From these two measurements and 

the known beam separation, the true fish length was derived. There are several potential sources 

of error in laser size estimates, including (1) fish body angle less than 90 degrees from beams, 

(2) body curvature, (3) fish too far away, and (4) blurring/dimming of beams caused by water 

turbidity. To account for these potential sources of error, each measurement was rated for 

potential accuracy on a subjective scale of one (good) to three (poor). Volunteer undergraduates 

who were trained in fish identification and the measuring process made all video-based size 

estimates in the lab. 

 
Final Study Report – Carr et al 

22

Figure 3. Pattern of sampling conducted by divers and ROV on platforms. Depicted are the five depth levels of 

which divers sampled levels 1-3 and the ROV sampled levels 3-5. The actual number of horizontal cross members 

varied from four (Henry, Houchin, Hogan) to five (A, B, C). The diver and ROV patterns illustrated here indicate 

one half of a sample. The path of the divers and ROV was duplicated on the opposite side of the platform to 

complete a sample on a sampling date. 

3 (31 m)

4 (43 m)

5 (57 m)

2 (20 m)

1 (8 m)

DIVER

Sampling level (depth)

3 (31 m)

4 (43 m)

5 (57 m)

2 (20 m)

1 (8 m)

ROV

3 (31 m)

4 (43 m)

5 (57 m)

2 (20 m)

1 (8 m)

DIVER

Sampling level (depth)

3 (31 m)

4 (43 m)

5 (57 m)

2 (20 m)

1 (8 m)

ROV
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

23

Fish Assemblages on Shallow Natural Reefs 

Sampling schedule-- In order to compare fish assemblages between oil platforms and natural reef 

habitat, three shallow rocky reefs (Horseshoe, 3-Spot, and Carpinteria) in the vicinity of the oil 

platforms were also sampled by scuba divers (Figure 1). These three reefs were selected because 

they were the only three shallow reefs in close proximity to the study platforms. Carpinteria and 

3-Spot were sampled at the same frequency as the platforms and always within one week of the 

platform sample date (15 and 16 samples, respectively; Table 3). Horseshoe reef was sampled 

twice in each sampling period (32 samples), usually on two consecutive days within one week of 

the platform sample (Table 3). Data collected were the same as that on production platforms, but 

surveys of natural reefs also included quantification of habitat variables (e.g., substratum type 

and relief, epibenthic cover, density and size of macroalgae, temperature and visibility) that 

might explain patterns of species abundance. 

Sampling design-- On natural reefs, divers identified, counted, and recorded sizes for all fish 

encountered on transects of standardized volumes (2 m wide x 2 m tall x 30 m long). Two of the 

reefs (Carpinteria and 3-Spot) contained beds of giant kelp (Macrocystis pyrifera) during some 

or all of the surveys. At these two reefs, divers sampled three different depth strata: 1) surface, 

0-2 m below the kelp canopy; 2) mid-water, halfway between the surface and the bottom, and; 3) 

bottom. Each of the three depth strata was sampled four times on each sampling date. 

Horseshoe reef, the deepest of the group, never contained giant kelp. Due to the absence of 

canopy fish habitat, the surface stratum was not sampled at this site. Because there was no kelp 

on which to attach a meter tape, mid-water transects at Horseshoe reef were located 3-5 m above 

the bottom, and the bottom tape was used as a visual reference for transect length. Transects 

were stratified horizontally across the reef from onshore to offshore in order to encounter fish 

distributed throughout the kelp forest and across all depths of the reef. Transect locations were 

established haphazardly within each depth stratum across the reef at each visit. At the start of 

each transect, the fish-counting diver temporarily fastened to the substratum, or to kelp stipes, a 

30 m tape. Following a compass bearing parallel to the depth contour, the diver swam at a slow, 

steady rate while counting fish and deploying the tape. Upon reaching the far end, the tape was 

tied in place and the diver proceeded to the next depth level (above the bottom transect). Other 

divers following the fish counter collected habitat data and retrieved the tapes. Across all three 

reefs and sampling dates, a total of 69,120 m3

 was sampled over the course of the study. 

Size distribution--In addition to the size estimates made by the diver recording fish density, a 

second diver made size measurements using the paired-laser video method described in the Size 

distribution section above. 

Reef habitat attributes--In addition to fish density and size estimates, divers quantified the relief, 

substratum, and macroalgal characteristics of each natural reef on each sampling date. The 

abundance (density or cover) of key reef substratum and macroalgae characteristics were 

estimated as follows: 

1. Macrocystis canopy percent cover (recorded in the surface stratum only): Divers visually 

estimated the presence or absence of Macrocystis canopy directly above 60 stratifiedrandom points (2 random points per m) along each of the 30 m long surface transects. 
Final Study Report – Carr et al 

24

These samples generated an estimate of the percent cover of Macrocystis canopy for each 

replicate transect. 

2. Macrocystis stipe density (surface and bottom transects only): Divers visually counted the 

number of Macrocystis plants, and number of stipes per plant within the 2 m wide X 30 m 

long belt transect. These counts generated an estimate of the density of Macrocystis plants 

(number per 60m2

) and stipes for each replicate transect. 

3. Pterygophora stipe density (bottom transects only): Divers counted the number of 

Pterygophora californica plants, a prominent understory macroalga, within the 2 m wide x 

30 m long belt transect. These counts generated an estimate of the density of Pterygophora

plants (number per 60m2

) for each replicate transect. 

4. Substratum type and cover (bottom transects only): Classification of the substratum at 60 

stratified-random points (2 random points per m) along each of the 30 m long bottom 

transects. Substratum type was categorized by the bare substratum type 

(mud/sand/cobble/shell/rock) or the invertebrate or macroalga directly attached to the 

substratum (e.g., Diopatra tubes, erect coralline algae, foliose red algae, Macrocystis

holdfasts). These records generated an estimate of the percent cover of substratums for 

each replicate transect. 

5. Reef vertical relief cover (bottom transects only): Divers visually estimated the vertical 

relief within 1 m of 60 stratified-random points (2 random points per m) along the 30 m 

long bottom transect. Relief was categorized into one of four categories (0-0.1m, 0.1-1m, 

1-2m, >2m). These records generated an estimate of the percent cover of substratum relief 

for each replicate transect. 

Fish Assemblages on Deep Portions of Platforms 

The deepest portions of the six study platforms, from 39 to 57 m depth, were sampled with a 

Remotely Operated Vehicle (ROV), a tethered submersible controlled from the surface. The 

ROV (a Phantom 500, operated by the Marine Diving Technology program at Santa Barbara 

City College) was capable of moving in 3-dimensions and following transects at speeds 

equivalent to scuba divers. The ROV carried lights and a forward-looking black and white video 

system cabled to a monitor on the vessel at the surface. The video and surface monitor allowed 

the vessel path to be directed by the operator while an observer logged the depth and location of 

transects, and identified fish species throughout the sampling period. The video was recorded on 

Hi-8 videotape. 

Sampling schedule-- ROV samples were taken on a total of seven or eight dates at each platform: 

three samples in 1995, three in 1996, and one or two in 1997 depending on the platform (Table 

3). In 1997, sampling was incomplete due to mechanical failure of the ROV, and was limited to 

one (platforms Hogan, Houchin, and Henry) or two samples (platforms A, B, and C). 

Density estimates-- All fish counts and species identifications for ROV samples were taken 

directly from video. To provide a scale of reference and to avoid getting lost, the ROV always 

followed and filmed the platform legs and crossbeams when sampling. These structures, of 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

25

known diameter, provided a scale for estimating transect width and height. All fish within 

approximately 1-2 m of the legs and crossbeams were considered “on the transect” and counted. 

Fish were identified to species, or in some cases to broader categories when species 

identification was impossible. Juvenile rockfish, in particular, were difficult to identify to 

species from ROV videos, and were usually classified by group (see Table 4). These surveys 

generated fish density estimates (fish per water volume sampled) for replicate transects along the 

length of structural members. 

 

Table 4. Taxonomic categories of rockfish species used for analyses. 

Analyses of the videos for fish identification and species counts were limited to transects along 

the vertical, horizontal, and diagonal legs and crossbeams of the platform perimeter, and to the 

seafloor at the base of the structure. The vehicle was not able to survey the interior of the 

platform because of the risk of entangling the umbilical line. Due to the presence of submerged 

cables, sunken debris, and occasionally strong water currents, the ROV was not able to follow a 

standard path on each of the platforms. For this reason, sample volume varied slightly from 

Shallow benthic complex

vermilion rockfish (S. miniatus)

calico rockfish (S. dalli)

brown rockfish (S. auriculatus)

treefish rockfish (S. serriceps)

flag rockfish (S. rubrivinctus)

halfbanded rockfish (S. semicinctus)

Unidentified Sebastomus rockfish (rosy, starry, greenspotted)

Unidentified “benthic” Young-of-Year

Copper complex

kelp rockfish (S. atrovirens)

copper rockfish (S. caurinus)

gopher rockfish (S. carnatus)

black & yellow rockfish (S. chrysomelas)

Unidentified “copper complex” Young-of-Year

Midwater complex

olive rockfish (S. serranoides)

blue rockfish (S. mystinus)

widow rockfish (S. entomelas)

squarespot rockfish (S. hopkinsi)

bocaccio rockfish (S paucispinis)

yellowtail rockfish (S. flavidus)

Unidentified “blackspot” Young-of-Year

Shallow benthic complex

vermilion rockfish (S. miniatus)

calico rockfish (S. dalli)

brown rockfish (S. auriculatus)

treefish rockfish (S. serriceps)

flag rockfish (S. rubrivinctus)

halfbanded rockfish (S. semicinctus)

Unidentified Sebastomus rockfish (rosy, starry, greenspotted)

Unidentified “benthic” Young-of-Year

Shallow benthic complex

vermilion rockfish (S. miniatus)

calico rockfish (S. dalli)

brown rockfish (S. auriculatus)

treefish rockfish (S. serriceps)

flag rockfish (S. rubrivinctus)

halfbanded rockfish (S. semicinctus)

Unidentified Sebastomus rockfish (rosy, starry, greenspotted)

Unidentified “benthic” Young-of-Year

Copper complex

kelp rockfish (S. atrovirens)

copper rockfish (S. caurinus)

gopher rockfish (S. carnatus)

black & yellow rockfish (S. chrysomelas)

Unidentified “copper complex” Young-of-Year

Copper complex

kelp rockfish (S. atrovirens)

copper rockfish (S. caurinus)

gopher rockfish (S. carnatus)

black & yellow rockfish (S. chrysomelas)

Unidentified “copper complex” Young-of-Year

Midwater complex

olive rockfish (S. serranoides)

blue rockfish (S. mystinus)

widow rockfish (S. entomelas)

squarespot rockfish (S. hopkinsi)

bocaccio rockfish (S paucispinis)

yellowtail rockfish (S. flavidus)

Unidentified “blackspot” Young-of-Year

Midwater complex

olive rockfish (S. serranoides)

blue rockfish (S. mystinus)

widow rockfish (S. entomelas)

squarespot rockfish (S. hopkinsi)

bocaccio rockfish (S paucispinis)

yellowtail rockfish (S. flavidus)

Unidentified “blackspot” Young-of-Year
Final Study Report – Carr et al 

26

platform to platform and from date to date. Nonetheless, for each sampling date on each 

platform, similar paths were attempted, which included several vertical legs, horizontal and 

diagonal members at each depth from roughly 35 m depth to the bottom, and surveys along short 

sections of the bottom from a vertical leg. ROV sample volumes were calculated by summing 

the total distance traveled by the vehicle at each depth, and multiplying this distance by the 

dimensions of the transect. Across all study platforms and sampling dates, a total of 92,524 m3

was sampled over the course of the study. 

The linear distance was computed by summing the length of all the legs and crossbeams 

sampled. Crossbeam lengths were obtained from schematic diagrams of each platform. The 

height and width of the transect dimension (i.e. field of view) varied with visibility (i.e. depth of 

field) and sample location (i.e. whether the ROV was moving vertically, horizontally, or rotating 

on the bottom). Visibility (i.e. water clarity) was typically consistent within a depth level on a 

given day at a given site. Depth of field was estimated as visibility changed between depth 

levels and sites. 

Field of view (height and width of view) along a horizontal transect was estimated from (1) the 

relationship between visibility and the horizontal field of view, and (2) the ratio of the horizontal 

to vertical field of view. (1) was derived from the relationship between the distance that an 

object of known size (e.g., structural member dimension) became clearly visually detectable and 

the total width of view (H), determined by the width of that object relative to the total width of 

the field of view. (2) was derived from the constant ratio of horizontal to vertical dimensions 

(vertical = 0.756 horizontal dimension) of an image on the monitor, as determined by the fixed 

field of view of the camera lens (82o

 horizontal). 

Field of view (height and width of view) along a vertical transect was estimated from (1) the 

relationship between visibility and the horizontal field of view (H), and (2) the area of a sector 

for that horizontal field of view. (1) was derived as described in the preceding paragraph. (2) 

was derived from the horizontal field of view (H), the fixed field of view of the camera lens 

(82o

= 1.43117 radians), and r, the radius of the sector (0.7621 radians x H). Thus, the horizontal 

area of the sector of view was 1⁄2 r2

(1.43117). This horizontal area was multiplied by the transect 

length to determine the total volume sampled. 

Field of view (height and width of view) as the ROV rotated in a circle on the bottom, was 

calculated from (1) the relationship between visibility and the horizontal field of view (H), (2) 

the area of a sector for that horizontal field of view, and the constant ratio of the horizontal field 

of view and the vertical field of view (vertical = 0.756 horizontal dimension). All three values 

were derived as in the previous two paragraphs. The number of contiguous sectors sampled was 

determined by objects identified on the bottom. 

Size distribution-- Fishes recorded on ROV transects were classified as Young-Of-Year (YOY) 

or adult, based on estimated size. The ROV also carried two parallel-mounted lasers to aid in 

size estimation. Due to the limited ability of the ROV to turn and aim its lasers quickly, hits 

were less frequent in ROV samples than diver samples. 

Fish Assemblages on Deep Natural Reefs 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

27

To compare fish assemblages inhabiting the deep portion of platforms with nearby natural reefs, 

two deep rocky reefs, 4-Mile and Crouch, were also sampled by ROV (Figure 1). These two 

reefs, though shallower than the bottom of the study platforms, were the only rocky reefs in the 

study area. Characteristics of the substratum are described qualitatively in Table 2. 

Sampling schedule--These two reefs were sampled in conjunction with the ROV platform 

samples: three times in 1995, three in 1996, and once in 1997 (Table 3). 

Density estimates-- Deep reef transects were sampled by running the ROV parallel to the bottom, 

< 1 m above the substratum, and slowly following the contour of the ridges and boulders 

encountered. The ROV sampled out-and-back transects of variable length, in four directions (N, 

S, E, and W) radiating out from a central reference point near the ship’s anchor. Across both 

natural reefs and sampling dates, a total of 5,764 m3

 was sampled over the course of the study. 

The ROV carried four lasers on reef dives: two parallel-mounted lasers for measuring fish 

length, and two crossing lasers to establish the distance to objects in the foreground. The 

crossing lasers bisected each other at a known distance (2.0 m) in front of the ROV. It was 

possible to estimate the vehicle’s speed by timing it over this distance as it approached and 

passed boulders and ridges. Transect length was estimated by multiplying the vehicle’s average 

speed by the time required for each transect. Because water clarity was often quite poor (< 2 m 

visibility) on deep natural reefs, transect width and height varied to reflect ambient conditions. 

Visibility (i.e. water clarity) was typically consistent within a given day at a given site. Depth of 

field was estimated as visibility changed between sampling days and sites. Field of view (height 

and width of view) along a horizontal transect was estimated from (1) the relationship between 

visibility and the horizontal field of view, and (2) the ratio of the horizontal to vertical field of 

view. (1) was derived from the relationship between the distance that an object of known size 

(e.g., boulder) became clearly visually detectable and the total width of view (H), determined by 

the width of that object relative to the total width of the field of view. The width of objects along 

the transect were derived by extrapolating the known distance between the parallel laser points 

across the total horizontal width of the object. (2) was derived as described above for the 

platforms; from the constant ratio of horizontal to vertical dimensions (vertical = 0.756 

horizontal dimension) of an image on the monitor, as determined by the fixed field of view of the 

camera lens (82o

 horizontal). 

Analyses 

We used two general approaches for comparing the fish assemblages and the relative density of 

species on the study platforms and the natural reefs. We used the density estimates (number of 

fish per unit volume of water) generated from the diver and ROV surveys to calculate the relative 

density of a species between the two habitat types. These data allowed us to identify which 

species occur on platforms, how their densities compare with that on natural reefs, and provide 

us with a first approximation of whether of not activities associated platforms would 

substantially influence regional populations on natural reefs. For example, if a species was 

common on natural reefs but rarely encountered on platforms (95% and 5% relative density, 

respectively), any decommissioning option would likely be of little importance to the regionwide population of that species. Fish density was calculated as the total quantity of each species 

divided by the total volume of water sampled by divers and ROV in each habitat, combined over 

all three years of study. For comparison between habitat types (platforms versus reefs, between 
Final Study Report – Carr et al 

28

depth strata), the relative density of species or species complexes was calculated. These values 

indicate the relative density of a species across the habitats compared. For example, percent 

density of species X on natural reefs = (density of X on reefs) / [(density of X on reefs) + 

(density of X on platforms)]. These values allow one to compare the relative number of a 

species associated with a comparable (i.e. standardized) volume of water in each habitat type. 

A second approach to comparing the patterns of fish assemblages among habitat types involved 

multivariate canonical discriminant analyses (CDA). This analysis considers the assemblage 

structure (absolute and relative abundance of fish species) of 1 year and older fishes sampled by 

either divers or ROV, separately, in each year and examines the amount of variation in 

assemblage structure explained by five different depth strata (“levels”) and habitat type 

(platforms and natural reefs). Thus, the CDA calculated the yearly centroids for a given 

site/level combination (ie. the average of samples within a single year) for a combined site||level 

classification variable. Examination of the bi-plots of the first two canonical variates allows one 

to examine how much variation is explained by each variate and what factors contributed to 

explaining that variation. Also, a bi-plot of the first two structure coefficients allows one to 

examine which species contributed to the variation among site||levels. Data were root-root 

transformed (X0.25) to reduce both skew and the effect of particularly abundant variables (fish 

taxa). Taxa that occurred in less than 20 samples were not included in the analyses. 

Data were transcribed from underwater sheets (divers) and videotapes (diver and ROV) to 

Microsoft Excel spreadsheets. Univariate parametric analyses were conducted with Systat. 

Multivariate analyses (canonical discriminant analysis: CDA) were conducted with SAS. 

Vertical Stratification of Fish Species and Life Stages on Platforms 

Most of the proposed platform decommissioning options result in a marked reduction in the 

overall height of the structure above the seafloor (Figure 2). The absence of structure in the 

upper portion of the water column may result in substantial reductions of species in one of three 

ways. First, species that associate with the shallow portions of platforms as adults may not occur 

on platforms in the absence of that structure in the upper portion of the water column. Secondly, 

species that occur in the deeper portion of platforms may recruit from the plankton to the upper 

portion of platforms and eventually move to the bottom as they get larger. Removal of structure 

in the upper portion of the water column may prevent recruitment of these species and eventually 

cause reductions or absence of these species on decommissioned platforms. A third scenario 

involves the production of mussels on the shallow portion of platforms that eventually fall to the 

seafloor beneath platforms. For species that use the mounds of mussel shells that form beneath 

platforms as recruitment habitat, adult habitat or a source of food, loss of structure in the upper 

water column may cause reductions or loss of these species. Therefore, predicting the 

consequence of alternative decommissioning options to fish populations and assemblages 

requires knowledge of the relationships between species, their life stages and the presence of 

shallow portions of platforms as well as with the mussel mounds that form beneath platforms. 

To address this, we quantified both the abundance and size distributions of fishes at discrete 

depth strata along the entire height of the study platforms (Figure 3). We used these data to 

describe which species use the shallow portions of platforms as either recruitment and/or adult 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

29

habitat. We also noted which species and life stages (juveniles or adults) associate with mussel 

shells on the seafloor beneath the platforms. 

Comparison of Fish Density Estimates by ROV and Diver Surveys 

To compare the estimates of total fish and species density (number of individuals and species per 

distance sampled, respectively) generated from diver and ROV sampling, we sampled the same 

depth stratum (level 3: 30 – 39 m) of three production platforms (Henry, Hogan and Houchin) 

on seven sampling periods with both divers and the ROV (Figure 3). Diver and ROV samples 

were typically conducted within a two-week period of one another. Over the three-year 

sampling period, a total of seven ROV and diver comparisons were made. Both total fish density 

(all species combined) and species richness (number of species) were standardized per 100m 

distance. To examine variability among platforms in the difference between diver and ROV 

estimates, the mean total fish and species density across the seven sampling dates (n= 7) was 

compared for each platform. To examine temporal variability in the difference between diver 

and ROV estimates across the seven sampling dates, we compared the mean of each variable 

across the three platforms on each date. 

