Relative Importance of POCS Oil Platforms 

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FINAL TECHNICAL SUMMARY 

STUDY TITLE: Relative importance of POCS oil platforms on the regional population 

dynamics of reef fishes in the Eastern Santa Barbara Channel 

REPORT TITLE: Relative contribution of POCS oil platforms to regional population 

dynamics of a model reef fish, the blackeye goby Rhinogobiops nicholsii, in the Eastern Santa 

Barbara Channel 

CONTRACT NUMBER: 14-35-0001-31063 

SPONSORING OCS REGION: Pacific 

APPLICABLE PLANNING AREA(S): Southern California 

FISCAL YEAR(S) OF PROJECT FUNDING: FY 02, FY 03 

COMPLETION DATE OF REPORT: November 2006 

COST(S): FY 02-03: $112,348 

CUMULATIVE PROJECT COST: $112,348 

PROJECT MANAGER: Russell J. Schmitt 

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

Barbara, CA 93106-6150 

PRINCIPAL INVESTIGATORS: Hunter S. Lenihan and Andrew J. Brooks 

ADDRESSES: Bren School of Environmental Science and Management, University of 

California, Santa Barbara, CA 93106-5131; Marine Science Institute, University of California, 

Santa Barbara, CA 93106 

BACKGROUND: 

Determining the effect of each decommissioning alternative on the regional production of reefassociated fish species is the primary ecological question concerning the decommissioning of the 

POCS offshore oil platforms (Holbrook et al. 2000). Surveys of the 27 platforms in California 

waters reveal that they harbor rich but highly variable assemblages of reef-associated fishes and 

invertebrates (Love et al. 1999; Page et al. 1999). However, the total habitat area provided by 

platforms is relatively small in relation to the regional availability of natural reef habitat thus 

suggesting that platforms may have little influence on population dynamics at regional scales. 

Nevertheless, platforms may negatively influence the regional population dynamics if they 

attract individuals from more suitable habitat, or they may enhance populations in areas that have 

relatively little natural habitat and where the structures have positive influences on demographic 
Final Technical Summary – Lenihan and Brooks 

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processes, including individual growth, reproduction, and survival. Regional stocks of most 

reef-associated species are composed of local populations that are linked together through the 

dispersal of larvae and/or the migration of adults or juveniles (Lipcius et al. 1997; Lenihan et al. 

2001). Oil platforms most likely enhance regional population abundance by acting as (1) selfmaintained local populations, or (2) source populations that continually supply individuals to 

less-productive sink populations. 

OBJECTIVES: 

Our objectives were to test whether POCS oil platforms in the Eastern Santa Barbara Channel 

influence the regional population abundance of a model reef fish, the blackeye goby 

Rhinogobiops nicholsii, through examination of the relative contribution of one POCS oil 

platform, OP Gina, and natural rocky reefs. We examined the population demographics of the 

blackeye goby because this species is the most common demersal fish found on oil platforms 

(Carr et al. 1999), provides the best model species to examine population dynamics, and as a 

very common, small benthic species plays an important role in reef food webs as both a predator 

on zooplankton and benthic invertebrates (e.g., amphipods, isopods, and polychaete worms) and 

prey to rockfish, kelp bass, and other groundfish species. Blackeye goby utilize a limited amount 

of benthic habitat, have limited migratory behavior as adults, closely guard non-cryptic nests, 

and produce eggs that can be used to quantify fecundity. Therefore, it was possible to quantify 

key demographic features (reproductive output, recruitment, deaths, immigration, and 

emigration) necessary to relative contributions to regional population dynamics as they may vary 

on POCS oil platforms and natural rocky reef habitat. 

 

If oil platforms influence the population dynamics of a fish species on a regional scale, this effect 

can be accurately estimated for blackeye goby in the Eastern Santa Barbara Channel (ESBC). 

