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Technical Summary

STUDY TITLE: Seabird and Marine Mammal Surveys off the Northern California, Oregon, and 

Washington Coasts

REPORT TITLE: Pacific Continental Shelf Environmental Assessment (PaCSEA): Characterization of 

Seasonal Water Masses within the Northern California Current System Using Airborne Remote Sensing 

off Northern California, Oregon, and Washington, 2011–2012

OCS STUDY NUMBER: BOEM 2020-012

NUMBER OF PAGES: 26

CONTRACT NUMBER: M10PG00081, Task 1

SPONSORING OCS REGION: Pacific

APPLICABLE PLANNING AREAS: Northern California, Washington-Oregon

FISCAL YEARS OF PROJECT FUNDING: FY 2010: $1,700,000; FY 2011: $0; FY 2012: $547,000; 

FY 2013: $0; FY 2014: $0; FY 2015: $0; FY 2016: $0; FY 2017: $0; FY 2018: $0; FY 2019: $0; FY 2020: $0

COST BY FISCAL YEAR: FY 2010: $425,000; FY 2011: $425,000; FY 2012: $425,000; FY 2013: 

$425,000; FY 2014: $262,000; FY 2015: $285,000; FY 2016: $0; FY 2017: $0; FY 2018: $0; FY 2019: $0; 

FY 2020: $0

CUMULATIVE PROJECT COST: $2,247,000

COMPLETION DATE OF REPORT: February 2020

PROJECT MANAGERS: John Takekawa, Josh Adams

AFFILIATION OF PROJECT MANAGER: U.S. Geological Survey, Western Ecological Research Center

ADDRESS: U.S. Geological Survey, Western Ecological Research Center Headquarters, 3020 State 

University Drive East, Modoc Hall, Room 3006, Sacramento, CA 95819

PRINCIPAL INVESTIGATOR: Josh Adams, John Y. Takekawa

KEY WORDS: water mass, California Current, radiometry, chlorophyll a, ocean color, remote sensing, 

k-means

BRIEF ABSTRACT: The California Current System (CCS) is an eastern boundary current spanning the 

region from Baja California, Mexico to British Columbia, Canada and extending up to 1,000 km offshore.

Frontal boundaries related to the Columbia River, submarine canyons that enhance coastal upwelling, 

internal waves generated by remote winds, broad continental shelves, and coastlines without capes (and 

associated local bathymetry) make the Northern California Current System (NCCS) one of the most 

productive areas within the CCS. To inform management and marine spatial planning, classification of 

regions of similar water properties over appropriate spatial scales may provide useful descriptions of 

species habitats and help efforts to better predict species distributions and species abundances at sea.

Here, we used ocean color measurements and sea surface temperature (SST) data collected with 

sensors mounted on low-flying aircraft to characterize NCCS water masses and identify patterns among 

seasons and between years. To accomplish this, we applied k-means clustering to measured and derived 

ecologically relevant physical and bio-optical variables (SST, Chla, absorbance by colored dissolved 
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organic matter [aCDOM], proxy particle load). These classifications will be used in the future to evaluate 

species habitat distributions in the NCCS.

BACKGROUND: Interest in developing renewable energy in the ocean has recently increased, some of 

which will include power generation infrastructure and support activities located within continental shelf 

(and potentially deeper) waters off the U.S. Pacific coast, beyond state waters (i.e., outside three nautical 

miles). The Bureau of Ocean Energy Management (BOEM) is currently considering renewable energy 

proposals off the coast of Oregon, California, and Hawaii. The 2011–2012 USGS Pacific Continental 

Shelf Environmental Assessment study (PaCSEA, Adams et al., 2014) was intended to provide up-todate information on species composition, distribution, abundance, seasonal variation, and habitat 

utilization among marine birds and mammals on the outer continental shelf (OCS) within a broad region of 

the NCCS (herein, the region between Fort Bragg, California [39.3°N] to Grays Harbor, Washington 

[47°N]). In situ sensing of the ocean environment in the aerial surveys prior to PaCSEA was limited to 

SST measured with pyrometry and composite imagery of the ocean collected via earth-orbiting satellites.

OBJECTIVES: The three primary objectives for PaCSEA were to (1) conduct aerial at-sea surveys of 

seabirds and marine mammals in shelf and slope waters off northern California, Oregon, and Washington 

and summarize species and seasonal at-sea densities, (2) conduct a comparison with existing similar 

surveys in northern California, Oregon, and Washington, and (3) validate and enhance aerial survey data 

for numerically abundant indicator species and certain resident breeding and non-resident migratory 

seabird species. Objective 1 included enhancing in situ remote sensing of the ocean by including a 

hyperspectral radiometer to collect continuous, ocean color data during surveys.