Fish Movement Among Natural Reefs and Platforms 

Our approach to estimating the net movement of fishes among reefs and platforms involved 

tagging fishes individually at all five of the natural reefs surveyed by divers and ROV. Initially 

we also planned to tag fish at the six study platforms in addition to the five natural reefs, but the 

platform operators were unable to grant us permission to fish in close proximity to the structures 

(perhaps because doing so would have involved anchoring or tying to the structure or encouraged 

other sport fishing boats to attempt the same; in almost all cases, recreational boats are not 

permitted within 400 m of oil platforms). We were able to tag fish just once at one of the study 

platforms (Houchin). 

Fish were caught by hook and line using standard recreational fishing equipment, identified, 

measured, tagged in the dorsal musculature with standard 60mm-long Floy tags, and 

immediately released. When necessary, their swim bladders were vented to enable fish to return 

to the bottom. Floy tags are external and are similar in design to garment tags, and each tag 

bears a unique tag number and other information (in this case, the word “reward” followed by 

the name and phone number of Mark Carr). This allowed fishers to call and inform us of where 

and when they caught each fish. Tags were color coded by the reef on which they were tagged 

and released. Tagged fish were also occasionally seen by divers and the ROV during censuses, 

and in most cases the color of the tag could be determined. 

We conducted sixteen fishing/tagging trips between June 1996 and January 1997, utilizing 

anywhere from 3 to 20 volunteer fishers per trip (Table 5). Collectively, 459 fish of 26 species 

were tagged at the 6 tagging sites (Table 6). 

Over 600 fisherman-hours contributed to the tagging effort. Tagging was conducted from two 

platforms; university vessels and the Channel Islands National Marine Sanctuary’s R/V Ballena. 

CINMS kindly volunteered their research vessel and her captain for four days of tagging. More 

than 40 volunteers from the University of California at Santa Barbara and others from the local 
Final Study Report – Carr et al 

30

sportfishing community also joined us one or more times. The local sport fishing community 

and sport vessel operators were very supportive. Tag returns and information on recaptures 

could not have been obtained without the interest and assistance of the sport fishing community. 

As a reward for returned tags and recapture information (date and location of catch), we sent a 

pair of California lottery tickets. 

Table 5. Date and location of fishes (all species combined) tagged during the movement study. 

Date 

Tagged 3-spot 4-mile Crouch Carpinteria Horseshoe Plat. Houchin Total

6/12/96 5 30 26 61

6/13/96 31 9 4 44

6/14/96 8 6 1 3 5 23

6/15/96 2 2

9/5/96 9 1 1 2 13

9/12/96 16 83 99

9/22/96 16 16

10/5/96 6 1 1 10 18

10/10/96 2 15 11 28

11/5/96 3 5 8

11/6/96 6 20 26

11/16/96 29 29

12/5/96 10 5 15

12/8/96 4 15 19

12/15/96 36 36

1/30/97 11 2 2 7 22

Total 88 61 3 38 254 15 459

Location Tagged
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

31

Table 6. Number of individuals of each species tagged at each site where tagging was conducted. Numbers are for 

all dates combined at each site. 

Species

Tagged 3-spot 4-mile Crouch Carpinteria Horseshoe Plat. Houchin Total

kelp bass 48 8 2 7 97 1 163

brown rockfish 1 5 38 13 57

barred sandbass 12 23 17 52

blacksmith 11 3 1 25 40

gopher rockfish 1 6 26 33

treefish rockfish 15 11 26

squarespot rockfish 15 15

senorita 8 5 13

olive rockfish 1 1 6 8

copper rockfish 7 7

ocean whitefish 5 1 6

kelp rockfish 1 4 1 6

California scorpionfish 2 3 5

California sheephead 1 1 3 5

smoothhound shark 2 3 5

swell shark 2 2 4

black and yellow rockfish 1 2 3

white seabass 2 2

calico rockfish 2 2

spiny dogfish 1 1

lingcod 1 1

rubberlip surfperch 1 1

California barracuda 1 1

unidentified sculpin 1 1

vermilion rockfish 1 1

rosy rockfish 1 1

Total 88 61 3 38 254 15 459

Location Tagged

Relative Performance of Fishes on Platforms and Natural Reefs 

Our approach to determining the relative performance of fishes on platforms and natural reefs 

was to compare cohort growth and survivorship for a species that co-occurred abundantly in both 

habitat types. Our approach was to identify a group of fishes of the same species that had 

recently settled from the plankton and follow the modal individual length of the cohort to 

determine an average individual growth rate. Following change in abundance of that cohort 

could also estimate the rate of loss of individuals. With assumptions for the source of losses 

(mortality versus emigration), attributing losses to actual mortality might be inferred. 

Contribution of Platforms to the Abundance of Regional Reef Structure 

To determine the relative contribution of platforms to the total amount of hard substratum in the 

study area, we first determined the basal footprint and total submerged surface area of the six 

study platforms based on detailed schematic diagrams provided by the platform operators. We 

calculated the footprint of each platform as the area of the seafloor enclosed by the platform at 

the base of the platform jacket. The surface area of each study platform was calculated by 

adding the total length of all underwater structural elements (i.e., all platform legs, well 

conductors, and horizontal, diagonal, and vertical crossmembers) that appeared on the schematic 

diagram, and multiplying these values by the circumference of the crossmember. Since all main 
Final Study Report – Carr et al 

32

structural elements consist of cylindrical steel pipe, the circumference of each leg or 

crossmember can be determined from the diameter of the pipe, which in most cases was 

indicated on the diagrams provided. On average, platform legs (vertical piles) are just over 1 m 

diameter, whereas horizontal and diagonal elements and well conductors are about 0.5 m 

diameter. Surface area calculations did not account for the fouling organisms (mussels, scallops, 

anemones) that grow abundantly on the structure and add a complex organic matrix up to 0.3 m 

thick throughout the upper portion of each platform. 

To determine the total amount of natural hard substratum (rocky reef) in the study area, we 

attempted to obtain detailed seafloor maps or seafloor sonar images of the Santa Barbara Basin 

and the coastal shelf between Pt. Conception and Ventura. Specifically, we tried to obtain maps 

that would show quantifiable zones of hard rocky bottom in 10-100 m water depth in the vicinity 

of the six study platforms and five natural reefs. We contacted various agencies, including the 

U.S. Geological Survey, National Oceanic and Atmospheric Administration, California 

Department of Fish and Game GIS Laboratory, Monterey Bay Aquarium Research Institute, 

California State University at Monterey Bay, Moss Landing Marine Laboratory, and maps stored 

at the Camarillo Office of the Minerals Management Service (e.g., Southern California Possible 

Hard Substrate Areas, in Disturbance of Deep Water Reef Communities by Exploratory Oil and 

Gas Operations; MEC Inc.). 

Results 

Fish Assemblages on Natural Reefs and Production Platforms 

Our quantitative comparisons of the species composition, sizes and vertical distribution of fishes 

associated with shallow and deep portions of production platforms and natural reefs revealed 

several patterns pertinent to predicting and understanding the consequences of alternative 

decommissioning scenarios. It was sometimes difficult to visually identify some fish to species, 

particularly the younger stages of rockfishes, with poor visibility and using the ROV. Therefore, 

results are presented for both individual species and species complexes (Table 4). The common 

and scientific names, taxonomic categories and relationships (i.e. families) observed and used for 

analyses are summarized in Appendix 1. Because of the economic importance and 

preponderance of rockfishes observed on production platforms, patterns of rockfish and other 

species are often presented separately. 

A number of non-rockfish species (opaleye, giant kelpfish, sandbass) were not observed on the 

six study platforms, but present on nearby natural reefs (Figure 4). This was particularly evident 

for several species of the “live bearing” surf perches (Figure 5). Other non-rockfish species 

occurred on platforms, but their relative density was far greater on natural reefs. Most notably, 

the relative density of senorita, kelp bass, lingcod and sheephead on platforms was less than 25 

percent of that on natural reefs (Figure 4). Possible explanations for these patterns include the 

affinity of many non-rockfish species for macroalgae, and the limited dispersal of the live borne 

young of the surfperches. We explored the relationship between reef fishes and macroalgae at 

Carpinteria reef, where the density of the giant kelp, Macrocystis pyrifera, varied temporally 

from year-to-year and spatially across the reef. The density of several species was positively 

related to the density of giant kelp as indicated by both or either a significant regression or rank 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

33

(Spearman rs) correlation (Table 7). In particular, the kelp fishes, kelp surfperch, kelp bass and 

senorita were most strongly associated with the local density of giant kelp. In contrast, 

macroalgae on production platforms is typically comprised of foliose red species, and large kelps 

are conspicuously absent. Thus, the paucity of several of these species may reflect the absence 

of the macroalgal habitats with which they associate. The absence of several species of 

surfperches more likely reflects the limited dispersal of young and their restricted presence in 

shallow water. Together, these traits suggest that surfperches associated with shallow natural 

reefs neither recruit or migrate to offshore platforms isolated by deep water. The lower density of 

California sheephead may reflect the low density of their primary prey (urchins) on platforms 

and their requirement to shelter on the reef substratum at night. 

Figure 4. Relative density of shallow non-rockfish species between platforms and natural reefs. Data are combined 

across all size classes, all three years (1995-1997) and both sampling methods (divers and ROV) combined. Open bars are 

natural reefs, shaded bars are platforms. Relative density is explained in the Methods section text. Actual density values are 

presented in Appendix 2a. 

In contrast, the relative density of several non-rockfish species was at least as great on platforms 

as on natural reefs. This included blacksmith, painted greenling, cabezon, Garibaldi and 

halfmoon. The high densities of the planktivorous blacksmith and halfmoon probably reflect the 

great availability of zooplankton that constant passes through the platform structures. The 

presence of the other species appears to reflect their strong affinity to reef structure and low 

affinity for macroalgae (Table 7). All of these species produce young that disperse in the 

plankton, enabling them to recruit to and colonize isolated structures offshore. 

0

25

50

75

100

halfmoon

Garibaldi

cabezonsenorita

sand bass

G. kelpfish

opaleye

0

25

50

75

100

lingcod

P. greenling

kelp bass

Reefs

Platforms

Percent Density 

blacksmith

sheephead

0

25

50

75

100

halfmoon

Garibaldi

cabezonsenorita

sand bass

G. kelpfish

opaleye

0

25

50

75

100

lingcod

P. greenling

kelp bass

Reefs

Platforms

Percent Density 

blacksmith

sheephead
Final Study Report – Carr et al 

34

Figure 5. Relative density of seven common species of surfperch (Embiotocidae) between platforms and 

natural reefs. Data are combined across all size classes, all three years (1995-1997) and both sampling methods 

(divers and ROV) combined. Open bars are natural reefs, shaded bars are platforms. Relative density is explained 

in the Methods section text. 

0

25

50

75

100

sharpnose

pile

rubberlip

0

25

50

75

100

rainbow

kelp

Reefs

Platforms

Percent Density 

blackwhite

0

25

50

75

100

sharpnose

pile

rubberlip

0

25

50

75

100

rainbow

kelp

Reefs

Platforms

Percent Density 

blackwhite
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

35

The many species of rockfishes observed over the study area also varied markedly in their 

relative density on platforms and natural reefs. Taken together, for all rockfishes combined, 

rockfishes on platforms constituted roughly 60% of the entire density of rockfishes sampled 

(Figure 6). This pattern of relative density between the two habitat types varied somewhat 

among the rockfish species complexes, and markedly for some species. Whereas the relative 

density of the midwater and benthic rockfish complexes was substantially greater on platforms 

than natural reefs (roughly 70% of the overall density), the relative density of the copper 

complex was only slightly higher on natural reefs (54%; Appendix 2b). 

Table 7. Relationship between fish density and Macrocystis stipe density at Carpinteria reef from 1995 to 1997. All 

samples at the indicated depth level are included in analysis. C= Canopy, B= Bottom. Each sample is the mean of four 2 x 

2 x 30 m transects, collected on the same day at the same depth level. Probabilities < 0.05 are shown in bold. 

Common Name

Depth 

Level

No. 

Samples

Fish/Sample 

(mean + s.d.) R R2 F d.f. P

Spearman 

coefficient 

(rs) P (rs)

topsmelt, jacksmelt C 15 6.95 + 11.4 0.06 0.00 0.04 1, 13 0.84 -0.09 > 0.5

kelp perch C 15 3.2 + 4.1 0.78 0.61 20.13 1, 13 0.00 0.67 < 0.01

giant kelpfish C 15 0.22 + 0.35 0.37 0.13 2.02 1, 13 0.18 0.60 < 0.05

blacksmith C, B 30 0.57 + 1.13 0.07 0.00 0.12 1, 28 0.73 0.03 > 0.5

kelp bass C, B 30 4.44 + 6.19 0.49 0.24 9.05 1, 28 0.01 0.58 < 0.001

senorita C, B 30 3.67 + 5.48 0.44 0.19 6.57 1, 28 0.02 0.57 < 0.002

rainbow surfperch B 15 2.93 + 6.55 0.10 0.01 0.14 1, 13 0.71 0.26 > 0.2

black surfperch B 15 1.25 + 1.13 0.54 0.29 5.43 1, 13 0.04 0.47 > 0.05

pile surfperch B 15 1.95 + 1.67 0.31 0.10 1.39 1, 13 0.26 0.30 > 0.2

white surfperch B 15 0.90 + 1.81 0.40 0.16 2.48 1, 13 0.14 0.70 < 0.01

rubberlip surfperch B 15 0.13 + 0.34 0.12 0.01 0.19 1, 13 0.67 -0.08 > 0.5

kelp rockfish B 15 0.07 + 0.20 0.09 0.01 0.12 1, 13 0.74 -0.16 > 0.5

gopher rockfish B 15 0 + 0 na na na na na na na

olive rockfish B 15 0.03 + 0.09 0.16 0.03 0.36 1, 13 0.56 0.18 > 0.5

California sheephead B 15 0.18 + 0.35 0.14 0.02 0.24 1, 13 0.63 -0.01 > 0.5

opaleye B 15 0.20 + 0.40 0.18 0.03 0.45 1, 13 0.51 -0.17 > 0.5
Final Study Report – Carr et al 

36

Figure 6. Relative density of rockfish groups between platforms and natural reefs. Species composition of each 

taxonomic group is described in Table 4. Data are combined across all size classes, all three years (1995-1997) and 

both sampling methods (divers and ROV) combined. Open bars are natural reefs, shaded bars are platforms. 

Relative density is explained in the Methods section text. Actual density values are presented in Appendix 2b. 

As indicated by the four most common species that constituted the benthic rockfish complex 

(which excludes the copper complex), some species occurred in relatively far greater density on 

natural reefs (75% or greater) than on the platforms (Figure 7). With the exception of treefish, 

these are species that occur on deeper reefs, sampled with the ROV. However, vermillion and 

the other benthic species (flag, halfbanded, and species that constitute the Sebastomus group; 

Table 4) occurred in relatively higher densities on platforms, contributing to the overall higher 

density of this group on platforms relative to natural reefs. 

0

25

50

75

100

All Species

MRF complex

Copper complex

0

25

50

75

100

Reefs

Platforms

Percent Density 

BRF complex

0

25

50

75

100

All Species

MRF complex

Copper complex

0

25

50

75

100

Reefs

Platforms

Percent Density 

BRF complex
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

37

Figure 7. Relative density of the four most common rockfish species in the shallow benthic group (excluding 

“copper complex” species; see Figure 9) between platforms and natural reefs. Open bars are natural reefs, shaded 

bars are platforms. Data are combined across all three years (1995-1997) and both sampling methods (divers and 

ROV). Young-of-Year fish (YOYs) not included in species marked with *. “All Species” includes unidentified 

shallow benthic adults and YOYs. Relative density is explained in the Methods section text. Actual density values 

are presented in Appendix 2b. 

As indicated by the four most common species that constituted the midwater rockfish complex, 

the overall relative density of this group was far greater on platforms (70%) than natural reefs 

(Figure 8). But again, this pattern varied markedly among species. Whereas squarespot were 

observed only on natural reefs and 65% of the overall density of olive rockfish occurred on 

natural reefs, both widow and blue rockfish were observed only on platforms. While these 

differences cannot be interpreted as absolute, some species clearly occur in much greater density 

in one habitat relative to the other (e.g., blue and widow rockfish on platforms). Additional 

species that constituted this complex (boccacio, yellowtail) also contributed to the overall higher 

density of this group on platforms compared to natural reefs. Importantly, the behavior of 

species constituting this group to form large aggregations in the water column well above the 

bottom, allows them to occupy large areas of the water column, while maintaining proximity 

with the physical structure of the platform. This is a feature unique to platforms compared to 

natural reefs. 

0

25

50

75

100

All Species

* calico

* vermilion

0

25

50

75

100

* treefish

Reefs

Platforms

Percent Density 

* brown

0

25

50

75

100

All Species

* calico

* vermilion

0

25

50

75

100

* treefish

Reefs

Platforms

Percent Density 

* brown
Final Study Report – Carr et al 

38

Figure 8. Relative density of the four most common rockfish species in the midwater group between platforms 

and natural reefs. Open bars are natural reefs, shaded bars are platforms. Data are combined across all three years 

(1995-1997) and both sampling methods (divers and ROV). Young-of-Year fish (YOYs) not included in species 

marked with *. “All Species” includes unidentified midwater adults and YOYs. Relative density is explained in the 

Methods section text. Actual density values are presented in Appendix 2b. 

As indicated by the four species that constituted the copper rockfish complex, the overall relative 

density of this group was relatively similar between platforms and natural reefs (Figure 9). But 

again, this pattern varied markedly among species. Whereas the relative density of the shallow 

(< 30 m) dwelling gopher and black-and-yellow rockfish was substantially higher on natural 

reefs (> 80%), the relative density of kelp and copper rockfish was more equitable between 

habitat types. Importantly, the vast majority of kelp and copper rockfish encountered on 

platforms were at the bottom of the platforms. Thus, the difference in the relative density of the 

different species that constitute this complex may reflect the ability of species to exist at depth as 

adults. This may explain the absence of the shallow dwelling adults of the gopher and blackand-yellow rockfishes on platforms. This pattern does not appear to reflect differences in 

recruitment between platforms and natural reefs, based on patterns of recruitment described later 

in this section. 

0

25

50

75

100

All Species

* blue

* widow

0

25

50

75

100

* squarespot

Reefs

Platforms

* olive

Percent Density 

0

25

50

75

100

All Species

* blue

* widow

0

25

50

75

100

* squarespot

Reefs

Platforms

* olive

Percent Density 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

39

Figure 9. Relative density of all four rockfish species in the copper complex group between platforms and natural 

reefs. Open bars are natural reefs, shaded bars are platforms. Data are combined across all three years (1995-1997) 

and both sampling methods (divers and ROV). Young-of-Year fish (YOYs) not included in species marked with *. 

“All Species” includes unidentified copper complex adults and YOYs. Relative density is explained in the Methods 

section text. Actual density values are presented in Appendix 2b. 

Distribution of life stages between platforms and natural reefs--Many species demonstrated 

marked differences in the relative density of young (< 1 year) and older life stages between 

platforms and natural reef habitats. For example, while older rockfish individuals occurred on 

both platforms and natural reefs, the relative density of young fish was far greater on platforms 

(Figure 10). Such was the case for the “copper”, “midwater” and “shallow benthic” complexes 

(Figure 10). This pattern was even stronger for two non-rockfish species, the blacksmith and the 

California sheephead (Figure 11). Whereas recruitment of these two species was greater on 

platforms, the relative density of older stages was much greater on natural reefs.

Of the other non-rockfish species, the relative density of life stages between platforms and 

natural reefs varied among species. For example, the relative density of both young and older 

Garibaldi and halfmoon was vastly greater on platforms than natural reefs (Figure 11). In 

0

25

50

75

100

All Species

* copper

* kelp

0

25

50

75

100

* black & yellow

Reefs

Platforms

* gopher

Percent Density 

0

25

50

75

100

All Species

* copper

* kelp

0

25

50

75

100

* black & yellow

Reefs

Platforms

* gopher

Percent Density 
Final Study Report – Carr et al 

40

contrast, the relative density of both young and older senorita and kelp bass was far greater on 

natural reefs (Figure 11). 

Comparison of size distributions on platforms and natural reefs--Overall, laser estimates of size 

distributions missed both the smaller, juvenile size classes as well as rare larger individuals when 

compared with visual estimates on either platforms or natural reefs. Therefore, we restricted our 

comparison of size distributions between platforms and natural reefs to individuals ≥ 9 cm Total 

Length. For that restricted size distribution, the two methods generally produced similar 

estimates of both mean size and size-frequency distributions (Appendix 4). Of the 19 species 

that we compared, lasers estimated larger mean adult sizes than visual estimates for only three 

species (blacksmith, pile surfperch and blue rockfish), and visual estimates were greater than 

laser estimates for four species (rubberlip surfperch, brown surfperch, barred sand bass and 

widow rockfish). 

