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OCSStudy

MMS 2004-005

ECOLOGICAL PERFORMANCE

OF oes PLATFORMS

AS FISH HABITAT OFF CALIFORNIA

Authored by:

Milton S. Love

DonnaM. Schroeder

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Subnlitted by:

~! Marine Science Institute

;\ ~i , University of California

, ,,\ Santa Barbara, CA 93106

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Prepared under:

MMS Cooperative Agreement No.1435-01-03-CA-72694

u.s. Department of Interior

Minerals Management Service

Pacific OCS Region

Camarillo

March 2006
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TABLE OF CONTENTS

Technical Summary

Study Product

Executive Summary

Task 1:

Distribution of Bocaccio (Sebastes paucispinis) and Cowcod

(5. levis) around Oil Platforms and Natural Outcrops off

California with Implications for Larval Production

Task 2: .Ecological Performance ofYoung-of-the-Year Blue Rockfish

(Sebastesmystinus) Associated with Oil Platforms and Natural

Reefs in California as Measured by Daily Growth Rates

Task 3:

Comparative Preda'tion Rate on Painted Greenling Between

Natural Habitat and an Offshore Oil Platform

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TECHNICAL SUMMARY

Study Title: Ecological Performance of OCS Platforms as Fish Habitat off California

Report Title: Ecological Performance of OCS Platforms as Fish Habitat off California

Contract Number: 1435-01-03-CA-72694

Sponsoring OCS Region: Pacific

Applicable Planning Area: Central and Southern California

Fiscal Years of Project Funding: FY2003-FY2005

Completion Date ofthe Report: March 2006

Costs: $175,000

Cumulative Project Cost: $175,000

Principal Investigator: Milton Love

Key Words: oil platforms, platforms, California, rockfishes, Sebastes, ecological performance, decommissioning, platform decommissioning, bocaccio, cowcod, blue rockfish, Sebastes paucispinis, Sebastes levis,

Sebastes mystinus

Background and Objectives:

There are 27 oil and gas platforms in the waters off California. All platforms have a finite economic life

and the life spans of some California platform may be nearing an end. Once an industrial decision is made

to cease oil and gas production at a platform, managers must decide what to do with the structure, a process

known as decommissioning. During the decommissioning process, the MMS conducts detailed environmental reviews of any proposed projects to evaluate the impacts from platform removal on regional fish

populations. Removing pltitforms removes potentially usefill habitat, kills numerous fishes, and may have

adverse impacts on regional populations of rockfishes and othel' sp~cies on the Pacific OCS. Thus, the assessing of habitat quality greatly bears upon platform ,decommissioning issues, as questions about Essential

Fish Habitat and the ecological role of Pacific OCS platforms are still unresolved.

Previous federal government funded investigations found that platform fish assemblages are similar to

those of natural reefs and differences were due almost entirely to the greater numbers of more species of fishes

around platforms, rather than differences in species composition. At least 85 species of fish were observed at

platforms and 94 species at the outcrops. Rockfishes dominated both habitats, comprising 89.7% of all fishes at

platforms and 92.5% at outcrops. Almost all of the more abundant species that the researchers observed were

more common around platforms. Species that were more common at one or ri10re platforms than at liatural

reefs included cowcod and bocaccio (young-of-the-year (YOY), juvenile, and adult), copper, greenspotted,

greenstriped, YOY widow, vermilion, canary and flag rockfishes and YOY juvenile and adult lingcod.

In particular, these studies found that (1) platforms tended to have higher abundances oflarge fishes, particularly ofsuch economically important species as cowcod, bocaccio, and lingcod,than did most or all natural

reefs and that (2) in general, platforms harbored higher densities of young-of-the-year (YOY) rockfishes than

did nearby natural outcrops or, indeed, most other outcrops surveyed in central and sOllthern California.

However, less well known is how important these fishes are on a regional basis and how well they fare

around these artificial habitats compared to natural reefs. This is often referred to as "ecological performance." Among the key issues in the Pacific OCS platform reefing debate is defining the ecological performance of fishes, and by extension the role that these fishes may play in the recovery of fish populations.

Thus, the goal of this study was to determine certain aspects of the ecological performance of fishes

living on offshore platforms compared to those living 011 natural reefs.
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Description:

The comparative ecological performance of fishes at oil platforms and natural outcrops was measured

through three tasks.

Task One: Larval production of bocaccio and cowcod at platforms and natural reefs

In this task, the amount of larvae per unit area produced by bocaccio and cowcod was estimated and

compared with that produced by both species on natural outcrops in the same general area. Thiswas done

by determining the densities and sizes of bocaccio and cowcod at platforms and natural reefs and, knowing

the size-specific fecundity of each species, computing the larval production of the fishes at each location.

Task Two: Ecological performance of young-of-the-year blue rockfish associated with oil

platforms and natural reefs.

Comparing the growth rates offishes living around platforms with those on natural reefs is one method of contrasting the overall health of these animals. If growth rates of juvenile rockfish at platforms are

similar (or better) thanthose from reefs, it implies that the young rockfishes at the platforms are at least as

likely to grow and develop as those from reefs. In this task, the daily growth rates of young-of-the-year blue

rockfish living around three platforms and three natural outcrops were compared.

Task Three: Predation Rate on Painted Greenling Between Natural Habitat and an Offs~ore Oil

Platform.

Another measure of ecological performance is mortality rate. In this task we compared the mortality

rate of young painted greenling at a platform with that of fish at a natural outcrop..

Significant Results:

Task 1: In this stpdy, we used data from manned submersible studies conducted between 1995 and

2002 around seven platforms and over 80 deeper water reefs in southern and centtal California. We focused

our analyses on bocaccio and cowcod, species that had been economically important to recreational and

commercial fishermen and were declared over-fished by the National Marine Fisheries Service.

OveraIl, we observed 1,054 bocaccio of all sizes at platforms and 976 at reefs, and 125 cowcod at platforms and 134 at reefs. Among bocaccio estimated to be mature, we observed 313 bocaccio at platforms and

313 at natural reefs and 38 mature cowcod at platforms and 61 at reefs. Adult fishes were patchily distributed

among both platforms and natural reefs. Fifty-seven percent of the natural reefs had mature bocaccio, as

did four of seven platforms. Forty-two percent of natural reefs harbored mature cowcod, as did two of five

platforms. Two platforms, Gail and Hidalgo, harbored relatively high densities of both species. Individuals

of both species tended to be larger at the platforms, particularly those inhabiting Platform Gail.

Because both densities and mean lengths of both species were higher at Platform Gail than at any

natural reef, their potential larval production at that platform was far higher than at any natural reef. We

estimated that if Platform Gail (whose footprint is 0.5337 ha) were removed, it would be the equivalent of

removing 12.57 l1a of average-producing natural habitat in southern California for cowcod, or equivalent to

removing 29.24 ha ofaverage-producing natural habitat in southern California for bocaccio.

, This study demonstrated that, in some instances, fishes at platforms provide significant amounts of

larvae, numbers that may be of regional importance.

Task 2: The daily growth rates ofYOY blue rockfish collected during the fall of 1999 at three platforms

and three natural reefs were compared. There was no evidence that fish at platforms grew more slowly than

those living on natural reefs. Comparison of growth rates between fishes living at Platform HoIly and Naples

Reef implied that YOY blue rockfish may, in some instances, grow faster at platforms.

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Disclaimer

This report had 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 ofthe authors, 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

Available for viewing and in PDF at:

www.lovelab.id.ucsb.edu

Minerals Management Service

Pacific OCS Region

770 Paseo Camarillo

Camarillo, CA 93010

805-389-7621

Milton Love

Marine Science Institute

University of California, Santa Barbara

Salita Barbara, CA 93106

805-893-2935

Suggested Citation

Love, M.S. and D.M. Schroeder. Ecological performance of OCS platforms as fish habitat off California.

MMS OCS Study 2004-005. Marine Science Institute, University of California, Santa Barbara, California.

MMS Cooperative Agreement Number 1435-01-03-CA-72694.

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Task 3: This research was conducted at l:\-vo sites, Platform Holly and Naples Reef, that are located near

each other in the Santa Batbara Channel using the painted greenling, Oxylebius pictus (Hexagrammidae),

a small reef fish common to offshore platforms and kelp beds off California. The experiment showed that

juvenile painted greenling residing at Naples Reef experienced a relative predationrate more than 2.5 times

greater than the estimated rate experienced by juveniles residing at Platform Holly. This is likely due to the

relatively low density of predators that live in platform midwaters compared to natural reefs. This implies

that the large numbers of young fishes living around the platforms of southern California have lower mortality rates due to predation, than do these fishes inhabiting natural reefs.

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STUDY PRODUCTS

PAPERS

2005 Love, M. S. D. M. Schroeder, and W. H. Lenarz. Dis~ribution of bocaccio (Sebastes paucispinis) and

cowcod (Sebastes levis) around oil platforms and naturaloutcrops off California with Implications for

larval production. Bull. Mar. Sci. 77:397~408.

2005 Love, M. S., E. Brothers, D. M. Schroeder, and W. H. Lenarz. Ecological performance of young-of~the

year blue rockfish (Sebastes mystinus) associated with oil platforms and natural reefs in California as

measured by daily growth rates. Bull. Mar. Sci. Submitted for Publication.

PAPERS PRESENTED

Presentations by Milton Love:

Oil platforms as fish habitat. Minerals Management Service Symposium, Oceanology International, New

Orleans, Louisiana. May 2003.

Fish Assemblages of southern California oil platforms. Mineral Management Service, Decommissioning

Offshore Platforms and Pipelines: Environmental Studies Workshop, Catalina Island. October 2003.

Fish Assemblages of southern California oil platforms. Cabrillo Marine Aquarium, San Pedro, CA. November 2003.

Oil platforms as fish habitat. Pt. Lobos Association, Monterey, California. January 2004.

For now we see through a glass, darkly: a potpourri of observations on the fish assemblages of oil/gas platforms and natural reefs in southern California. Western Groundfish Conference, Victoria, British Columbia. February 2004.

Oil platforms as fish habitat. Centro de Investigacion Cientifica y de Educacion Superior Ensenada (CICESE),

Ensenada, Mexico. March 2004.

The role of oil and gas platforms in fish production and aggregation in southern and central California.

Friends of Moss Landing, Moss Landing, California. July 2004.

The role of oil and gas platforms in fish production and aggregation in southern and central California.

University of Alaska, Juneau. July 2004.

The role of oil and gas platforms in fish production and aggregation in southern and central California.

Plains Oil Company, Santa Maria, CA. Oct. 2004.

The role of oil and gas platforms in fish production and aggregation in southern and central California.

Ocean Explorers, 27 January 2005.

The role of oil and gas platforms in fish production and aggregation in southern and central California.

Environmental Defense, Oakland, CA. 24 March 2005.

More fun than working for a living - tales of 10 years of research on the fishes of California oil platforms,

CARAH, Biloxi, 11 April 2005.

An overview of fish assemblages of offshore oil and gas platforms and natural reefs in southern and central

California. American Fisheries Society, Anchorage, Alaska, 11 September 2005.

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Presentations by Donna Schroeder:

Comparative juvenile reef fish recruitm~iit ahd ni.ortality between bffshore oillgas platforms and natural

reefs. CARAH, Biloxi, Miss.12 April 2005.

Patterns in juvenile reef fish recruitment to offshore oil/gas platforms and natural reefs in relation to upwelling. American Fisheries Society, Anchorage, Alaska, 11 September 2005.

POSTERS

Emery, B.M., M.M. Nishimoto 1. Washburn, M. Love, 200~, "Alternative fate estimation of oil rig bocaccio

recruits using HF radar;' Eastern Pacific Ocean Conference, Catalina Island, CA, 24-27 Sept., poster

presentation

Emery, B., M. Nishimoto, L. Washburn, and M. Love. Do offshore platforms affect the fate of recruiting

bocaccio? An analysis based on HF radar derived surface trajectories. Western Groundfish Conference,

Victoria, British Columbia, Feb. 2004.

