OCS Study 

MMS 2006-066 

Winter distribution and abundance of 

Steller’s eiders (Polysticta stelleri) in Cook Inlet, Alaska 

2004-2005 

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LEASE SALE

 AREA 199

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20 0 20 40 60 80 Kilometers

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Prepared for 

U.S. Department of Interior 

Minerals Management Service 

Alaska Outer Continental Shelf Region 

Environmental Studies Section 

3801 Centerpoint Drive, Suite 500 

Anchorage, AK 99503-5823 
OCS Study MMS 2006-066 

FINAL REPORT 

December 2006 

Winter distribution and abundance of 

Steller’s eiders (Polysticta stelleri) in Cook Inlet, Alaska 

2004-2005 

By 

William W. Larned 

U. S. Fish and Wildlife Service 

1011 E. Tudor Road 

Anchorage, AK 99503 

Prepared for 

U.S. Department of Interior 

Minerals Management Service 

Alaska Outer Continental Shelf Region 

Environmental Studies Section 

3801 Centerpoint Drive, Suite 500 

Anchorage, AK 99503-5823 

This study was funded, in part, by the US Department of the Interior, Minerals 

Management Service Alaska Outer Continental Shelf Region, Anchorage, Alaska Under 

Contract No. 0104RU34160, as part of the MMS Alaska Environmental Studies Program 

The opinions, findings, conclusions, or recommendations expressed in this report are 

those of the author and do not necessarily reflect the views of the U.S. Department of the 

Interior, nor does mention of trade names or commercial products constitute 

endorsement or recommendation for use by the Federal Government
PROJECT ORGANIZATION 

William W. Larned, USFWS, Soldotna, Alaska: 

Principal Investigator, lead pilot and aerial observer, data analyst, report compiler 

Paul Anderson, USFWS, Anchorage, Alaska : 

Pilot and aerial observer, logistics assistant 

Christian Dau, Heather Wilson, Robert Platte, William Eldridge, Dennis Marks, USFWS, 

Anchorage, Alaska: aerial observers 

Ed Mallek, USFWS, Fairbanks, Alaska: 

Pilot and aerial observer 

Julian Fischer, USFWS, Anchorage, Alaska: 

Financial Data analyst and assistance with statistical analysis 

Charles Monnett, PhD, MMS, Anchorage, Alaska: 

Contracting Officer’s Technical Representative and project Administrator (through 

summer 2004). 

Jeffrey S. Gleason, PhD, MMS, Anchorage, AK: 

Contracting Officer’s Technical Representative and project Administrator (Summer 2004 

through project’s conclusion).

REPORT AVAILABILITY 

U.S. Fish and Wildlife Service 

Waterfowl Management Branch 

1011 E. Tudor Rd. 

Anchorage, AK 99503 

Telephone: (907) 786-3443 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

Telephone (800) 553-6847

SUGGESTED CITATION 

Larned, W. W. 2006. Winter distribution and abundance of Steller's eiders (Polysticta 

stelleri) in Cook Inlet, Alaska, 2004-2005. U.S. Fish and Wildlife Service, 

Waterfowl Management Branch, Anchorage, Alaska. OCS Study, MMS 2006-066. 

37 pp.
i

ABSTRACT 

The U.S. Department of Interior documented the spatial distribution and abundance estimates of 

Steller's eiders (Polysticta stelleri) wintering in Lower Cook Inlet, Alaska, 2004-05. The Alaska 

breeding population of Steller’s eiders is listed as threatened under the Endangered Species Act 

(ESA). Objectives of this study were to document spatial and temporal patterns of use by 

wintering Steller’s eiders in Cook Inlet which would provide the Minerals Management Service 

with information relative to the National Environmental Policy Act and Section 7 consultation of 

the ESA for future exploration and development of offshore oil and natural gas resources in the 

area. Observations were collected along fixed aerial transects, perpendicular to shorelines, 

extending from the shoreline to the nearest 20m depth contour with a 2km lateral spacing. 

Steller's eiders in flocks containing <20 birds were recorded within strips 600m in width. 

Densities were extrapolated from surveys to the entire survey area. Steller's eiders in flocks of 

≥20 birds within the sampled area inside and outside the 600m strips were also recorded. 

Observations were assigned geographic coordinates via laptop computers equipped with a GPSlinked voice recording program. Replicate same-day surveys using a second aircraft were 

sometimes conducted. Surveys were accomplished monthly in March, April, and December, 

2004, and from January – April, 2005. Largest monthly Steller's eider estimates were 1,247 and 

4,200, in eastern and western survey areas, respectively, in January 2005. December estimates 

typically accounted for <50% of monthly peaks, and by April most birds had departed for Arctic 

breeding grounds. A pattern of use at wintering sites that was relatively consistent among 

months and years is described. Temporary departure from this pattern during mid-winter 2005 

appeared related primarily to displacement of birds by sea ice. A preliminary conceptual model 

of Steller's eider distributional dynamics in Cook Inlet is described, based on historical data and 

results from this study. 

KEY WORDS: Aerial survey, Alaska, Cook Inlet, distribution, Polysticta stelleri, sea duck, sea 

ice, Steller’s eider 
ii

TABLE OF CONTENTS 

INTRODUCTION ..................................................................................... 1

 Historical data ................................................................................... 2

OBJECTIVES .......................................................................................... 4

METHODS ............................................................................................. 4

 Study area ....................................................................................... 4

 Equipment, transect layout, data recording and analysis ................................. 8

 Accuracy of observational data ............................................................... 10

RESULTS AND DISCUSSION ..................................................................... 13

 Environmental conditions ..................................................................... 13

 Abundance and distribution of Steller's eiders ............................................. 16

SUMMARY AND CONCLUSIONS ............................................................... 32

RECOMMENDATIONS ............................................................................ 33

ACKNOWLEDGEMENTS ......................................................................... 34

LITERATURE CITED .............................................................................. 34

LIST OF TABLES 

Table 1 Comparison of bird and sea otter observations among left and right paired 

observers during aerial waterfowl surveys in lower Cook Inlet, Alaska during 

year 1 (January – April 2004) and year 2 (December 2004 – April 2005)........ 12

Table 2 Estimates of Steller's eiders observed during aerial surveys, Cook Inlet, 

Alaska, January to April 2004 ......................................................... 18

Table 3 Estimates of Steller's eiders observed during aerial surveys, Cook Inlet, 

Alaska, December 2004 to April 2005................................................ 19
iii

Table 4 Monthly Steller's eider estimates averaged over March, April, and December 

2004, and January – April, 2005, aerial Steller's eider survey, Cook Inlet, 

Alaska.................................................................................................. 21

LIST OF FIGURES 

Figure 1 Distribution of the Pacific population of the Steller's eider.......................... 1

Figure 2 Cook Inlet, Alaska, showing MMS Lease Sale Area 199............................ 3

Figure 3 True color image of Cook Inlet acquired 2 September 2002.......................... 5

Figure 4 Mean ice conditions, Cook Inlet, Alaska, for the period 16-28 February 1986-

99............................................................................................. 6

Figure 5 Probability of occurrence for ice of at least 5/10ths concentration, Cook Inlet, 

Alaska, for the period 16-28 February, based on 1986-99 data........................... 7

Figure 6 Study area showing survey units, aerial transects, bathymetry, and prominent 

shoreline features, Cook Inlet, Alaska, 2004-05....................................... 8

Figure 7 Sea ice cover in Cook Inlet, Alaska, 13 February 2004............................... 14

Figure 8 Sea ice cover in Cook Inlet, Alaska, 10 January 2005................................ 15

Figure 9 Sea ice cover in Cook Inlet, Alaska, 11 February 2005................................. 15

Figure 10 Steller's eider estimates from survey units completed by the primary survey 

crew during monthly aerial surveys in Cook Inlet, Alaska, January – April 2004 

and December 2004 – April 2005....................................................... 22

Figure 11 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 23 January 2004................................... 23

Figure 12 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 11-14 February 2004.............................. 

 

24

Figure 13 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 11-17 March 2004................................. 25

Figure 14 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 12-13 April 2004..................................... 26

Figure 15 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 4-8 December 2004.................................. 27
iv

Figure 16 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 6-11 January 2005................................ 28

Figure 17 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 3-12 February 2005.................................. 29

Figure 18 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 2-4 March 2005.................................... 30

Figure 19 Sample transects and locations of Steller's eider flocks observed during an 

aerial survey, Cook Inlet, Alaska, 12-14 April 2005..................................... 31
1

INTRODUCTION 

The Pacific population of the Steller’s eider (Polysticta stelleri) breeds in arctic Russia, arctic 

and sub arctic Alaska, and winters primarily in coastal waters of southwest Alaska (Fig. 1). 