Of the 11 species whose adults (≥ 9 cm TL) co-occurred in both habitats in sufficient numbers to 

compare size distributions with either or both sampling methods, mean size of adults tended to 

be greater on platforms (pile perch, senorita, kelp bass, and copper, olive, kelp, gopher 

rockfishes). Sheephead and painted greenling adults tended to be larger on natural reefs. Mean 

size of adult halfmoon and blacksmith were similar on platforms and natural reefs (Appendix 4). 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

41

Figure 10. Relative density of rockfish size classes between natural reefs and platforms. Open bars are natural 

reefs, shaded bars are platforms. Data are combined across all three years (1995-1997) and both sampling methods 

(divers and ROV). “Older” fish are all fish ≥ 9 cm TL. Relative density is explained in the Methods section text. Percent Density 

60

80

100

40

20

0

60

80

100

40

20

0

Reefs

Platforms

“copper complex” rockfish “midwater” rockfish

Percent Density 

60

80

100

40

20

0

60

80

100

40

20

0

“shallow benthic” rockfish all rockfish species

< 1 Year Older < 1 Year Older

< 1 Year Older < 1 Year Older

Percent Density 

60

80

100

40

20

0

60

80

100

40

20

0

60

80

100

40

20

0

60

80

100

40

20

0

Reefs

Platforms

“copper complex” rockfish “midwater” rockfish

Percent Density 

60

80

100

40

20

0

60

80

100

40

20

0

60

80

100

40

20

0

60

80

100

40

20

0

“shallow benthic” rockfish all rockfish species

< 1 Year Older < 1 Year Older

< 1 Year Older < 1 Year Older
Final Study Report – Carr et al 

42

Figure 11. Relative density of non-rockfish size classes between natural reefs and platforms. Open bars are 

natural reefs, shaded bars are platforms. Data are combined across all three years (1995-1997) and both sampling 

methods (divers and ROV). “Older” fish are all fish ≥ 9 cm TL. Relative density is explained in the Methods 

section text. 

halfmoon

60

80

100

40

20

0

Percent Density 

< 1 Year Older

60

80

100

40

20

0

< 1 Year Older

senorita

Percent Density 

< 1 Year Older < 1 Year Older

kelp bass California sheephead

60

80

100

40

20

0

60

80

100

40

20

0

Percent Density 

< 1 Year Older < 1 Year Older

60

80

100

40

20

0

60

80

100

40

20

0

blacksmith Garibaldi

halfmoon

60

80

100

40

20

0

Percent Density 

< 1 Year Older

60

80

100

40

20

0

< 1 Year Older

halfmoon senorita

60

80

100

40

20

0

Percent Density 

< 1 Year Older

60

80

100

40

20

0

< 1 Year Older

60

80

100

40

20

0

60

80

100

40

20

0

Percent Density 

< 1 Year Older

60

80

100

40

20

0

60

80

100

40

20

0

< 1 Year Older

senorita

Percent Density 

< 1 Year Older < 1 Year Older

kelp bass California sheephead

60

80

100

40

20

0

60

80

100

40

20

0

Percent Density 

< 1 Year Older < 1 Year Older

kelp bass California sheephead

60

80

100

40

20

0

60

80

100

40

20

0

60

80

100

40

20

0

60

80

100

40

20

0

Percent Density 

< 1 Year Older < 1 Year Older

60

80

100

40

20

0

60

80

100

40

20

0

blacksmith Garibaldi

Percent Density 

< 1 Year Older < 1 Year Older

60

80

100

40

20

0

60

80

100

40

20

0

60

80

100

40

20

0

60

80

100

40

20

0

blacksmith Garibaldi
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

43

Comparison of assemblage structure--The many differences among species in their patterns of 

relative density between platforms and natural reefs are manifested in the composition and 

structure (i.e. relative abundance) of fish assemblages associated with the two habitat types. 

These differences are also manifested in the structure of fish assemblages across the depth strata 

sampled. For example, as indicated by the Canonical Discriminant Analysis (CDA) comparing 

the structure of the fish assemblages sampled by divers in the upper three depth strata (Figure 3: 

levels 1,2,3), roughly 65% of the variation in assemblage structure is explained by differences 

between platform and natural reefs (1st canonical variate) and another 20% of the variation is 

related to differences in fish assemblages across the three depth strata on the platforms (2nd

canonical variate; Figure 12). In particular, the fish assemblage sampled by divers at the deepest 

stratum of natural reefs (level 3: many of the surfperches, opaleye, barred sandbass, brown 

rockfish, gopher rockfish) was distinctly different from all other habitats sampled (Figure 3). 

The fish assemblages occupying the shallow (Garibaldi, blacksmith, halfmoon) mid-depth 

(cabezon, copper, painted greenling, olive rockfish,) and deep (sharpnose perch, blue and kelp 

rockfish) strata of platforms sampled by divers were also distinctive (Figure 12). There was 

much overlap in the assemblages sampled at the middle stratum of the platforms with the 

shallow and middle strata of natural reefs (white perch, painted greenling, copper, olive and kelp 

rockfish) as indicated at the intersection of the two canonical variates (Figure 12). 
Final Study Report – Carr et al 

44

Figure 12. Patterns of fish assemblages derived from the Canonical Discriminant Analysis of 1+ and older 

fishes sampled by divers on platforms and natural reefs. Natural reef; Platform. Shading 

represents each of the three depth levels surveyed by divers from deep (black) to shallow (white). Each 

point represents the centroid of a fish assemblage of a given site-depth level combination for a given year. 

Canonical Variate 1 (65.4%)

-4 -2 0 2 4 6 8 10

Canonical Variate 2 (20.6%)

-3

-2

-1

0

1

2

3

4

5

Structure Coefficient 1

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Structure Coefficient 2

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Blacksmith

Kelp bass

Kelp rockfish

Senorita

Pile perch

Halfmoon

Garibaldi

Olive rockfish

Cabezon

Blue rockfish

White perch

Sharpnose perch

Barred sandbass

Copper rockfish Gopher rockfish

Painted greenling

SheepheadBlack perch

Rainbow perchOpaleye Brown rockfish

Rubberlip perch

Among the six study platforms, depth stratification was again the strongest correlate with 

variation in fish assemblages (Figure 13). Depth stratification explained 44% of the variation in 

fish assemblages (canonical variate 1). In addition, there was some variation among platforms, 

but this did not seem to correspond to any spatial pattern. Platforms A and B (offshore), and 

Hogan (the innermost platform) separatd from the other platforms based on a general higher 

density of fish (all species combined) relative to the other platforms. However, this was not a 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

45

strong trend, given that it explained only an additional 17 of the variation in assemblage 

structures among platforms (Figure 13; canonical variate 2). 

Figure 13. Patterns of fish assemblages derived from the Canonical Discriminant Analysis of 1+ and older 

fishes sampled by divers on platforms only. Platform ‘A’; Platform ‘B’; Platform ‘C’; 

Platform ‘Henry’; Platform ‘Hogan’; Platform Houchin. Shading represents each of the three depth 

levels surveyed by divers from deep (black) to shallow (white). Each point represents the centroid of a fish 

assemblage of a given site-depth level combination for a given year. 

Canonical Variate 1 (43.6%)

-4 -3 -2 -1 0 1 2 3 4 5

Canonical Variate 2 (16.6%)

-2

-1

0

1

2

3

4

Structure Coefficient 1

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Structure Coefficient 2

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Blacksmith

Senorita

Sheephead

Pile perch

Sharpnose perch

Halfmoon

Garibaldi Olive rockfish

Cabezon

Opaleye

Blue rockfish

Copper rockfishWhite perch

Barred sandbass

Kelp rockfish Gopher rockfish

Painted greenling Kelp bass

Brown rockfish

Rubberlip perch

Fish assemblages on the deepest natural reefs and the deepest portion of the platforms also varied 

by habitat (platform versus natural reef) and, especially, depth stratum. Most (79%) of the 

variation in assemblage structure among samples was related to whether samples were collected 

on the bottom of the platforms (or deepest reef) versus shallower depth strata above the bottom 

(Figure 14: canonical variate 1). The deepest natural reef sampled (36 m depth) was shallower 

than the bottom of the platforms (50-58 m) and this was reflected in the assemblage structure. 

The deepest natural reef (ROV) samples were comprised of more shallow dwelling species 

(sheephead, blackeye goby, blacksmith, kelp bass) than the bottom of the platforms (Figure 14). 
Final Study Report – Carr et al 

46

Above the bottom, platforms and natural reefs supported more similar fish assemblages within 

the lower depth strata sampled by the ROVs. 

Figure 14. Patterns of fish assemblages derived from the Canonical Discriminant Analysis of 1+ and older 

fishes sampled by ROV on platforms and deep natural reefs. Natural reef; Platform. Shading 

represents each of four depth levels surveyed by ROVs on platforms from deep (black) to shallow (white), 

and the single depth level sampled on the two deep natural reefs. Each point represents the centroid of a 

fish assemblage of a given site-depth level combination for a given year. 

Canonical Variate 1 (78.6%)

-4 -2 0 2 4 6 8 10

Canonical Variate 2 (13.1%)

-6

-4

-2

0

2

4

6

Structure Coefficient 1

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Structure Coefficient 2

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

Kelp rockfish

Blacksmith

Blackeye goby

Copper rockfish

Pile perch

Sharpnose perch

Rubberlip perch

Halfmoon

Kelp bass

Sheephead

Lingcod

Painted greenling
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

47

This strong distinction between bottom and water column assemblages was again manifested 

among samples across the six study platforms (Figure 15). Bottom versus all samples shallower 

in the water column explained 67% of the variation in fish assemblage structure among samples 

across all six platforms (canonical variate 1). Actual depth explained only 13% more variation 

(canonical variate 2) because of the similarity of assemblages across the deeper strata above the 

bottom. 

Figure 15. Patterns of fish assemblages derived from the Canonical Discriminant Analysis of 1+ and older 

fishes sampled by ROV on platforms only. Platform ‘A’; Platform ‘B’; Platform ‘C’; 

Platform ‘Henry’; Platform ‘Hogan’; Platform Houchin. Shading represents each of four depth 

levels surveyed by ROVs on platforms from deep (black) to shallow (white). Each point represents the 

centroid of a fish assemblage of a given site-depth level combination for a given year. 

Canonical Variate 1 (66.9%)

-4 -2 0 2 4 6 8 10

Canonical Variate 2 (12.7%)

-5

-4

-3

-2

-1

0

1

2

3

4

5

Structure Coefficient 1

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Structure Coefficient 2

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

Kelp rockfish

Blackeye goby

Copper rockfish

Pile perch

Rubberlip perch

Halfmoon

Kelp bass

Sheephead

Lingcod Sharpnose perch

Blacksmith

Painted greenling
Final Study Report – Carr et al 

48

Habitat type (platforms versus natural reefs) also explained a substantial amount of variation 

(51%) of the assemblage of young-of- year (less than 1 yr old fishes) fishes sampled (Figure 16; 

canonical variate 1). Deep portions of platforms harbored a number of rockfish species in much 

greater density than observed shallower on platforms or on any of the natural reefs sampled. 

Young of shallow dwelling species (Garibaldi, blacksmith) contributed more to the young-ofyear assemblages on the shallower strata of platforms, and kelp-associated young (e.g., kelp 

bass) contributed more to assemblages of young on natural reefs (Figure 16). Thus, with respect 

to which species recruited as young from the plankton, the platforms and natural reefs differed 

substantially as recruitment habitat in the study area. As for assemblages of adult fishes, bottom 

versus above-bottom strata explained substantial variation (55%) in the assemblages of youngof-year recruits across the six study platforms (Figure 17; canonical variate 1). Variation across 

platforms was not strong. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

49

Figure 16. Patterns of fish assemblages derived from the Canonical Discriminant Analysis of YOY fishes 

sampled by divers on platforms and natural reefs. Natural reef; Platform. Shading represents each 

of the three depth levels surveyed by divers from deep (black) to shallow (white). Each point represents the 

centroid of a fish assemblage of a given site-depth level combination for a given year. 

Canonical Variate 1 (51.3%)

-5 -4 -3 -2 -1 0 1 2 3 4 5

Canonical Variate 2 (33.3%)

-2

-1

0

1

2

3

4

Structure Coefficient 1

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

Structure Coefficient 2

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

Blacksmith

KGB

Treefish

Blue rockfish

Rosy group

Kelp bass

Garibaldi

OYT
Final Study Report – Carr et al 

50

Figure 17. Patterns of fish assemblages derived from the Canonical Discriminant Analysis of YOY fishes 

sampled by divers on platforms only. Platform ‘A’; Platform ‘B’; Platform ‘C’; Platform 

‘Henry’; Platform ‘Hogan’; Platform Houchin. Shading represents each of the three depth levels 

surveyed by divers from deep (black) to shallow (white). Each point represents the centroid of a fish 

assemblage of a given site-depth level combination for a given year. 

Canonical Variate 1 (55.1%)

-3 -2 -1 0 1 2 3 4

Canonical Variate 2 (12.9%)

-2

-1

0

1

2

Structure Coefficient 1

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

Structure Coefficient 2

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

Blacksmith

KGB

OYT

Blue rockfish

Kelp bass

Garibaldi

Rosy group
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

51

Vertical Stratification of Fish Species and Life Stages on Platforms 

Comparison of Fish Density Estimates by ROV and Diver Surveys 

Our characterization of fish assemblages on platforms and natural reefs indicated that much of 

the variation in fish assemblage structure between and within these two habitat types was related 

to water depth in two ways. First by the actual bottom depth, and secondly by position in the 

water column; i.e. the strong differences between assemblages on the bottom and all strata above 

the bottom. But our ability to describe this depth stratification across all 5 depth strata sampled 

was dependent, in part, on differences in sampling bias by the two methods we used to sample 

fish at different depth strata; divers and ROV. Because we are interested in both spatial and 

temporal variation among platforms, we compared the amount of habitat sampled (i.e. water 

volume), species density and total fish density sampled by divers and ROV between the three 

platforms (Hogan, Houchin and Henry) at which diver and ROV sampling overlapped with one 

another and across the 7seven ROV sampling dates. Diver and ROV samples overlapped along 

the outer perimeter cross members at the 36 m depth (level 3, Figure 3). 

Water volume sampled by divers at level 3 tended to be somewhat greater (20-25%) than by the 

ROV with the exception of two sampling dates in which the ROV sampled substantially greater 

(25%) water volume and substantially less (10%) water volume sampled by divers (Figure 18). 

Although samples comparing species density (number of species per unit water volume) and 

total fish density were standardized per unit water volume, the greater volume sampled could 

contribute to greater likelihood of encountering rare species and bias species number estimates 

recorded by divers, which would lead to a greater species density in shallower water sampled by 

divers. However, at level 3, there was no clear difference in the density of species recorded by 

ROV than by divers across the three platforms sampled, nor was there any evidence of a 

consistent difference in species density across the 7 sampling dates (Figure 18). It is more likely 

that sampling with both methods was sufficient to pick up most of the conspicuous species on 

platforms, and the relatively lower volume sampled by ROV contributes to the greater number of 

species per unit water volume sampled by the ROV. Similarly, differences in total fish density 

between the two methods did not differ substantially or consistently across the three platforms 

and differences flip-flopped across sampling dates erratically (Figure 18). These patterns 

suggest that any strong depth-related differences in fish assemblages were more likely real 

differences, rather than differential bias in the sampling methods used at different depths of the 

platforms. 
Final Study Report – Carr et al 

52

Figure 18. Comparison of the volume of water sampled, species density, and fish density (all species combined) by 

ROV and divers on each of the three study platforms where both methods sampled the perimeter cross members at 

level 3 (36 m depth). Plotted are the mean and standard error across the 7 sampling dates (n= 7) on the left-hand 

column, and across the 3 platforms (n=3) on the right-hand column. sample water volume (m3)

0

500

1000

1500

divers

ROV

0

1

2

HENRY

HOGAN

HOUCHIN

0

5

10

species density (species/100m3)

0

500

1000

1500

2000

0

1

2

3

Jun 1995

Aug 1995

Oct 1995

Jun 1996

Aug 1996

Oct 1996

Jun 1997

sample date

0

5

10

platform

total fish density (fish/100m3) sample water volume (m3)

0

500

1000

1500

divers

ROV

0

1

2

HENRY

HOGAN

HOUCHIN

0

5

10

HENRY

HOGAN

HOUCHIN

0

5

10

species density (species/100m3)

0

500

1000

1500

2000

0

1

2

3

Jun 1995

Aug 1995

Oct 1995

Jun 1996

Aug 1996

Oct 1996

Jun 1997

Jun 1995

Aug 1995

Oct 1995

Jun 1996

Aug 1996

Oct 1996

Jun 1997

sample date

0

5

10

platform

total fish density (fish/100m3)
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

53

Of particular importance with respect to depth is the degree to which the shallow portion of 

platforms provides recruitment habitat and is key to the replenishment of populations associated 

with platforms. This is particularly clear for those species whose juveniles and adults occur 

strictly in the upper portion of platforms (e.g., blacksmith, Garibaldi). It is less clear for the any 

rockfishes whose adults occupy deeper portions of platforms. The importance of the upper 20 m 

of platforms for recruitment varied markedly among the three major groups of rockfishes 

(copper, midwater, and benthic complexes). The vast majority of recruitment of the copper 

complex species occurred in the upper 20 m of the platforms (Figure 18). In contrast, 

recruitment of the benthic complex occurred near or on the bottom at the same depth stratum as 

adults. The midwater rockfishes exhibited recruitment patterns intermediate of these two 

extremes. Juveniles recruited at depths in the middle strata of the platforms (especially levels 3 

and 4), but shallower than strata occupied by adults. Because of the numerical predominance of 

the midwater rockfishes, the vast majority of rockfish recruitment occurred in the middle strata 

of the platforms. Based on their small size (4-8 cm Total Length), it is clear that these recruits 

settled as pelagic juveniles from the plankton, rather than migrating from other habitats. 

Figure 19. Relative depth distribution of young-of-year and older individuals of each of three rockfish complexes. 

Plotted is the percent of the total density of each size category across depth strata. Shaded bars are percent of total 

young-of-year within each depth stratum, solid bars are percent of total adults within each depth stratum. See Table 

4 for species composition of the copper, benthic (BRF), and midwater (MRF) complexes. The benthic complex 

does not include the copper complex. Depth ranges included within each stratum are 8m= 0-9m, 20= 10-22m, 31= 

23-36m, 43= 37-49m, 57= 50-57m. 

Proportion of size class

A. copper complex

31 m

43 m

57 m

20 m

8 m

0 20 40 60 80 1

Adult

Young of Year

B. benthic rockfish C. midwater rockfish

0 20 40 60 80 1 0 20 40 60 80 1

Proportion of size class

A. copper complex

31 m

43 m

57 m

20 m

8 m

0 20 40 60 80 1

Adult

Young of Year

B. benthic rockfish C. midwater rockfish

0 20 40 60 80 1 0 20 40 60 80 1
Final Study Report – Carr et al 

54

Fish Movement Among Natural Reefs and Platforms 

Of the 459 fish tagged in this study, 10% (48) were re-caught (Table 8). Recreational fishers 

were responsible for almost all recaptures. This relatively high return rate (10%) is not 

surprising for nearshore fishes. Of the fish re-caught, 67% (32 of 48) were caught where they 

were tagged, suggesting that many of the species tagged remain on the reefs where they were 

tagged. Most of the fish recaptured were kelp bass and rockfishes (38 and 44%, respectively). 

Collectively, kelp bass and brown rockfish accounted for 60 percent of all fish recaptured. For 

these two species, 61% (11 of 18) and 82% (9 of 11), respectively, were re-caught within 1 km 

of the tagging site. Of course, it is not clear how much movement occurs by the many fish that 

were not recaptured. But these data suggest that some individuals are generally residential, 

remaining on nearby reefs at least over the duration of the tagging study. 

We made note of any tagged fish that were observed on diver surveys or on video footage 

recorded by divers or ROV on both natural reefs and platforms. We never observed tagged fish 

on platforms other than two brown rockfish at Platform Houchin, both of which were previously 

tagged there. Platform Houchin was the only platform we were able to tag fish at. Roughly 50 

percent (254) of the 459 fish tagged in our study were tagged at one site, Horseshoe Reef. 