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ECOLOGICALPERFORMANCE OF

OCS PLATFORMS AS FISH HABITAT OFF CALIFORNIA

EXECUTIVE SUMMARY

Information Needed

There are 27 oil and gas platforms in the waters offCalifornia. These platforms are located benveen 1.2

and 10.5 miles from shore and at depths ranging from 11 to 363 m (35~1,198 ft.). All platforms have a finite

economic life and the life spans of some California platform may be nearing an end. Once an industrial

decision is made to cease oil and gas production at a platform, managers must decide what to do with the

structure, a process known as decommissioning. Regarding oil and gas platforms, the Minerals Manage~

ment Service (MMS) defines decommissioning as the process of ending operations and returning the lease

or pipeline right-of-way to a condition that meets the requirements of the regulations. The MMS works to

ensure that wells are plugged to preventpollutionj that pipelines are decommissioned to prevent seepage of

hydrocarbons and removed to minimize conflicts with other uses ofthe Outer Continental Shelf (OCS); and

that all sites are cleared of obstructions to minimize use conflicts. During the decommissioning process, the

MMS conducts detailed environmental reviews of any proposed projects to evaluate the impacts from platform removal on regional fish populations. Removing platforms removes potentially useful habitat, kills numerous fishes, and may have adverse impacts on regional populations ofrockfishes and other species on the

Pacific OCS. Thus, the assessing of habitat quality greatly bears upon platform decommissioning issues, as

questions about EssentialFish Habitat and the ecological, role of Pacific OCS platforms are still unresolved

Several MMS- and USGS-funded investigations and a number of pilot studies have been completed

and provide background for the present effort. The habitat value of a number of platfonns on the Pacific

OCS was determined under OCS Study MMS 99-0015, The Ecological Role ofNatural Reefs and Oil and Gas

Production Platforms on Rocky ReefFishes in SOl/them California [available as a pdf at www.1oveJab.id.ucsb.

edu]. hi that study, researchers from the University of California at Santa Barbara (UCSB) compared fish

assemblages from eight platforms and many natural outcrops throughout southern California.

Overall, the study found that platform fish assemblages are similar to those of natural reefs and differences were due almost entirely to the greaternumbers of more species of fishes around platforms, rather

than differences in species composition. At least 85 species offish were observed at platforms and 94 species

at the outcrops. Rockfishes dominated both habitats, comprising 89.7% of all fishes at platforms and 92.5%

at outcrops. Almost all of the more abundant species that the reseai'chers observed were more common

around platforms. Species th~lt were more common at one or more phltforms than at natural reefs included

cowcod and bocaccio (young-of-the·year (YOY), juvenile, and adult), copper, greenspotted, greenstriped,

YOY widow, vermilion, canary and flag rockfishes and YOY juvenile and adult lingcod.

Two of the major conclusions frol11 this study were:

1) Platforms tended to have higher abundances of large fishes, particularly of such economicaIly"important species as cowcod, bocaccio, and lingcod, than did most or all natural reefs. It is likely that this is

due to the relatively low fishing. effort around many platfornis in southern California, thus the platforms

are acting as de facto marine protected areas. The study compareddensities of all rockfishes (of all sizes), all

rockfishes greater than or equal to 30 cm, and adult bocaccio and cowcod that they observed at platforms

and at natural outcrops. In most instances, fishes 30 cm or larger were less abundant, or sometimes absent,

from many natural reefs compared to most platforms. Pla,tforn'! Gail, in particular, held some of the highest

densities of the important but severely depleted cowcod and bocaccio that were seen anywhere during the

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observations. The study speculatedthat platforms, such as Platform Gail, might be a major source of cowcod

and bocaccio larvae and thus might be important fish habitat on a regional level.

2) The research also found evidence that, in general, platforms harbored higher densities of youngof-the-year (YOY) rockfishes than did nearby natural outcrops or, indeed, most other outcrops surveyed in

central and southern California. The study pointed out that platforms occupy more of the water column

than do most ~aturat outcrops and presettlement pelagic juvenile rockfishes are much more likely to en.

counter these tall structures than the relatively low-lying natural structures. The researchers also observed

that many of the major predators of young rockfishes are species that live and stay close to the bottom and

that, in general, these species do not ascend the platform jacket up into the water column, and thus are absent from the platform midwaters.

However, while it is undisputed that large numbers of both YOY and adult fishes populate platform

habitats, less well known is how important these fishes are on a regional basis and how well they fare around

these artificial habitats compared to natural reefs. This is often referred to as "ecological performance."

Among the key issues in the Pacific OCS platform reefing debate is defining the ecological performance of

fishes, and by extension the role that these fishes may play in the recovery of fish populations.

One way to determine the ecological performance and relative importance of a platform as fish habitat

is to compare the amount oflarvaeproduced by fishes at platforms with that produced on natural outcrops

in the same general area. This may indicate whether a platform is a significant source of larvae when compared to natural reefs

Regarding YOY rockfishes, soine observers have suggested that, while settlement of young rockfish

may be high around some platforms, these structures may not supply suitable habitat or sufficient food for

adequate growth and maturity. One way of addressing these concerns is to examine the health of young

rockfishes around platforms and compare this to the health Of young rockfish of the same species living on

natural reefs. Comparing the growth rates of fishes living around platforms with those on natural reefs is

one method of contrasting the overall health of these animals. If growth rates of juvenile rockfish at platforms are similar (or better) than those from reefs, it implies that the young rockfishes at the platforms are

at least as likely to grow and develop as those from reefs.

A third way of approaching ecological performance is by comparing the mortality rate of young fishes

at platforms with those at natural reefs. If survival and mortality rates of at platforms are similar (or better

in the case of survival) than those from reefs, it implies that fishes at the platforms' are at least as likely to

survive to adulthood or to enter a fishery as those from natural reefs.

Thus, the goal of this study was to determine certain aspects of the ecological performance of fishes

living on offshore platforms compared to those living on natural reefs.

Research Sumnlary

Task 1. Distribution of bocaccio (Sebastes paucispiuis) and cowcod (Sebastes levis) Around Oil

Platforms and Natural Outcrops off California with Implications for Larval Production

In this study, we used data from manned submersible studies conducted between 1995 and 2002 around

seven platforms and over 80 deeper water reefs in southern and central California. We focused our analyses

on bocaccio and cowcod, species that had been economically important to recreational and commercial

fishermen and were declared over-fished by the National Marine Fisheries Service.

We considered a reef site appropriate for inclusion in this study if it was in a depth of least 60 m for

bocaccio and 80 m for cowcod and was categorized as "rocky high relief," "rocky low relief," or "boulders."

Based on these parameters, 63 reefs and seven platforms (Gail, Grace, Harvest, Hermosa, Hitlalgo, l'IoJly, and

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Irene) were used in the bocaccio analyses and 52 reefs and five platforms (Gail, Grace, Harvest, Hermosa, .

and Hidalgo) in the cowcod dataset. At each survey site, we computed the adult densities and the length frequencies of both species. From these densities and length frequencies and from published data on fecundity

at length, we then computed the potential larval production of each species at each site. In general, because·

densities of both species were quite low or nonexistent, particularly at natural reefs, there was little or no

potential larval production.

Overall, we observed 1,054 bocaccio of all sizes at platforms and 976 at reefs, and 125 cowcod at platforms and 134 at reefs. Among bocaccio estimated to be mature, we observed 313 bocaccio at platforms and

313 at natural reefs and 38 mature cowcod at platforms and 61 at reefs. Adult fishes were patchily distributed

among both platforms and natural reefs. Fifty-seven percent of the natural reefs had mature bocaccio, as

did four of seven platforms. Forty-two percent of natural reefs harbored mature cowcod, as did two of five

platforms. Two platforms, Gail and Hidalgo, harbored relatively high densities of both species. Individuals

of both species tended to be larger at the platforms, particularly those inhabiting Platform Gail.

Because both densities and mean lengths of both species were higher at Platform Gail than at any

natural reef, their potential larval production at that platform was far higher than at any natural reef. We

estimated that if Platform Gail (whose footprint is 0.5337 ha) were removed, it would be the equivalent of

removing 12.57 ha of average-producing natural habitat in southern California for cowcod, or equivalent to

removing 29.24 ha of average-producing natural habitat in southern California for bocaccio.

This study demonstrated that, in some instances, fishes at platforms provide significai1t amounts of

larvae, numbers that may be of regional importance.

Task 2. Ecological Performance ofYoung-of-the-Year Blue Rockfish (Sebastes mystilluS) Associated

with Oil Platforms and Natural Reefs in California as Measured by Daily Growth Rates

In this study, we compared the daily growth rates ofYOY blue rockfish collected during the fall of 1999

at three platforms and three natural reefs. Comparisons were made between fish at Platform Irene and a reef

at Santa RosaIsland (both are in the California Current and are 84 km apart), Platform Holly and Naples Reef

(in the same water mass and located with 8 km of each other) and Platform Gilda and Anacapa Island (in

different water masses and within 16 km of each other). Collections. were made during one day at each site. In

the laboratory, each fish was measured (standard length, SL) to the nearest millimeter and its sagittal otoliths

removed. A mid-sagittal section was prepared to preserve both the otolith margin and as well as early growth

around the primordium. Microincrements were counted with the aid of a video microscope (to about 1500x

magnification). The typical counting path was from the primordium to the dorsal otolith margin.

We collected a total of 187 blue rockfish; collections ranged in number from 15 fish at Santa Rosa Island to 39 fish at Naples Reef. Fish were sampled between 15 September and 23 November 1999. Calculated

mean daily growth rates of individuals ranged from 0.27 to 0.46 mm/day and mean growth rates at each

site varied between 0.30 and 0.38 mm/day. Mean growth rates were statistically different among most sites.

Growth rates were significantly different between fish living at Platform Holly and Naples Reef and those.

living at Platform Gilda and Anacapa Island. In both instances, fish grew more rapidly at the platforms.

However, because fish at Gilda and Anacapa were collected two months apart, growth comparisons were not

considered valid. There was no statistical difference between blue rockfish growth rates at Platform Irene

and Santa Rosa Island. We combined the growth rates of fish from Platform Irene and Holly and compared

the mean growth rate with that offish living at Naples Reef and Santa Rosa Island. Blue rockfish living at the

platforms gi'ew 0.016mm/day more quickly.

In this study there was no evidence that fish at platforms grew more slowly than those living on natural

reefs. Comparison of growth rates between fishes living atPlatform Holly and Naples Reef implied that YOY

blue rockfish may, in some instances, grow faster at platforms.

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Task 3. Comparative Predation Rate oil Painted Greenling Between Natural Habitat and an

Offshore Oil Platform

We conducted this study at two sites, Platform Holly and Naples Reef that are located near each other

in the Santa Barbara Channel. We conducted our study at Platform Holly on the shallowest (9m) horizontal

crossbeams and at Naples Reef in 10 m depth. Our model organism, the painted greenling, OxylebiHS pictus (Hexagratnmidae), is a small reef fish common to offshore platforms and kelp beds off California. We

employed a tethering approach to compare relative predation rates on juvenile painted greenling between

the platform and natural habitat. This benthic fish lacks a swim bladder, and its most frequently observed

daytime behavior is to simply rest on the bottom, making tethering a suitable experimental technique.

Relative predation rate on painted greenling was significantly higher at Naples Reef than at Platform

Holly. Naples Reef also had higher painted greenling density and higher predator density. We also found that

the number of predator species was much greater at Naples Reef than at Platform Holly.

The tethering experiment shows that juvenile painted greenling residing at Naples Reef experienced a 0

relative predation rate more than 2.5 times greater than the estimated rate experienced by juveniles residing

at Platform Holly. This is likely due to the relatively low density of predators that live in platforl11midwaters

compared to natural reefs. This implies that the l,arge numbers of young fishes living around the platforms of

southern California have lower mortality rates due to predation, than do these fishes inhabiting natural reefs.

Conclusions

We conducted three studies that measured and compared various aspects of the ecological perfor- o •

mance of fishes living on platforms and natural reefs. From this research, it is apparent that fishes living

around platforms perform at least as well as those inhabiting natural reefs and, in some instances, better.

For instance, it is clear that Platform Gail, and to a lesser extent Platform Hidalgo, are very important

regional sources oflarvae for both cowcod and bocaccio. This is likely to remain the case for as long as these

platforms act as de facto marine reserves and for as long as stocks of these two species remain depressed.

Parenthetically, our unpublished density pattems of other species, for instance greenspotted, greenblbtched,

and flag rockfishes, strongly imply that platforms are also majm: exporters of these larvae.