This species inhabit most of the 13 oil platforms in the area (Carr et al. 1999). There are also 

relatively few local natural reefs in the ESBC within the normal range of movement of adult 

blackeye goby, or that are hydrographically connected with local oil platforms (Harms and 

Winant 1998). Consequently, populations of goby inhabiting ESBC platforms are either selfmaintained on individual or proximal platforms, or are subsidized by, or subsidize natural reefs 

through limited immigration/emigration. They can also be connected through larval transport as 

blackeye goby has pelagic larvae that spend a relatively short time in the water column during 

dispersal. Therefore, identifying connectivity between local populations of blackeye goby will 

entail understanding hydrographic connectivity between habitats, larval transport processes, and 

adult/juvenile migration (Hench et al. 2001). 

Understanding the population dynamics of blackeye goby on ESBC POCS oil platforms and 

natural reefs, and estimating whether platforms influence regional population dynamics through 

supply of "excess production", are a means of estimating the relative contribution of oil 

platforms and natural rocky reefs. It also provides the means of executing the three major 

research objectives proposed by Holbrook et al (2000): (1) assessing the quality of platforms as 

reef habitat, (2) estimating connectivity between local populations, and (3) modeling effects on 

the regional population of maintaining, moving, removing, or topping the oil rigs. Our specific 

objectives were to (1) quantify population demographic processes (abundance, growth rates, 

births, mortality, immigration, and emigration) of blackeye goby through sampling using scuba; 
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and (2) assess the relative contribution of an oil platform and natural reefs as a means of 

estimating the influence of platforms on the regional population dynamics of a reef fish.

DESCRIPTION: 

Overview: Between May 2003 and November 2004, we made 90 total trips to oil platform Gina 

in the eastern Santa Barabara Channel and three natural rocky reef control sites at Santa Cruz 

Island, Orizaba Reef, Chief Reef, and Potato Reef. At each site we measured the following life 

history parameters of the blackeye goby (Rhinogobiops nicholsii), egg production, recruitment, 

abundance of adults, and population size structure. Additionally, we conducted tethering 

experiments to estimate mortality from predation, and a tag-recapture study to track mortality 

and immigration and emigration of individuals from the study areas. Finally, we collected 

individuals from all sites and removed otoliths (sagittae and lapillae) for size-at-age and 

microchemical analyses. The methods employed for each of these procedures is described in 

detail below. 

We examined the population dynamics of blackeye gobies at four locations, POCS oil platform 

Gina (OP Gina) and three natural, subtidal rocky reefs located on Santa Cruz Island (SCI). We 

selected OP Gina as our oil platform treatment because it is the only platform located at a water 

depth (31 m) at which scuba divers can dive to the seafloor and work for acceptable lengths of 

time (>10 min) safely. The seafloor around all other platforms in the SB Channel is too deep for 

diving, even with Nitrox gas. Natural reefs were selected on SCI because they were the reefs that 

were nearest to OP Gina, were located at similar water depths (20-30 m), and were inhabited by 

blackeye goby. 

Demographic study: Our first objective in the field was to identify the most abundant benthic 

fish species at OP Gina. We counted the total numbers of individuals of all species encountered 

on four transects (30 m long x 2 m wide) placed around OP Gina in June, July, and August 2003. 

We also counted on the same dates all fishes located in the water column (from the seafloor to 

the surface) within the footprint of the platform from the bottom to the surface of the water on 

the same dates. We found the blackeye goby was by far the most abundant species at OP Gina. 

Survey dives made during the same period at SCI confirmed that this species was also one of the 

most abundant species at our control sites. Therefore, we concentrated our effort throughout the 

project on this species. We had initially planned to study a surf perch species and the painted 

greenling but saw only a few individuals at all sites, and had substantial difficulty in capturing 

them in preliminary fish tagging trials. 

To test whether the abundance of gobies varied between OP Gina and natural reef control sites, 

divers counted the abundance of adults, juveniles, and young-of-the-year (YOY) along four 

replicate transects (30 m x 2 m) placed along the reef/sand interface at each site. Our counts of 

YOY provided an estimate of goby recruitment. Transect counts were made in September, 

October, and November 2003, and January and June 2004. 