Smaller numbers winter in Kamchatka and other areas in southeastern Russia. The Russian 

breeding population currently, and probably historically, represented >95% of the world 

population (Fredrickson 2001). The Alaska breeding population historically nested in the coastal 

fringe of the Yukon-Kuskokwim Delta and the western portion of the Arctic Coastal Plain 

(Kertell 1991, Fredrickson 2001, Quakenbush et al. 2002, USFWS 2002). The Alaska breeding 

Steller’s eider population has shown recent declines in both abundance and geographical extent 

in both breeding areas recently, and therefore that population was listed as threatened in 1997 

under the authority of the Endangered Species Act (ESA) (USFWS 2002). 

 

Figure 1. Distribution of the Pacific population of the Steller's eider (U. S. Fish 

and Wildlife Service 2002). 
2

Any proposed federal action that may affect individuals or modify critical habitat of a listed 

species, and thus reduce the likelihood of survival of that species, must undergo interagency 

consultation (50 CFR 402.14). The winter range of the listed Alaska breeding population is 

poorly known, as is the temporal and geographic extent to which it intermixes with the unlisted 

Russian breeding population. Hence, all Steller's eiders in Alaska are treated as belonging to the 

listed population. Cook Inlet (CI) in south central Alaska is known to provide winter habitat for 

substantial numbers of Steller's eiders (Agler et al. 1995, USFWS 2002, Larned unpubl. data), so 

federal actions potentially affecting them or their habitat must undergo formal ESA consultation 

procedures. 

The Minerals Management Service (MMS) has offered oil and gas leases in offshore waters 

(approximately 5-48km seaward of the state of Alaska submerged lands) of CI, so far with only 

limited interest in the offshore zone by the petroleum industry through May of 2006 (MMS 

2003). Lease sale 199 (Fig. 2) is to be offered again in May of 2007, pending sufficient interest 

by industry. This study was designed by the U.S. Fish and Wildlife Service (FWS) to address 

MMS's obligation to evaluate potential effects of their action upon Steller's eiders, as required in 

the implementing regulations for Section 7(a)(2) of the ESA (50 CFR 402.14(i)(3)). 

Furthermore, this study partially fulfills MMS's obligations under section 7(a)(1) of the ESA and 

provides preliminary information useful for long-term monitoring. 

Historical data

Few avian surveys were conducted in Lower CI before 1976. Since then, four major surveys 

have been completed in an effort to monitor seabird and sea duck (including Steller’s eiders) 

distribution and abundance in marine habitats in Lower CI. Arneson (1980) conducted 

comprehensive pelagic and shoreline aerial surveys in 1976-77 (once each season) in marine 

waters of southwestern Alaska including CI. Primary objectives were to describe seasonal 

distribution, abundance and habitat associations of 134 species of marine and coastal birds, to 

evaluate their vulnerability to potential oil spills associated with Outer Continental Shelf (OCS) 

oil and gas development. Most of these surveys did not provide detailed data on Steller’s eiders, 

but did identify habitats seasonally important to “sea ducks”, including major shoals and 

estuaries in Kachemak Bay, and along the west side of CI from Cape Douglas to Redoubt Bay 

(Erikson 1977). During these surveys only eight Steller’s eiders were specifically identified and 

recorded along the shoreline of Lower CI in spring 1976, and no Steller’s eiders were recorded 

during the other three seasons. No Steller’s eiders were reported from four seasonal pelagic 

surveys flown across CI during this project, or they were simply included as “sea ducks”, and no 

Steller's eiders or "unidentified eiders" were reported from within a large area covered in 

northwestern Kachemak Bay. However, during a survey flight recording marine mammals and 

marine birds in Kamishak Bay, 1 April, 1976, Erikson (1977) observed a density of 0.1 Steller’s 

eiders/km2

 , along with 2.7 unidentified eiders/km2 and 6.1 unidentified sea ducks/km2, which 

were "most likely eiders”. 

Preparatory to anticipated OCS oil and gas leasing, Agler et al. (1995) conducted both aerial 

and boat surveys of coastal and pelagic habitats in Lower CI 9-16 February 1994, in which 

Steller’s eiders and other sea ducks were included. These surveys followed the study design 

used by Erikson (1977). During the aerial surveys, 442 Steller’s eiders were observed along the 

southwest and northwest shorelines of Kachemak Bay. In western CI, 1,363 Steller’s eiders 

were observed from McNeil Cove to Iniskin Bay. Eiders were also observed during pelagic boat 

surveys, but were not identified to species. 
3

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 Figure 2. Cook Inlet, Alaska, showing MMS Lease Sale Area 199. 

Aerial surveys were flown from 1994-96 by the National Park Service along the Lake Clark 

National Park shoreline, including Tuxedni and Chinitna Bays (Bennett 1996), to characterize 

seasonal use of coastal habitats by waterfowl. The surveys were conducted weekly from 15 

April - 20 May and from 15 August - 15 October each year, as well as single monthly surveys 

from December through March. The survey revealed heavy use of these habitats by sea ducks 

(primarily scoters (Melanitta spp.) during spring, summer and fall, but few waterfowl were 

present during winter, presumably because much of the area was covered with sea ice. No 

Steller’s eiders were reported from any of these surveys. 

A 5-year study (1999-2003) was conducted by the Alaska Department of Fish and Game 

(ADFG) to determine abundance and population trends of sea ducks wintering in Kachemak Bay 

in response to reported declines of some species (Petrula and Rosenberg 2005). Small boat 

surveys were conducted from late February through early March along shorelines in addition to 

random offshore aerial transects stratified by 3 water depth ranges. The 5-year mean Steller’s 

eider estimate from shoreline boat surveys was 63 eiders (range 16-161), while the mean from 

offshore aerial surveys was 649 eiders (range 165-1,459). Ninety-five percent of the Steller’s 

eiders observed were shoreward of the 20m depth contour and most were clustered in two 

locations; south of Anchor Point at the mouth of Kachemak bay, and south of Homer 

immediately southwest of Homer Spit. 
4

Four opportunistic shoreline aerial surveys have also been conducted during February and 

March 1997 – 2002 from the mouth of Kachemak Bay north to Kenai (W. Larned, U.S. Fish and 

Wildlife Service, unpubl. data). Clusters of flocks of Steller’s eiders were observed on each of 

these occasions, in locations ranging from Anchor Point to 15km north of Ninilchik, most within 

2km of shore. Estimates of eiders observed ranged from 252 (2 Feb. 2002) to 2,370 (5 Mar. 

2001). 

Finally, The U. S. Army Corps of Engineers conducted a series of eight small boat surveys 

along both sides of Homer Spit from December 2002 through March 2003. Steller’s eider totals 

ranged from 71 to 301 with nearly all sightings occurring in the area immediately adjacent to the 

southwest shore of Homer Spit (C. Hoffman, U.S. Army Corps of Engineers, unpubl. data). 

In summary, historical survey data for CI Steller’s eiders are scarce, and the most 

geographically comprehensive data sets, from surveys which occurred prior to widespread 

concern about Steller's eider populations, are difficult to interpret because observations and 

results for eiders and other sea ducks were usually combined as "eiders" or "sea ducks" rather 

than identified to individual species. However, data from the most recent winter surveys 

suggested that there were from a few hundred to about 1,000 Steller’s eiders in Kachemak Bay, 

primarily near the southwest side of the Homer Spit and south of Anchor Point. In addition, 

estimates in the low hundreds to >2,000 Steller’s eiders may be found along the shoreline 

between Anchor River and Kenai, with an additional >1,000 birds inhabiting the nearshore 

waters of Kamishak Bay between McNeil Cove and Iniskin Bay. 

 

OBJECTIVES 

The following objectives of this study were determined by MMS: 

1. Identify habitats important to Steller’s eiders wintering in Lower CI, as evidenced by 

persistent use within and among years. 

2. Describe temporal variation in Steller’s eider winter use of the waters in Lower CI during 

two winters. 

3. Estimate total numbers of Steller’s eiders wintering in the eastern and western portions of 

Lower CI. 

METHODS 

Study area

Cook Inlet is a large estuary, approximately 320km in length and varying from 20 - 90km in 

width (Fig. 3). It is bordered by the volcanic Alaska Range to the west and northwest, the 

Aleutian Range to the southwest, and the Kenai/Chugach mountains to the east. For 

convenience, the main body of CI is often divided into north and south regions, called “Upper” 

and “Lower” CI, by a geographic constriction called the “Forelands”, which lies just north of the 

city of Kenai. The subject study is limited to "Lower" CI. 