Our research also has considerable bearing on the issue of the extremely heavy densities of youngof-the-year rockfishes living around oil platforms. In many years, platform midwaters harbor tens or even

hundreds of thousands of young blue, olive, squarespot, widow, and yellowtail rockfish and bocaccio. Some

observers have questioned the fate of these fishes, implying that their mortality rates might be higher than

congeners living on natural reefs. Our research demonstrates that, in some instances, young rockfishes living

around oil platforms suffer less mortality than those living over natural reefs and there is no evidence that

mortality rates of fishes living around oil pbtforms is greater than that of natural reef fishes.

"'Vhile these studies were limited in scope, we consider our results to be sufficiently strong to demonstrate the importance ofsome artificial structure in driving marine population dynamics. It is now arguable

that fishes living around oil platforms may be quite important to regional fish production.

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Task 1: Distribution of Bocaccio (Sebastes paucispinis) and Cowcod

(So levis) around Oil Platfonlls and Natural Outcrops off California with

Implications for Larval Producti6n . .

Milton S. Love, Donna lvI. Schroedel~ and William H. Lenarz

.Absttact

Thereis increasing evidence that some California oil platforms form important habitats for a

number of economically ih1portant fishes. We asked to what extent might platforms be important

as producers of larvae of several overfished species (bocaccio, Sebastes paucispinis Ayres, 1854 and,

cowcbd, S. levis Eigenmann and Eigenmanri, 1889) on a local or regional basis. We compared adult

densities and potentiallarval production of these species at platforms and natural outcrops in California. Densities of mature bocaccio and cowcod were highly variable among survey sites, but were

generally very low at both natural reefs and platforms. However, the mean densities for both species

were higher around platforms than at natural reefs. Two of the three platforms (Gail and Hidalgo)

that harbored mature bocaccio had larger mature individuals than did any natural reef. Platform

Gail had by far the highest densities of both mature bocaccio and cowcod of any natural or humanmade habitat and the potential larval production of both species at Platform Gail was much higher

than at any other site surveyed. We estimated the removal of Platform Gail would be the equivalent

of removing 12.57 ha of average- producing natural habitat in southern California for cowcod or

29.24 ha of average-producing natural habitat for bocaccio. These results may have implications for

the platform decommissioning process.

Introduction

There are 27 oil and gas platforms off the coast of southern and central California. Located in both

state and federal waters, these structures are situated in bottom depths ranging from 11 to 363 m and can

have footprints as large as 10,606 m2 (Love et a1., 2003). While all of these platforms are currently either

pumping oil or gas or are being used as transfer st~ltions for these products, platforms have a finite economic

life span. Once an industrial decision is made to cease oil and gas produ~tion, managers must decide what

to do with the structure, a process known as decommissioning. Decommissioning is a complex process, involving state and federal agencies, corporate entities, and such stakeholders as recreational and commercial

fishermen and non-consumptive users (Schroeder and Love, 2004). Ultimately, a decommissioned platform

could be left in place, removed to some point below the sea surface, toppled to lie on the sea floor, or totally

removed (Schroeder and Love, 2004).

One issue in the decommissioning process is the role that platforms may playas fish habitat. There

is increasing evidence that some California platforms form important habitats for many economically il11-

pOl'tant fishes. This is particularly true of the rockfishes (genusScbastes) that often comprise over 90% of

all fishes observed around platforms in southern and central California waters (Love et a1., 2003). Platform

habitat may serve at least two functions for these fishes. First, the midwaters of many platforms serve as

mirsery habitat for a suite of rockfishes and other fish species, often harboring higher densities of these

species than do nearby natural outcrops (Love et aI., 1999; Carr et aI., 2003; Love et aI., 2003). Compared to

most natural reefs, a platform's size, structural complexity, and high vertical profile probably provide pelagic
2

a b

Figure 1. a) Adult bocaccio (Sebastes pallcispinis) and b) cowcod (5. levis) at the bottom of Platform Gail, eastern Santa

Barbara Channel. Note the undercut area below the bottom-most cross beam, this provides shelter for both species.

juvenile rockfishes and larvae ofother species with a relatively strong stimulus to trigger settlement. In addition, most platforms have few large fisheS il1 the midwaters and thUs predation on young fishes is likely to

be low (Schroeder et al., 2000; Love et al., 2003). Platform bottoms, where the jacket and conductor pipes

meet the seafloor, may harbor high densities ofsubadult and adult fishes, again usually comprised primarily

of rockfishes (Love et al., 1999; Carr et el., 2003; Love et aI., 2003). The high densities of larger fishes at the

platform bottoms is due to both acceptable habitat and because some platforms are rarely fished and thus

act as de facto marine reserves (Schroeder and Love, 2002; Love et al., 2003).

Off southern California, fishing pressure by both recreational and commercial fishermen on natural

outcrop species has been very heavy for many decades (Love et al., 1998,2002). In particular, the adults of

economically important species such as bocaccio (5ebastes paucispinis Ayres, 1854) and cowcod (5. levis Eigenmann and Eigenmann, 1889) are now uncommon or even absent on many natural outcrops in southern

California (Love et aI., 1998,2003; Love and Yoklavich, unpubl. data).

Given the depleted state of many rockfish species on natural reefs (seven species have been declared

overfished by NOAA Fisheries), and the relative abundance ofsome ofthese species on some platforms, we

asked to what extent nlight platforms be important as producers oflarvae on a local, or even regional, basis?

That is, how important are adult populations of rockfishes on platforms? To help answer that question, we

conducted a pilot study that focused on cowcod and bocaccio (Fig. I), two species declared overfished by

NOAA Fisheries and the two overfished species that are most abundant as adults around California platforms. We compared adult densities and potential larval export of these species at both offshore platforms

and natural outcrops in central and southern California. A knowledge of the relative importance of these

human-made structures as fish habitat could playa role in decommissioning decisions.

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Materials and Methods

Fish surveys

Between 1995 and 2002, we surveyed platforms sited over a wide range of bottom depths, ranging between 29 and 224 m, and sited from north of Point Arguello to off Long Beach, southern California. Most

of our platform surveys were conducted at seven structures (Platforms Irene, Hidalgo, Harvest, Hermosa,

Holly, Grace, and Gail) located in the Santa Barbara Channel and Santa Maria Basin. In addition, we surveyed over 80 deeper-water outcrops (many in the vicinity of platforms), in waters between 30 and 360 m

deep. Most ofthese deeper-water natural sites were visited once, a few were surveyed during as many as four

years and, one outcrop, North Reef near Platform Hidalgo, was sampled annually.

We surveyed fish assemblages using the Delta submersible, a 4.6-meter, 2-person vessel, operated by

Delta Oceanographics of Oxnard, California. Aboard the Delta, we conducted belt transects about two meters from the substrata, while the submersible maintained a speed of about 0.5 knots. At the platforms,

transects were made around the bottom of the platform and around each set of crossbeams to a minimum

depth of20-30 m below the su,rface (e. g., midwater habitat). The belt transect was also used to sample the

shell mounds surrounding the platforms and natural rock outcrops. The shell mounds and outcrops were

sampled in consistently the same fashion as the platform method described above.

Submersible surveys were conducted during daylight hours between one hour after sunrise and two

hours before sunset. During each transect, observations were taken from one viewing port on the starboard

side of the submersible. An externally mounted hi-8 mm or digital video camera with associated lights

filmed the same viewing fields as seen by the observers. The observer identified, counted, and estimated the

lengths of all fishes and verbally recorded those data on the video. All fishes within 2 m of the submarine

were counted. AlI.fish larger than the size of first maturity were observed within 2 m of the bottom (none.

were seen in midwater transects). Thus, densities were calculated as fish per m2

• Fish lengths were estimated

using a pair of parallel lasers mounted on either side of the external video camera. The projected reference

points were 20 cm apart and were visible both to the observer and the video camera. An environmental

monitoring system aboard the submarine continuously recorded date and time, depth and altitude of the

vessel above the sea floor. The environmental data were overlaid on the original videotape upon completion

of each survey. .

Transect videos were reviewed aboard the research vessel or in the laboratory. Field observations were

transcribed into a database. For each fish, we recorded the following information: 1) species (if known); 2)

its estimated total length; and 3) in the surveys over natural reefs, the habitat it occupied (e.g., rock, sand,

mud, cobble, or boulder).

Many years of experience along the Pacific Coast have shown that if the Delta is moving at a constant

and slow rate ofspeed, as in these surveys, there is very little obvious effect on demersal rockfishes (M. Love,

pers. obs., V. O'Connell, per. obs., Alaska Department of Fish and Game, and M. Yoldavich, NOAA Fisheries,

pers. obs.). Certainly, we noticed virtually no movement at all from most of the fishes in this study as the

research submersible passed by.

Data analyses

While our surveys estimated size for most observed fish, we were not able to estimate sex ratios. Cowcod are not sexually dimorphic and it seemed reasonable to assume an equal female to male ratio. Bocaccio

are sexually dimorphic and sex ratios of commercial catches are not 1:1 and are related to size. We obt~ined

data to estimate length-specific sex ratios for bocaccio from Mark Wilkins (NOAA Fisheries, AFSC, Seattle, WA), in the form oflength compositions by sex from the triennial bottom trawl survey conductedby

the AFSe. The trawl survey uses finer meshed nets than comn1ercial operations and all captured fish are

3
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sampled for length compositions. Commercial operations also discard some fish due to market demand or

. regulations.

Our submersible survey estimated fish size to the nearest 5 cm. Observers were not able to estimate

size for a small proportion of fish (0.006 for bocaccio and 0.048 for cowcod). These fish were assumed to

be smaller than the size of maturity and not included in the estimates. The trawl survey measured size to

the nearest 2 cm. We converted the trawl survey length compositions to 5 cm intervals. NOAA Fisheries

estimated the total abundailCe of bocaccio off southern and central California in numbers of fish by size

and sex for each year of the survey. The estimates of total numbers of fish varied considerably among years.

Since growth is sexually dimorphic for bocaccio and there is considerable variation in year-class strength, we

decided it would be best to calculate the ratios of females to total fish at each year and then average the ratios,

in order to give equal weight to each year's estimates. The results indicated that ratios varied without trend

through 60 cm and then rapidly increased to 1 (all females) at 70 cm. We concluded that because females

grow faster and to larger size than males it would be reasonable to apply the average female to total fish ratio,

0.44, behveen 25 and 60 cm, the observed value, 0.82, for 65 cm, and 1 for larger fish (Table 1).

We used estimates of maturity schedules for bocaccio and cowcod obtained from the study area (M.

Love, unpub1. data). We believe it was more appropriate to use these data than other published results from

fish that were collected from more northern waters. These data are summarized in Love et a1. (1990), but the

published results were not in sufficient detail for the purpose ofthe present study. We converted to maturity

data in 1-5 cm intervals. We estimated maturity schedules for combined sexes by sum for each sex of proportion mature weighted by proportion for that sex (Table 2).

We used the size fecundity estimates of Love et a1. (1990) to estimate number of eggs of mature females

as these were derived from fishes collected from the study area. The bocaccio estimates are similar to those

estimated by Phillips (1964) from fish that were collected from more northern waters.

For bocaccio, Fecundity =1.15 (LI\3.2696), and for cO\vcod, Fecundity =1.702(LI\3.1542), where L is

total length in centimeters.

To calculate the number of larvae that could be produced by resident bocaccio and cowcod at a given

area, we first segregated all observed fish during a survey into size classes. For bocaccio, we estimated the

number of females in each size class using the sex ratio data in Table 1 (cowcod are assumed to have a 1:1

ratio). Next, for each species in each size class, we used maturit); schedules (Table 2) to estimate the proportion of mature females in each class. Length-fecundity equations were then used to determine the number

oflarvae each female could produce. Larval production is therefore linked to fish density and rates are scaled

appropriately across sites.

We estimated area surveyed by multiplying transect distance by 2, because survey width was 2 m, and

then calculated densities per area for each species and size. Transect lengths were estimated using a pair of

parallel lasers mounted on either side of the external video camera. The projected reference points were 20

cm apart and were visible both to the observer and the video camera. Transect lengths were computed by

counting the number of 20 em laser segments in 15 s subsamples (one per min) throughout the transect,

calculating speed based on those counts and averaging them over the whole transect, and multiplying that

average speed by the transect duration. The 15 s subsamples were made during the first 15 s of each minute

of the transect in which the laser points were visible. We first summed all data for a dive. Sometimes there

was more than one dive for a station in a year. In this case, we averaged the results of the dives for estimates

of the station-year. In many cases a station was surveyed in more than one year and we averaged the results·

over years for each of those stations. We also grouped stations that were adjacent to each other.