Horseshoe Reef lies roughly 8 km from the six study platforms (Figure 1). Divers recorded 17 

re-sightings of tagged fishes, mostly benthic rockfishes. All 17 re-sightings were made on 

Horseshoe reef, all of which were tagged at that site. We never observed tagged fish on 

platforms that were tagged on natural reefs. 
Consequences of Alternative Decommissioning Op

55

Table 8. Fish species tagged and recaptured on reefs and oil platforms in the area off Santa Barbara from 1996 to 1998. Distances moved c

between the following: a = 3-spot reef to Horseshoe reef, b = Horseshoe reef to 1-mile reef, c = Horseshoe reef to Carpinteria reef, d = 3-sp

Carpinteria reef to Loginelle wreck (Ventura), 

f = Plat. Houchin to Plat. Hogan, 

g = Horseshoe reef to Campus Pt, h = 4-mile reef to 1-mile 

miles of Summerland, j = Horseshoe reef in channel between Anacapa Island and Santa Cruz Isand, 

k = Horseshoe reef to 3-spot reef, l = lo

Distance from in

Species No. tagged No. recaptured % Return Mean days between capture 

(± 1 sd) 

Mean distance 

traveled (km)

(± 1 sd) 

Most days 

between 

capture 

Maximum 

distance 

(km) 

0 1-2 3

kelp bass 

163 18 11.0 97.8 

± 112.1 1.8 

± 3.4 350 9.5 11 2a 

sand bass 

52 5 9.6 109.2 

± 67.9 13.9 

± 18.6 197 40.9 2 

brown rockfishs

57 11 19.3 246.3 

± 126.4 2.4 

± 7.5 446 25.0 9 1f 

gopher rockfish 

33 2 6.1 182.5 

± 181.7 0 311 0.0 2 

treefish 

26 4 15.4 365.5 

± 283.5 12.71 

± 19.4 772 41.6 1 2 

squarespot rockfish 

15 1 6.7 84.0 0 84 0.0 1 

copper rockfish 

7 1 14.3 54.0 0 54 0.0 1 

olive rockfish 

8 2 25.0 33.0 

± 18.4 0.8 

± 1.1 46 1.6 1 1k

blacksmith

40 2 5.0 59.5 

± 7.8 0.0 

± 0.0 65 0.0 2 

ling cod

1 1 100.0 44.0 0.0 44 0.0 1 

California scorpion fish 5 1 20.0 54.0 0.0 54 0.0 1 All other species 52 0 0.0 Total 459 48 10.5 

55 
Final Study Report – Carr et al 

56

Relative Performance of Fishes on Platforms and Natural Reefs 

Unfortunately, species that recruited in sufficient abundance to platforms (e.g., blacksmith or 

rockfish) or natural reefs (senorita, kelp bass) recruited in insufficient numbers to the other 

habitat type (Figures 10 and 11). This precluded our ability to make this very important 

comparison from the surveys we conducted at the different study platforms and natural reefs. 

Contribution of Platforms to the Abundance of Regional Reef Structure 

All available maps and images were of insufficient resolution to estimate in any quantitative way 

the amount of rocky habitat in the region. 

Discussion 

Several offshore oil and gas production facilities in the Pacific Outer Continental Shelf (POCS) 

region are nearing the end of, or have ended, their economic lives. Present legislation requires 

complete removal of decommissioned platforms. However, alternative decommissioning options 

including partial removal in place or relocation have been implemented in other areas of the 

country. The removal of four offshore platforms in the Santa Barbara Channel during the 

summer of 1995 created interest by some user groups in pursuing such alternatives on the West 

coast (MMS-CSLC Abandonment Workshop 1994, MMS 1998). Critical to formulation of 

appropriate decommissioning policy is an understanding of the ecological, economic and social 

consequences of different decommissioning options and identification of the mechanisms by 

which such information is incorporated, or not, into legislation and public policy. 

Central to understanding the ecological role of anthropogenic structures on regional fish 

production is knowledge of their relationship with fish assemblages on natural reefs (Alevizon 

and Gorham 1989, Ambrose and Swarbrick 1989, Ambrose 1994, Beets and. Hixon 1994, Carr 

and Hixon 1997, Osenberg et al 2002). It is difficult to conclude to what extent species 

associated with a structure influence regional production without distinguishing local production 

from the redistribution of individuals (i.e., “attraction”) from natural habitat. Also critical to the 

development of decommissioning is an understanding of how the local environment (i.e., 

oceanographic conditions and proximity to natural reef habitat) and structural characteristics of 

decommissioned structures influence the kinds and numbers of species associated with it. Thus, 

our multi-year investigation of the ecological role of offshore structures had three primary 

objectives. One objective of this study was to quantify the species and sizes of fishes associated 

with platforms and natural reefs. Such information is required to determine what species and life 

stages might be influenced by the various decommissioning options. Because several of the 

various options for platform decommissioning alter the vertical height of the remaining structure 

(e.g., “topping”, “toppling”, moving to different water depths), a second objective of our study 

was to quantify the vertical distribution of each species from the surface to the bottom of the 

platforms to estimate the potential consequences of these options. Fundamental to understanding 

the net contribution of local populations to regional production is information on the sizespecific rate of migration of fishes among local, reef-associated populations. In the context of 

platform decommissioning, knowledge of the net direction and rate of transfer of biomass 

between platforms and natural reefs is crucial. Therefore, a third objective was to determine how 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

57

much and what direction fish move (from platforms to reefs or vice versa), the rate of that 

movement, and net direction of exchange. 

Fish Assemblages on Natural Reefs and Production Platforms 

Several key results were generated from our comparisons of fish population and assemblages 

between natural reefs and productions platforms in the eastern Santa Barbara Channel. Clearly, 

platforms create a different kind of reef environment than is characteristic of nearby natural 

reefs. Three habitat characteristics are particularly relevant. Most conspicuous is the unique 

occurrence of physical structure high in the water column in deep water. This provides structure 

for the young of species that recruit to reef-associated populations after surviving a dispersive 

planktonic larval phase. Many species that occupy platforms clearly recruited to platforms this 

way (e.g., Garibaldi, blacksmith, cabezon and several species that constitute the midwater 

rockfish complex). These species were far less abundant as recruits on the natural reefs we 

sampled. The presence of physical structure high in the water column also allowed large 

numbers of midwater rockfishes (including blue, widow, olive, yellowtail, and boccacio) to 

aggregate well above the bottom and forage on planktonic prey (especially blue rockfish and the 

juveniles of all of these species). A second habitat distinction is the absence of large macroalgae 

(kelps) on platforms. The absence of kelp, especially the giant kelp, Macrocystis pyrifera, 

contributed to the paucity of species that associate closely with this alga on natural reefs (e.g., 

senoritas, kelp bass, kelp fishes, opaleye). A third habitat feature is the apparent lower rugosity 

(cracks and crevices) of the platform structure compared to natural reefs. Although this did not 

contribute to a reduction in the relative density of several species closely associated with the reef 

substratum (e.g., Garibaldi, cabezon, painted greenlings), it may have contributed to the 

relatively lower density of some (e.g., sheephead, lingcod, gopher and black-and-yellow 

rockfishes). Taken together, these three differences in structural aspects of platforms and natural 

reefs contributed to the population and assemblage differences we detected between the two 

habitat types. 

Another important cause for differences in fish assemblages between platforms and natural reefs 

were broader landscape scale differences. Platforms are isolated in deeper water from the 

shallow reefs along the coast. For species whose young do not disperse in the plankton, this 

isolation is a barrier to colonization and replenishment. This probably explains the lower relative 

density of the many surfperch species whose young are not dispersed in the plankton and 

primarily replenish populations where they are born. In addition, the location of platforms 

offshore in deeper water appears to expose them to recruitment of species whose young (larvae 

and pelagic juveniles) are delivered in far fewer numbers to shallower natural reefs closer to 

shore. This may explain the higher density of species (especially juveniles) of blacksmith and 

several rockfish species constituting the copper and midwater rockfish complexes. In fact, it is 

surprising that relative densities of young and adults of some of the other rockfishes (e.g., calico, 

brown, and treefish) were not greater on platforms. This may reflect the episodic recruitment 

characteristic of rockfishes and it is possible that recruitment of these species may be greater on 

platforms when recruitment events occur. 

Taken together, these surveys indicate that some species are likely to be more strongly 

influenced by decommissioning decisions than others and the patterns presented in this study 
Final Study Report – Carr et al 

58

identify those species for the area we sampled. For those species with much greater relative 

densities on platforms, or were altogether absent from the natural reefs we sampled, platforms 

may be not just represent “extra” habitat that is interchangeable with natural reef habitat. 

Platforms would add or enhance populations that are otherwise sparse in the study region. But 

two notes of caution are required in interpreting these patterns. First, our study area was rather 

small, limited to the eastern portion of the Santa Barbara Channel and only those natural reefs 

adjacent to the mainland. We restricted our focus on natural reefs in that area because (1) of the 

limited logistical scope of the study, (2) natural reefs near the platforms probably provide the 

best direct comparison of the role of these habitat types exposed to similar oceanographic 

conditions and larval supply, and (3) these natural reefs are the most likely to be influenced by 

the presence of the study platforms and future decommissioning activities, thereby providing a 

baseline for future studies of their response to such activities and for the evaluating the 

consequences of decommissioning activities. However, the limited spatial scope of our study is 

far smaller than the region-wide collection of fish populations that likely share larvae, and 

perhaps adults. Decommissioning of the platforms in our study area might influence natural 

reefs in other areas of the Channel and those reefs may support different fish assemblages than 

the natural reefs we studied. Recognizing this, our study was conducted in collaboration with 

studies funded jointly by the Minerals Management Service and the United States Geologic 

Survey’s Biological Research Division (Love et al. 1999, 2001) designed collaboratively with 

very similar sampling protocols but over a much broader (Channel-wide) area. Thus, a more 

thorough comparison of the platform and natural reef fish assemblages would benefit greatly 

from analyses that include the combined datasets from these two studies. Indeed, recognizing 

the importance of such a comparison, the two studies were designed for this purpose. 

Also key to interpreting the results of our study is an explicit identification of the purpose of 

decommissioning activities and the creation of artificial reefs (Ambrose 1994, Carr and Hixon 

1997). One aim of decommissioning might be to produce more habitat similar to natural reefs, in 

order to expand spatial coverage and increase abundance of the overall natural fish assemblages 

in an area. Key to this purpose is identifying the area of the natural fish assemblage of interest. 

Different conclusions would be drawn for an area the size of our study versus the Channel-wide 

fish populations and assemblages that are likely to share larval recruitment with one another. For 

this purpose, managers and policy makers can use the results of our study to ascertain the extent 

to which the different decommissioning options would contribute to this purpose. If, on the 

other hand the aim is to enhance local or regional populations of economically or endangered 

species, regardless of their natural occurrence or abundance in the study area, our results have 

identified those species that inhabit platforms over the period of our study. Another important 

caveat for all these comparisons is the well-documented changes in region-wide populations and 

assemblages of fishes in response to large-scale climatic conditions (Stephens et al. 1986, 

Ebeling and Hixon 1991, Holbrook et al. 1997, Love et al 1998, Brooks et al. 2002). Thus, 

differences in fish assemblages on platforms and natural reefs may diminish the time period over 

which comparisons are made increases. Another critical aspect of this comparison is the effect 

of fishing on local population and assemblage structure, which is now confounded with these 

two habitat types. Fishing effort is strong on the natural reefs that we studied and the influence 

of this mortality on the size/age structure and density of targeted populations (as well as indirect 

effects on non-targeted species) may be pronounced as well. In contrast very little, if any, 

recreational and live-fish fishing has been allowed for many years on the platforms we studied. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

59

Thus, some of the differences we detected in population size structure, density and assemblage 

structure may simply reflect the effects of both the recreational and commercial live-fish fishery, 

rather than differences between habitat types. This is most likely for those species targeted by 

these two fisheries (e.g., kelp bass, sheephead, all rockfishes). 

Vertical Stratification of Fish Species and Life Stages on Platforms 

Our analyses of assemblage structure indicated time and again that the structure of fish 

assemblages on platforms and differences between these and assemblages on nearby natural reefs 

was strongly influenced by the vertical structure of the platforms. The abundance of many 

species varied markedly with depth along the height of platforms, and especially between the 

bottom and all shallower depth strata. Often, these depth-related differences were also related to 

the age/size of individuals. For example, the young of many shallow dwelling rockfish occurred 

only at the shallower depths sampled, whereas older stages (juveniles and adults) occurred more 

frequently at greater depths. These results have critical implications for the consequence of 

decommissioning options with respect to the subsequent occurrence or abundance of species and 

the structure of the fish assemblages on decommissioned platforms. Removal of the upper (20-

30 m) portion of platforms is likely to reduce the abundance of many species whose depth range 

was restricted to that portion of platforms. Moreover, to the extent that young fish that settle to 

the upper portion of platforms constitute an important prey source to the remainder of the fish 

assemblage (especially the midwater rockfish complex), reduced recruitment may translate into 

lower productivity of the fish assemblages associated with decommissioned platforms. In 

contrast, both the young and older stages of other species (many midwater rockfishes including 

olives, widows, bocaccio) occurred at depth, suggesting that recruitment and adult abundance of 

these species may not be reduced by the removal of the upper portions of platforms. Another 

consideration is the ecological role of sea mussel (Mytilus species) production on platforms and 

the restricted depth range of mussel beds (surface to 20 m depth). If platforms are 

decommissioned in a manner that eliminates structure in the upper 20-30 m of the water column, 

mussel production will be eliminated. To the extent that mussel beds provide habitat for fishes 

on platforms, and the mounds of mussel shell litter provide habitat for small fishes on the bottom 

beneath platforms, the survival and density of species reliant on such structure would be 

diminished if an alternative source of structure was not provided. Our observations and others 

(Love et al. 1999, 2000, 2001) suggest that the litter mounds beneath platforms are important 

sources of habitat structure for many juvenile rockfishes and other small fishes. These 

implications for changes in fish assemblages and overall fish density associated with platforms 

have been manifested on toppled platforms in the Gulf of Mexico. To fulfill Louisiana state 

monitoring requirement, hydroacoustic surveys are taken yearly to monitor fish populations at 

standing platforms versus toppled platforms (Kasprzak 2000). Results from these surveys have 

shown higher fish biomass associated with standing platforms relative to toppled platforms 

(Kasprzak, 2000). 

The robustness of our conclusions about the vertical stratification of fishes along platforms is 

supported in two ways. Firstly because many of the depth restrictions we detected were within 

the depth range sampled by divers. Thus, there was no confounding of different sampling 

methods used at different depths over the depth range that restricted distributions were recorded. 

Furthermore, the physical habitat (e.g., cross members) sampled at each depth stratum was 
Final Study Report – Carr et al 

60

similar. Secondly, our comparison of the effectiveness of sampling between the ROV and the 

divers both with respect to species composition and total fish density suggested, to our 

amazement, that the effectiveness of these two methods were sufficiently similar so as not to be a 

substantial source of bias. It is more likely that the depth-related differences we detected are due 

to real differences in species occurrence or abundance across the entire vertical extent of the 

platforms. Where sampling method was very likely to contribute to a bias in these species 

composition and density, is by underestimating the species at the bottom of the platforms. Here, 

reduced visibility and the very limited spatial coverage of sampling may have biased our 

estimates to underestimate either species or total fish density. 

Fish Movement Among Natural Reefs and Platforms 

Our limited re-capture data suggest rather limited movement for most species sampled. Indirect 

evidence, based on differences in the relative distribution of life stages, supports this pattern of 

restricted movement for both the Garibaldi and halfmoon. The relative density of both young 

and older Garibaldi and halfmoon was far greater on platforms than natural reefs. This was also 

the case for the many kelp-associated species (e.g. senorita, kelp bass) whose young and adults 

occurred only on natural reefs. However, indirect evidence, based on differences in the relative 

distribution of life stages, and movement data from other studies, suggests that some species do 

move between natural reefs and platforms. In particular, the greater relative density of young 

rockfishes on platforms, and more equitable density of adults between habitats, suggests either 

greater recruitment and subsequent emigration from platforms to natural reefs, or greater relative 

mortality of juveniles on platforms. Similar patterns exist for blacksmith and California 

sheephead. One possible example of recruitment to natural reefs and subsequent migration to 

platforms, though not strongly supported by our data, includes kelp bass. Small kelp bass (< 15 

cm) were rarely observed on our study platforms, but were present with older life stages on 

natural reefs (Figure 11). Large (> 15 cm) kelp bass, though relatively sparse on platforms, 

occurred there despite the paucity of young recruits. Combined with some evidence for limited 

movement in our study and greater movement observed by others (Love et al. 2001), these data 

suggest that platforms may not be suitable settlement habitat for larval kelp bass, but that 

juveniles, and adults especially, migrate in low numbers onto platforms after first recruiting 

elsewhere. Such equivocal results from our movement study, in which differential movement 

and differential mortality may both contribute to differences in the size structure of populations 

between habitat types, emphasizes the importance of assessing both relative survival and 

emigration of fishes on platforms and natural reefs. 

Relative Performance of Fishes on Platforms and Natural Reefs 

In addition to comparing the relative density and structure of fish populations and assemblages 

on platforms and natural reefs, ascertaining the relative performance (survival, growth and 

reproductive success) of a species in these two habitat types was the next most important 

ecological objective of our study. The ultimate objective of the ecological studies currently 

being conducted is to provide information that will inform predictions on the regional 

consequences of leaving, removing or relocating (i.e. adding) artificial structures. Unfortunately, 

no information exists on the state of fish populations or assemblages on natural reefs prior to the 

presence of the platforms. Therefore, analytical approaches based upon time series, such as 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

61

Before-After-Control-Impact (BACI; Stewart-Oaten et al. 1986, Stewart-Oaten 1996), are not 

applicable for either estimating the influence of the existing platforms or predicting responses to 

changes in their location or structure. Instead, information on the density and performance of 

fishes inhabiting each habitat type, seem the most logistically feasible approach to estimating 

region-wide platform effects and predicting the regional response to changes in these structures 

(see Alevizon and Gorham 1989, Ambrose and Swarbrick 1989, and Beets and Hixon 1994 for 

similar approaches). But it is critical to recognize the limitation of this approach as well. 

Because density is a critical response variable and is likely to have some effect on individual 

performance (growth, survival, reproduction), any estimate of performance must account for 

density. Performance, standardized by density, can be greater, equivalent, or lower on platforms 

relative to natural reefs. If performance on platforms is greater, than the presence of platforms 

(in their present configuration) are more likely to have a net benefit to a regional population. 

Even if fish have simply been redistributed from the natural to the artificial habitat, their greater 

performance there is likely to translate into a positive regional effect. This, of course, assumes 

that the fate of larvae and contribution to replenishment of the regional population is comparable 

to that of populations on natural reefs. If density-specific individual performance of a species on 

platforms is equivalent to that on natural reefs, then the regional effect is unlikely to be negative 

(at most, fishes have been redistributed but still performing as well) and may have a net positive 

effect (larvae that recruit to a platform may not have survived to recruit to a natural reef, thereby 

enhancing region-wide recruitment). Critical to this result is whether or not performance on 

natural reefs is resource limited and, therefore, density-dependent. If however, performance on 

platforms is less than natural reefs, the results are equivocal and potentially negative. The 

unknown balance between an unknown enhancement of regional recruitment (by intercepting 

larval recruits that would have otherwise no survived to recruit to natural habitat), and the poorer 

post-settlement performance in terms of survival, growth and reproduction, make it very difficult 

to estimate the net regional consequence of the presence of platforms. 

Two approaches are recommended for future progress in understanding the consequences of 

decommissioning options. First is the implementation of the comparative density-specific 

performance approach that we hoped to conduct in our study. Second, is an adaptive 

management approach based on observations of the response of regional populations to an 

experimental decommissioning. If monitoring of species composition, density and performance 

was conducted before and after the removal or relocation (i.e. addition) of a platform, much 

could be learned about the consequence of these activities. Such comparative time series 

approaches, most likely to be unreplicated (i.e. a single platform at a time) could employ 

analytical approaches such as BACI. A critical design constraint with this approach is 

identifying single or multiple natural “control” reefs similar to natural “impact” reefs, but also 

independent of the effects of the putative “impact” (i.e. addition or removal of a platform; 

Osenberg et. al. 2002). This design constraint is no different to that of identifying control reefs 

or control areas for assessing the effect of establishing marine reserves, plagued by the long 

dispersal potential of marine larvae, the openness of marine populations, and the great spatial 

scale over which marine populations potentially interact. 
Final Study Report – Carr et al 

62

Contribution of Platforms to the Abundance of Regional Reef Structure 

To our surprise, and after extensive and repeated efforts (see list of contacts in Methods section), 

we were unable to obtain geological maps of the resolution and coverage necessary to make our 

simple estimate of the relative contribution of platforms to the hard substratum throughout the 

Santa Barbara Channel region. Three aspects of this question are important considerations. 