Population structure, immigration, and emigration: We conducted monthly tagging of 

blackeye goby at each site during September, October, and November 2003, and January 2004 to 

test whether rates of population size structure, mortality, survival, immigration, and emigration 
Final Technical Summary – Lenihan and Brooks 

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varied among natural reefs and OP Gina. Gobies were captured by divers, brought to the surface, 

measured, and tagged with a small subcutaneous injection of latex paint placed near the dorsal 

fin. Gobies were then released in the general area (within 2-5 meters) from which they were 

caught. Divers remained with the gobies upon release and chased away potential predators until 

the gobies regained awareness of their surroundings and exhibited what appeared to be normal 

behavior, mainly using the shelly bottom as refuge. A different color tag was applied each 

month, and colors were easily visible and distinguishable underwater at all our sites. 

Surveys for tagged fish were conducted September, October, November, and December 2003, 

and January, June, and July 2004. Length-frequency data recorded during tagging were used to 

construct adult population structure histograms for each site. Estimates of mortality, growth, 

immigration, and emigration are generated from the number of individuals tagged and recovered 

at each site during each sampling period. 

Fecundity: To test whether fecundity of blackeye gobies varied among natural reefs and OP 

Gina, we estimated the total number of eggs produced by individual fishes from each site. In 

April 2004, we collected egg masses of our target species from platform Gina (n=15), Chief Reef 

(n=11), Orizaba Reef (n=11), and from two depths at Potato Reef (n=11 from 20 m, and n=11 

from 30 m). This species deposit egg masses on the undersides of small boulders and/or shell 

fragments, which allowed for collection of entire egg clutches from an individual female. Eggs 

were collected by divers who non-destructively flipped loose pieces of material on the seafloor 

that appeared to be guarded by an adult goby. Samples were then placed in a cooler filled with 

seawater and returned immediately to flow-through seawater aquaria at the UC Santa Barbara’s 

Marine Science Institute. Estimates of egg mass area, egg density, and total number of eggs per 

clutch (fecundity) were then determined for each location. We examined each egg mass for data 

yielding a mean density of eggs (eggs/cm2

) and total number of eggs, which was calculated by 

multiplying the area of an egg mass by the mean density. 

Predation mortality of blackeye goby: To test whether rates of predation on gobies varied 

among natural reefs and OP Gina, we conducted a tethering experiment in which live, adult 

blackeye gobies were attached to lines and their fate was followed by divers. We deployed three 

replicate lines (33 m long) to which we tethered 10 gobies (10 gobies x 3 replicate lines = 30 

total gobies per site). The long-lines were placed along our “permanent” survey transects. We 

conducted this experiment at the conclusion of our study from 10-17 July 2004 to avoid impacts 

to our study area). After long-lines were deployed and inspected, gobies were captured and 

brought to the surface as described above (Tagging). Gobies were measured and hooked through 

the base of the dorsal fin with a small, barbed live-bait type fish hook connected to 1 m of 4lb 

monofilament with a size 7 (15 lb) snap swivel attached to the other end. The diver then released 

the goby from the plastic bottle and noted the loop location and bottle number of each fish. 

Gobies were tethered to the long-lines and sampled by divers after 1 hour. Tethered individuals 

were scored as “goby present”, “hook only present”, or “snapped”. Predators hooked on the goby 

lines were recorded and released. To address the possibility that “hook only present” individuals 

may have shaken off the hook without being preyed upon, we ran a control study at in which 

divers monitored the longlines continually. The depths at our study sites were prohibitive to 

prolonged bottom times, and so this study was conducted at Naples reef off of Santa Barbara, 

CA, at a depth of 12 meters. 
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Age and Growth estimates: To test whether growth rates of blackeye goby varied among 

natural reefs and OP Gina, we collected 60 individuals from each site and dissected the saggitae 

and lappillae (otoliths) for age-at-size and microchemical analyses. The collection process was as 

described above (Tagging) with the exception that fish were measured and then placed in ethanol 

immediately upon capture. Weight-length measurements were made from the 60 fish sacrificed 

for otiliths. Weights were taken prior to the removal of otoliths but after they were stored in 70% 

ETOH for 1-2 weeks. 