METHODS: We conducted six low-altitude aerial surveys (twin-engine, fixed, high-wing aircraft: 

Partenavia P-68 or Commander AC-500). We flew 32 east-west-oriented uniform transects (spaced at 15ˈ 

latitude [27.8-km] intervals) when possible to the 2000-m isobath (includes shelf, slope, and rise waters) 

to ensure comparable spatial and temporal coverage with similar historic datasets. The primary survey 

area extended from Fort Bragg, California (39.3°N) to Grays Harbor, Washington (47°N) and focused on 

federal waters outside of the 3-mile boundaries. We included six focal-area surveys nested within the 

overall broad transect survey area at the request of BOEM. Each focal-area survey consisted of ten, 25-

km long, parallel transect lines targeting shelf waters and spaced at 6-km intervals. This pattern (broad 

survey lines and focal-area survey lines) was surveyed during each of three oceanographic seasons: 

summer during upwelling, autumn during upwelling/relaxation, and winter during downwelling. Raw 

HydroRad3 (HR3; HOBI Labs, Bellevue, Washington) measurements of downwelling irradiance (Ed), 

downwelling radiance (Ld), and upwelling radiance (Lu) were first calibrated and processed to full 

engineering units. To evaluate coarse-scale, seasonal and inter-annual variability in ocean conditions, we 

present monthly composite averages of Chla concentrations determined using the National Aeronautics 

and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS).

Additionally, we compared two sub-regions of daily 1-km MODIS Chla values to HR3-derived 

measurements to evaluate the ability of the HR3 to retrieve meaningful ocean color data from our lowelevation survey aircraft. We used k-means cluster analysis, a feature-based classification technique, to 

delineate and characterize water masses in the NCCS. Feature-based classification uses the inherent 

variability in multivariate data to reveal structure, making no a priori knowledge necessary and thus, 

introducing less bias. Input variables used in our k-means analysis included SST, log10 transformed 

Chla, aCDOM, and proxy particle load (i.e, nLw[555]).

RESULTS: We completed a total 26,752 km of standardized survey effort (not including coastal and 

offshore deadhead segments between transect lines). Effort allocated according to bathymetric domain 

(i.e., depth strata) was approximately proportional to areas occupied by the bathymetric domains of the 

shelf-slope region, with additional effort targeting regions of the continental shelf (mostly <200-m depth) 

within the focal areas. Effort was similar among seasons (winter, summer, and autumn) and between 

years. With respect to depth strata, 47% (12,646 km) covered the slope domain (200–2000-m depth), 

33% (8887 km) covered the inner-shelf (0–100-m depth), and 20% (5219 km) covered the outer-shelf.

During winter 2011 and 2012, k-means clustering identified a bi-directional Columbia River Plume (CRP)

water mass that bulged at the Columbia River mouth. During summer, July 2012 boundaries of the CRP 

were less distinct and different from clusters observed in June 2011. South of Cape Blanco, nearshore 
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south water was colder and had greater Chla, aCDOM, and proxy particle, indicative of strong upwelling 

at Cape Mendocino and with the presence of a frontal boundary extending offshore. The Autumn surveys 

(October 2011) occurred during the lowest Columbia River flow rates when wind speeds were among the 

greatest observed. K-means clustering identified CRP water extended offshore and north of the river 

mouth. We observed high Chla values north of the CRP during October 2011. This pattern was similar to 

July 2012, and also indicates a northward flowing plume retained on the Washington shelf. In contrast to 

October 2011, during September 2012, we sampled during some of the weakest wind speeds observed. 

The CRP was bi-directional and extended southwestward near Heceta Bank. During September 2012, 

weak, southerly, downwelling-favorable winds persisted for most of the survey, then switched to upwelling 

favorable winds. A bi-directional CRP was consistent with alongshore wind stress that switched from 

southerly to northerly partially through the survey.

CONCLUSIONS: This study has demonstrated that airborne ocean color and SST data can be used to 

characterize water masses associated with the NCCS, including the CRP. We observed variability in 

water mass boundaries between years and during all seasons, consistent with the expectation of a 

dynamic, bi-modal CRP (Hickey et al. 2005) and variable forcing driving upwelling. Aircraft-mounted 

sensors flown at relatively low altitude (60 m) allowed data to be collected when satellite data would have 

otherwise been unavailable due to cloud cover. For example, of 46 survey days, none had satellite 

remotely sensed ocean color data (daily) in >50% of the image. Additional study in the future will use 

these data to assist in the quantification of NCCS seabird community patterns and evaluation of 

environmental predictors that may prove useful for predicting at-sea abundance.

STUDY PRODUCTS:

1. BOEM final report: Adams, J., J.J. Felis, J.W. Mason, and J.Y. Takekawa. 2014. Pacific 

Continental Shelf Environmental Assessment (PaCSEA): aerial seabird and marine mammal 

surveys off northern California, Oregon, and Washington, 2011–2012. Camarillo (CA): U.S. 

Department of the Interior, Bureau of Ocean Energy Management, Pacific OCS Region. OCS 

Study BOEM 2014-003. 267 p.

2. BOEM final report: Schulien, J.A., Adams, J., Felis, J. 2020. Pacific Continental Shelf 

Environmental Assessment (PaCSEA): characterization of seasonal water masses within the 

northern California Current System using airborne remote sensing off northern California, 

Oregon, and Washington, 2011–2012. Camarillo (CA): U.S. Department of the Interior, Bureau of 

Ocean Energy Management, Pacific OCS Region. OCS Study BOEM 2020-012. 26 p.
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MAP SHOWING AREA OF STUDY

Pacific Continental Shelf Environmental Assessment (PaCSEA) study area showing 32 broad transects, 

six focal-area transect zones, and geographic place names referenced in text. (Figure 3 of report OCS 

Study 2020-012).