Cook Inlet is a dynamic, high energy marine system dominated by powerful tides and 

associated currents (Alaska Inst. of Marine Sci. 1999, Okkonen 2004). The twice-daily tide 
5

cycle can exceed 10m from low to high, and generates currents that can range from 8-12kts. at 

the Forelands (MMS 1984). These currents often amplify storm and wind-generated surface 

waves, especially when winds are along the long axis (northeast/southwest) of CI (Alaska Inst. of 

Marine Sci. 1999, MMS 2003). 

Cook Inlet has extensive ice cover for several months during the winter in most years. Ice 

typically begins to form in November, particularly in shallow bays with salinities diluted by 

fresh water from rivers. Peak ice extent is in February and early March, and most ice is gone by 

mid-April (Mulherin et al. 2001). The dynamic tidal environment normally keeps ice broken 

into small pans, collectively known as "brash", which disperse southward due to net effect of 

currents, and generally melt before they leave CI. As a result the ice rarely gets very thick, and 

changes in pattern and extent can occur relatively quickly. Mean ice cover for the period 16-28 

February 1986-99 incorporated all of the estuaries in western Lower CI, and extended over most 

of the shoals at least to Augustine Island (Fig. 4). Mean ice during this period extended north 

and west of a line roughly from Cape Douglas to 20km north of Ninilchik with a >25 percent 

probability (Fig. 5). 

Figure 3. True color image of Cook Inlet acquired 2 September 2002 

(Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC). 
6

Figure 4. Mean ice conditions, Cook Inlet, Alaska, for the period 16-28 February 

1986-99 (Mulherin et al. 2001).
7

 

Figure 5. Probability of occurrence for ice of at least 5/10ths concentration, 

Cook Inlet, Alaska, for the period 16-28 February 1986-99 (Mulherin et al., 

2001). 
8

Equipment, transect layout and data recording

We used two Cessna 206 aircraft, equipped with amphibious floats and long range fuel tanks 

(>6.5 hour fuel duration at survey power settings). The survey was flown at 61m (200ft) altitude 

and approximately 185km/hr. The crew in each plane consisted of a FWS pilot/biologist who 

flew the plane and observed and recorded birds on the left (port) side of the aircraft, and a FWS 

biologist who observed and recorded on the right (starboard) side of the aircraft. Systematic 

parallel survey transects (flight lines on which survey data were recorded) at 2km intervals were 

oriented perpendicular to the shoreline to the nearest 20m depth contour (Fig. 6). Steller's eiders 

are typically associated with the nearshore environment, in protected waters generally <10m in 

depth (Cottam 1939, Hogstrom 1977, Petersen 1981, U. S. Fish and Wildl. Serv. 2002, Zydelis 

2002). We selected the maximum survey depth of 20m as a practical buffer to ensure the 

inclusion of most eiders, including those that might be displaced seaward by shorefast ice. The 

perpendicular orientation of the transects was selected to minimize sampling error by crossing 

the average Steller's eider density gradient (Eberhardt 1978) which, through our survey 

experience we believed to be related primarily to water depth and distance from shore. This 

design also minimized transit time between adjacent transects, which reduced the possibility of 

counting errors resulting from birds moving among transects during the survey (compared with 

multiple transects parallel to shorelines). The survey area was split into eight alphanumericcoded polygons ("survey units"); numbers 1E-3E on the east side of CI, and numbers 1W-5W on 

Tuxedni Bay

Chinitna

 Bay

Iniskin

Bay

Iliamna

 Bay

Ursus

Cove

Bruin

Bay

McNeil

 Cove

Akumwarvik

 Bay

Cape

 Douglas

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Anchor

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Kachemak Bay

Kamishak Bay

2W

3W

4W

5W

1E

2E

3E

COOK

INLET

Douglas 

River shoals

1W

N

20 0 20 40 Kilometers

10m depth

20m depth

Figure 6. Study area showing survey units, aerial transects, bathymetry, and 

prominent shoreline features, Cook Inlet, Alaska, 2004-05. 
9

the west side, which facilitated field operations and data summary. Borders between survey 

units were shoreline features we judged likely to cause natural breaks in wintering eider 

distribution. Aircraft were navigated along transects, which were displayed in a “moving map” 

on a laptop computer linked to an instrument-panel-mounted Global Positioning System (GPS), a 

survey aid developed by John Hodges (U. S. Fish and Wildlife Service, Juneau, Alaska). The 

recording program consisted of two modules. The first automatically recorded the aircraft GPS 

coordinates and current time (seconds past midnight) at 5-second intervals, and wrote each 

position as a line in a computer file in ASCII format. In the second module, each bird 

observation was recorded into the computer vocally via a microphone, and the program timelinked the current GPS coordinate to the voice recording (.wav file). Each observer used a 

separate computer for data input. The recorded observations were later transcribed using another 

custom program, resulting in an ASCII format output file in which each text line contained GPS 

coordinates, time, species and group size for one observation, plus "header" and auxiliary data 

(date, observer position in the aircraft, observer initials, survey unit, tide state, Beaufort-scale sea 

state (http://www.hpc.ncep.noaa.gov/html/beaufort.shtml), tenths of sea-ice cover, wind 

direction, wind speed, air temperature, visibility and cloud cover.) 

Steller’s eiders in flocks containing <20 birds ("small" flocks) were counted within 300m of 

the aircraft’s flight path. The 600m wide area along a transect we called a "sample strip". The 

outer limits of a sample strip were determined using calibrated marks on the wing struts. Flocks 

containing ≥20 birds ("large" flocks) observed within or outside sample strips, to ≤1km, were 

also counted. Since transects were 2km apart this was considered a complete census of large 

flocks. Aircraft departed transects as necessary to ensure species identification and increase 

precision of estimates of flock size. 

Recorded flight tracks (excluding the off-transect deviations) were displayed and converted to 

line shapefiles using ARCVIEW GIS (ESRI 2001), buffered to 300m, and the resulting polygons 

intersected with the displayed survey units. Areas were calculated for the survey units and 

sample strips using ARCVIEW script "ViewCalculateFeatureGeometry", and the point estimates 

for all sampled eiders calculated as simple extrapolations: 

O ASU ÷ AS ∑ ∗

Where: 

 O = Total birds recorded 

 Asu = Total area of survey unit 

 As = Total area of sample strips 

The population estimate for each survey unit was calculated as the expanded sample ("small" 

flock) estimate plus the sum of all birds in "large" flocks. 

We used this two-tiered procedure because past survey experience with this species indicated 

that distribution of birds would consist of clusters of large dense flocks and, in some areas, 

scattered individuals and small flocks (Larned 2001, Larned 2005, W. Larned, U.S. Fish and 

Wildlife Service, unpubl. data). Ideal transect spacing would be about 500-600m for all birds to 

be seen. However, our experience suggests that such spacing would likely have caused birds to 

flush from adjacent transects ahead of the plane, resulting in under-counting or distributional 

errors. Also, funding constraints and narrow windows of opportunity due to weather would have 

precluded inclusion of additional flight hours required for increased sampling intensity. Our 
10

experience suggested that dense flocks of approximately ≥20 birds could be readily seen at 1km 

under anticipated survey conditions, particularly since such flocks tend to occur as clusters. We 

further reasoned that any flocks missed with the present sampling strategy would be small, and 

birds that weren’t detected would not detract significantly from the utility of the results for their 

intended purposes. In our opinion the alternative random or systematic partial samples for all 

flock sizes would have had high sampling errors due to the clumped distribution, requiring 

replication within each month, and such replication was not feasible due to weather and funding 

constraints. In summary we reasoned that, if a seasonal pattern of distribution existed that was 

consistent among years, our design should have been able to characterize it to provide adequate 

guidance to help MMS avoid conflict between Steller's eiders and industrial activities, 

infrastructure, and for contingency (e.g., spills of crude oil or fuel) planning. 