Estimates of footprint areas for the platforms come from Love et a1. (2003). We estimated area of natural reefs needed to produce the same amount of larvae as an average platform by multiplying the average

area of a platform by the ratio of average platform production to average reef production..

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Table I. Estimated ratio of female to total boeaeeio, in 5 e111 intervals, in sOllthern California.

Female:Total

Size em Observed Estimated

25 0.40 0.44

30 0.45 0.44

35 0.48 0.44

40 0.45 0.44

45 0.55 0.44

50 0.34 0.44

55 0.40 0.44

60 0.48 0.44

65 0.82 0.82

70 1.00 1.00

75 1.00 1.00

Table 2. Maturity schedules, in 5 em intervals, estimated for boeaecio and cowcod in southern California.

Bocaccio Cowcod

Sizecm Female Male Combined Female Male Combined

30 0.00 0.00 0.00 0.00 0.00 0.00

35 0.22 0.33 0.29 0.00 0.07 0.03

40 0.78 0.92 0.86 0.02 0.35 0.19

45 0.99 1 1 0.64 0.70 0.67

50 1.00 1 0.95 1.00 0.97

55 1.00 1.00 1.00 1

Results

In comparing larval production, fish densities, and ultimately habitat equivalence between platforms

and natural outcrops we restricted our analyses to habitats and depths most likely to harbor adult cowcod

and bocaccio (based on data from Love et aI., 2002 and Yoklavich et aI., 2000). A site was considered to be

appropriate habitat and retained for analyses if any starting depth was;::: 60 m for bocaccio or ;::: 80 m for

cowcod and if any patch bottom in that site was classified as "rocky high relief", "rocky low relief", or "boulders". Based, on these parameters, 63 reefs and seven platforms (Gail, Grace, Harvest, Hermosa, Hidalgo,

Holly, and Irene) were used in the bocaccio dataset and 52 reefs and five platforms (Gail, Grace, Harvest,

Hermosa, and Hidalgo) in the cowcod dataset.

Overall, we observed 1054 bocaccio of all sizes at platforms and 976 at reefs, and 125 cowcod at platforms and 134 at reefs. Among bocaccio estimated to be mature, we observed 313 individuals around platforms and 313 at reefs, and 38 mature cowcod at platforms and 61 at reefs. Adult fishes were patchily distributed among both platforms and natural reefs. Fifty-seven percent of s.urveyed natural reefs (36 out of

63) with appropriate habitat (as defined above) had mature bocaccio on them and 42% (23 out of 54) of

5
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Figure 2. Densities of mature bocaccio at seven platforms and 63 natural reefs in the southern California Bight and off central California, 1995-2002. Included are sites that were classified as "rocky high relief': "rocky low relief': or "boulders" and in depths of 60 m Or more.

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California Bight and off central California, 1995-2002. Included are sites that were classified

as "rocky high relief", "rocky low relief", or "boulders" and in depths of 80.m or more.

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surveyed natural reefs with appropriate habitat had adult cowcod on them. Platforms had nearly identical

ratios as at natural reefs, as 57% (4 out of 7) had adult bocaccio and 40% (2 out of 5) had adult cowcod.

Densities of mature bocaccio and cowcod were highly vatiable among survey sites, but were generally ve'ry low at both natural reefs and platform habitats (Figs. 2 and 3). The mean density on natural reefs

for bocaccio and cowcod was 0.15 per 100 m2 (SE 0.03) and 0.04 per 100 m2 (SE 0.01) respec~ively.Higher

densities of mature fishes on natural reefs tended to occur in more remote areas (Figs. 2 and 3). The mean

density around platforms for bocaccio and cowcod was higher, 1.25 per 100 m2 (SE 1.16) and 0.21 per 100

m2 (SE 0.19), respectively. While densities were much lower on reefs than on natural reefs at most sizes, relative numbers of medium-size fish tended to be higher on reefs than on platforms (Fig. 4).

For both species, the larger average adult size at platform habitat proportionally increased the potential

larval production at platforms compared to natural reefs, especially for bocaccio (Fig. 5). Mean (±lSE) larval production (no. eggs/m2

) at platform sites was 2883 (2597) for bocaccio and 743 (676) for cowcod, while

mean production for natural outcrop sites was much less, 254 (58) for bocaccio and 132 (34) for cowcod.

Of particular interest, Platform Gail had by far the highest densities of mature bocaccio (8.17 per 100

m2 compared to 1.46 for the highest density on a natural reef) and cowcod (1.00 pet 100 m2 compared to a

maximum of 0.23 for natural reefs) of any natural or human-made habitat in this study (Figs. 2 and 3). Platform Gail also had the highest potential larval production values, topping out at 18,397 eggs/m2 for bocaccio

and 3440 eggs/m2 for cowcod (Fig.S). Thismeansthat if Platform Gail (whose footprint is 0.5337 ha) were

removed during decommissioning it would be the equivalent of removing 12.57 ha of average-producing

natural habitat in southern California for cowcod, or equivalent to removing 29.24 ha of average-producing

natural habitat in southern California for bocaccio.

Discussion

Our study provides the first published evidence, based on direct underwater observations, for intense

depletion of both adult bocaccio and cowcod on many natural structures in southern California (previous

evidence came from fishery-dependent data, e.g., Love et al., 1998 and Butler et aI., 2003; and larval or juvenile surveys, e.g., Love, et al., 1998; Moser et aI., 2000; Butler et al., 2003). It is likely that these low densities

were due both tooverfishing and to poor larval and pelagic juvenile survivorship (Love et aI., 2002; Love et

aI., 2003). With the exception of Platforms Gail and Hidalgo, densities were also low for adults of both species at platforms.

Platform Gail harbored unusually high densities of adult bocaccio and cowcod. The high densities of

both species at Platform Gail are likely due to its status as a de facto marine protected area (Schroeder and

Love, 2002), a bottom depth that is commonly occupied by adult bocaccio and cowcod, and the presence

of a bottom crossbeam that provides a sheltering area for both species (Fig. 1). It is probable that the adult

bocaccio andcowcod living at Phltform Gail were derived from young-of-the-year (YOY) that had recruited

from the plankton to that platform's jacket, shell mound, or pipeline. During nine years ofsurveys, we have

on several occasions observed relatively high densities ofYOY bocaccio recruiting to the midwaters ofPlatform Gail and YOY cowcod to its shell mound and pipeline (Love et aI., 2003; Love and York, in press). In

addition, our research indicates that both species not only have recruited as YOYs to the jacket 01: surrounding structures, these year classes also have remained at the platform over succeeding years (Love et aI., 2003;

Love; unpubL data).

The densities ofbocaccio and cowcod we observed at Platform Gail were not only far higher than those

of any other platform or natural reef in southern California, they were higher than four of five deeper-water

sites surveyed in Soquel Canyon in central California and were surpassed only by an outcrop that likely has

never been fished (Yoklavich et aI., 2000). This natural refuge provides a comparison from deeper waters

7
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Figure 4. Average densities by size ofbocaccio and cowcod observed at natural reefs and platforms. Data from all dives

in suitable habitat and all fish sizes are included.

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Natural outcrops 0

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off central California, as most of the abundant species at the Soquel Submarine Canyon site (e.g., bocaccio,

cowcod, lingcod, greenspotted, and greenblotched rockfishes) are also those most characteristic ofthe jacket

bottom at Platform Gail (Love et aI., 2003). Yoklavich et al. (2000) make the point that the Soquel Canyon

site may be an important site for larval production, noting that "These areas appear to function as a natural

harvest refugium, potentially contributing new recruits to adjacent fished areas" through larval export. The

high densities and relatively large size of fishes at Platform Gail translate into substantially higher potential

larval export per unit area for that platfol"m than for any other site surveyed in our study.

On a regional basis, how important is larval bocaccio and cowcod production at Platform Gail? First,

from our research submersible surveys it is clear that there is little larval production from bocaccio and cow-· .

cod that live on natural outcrops in the Santa Barbara Channel. With the exception of the carbonate feature

Twelve Mile Reef (Fig. 2), located in the center of the Santa Barbara Channel, much of the sea floor in the

Channel (at depths frequented by adult bocaccio and cowcod) is composed ofsoft substrata (G. Cochrane,

United States Geological Survey, pel'S, comm.). The Twelve Mile Reef was at one time the major Santa Barbara Channel fishing ground for a number of rockfish species, including both cowcod and bocaccio (M.

Kronman, Santa Barbara Harbor Department, pel's. comm.; M. Love, unpub!. data). However, during our

surveys we observed no adult bocaccio and cowcod on that outcrop. Other, and smaller, Santa Barbara

Channel features (Fig. 2) also harbot'ed few or no adults of these species.

Figure 5. Comparison of potential larval production (no. eggs/m2) of sites that had at least one mature bocaccio (40

.natural reefs and four platforms) or one mature cowcod (25 natural reefs and two platforms). Bars representing platforms are darkened. Platforms in the appropriate depth range that did not harbor mature cowcod included Grace,

Harvest, Hermosa, and for bocaccio, Harvest, Hermosa and Holly.

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Rockfish'larvae may be partially retained in the east Santa Barbara Channel, ,vhere Platform Gail is

sited, through oceanographic fronts and eddies (Nishimoto, 2000). Under certain conditions, larvae generated within the Santa Barbara Channel may also be entrained in seasonal gyres located in the western Channel (Nishimoto and Washburn, 2002). Thus local sources of larvae may be critical to the maintenance of

Santa Barbara Channel rockfish populations and Platform Gail, apparently one of the major producers of

bocaccio and cowcod larvae in the Channel, may be quite important. It is interesting to note that some ofthe

highest densities ofYOY bocaccio we have observed anywhere in our studies were found at platforms Gilda

and Grace, which are located within a few kilometers of Platform Gail (M. Love, unpub!. data). Thus, there

is a possibility that these young fishes were generated as larvae at the latter structure.

While ~latform fish assemblages vary with platform bottom depth, it is clear that many ofthe platforms

off southern California, regardless of bottom depth, act as de facto marine reserves. At these platforms, fish

species in addition to bocaccio and cowcod have also responded to protection from fishing as densities of

other economically il~1portant species (e. g., brown, Sebastes allriculatlls, copper, Sebastes caurinus, flag, S.

rubrivinctus, greenblotched, S. rosenblatti, and greenspotted, S. chlOl'ostictus, rockfishes, and lingcod, Ophiodon elongatlls) are higher at platforms than at most or all southern California natural reefs (Schroeder and

Love, 2002; Love et al., 2003). It is likely that larval production of these species, per unit area, will also be

higher at platforms than at most natural habitats. Thus, the potential importance of platforms as marine refugia may be large given the generally very low densities of adults of a number of rockfish species on natural

reefs in southern California. If future platform decommissioning involves retaining some of the platform

jacket in place, it important to note that the high fish densities we observed would only be maintained if the

platforms remained protected from fishing.

Clearly, southern and central California platforms vary widely in size, bottom depth, and fish assemblages. For instance, ofthe platforms we surveyed, Platform Gail, and to a lesser extent, H~dalgo, were unique

in having high densities of mature bocaccio and cowcod. Given these variables, it would be premature to

judge the importance of all of these structures as fish habitat. In addition, all of our surveys were conducted in the fall and we do not know whether adult cowcod and bocaccio remain at any of these structures

throughout the year, although the interannual persistence of high densities oflarge bocaccio and cowcod at

Platform Gail lends credence to this hypothesis. However, i~ is clear from our analysis that platforms can be

important habitat for adult fishes, particularly of species that have been heavily exploited. Given the high

densities of adults ofmany species of economically important rockfishes and lingcod atound platforms and

the low densities of these san1e species on many or most natural reefs in southern California, it is quite possible that some platforms are of regi<?nal significance as sources of larval production and export for some

species. The extent oftbis significance should play an important role in determining the preferred option of

future decommissioning activities (removal or leave-incplace) once oil and gas production ceases.

10
Acknowledglnents

We would like to thank A. Bull, L. Thorsteinson, and G. Steinbach for their support of this research.