First, and most simple, is what proportion of the total hard substratum (i.e. rocky reef) in the 

Channel platforms constitute. Based on the general amount of hard substratum in shallow 

regions of the Channel, including the Santa Barbara Channel Islands, this contribution is very 

small (Holbrook et. al. 2000). However, relative to the amount of hard substratum at the depths 

that platforms occur, this contribution may increase markedly. Moreover, there are no natural 

reefs with the physical relief comparable to platforms, especially at bottom depths that platforms 

occur. As such, these platform habitats are very unique. Thus, depending on the overall intent 

of creating artificial reef habitat, the relative contribution varies from miniscule if the purpose is 

to simply contribute to the overall natural reef habitat in the region, to 100% if the interest is for 

the unique habitat created by platforms. 

Future Recommendations 

We strongly recommend that studies be pursued to conduct those aspects of our proposed 

research that we were not able to complete. Most importantly, this should entail a study of the 

relative performance (survival, growth, reproduction) of species on platforms and natural reefs. 

We believe that this is the most direct line of evidence for assessing the contribution of platforms 

to the regional fish populations in the Santa Barbara Channel. Secondly, a comprehensive 

analysis of the type and amount of natural reef habitat throughout the Channel is critical to 

understanding the potential magnitude of decommissioning effects on the region-wide fish 

assemblage. Means to identify, collect and analyze existing maps, identify gaps in mapping data 

applicable to such an analysis, including coverage and resolution need to be developed and the 

appropriate analyses need to be conducted. Third, a more thorough and comprehensive 

comparison of the fishes that inhabit our study platforms and natural reefs throughout a broader 

area of the Channel should be conducted in collaboration with the Love et al. (2001) study 

designed for this purpose. Fourth, our study of fish movement would have benefited greatly by 

greater tagging effort and success at the platforms themselves. This was not accomplished for 

two critical reasons. We were not allowed to anchor and fish in close proximity to the platforms. 

This was because of the potential danger and costs of entangling an anchor in debris and cabling 

on the bottom around the platforms. Also, only smaller vessels could conduct such sampling in 

close proximity to the platforms and this would be too time and labor intensive for the scope of 

our study. If fishers could use the platforms themselves as platforms for collecting and tagging 

fishes to better estimate movement away from or retention on platforms, we would have a better 

understanding of the interaction and relationships between these platforms and nearby natural 

reefs. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

63

Section III: Ecological Information and the Development of 

Decommissioning Policy 

This section's focus is on the role of science and the scientific community in the development of 

offshore platform decommissioning policy. While we show that science and the scientific 

community are factors that contribute to the development of platform decommissioning policy, it 

is important to recognize that social, economic and perceptual factors associated with the Gulf 

states and California shape the politics and history of oil exploration, development and 

decommissioning policy (Freudenberg and Gramling 1994; Gramling 1996; McGinnis 1998). 

The social science literature shows that the history and politics of offshore oil development in 

southern California is very different from the Gulf experience. While this section does not 

provide a detailed overview of the diverse social, economic and political factors shaping 

decommissioning policy, McGinnis et al. (2001) show that environmental organizations and 

alliances played an important role in defeating policy initiatives for a rigs-to-reefs option to 

complete removal of offshore platforms in California while in the Gulf states, environmental 

groups have not taken a stand against state rigs-to-reefs program development. 

Methods 

Documentary Analysis 

The study included documentary analysis of technical, scientific, and government reports 

produced by policymakers, scientists and members of resource agencies on the subject of 

decommissioning of platforms and the rigs-to-reefs alternative to complete removal. For the 

Gulf of Mexico, material was collected from V.C. Reggio, Jr. of the Minerals Management 

Service (MMS) in 1998, who provided documents and technical reports on the historical 

development of the rigs-to-reefs alternative to the region. For the California OCS, material was 

collected in 1998 from Sacramento on state oil and gas activities. Material was also gathered at 

the MMS Pacific Region office in Ventura County, California and at the Santa Barbara County 

Energy Division. 

Analytical Framework: the “Revised Garbage Can” Model 

Kingdon (1995) provides a useful framework to characterize policy development. Kingdon 

(1995) uses a revised version of a classic essay by Cohen-March-Olsen (1972) on the “garbage 

can model of organizational choice” to explain the politics of agenda setting and policy 

generation. 

Kingdon (1995) describes the policy making process as chaotic and turbulent. Public choices are 

not always based on scientific understanding. This type of political process operates on the basis 

of “trial and error”, “learning from accidents of past experiences, “ or on the basis of “inventions 

of necessity” (Cohen, March and Olsen 1972: 1). Choices are based on a variety of “inconsistent 

and ill-defined preferences”, according to Cohen, March and Olsen (1972: 1-2), “To understand 

processes ... one can view a choice opportunity as in a garbage can into which various kinds of 

problems and solutions are dumped by participants as they are generated.” 
Final Study Report – Carr et al 

64

Ideas are generated by policy “entrepreneurs”, specialists, techno-experts in government, 

industry or non-government organization. Kingdon (1995) and other social scientists (such as 

Anton 1989 among others) describe the policy entrepreneur as an advocate who plays the 

fundamental role in “opening” a policy window by offering a solution to a perceived problem. 

These solutions are not only based on some level of scientific information but perceptions and 

values as well. This process of exchange of information, partisan mutual adjustment, and 

communication is dynamic and fluid. Political elites and other participants in the process can act 

as policy entrepreneurs. 

The specialist, technocrat, bureaucrat, policy elite, and expert play the role of policy 

entrepreneur. “Many ideas are possible in principle,” notes Kingdon (1995: 19), “and float 

around in a primeval soup in which specialists try out their ideas in a variety of ways – bill 

introductions, speeches, testimony, papers and conversation.” The policy entrepreneur identifies

the problem and offers solutions. Without the entrepreneur, the idea will remain floating in the 

“primeval soup”. Experts, specialists, and policy elites couple solutions to problems and couple 

“problems and solutions to politics” (Kingdon 1995: 20). 

The capability of the entrepreneur to open “policy windows” and set government agendas 

depends on three separate, but interrelated, processes: 

• Problems: the set of issues in particular public policy areas that come to capture the 

attention of those in and around government at any one time; 

• Policy articulation: a process involving gradual accumulation of knowledge and 

perspectives among specialists in a policy area, and the resulting generation of policy 

proposals by those specialists; 

• Politics: trends and events in the overall political environments, such as interest group 

campaigns and administrative changes. 

Kingdon metaphorically refers to these processes as separate “streams” -- the political, problem 

and policy stream.2

 Policy change can occur when the streams join to form a “policy window of 

opportunity”. The window opens when the political climate is ripe for policy change, when a 

problem is recognized by political elites, and when a solution is successfully developed and 

proposed by policy “entrepreneurs”. Kingdon’s model and framework are used here to show that 

there is a political ecology to decommissioning policymaking in the Gulf and California OCS. 

 

2

 Kingdon’s model is based on the earlier work of Michael Cohen, James March and Johan Olsen, “A Garbage Can 

Model of Organizational Choice, “ Administrative Science Quarterly 17 (March 1972): 1-25. Cohen et al. argue that 

“...organizations can be viewed for some purposes as collections of choices looking for problems, issues and 

feelings looking for decision situations in which they might be aired, solutions looking for issues to which they 

might be an answer, and decision makers looking for work.” The Cohen et al. “garbage can model” is the 

foundation for Kingdon’s framework to study agenda setting. For a critique of the “garbage can model” see Gary 

Mucciaroni, “The Garbage Can Model and the Study of Policy Making: A Critique,” Polity, Vol. 24, 3 (Spring 

1992): 459-482. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

65

Results 

Work on this section of the report contributed to and therefore draws upon the analysis of 

McGinnis et al. (2001) that compares the Gulf States and the West Coast decommissioning 

policy. 

Political Ecology of Decommissioning Policy Development in the Gulf of Mexico 

This section describes how and why the policy of decommissioning platforms at sea as artificial 

reefs evolved in the distinct political, intergovernmental, regional and ecological context of the 

Gulf of Mexico. It describes how each of the political, problem and policy streams met to form a 

window of opportunity for the development of such a policy. Various policy entrepreneurs from 

the MMS, oil and fishing industries, and others advocated the idea of what became known as a 

“rigs-to-reefs” alternative to complete removal of Gulf Outer Continental Shelf (OCS) oil 

platforms (Reggio 1987a, b, Reggio and Kasprzak 1991, Murray 1994). Reggio, from the Gulf 

Region of the Minerals Management Service (MMS), and Kasprzak, from the Louisiana State 

University, (1991: 15) explain: 

[T]here are ever increasing demands on marine fish and restrictions on fishing. 

Through state and industry leadership, we have an unprecedented opportunity in the 

Gulf of Mexico to create artificial reefs with oil and gas structures, which will 

concentrate marine life and enhance fishing. 

The Gulf’s commercial and recreational fisheries are the largest in the United States. Fishing 

activity in the region is supported by a history of large-scale OCS oil and gas activity in the Gulf. 

This has led to “over-adaptation” to these platforms as fishery enhancement structures. There 

are currently approximately 4,000 platforms in the Gulf of Mexico, and it is estimated that 150 

per year will be decommissioned. This significant development of offshore oil on the TexasLouisiana OCS has led to a network of artificial habitats or “organic machines” that either attract 

or produce species that are harvested by the commercial and recreational fisheries. In the Gulf 

OCS, removal of offshore platforms would have associated economic impacts (and potential 

ecological impacts) to these fisheries. Removal of a platform would mean the removal of a 

“fishing hole”, such as the removal of the “best snapper fishery in the world” offshore Alabama 

(a state with very little natural habitat for reef fishes). 

Why was complete removal of offshore platforms a “perceived problem”? There are many 

reasons, some of which are introduced below: 

• Field studies show the lack of “natural” habitat for fish in the Gulf region. Field 

studies also show the link between offshore platforms and marine life, including 

commercially and recreationally valuable finfishes and oysters. 

• Social scientists show the link (in terms of recreation days and levels of use) between 

offshore platforms and sportfishing. State, regional and local economies benefit from 

offshore oil and gas activity, and artificial reef building (in Florida, Alabama, 

Louisiana, Mississippi, and Texas). 
Final Study Report – Carr et al 

66

• In the Gulf, commercial and recreational fishing groups have been receptive to the oil 

industry (Freudenberg and Grambling 1994; Grambling 1996). Special interests in 

the Gulf sought out a OCS policy that could provide guidance, coordinate local, state, 

and federals efforts as well as streamline the permitting process for the rigs-to-reefs 

alternative. 

• Gulf state governments had artificial reef programs in place, many of which were 

operated by local and regional administrators on a part-time basis or as volunteers. 

There was no major state-based funding or private source to develop and implement 

artificial reef programs. Alabama established the first program in the Gulf of Mexico 

in 1954. Alabama’s program started with the sinking of 250 car bodies and now 

includes several thousand individual artificial reefs in state waters (Harrison 2000). 

 

• A number of policy entrepreneurs and advocates campaigned for the rigs-to-reefs 

alternative, basing their preferences on available scientific information, and fishery 

values associated with offshore structures. 

This section shows that the passage of the National Fisheries Enhancement Act (NFEA) was 

followed by the creation of formal state artificial reef programs in Louisiana (1986), Texas 

(1989), Florida (1990), and Mississippi (1999). 

The Problem Stream: The Perceived Lack of Reef Habitat 

The reliance of commercial and recreational fishers on OCS oil and gas structures contributed to 

a perceived problem --- complete removal of structures would have significant economic impacts 

on the fisheries of species associated with these structures. Policy entrepreneurs defined the 

problem based on the perceived lack of natural fishery habitat in the Gulf, and the link between 

the development of offshore oil and commercial and recreational fishing. As Reggio (1987a: 2) 

writes, “Since the inception of the federal offshore leasing program in 1954, the Gulf of Mexico 

OCS Region has led the nation in offshore energy production and has retained its pre-eminence 

in offshore fishery production.” The ecology of the Gulf, the history of Gulf OCS oil 

development, the relationship between offshore oil development and fishing (such as commercial 

hook-and-line fishing) and scuba diving were also factors associated with the problem stream. 

Within the Gulf, accumulation of sedimentary layers since the beginning of the Tertiary period 

created a continental slope (0 to 200 m) that now makes up nearly 35% of the bottom habitat, 

with 25% being very deep water (>3000 m) and reaching a maximum depth of 3850 meters 

(Darnell & Defenbaugh 1990). The northern shelf and slope offshore Texas and Louisiana 

receive extensive accumulations of sediment from stream, estuarine, and river discharges. Riverborne sediments composed of silt, sand, clay and anthropogenic pollutants create a soft bottom 

habitat that stretches from the coastline to the middle and outer shelf off most of Louisiana and 

Texas (Darnell & Defenbaugh 1990). Although occasional small shoals and rocky ridges occur 

throughout the Gulf OCS, the broad and vast area lacks hard-bottom habitat. Only one-third of 

the estimated natural reef habitat is located offshore Texas and Louisiana where more than 95% 

of the platforms stand. The nearest natural hard-bottom habitat is located approximately 92 km 

offshore Louisiana (Sonnier et al. 1976). Nearly 4,000 offshore production platforms and 22,000 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

67

miles of oil and gas pipelines exist within the Gulf of Mexico (MMS 2000). Ranging in size and 

structure, the average depth of these platforms is 100 to 300 feet in state and federal waters. 

Most of the oil and gas structures are set in the soft, sandy bottom of the Gulf where there exists 

very little hard substrate for natural reefs (Sonnier et al. 1976). The platforms of the TexasLouisiana OCS have created a web of artificial habitats for some marine life. There is some 

indication that platform development increases the amount of habitat available for marine species 

that depend on hard bottom substrates (Sonnier et al. 1976, Continental Shelf Associates 1982, 

Gallaway and Lewbel 1982). Filter feeding organisms proliferate on the platform structures, 

providing food and shelter for economically valuable and commercially and recreationally 

sought fish species (Sonnier et al. 1976, Wolf et al. 1979, Gallaway & Lewbel 1982, Gallaway et 

al. 1988). Underwater platforms structures serve as a point of concentration for many biofouling 

organisms (Wolf et al. 1979). Marine studies describe the biofouling community associated with 

platforms as rich and diverse (Sonnier et al. 1976, Gallaway and Lewbel 1982, Gallaway et al. 

1988). The colonial species provide additional habitat for small and motile, cryptic organisms 

such as ophioroids and caprellid and gammarind amphipods who feed on the abundant food 

supply and in turn are consumed by fishes (Gallaway et al. 1988, Gallaway and Lewbel 1982). 

The increased biological activity associated with platforms attracts a wide variety of fish species 

from the sea surface to the bottom of the platforms (Continental Shelf Associates 1982, 

Gallaway and Lewbel 1982, Gallaway et al. 1988, LGL and SAIC 1988, Sonnier et al. 1976). 

Following the installation of a new platform, fish colonization can occur in as little as 15 months 

(Lukens 1983) in search of food and/or shelter (Gallaway 1982). Dressen (1989) estimates that 

nearly 20-50% more fish occur beneath or adjacent to platforms compared to nearby soft bottom 

areas in the Gulf. Fish assemblages vary from a few hundred individuals to a few thousand, 

depending on platform, size, location and season (Continental Shelf Associates 1982). Stanley 

and Wilson (1990) surveyed catch records from recreational and charter boat anglers in the 

northern Gulf and found that the fish species and number caught varied with season, platform 

size and structural complexity, and water depth. 

The Perceived Problem--More than one-quarter of the remaining platforms in the Gulf are over 

25 years old, and may be removed within the next ten years (MMS 2000). This means that 

nearly one thousand structures may be removed in the next ten years. But offshore oil and gas 

activity over the past fifty years has contributed to the development of commercial and 

recreational fishing. For this reason, a number of government and non-government organizations 

began to “campaign for changes in public attitudes and existing laws to facilitate use of 

petroleum platforms as artificial reefs for fish concentration” (Harville 1983: 5). The oil and gas 

industry was also anxious to cooperate with responsible reef developers willing and able to 

accept future responsibility and liability for rigs-to-reefs projects (DuBose 1984, Reggio 1987a). 

A strong coalition of fishery and oil interest groups had emerged during a long history of oil 

development in the Gulf OCS region (Freudenberg & Grambling 1994, Grambling 1996). In 

addition, many coastal inhabitants of the Gulf regularly fish coastal and marine waters for 

recreation, sport, commerce, and subsistence. 

The southeastern recreational fisheries are the largest in the nation. Between 1955 and 1980, 

participation in saltwater recreational fishing increased 2.7 times and related expenditures grew 
Final Study Report – Carr et al 

68

sevenfold. In 1998, 5.8 million anglers took 53 million trips and caught 284 million fish, 

nationwide (NMFS 1998). The increased interest in sportfishing is attributed to advances in 

technological design of recreational motorboats, outboard motors, navigational equipment and 

gear (NMFS 1999). Recreational fishermen operate from private boats, charter boats, head boats 

and shore using fish traps, hooks and lines, longlines, spears, trammel nets, bang sticks and 

barrier nets (NMFS 1999). 

As the number of platforms dominated the Texas-Louisiana shelf, commercial and recreational 

harvest efforts became more concentrated around the structures. Studies document the levels of 

fishing activity near or around platforms. During the 1960s, Gulf newspapers and magazines 

featured the “fabulous” sites associated with rig structures (Reggio and Kasprzak 1991). Gunter 

(1955) describes the area between Pascagoula, Mississippi and Port Arthur, Texas as the “Fertile 

Fisheries Crescent” claiming it contains the most productive waters on earth. Oil platforms 

became a principal fishing destination for many local recreational fishermen (Ditton & Graefe 

1978, Dugas, et al. 1979). In Louisiana, over 70% of all recreational angling trips occur near the 

platforms in Federal waters (Reggio 1987). 

Ditton and Graefe (1978) showed that 87% of registered sport-fishing boats from Galveston, 

Texas target the platforms for fishing. One half of the 66,924 offshore fishing trips by resident 

boat owners in Galveston and eight adjacent counties, were primarily to the platforms (Ditton 

and Graefe 1978). One MMS survey (conducted in 1980) of offshore platform personnel on 300 

platform structures offshore Texas and Louisiana shows that employees also fish off the 

structures. Stanley and Wilson (1989) found that the average distance traveled by recreational 

users was at least 62 km to the platform, and the distance increased from east to west and from 

anglers to divers. 

Commercial fisheries harvest in the Gulf of Mexico lead the nation. From 1950 to 1998, 

commercial landings totaled more than 34 million metric tons and generated more than $1.8 

billion in dockside revenues (NMFS 1999). Louisiana accounted for nearly 65 percent (22 

million metric tons) of the landings and 38 percent ($22 million) of the revenues (NMFS 2000). 

Texas holds the second largest fishery, contributing 2.7 million metric tons of commercial 

landings and generating $5 million in dockside revenues (NMFS 1999). 

Overall, the recreational fishing industry has grown significantly since the first platform was 

placed in Louisiana waters in 1947 (GSMFC 1997, Howe 1985). Fishers have benefited from 

the increased biological activity associated with offshore platforms. As the number of removals 

increased from one year to the next, fishers became alarmed by the loss of habitat and reduction 

in fishing opportunities (Kasprzak 2000). The reduction in available habitat from the removal of 

platforms has unknown consequences to fish populations. At the very least, a huge amount of 

reef fish biomass is lost and fishes move to other places. As regular users of offshore platform 

structures, the sport fishing clubs, local artificial reef committees and dive clubs actively 

advocated the benefits of converting obsolete platforms into artificial reefs for fishery 

enhancement. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

69

The Political Stream 

The Gulf of Mexico contains approximately two-thirds of the world’s offshore oil and gas 

structures, and 95% of the production platforms in waters off the coast of the Unites States 

(Reggio and Kasprzak 1991: 11). A coalition of oil and fishery interest groups, federal and state 

resource agency personnel, and other individuals, such as Congressional representatives, favored 

a platforms-to-artificial reef alternative to complete removal of Gulf OCS oil and gas facilities. 

For example, in 1979, the Sport Fishing Institute initiated action by urging a resolution to the 

Secretary of Commerce and the Secretary of the Interior to develop policies, procedures and 

guidelines to convert platforms to artificial reefs. The Sports Fishing Institute also pointed out 

the importance of existing artificial reefs in the Gulf to fisheries. 

Early Artificial Reef Program Development -- Local governments, private parties and individuals 

have carried out artificial reef programs in the Gulf of Mexico since the 1940s and 1950s. In 

1954, Alabama initiated the first artificial reef program in the Gulf. Natural reefs are virtually 

nonexistent in Alabama waters. As a result of artificial reef building, the state is now referred to 

as the “Red Snapper Capital of the World”, because Alabama waters provide the highest catch of 

red snapper in the Gulf (Harrison 2000). Since the late 1940s, the Texas Parks and Wildlife 

Department has also been involved in artificial reef activities, such as the development of oyster 

reefs in Texas bays since 1947 (Joyce 1981, Osburn & Culbertson 1993). Some of the materials 

used during the 1940s and 1950s were not durable enough to withstand the shifting currents and 

eventually dissolved or moved to an unknown location. Used cars and vessels have also been 

used (Joyce 1981, Osburn & Culbertson 1993). In Louisiana, local fishermen created small 

artificial reef sites in an effort to increase their personal fish catch (Kasprzak 2000). Early 

artificial reef development in this state was not part of a state artificial reef program. Unwanted 

materials such as old automobiles, large appliances, and concrete rubble were dumped in secret 

locations in estuaries and coastal waters to create personal fishing areas (Kasprzak 2000). 