Accuracy of observational data,

Aerial surveys have been used extensively for many years for gathering abundance, trend, and 

distribution data needed for management of waterfowl and many other wildlife taxa. However, 

this technique is fraught with problems and concerns over sampling and detection bias 

(Anderson 2001). Detection bias is an especially challenging problem in the marine environment 

due mainly to spatial and temporal variation in the viewing environment, i.e., the color, wave 

action, and illumination of the sea surface itself (Stott and Olsen 1972). Other variables we have 

found to affect detection of birds at sea among and within survey replicates include 

characteristics of the birds themselves (e.g., size, color, flock size and density, types and 

frequency of escape behaviors like flushing or diving), observer distractions (e.g., non-target 

animals, sea ice, whitecaps, flotsam), experience level of individual observers, and to a lesser 

extent, temporal variation in bias among observers (e.g., "learning curve", fatigue and other 

physiological effects). Ideally, net influence of all these variables (net bias) may be quantified 

using some form of double sampling technique, wherein a precise (unbiased) count of 

individuals is obtained from a representative subset of the survey sample, the result compared 

with the estimate from the corresponding (biased) operational subset, and the resulting ratio 

applied to adjust the entire operational data set (Stott and Olson 1972, Eberhardt and Simmons 

1987, Estes and Jameson 1987, Bart and Earnst 2002, Thompson 1992). However, though we 

considered this approach for our study, it was clearly not a viable option for three reasons. First, 

we could not envision a sampling strategy that would produce a relatively precise estimate from 

a survey subsample that would be affordable, representative, and would not create its own bias 

by disturbing sampled birds. Observation platforms that came to mind for the precise subsample 

were vessels, shoreline promontories, and helicopters. Safety, cost, and challenges involving 

logistics and coordination, eliminated the shipboard option. We knew of only one or two 

locations where eider aggregations might be occasionally visible from the shoreline, potentially 

yielding only partial counts, and again logistics and coordination would be extremely 

challenging. The helicopter option was dismissed due to the great distances involved, with 

associated issues of safety, coordination, logistics, and increased cost. 

The second reason we did not choose a double sample technique was that we anticipated an 

eider distribution composed primarily of a few widely scattered clusters of large flocks. We 

settled on a systematically designed total census of these large flocks to avoid the large sampling 

error usually associated with sampling clumped distributions. Lastly, in consideration of the 

ultimate management objective of avoiding or reducing conflicts between commercial resource 
11

development activities and Steller's eiders, we were less concerned with precision of estimates or 

total counts than with spatial distribution of flocks and persistence of habitat associations 

through time and space. 

The above rejection of double-sampling notwithstanding, we were still interested in reducing 

detection and estimation bias as much as practicable. We addressed the above listed known 

sources of detection bias using the following procedures: 

One of the most important variables is wave action, especially the presence or absence of 

whitecaps. We therefore stipulated in our protocol that we would avoid surveying when 

whitecaps were prevalent, or when sea state >3 on the Beaufort scale (wind 13-18kph, sea with 

large wavelets, crests beginning to break, and scattered whitecaps). We tried to minimize the 

effects of surface glare by favoring days with high overcast conditions, but found that we rarely 

had the luxury of choosing such conditions during the mid-winter months given the short 

daylight intervals and generally persistent inclement weather. Mitigation of the effects of bird 

characteristics on detection and identification came primarily from training and experience of 

observers both prior to and during the survey, and deviation as needed from transects (see 

above). Steller's eiders are small as sea ducks go, but strikingly marked and gregarious, thus 

relatively easy to detect and identify compared to most other water birds. Observer distractions 

including the presence of ‘other’ species may have influenced, at least to some extent, our ability 

to detect Steller’s eiders, but only if (and when) Steller’s eiders presence overlapped that of other 

species. We attempted to minimize the distractive effects of ice chunks or ice sheets and other 

flotsam by selecting intervals to survey when wind and tides distributed these objects against the 

shore or ice edge versus dispersing them seaward. Again, opportunities for such selectivity 

were, in reality, limited by the scarcity and brevity of weather windows. 

Our organization avoids changes in crew composition (particularly observers) whenever 

possible, to help minimize observer bias both among and within survey replications. This was 

our intent with this project as well, but due to unpredictable weather conditions and windows of 

opportunity to conduct surveys, logistical challenges, conflicting schedules of survey personnel, 

and an injury to one crewmember; some changes were made in both pilots and observers Tables 

2, 3). Although aerial survey experience varied considerably among observers, each observer 

had previous experience participating in Steller's eider aerial surveys. The principal investigator 

had flown previously with each observer or had spent some time in the air during this study to 

ensure competency at identifying Steller’s eiders. During the surveys, observers worked closely 

to resolve any identification uncertainties and the protocol used allowed for aircraft to depart 

transects for positive identification and to allow sufficient time for flock estimation. 

We used an indirect method to evaluate comparability of observers post-survey. Given the 

arrangement of transects perpendicular to the anticipated average density gradient of sea ducks 

(and sea otters, Enhydra lutris), and the roughly equal average among-observer viewing 

conditions, we reasoned that each observer should have had equal opportunity to detect animals, 

provided the animals had a widely dispersed rather than clumped distribution. Steller's eiders 

clearly did not fit this description. However, following standard USFWS survey protocol we 

recorded all identifiable birds and other taxa of interest to the agency (i.e., USFWS) in addition 

to Steller's eiders. Among these we selected three taxa (long-tailed ducks Clangula hyemalis, 

combined scoters Melanitta spp., and sea otters Enhydra lutris) that were recorded by all 

observers within the 600m sample strips, and were relatively abundant and well-dispersed 

throughout much of the survey area. We compared total observations of non-target species 
12

(numbers of separate groups or flocks observed, rather than total individuals) made by each 

observer during all surveys in which observers were paired. These taxa were not considered 

valid surrogates for Steller's eiders, particularly relative to flock configuration and distribution. 

In addition, among-observer variation is assumed to be lower on average for target than nontarget species because survey protocol calls for higher priority to be given to target species 

whenever workload precludes careful recording of all birds present. However, among-observer 

comparisons using the three non-target species groups should provide some measure of amongobserver variation in detection rates of animals of size roughly comparable to that of Steller's 

eiders under similar environmental conditions (admittedly a stretch for sea otters, but frequently 

only the head is visible). We did not complete a detailed statistical treatment of the data, but 

qualitative assessment revealed some patterns among pairs of observers for which we had 

sufficient data (Table 1). Observer number 3 generally had similar or slightly higher numbers of 

detections compared to observers 1, 5, 6, and 9, but was consistently higher than observer 4. 

Table 1. Comparison of bird and sea otter observations among left and right paired observers 

during aerial waterfowl surveys in lower Cook Inlet, Alaska, during year 1 (January-April 2004) 

and year 2 (December 2004-April 2005). Numbers are total observations for each taxon during 

all surveys in which the listed observers were paired, and, in parentheses, the percentage of total 

observations made by the respective observer. LTDU = long-tailed duck (Clangula hyemalis), 

SCOT = combined scoter species (Melanitta spp.), SEOT = sea otter (Enhydra lutris) 

 Year 1 Year 2

Observers LTDU SCOT SEOT LTDU SCOT SEOT 

3 113 (62) 306 (52) 232 (52) 120 (66) 68 (53) 117 (45) 

1 70 (38) 280 (48) 216 (48) 63 (34) 60 (47) 145 (55) 

 

3 155 (67) 282 (76) 188 (66) 94 (62) 325 (81) 89 (64) 

4 78 (33) 90 (24) 97 (34) 57 (38) 77 (19) 51 (36) 

3 50 (49) 90 (48) 98 (53) 

5 52 (51) 97 (52) 87 (47) 

3 108 (63) 37 (49) 248 (55) 

6 64 (37) 38 (51) 203 (45) 

3 56 (55) 191 (48) 197 (48) 

9 46 (45) 208 (52) 214 (52) 

4 32 (40) 60 (27) NS 113 (43) 117 (24) 292 (34) 

1 49 (60) 163 (73) NS 150 (57) 377 (76) 555 (66) 

4 18 (44) 13 (22) 100 (30) 

7 23 (56) 46 (78) 228 (70) 

2 170 (47) 444 (53) 315 (55) 111 (45) 48 (45) 88 (34) 

9 191 (53) 395 (47) 262 (45) 133 (55) 58 (55) 174 (66) 
13

Observers 1 and 7 were also consistently higher than observer 4, while observers 2 and 9 were 

reasonably similar to one another. Among-observer differences in ability to detect Steller’s 

eiders and differences in their counts may not have been important in the overall estimates and 

assessment of distribution given the objectives of the survey and because precise population 

estimates were not a high priority for this study. The primary reason for presenting this 

comparison is to point out the importance of implementing a more rigorous evaluation of 

observers prior to any future surveys, such that any discrepancies among observers can be dealt 

with through remedial training, a numerical correction factor for paired observers, or 

replacement of observers who cannot meet standards (see below). 