This research was funded by the Minerals Management Service (Contract Numbei' 1435-01-03-CA-72694

OCS/MMS 2004-005), Biological Resources Division, U. S. Geological Survey (National Offshore Environmental Studies Program 1445-CA-0995-0386) based on an information need identified by the Minerals

Management Service's Pacific OCS Regions, and by the California Artificial Reef Enhancement Program

(CARE). A. MacCall recommended the NOAA triennial trawl survey for use in our bocaccio sex ratio analysis. We thank the pilots of the submersible Delta, C. Ijames, J. Lily, and D. Slater, for their very professional

handling of the technical aspects of that survey, as well as the crews of the RIV Cavalier and RIV Valero. R.

Lea, M. Nishimoto, L. Snook, R. Starr, and M. Yoklavich conducted some ofthe surveys and L. Snook managed the survey data.

Literature Cited

Butler, J. L., L. D. Jacobson, J. T. Barnes, and H. G. Moser. 2003. Biology and population dynamics of cowcod

(Sebastes levis) in the southern California Bight. Fish. Bull. 101:260-280.

Carr, M. H., M. V. McGinnis, G. F. Forrester,]' A. Harding, and P.T. Raimondi. 2003. 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.

Love, M. S. and A. York. A comparison of the fish assemblages associated with an oil/gas pipeline and adjacent seafloor in the Santa Barbara Channel, Southern California Bight. Bull. Mar. Sci., in press.

____, J. Caselle, and K. Herbinson. 1998. Declines in nearshore rockfish recruitment and populations

in the Southern California Bight as measured by impingement rates in coastal electrical power generating stations. Fish. Bull. 96:492-501.

_________, and L. Snook. 1999. Fish assemblages around seven oil platforms in the Santa

Barbara Channel area. Fish. Bull. 98:96-117.

_____, and W. Van Buskirk. 1998. A severe decline in the commercial passenger

fishing vessel rockfish (Sebastes spp.) catch in the southern California Bight, 1980-1996. CalCOPI

Rep.30:180195.

_____, D. M. Schroeder, and M. M.Nishimoto. 2003. The ecological role of oil and gas production.

platforms and natural outcrops 011 fishes in southern and central California: a synthesis of information.

U. S. Dept. Int., U. S. Geological Survey, Biological Resources Division, Seattle, WA, 98104, OCS Study

MMS 2003-032. Available at http://www.id.ucsb.edullovelab.

_____, M. Yoklavich, and L. Thorsteinson. 2002. The rockfishes of the northeast Pacific. University

of California Press, Berkeley, CA. 405p.

_____, P. Morris, M. McCrae, and R. Collins. 1990. Life history aspects of 19 rocktlsh species (Scorpaenidae: Sebastes)from the southern California Bight. NOAA Tech. Rep. NIvIFS 87.

Moser, H. G., R. L. Charter, W. Watson, D. A. Ambrose, J. L. Butler, S. R.Charter, and E. M. Sandknop. 2000.

Abundance and distribution ofrockfish (Sebastes) larvae in the Southern California Bight in relation to

environmental conditions and tlshery exploitation. CalCOFI Rep. 41:132-147.

II
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•

Nishimoto, M. M. 2000. Distributions of late-larval and pelagic juvenile rockfishes in relation to water

masses around the Santa B<lrbara Channel Islands in early summer, 1996. In Fifth California Islands

Symposium, US Minerals Management Service and Santa Barbara Museum of Natural History, March

29- April 1, 1999. OCS Study MIvlS 99-0038 (CD-ROM).

Nishimoto, M. M. and L. Washburn. 2002. Patterns of coastal eddy circulation <lnd abundance of pelagic

juvenile fish in the Santa Barbara Channel, California, USA. Mar. Eco!. Prog. Sel'. 241:183-199.

Phillips, J. B. 1964. Life history studies on ten species of rockfish (genus Sebastodes). Calif. Dep. Fish and

Game, Fish Bull. 126.

Schroeder, D. M., A. J. Ammann, J. A. Harding, L. A. MacDonald, and W. T. Golden. 2000. Relative habitat

value of oil <lnd gas production platforms and natural reefs to shallow water fish assemblages in the

Santa Maria Basin and Santa Barbara Channel, California. In Fifth California Islands Symposium, US

Minerals Management Service and Santa Barbara Museum of Natural History, March 29-Aprill, 1999.

OCS Study MMS 99~0038 (CD-ROM). p. 493-498.

-,----- and M. S. Love. 2002. Recreational fishing and marine fish populations hI California. CalCOFI Rep. 43:182-190.

----- and ' . 2004. Ecological and political issues surrounding decommissioning of offshore oil facilities in the Southern California Bight. Ocean Coast. Manage. 47:21-48.

Yoklavich, M. M., H. G. Greene, G. M. Cailliet, D. E. Sullivan, R. N. Lea, and M. S. Love. 2000. Habitat associations of deep-water rockfishes in a submarine canyon: an example of a natural refuge. Fish. Bull.

98:625-641.

Addresses

(M.L., D. S.) Marine Science Institute, University of California, Santa Barbara, California 93106. (W. H. L.)

P.O. Box251, Kentfield, California 94914.

Corresponding Author

(M.L.) and E-mail: <love@lifesci.ucsb.edu>.

12

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Task 2: Ecological Perfonnance ofYoung-of-the-Year Blue Rockfish

(Sebastes mystinus) Associated with Oil Platfornls and Natural Reefs in

California as Measured by Daily Growth Rates

Milton S. Love, Edward Brothers, Donna M. Schroeder, William H. Lenarz

Abstract

Some decommissioning alternatives regarding the fate of offshore oil platforms include leaving

some or all of the platform structure on the seabed as an artificial reef. Questions surrounding the

utility ofsuch structures as productive fish habitat have not been resolved. Despite the high numbers

of fishes that can reside around offshore platforms, little is known about the comparative ecological

performance between natural and artificial habitats, where higher growth, reproduction or survival

rates would be beneficial to regional fish populations. To address this need, we analyzed the otolith

microstructure of 187 young~of~the-year (YOY) blue rockfish (Sebastes mystinus) to compare mean

daily growth rate and birth date distribution among three platforms and three natural reefs in the

. Santa Barbara Channel region. Paired natural and platform sample sites were selected to include a

range of oceanographic conditions present in the region. We found a significant though modest lunar pattern in birth dates where blue rockfish produced (or successfully recruited) fewer larvae in the

week following the full moon. Channel-wide patterns of birth date distribution were present. Sites

located in the west channel region included a range of birth datesOanuary through March) whereas

those in the east channel were limited to January and February. Mean growth rates were significantly

different across sites (ANOVA, F =71,96, df =5, 180, P.s;. 0.01). At the one site pair where comparisons were valid, YOY rockfish growth rates were significantly higher at the platform habitat. This

study demonstrates that, as measured by daily growth rates, blue rockfish living around oil and gas

production platforms may perform at least as well as those fish living on natural reefs, and supports

previous research implying that some platforms may benefitregional fish populations.

Introduction

All 27 oil and gas platforms located off the coast of southern and central California will at

some time reach the end cif their economic life spans. California platforms are located in both state

and federal waters and are sited in bottom depths ranging from 11 to 363 m. The largest of these

structures has a footprint of 10,606 m2 (Love et aI., 2003). While platform operators are responsible for the costs of disposition of an uneconomical platform, managers must decide what to do

with that structure, a process known as decoI11missioning. Ultimately, a decommissioned platform

could be left in place, removedtos'ome point below the sea surface, toppled to lie on the sea floor,

or totally removed (Schroeder and Love, 2004). Decommissioning can be a lengthy process, as it

requires input from state and federal agencies, corporate entities, and such stakeholders as recreational and commercial fishermen, and non-consumptive users. It may involve extensive analyses

of the biological, economic, and other sociological impacts of retaining or removing these structures (Schro'eder and Love, 2004).

Since 1995, much of our research has focused on the potential biological impacts of platforms

as fish habitats. A number of economically important fishes, particularly rockfishes (genus Sebastes),

are found at high densities around some California platforms. Rockfishes, a group that dominates

13
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many of the shelf and slope habitats of southern and central California (Love et aI., 2002), often

comprise over 90% of all fishes observed around these structures (Love et a1., 2003).

Platform midwaters (and the bottoms of some shallow-water structures) often act as nursery grounds for rockfishes and other species; densities of many rockfish species are almost always

higher than at nearby natural outcrops (Love et aI., 1999; Carr et aI., 2003; Love et aI., 2003). It is

likely that, compared to most natural reefs, a platform's size, structural complexity, and high vertical profile provides pelagic juvenile rockfishes and larvae of other species with a relatively strong

stimulus to trigger settlement (Carr et aI., 2003). While we have observed young-of-the-year (YOY)

of at least 28 rockfish species at platforms, five rockfish species (bocaccio, Sebastes paucispinis Ayres,

1854; widow, Sebastes entomelas Jordan and Gilbert, 1880; squarespot, Sebastes hopkinsi Cramer, 1895; olive, Sebastes sernmoides Eigenmann and Eigenmann, 1890; and blue, Sebastes mystinus Jordan and Gilbert,

1881) recruit to many of these structures in particularly large numbers (Love et aI., 2003; Carr et

aI., 2003). As an example, we estimated that during 2003, Platform Grace (located in the Santa Barbara

Channel) harbored more than 350,000 yay bocaccio (Love et aI., in press). Young-of-the-year rockfish recruitment to both platforms and natural reefs varies greatly from year to year.

The high densities of yay rockfishes inhabiting platform midwaters notwithstanding, there remain

questions regarding the importance of these young fishes to regional fish populations. The relative ecological contribution fishes living around artificial and natural habitats (as measured by fish growth, survival, and

reproduction) is a major determinant of that habitat's importance (Carr and Hixon, 1997; Carr et aI., 2003;

Mason, 2003). In 1999, a relatively strong recruitment of yay blue rockfish to both platforms and natural

reefs in southern and central California allowed us to compare daily growth rates ofthese young fishes.

Methods

SampleCollections

During the fall of 1999, yay blue rockfish were collected by pole spear at three platforms and three

natural reefs (Fig. 1). We selected our collection sites based on where yay blue rockfish were sufficiently

abundant to allow for inter-site growth rate comparisons. Comparisons were made between fish at Platform

Irene and a reef at Santa Rosa Island (both are in the Califorllia Current and are 84 km apart), Platform

Holly and Naples Reef (in the same water mass and located with 8 km of each other) and Platform Gilda and

Anacapa Island (in different water masses and within 16 km of each other). Collections were made during

one day at each site.

In the laboratory, each fish was measured (standard length,SL) to the nearest millimeter and its sagittal otoliths removed. After removal, sagittae were cleaned in water, soaked in a solution of 50% household

bleach and 50% water for a few minutes, then rinsed in water, air dried and stored in vials. Prior to their

being read, each otolith was embedded in Spurr's low viscosity epoxy medium before wet griJ1ding with 800

grit aluminum oxide. A mid-sagittal section was pl'epared to preserve both the otolith margin and as well

as early growth around the primordium. The final curvilinear (convex) surface was produced by applying

variable pressure and tilt during the grinding process. The samples were polished with diamond paste (3

um followed by 1 um). Microincrements were counted with the aid of a video microscope (to about 1500x

magnification). The typical counting path was from the primordium to the dorsal otolith margin. Methods '

generally followed techniques outlined in Brothers (I987) and Ralston et a1. (1996).

We did not validate the daily nature of the sagittal increments. However, in the eastern Pacific increments in rockfish otoliths have been determined to be produced daily in the yays of black (Sebllstes mklanops Girard, 1856) (Yoklavich and Boehlert, 1987), pygmy (Sebastes wilsoni Gilbert, 1915) (Laidig et aI.,

2004), shortbelly (Sebl1stes jordani Gilbert, 1896) and brown (Sebllstes Iluriculatus Girard, ] 854) rockfishes

14
Figure 1. Location and number of young-of-the-year blue rockfish collected at SL"'<: sites in southe1'11 and central California, September-November 1999. Platform and natural reef comparison pairs are noted by stars, triangles! and squares. ,

~.

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Island

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San Miguel*Santa Rosa

ISlanc~ 15 Island

(Laidig et aI., 1991). In the western Pacific, similar studies have shown this to be true for Sebastes th01npSolli

(Jordcln and Hubbs, 1925) (Kokita and Omori, 1998) and Sebastes illerl11is euvier, 1829 (Plaza et aI., 2001).

