ACCESS NUMBER: M12PG00027

1

STUDY TITLE: Characterizing and Quantifying Sea Lion and Seal Use of Offshore Manmade 

Structures off California

REPORT TITLE: Characterizing and Quantifying California Sea Lion (Zalophus califorianus) 

Use of Offshore Oil and Gas Platforms in California

CONTRACT NUMBER: M12PG00027

SPONSORING OCS REGION: Pacific

APPLICABLE PLANNING AREA(S): Southern California

FISCAL YEAR(S) OF PROJECT FUNDING: FY 2012: $250,000

COMPLETION DATE OF REPORT: July 2016

COSTS BY FISCAL YEAR: FY 2012: $0; FY 2013: $122,820.24; FY 2014: $42,608.02; 

FY 2015: $60,767.91; FY 2016: $19,538.77

CUMULATIVE PROJECT COST: $245,734.94

PROJECT MANAGER(S): Robert L. DeLong and Anthony J. Orr

AFFILIATION: Marine Mammal Laboratory, Alaska Fisheries Science Center, NOAA Fisheries, 

National Oceanic and Atmospheric Administration

ADDRESS: 7600 Sand Point Way NE, Seattle, WA 98115

PRINCIPAL INVESTIGATOR(S)*: Anthony J. Orr, Jeffrey D. Harris, Kari A. Hirschberger, 

Jeffrey L. Laake, Robert L. DeLong, and Gregory S. Sanders

KEY WORDS: California sea lion, oil and gas platform, Pacific Outer Continental Shelf, 

pinniped, time-lapse camera system, Zalophus californianus.

BACKGROUND: There are 23 oil and gas production platforms in federal waters offshore 

southern California. These platforms provide haulout space near foraging areas for California 

sea lions (Zalophus californianus), a species protected under the Marine Mammal Protection 

Act. Information on abundance, and age, sex and seasonal-use patterns of California sea lions 

on oil and gas platforms is useful for the environmental review of ongoing activities and the 

eventual removal of platforms when oil and gas production ceases (i.e. decommissioning). 

Quantitative estimates of potential harassment, injury, or mortality for future activities may be 

derived from data collected during this study.

OBJECTIVES: Characterize California sea lion use of offshore oil and gas platforms in 

southern California. Quantify sea lion use of platforms and assess their age, sex, and seasonal 

use patterns over a two-year period.

DESCRIPTION: Five of the 23 federal platforms offshore California were selected as focal 

study sites based on their geographical location and relative accessibility by sea lions. Timelapse camera systems were deployed on these platforms from January 2013 to January 2015. 

Photos were taken every 30 minutes during day and night. A subsample of images was 
ACCESS NUMBER: M12PG00027

2

randomly selected from six-hour blocks of time throughout the day, and during randomly 

selected days throughout each month. Individual sea lions were counted and identified to a 

particular age/sex class, when possible. Counts of animals by month and hour were conducted 

to examine intra-platform (temporal) and inter-platform (spatial) comparisons.

SIGNIFICANT CONCLUSIONS: Offshore oil and gas platforms provide benefits to pinnipeds 

(esp. California sea lions). Although some human activities may be disruptive to resting 

pinnipeds, the presence of a structure on which they can rest in areas where they feed or forage 

is likely to be more beneficial than disruptive and to provide a net benefit. The temporal and 

spatial variability in number of California sea lions using the platforms was pronounced for some 

platforms and minimal at others. Sea lions were observed on the platforms year-round and 

during all hours of the day. Most of the identified animals were juveniles; however, proportionally 

relatively few of the animals were identified to a particular age/sex class in comparison to all 

counted individuals. Therefore, caution should be taken when using or interpreting findings.

STUDY RESULTS: A total of 464,174 photographs were obtained from all sampled platforms 

during this study. A subsample of these photographs (ntotal = 12,489; Platform Elly = 1,981, 

Platform Gina = 1,960, Platform Habitat = 4,742, Platform Heritage = 2,551, Platform Harvest = 

1,255) was used in data analyses. There were no consistent spatial trends (e.g. south to north) 

in numbers of sea lions using the platforms. Platform Habitat (central) had the highest counts of 

sea lions (Median: 2013range = 32 – 134; 2014range = 40 – 110); whereas Platform Gina (south) 

had the lowest (Median: 2013range = 1 – 21; 2014range = 3 – 22) throughout the study. Also, there 

were no consistent seasonal trends in numbers across all platforms. At some platforms (i.e. 

Platforms Gina and Habitat), the animals primarily hauled out at night and were away during the 

middle of the day; whereas at others (i.e. Platforms Heritage and Harvest), the opposite trend 

was apparent. At Platform Elly, the sea lions used the platform consistently throughout the day.

STUDY PRODUCT(S): 

1. BOEM study report: Orr, A.J., J.D. Harris, K.A. Hirschberger, J.L. Laake, R.L. DeLong, 

and G.S. Sanders. 2016. Characterizing and quantifying California sea lion (Zalophus 

californianus) use of offshore oil and gas platforms in California. US Department of the 

Interior, Bureau of Ocean Energy Management, Pacific OCS Region, Camarillo, CA. 

OCS Study BOEM 2016-009. 36 p.

2. Complete photograph image library: (464,174 images) for future analyses. Copies of the 

digital libraries are archived in the BOEM Pacific Regional Office and NOAA’s Alaskan 

Fisheries Science Center.

* P.I.’s affiliation may be different than that listed for Project Manager(s).
ACCESS NUMBER: M12PG00027

3

MAP SHOWING AREA OF STUDY (Figure 2 of report OCS Study BOEM 2016-009):