Each observer practiced flock estimation using a computer wildlife counting simulation 

training program (Hodges 1993) prior to and periodically during the study. We initially 

considered using oblique 35mm photography of as many eider flocks as possible, counting birds 

in photographs to increase precision for the flocks successfully photographed, and to use the 

results to compensate for observer estimation bias for unphotographed flocks through double 

sampling statistical techniques (Eberhardt and Simmons 1987, Lock 1986). However, in prior 

Steller's eider surveys, including a pilot study in CI (Larned 2005, U. S. Fish and Wildlife 

Service, unpubl. data) we found that behavior of Steller's eiders rendered this technique 

unreliable. Specifically, eiders in flocks dove frequently and sequentially as we passed over 

them in the aircraft, thus resulting in images of partial flocks which were consequently biased 

low. Also, during aircraft maneuvers required for photographs clustered flocks disturbed by the 

survey aircraft tended to split and/or be joined by other flocks making it extremely difficult to 

obtain a single set of images containing all birds. Perhaps more importantly, such maneuvers 

often caused observers to become disoriented, losing track of focal flocks which almost certainly 

reduced the precision of our estimates. We therefore rejected the use of aerial photographs in 

assessing observer bias during this study. 

RESULTS AND DISCUSSION 

Environmental conditions

Our observations during this study indicated that sea ice extent throughout the two winters 

covered by this survey was considerably less than average conditions from 1986-1999 (Mulherin 

et al. 2001). Ice cover in mid-February 2004 within the survey area consisted of limited brash 

ice in the McNeil Cove/Akumwarvik Bay area, heavier brash ice from Tuxedni Bay northward, 

and extensive shorefast ice in the more protected west CI bays (Fig. 7). The month of February 

represented the maximum ice extent during the winter of 2003-04. The winter of 2004-05 was 

mild in early January and sea ice extent was minimal south of the forelands (Fig. 8). A cold snap 

in February, however, covered most of the shoals in Kamishak Bay and all west shore estuaries 

with brash and continuous ice. Continuous ice also covered most of the east shoreline north of 

Anchor Point (Fig. 9). Sea ice in Lower CI is presumably a major factor influencing use of 

winter habitats by Steller’s eiders and other marine birds, and may account for some of the 

apparent changes in bird distribution observed among months and years in this survey and 

previous studies. 

Weather during the surveys was mostly within the acceptable parameters we set, and we found 

viewing conditions generally favorable. However, the area offshore south of Anchor Point (Fig. 
14

6) often had stronger winds than the rest of the eastern survey units. Often when the rest of the 

survey area was Beaufort 2 or less with no whitecaps, the area south of Anchor Point had 

Beaufort 3 conditions with some whitecaps present. It became readily apparent that we would 

have to occasionally fly surveys under these conditions in order to complete the surveys per the 

survey schedule to meet objectives of the study. We believe this may have resulted in slightly 

poorer eider detection rates in this area compared to adjacent areas, hence the estimates for that 

area may be biased low. The same was occasionally true for the more exposed shorelines in 

survey units 3W and 4W between Bruin and Illiamna Bays. We do not consider the magnitude 

of this problem to have been great enough to have significantly affected our conclusions 

regarding the overall distribution pattern. However, in future studies we recommend reducing 

widths of transect strips, either throughout the survey or only for those areas where detection 

probabilities are likely poor or lessened due to ice and sea state conditions. We felt that 

detection probabilities of birds were also lower during the period of winter when sun angles are 

at the lowest, especially when coupled with choppy sea surface conditions. 

Figure 7. Sea ice cover in Cook Inlet, Alaska, 13 February 2004. Graphic 

developed by Sea Ice Desk, National Weather Service, Anchorage, Alaska. 
15

Figure 8. Sea ice cover in Cook Inlet, Alaska, 10 January 2005. Graphic 

developed by Sea Ice Desk, National Weather Service, Anchorage, Alaska. 

Figure 9. Sea ice cover in Cook Inlet, Alaska, 11 February 2005. Graphic 

developed by Sea Ice Desk, National Weather Service, Anchorage, Alaska. 
16

Abundance and distribution of Steller's eiders

We present Steller's eider estimates as crew totals for each survey unit by month with primary 

crew data highlighted and summarized by eastern and western Inlet areas (Tables 2 and 3). 

Monthly Steller's eider totals are compared by survey unit (Figure 10), and locations of 

individual observations are graphically depicted (Figs. 11-19), graduated symbols representing 

flock size ranges. Data for both aerial crews are displayed simultaneously in each map, so that 

all locations of recorded eiders are represented. Therefore, flocks observed by both survey crews 

are displayed twice, while those flocks observed by one crew only are displayed once. Though 

this procedure gives an inaccurate representation of the density of eider flocks, it depicts habitats 

used as inclusively as possible, in light of our knowledge that neither aerial crew detected all 

Steller's eiders present, and in the interest of leaving no habitats used by eiders unidentified. 

Eiders were frequently associated with certain habitats within specific areas surveyed during 

this study. Survey unit 4W included the bulk (n = 1713) of Steller’s eiders observed during this 

survey, followed by 1E (n = 463), 2E (n = 134), and 3W (n = 125) (Table 4). Very few eiders 

were recorded among the remaining four survey units: 3E, 5W, 1W and 2W. An important index 

to use was the relative proportion of CI wintering eider population found along the eastern vs. 

western shoreline. While the survey was initiated too late during the winter of 2003-2004 for 

such a determination, during the second year of the survey on average we observed 25% of the 

Steller's eiders in eastern vs. 75% in western CI (Table 4). The highest monthly estimate among 

both years (n = 1499) for the eastern survey units occurred in February 2004 (Table 1) with the 

highest monthly estimate (n = 4284) for the western units occurring in January 2005 (Table 3). 

Peak estimates of Steller’s eiders varied considerably among years in both number and timing 

for individual survey units (Fig. 10). Pooled estimates for the eastern units peaked in February 

2004 (n = 1499, Table 2) and January 2005 (n = 1247, Table 3). Numbers of Steller's eiders 

observed during a series of small boat surveys along the Homer Spit during the winter of 2002-

03 peaked in mid-January, though numbers observed varied only slightly through the survey 

period from mid-December to early March (C. Hoffman, U. S. Army Corps of Engineers, pers. 

comm.). The Western CI units were not surveyed completely in 2004 until March. In 2005, a 

peak in the pooled estimate occurred in January followed by a dramatic decline in February and a 

large increase in March (Fig. 10). Most of January 2005 was mild with little sea ice in Kamishak 

Bay, then a cold snap occurred from late January through most of February which generated 

extensive sea ice cover that apparently displaced Steller’s eiders from that area. A coincidental 

decline in Steller’s eider estimates in the eastern survey units (Fig. 10) indicated a low 

probability that Kamishak Bay birds relocated eastward across CI. We speculate that these 

eiders dispersed outside the survey area south along the Alaska Peninsula coast or possibly to 

open water areas near the Kodiak archipelago. 

Locations of Steller's eiders implanted with satellite transmitters showed a pattern of 

movement between Chiniak Bay (Kodiak) and Kamishak Bay, suggesting that some birds used 

the Douglas River Shoals area in Kamishak Bay during the August - September post-nuptial molt 

(D. Rosenberg, Alaska Department of Fish and Game, pers. comm.). The use of this area by 

substantial numbers of molting eiders was confirmed during two independent aerial surveys in 

2005. The first survey was conducted on 29 August in the Douglas River Shoals area only and 

counted 2,225 Steller's eiders (D. Rosenberg, Alaska Department of Fish and Game, unpubl. 

data). The second was a shoreline survey conducted on 14 September from the Douglas River to 

Tuxedni Bay. A total of 2,190 Steller's eiders were recorded, all within the reefs, shoals, and 
17

islands of the Douglas River area (W. Larned, U.S. Fish and Wildlife Service, unpubl. data). It is 

not known how many of these birds remained in the area until winter. Data from four eiders 

instrumented with satellite transmitters in Chiniak Bay, Kodiak, in March 2005, indicated that 

they spent the breeding season in the Russian Arctic, returned to molt in the Douglas River area 

and remained in the latter area from late August or early September until mid-November or later 

(D. Rosenberg, Alaska Department of Fish and Game, pers. comm.). 

Data obtained from this aerial survey suggest that Steller’s eiders use certain key winter 

habitats in CI within and among years (Figs. 11-19). Very few Steller’s eiders were observed in 

upper Kachemak Bay, northeastward of the Homer Spit. However, flocks of various sizes were 

consistently observed from the west shore of Homer Spit to Clam Gulch. Variables that may 

have influenced observed distribution and movements include sea ice extent, sea surface 

conditions, tides, and local prey distribution and abundance. In Kachemak Bay, the two sites 

most consistently occupied were adjacent to the Homer Spit and an extensive shoal south of 

Anchor Point. In eastern CI, the largest flocks, and during most surveys the majority of Steller’s 

eiders observed were north of Anchor Point. 

Steller's eiders in western CI were consistently distributed and most abundant in the extensive 

shoals surrounding the mouth of the Douglas River (Figs. 12-19). The only exception was 

during the February 2005 survey when these shoals were almost completely ice covered (Fig. 