Increments were inferred to be daily in studies of larval, pelagic juvenile, or benthic YOY blue (Yoklavich et

aI., 1996), stripetail (Sebastes saxicola Gilbert, 1890) and greenstriped (Sebastes elongatus Ayres, 1859) rockfishes and cowcod (Sebastes levis Eigenmann and Eigenmann, 1889) (Johnson et aI., 2001), and widow and

yellowtail (Sebastes flavidus Ayres, 1862) rockfishes, bocaccio and chilipepper (Sebastes goodei Hilgendorf,

1880) (Woodbury and Ralston, 1991).

Analytic Methods

We estimated average growth (mm/day) of each fish by dividing its standard length by its age. This

metric includes both growth prior to, and after, benthic settlement. Since most blue rockfish settle between

early May and late June (Love et al., 2002) and our collections were made from September to November, our

measurement oftotal growth includes a significant period of benthic growth.

. We used one-way ANOVA's to test the hypotheses that mean birthdate (day of the year), age, standard

length, and growth did not vary among sites. ANOVA's are robust to minor deviations from the assumption

that observations are normally distributed. We compared the results of the ANOVA's using untransformed

data with ANOVA's using log-transformed data and the F values were very close. We chose to use untransformed data for the analyses. We used Scheffe's Post Hoc Test to contrast means 9fthe six sites.

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Results

We collected a total of 187bltie rockfish; collections ranged in number from 15 fish at Santa Rosa

Island to 39 fish at Naples Reef (Table 1, Fig. I). Fish were sampled between 15 September and 23 November 1999. Otoliths of all fish collected, except for one individual from Naples Reef, were readable and were

included in this study.

Lengths of individual fish sampled ranged from 6.7-11.1 cm and mean lengths of fish sampled at each

site ranged from 8.1 to 10.0 cm (Fig. 2, Table 1). The ANOVA showed that lengths were significantly different

among sites (F =31.69, df =5,180, P ~0.0l). Scheffe's contrasts were significant for the site pairs Platform

Holly - Naples Reef and Platform Gilda- Anacapa Island (Table 2). Mean lengths were not statistically different at the site pair Platform Irene- Santa Rosa Island (Table 2). Young.:of-the-year blue rockfish ranged in

age from 199 to 316 days and mean ages of fish at each site varied between 215 to 301 days (Table 1, Fig. 3).

MeaJi ages were statistically different between almost all sites (one-way ANOVA, F =205.60, df =5,180,

PSO.Ol, and Scheffe's test Table 2); a notable exception was the site pair Platform Irene '-- Santa Rosa Island.

Back-calculated birth or parturition dates (Ralston et a1:1996) for individual fish ranged from early lanuary to mid-March (Table 1, Fig. 4). While mean parturition dates varied considerably between sites (F =22.20,

df=5,180,P~0.01), they were similar for the site pairs Platform Irene-Santa Rosa Island (mean =mid-February) and Platform Holly-Naples Reef (mean =late January) (Scheffe's Test P>0.05, Table 2). In both instances

mean birth dates were within four days of each other (Table 1). Patterns of birth .dates were very similar at

Platform Irene and Santa Rosa Island; parturition in March was only observed in fish inhabiting these two

sites (Fig. 4). Mean birth dates were 18 days apart for fish at Platform Gilda and Anacapa Island (Scheffe's Test

P<0.05, Table 2).

Table L Data on collections and biological parameters of blue rockfish used in the study. Minimum and maximum values

in parentheses. Note that the otoliths of one ofthe fishes collected from Naples Reef was not readable, thus the total usable

fish from that site is 39.

Date Mean Mean Mean Mean Growth

Site n ofSample Date of Birth Age (days) Length (SL em) (n1l11/day)

Platform Irene 31 16-Nov-99 18Feb(5Jan-16Mar) 270(245-315 ) 8.6(7.4-10.5 ) 0.32 (0.27-0.39)

Santa Rosa 1. 15 16-Nov-99 14Feb(10]an-21Mar) 275 (240-310) 8.5(6.7-9.5) 0.31(0.27-0.36)

Platform Holly 31 15-0ct-99 26Jan(9Jan-19Feb) 262(238-279) 10.0(8.7-11.1) (US( 0.33-0.46)

Naples Reef 40 25-Sep-99 30Jan(3Jan-16Feb) 240(221-265 ) 8.6(7.5-9.7) 0.36(0.33"0.40)

Platform Gilda 39 15~Sep-99 12Feb(13]an-28Feb) 215(199-245) 8.1(6.9-10.3) 0.38(0.33-0.44)

Anacapa I. 31 23-Nov-99 25Jan(1 l]an-18Feb) 301(278-316) 9.0(7.9-9.4) O.30( 0.28-0.33)

There wassome indication that the timing oflarval release was related to moon phase (Rayleigh's Test,

Table 3, Fig. 5). While at most sites parturition dates were statistically uniform over a lunar cycle, when data

was pooled it appeared that few larvae were extruded during the week following the'full moon.

Calculated mean daily growth rates ofindividuals ranged from 0.27 to 0,46 mm/day and mean growth

rates at each site varied between 0.30 and 0.38 mm/day (Table 1, Fig. 6). Mean growth rates were statistically

different among most sites (ANOVA, F =71.96, df =5,180, PSO.OI). Growth rates were significantly different between .fish living at Platform Holly and Naples Reef and those living at Platform Gilda and Anacapa

Island (Table 2). In both instances, fish grew more rapidly at the platforms. There was 110 statistical difference between blue rockfish growth rates at Platform Irene and Santa Rosa Island (Scheffe's Test P>0.05,

Table 2).

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Table 2. Differences (column - row), as contrast@dby Schefi'e's Post Hoc Test, between pairs ofsites inmeanlengtb, mean age,

mean birth date, and mean grow.th ofYOY blue rockfisb. Fish collected between September and November 1999. *= Ps::0.05;

**=p.::;0.01. Platform and natural reefsite pair contrasts are denoted in bold.

, Mean Length (mm, SL)

Naples Platform Platform Platform Anacapa Reef Gilda Irene Holly Island

Platform Gilda 0.51

Platform Irene -0.03 -0.54

Platform Holly -1.46** -1.97** - 1.43**

Anacapa Island -0.37 -0.88** -0.34 1.09**

Santa Rosa Island 0.07 -0.44 0.10 1.53** 0.44

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Platform Gilda

Platform Irene

Platform Holly

Anacapa Island

Santa Rosa Island

Naples

Reef

23.33**

-32.44**

-24.05**

-63.15**

-36.85**

Platform

Gilda

-55.77**

-47.38**

-86.48**

-60.18**

Mean Age (days)

Platform

Irene

8.39

-30.71 **

-4.41

Platform

Holly

-39.10**

-12.80

Anacapa

Island

26.30**

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Mean Birth Date (day of year)

Naples Platform Platform Platform Anacapa Reef Gilda - Irene Holly Island

Platform Gilda -13.33**

Platform Irene -19.56** -6.23

Platfoi'lll Holly 4.05 17.38** 23.61**

Anacapa Island 4.15 17.48** 23.71** 0.10

Santa Rosa Island -15.15** -1.82 4.41 -19.20** -19.30**

Mean Growth Rate (mm/day)

Naples Platform Platform Platform Anacapa Reef Gilda Irene Holly Island

Platform Gilda -0.015

Platform Irene 0.042** 0.057**

Platform Holly -0.023* -0.008 -0.065**

Anacapa Island 0.064** 0.078** 0.022* 0.086**

Santa Rosa Island 0.052** 0.067** 0.010 -0.074** -0.012

, We wished to make an overall comparison of growth rates of blue rockfish combining all platform data

and comparing that to all natural reef data. However, because fish at Platform Gilda and Anacapa Island

were sampled two months apart and because growth rates may decline later in the season (thus complicating

inter-site comparisons), in these comparisons we did not include data from these two sites. We combined

the growth rates offish from Platform Irene and Holly and compared the mean growth rate with that offish

living at Naples Reef and Santa Rosa Island. Blue rockfish living at the platforms grew O.OI6mm/day more

quickly (Scheffe's Test, P<O.OS).

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Figure 2. Size distribution of young-of-the-year blue rockfish collected at six sites in southern and central California,

September-November 1999.

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Age (days)

Figure 3. Age distribution of young-of-the-year blue rockfish collected at si:x sites in southern and central California, September-November 1999.

19

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February March

Month of Birth

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Santa Rosa Island

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Figure 4. Parturition date distribution of young-of-the-year blue rockfish collected at six sites in sOllthern and central

California, September-November 1999.

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Table 3. Statistics of Rayleigh's test (Z) for distl"ibutions of parturition dates for blue rockfish in 1999.

Site Z Significance Level

Platform Irel1e 0.61 ns

Santa Rosa 1. 1.60 ns

Platform Holly 2.51 ns

Naples Reef 2.97 ns

Platform Gilda 4.77 0.01

Anacapa 1. 1.07 ns

Pooled Data 3.51 0.05

Pooled Sites

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3 .5 7 9 11 13 15 17 19 21 23 25 27 29

Day ofLunar Month • new moon

o full moon

'.

Figure 5. Distribution of parturition over the lunar month, as back-calculated from otoliths of young-of-the-year blue

rockfish. Three lunar cycles are pooled. Arrow indicates the mean lunar day of parturition. New moon (filled circle)

was set as the first day, full moon (open circle) as the 15th day.

Discussion

For blue rockfish, we identified a number of patterns in growth and birth date distribution across the

sampling region.

First, we observed a significant, albeit subtle, lunar pattern in blue rockfish birth dates. In 1999, blue

rockfish appeared to produce fewer larvae in the week following the full moon. Because parturition has not

been observed in Eastern Pacific rockfishes, it is not possible to compare our data with direct observations

of the timing of blue rockfish (or any other rockfish species) larval release. Thus we do not know if the pattern we observed represents reduced parturition in the third lunar quarter or if there is no lunar parturition

pattern, but rather increased larval mortality (e.g., from increased predation or lowered food availability) on

those larvae produced during that time. Studies of tropical reef fishes, by both direct observation and backcalculations from daily growth rings, demonstrate that spawning by many species is closely linked to lunar

phase (Thresher, 1984; Robertson etal., 1988; Sponapgle and Cowen, 1994). However, studies on gray snap~

per (Lutjal1us griseus (Linnaeus, 1758» imply that lunar spawning patterns may occur in some years but not

in others (Denit and Sponaugle, 2004). Only one other study has examined lunar parturition periodicity in

rockfishes. Pasten et al. (2003), using back calculations of daily growth rings of Sebastes il1ennis collected off

Japan, found that parturition occurred significantly more often around the new and full moons.

21
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Figure 6. Distribution of growth rates of young-of-the-year blue rockfish collected at six sites in southern and central

California, September-November 1999.

22

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There is some evidence that the YOY blue rockfish living at Platform Irene and Santa Rosa Island and

those living at Platform Holly and Naples Reef either came from similar source populations or had larvae

and pelagic juveniles that had experienced similar pelagic environmental conditions. Evidence is strongest

for fish living at Platform Irene and Santa Rosa Island. Fish at these two sites had statistically identical

mean birth dates (Platform Irene, 18 February; Santa Rosa Island, 14 February) and mean lengths (Platform

Irene, 8.6 mm; Santa Rosa Island, 8.5 mm), and they were the only sites harboring fish that had been born

in March (Tables 1, 2; Figure 4). Fish at Platform Holly and Naples Reef had non-significantly diffetent

birth dates (Platform Holly, 25 January; Naples Reef, 30 January). Interestingly, Platform Gilda and Anacapa

Island, although relatively near each other, harbored blue rockfish YOYs that ~ere quite dissimilar in all

measured variables (Tables 1,2; Figures 2-4). Platform Irene and Santa Rosa Island are often strongly bathed

by the California Current and it is likely that in 1999 larvae produced off central California were carried

southwards to both platform and island. The source populations for the other sites are more problematic.

For instance, while we have little data on current patterns in the eastern Santa Barbara Channel (site of

Platform Gilda and Anacapa Island) in 1999, research on the source populations of 2004 YOY bocaccio living around Platform Gilda implies that pelagic juveniles were brought to that site on currents flowing from

several directions (M. Nishimoto et al., 2005).