Mircochemistry of otoliths: We have yet to conduct this additional aspect of our study because 

we seek additional funding for the relatively expensive and time consuming analysis. 

Population modeling: We are in the process of modeling the population dynamics of blackeye 

goby and providing predictions for the regional-scale impacts of the five proposed 

decommissioning methods. We will undertake and complete our modeling component when we 

complete preparation of our population demographics paper. 

Summary: We expect that we will generate a total of four publications from our study: (1) a 

population demographics paper comparing a POCS oil platform and natural reef populations of 

blackeye goby, (2) a regional population dynamics modeling paper, (3) and age-growth analysis, 

and (4) potentially a paper that reports use of otolith microchemistry to analyze temporal patterns 

of habitat utilization by populations of gobies inhabiting POCS Gina and natural rocky reef 

control sites. 

 

SIGNIFICANT CONCLUSIONS: 

We assembled a thorough and spatially and temporally comprehensive field-based demographic 

data set of blackeye goby populations OP Gina and three natural rocky reefs located on the north 

shore Santa Cruz Island in the ESBC. The natural reefs we used were those located closest in 

space to OP Gina that also were inhabited by the blackeye goby. Our results provide information 

that can be used to estimate the relative contribution of goby populations from OP Gina and the 

natural reefs to the regional population pool of this species. 

We found that abundance did not differ among the oil platform and natural reefs; that 

recruitment was slightly lower at OP Gina than at natural reefs, that the size structure of the 

population was greater at Op Gina than natural reefs; that the differences in size structure may be 

explained by reduced predation mortality; that fecundity may be relatively low OP Gina OP, but 

that fish may live longer and therefore produce more population output over the long-term. 

Our general finding is that populations of blackeye goby at OP Gina do not make a substantial 

contribution to the regional stock of blackeye goby, indicating that OP Gina’s removal, or 

modification based on other decommissioning strategies, would have little effect on the regional 

abundance and population dynamics of this species. Because this species is found on many other 

POCS oil platforms in the ESBC, our findings are relevant to decommissioning strategies in 

general. We predict that removal or in-situ modification of a platform will not have an important 

influence on regional populations of this model benthic species. OP Gina is not an important 

population source or sink. Therefore we also predict that (1) if the platforms were to remain in 
Final Technical Summary – Lenihan and Brooks 

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place it would not have a negative impact on the regional populations of blackeye goby, and (2) 

that OP Gina should be not considered a potential marine reserve based on this ecologically 

relevant species. 

STUDY PRODUCTS: 

Published work 

Lenihan, H.S., A.J. Brooks, and M.C. Kay. In preparation. Relative contribution of POCS oil 

platforms to regional population dynamics of a model reef fish, the blackeye goby 

Rhinogobiops nicholsii, in the Eastern Santa Barbara Channel. Target: Ecological 

Applications. 

A.J. Brooks, H.S. Lenihan, and M.C. Kay. In preparation. Age and growth of the blackeye goby 

Rhinogobiops nicholsii, in the Eastern Santa Barbara Channel. Target: Environmental 

Biology of Fishes. 

Presentations 

H.S. Lenihan, A. Brooks, and M.C. Kay. 2005. Relative Importance of POCS Oil Platforms on 

the Population Dynamics of Reef Fishes in the Eastern Santa Barbara Channel. Bren 

School, UCSB. October, 2005. 

H.S. Lenihan. 2005. Population ecology and problem solving in the marine environment. Bren 

School, UCSB. December 2005. 

H.S. Lenihan. 2006. Population source-sink dynamics and POCS oil platform decommissioning. 

March, 2006.