17). The site with the next highest abundance within the western survey area was in the general 

vicinity of Bruin Bay. Distribution within the latter area was more variable (compared to 

Douglas River Shoals), possibly due in part to greater variability in factors such as sea ice cover 

and surface conditions. Within the vicinity of Bruin Bay, the two most consistently used sites 

were an extensive shoal centered about 8km southeast of Bruin Bay and an area very close to the 

shoreline between Bruin Bay and Ursus Cove (Figs. 12-19). A third area in which we 

consistently observed eiders during the second year of the survey was at the mouth of Iniskin 

Bay (range 160 - 435 eiders; Figs. 15-18). In 2004, we had only one observation of 28 eiders in 

Iniskin Bay (April; Fig. 14), but the area was only surveyed in March and April. The only 

Steller's eiders recorded north of Iniskin Bay were two very small flocks (n = 8, n = 5) in 

Chinitna Bay (Figs. 15 and 17) and a single bird observed in Tuxedni Bay (Fig. 19). 
18

Table 2. Estimates of Steller's eiders observed during aerial surveys, Cook Inlet, AK, January to April 2004. Data from Primary

 crew used to calculate monthly totals are in bold typeface.

Date of Survey Flocks <20 Flocks <20 expansion Flocks <20 Flocks ≥ 20 Flocks ≥ 20 Steller's eider

Survey Unit1 Crew2 N birds observed factor3 Estimate N birds observed Total 

Jan. 2004

1/23/2004 1E PA/HW 11 74 3.22 238 10 440 678

1/23/2004 2E PA/HW 12 54 3.16 171 1 48 219

1/23/2004 3E PA/HW 0 0 3.29 0 0 0 0

January Total for East Units 897

January Total for West Units not surveyed

Feb. 2004

2/11/2004 1E WL/PA 5 47 4.07 191 6 930 1121

2/11/2004 2E WL/PA 24 105 3.22 338 0 0 338

2/11/2004 3E WL/PA 1 3 3.34 10 1 30 40

2/16/2004 3E EM/CD 1 5 3.33 17 0 0 17

2/14/2004 1W EM/CD 0 0 3.74 0 0 0 0

2/14/2004 2W WL/HW 0 0 3.39 0 0 0 0

3W Not completed

4W Not completed

5W Not completed

February Total for East Units 1499

February Total for West Units not completed

Mar. 2004

3/11/2004 1E WL/PA 15 54 2.98 161 3 180 341

3/23/2004 1E EM/CD 17 42 3.01 126 0 0 126

3/11/2004 2E WL/PA 6 24 2.95 71 1 30 101

3/23/2004 2E EM/CD 18 39 3.00 117 0 0 117

3/11/2004 3E WL/PA 1 6 2.97 18 0 0 18

3/23/2004 3E EM/CD 2 16 3.11 50 0 0 50

3/17/2004 1W WL/PA 0 0 3.33 0 0 0 0

3/16/2004 2W WL/PA 0 0 3.16 0 0 0 0

3/16/2004 3W WL/PA 1 7 3.02 21 0 0 21

3/15-16/04 4W WL/PA 7 49 3.11 152 14 2093 2245

3/16/2004 4W EM/CD 32 146 3.04 444 19 1860 2304

3/15/2004 5W WL/PA 0 0 2.47 0 0 0 0

3/16/2004 5W EM/CD 0 0 3.06 0 0 0 0

March Total for East Units 460

March Total for West Units 2266

Apr. 2004

4/12/2004 1E WL/HW 1 3 3.34 10 0 0 10

4/12/2004 1E EM/CD 14 30 3.26 98 0 0 98

4/13/2004 2E WL/HW 11 38 3.32 126 0 0 126

4/12/2004 2E EM/CD 7 18 3.37 61 0 0 61

4/13/2004 3E WL/HW 3 8 3.32 27 0 0 27

4/13/2004 1W WL/HW 0 0 4.28 0 0 0 0

4/13/2004 2W WL/HW 0 0 3.50 0 0 0 0

4/13/2004 3W WL/HW 1 8 3.47 28 0 0 28

4/12/2004 4W WL/HW 14 123 3.42 421 9 885 1306

4/13/2004 4W EM/CD 49 211 3.37 711 4 195 906

4/12/2004 5W WL/HW 1 1 2.73 3 0 0 3

4/13/2004 5W EM/CD 0 0 4.01 0 0 0 0

April Total for East Units 163

April Total for West Units 1337

1. Data are listed for completed units only. 2. Crew: CD=Christian Dau, EM=Edward Mallek, HW=Heather Wilson,

PA=Paul Anderson, WL=William Larned 3. Expansion factor = survey unit area/sampled area. Sampled area is calculated from km

flown while actually surveying.
19

Table 3. Estimates of Steller's eiders observed during aerial surveys, Cook Inlet, Alaska, December 2004 to April 2005. Data from 

primary crew used to calculate monthly totals is in bold typeface.

Date of Survey Flocks <20 Flocks <20 expansion Flocks <20 Flocks ≥ 20 Flocks ≥ 20 Steller's eider

Survey Unit1 Crew2 N birds observed factor3 Estimate N birds observed Total 

Dec. 2004

12/8/2004 1E WL/CD 0 0 3.27 0 6 825 825

12/8/2004 1E PA/TB 5 22 3.21 71 5 570 641

12/8/2004 2E WL/CD 1 4 3.20 13 1 30 43

12/8/2004 2E PA/TB 3 7 3.20 22 0 0 22

12/8/2004 3E WL/CD 0 0 3.31 0 0 0 0

12/5/2004 2W WL/CD 0 0 3.44 0 0 0 0

12/5/2004 3W WL/CD 0 0 3.43 0 1 160 160

12/5/2004 3W PA/HW 0 0 3.52 0 1 250 250

12/4-5/2004 4W WL/CD 2 13 3.43 45 6 930 975

12/4-5/2004 4W PA/HW 5 26 3.31 86 5 1981 2067

12/4/2004 5W WL/CD 0 0 2.56 0 0 0 0

12/5/2004 5W PA/HW 0 0 3.71 0 0 0 0

December Total for East Units 868

December Total for West Units 1135

Jan. 2005

1/6/2005 1E WL/RP 2 14 3.26 46 11 1095 1141

1/6/2005 1E PA/HW 3 15 3.22 48 6 1245 1293

1/6/2005 2E WL/RP 5 25 3.26 82 1 25 107

1/6/2005 2E PA/HW 5 17 3.28 56 0 0 56

1/6/2005 3E WL/RP 0 0 3.41 0 0 0 0

1/6/2005 3E PA/HW 0 0 3.31 0 0 0 0

1/7/2006 2W WL/RP 0 0 3.88 0 0 0 0

1/7/2006 3W WL/RP 1 10 3.32 33 2 330 363

1/7/2006 3W PA/HW 2 8 3.44 28 1 220 248

1/11/2005 4W WL/WE 4 15 3.37 51 9 3870 3921

1/11/2005 4W PA/HW 5 21 3.47 73 0 0 73

1/11/2005 5W WL/WE 0 0 2.39 0 0 0 0

1/11/2005 5W PA/HW 0 0 3.47 0 0 0 0

January Total for East Units 1248

January Total for West Units 4284

Feb. 2005

2/3/2005 1E WL/HW 4 4 3.25 13 9 635 648

2/3/2005 1E EM/CD 1 5 3.26 16 3 128 144

2/3/2005 2E WL/HW 11 26 3.24 84 1 20 104

2/3/2005 2E EM/CD 5 12 3.40 41 0 0 41

2/3/2005 3E WL/HW 1 2 3.34 7 0 0 7

2/3/2005 3E EM/CD 0 0 3.39 0 0 0 0

2/4/2005 1W WL/HW 0 0 4.84 0 0 0 0

2/4/2005 1W EM/CD 0 0 3.83 0 0 0 0

2/4/2005 2W WL/HW 0 0 3.65 0 0 0 0

2/4/2005 2W EM/CD 1 5 3.73 19 0 0 19

2/4/2005 3W WL/HW 0 0 3.36 0 0 0 0

2/4/2005 3W EM/CD 0 0 3.47 0 3 435 435

2/4,12/2005 4W WL/HW/DM 2 5 3.46 17 3 206 223

2/4,12/2005 4W EM/CD 0 0 3.46 0 5 290 290

2/12/2005 5W WL/DM 0 0 2.32 0 0 0 0

2/12/2005 5W EM/CD 0 0 3.44 0 0 0 0

February Totals for East Units 759

February Totals for West Units 223
20

Table 3. (Continued).