The growth rates of YOY blue rockfish in our studies (with mean per site ranging from 0.30 to 0.38

mm/day) are similar to those found in other young rockfishes. Sllln'marizing a range of rockfish studies of

both larval and pelagic juvenile phases, including both field and laboratory studies, Love et a1. (1991) cal·

culated a mean growth rate of 0.29 mm/day in field studies and 0.27 mm/day in laboratory experiments.

However, only one other study, Johnson et al (2001), examined the daily gro~th rates of benthic YOY rockfishes integrated over the life of the animals from larval extrusion to post settlement. In that study, growth

rates were 0.17 mm/day in greenstriped rockfish (Sebastes elongatus Ayres, 1859),0.25 mm/day in cowcod

(Sebastes levis (Eigenmann and Eigenmann, 1889), and 0.32 mm/day in stripetail rockfish (Sebastes saxicola

(Gilbert, 1890». The growth rates of young rockfishes are low compared to a wide range of other fishes,

(e.g., European hake, Merlueeius merluceius (Linnaeus, 1758), 0.71-0.74 mm/day, Kacher a11d Amara 2005;

gray snapper, Lutjanus griseus (Linnaeus, 1758),0.62-0.88 mm/day, Denit and Sponaugle, 2004; greater amberjack, Seriola dumerili (Risso, 1810), 1.65-2.00 mm/day, Wells and Rooker 2002; blue marlin, Makaira

nigriains Lacepede, 1802, 16.6 mm/day).

The two-month disparity in collection dates among locations complicated our comparing the growth

rates of fish from Platform Gilda and Anacapa Island and from comparing growth rates among all sites.

Nevertheless, it is clear that there is no evidence that fish at platforms grew more slowly than those living

on natural reefs. Comparison of growth rates between fishes living at Platform Holly and Naples Reef implied that YOY blue rockfish may, in some instances, grow faster at platforms. Growth might be accelerated

at platforms for several reasons. Young-of-the-year blue rockfish are midwater feeders; they prey on such

zooplankters as barnacle larvae, larvaceans, and copepods (Gaines and Roughgarden, 1987; Singer, 1985)

and zooplankton density may be greater around Platform Holly than over Naples Reef. The zooplankton

living in the nearshore waters flowing along and over the extensive kelp beds and rock reefs associated with

Naples Reef may have been exposed to many more predators than organisms inhabiting the open ocean waters flowing into the platform jacket. In addition, the waters inside the platform may harbor higher densities

of barnacle and other invertebrate larvae because the platformjacket is heavily encrusted with these forms

(Love et aI., 2003). Lastly, compared to natural reefs, the midwaters of 1110St California platforms harbor

low densities of those piscivorous fishes (e.g., kelp bass, Paralabax clathratus (Girard, 1854); cabezon, Seorpaenichthys marmoratus (Ayres, 1854); Pacific barracuda, Sphyraena argentea (Girard, 1854) and yellowtail,

Seriola lalandi Valenciennes, 1833) that are common on natural reefs. As an example, predation rates on

small fishes at Platform Holly are significantly lower than those at Naples Reef (Schroeder et aI., 2005). This

23
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•

may allow YOY blue rockfish (and other YOY rockfishes) inhabiting the platform midwaters to spend more

time on foraging activities rather than predator avoidance.

While such environmental factors as hypoxia, salinity, and the varied nutritional values of prey can

influence growth rates ofthe early life stages of marine fishes (Lee et al., 1994; McNatt and Rice, 2004; Wuenschel et al., 2004), in ocean waters temperature and food availability are usually the most important parameters (Boehlert and Yoklavich, 1983; Denit and Sponaugle, 2004; Kurita et al., 2004; Bacon et al., 2005). In

black rockfish (Sebastes melanops Girard, 1856), a species closely related to blue rockfish, water temperature.

was perhaps the major factor affecting growth rates (Boehlert and Yoklavich, 1983). We did not see a clear

temperature effect on growth rate in our study. This was particularly apparent when comparing growth

rates of fish living at Platform Irene, Santa Rosa and Anacapa islands. All of the fish from these sites were

taken in November (thus we measured growth over the same period) and growth rates were not significantly

different. However, these sites reside in two different oceanographic regimes; Platform Irene and Santa Rosa

Island are in the cold California Current and Anacapa Island in the warmer waters ofthe southern California Bight. In 1999, from July (when blue rockfish begin to settle out of the plankton) to November (when

the fish were captured), mean temperatures off Point Arguello (near Platform Irene) were about 30 colder

(13.8°C, s.d. 1.1dc) than near Anacapa Island 07.0°C, s.d. 0.8°C) (data from Point Arguello, Arguello MidShelf Mooring, 34.5202, -120.6970; Anacapa Island data from the Anacapa Mid-Shelf Mooring, 34.0542,

-119.3035, B. Emery, University ofCalifornia, Santa Barbara, pers. comm.). Thus water temperature, at least

as experienced by the fish our samples, may not have been the major factor in growth rates. Another possibility is that while temperature was important, differences in food availability may have been sufficiently

large that they swamped any temperature effect.

It has been argued that if the YOY rockfishes that recruit to California oil and gas platforms experience

.relatively pOOl~ecological performance, compared to fish living on natural reefs, these structures might act as

biological sinks (Krop, 1997). This would occur because those young fishes that recruited to these structures

would be less likely to survive to adulthood than individuals that settled on natural reefs. On the other hand,

as noted by Carr et al., (2003), "If species perform equivalently or better 011 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." Although limited in scope, the current study demonstrates that, as measured by daily growth rates,

young blue rockfish living around oil and gas platforms performed at least as well as those fish living on

natural reefs. Several previous studies have examined the fate ofYOY rockfishes that recruited to California

platforms. Love et al. (in press) presented data showing the survival and ultimate maturation of a year-class

ofYOY bocaccio at a platform in the Santa Barbal1a Channel. In a separate study, YOY bocaccio tagged at

several Channel platforms were recovered on natural reefs as adults years later as much as 150 km from the

tagging sites (Hartmann, 1987). Our current study supports previous research implying that at least some

platforms may benefit regional fish populations.

Acknowledgments·

We thank A. Bull, 1. Thorsteinson, and G. Steinbach for their support of this research. This

research was funded by the Minerals Management Service (Contract Number 1435-01-03-CA-72694

OCS/MMS 2004-005), Biological Resources Division, U. S. Geological Survey (National Offshore

Environmental Studies Program 1445-CA-0995-0386) based on an information need identified

by the Minerals Management Service's Pacific OCS Regions, and by the California Artificial Reef

Enhancement Program (CARE). We are also indebted to S. Clark, E. Bessell, S. Mau, <lnd C. Thompson

for helping to collect the specimens. M. Nishimoto, B. Emery, and L. Washburn provided much needed information on the oceanographic regimes of our study area.

24
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OCS Study 98-0023. Coastal Research Center, Marine Science Institute, University of California,Santa

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northward feeding migration during spring and summer. Fish. Oceanography 13(suppJ. 1):54-62.

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MMS 2003-032. Available at http://www.id.ucsb.edu/lovelab.

_____, M. Yoklavich, and L. Thorsteinson. 2002. The rockfishes of the northeast Pacific. University

of California Press, Berkeley, CA. 405 p.

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utility of offshore marine strlictures in rebuilding an overfished rockfish species. Fish. Bull. In press.

Mason, B. 2003. Doubts swirl around plan to use rigs as reefs. Nature 425:891.

McNatt, R. A. and J. A. Rice. 2004. Hypoxia-induced growth rate reduction in two juvenile estuary-dependent fishes. J. Exp. Mar. BioI. Ecol. 311:147-156.

Nishimoto, M. N., L. Washburn, M. S. Love, D. Schroeder, and B. Emery. 2005. Is the delivery of juvenile

fishes settling on offshore platforms linked to transport by ocean currents? (abstract). 8th International

Conference on Artificial Reefs and Artificial Habitats, Biloxi, MS. p. 46.

Pasten, G. P., S. Katayama, and M. Omori. 2003. Timing of parturition, planktonic duration, and settlemc;nt

patterns of the black rockfish, Sebastes inermis. Env. BioI. Fish. 68:229-239.

Plaza, G., S. Katayama, and M. Omori. 2001. Otolith microstructure of the black rockfish, Sebastes inermis.

Mar. BioI. 139:797-805.

Prince, E. D., D. W. Lee,]. R. Zweifel, and E. B. Brothers. 1991. Estimating age and growth of young Atlantic·

blue marlin, Makaira nigricans, from otolith microstructure. Fish. Bull. 89:441-459.

Ralston, S., E. B. Brothers, D. A. Roberts, and K. M. Sakuma. 1996. Aging accuracy oflarval Sebastes Jorclani.

Fish. Bull. 94:89-97.

Robertson, D. R., D. G. Green, and B. C. Victor. 1988. Temporal coupling of production and recruitment of

a larvae of a Caribbean reef fish. Ecology 69:370-381.

Schroeder, D. M. and M. S. Love. 2004. Ecological and political issues surrounding decommissioning of offshore oil facilities in the Southern California Bight. Ocean Coast. Manage. 47:21-48.

....-, , M. S. Love, and M. Nishimoto. 2005. Comparative juvenile reef fish recruitment and

mortality between offshore oil-gas platforms and natural reefs (abstract). 8th International Conference

on Artificial Reefs and Artificial Habitats, Biloxi, MS. p. 62.

Singer, M. M. 1985. Food habits ofjuvenile rockfishes (Sebastes) in a central California kelp forest. Fish.Bull.

83:531-542.

Sponaugle, S. and R. K. Cowen. 1994. Larval durations and recruitment patterns of two Caribbean gobies

(Gobiidae): coritrasting early life histories in demersal spawners. Mar. BioI. 120:133-143.

Thresher, R. E. 1984. Reproduction in reef fishes. T. F. H. Publications, Neptune City, New Jersey. 399 p.

Wells, R. J. and 1. R. Rooker. 2004. Distribution, age, and growth of young-of-the-year greater amberjack

(Serio/a clumcrili) associated ""ith pelagic Sargassum. Fish. Bull. 102:545-554.

26
.'

Woodbury, D. and S. Ralston. 1991. Interannual variation in growth rates and back-calculated birthdate

distributions of pelagic juvenile rockfishes (Sebastes spp.) off the central California coast. Fish. Bull.

89:523-533.

Wuenschel, M. ]., A. R. ]ugovich,and ]. A. Hare. 2004. Effect oftemperature and salinity em the energetics of

juvenile gray snapper (Lutjanus griseus): implications for nursery habitat value. ]. Exp.Mar. BioI. Ecol.

312:333-347.

Yoklavich, M. M. and G. W. Boehlert. 1987. Daily growth increments in otoliths ofjuvenile black rockfish, Sebastes melanops: an evaluation of autoradiography as a new method of validation. Fish. Bull. 85:826-832.

-------,V. L. Loeb, M. Nishimoto, and B. Daly. 1996. Nearshore assemblages oflal'val rockfishes

and their physical environment off central California during, an extended EI Nii'io event, 1991-1993.

Fish. Bull. 94:766-782.

Addresses

(M.L., D. S.) Marine Science Institute, University of California, Santa Barbara, California 93106. (E. B.) EFS

Consultants, 3 Sunset West, Ithaca, New York 14850. (W. H. L.) P.O. Box 251, Kentfield, California 94914.

Corresponding Author

(M.L.) and E-mail: <love@lifesci.ucsb.edu>.

27
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Task 3: Comparative Predation Rate on Painted Greenling Between Natural

Habitat and an Offshore Oil Platfoflll

Donna M. Schroeder and Milton S. Love

Abstract

Off southern California, decisions regardilig decommissioning of offshore oil platforms will

rely in part on the ecological performance of platforms as juvenile fish habitat. Here we use a tethei"ing experiment to determine the relative risk of predation for a small benthic fish, the painted

greenling (Oxylebius pictus), between a natural reef and an oil platform. We found that juvenile

painted greenling at the natural reef suffered a predation rate more than 2.5 times greater than

platform juveniles. Platform habitat had lower painted greenling density (t =-3.941, P = 0.017 ) and·

lower piscivore density ( t =-3.965, P = 0.017), but there was no significant difference among habitats in the ratio of predators to prey (Mann-Whitney U = 3.00, P =0.513). The number of predator

species was greater at the natural reef (7 reefspecies vs 1 platform species), which suggests that relative predation risk among habitat types may be governed by the habitat-specific suite of predators.