Since 1978, several divisions with the Florida Department of Natural Resources have been 

involved with artificial reef activities to enhance fishery habitat (Joyce 1981). In 1980, the State 

of Florida set the precedent and made an important step toward the development of a rigs-toreefs alternative. Through the cooperative effort between the Southeastern Fisheries 

Association, the Gulf and South Atlantic Fisheries Development Foundation, Exxon Corporation 

and the State of Florida, an oil production template was removed and transported from Louisiana 

waters to Florida offshore waters for use at an artificial reef site (Joyce 1981, Wilson & Van 

Sickle 1987). The oil industry has also contributed offshore structures to fishery enhancement 

projects. In 1980, a joint effort between Exxon and Florida’s Department of Natural Resources 

permitted the towing of a 2,200 ton submerged production system from Louisiana waters to a 

pre-selected site in Florida (Wilson and Van Sickle 1987). The structure was placed without an 

underwater survey of the site before placement (Mathews 1985). Two years after the Exxon 

project, Tenneco Oil donated a production platform removed from offshore Louisiana. The 

structure was towed 275 miles and placed offshore Pensacola, Florida (Frishman 1982, Bohnsack 

and Sutherland 1985). The following year, the Alabama Department of Conservation and 

Natural Resources permitted Marathon Oil Company to tow a 1,650 ton oil platform 220 miles 

from Louisiana waters to southeast Mobile, Alabama (Wilson and Van Sickle 1987).3

 

3

 On October 2, 1985, two more Tenneco structures were towed 920 miles from Louisiana to 1.5 miles off Dade 
Final Study Report – Carr et al 

70

By the end of 2000, many materials such as used automobiles, refrigerators, derelict ships, 

concrete rubble and other structures (such as military tanks and oil structures) have been used to 

construct over 150 permitted artificial reefs off Florida, Alabama, Mississippi, and Texas 

(Reggio personal communication, 2000). Three-fourths of all the existing, dedicated, or 

permitted reef sites in the Gulf are off the west coast of Florida and the Florida Keys (Reggio and 

Kasprzak 1991). Advocacy of artificial reef building has a long history in the Gulf. In 1979, the 

American Fisheries Society and Sport Fishing Institute supported artificial reef building in the 

Gulf (Harville 1983). 

Since the late 1970s, the National Marine Fisheries Service (NMFS) has supported artificial reef 

research through technical and financial assistance to states, counties, and private interests 

(Harville 1983). NMFS has participated in artificial reef planning, design, permitting, 

construction, monitoring and evaluation (GSMFC 1993). The MMS also supported converting 

obsolete oil and gas structures to artificial reefs. MMS sponsored “Information Transfer 

Meetings” in 1982, 1984, 1985, 1986, and 1987, which included sessions on present and 

potential fishery uses of oil and gas structures. Reflecting on these public forums and 

information transfer meetings, Reggio and Kasprzak (1991: 10-11) write: 

Public forums organized and sponsored by the MMS in a series of annual information 

transfer meetings during the 1980s elicited additional information on the present and 

potential fishery uses of oil and gas structures. Federal and state conservation officials, 

private conservation groups, fishing organizations, oil and gas companies, university 

researchers, and others encouraged the conversion and use of oil and gas structures as 

artificial reefs. Workshops included a review of data available and information on Gulf 

fisheries, and explored the economic, social, political, biological and technical benefits of a 

rigs-to-reefs alternative. 

In August 1983, Secretary of Interior, James Watt created the Recreation, Environmental 

Enhancement and Fishing in the Sea (REEFS) task force to “pave the way for aggressive 

movement towards a national rigs-to-reefs program which will enhance fishery resources and 

improve recreational and sport fishing opportunities within America’s offshore marine 

environments.” (DuBose 1985). The primary agenda of the REEF task force was to assess the 

use of obsolete platforms as artificial reefs as a means to enhance local fisheries and to develop 

policy that set national standards for artificial reef building. 

The Policy Stream 

Most ideas never find the light of day. Ideas that survive to shape public policy in a dynamic 

intergovernmental process must meet several criteria, including their scientific merit, their fit 

with dominant values, and the political support or opposition that ideas may experience. 

The Role of the Scientific Community--As the number of platforms increased in the Gulf, the 

number of scientific studies on the economic benefits of offshore platforms also increased. Since 

the 1950s, a number of field studies have described the invertebrate species, fish species and the 

 

County, Florida (Wilson and Van Sickle, 1987). 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

71

impact of potential pollutants on waters and biota associated with offshore platforms. The 

Offshore Ecological Investigation (1972 to 1974) by the Gulf Universities Research Consortium 

(GURC) investigated the sedimentology, hydrography, microbiology, plankton, benthos, biofouling communities, trace metals, and hydrocarbons associated with platforms sited in 

Louisiana bays and inner shelf. Sonnier, et al. (1976) compared natural reef fish assemblages to 

fish fauna associated with offshore platforms in the Gulf of Mexico. 

Interest spread to government agencies, particularly the MMS, who funded a number of largescale, multi-year scientific projects. For example, MMS sponsored a $4.4 million study in 

cooperation with Texas A&M University and the oil industry to assess the environmental 

impacts on the benthos surrounding oil platforms. The study, known as the Gulf of Mexico 

Offshore Monitoring Experiment (GOOMEX), was intended to provide detailed information on 

the biological, geological, and chemical impacts of discharged effluents on the surrounding 

marine biota.

The Move to the Federal Level: Congressional Activity--The heightened awareness of 

converting rigs-to-reefs for fisheries enhancement among commercial and recreational user 

groups and the need to coordinate state and local efforts initiated hearings before the 

Congressional Subcommittee on Fisheries and Wildlife Conservation and the Environment on 

September 11, 1981. State representatives from Louisiana (John Breaux), New Jersey (William 

Hughes and Edwin Forsythe) and Rhode Island (Claudine Schneider) introduced two bills, H.R. 

1041 and H.R. 1897, to: (1) develop marine artificial reefs in U.S. waters and, (2) provide funds 

to develop, maintain, and monitor offshore artificial reef sites. 

The two bills, H.R. 1041 and H.R. 1897, designated the NMFS the primary responsibility to 

fund, develop, and monitor Gulf state artificial reef activities. The two bills stipulated that any 

construction of a “fishery conservation zone” (3 to 200 nautical miles) could only be constructed 

by the NMFS. Despite the fact that both of these bills were defeated, the bills demonstrate the 

idea for the need of federal backing for an artificial reef plan. One important policy entrepreneur 

Congressman John Breaux expressed his support for the development of a comprehensive 

artificial reef program for the Gulf as follows: 

“We are missing a golden opportunity. There is, for example an oil and gas industry out 

there that has thousands of platforms that are going to have to be dismantled and towed in 

and broken up at a great deal of expense. It would be cheaper to be able to cut those and use 

them as artificial reefs. I think a coordinated policy could be greatly beneficial to both the 

fishing industry and the people who own those structures. If we need to change, or draft new 

legislation that would allow them to do that, I believe we should.” 

Two years later, on July 18, 1983 Congressman John Breaux of Louisiana along with 17 other 

members of Congress introduced H.R. 3474 in an effort to establish a national artificial reef 

policy. Testimony from federal, state and local agencies as well as user groups and 

environmental organizations supported the establishment of a comprehensive federal artificial 

reef program that included the rigs-to-reefs option. Some portions of the bill were amended and 

it was reintroduced as H.R. 5474. The amendments were approved and passed on April 12, 

1984. 
Final Study Report – Carr et al 

72

The political stream included Congressional representatives, federal and state resource agency 

personnel, members of the oil and fishery industries who supported the idea of the rigs-to-reefs 

alternative to complete removal of offshore oil structures in the Gulf. Various studies of the 

marine ecology and socio-economic uses associated with commercial and sports fishing also 

supported the idea of the platforms to reefs alternative. MMS personnel (such as Villere Reggio) 

and other resource managers and scientists played a major role in promoting the use of platforms 

as artificial reefs to enhance fisheries. These individuals acted as policy entrepreneurs, pushing 

and advocating their particular proposals and ideas in the intergovernmental policymaking 

process. 

The rigs-to-reefs “idea” was less an invention and more a mutation of an old idea. The rigs-toreefs idea represented the coupling of an already familiar activity of building artificial reefs in 

the Gulf. The use of familiar ideas, such as the idea of artificial reef building in the Gulf, by 

policy entrepreneurs and experts is referred to by Kingdon (1995: 201) as the “act of 

recombination”. The rigs-to-reef policy idea represented a recombination of an old solution (the 

reliance on artificial reefs to enhance fisheries) to a perceived new problem (the lack of natural 

habitat and potential economic impacts associated with complete removal of OCS oil and gas 

structures). 

The Window of Opportunity: Passage of the National Fisheries Enhancement Act of 1984--The 

National Fishing Enhancement Act (NFEA) of 1984 (Title II of Public Law 98-623) was passed 

by Congress and signed into law by President Reagan on November 8, 1984. The NFEA defines 

an artificial reef as “a structure which is constructed or placed...for the purpose of enhancing 

fishery resources and commercial and recreational opportunities.” The NFEA states the 

following: 

Properly designed, constructed, and located artificial reefs...can enhance the habitat and 

diversity of fishery resources; enhance recreational and commercial fishing opportunities; 

increase the production of fishery products in the United States; increase the energy 

efficiency of recreational and commercial fisheries; and contribute to the United States 

coastal economies. 

The NFEA consolidated several decades of localized and state laws to maximize the potential 

benefits of artificial reefs as fishery enhancement mechanisms. State governments are 

responsible for carrying out the general goals of the NFEA in federal and state waters by 

funding, promoting, and maintaining artificial reefs. The NFEA provides a foundation for the 

establishment of a national artificial reef program based on the following goals: to (1) enhance 

fishery resources; (2) facilitate access for recreation and commercial fishing; (3) lessen conflicts 

between users of marine resources; (4) minimize environmental risks; (5) follow principles of 

international law; (6) prevent unreasonable obstruction to navigation; and (7) promote 

consistency with the National Artificial Reef Plan. The NFEA directed the NMFS to develop the 

National Artificial Reef Plan within one year. The Plan was published one year later through the 

combined efforts of fishermen, divers, scientists, state and federal resource agencies (Stone 

1985; Harrison 2000). The Plan serves three purposes: 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

73

1. To provide guidance to individuals, organizations, and government agencies on technical 

aspects of artificial reef planning, design, siting, construction, and management for effective 

artificial reef development; 

2. To serve as a reference for federal and state resource agencies involved in artificial reef 

permitting; and 

3. To ensure that the national standards and objectives established by the NFEA are met. 

The Plan serves as one guide to develop state artificial reef programs. It includes information 

on design criteria, permit compliance, management methods, and ideas for increasing 

artificial reef development. In addition, the Plan emphasizes the need for research and 

monitoring of artificial reef activity. 

Federal Guidance and Assistance4--Since the NMFS developed and published the Plan, they 

have continued to support regional, state, and local artificial reef development activities. The 

NMFS provides technical consultation, resources, and contributes to various regional artificial 

reef management committees established by interstate marine fisheries commissions. 

The U.S. Fish and Wildlife Service administers the Federal Aid in Sport Fish Restoration 

Program (U.S.C. Sec 777), which provides funding for important recreational fisheries work. 

Coastal states in Region 4 (North Carolina, South Carolina, Georgia, Florida, Alabama, 

Mississippi, and Louisiana) and Region 2 (Texas) of the Service can apply for funds from the 

Federal Aid for sport fish restoration and boating projects. Money for this program is collected 

from taxes placed on fishing tackle and motorboat fuel. In 1984, the Wallop Breaux amendment 

to the Sport Fish Restoration Act allocated funds for use in artificial reef programs. 

MMS amended its guidelines on the “Disposal of Oil Platforms” to reflect the goals of the 

NFEA. MMS’s new policy statement encourages the “reuse of obsolete offshore petroleum 

structures as artificial reefs in US waters” so long as the structures do not “pose an unreasonable 

impediment to future mineral development”. MMS also provides information to state programs, 

such a geophysical data, offshore area/lease block maps, bathymetric maps, pipeline and 

platform location maps, numerous technical reports and environmental impact statements, and 

visuals (maps that illustrate bottom sediment types, oceanographic currents, shrimp trawling 

areas, etc.; MMS 2000). 

The Permits and Evaluation Branch of the Corps of Engineers (COE) regulates planning and 

development activities in OCS under the jurisdiction of the Rivers and Harbors Act of 1899, the 

National Environmental Protection Act of 1969, the Clean Water Act of 1972, and the Marine 

Protection Research and Sanctuaries Act of 1972. It is the lead federal agency that permits and 

monitors artificial reef development under NFEA. All state natural resource agencies must 

obtain a COE permit before any construction of an artificial reef site. The COE reviews the 

 

4

 A comprehensive review of policy and regulatory issues associated with decommissioning of OCS oil and gas 

structures is found in County of Santa Barbara Energy Division (July 2000). This information will not be reviewed 

in this section.
Final Study Report – Carr et al 

74

permit, inspects the materials and then issues the appropriate permit or makes recommendations 

to improve the permit application. 

Gulf State Artificial Reef Programs5 in the era of NFEA--In the Gulf, the primary purpose of the 

platforms to reefs policy is to enhance fisheries (Murray 1994). Since the implementation of the 

Plan of 1985, most state marine fisheries agencies have assumed the lead in developing artificial 

reefs through state developed programs. State natural resources agencies currently direct or 

coordinate with local agencies in obtaining permits, maintaining liability, financing, 

constructing, researching and monitoring marine artificial reefs. Many coastal states have 

adopted state-specific plans based on the guidance of NFEA. 

Louisiana was the first among the Gulf states to create a formal artificial reef program. Passed in 

1986, the Louisiana Fishing Enhancement Act (Act 100) is the most comprehensive reefing 

policy and program in the Gulf (Murray 1994). The Act provides for: 1) establishment of the 

artificial reef program, 2) creation of the Louisiana Artificial Reef Council, 3) establishment of a 

Louisiana Artificial Reef Development Fund, 4) development of a reef plan, 5) establishment of 

the state as the permittee for artificial reefs developed under the plan, and 6) relief from liability 

(Wilson and Van Sickle 1987). The Louisiana Act sets up a means to transfer the ownership and 

liability of the platforms from the oil and gas companies to the State when the platform ceases its 

production. The Plan established an Artificial Reef Trust Fund for funding costs associated with 

each artificial reef project (Kasprzak 2000). When oil and gas companies donate platform 

structures, they are asked to donate half of the cost savings for participation directly into the trust 

fund. As of 2000, the Artificial Reef Trust Fund has accrued $13 million and uses the 5% 

interest to fund the artificial reef program (Kasprzak 2000). Since 1987, the Louisiana Artificial 

Reef Program has created 25 artificial reef sites that utilize 85 obsolete platform jackets and/or 

parts. Approximately 7-10 platforms are donated per year as platforms become available 

(Kasprzak 2000). Most of the reef development spans between 30 to 70 miles offshore and 

extends down a minimum of 50 feet from the surface to satisfy Coast Guard navigational 

guidelines. A discussion of the other Gulf state programs is found in McGinnis and Navaro 

(2001), and will not be summarized in this section. 

Political Ecology of Decommissioning Policy in the Southern California Bight 

The California experience with the rigs-to-reefs option to complete removal of offshore oil 

platforms is very different from the political ecology that has shaped program development in the 

Gulf of Mexico (McGinnis 1998). The political debate is shaped by the ecological setting of the 

Southern California Bight, which is a marine area between Point Conception and Punta Banda in 

Baja California, Mexico. 

The politics of California decommissioning policy includes such issues as the question of 

“attraction versus production”, liability considerations, and funding to administer a potential 

rigs-to-reefs program. These are similar issues that are also found in the Gulf of Mexico states 

artificial reef programs. As in the case of the Gulf of Mexico, there are recreational fishing 

 

5

 This report and section is not intended to provide a comprehensive review of state artificial reef programs but 

rather a characterization of the historical development of the rigs-to-reefs alternative. In addition to the state 

programs that are described in this section, Alabama and Mississippi have artificial reef programs. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

75

interests who support the use of offshore oil platforms as artificial reefs in southern California. 

For example, in California rockfish represent $3 billion in sports fishing values and between 

$200 to 300 million annually in commercial landings. Like the ecological surveys presented in 

this report, other studies suggests that the vast majority of fishes near some platforms are 

rockfishes (Love and Westphal 1990, Love et al. 1999a,b, 2000, 2001). Populations of rockfish 

off southern California -- an area within the Southern California Bight that includes about 70 

species of fish harvested by both recreational and commercial fisherman -- have dropped to 8% 

of their 1960 populations (Love et al 1998). The significant decline of several rockfish species 

reflects the combined effects of long-term (decades) climatic conditions of low productivity 

(which began in 1977) and fishing mortality by recreational and commercial fishers (McGinnis 

2001, Schroeder and Love 2002). Field studies show that some platforms in the Santa Barbara 

Channel include juvenile and adult bocaccio, Sebastes paucispinis, (Love et al. 2000). This 

species has been listed as a threatened fishery (Pacific Marine Conservation Council 1999).6

Despite the recreational fishing values associated with offshore platforms, the California 

experience with the rigs-to-reefs initiative represents a departure from the federal and Gulf states 

program development. Recent evidence in the decline of several marine species during the warm 

water regime of the Southern California Bight led State Senator Alpert on behalf of the 

recreational fishing and oil industry to support a rigs-to-reefs alternative to complete removal 

(McGinnis et al. 2001).7

 Pomeroy, in McGinnis et al. (2001), characterizes the major actors and 

interest groups that have been involved in the California debate over the rigs-to-reefs option. 

Albert’s SB 241 (2000) failed in the California Legislature while SB 1 was vetoed by the 

Governor in 2001. Pomeroy writes: 

The growth in public concern for the marine environment between the time of its 

introduction in early 1998 and its re-introduction in 1999 (and 2000) led to the clear 

identification of the problems a rig-to-reef program could help to address. During 

that time, the proposal was re-shaped to address some of its deficiencies, and over 

its two-year course through the legislature as SB 241, it underwent further 

refinement to address critical issues including program funding, scientific merit and 

liability. Moreover, it was reshaped to mesh with state and federal fishery (and 

other marine) management resource management, especially recent policy changes 

and new concepts pertaining to marine resource restoration, marine reserves, and 

essential fish habitat. 

Yet the rig-to-reef policy proposal embodied in SB 241 has fallen short in meeting these 

and other myriad concerns. Uncertainties regarding liability issues, start-up and ongoing 

 

6 In February 2001, the Center for Marine Conservation, the National Resources Defense Council and the Center for 

Biodiversity sued the National Marine Fisheries Service for failing to list the bocaccio as a threatened species in 

accordance to the U.S. Endangered Species Act. show that the abundance of Bocaccio is less than 5% of their 

historical population in the northern Channel Islands. The Bocaccio is one species among several species of rockfish 

that are showing serious signs of decline in abundance and distribution in the Bight. 7

 A complete characterization of the rigs-to-reefs debate and the various policy initiatives in California are beyond 

the scope of this section. Please refer to Pomeroy (2001) for a historical treatment of the California artificial reef 

program and the rigs-to-reefs debate. Pomeroy uses Kingdon’s analytical model to characterize the major political 

actors and interest groups in the California debate.
Final Study Report – Carr et al 

76

funding, and the scientific merits of such a policy, together with strong opposition from 

certain interests proved insurmountable. The increased attention to problems in the 

marine environment and rigs-to-reefs as a policy solution, and the active debate of 

liability, funding and ecological impact concerns, however, have likely prompted policy 

entrepreneurs to seek solutions to those issues, and incorporate them into a revised policy 

proposal, ready for the next window of opportunity. 

In addition, Murray (1994: 960) shows in an analysis of the National Artificial Reef Plan, “The 

Plan of 1985 suggested that states should play a major role in the development of guidelines for 

artificial reefs. However, most coastal states have not established clear artificial reef 

development plans that consider social, economic, environmental and biological factors 

associated with artificial reef programs.” In contrast to the Gulf experience, these political and 

ecological factors have carried more weight in the California context. 

California’s unique Political Ecology 

There are currently 27 platforms in the Bight and approximately 200 miles of associated 

pipelines. Both the installation date and platform depth should be recognized as important 

factors related to decommissioning (Fernandez, in McGinnis et al. 2001). For example, 

decommissioning costs vary by water depth (MMS 1999). A few of the offshore structures are 

over 1,000 feet deep. California OCS oil and gas production has occurred since the mid-1960s 

(Lima 1994). These oil platforms have a finite economic lifespan; several platforms are nearing 

the end of the economic operation. 