Date of Survey Flocks <20 Flocks <20 expansion Flocks <20 Flocks ≥ 20 Flocks ≥ 20 Steller's eider

Survey Unit1 Crew2 N birds observed factor3 Estimate N birds observed Total 

Mar. 2005

3/4/2005 1E PA/WL 12 66 3.23 213 1 40 253

3/7/2005 1E WL/PA 3 34 3.27 111 2 175 286

3/4/2005 2E PA/WL 37 118 3.22 380 1 45 425

3/7/2005 2E WL/PA 6 28 3.29 92 3 86 178

3/4/2005 3E PA/WL 0 0 3.30 0 0 0 0

3/7/2005 3E WL/PA 1 3 3.22 10 1 29 39

3/2/2005 1W WL/DM 0 0 3.78 0 0 0 0

3/2/2005 1W PA/RP 0 0 3.94 0 0 0 0

3/2/2005 2W WL/DM 0 0 3.49 0 0 0 0

3/2/2005 2W PA/RP 0 0 3.34 0 0 0 0

3/2/2005 3W WL/DM 0 0 3.33 0 1 300 300

3/2/2005 3W PA/RP 0 0 3.36 0 1 520 520

3/1-2/2005 4W WL/DM 4 33 3.39 112 18 2540 2652

3/1-2/2005 4W PA/RP 31 101 3.39 342 20 2176 2518

3/1/2005 5W WL/DM 0 0 2.42 0 0 0 0

3/1/2005 5W PA/RP 0 0 3.26 0 0 0 0

March Totals for East Units 678

March Totals for West Units 2952

Apr. 2005

4/12/2005 1E WL/PA 2 5 3.20 16 1 21 37

4/12/2005 2E WL/PA 3 3 3.27 10 1 25 35

4/12/2005 3E WL/PA 0 0 3.30 0 0 0 0

4/14/2005 1W WL/CD 0 0 3.96 0 0 0 0

4/14/2005 1W PA/HW 1 4 4.01 16 0 0 16

4/14/2005 2W WL/CD 0 0 3.45 0 0 0 0

4/14/2005 2W PA/HW 1 2 3.30 7 0 0 7

4/13-14/2006 3W WL/CD 0 0 3.36 0 0 0 0

4/13-14/2006 3W PA/HW 1 3 3.28 10 0 0 10

4/13/2005 4W WL/CD 13 75 3.43 257 10 410 667

4/13/2005 4W PA/HW 7 35 3.41 119 2 115 234

4/13/2005 5W WL/CD 0 0 2.42 0 0 0 0

4/13/2005 5W PA/HW 3.47 0 0

April Totals for East Units 72

April Totals for West Units 667

1. Data are listed for completed areas only. 2. Crew: CD=Christian Dau, DM=Dennis Marks, EM=Edward Mallek, HW=Heather Wilson, 

PA=Paul Anderson, RP=Robert Platte, TB=Timothy Bowman, WE=William Eldridge, WL=William Larned. 

3. Expansion factor = survey unit area/sampled area. Sampled area is calculated from km actually flown while surveying.
21

Table 4. Monthly Steller's eider estimates averaged over all months in which surveys were 

completed (March, April, and December, 2004, and January – April, 2005), aerial Steller's eider 

surveys, Cook Inlet, Alaska. 

Survey Unit 

Average Monthly 

Means Rank 

1E 462.7 2 

2E 134.4 3 

3E 7.4 5 

East Total 604.5 

 

1W 0 7 

2W 0 7 

3W 124.6 4 

4W 1712.7 1 

5W 0.4 6 

West Total 1837.7 
22

 

SURVEY UNIT 1E

0

200

400

600

800

1000

1200

Dec. Jan. Feb. Mar. A pr.

Eider Estim ate

1st

year

2nd

year

 

SURVEY UNIT 2E

0

100

200

300

400

500

Dec. Jan. Feb. Mar. A pr.

Eider Estim ate

1st

year

2nd

year

SURVEY UNIT 3E

0

10

20

30

40

50

Dec. Jan. Feb. Mar. A pr.

Eider Estim ate

1st

year

2nd

year

 

SURVEY UNIT 3W

0

50

100

150

200

250

300

350

400

Dec. Jan. Feb. Mar. A pr.

Eider Estim ate

1st

year

2nd

year

SURVEY UNIT 4W

0

1000

2000

3000

4000

5000

Dec. Jan. Feb. Mar. A pr.

Eider Estim ate

1st

year

2nd

year

 

EAST INLET TOTALS

0

200

400

600

800

1000

1200

1400

1600

Dec. Jan. Feb. Mar. A pr.

Eider Estim ate

1st

year

2nd

year

WEST INLET TOTALS

0

1000

2000

3000

4000

5000

Dec. Jan. Feb. Mar. A pr.

Eider Estim ate

1st

year

2nd

year

 

INLET TOTALS

0

1000

2000

3000

4000

5000

6000

Dec. Jan. Feb. Mar. A pr.

Eider Estim ate

1st

year

2nd

year

Figure 10. Steller's eider estimates from survey units completed by the primary 

survey crew during monthly aerial surveys in Cook Inlet, Alaska, January – April 

2004 and December 2004 – April 2005. Note that no data are included from survey 

units and area totals not completely surveyed. 
23

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ÊÚ

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Nin ilc hik

An ch or

Po int

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Anchor

Point

Homer

1E

2E

3E

4E

Kenai

COOK

INLET

Kachemak Bay

1W

2W

3W

4W

5W

Kamishak Bay

Tuxedni Bay

Chinitna

 Bay

Iniskin

Bay

Illiamna

 Bay

Ursus

Cove

Bruin

Bay

McNeil

 Cove

Akumwarvik

 Bay

Douglas

R. Shoals

Cape

 Douglas

10m isobath

20m isobath

Transects flown

STEI Flocks Observed

# 1 - 6

# 7 - 15

# 16 - 28

# 29 - 55

# 56 - 120

N

20 0 20 40 Kilometers

Figure 11. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 23 January 2004. Flock symbol sizes are proportional to ranges 

of numbers of eiders as noted in the legend. 

 
24

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Homer

1E

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COOK

INLET

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R. Shoals

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STEI Flocks Observed

# 1 - 37

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# 701 - 1500

N

20 0 20 40 Kilometers

Figure 12. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 11-16 February 2004. Flock symbol sizes are proportional to 

ranges of numbers of eiders as noted in the legend.
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Point

Homer

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COOK

INLET

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20m isobath

Transects flown

STEI Flocks Observed

# 1 - 30

# 31 - 90

# 91 - 150

# 151 - 300

# 301 - 600

N

20 0 20 40 Kilometers

Figure 13. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 11-17 March 2004. Flock symbols are proportional to ranges of 

numbers of eiders as noted in the legend.
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Homer

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Kenai

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INLET

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# 1 - 7

# 8 - 30

# 31 - 95

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# 176 - 370

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20 0 20 40 Kilometers

Figure 14. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 12-13 April 2004. Flock symbols are proportional to ranges of 

numbers of eiders as noted in the legend.
27

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Point

Homer

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2E

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Kenai

COOK

INLET

Kachemak Bay

1W

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Douglas

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Cape

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STEI Flocks Observed # 1 - 19

# 20 - 60

# 61 - 200

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# 426 - 1275

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20 0 20 40 Kilometers

Figure 15. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 4-8 December 2004. Flock symbols are proportional to ranges 

of numbers of eiders as noted in the legend.
28

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Kenai

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INLET

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Ursus

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Bruin

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McNeil

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Douglas

R. Shoals

Cape

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STEI Flocks Observed # 1 - 19

# 20 - 140

# 141 - 360

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20 0 20 40 Kilometers

Figure 16. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 6-11 January 2005. Flock symbols are proportional to ranges of 

numbers of eiders as noted in the legend.
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INLET

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STEI Flocks Observed # 1 - 19

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20 0 20 40 Kilometers

Figure 17. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 3-12 February 2005. Flock symbols are proportional to ranges 

of numbers of eiders as noted in the legend.
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Kenai

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Transects flown

STEI Flocks Observed # 1 - 19

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20 0 20 40 Kilometers

Figure 18. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 2-4 March 2005. Flock symbols are proportional to ranges of 

numbers of eiders as noted in the legend.
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Kenai

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STEI Flocks Observed # 1 - 19

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20 0 20 40 Kilometers

Figure 19. Transects flown and locations of Steller's eider groups recorded during an aerial 

survey, Cook Inlet, Alaska, 12-14 April 2005. Flock symbols are proportional to ranges of 

numbers of eiders as noted in the legend.
32

SUMMARY AND CONCLUSIONS 

The general goal of this study was to provide information that would enable MMS to avoid or 

mitigate potential impacts to threatened Steller's eiders during oil and gas development activities 

in CI. Based on prior survey experience in CI (U.S. Fish and Wildlife Service, unpubl. data; 

Petrula and Rosenberg 2005) and other portions of this species' winter range (Larned 2001, 

Larned 2005) we considered it unlikely that proposed Federal Lease Sale 199 would include 

habitats used frequently by Steller's eiders. Steller's eiders are normally associated with the near 

shore environment, in protected waters generally <10m in depth (Cottam 1939, Hogstrom 1977, 

Petersen 1981, U. S. Fish and Wildl. Serv. 2002, Zydelis 2002). In CI all such habitats are well 

shoreward of the lease sale area. However, many related activities (e.g., seismic exploration, 

transportation vessels in support of drilling, production, product and waste removal, and mishaps 

like crude oil and fuel spills) have considerable potential to damage important eider habitat, force 

the birds to relocate to alternate habitats of lower quality, or cause the loss of eiders directly. 