Decommissioning decisions can alter platform fish assemblages, including the piscivore assemblage.

Thus, the ecological performance of platform structure as juvenile fish habitat should be considered

a dynamic property that will be impacted by the decommissioning process.

Introduction

In decommissioning offshore oil platforms, options that leave some or all of the platform structure on

the seabed ("rigs-to-reefs") engender a great deal of controversy (Schroeder and Love 2004). Assessment of

the quality of platform habitat bears greatly upon decommissioning decisions, because such information

aids in understanding the ecological role of platforms at a regional scale. Thus, measuring the comparative

ecological performance (Le., a species' reproduction, growth and survivorship rates) between natural and

platform habitats has been identified as a priority research area by marine scientists and resource managers

(Manago and Williams 1998, Holbrook et al. 2000).

For example, in certain years, many offshore platforms host large numbers of juvenile fishes (Schroeder et al. 2000, Love et al. in press). These observations might imply that, forthese species, platforms are

high quality habitat. However, the ultimate fate ofthese juveniles remains unclear. Specifically, it is unknown

whether these fish may suffer higher rates of mortality than they would at natural habitats.

In thi.s study, we estimate the relative predation rate of a juvenile fish between natural habitat and an

offshore oil platform. We used a tethering technique because, despite inherent artifacts of a tetheringapproach (Peterson and Black 1994, Halpin 2000), the technique is useful to evaluate relative differences in

predation rate at small scales (Aronson et al. 2001). Further, tethering is a more direct approach than other

field techniques, such as visual surveys or tag and recapture, where changes in fish abundance may be due to

a combination of immigration and mortality rates. To provide insight in explainingpotenti'l] differences in

predation rate, we also compared densities of painted greenling and piscivores between habitat types. Studies that investigate comparative ecological performance among natural and artificial habitats are useful in

fisheries management and restoration ecology, where use of artificial reefs plays an increasingly important

role (Powers et al. 2003).

28
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Methods

We conducted the study at two sites located in the Santa Barbara Channel offsouthern California. Platform Holly (34.3897 N, 119.9055 W) is located in 64 m of water, and 2.9 km offshoi-e of the mainland. The

subsurface platform structure (called the jacket) is supported by steel tubular legs anchored in the seafloor.

Steel horizontal, diagonal, and oblique crossbeams extend both around the perimeter ofthe jacket and reach

inside and across the platform. We conducted our study at Platform Holly on the shallowest (9 111) horizontal crossbeams. In depths less than 10 m, the platform structure is anntlally cleaned ofsessile organisms. At

the time of the study, the substrate was encrusted with a dead "turf" matrix (old byssal threads, decaying

holdfasts, etc), red algae, bryozoans, and a number ofsmall mussels. Naples Reef (34.4222 N, 119.9523 W) is

located approximately 1 km offshore the mainland coast, with a depth range of 6.5 to 18 m. Here sedimentary rock outcrops form a series of ridges and pinnacles that frequently exceed a meter or more in height,

and proVide numerous caves and crevices for shelter-seeking fishes. We conducted our study in a high relief

area at 10m depth. In certain years, giant kelp, Macrocystis pyrifera, forms extensive stands on the reef.

Our model organism, the painted greenling, Oxylebius pictus (Hexagrammidae), is a small reef fish

common to offshore platforms and kelp beds off California. We employed a tethering approach to compare

relative predation rates on juvenile painted greenling between a natural and an artificial (platform) habitat.

This benthic fish lacks a swim bladder, and its most frequently observed daytime behavior is to simply rest

on the bottom, making tethering a suitable experimental technique.

The tethering apparatus consisted of two JO m horizontal lines secured to the rock or platform substrate. Two lines were used for ease of deployment, and were laidend-to-end to simulate a continuous line.

To these lines we attached ten 0.5 m monofilament tethers ("21b" test) spaced approximately 5 m apart, with

a swivel at the origin and a small, 0.6 cm hook at the terminus.

Scuba divers used hand nets to collect juveniles between 6 and 9 cm total length. After capture, divers attached the fish to the monofilament line by inserting the small hook into the dorsal musculature just

posterior ofthe soft dorsal fin. Painted greenling were then placed into a small underwater holding chamber

for approximately ten to thirty minutes so that the fish could acclimate and all fish could be released at the

same time. All sets occurred between 1000 and 1400 hrs. After a one hourtime peri.od, divers enumerated

the number offish losses and released the remaining fish back in to the field. We deployed 5 sets often tethers

at each site. Tethering trials were conducted between November 15 and December 10,2003.

To detect potential tethering artifacts that may occur with this experimental protocol, we installed an

underwater video system on Naples Reef to observe the activity of a tethered painted greenling and its interactions with other organisms during a one hour set that was distinct from the experimental sets.

We tested the hypothesis of no difference in mean fish losses between platform and natural habitat

using a two-tailed t-test (n=5). Fish losses were recorded as the proportion of fish remaining after each set.

Prior to statistical analysis, we arcsine transformed the data to improve normality.

We used scuba to visually survey the fish assemblages at Platform Holly and Naples Reef. At each

habitat type, density (individuals per hectare), mean size (total length) and species composition of reef

fishes were estimated in shallow portions of platforms (0 t09 mdepth) and natural reefs (7 to 15111). We

performed three surveys during the Fall of 2003. All divers performing visual counts had completed previous training in size estimation. In each platform survey, scuba divers swam a pattern which incorporated all

four corner legs as well as major horizontal crossbeams and portions inside the platform jacket. Natural reef

surveys consisted of divers recording observations along eight haphazardly placed 30 111 length x 2 m width

x 2 m height belt transects. We tested the hypothesis of no difference in mean painted greenling density (no.

I1shI1000m3 ), mean predator density (no.fishI1000mJ

), and mean ratio of predators to painted greenling

density, between platform and natural habitat llsing two-tailed t-tests (n=3). For each fish assemblage, we

29
Table 1. Mean (1SE) density (no. fish/l 000 m3) of each predator species between habitat types.

Results

determined the proportion of potential pt'edators by referring to Quast (1968), who enumerated the percent

occurrence of perciform fishes in gut contents of kelp bed fishes.

3.0 (2.5)

Naples Reef Platform Holly

0.3 (0.3)

5.7 (1.9)

0.3 (0.3)

0.3 (0.3)

1.7 (0.9)

0.7 (0.3)

20.0 (2.5)

Scientific name

Ophiodon dongatus

Paralabmx clathmtus

Paralabrax Ilebulifer

Scorpaellichthys marmoratlls

Sebl1stes atrovirells

Sebastes mrllatus

Semicossyphus pulcher

30

Common name

Lingcod

Kelp bass

Barred sand bass

Cabezon

Kelp rockfish

Gopher rockfish

Sheephead

Experiments employing tethering techniques must include a thorough assessment of any treatment

artifacts, particularly those relating to fish behavior. Diver observations and video tape at the natural reef

revealed that after tethered painted greenling were released from the underwater holding chamber they either

directly settled down on the substrate, or swam to the end ofthe tether, stopped, and then either settle to the

bottom or swam to the nearest shelter (typically a patch of red algae or large cobbles). Fish did not exhibit

sustained struggling behavior or other apparent distress signs that might have attracted predators. At the platform, diver observations recorded that tethered greenling behaved much in the same way as those on the natural reef, except that there were fewer refuges forthe fish, and most remained exposed. Currents were stronger

at Platform Holly than at Naples Reef, and tethered fish generally swam in the downstream direction.

During the videotaped session at Naples Reef, we observed three predator strikes on two different

painted greenling. One kelp bass, Paralabrax clathratus, made two strikes (one successful) on an untethered

painted greenling (which was positioned near the tethered fish), and one sheephead, Semicossyphus pulcher,

made one successful strike on the tethered fish. Based on this video tape record and diver observations, we

assumed that fish losses are able to approximate the relative predation rate between habitat types.

Relative predation rate on painted greenling was significantly higher at Naples Reef than at Platform

Holly (Fig. 1). Naples Reef also had higher painted greenling density (t =-3.941, P =0.017 ) and higher predator density (all species combined, t = -3.965, P = 0.017; Fig. 1). The number of predator species was much

greater at Naples Reef than at Platform Holly (Table 1). In the test comparing the mean ratio of predators to

prey between habitats, unequal variances required the use of a nonparametric test; there was no significant

difference between means (Mann-Whitney U =3',00, P =0.513; Fig. I).

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Fig. L Comparison of (A) mean proportion of fish losses (representing relative predation risk; n = 5), (B) pail1ted

greenling density (n =3), (C) predator density (n =3), and (D) predator to prey ratio (n =3), between Naples Reef and

Platform Holly. Significance levels of p < 0.05 are indicated byasterisks.

Discussion

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The tethering experiment shows that juvenile painted greenling residing at Naples Reef experienced a

relative predation rate more than 2.5 times greater than the estimated rate experienced by juveniles residiilg

at Platform Holly. How can we interpret this result to actual differences in predation among habitat types?

It is important to note that experimental predation rates are generally not equivalent to natural predation

rates; the later tends to be much 10wer(Linehan et a1. 2001). Next, we consider whether common difficul- .

ties in using tethering as an experimental approach could negate the general result of higher predation on

juveniles at the natural reef.

Differences in the escape response between tethered and untethered prey could limit generality of experimental conclusions. For example, some studies found that highly mobile prey made poor experimental

subjects because, when tethered, they behaved in a manner that attracted predators (e.g., Zimmer~Faust et a1.

1994). Painted greenling are benthic fish and tethering did not prodllce obvious anomalous behavior. When

tethering trials were terminated, remaining fish were observed quiescent on the bottom much like freeranging fish. Further, the video tape record of an untethered fish being eaten by a piscivore before a nearby

tethered fish supports the supposition that behavior was not dtamatically altered in this experiment.

Another criticism of tethering is that the technique promotes predation by novel species. In particular,

tethered fish may be more susceptible to predation by aggressive invertebrates such as crabs (Curran and

Able 1998, Linehan et al 2001, Adams et al. 2004). Page et al. (1998) show that Platform Holly bosts large

densities rock crabs (Cancer spp.). If these crabs preyed upon tethered painted greenling, it would not have

changed the conclusion of a lower relative predation rate at Platform Holly compared to Naples Reef.

.' 31
t'

An implicit assumption of tethering experiments is that second-order interactions do not affect results

(Peterson and Black, 1994, Halpin 2000). That is, any artifact of tethering prey is equivalent across treatments.

Problems arise ifthere is an interaction between habitat and the degree to which a tethering artifact is expressed.

For instance, Adams et aI. (2004) show that tethered prey often became entangled in ·seagrass (further restricting prey movement and increasing risk) but not in other habitat types. In this study, fish may have more easily

broken free from their tethers at Platform Holly than at Naples Reef due to higher current flow and presence

ofsharp-edged mussel shells which could increase the chance ofline abrasion. Escaped fish wonld be recorded

as fish losses and artificially enhance estimates of predation rate. But if either ofthese.interactions occurred, it

would have not a}tered the general conclusion of a higher relative predatiOll rate at Naples Reef.

A number of studies show that mortality rates of juvenile reef fishes are higher when predatory fishes

are abundant (Connell 1996, Beets 1997, Stewart and Jones 2001, Webster 2002, but see also Nakamura and

Sano 2004). Connell (1997) experimentally demonstrated that tethered juvenile fishes on small artificial reefs,

where there are few predators, also had higher survivorship rates than juveniles on l!atural reefs. Caution

must be used in interpreting these results as a large number of predators does not necessarily translate into

higher mortality; there must be an increase in encounter, strike or success rate (Holling 1959). A higher risk of

predation at Naples Reef corresponded to a higher predator density, and a higher number ofpredator species.

However, the ratio of predator to juvenile painted greenling were not different between habitats (although

statistical power was weak). This result suggests that the relative predation risk among habitat types may

depend in part upon the habitat-specific suite of preda:ors. Fish assemblages (including piscivore density)

show a great deal ofvariability among platfOl:ms and decommissioning decisions can affect these assemblages

(Schroeder and Love 2004). Thus, the ecological performance of platform structure as juvenile fish habitat

should be considered adynamic property thatwill be impacted by the decommissioning process.

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33