To date, only seven relatively small structures have been decommissioned; all were located in 

State waters. The most recent project occurred in 1996 when Chevron removed Platforms Hope, 

Heidi, Hilda and Hazel. These platforms were in water depths ranging from 100 to 140 feet. 

One hundred and thirty-four wells were plugged and abandoned on these platforms. In order to 

remove the platforms to be brought ashore for recycling and disposal, explosives and heavy 

machinery were used to tear the platforms from their foundations. The biomass that accumulated 

around these OCS oil and gas structures was destroyed during the decommissioning activity 

(MMS 1997). 

California OCS oil and gas production is expected to decline by the year 2015. International, 

federal and California laws require the complete removal of offshore oil and gas structures 

(California Coastal Commission 1999). As a brief overview, the regulatory compliance 

requirements are as follows: 

• US Minerals Management Service: Federal law (30 CFR 250) requires the plugging and 

decommissioningof wells; full removal of well conductors and platform jackets to 15 feet 

below the mudline; decommissioning and full removal of platform decks; 

decommissioning and removal of pipelines and power cables as appropriate; and site 

clearance. 

 

• California Department of Conservation, Division of Oil, Gas and Geothermal Resources: 

The basic plugging requirements are found in the California Code of Regulations Title 14 

Division 2, Chapter 4, Section 1745. 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

77

• California State Lands Commission: The basic plugging requirements are found in the 

California Code of Regulations Title 2 Section 2128(q). 

There are also lease and permit requirements that must be met during decommissioning of 

California offshore oil and gas structures. Provisions of federal and state oil leases and MMS 

regulations can be changed by the state and federal government to allow the federal government 

to consider and approve methods of rig decommissioning other than complete removal, as 

evidenced in the Gulf of Mexico. With respect to California, Kallaur (1998), the Associate 

Director for Offshore Minerals Management with the U.S. Department of the Interior, MMS 

writes, “MMS does not have a position one way or the other as to the rigs-to-reefs program here 

in California. We believe that is an issue that falls primarily within the regulatory jurisdiction of 

the California Department of Fish and Game, Army Corps of Engineers, and the California 

Coastal Commission.” California’s Department of Fish and Game (CDFG), the agency with 

oversight over the state’s artificial reef program, has policy guidelines in place for artificial reefs 

with a preference for those structures that provide “good” habitat. 

The fundamental issue in California is whether or not offshore oil platform provide “good 

habitat” for marine life. The economics of platform removal, and the uncertainty over the 

potential “fishery-related values” that may be associated with particular platforms in the Santa 

Barbara Channel are additional factors that are contributing to the policy debate. 

One factor is the scientific uncertainty associated with the offshore platforms. A Scientific 

Advisory Committee on Decommissioning from the University of California (Holbrook et al. 

2000: 3-5) wrote: 

There is not any sound scientific evidence (that the Committee is aware of) to 

support the idea that platforms enhance (or reduce) regional stocks of marine 

species. The primary reason for this conclusion is that the 27 platforms represent a 

tiny fraction of the available hard substrate in the Southern California Bight, so 

their contribution to stocks of most reef organisms is likely to be small relative to 

the contribution from natural reefs... The Committee found that the possible 

regional effects on a stock of habitat removal are much harder to assess than the 

short-term ecological impacts localized at the site of the platform because most 

marine species are composed of a series of local populations that are connected via 

larval dispersal of young stages. Thus, populations are interdependent, and impacts 

at any one location (a reef or platform) must be viewed in the context of the 

regional set of local populations. Regional effects cannot be projected at present 

because we do not fully understand how local populations are connected (such as 

we know that larvae are transported and older individuals move between various 

reefs, artificial reefs and oil platforms, but we do not understand specific links 

among local populations) nor do we know the degree to which populations on 

artificial structures are self-sustaining...Thus, in light of the strong evidence of the 

benefit and the relatively small contribution of platforms to reef habitat in the 

region, evaluation of decommissioning alternatives in our opinion should not be 
Final Study Report – Carr et al 

78

based on the assumption that platforms currently enhance marine resources” [my 

emphasis]. 

The ecology associated with California offshore platforms and associated structures often 

depends on the relationship between the location of the structure and the oceanographic setting. 

This is a dynamic setting influenced by changing ecological patterns, oceanographic currents, 

and climate-related events, such as El Niño or La Niña. Life around a platform should not be 

thought of as a “steady state”. As the University of California’s Scientific Advisory Committee 

on Decommissioning (Holbrook, et al. 2000: 4) note, “The particular species present at any given 

platform depend on the biogeographic setting of the platform and its depth, as well as other 

factors.” The biogeographic setting of each platform can also change over time. Marine life 

around a platform may change in response to ocean-climate variability.8

The marine environment of southern California is one of the most studied marine systems in the 

world (Hickey 1993). Members of the California Cooperative Oceanic Fisheries Investigations 

(CalCOFI) have studied the SCB since 1950 (Scheiber 1995). These studies have described 

large-scale (i.e. Bight-wide), long-term (i.e. several decades) changes, or what is referred to as a 

regime shifts, in physical and biological processes that have contributed to changes in the 

distribution and abundance of some marine species, such as several species of rockfish.. 

McGowan, et al. (1998) state that the last regime shift occurred in 1977. Based on an analysis of 

CalCOFI data,9

 Roemmich and McGowan (1995a, b) document large-scale changes in primary 

and secondary productivity throughout the SCB between 1951 and 1993. Hayward et al. (1996) 

and McGowan, et al. (1998) show that large-scale biological responses in marine ecology due to 

climatic variations in the atmosphere has resulted in changes in geographical ranges and spatial 

patterns of species and in community structure. This evidence suggests that the maintenance of 

community structure and patterns of species diversity has changed in accordance to hydrographic 

perturbations and climate-ocean variability. The ecology of particular platforms may change 

with future regime shifts and ocean-climate variability. 

Offshore platforms are part of a dynamic ecological system. The reduction in biomass and 

significant decline in the abundance of a number of species of rockfish and other marine animals 

and habitats sets the current ecological stage or context for the debate over the utility of the rigsto-reefs option. Each offshore rig is situated in a particular ecological setting. There are wide 

differences between platforms in the numbers or biomass of various species (Love et al. 2001). 

There may also be differences in fish communities inhabiting platforms and nearby natural reefs 

(Section II). What is certain is that policymakers may need to make trans-scientific decisions 

that involve the intermingling of scientific information, values and interests. 

With respect to the California debate over the future of platforms, Pomeroy (in McGinnis et al. 

2001) notes that: 

 

8 McGinnis (1998) has proposed the idea of a “living permit” as one response to variability. 9

 CalCOFI has compiled several spatially and temporally comprehensive data sets for the SCB from strategically 

located offshore stations (Hickey 1993: 21-25). 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

79

Throughout, attention has focused upon a number of scientific, technical and 

institutional issues. These include: 1) whether platforms actually enhance, or 

simply attract reef fishes; 2) the net ecological benefits or costs of removal and of 

reefing; 3) the practicality of removal and of reefing, especially involving platforms 

in very deep waters; 4) concerns for navigational safety; 5) interference with other 

ocean uses; 6) funding to support maintenance and monitoring as well as initial 

reefing; and 7) liability, among others. Recent rig-to-reef policy proposals manifest 

in legislation first introduced in 1998, then re-introduced in 1999 and 2000, have 

sought to address many of these issues. And this is where the state’s artificial reef 

program and the rig-to-reef concept have become intertwined. 

In contrast to the experience in the Gulf states, concerns associated with the use of platforms as 

artificial reefs in California ultimately led to a veto of SB1 by Governor Davis. In an analysis of 

interviews with state artificial reef managers, Murray (1994) describes the current status of 

artificial reef programs in relation to administration, budget, siting, promotion, education, 

evaluation, future trends and major concerns. The major issues and concerns that state artificial 

reef managers raise are as follows (Murray 1994): 

(1) The Liability Issue. Since the publication of the National Artificial Reef Plan, which 

recommended that the US Army Corps of Engineers develop specific permit standards and 

conditions, the issue of liability remains vague and unclear. The Corps has developed a 

policy requiring the permit holder of an artificial reef to prove adequate liability coverage. 

States with reefing programs have assumed the role of the permittee. This has necessitated a 

close review of the role of the states and localities in implementing the NFEA (Murray 1994). 

As Murray (1994: 965) writes in an analysis of the interviews with state artificial reef 

managers: 

Because most private fishing associations cannot afford the insurance premium, many 

states have assumed the role of the permittee. Although many state managers welcomed 

this as a way of gaining control of artificial reef activities, it has necessitated a closer 

inspection of each state’s liability. The level of concern varied widely, but the general 

consensus was that clarification is needed from the state’s attorney general’s office. Most 

reef managers felt that even this would be vague and subject to interpretation until a case 

comes before a court. Clarification of this issue would improve operational procedures and 

potentially reduce uncertainty about exposure on the part of state artificial reef managers 

(Murray 1994: 968). 

(2) Scientific Uncertainty: Production versus Aggregation. State artificial reef managers 

remain concerned about the production versus aggregation question. It remains unclear if 

platforms attract or produce fishes. As Murray (1994: 966) writes, “One troublesome issue is 

related to the inability of artificial reefs to assist fishery production at all stages of the life 

cycle.” Artificial reef managers are concerned that too much emphasis has been placed on 

adult fishery enhancement activity and not enough on restoring essential coastal processes, 

such as estuarine habitats and wetland ecosystems (the “nurseries of the sea”). 
Final Study Report – Carr et al 

80

(3) Limited Funding. State artificial reef program funding remains a major concern of 

administrators and managers. In 1988, the average reported annual budget for reef programs 

was $139,000, with a range of 0$ to $400,000 (Murray 1994: 962). Most funds are generated 

from either state appropriations or Wallop-Breaux funds, which refer to the 1984 WallopBreaux Amendment to the Federal Aid in Sport Fish Restoration Act (16 U.S.C. sec. 777 

(1988)). 

Oil companies that “donate” structures are asked to contribute half of the disposal savings 

realized to the Fund. In a description of this process, Reggio and Kasprzak (1991: 15) write: 

Negotiations to obtain platforms and to determine the amount of donation are done 

on a case-by-case basis between the oil and gas operator and the state. The size, 

location, distance from shore, water depth, resale value, and proximity of the 

platform to the permitted reef site all affect the cost of converting a rig into a reef; 

thus, it is not always cost-effective for operators to participate. 

State artificial reef programs maintain an average staff size of 1 full-time employee. In addition, 

monitoring of existing artificial reefs and regulatory compliance issues remain important 

concerns of state artificial reef managers in the Gulf. State artificial reef programs have not 

received adequate funding (Murray 1994: 967). 

In addition to these general administrative concerns associated with artificial reef program 

development, Governor Davis vetoed California SB 1 because of the scientific uncertainties 

associated with the rigs-to-reefs alternative. 

Conclusion 

This section described the political, problem and policy streams that met to form a policy 

window of opportunity for the platforms to reefs alternative in the Gulf. In the case of the Gulf, 

an advocacy coalition that combined the interests of the oil industry, recreation and commercial 

fishing, scientists, and resource managers supported the use of offshore platforms as artificial 

reefs. The development of oil and gas in the Gulf OCS led to an increase in commercial and 

sports fishing activity. Scientific reports and workshops spoke to the benefit of artificial reefs in 

the Gulf. States and local artificial reef programs had been established before the passage of the 

NFEA. In passing the NFEA, the federal government granted discretionary authority to states to 

create their respective platforms to artificial reef program. Many of these programs were based 

on existing artificial reef programs. 

Despite the passage of the NFEA, there remain a number of management issues and concerns 

that have not been clearly addressed by federal and state resource policymakers who are 

interested in artificial reef development and building. In contrast to the Gulf experience, marine 

scientists raised serious questions with respect to the utility of a rigs-to-reefs alternative in 

California (McGinnis et al. 2001). Moreover, a strong coalition of environmentalists and 

commercial fishing interests have been successful in blocking a rigs-to-reefs policy initiative in 

California.
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

81

Acknowledgements 

We thank the Minerals Management Service, US Department of the Interior, under MMS 

agreement no. 14-35-0001-30758 for supporting this research. This work could not have been 

completed without the stellar efforts of technicians, Jeff Harding, Arnold Ammann, Laird 

MacDonald, William Golden, Rebecca Frodsham, and Amy McClean Findlay, responsible for 

the management and implementation of the diving, data collection and data management. Jeff 

Harding and Arnold Amman also contributed to the analysis and interpretation of data and 

results. Several dedicated volunteers, including Bryon Banks, David Chan, Bryn Evans, Neil 

Grider, Melissa Meeker and Lise Schickel contributed to many hours of underwater work. ROV 

sampling was only possible through our collaboration with the Santa Barbara City College 

Technical Diving Program, especially Don Barthelmess and our ROV drivers, Jeff Browning, 

Ryan Cummings and Jim Hayward. Fish tagging was accomplished with the help of Bernard 

Friedman and Martin Lee, and in collaboration with the Channel Islands National Marine 

Sanctuary, especially Superintendent Edward, who provided and captained the R.V. Ballena. 

Approximately 50 volunteer sportfishers contributed to the tagging effort, without whose efforts 

we could not have accomplished the sample size we achieved. Approximately 30 volunteer 

undergraduates contributed countless hours of watching ROV and diver video and recording 

species, number and sizes of fishes. Many discussions with Donna Schroeder and Dr. Richard 

Ambrose (UCLA) contributed to the design and development of the study and report. Dr. Craig 

Syms advised on and conducted the multivariate analyses. Bonnie Williamson provided us 

extraordinary administrative support throughout this project. The views and conclusions 

contained in this document are those of the authors and should not be interpreted as necessarily 

representing the official policies, either express or implied, of the US Government. 
Final Study Report – Carr et al 

82

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89

Appendix 1 

Appendix 1. Taxonomic categories of fish species used in analyses. Additional categories include 

ND= no data available; no census conducted; NF= no fish present; census conducted, no fish seen.

Common Name Family Genus Species Code 

smelt, unidentified sp. ATHERINIDAE ATHE 

giant kelpfish CLINIDAE Heterostichus rostratus HROS 

cabezon COTTIDAE Scorpaenichthys marmoratus SMAR 

kelp surfperch EMBIOTOCIDAE Brachyistius frenatus BFRE 

pile surfperch EMBIOTOCIDAE Damalichthys vacca DVAC 

black surfperch EMBIOTOCIDAE Embiotoca jacksoni EJAC 

surfperch, unidentified sp. EMBIOTOCIDAE EMBI 

rainbow surfperch EMBIOTOCIDAE Hypsurus caryi HCAR 

sharpnose surfperch EMBIOTOCIDAE Phanerodon atripes PATR 

white surfperch EMBIOTOCIDAE Phanerodon furcatus PFUR 

rubberlip surfperch EMBIOTOCIDAE Rhacochilus toxotes RTOX 

blackeye goby GOBIIDAE Coryphopterus nicholsii CNIC 

kelp goby GOBIIDAE Lethops connectens LCON 

sargo HAEMULIDAE Anisotremus davidsonii ADAV 

lingcod HEXAGRAMMIDAE Ophiodon elongatus OELO 

painted greenling HEXAGRAMMIDAE Oxylebius pictus OPIC 

opaleye KYPHOSIDAE Girella nigricans GNIG 

halfmoon KYPHOSIDAE Medialuna californiensis MCAL 

rock wrasse LABRIDAE Halicoeres semicinctus HSEM 

senorita LABRIDAE Oxyjulis californica OCAL 

california sheephead LABRIDAE Semicossyphus pulcher SPUL 

blacksmith POMACENTRIDAE Chromis punctipinnis CPUN 

garibaldi POMACENTRIDAE Hypsypops rubicundus HRUB 

rockfish, blackspot YOY SCORPAENIDAE Sebastes sp BKSP 

rockfish, shallow benthic 

unidentified SCORPAENIDAE Sebastes sp BRF 

rockfish, copper complex YOY SCORPAENIDAE Sebastes sp KGB 

rockfish, midwater complex, 

unidentified sp. SCORPAENIDAE Sebastes sp MRF 

rockfish, Sebastomus

unidentified YOY SCORPAENIDAE Sebastes sp ROS 

kelp rockfish SCORPAENIDAE Sebastes atrovirens SATR 

brown rockfish SCORPAENIDAE Sebastes auriculatus SAUR 

gopher rockfish SCORPAENIDAE Sebastes carnatus SCAR 

copper rockfish SCORPAENIDAE Sebastes caurinus SCAU 

black and yellow rockfish SCORPAENIDAE Sebastes chrysomelas SCHR 

rockfish, unidentified sp. SCORPAENIDAE Sebastes sp SCOR 

calico rockfish SCORPAENIDAE Sebastes dalli SDAL 

widow rockfish SCORPAENIDAE Sebastes entomelas SENT 

california scorpionfish SCORPAENIDAE Scorpaena guttata SGUT 
Final Study Report – Carr et al 

90

Appendix 1 cont’d. Taxonomic categories of fish species used in analyses. Additional categories include 

ND= no data available; no census conducted; NF= no fish present; census conducted, no fish seen.

Common Name Family Genus Species Code 

squarespot rockfish SCORPAENIDAE Sebastes hopkinsi SHOP 

vermilion rockfish SCORPAENIDAE Sebastes miniatus SMIN 

blue rockfish SCORPAENIDAE Sebastes mystinus SMYS 

bocaccio SCORPAENIDAE Sebastes paucispinis SPAU 

rosy rockfish SCORPAENIDAE Sebastes rosaceus SROS 

flag rockfish SCORPAENIDAE Sebastes rubrivinctus SRUB 

halfbanded rockfish SCORPAENIDAE Sebastes semicinctus SSEM 

olive rockfish SCORPAENIDAE Sebastes serranoides SSER 

treefish SCORPAENIDAE Sebastes serriceps STRE 

widow/blue rockfish SCORPAENIDAE Sebastes sp WB 

kelp bass SERRANIDAE Paralabrax clathratus PCLA 

barred sandbass SERRANIDAE Paralabrax nebulifer PNEB 
Consequences of Alternative Decommissioning Options 

91

Appendix 2a. Total number of individuals, density, and percent density of each non-rockfish species in each habitat type across all saAlso summarized is the total water volume sampled by each method in each habitat type. Platforms abbreviated as "rigs". 

ROV divers ROV

species category rigs rigs reefs canopy midwater bottom total rigs cabezon benthic 4 75 0 0 0 2 2 0.17 blacksmith midwater 556 56742 5275 15 627 1642 2284 121.36 lingcod benthic 18 1 9 0 0 4 4 0.04 sheephead benthic 9 194 22 0 0 111 111 0.43 kelp bass midwater 20 1299 19 96 252 1669 2017 2.79 barred sand bass benthic 0 1 3 0 2 253 255 0.00 giant kelpfish canopy 0 0 0 13 5 2 20 0.00 garibaldi benthic 12 211 0 0 0 4 4 0.47 halfmoon midwater 219 1989 0 1 7 2 10 4.68 senorita midwater 3 400 5 312 376 1237 1925 0.85 opaleye midwater 0 2 0 14 2 103 119 0.00 painted greenling benthic 119 315 12 0 0 32 32 0.92 sharpnose surfperch midwater 107 1160 1 0 0 1 1 2.68 pile surfperch benthic 69 340 4 2 20 278 300 0.87 rubberlip surfperch benthic 63 1 25 0 0 79 79 0.14 black surfperch benthic 0 0 0 0 3 366 369 0.00 kelp surfperch canopy 0 0 0 231 95 0 326 0.00 white surfperch midwater 0 1 0 14 92 55 161 0.00 rainbow surfperch benthic 0 0 0 0 2 302 304 0.00 sample method, locationROV, platforms 92524ROV, natural reefs 5764divers, platforms 379613divers, natural reefs, canopy only 12000divers, natural reefs, midwater only 28320divers, natural reefs, bottom only 28800divers, natural reefs, all 69120

divers - natural reefs density (fish / 

water volume sampled (m3)

91 
Final Study Report – Carr et al 

92

Appendix 2b. Total number of individuals, density, and percent density of each rockfish species in each habitat type across all sampli

summarized is the total water volume sampled by each method in each habitat type. Platforms abbreviated as "rigs". 