Such effects may be prevented or at least reduced by awareness and avoidance of Steller’s eider 

concentration areas and at times when the birds tend to congregate in these areas. 

Our strategy was to conduct a series of monthly aerial surveys and use the resulting periodic 

"snapshots" to help depict and describe, in as much detail as possible, the seasonal distribution of 

the eiders and location of habitats apparently important to their overwinter survival while in CI. 

Steller's eiders exhibit strong fidelity to wintering (Murie and Scheffer 1959, Jones 1965, 

Kistchinski 1973) and molting (Jones 1965, Petersen 1981, Dau et al. 1985, Flint et al. 2000) 

areas. We thought it reasonable to assume that eider distribution in future years would be similar 

to that observed during this study under similar environmental conditions in the future, 

particularly if we did not see any major inconsistencies between our data and those from earlier 

surveys. Our original study design called for two years of monthly surveys, December – April. 

However, coverage of all survey units during the first year was completed only for March-April, 

due to inclement weather and delays in funding approval. This was unfortunate, as two full years 

of surveys covering all months would have been very beneficial in documenting the patterns we 

observed, particularly since weather and sea ice conditions varied considerably among the two 

years. 

As noted earlier, we anticipated conducting a consistent series of aerial marine wildlife surveys 

during an Alaskan winter to be challenging, and precision of results to be less than desired. The 

difficulties we encountered resulted in an unmeasured and variable bias, presumably low, for 

monthly estimates based on discrepancies among data from two crews on comparable surveys 

(e.g., each crew occasionally recorded flocks that were apparently not recorded by the other 

crew, Tables 2, 3). However, given these limitations, our data, in conjunction with other survey 

and telemetry data reviewed in this report, provide the basis for a preliminary conceptual model 

of seasonal distribution that should enable industry and regulatory agencies to make management 

decisions that provide a large measure of protection for Steller's eiders wintering in CI. 

The conceptual model of arrival and dispersal for Steller’s eiders in Cook Inlet during winter 

we propose is described as follows: 

Following nesting in high Arctic Russia and Alaska, most Steller's eiders migrate to southwest 

Alaska, including lower CI. In Nelson Lagoon on the Alaska Peninsula, arrival of non-breeding 

subadults begins in mid-July and peaks in early August (Petersen 1980). In 1980 Steller's eiders 
33

arrived in Izembek Lagoon beginning 18-24 August (Laubhan and Metzner 1999). Birds 

molting in Izembek Lagoon are mostly adults, and they continue to arrive through the fall (Jones 

1965) with peak numbers occurring in mid-September (Laubhan and Metzner 1999). 

Independent observations of approximately 2,000 molting eiders in the Douglas River shoals 

area in late August and September (see p. 16 above) suggest a similar timing in CI. Additional 

surveys and/or satellite telemetry data are needed to further evaluate the timing and extent of 

eider presence in CI from mid-summer through the early winter period. 

Steller’s eider numbers continue to build in CI habitats through early winter, peak in January 

and February, then decline as they depart on spring migration to nesting grounds from early 

March through mid to late April. The chronology described likely varies somewhat among and 

within years depending on weather and sea ice dynamics, and perhaps also as a function of 

physiological condition of the birds. 

The highest wintering population estimates from this study were 1,247 and 4,284 eiders in 

eastern and western CI, respectively, in January 2005. We believe most of the estimates made 

during this study are biased slightly low because data were uncorrected, i.e., for eiders not 

detected during surveys. A higher estimate (2,370) for eastern CI was recorded during an aerial 

survey in early March, 2001 (W. Larned, U.S. Fish and Wildlife Service, unpubl. data). Nearly 

all of the birds seen on the latter survey were in one cluster of flocks near Ninilchik, and the 

survey area did not include Kachemak Bay, where more eiders were likely present. 

Areas frequented by substantial numbers of Steller's eiders in winter during these surveys 

(with maximum estimates recorded) included, in eastern CI, the nearshore area from Anchor 

Point to 25km north of Ninilchik (1,141 in January 2005, Table 3, Fig. 16, and 2,370 in March 

2001, W. Larned, U.S. Fish and Wildlife Service, unpubl. data), and the nearshore area from 

Homer Spit to Anchor Point (338 in February 2004, Table 2, Fig. 12). Important areas included 

in western CI, were southern Kamishak Bay from Douglas River to Bruin Bay, including the 

shoreline between Bruin Bay and Ursus Cove, and a shoal 12km southeast of Bruin Bay (3,921 

in January 2005, Table 3, Fig. 16), and the mouth of Iniskin Bay (363 in January 2005, Table 3, 

Fig. 16). 

During the winter, limited satellite telemetry data (D. Rosenberg, Alaska Department of Fish 

and Game, unpubl. data) indicated that birds in at least one location (southern Kamishak Bay) 

may have moved to Kodiak and other portions of the species winter range outside the study area, 

apparently in response to displacement from favored feeding areas by sea ice and possibly 

inclement weather. 

RECOMMENDATIONS 

The model we propose based on results of this study and other local and more general survey 

and research data, is incomplete and will hopefully be refined and validated, and any errors 

corrected, in the near future. Major questions inadequately addressed during this study that 

should be addressed in the future include: 

1. What is the sequence of arrival and departure of eiders in the populous and consistently 

used habitats? 

2. In the interest of safety and to maximize detection of birds, we surveyed only during mild 

weather conditions. In addition to those habitats occupied extensively by Steller's eiders during 
34

this study, are there other more sheltered sites, perhaps less productive but nonetheless important 

as alternates, used primarily during inclement weather? 

3. During the winter, is there any exchange of individuals between eastern and western CI, or 

other areas? If so, in the event of a major natural or anthropogenic disaster or disturbance could 

we expect eiders to readily move to these sites on their own, or after being intentionally hazed 

from an oil spill or other hazard? 

4. What are the breeding, molting and staging area affinities of eiders that winter in CI? 

Probably the best initial approach to answering these questions is through the use of satellite 

telemetry, supplemented with additional aerial surveys, to determine numbers of birds occupying 

sites initially identified by telemetry. 

Future winter aerial surveys should be redesigned to delete intensive coverage of that portion 

of the west shoreline north of Iniskin Bay that is apparently underutilized by Steller’s eiders (this 

survey, see also Bennett 1996). A single shoreline transect would suffice to document birds that 

unexpectedly appeared in this area. The resulting substantial savings of flight time could then be 

applied to reducing transect spacing, which should improve detection of birds and thus enhance 

precision of estimates. Another recommendation is to reduce the small-flock sampling strip 

width to 200m or possibly less, to better match the effective detection distance under the worst 

detection conditions likely to be encountered during winter surveys. Additionally or 

alternatively, further analysis of data from this study and habitat covariate data from other 

sources might provide the basis for a more efficient model-based stratified survey design. 

Finally, we recommend more rigorous testing of observer proficiency against negotiated 

standards in future surveys, and providing remedial training or substitute observers when 

deficiencies are identified. 

ACKNOWLEDGEMENTS 

I would like to thank the Minerals Management Service for providing most of the financial 

support. Charles Monnett and Jeffrey Gleason, Minerals Management Service provided valuable 

technical guidance and encouragement during the study. U.S. Fish and Wildlife Service 

employees listed under "project organization" who acted as aerial observers and pilots devoted a 

great deal of time, energy, and patience under often trying circumstances, and maintained their 

standby status through many "weather holds". My thanks also to U.S. Fish and Wildlife Service 

Waterfowl Management Branch project leader Russ Oates, for his support and patience. Finally, 

Dan Rosenberg, Alaska Department of Fish and Game coordinated with me on several 

complementary sea duck projects. Jeffrey Gleason and 2 anonymous reviewers provided 

comments that greatly improved this report. 
35

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