ROV divers ROV

species category rigs rigs reefs canopy midwater bottom total rigs rockfish: copper complex all 1021 1444 12 3 5 448 456 5.22 rockfish: midwater midwater 1845 1616 102 4 34 107 145 7.33 rockfish: shallow benthic benthic 1790 396 106 0 0 47 47 4.63 (excluding copper complex)rockfish: all species all 4704 3456 220 7 39 602 648 17.28 **kelp rockfish mid, benthi 910 727 5 0 4 386 390 3.47 

**copper rockfish benthic 85 16 1 0 0 18 18 0.21 **gopher rockfish benthic 0 42 5 0 0 37 37 0.09 **black and yellow rockfish benthic 0 3 1 0 0 6 6 0.01 **olive rockfish midwater 370 97 25 0 31 82 113 0.99 **blue rockfish midwater 334 246 0 0 0 0 0 1.23 **widow rockfish midwater 553 350 0 0 0 0 0 1.91 **squarespot rockfish midwater 0 1 63 0 0 0 0 0.00 **brown rockfish benthic 75 5 13 0 0 31 31 0.17 **calico rockfish benthic 75 0 32 0 0 1 1 0.16 **vermilion rockfish benthic 595 0 5 0 0 3 3 1.26 **treefish benthic 0 2 8 0 0 8 8 0.00 

**only individuals >= 9 cm TL. Smaller individuals were less easily classified to species, especially in ROV samples, and weplaced in broader multi-species groups such as copper complex, MRF, or BRF.

divers - natural reefs density (fish / 

92 
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

93

Appendix 3 

Appendix 3. Comparison of species composition of samples by diver and ROV on oil platforms Henry, 

Houchin, and Hogan at level 3 (36m) horizontal crossmembers (excluding interior zone samples). See 

Appendix 1 for codes and species common names.

sample DIVER ROV sample DIVER ROV

platform period species quantity species quantity platform period species quantity species quantity

Hogan Aug-95 RYOY 5 RYOY 8

Henry Jun-95 no fish RYOY 16 KGB 1 SPAU 24

SSER 1 SSER 2

Henry Aug-95 KGB 2 no fish PATR 7

SPAU 8 OPIC 1

SGUT 1 STRE 1

Henry Oct-95 CPUN 11 PATR 1 Hogan Oct-95 PATR 1 PATR 11

OYT 2 OPIC 3 DVAC 2 DVAC 2

Henry Jun-96 COTT 2 no fish KGB 6 RTOX 1

DVAC 1 OPIC 1 SSER 20

SPAU 6 RYOY 10 SPAU 10

OPIC 2 EMBI 1

ROS 1 RYOY 1

Henry Aug-96 OYT 1 no fish SATR 1

OPIC 1 SMYS 1

SMAR 1 OPIC 1

PCLA 1 Hogan Jun-96 CPUN 17 EMBI 2

Henry Oct-96 CPUN 1 OPIC 1 PCLA 2 SSER 1

SMAR 1 SSER 1 DVAC 1

Henry Jun-97 OYT 13 no fish SCAU 1

KGB 1 RYOY 2

SMYS 2 Hogan Aug-96 ROS 1 SSER 1

Houchin Jun-95 SGUT 1 RYOY 6 PATR 31 OPIC 1

Houchin Aug-95 SSER 7 RYOY 4 DVAC 3

Houchin Oct-95 KGB 6 SATR 5 OPIC 1

OPIC 1 Hogan Oct-96 CPUN 4 DVAC 3

Houchin Jun-96 no fish SATR 1 RYOY 1 PATR 5

Houchin Aug-96 SPAU 50 SATR 3 SSER 1 EMBI 5

CPUN 1 SSER 1 ROS 2

SATR 6 OPIC 1 Hogan Jun-97 CPUN 1 OPIC 1

SSER 4 STRE 1 SATR 1

Houchin Oct-96 OPIC 1 no fish SATR 1 DVAC 5

SATR 1 SMAR 1

DVAC 2

Houchin Jun-97 CPUN 2 OPIC 1

OYT 1 SSER 2

Hogan Jun-95 SSER 12 SSER 2

SMYS 4

OYT 100
Final Study Report – Carr et al 

94

Appendix 4 

Appendix 4. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs estimated visually 

by divers and by video with parallel lasers. Distributions are based upon all platforms and natural reefs 

combined across 3 years. N= total number of fish. 

0 10 20 30 40 50

Proportion

0 10 20 30 40 50

0 10 20 30 40 50

Proportion

0 10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

Total length (cm) Total length (cm)

n = 169

mean = 18 cm 

n = 319

mean = 25 cm

n = 389

mean = 20 cm 

n = 727

mean = 25 cm

kelp rockfish

laser, reefs 

kelp rockfish

laser, platforms 

kelp rockfish

visual, reefs 

kelp rockfish

visual, platforms 

0 10 20 30 40 50 0 10 20 30 40 50

0 10 20 30 40 50 0 10 20 30 40 50

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

Proportion Proportion

Total length (cm) Total length (cm)

copper rockfish

laser, reefs 

copper rockfish

laser, platforms 

copper rockfish

visual, reefs 

copper rockfish

visual, platforms 

n = 9

mean = 17 cm 

n = 2

mean = 25 cm

n = 18

mean = 20 cm 

n = 16

mean = 24 cm

0 10 20 30 40 50

Proportion

0 10 20 30 40 50

0 10 20 30 40 50

Proportion

0 10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

Total length (cm) Total length (cm)

n = 169

mean = 18 cm 

n = 319

mean = 25 cm

n = 389

mean = 20 cm 

n = 727

mean = 25 cm

kelp rockfish

laser, reefs 

kelp rockfish

laser, platforms 

kelp rockfish

visual, reefs 

kelp rockfish

visual, platforms 

0 10 20 30 40 50 0 10 20 30 40 50

0 10 20 30 40 50 0 10 20 30 40 50

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

Proportion Proportion

Total length (cm) Total length (cm)

copper rockfish

laser, reefs 

copper rockfish

laser, platforms 

copper rockfish

visual, reefs 

copper rockfish

visual, platforms 

n = 9

mean = 17 cm 

n = 2

mean = 25 cm

n = 18

mean = 20 cm 

n = 16

mean = 24 cm
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

95

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

0 10 20 30 40 0 10 20 30 40

0 10 20 30 40 0 10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

0.5

Proportion Proportion

Total length (cm) Total length (cm)

gopher rockfish

laser, reefs 

gopher rockfish

laser, platforms 

gopher rockfish

visual, reefs 

gopher rockfish

visual, platforms 

n = 13

mean = 17 cm 

n = 19

mean = 27 cm

n = 37

mean = 20 cm 

n = 42

mean = 27 cm

0 10 20 30 40 0 10 20 30 40

0 10 20 30 40 0 10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

Proportion Proportion

Total length (cm) Total length (cm)

olive rockfish

laser, reefs 

olive rockfish

laser, platforms 

olive rockfish

visual, reefs 

olive rockfish

visual, platforms 

n = 34

mean = 20 cm 

n = 32

mean = 23 cm

n = 113

mean = 21 cm 

n = 97

mean = 24 cm

0 10 20 30 40 0 10 20 30 40

0 10 20 30 40 0 10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

0.5

Proportion Proportion

Total length (cm) Total length (cm)

gopher rockfish

laser, reefs 

gopher rockfish

laser, platforms 

gopher rockfish

visual, reefs 

gopher rockfish

visual, platforms 

n = 13

mean = 17 cm 

n = 19

mean = 27 cm

n = 37

mean = 20 cm 

n = 42

mean = 27 cm

0 10 20 30 40 0 10 20 30 40

0 10 20 30 40 0 10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

Proportion Proportion

Total length (cm) Total length (cm)

olive rockfish

laser, reefs 

olive rockfish

laser, platforms 

olive rockfish

visual, reefs 

olive rockfish

visual, platforms 

n = 34

mean = 20 cm 

n = 32

mean = 23 cm

n = 113

mean = 21 cm 

n = 97

mean = 24 cm
Final Study Report – Carr et al 

96

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

0 10 20 30 40

0 10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

blue rockfish

laser, platforms 

blue rockfish

visual, platforms 

Total length (cm)

Proportion Proportion

n = 81

mean = 24 cm 

n = 246

mean = 21 cm 

blue rockfish

laser, reefs 

blue rockfish

visual, reefs 

no data

no data

8 12 16 20 24 28

8 12 16 20 24 28

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

widow rockfish

laser, platforms 

widow rockfish

visual, platforms 

Total length (cm)

Proportion Proportion

n = 68

mean = 17 cm 

n = 350

mean = 20 cm 

widow rockfish

laser, reefs 

widow rockfish

visual, reefs 

no data

no data

0 10 20 30 40

0 10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

blue rockfish

laser, platforms 

blue rockfish

visual, platforms 

Total length (cm)

Proportion Proportion

n = 81

mean = 24 cm 

n = 246

mean = 21 cm 

blue rockfish

laser, reefs 

blue rockfish

visual, reefs 

no data

no data

8 12 16 20 24 28

8 12 16 20 24 28

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

widow rockfish

laser, platforms 

widow rockfish

visual, platforms 

Total length (cm)

Proportion Proportion

n = 68

mean = 17 cm 

n = 350

mean = 20 cm 

widow rockfish

laser, reefs 

widow rockfish

visual, reefs 

no data

no data
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

97

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

10 20 30 40

10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

sharpnose surfperch

laser, platforms 

sharpnose surfperch

visual, platforms 

Total length (cm)

Proportion Proportion

n = 78

mean = 23 cm 

n = 1160

mean = 21 cm 

sharpnose surfperch

laser, reefs 

sharpnose surfperch

visual, reefs 

no data

no data

brown rockfish

laser, reefs 

10 15 20 25 30

brown rockfish

visual, reefs 

10 15 20 25 30

Total length (cm)

Proportion

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Proportion

n = 21

mean = 17 cm 

n = 31

mean = 20 cm 

brown rockfish

laser, platforms 

brown rockfish

visual, platforms 

no data

no data

10 20 30 40

10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

sharpnose surfperch

laser, platforms 

sharpnose surfperch

visual, platforms 

Total length (cm)

Proportion Proportion

n = 78

mean = 23 cm 

n = 1160

mean = 21 cm 

sharpnose surfperch

laser, reefs 

sharpnose surfperch

visual, reefs 

no data

no data

brown rockfish

laser, reefs 

10 15 20 25 30

brown rockfish

visual, reefs 

10 15 20 25 30

Total length (cm)

Proportion

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Proportion

n = 21

mean = 17 cm 

n = 31

mean = 20 cm 

brown rockfish

laser, platforms 

brown rockfish

visual, platforms 

no data

no data
Final Study Report – Carr et al 

98

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

5 10 15 20 25 30 35

Proportion

5 10 15 20 25 30 35

5 10 15 20 25 30 35

Total length (cm)

Proportion

5 10 15 20 25 30 35

Total length (cm)

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.4

n = 106

mean = 16 cm 

n = 819

mean = 16 cm

n = 1702

mean = 13 cm 

n = 11801

mean = 14 cm

blacksmith

laser, reefs 

blacksmith

laser, platforms 

blacksmith

visual, reefs 

blacksmith

visual, platforms 

0 10 20 30 40 50

Proportion

0 10 20 30 40 50 0 10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0

0.1

0.2

0.3

0.4

0.5

Proportion

Total length (cm) Total length (cm)

Garibaldi

laser, platforms 

Garibaldi

visual, reefs 

Garibaldi

visual, platforms 

n = 28

mean = 25 cm

n = 4

mean = 29 cm 

n = 172

mean = 24 cm

Garibaldi

laser, reefs 

no data

5 10 15 20 25 30 35

Proportion

5 10 15 20 25 30 35

5 10 15 20 25 30 35

Total length (cm)

Proportion

5 10 15 20 25 30 35

Total length (cm)

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.4

n = 106

mean = 16 cm 

n = 819

mean = 16 cm

n = 1702

mean = 13 cm 

n = 11801

mean = 14 cm

blacksmith

laser, reefs 

blacksmith

laser, platforms 

blacksmith

visual, reefs 

blacksmith

visual, platforms 

0 10 20 30 40 50

Proportion

0 10 20 30 40 50 0 10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0

0.1

0.2

0.3

0.4

0.5

Proportion

Total length (cm) Total length (cm)

Garibaldi

laser, platforms 

Garibaldi

visual, reefs 

Garibaldi

visual, platforms 

n = 28

mean = 25 cm

n = 4

mean = 29 cm 

n = 172

mean = 24 cm

Garibaldi

laser, reefs 

no data
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

99

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

5 10 15 20 25 30 35 5 10 15 20 25 30 35

5 10 15 20 25 30 35 5 10 15 20 25 30 35

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

0.5

Proportion Proportion

Total length (cm) Total length (cm)

senorita

laser, reefs 

senorita

laser, platforms 

senorita

visual, reefs 

senorita

visual, platforms 

n = 151

mean = 18 cm 

n = 58

mean = 22 cm

n = 1874

mean = 17 cm 

n = 400

mean = 20 cm

10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80

10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80

0.0

0.1

0.2

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

Proportion Proportion

Total length (cm) Total length (cm)

Calif. sheephead

laser, reefs 

Calif. sheephead

laser, platforms 

Calif. sheephead

visual, reefs 

Calif. sheephead

visual, platforms 

n = 38

mean = 38 cm 

n = 96

mean = 36 cm

n = 111

mean = 37 cm 

n = 188

mean = 34 cm

5 10 15 20 25 30 35 5 10 15 20 25 30 35

5 10 15 20 25 30 35 5 10 15 20 25 30 35

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

0.5

Proportion Proportion

Total length (cm) Total length (cm)

senorita

laser, reefs 

senorita

laser, platforms 

senorita

visual, reefs 

senorita

visual, platforms 

n = 151

mean = 18 cm 

n = 58

mean = 22 cm

n = 1874

mean = 17 cm 

n = 400

mean = 20 cm

10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80

10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80

0.0

0.1

0.2

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

Proportion Proportion

Total length (cm) Total length (cm)

Calif. sheephead

laser, reefs 

Calif. sheephead

laser, platforms 

Calif. sheephead

visual, reefs 

Calif. sheephead

visual, platforms 

n = 38

mean = 38 cm 

n = 96

mean = 36 cm

n = 111

mean = 37 cm 

n = 188

mean = 34 cm
Final Study Report – Carr et al 

100

 Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

0 10 20 30 0 10 20 30

0 10 20 30 0 10 20 30

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Proportion Proportion

Total length (cm) Total length (cm)

painted greenling

laser, reefs 

painted greenling

laser, platforms 

painted greenling

visual, reefs 

painted greenling

visual, platforms 

n = 3

mean = 15 cm 

n = 37

mean = 15 cm

n = 31

mean = 17 cm 

n = 304

mean = 15 cm

0 10 20 30 40 50

0 10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

cabezon

laser, platforms 

cabezon

visual, platforms 

Total length (cm)

Proportion Proportion

n = 22

mean = 30 cm 

n = 75

mean = 29 cm 

cabezon

laser, reefs 

cabezon

visual, reefs 

no data

no data

0 10 20 30 0 10 20 30

0 10 20 30 0 10 20 30

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Proportion Proportion

Total length (cm) Total length (cm)

painted greenling

laser, reefs 

painted greenling

laser, platforms 

painted greenling

visual, reefs 

painted greenling

visual, platforms 

n = 3

mean = 15 cm 

n = 37

mean = 15 cm

n = 31

mean = 17 cm 

n = 304

mean = 15 cm

0 10 20 30 40 50

0 10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

cabezon

laser, platforms 

cabezon

visual, platforms 

Total length (cm)

Proportion Proportion

n = 22

mean = 30 cm 

n = 75

mean = 29 cm 

cabezon

laser, reefs 

cabezon

visual, reefs 

no data

no data
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

101

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

5 10 15 20 25 30 35

5 10 15 20 25 30 35

0.0

0.1

0.2

0.3

0.0

0.1

0.2

black surfperch

laser, reefs 

black surfperch

visual, reefs 

Total length (cm)

Proportion Proportion

n = 25

mean = 19 cm 

n = 364

mean = 20 cm 

black surfperch

laser, platforms 

black surfperch

visual, platforms 

no data

no data

0 10 20 30

0 10 20 30

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

rainbow surfperch

laser, reefs 

rainbow surfperch

visual, reefs 

Total length (cm)

Proportion Proportion

n = 12

mean = 17 cm 

n = 292

mean = 15 cm 

rainbow surfperch

laser, platforms 

rainbow surfperch

visual, platforms 

no data

no data

5 10 15 20 25 30 35

5 10 15 20 25 30 35

0.0

0.1

0.2

0.3

0.0

0.1

0.2

black surfperch

laser, reefs 

black surfperch

visual, reefs 

Total length (cm)

Proportion Proportion

n = 25

mean = 19 cm 

n = 364

mean = 20 cm 

black surfperch

laser, platforms 

black surfperch

visual, platforms 

no data

no data

0 10 20 30

0 10 20 30

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

rainbow surfperch

laser, reefs 

rainbow surfperch

visual, reefs 

Total length (cm)

Proportion Proportion

n = 12

mean = 17 cm 

n = 292

mean = 15 cm 

rainbow surfperch

laser, platforms 

rainbow surfperch

visual, platforms 

no data

no data
Final Study Report – Carr et al 

102

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

0 10 20 30 40 0 10 20 30 40

0 10 20 30 40 0 10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.0

0.1

0.2

Proportion Proportion

Total length (cm) Total length (cm)

pile surfperch

laser, reefs 

pile surfperch

laser, platforms 

pile surfperch

visual, reefs 

pile surfperch

visual, platforms 

n = 35

mean = 23 cm 

n = 41

mean = 26 cm

n = 286

mean = 21 cm 

n = 340

mean = 22 cm

10 20 30 40 50

10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.4

Proportion Proportion

Total length (cm)

n = 14

mean = 22 cm 

n = 65

mean = 30 cm 

rubberlip surfperch

laser, reefs 

rubberlip surfperch

visual, reefs 

rubberlip surfperch

laser, platforms 

rubberlip surfperch

visual, platforms 

no data

no data

0 10 20 30 40 0 10 20 30 40

0 10 20 30 40 0 10 20 30 40

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.0

0.1

0.2

Proportion Proportion

Total length (cm) Total length (cm)

pile surfperch

laser, reefs 

pile surfperch

laser, platforms 

pile surfperch

visual, reefs 

pile surfperch

visual, platforms 

n = 35

mean = 23 cm 

n = 41

mean = 26 cm

n = 286

mean = 21 cm 

n = 340

mean = 22 cm

10 20 30 40 50

10 20 30 40 50

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.4

Proportion Proportion

Total length (cm)

n = 14

mean = 22 cm 

n = 65

mean = 30 cm 

rubberlip surfperch

laser, reefs 

rubberlip surfperch

visual, reefs 

rubberlip surfperch

laser, platforms 

rubberlip surfperch

visual, platforms 

no data

no data
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

103

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

0 10 20 30 40 50 60

Proportion

0 10 20 30 40 50 60

0 10 20 30 40 50 60

Proportion

0 10 20 30 40 50 60

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

Total length (cm) Total length (cm)

n = 333

mean = 24 cm 

n = 390

mean = 29 cm

n = 1977

mean = 26 cm 

n = 1287

mean = 29 cm

kelp bass

laser, reefs 

kelp bass

laser, platforms 

kelp bass

visual, reefs 

kelp bass

visual, platforms 

10 20 30 40 50 60 70

10 20 30 40 50 60 70

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

barred sand bass

laser, reefs 

barred sand bass

visual, reefs 

Total length (cm)

Proportion Proportion

n = 23

mean = 31 cm 

n = 252

mean = 34 cm 

barred sand bass

laser, platforms 

barred sand bass

visual, platforms 

no data

no data

0 10 20 30 40 50 60

Proportion

0 10 20 30 40 50 60

0 10 20 30 40 50 60

Proportion

0 10 20 30 40 50 60

0.0

0.1

0.2

0.3

0.4

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

Total length (cm) Total length (cm)

n = 333

mean = 24 cm 

n = 390

mean = 29 cm

n = 1977

mean = 26 cm 

n = 1287

mean = 29 cm

kelp bass

laser, reefs 

kelp bass

laser, platforms 

kelp bass

visual, reefs 

kelp bass

visual, platforms 

10 20 30 40 50 60 70

10 20 30 40 50 60 70

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

barred sand bass

laser, reefs 

barred sand bass

visual, reefs 

Total length (cm)

Proportion Proportion

n = 23

mean = 31 cm 

n = 252

mean = 34 cm 

barred sand bass

laser, platforms 

barred sand bass

visual, platforms 

no data

no data
Final Study Report – Carr et al 

104

Appendix 4 continued. Size distributions of reef fishes (> 9 cm TL) on platforms and natural reefs 

estimated visually by divers and by video with parallel lasers. Distributions are based upon all platforms 

and natural reefs combined across 3 years. N= total number of fish. 

10 20 30 40

10 20 30 40 10 20 30 40

0.0

0.1

0.2

0.3

0.0

0.1

0.2

0.3

0.4

0.5

0.0

0.1

0.2

0.3

0.4

Proportion

Proportion

n = 237

mean = 22 cm

n = 10

mean = 23 cm 

n = 1960

mean = 22 cm

halfmoon

laser, platforms 

halfmoon

visual, reefs 

halfmoon

visual, platforms 

Total length (cm) Total length (cm)

halfmoon

laser, reefs 

no data
Consequences of Alternative Decommissioning Options to Reef Fish Assemblages 

105

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 Royalty Management Program 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.