Status and Trends of Sea Otter Populations in 

Southeast Alaska, 1969–2003

Scientific Investigations Report 2009-5045

U.S. Department of the Interior

U.S. Geological Survey

Jointly supported by the U.S. Geological Survey, U.S. Fish and Wildlife Service, and 

Glacier Bay National Park and Preserve
Cover: Sea otters resting in Barry Arm, Prince William Sound, Alaska, typical of groups 

observed during aerial surveys in Southeast Alaska. (Photograph courtesy of Jennifer 

Coffey, private citizen, July 29, 2008.)
Status and Trends of Sea Otter Populations in 

Southeast Alaska, 1969–2003

By George G. Esslinger and James L. Bodkin

Jointly supported by the U.S. Geological Survey, U.S. Fish and Wildlife Service, and 

Glacier Bay National Park and Preserve

Scientific Investigations Report 2009–5045

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation:

Esslinger, G.G., and Bodkin, J.L., 2009, Status and trends of sea otter populations in Southeast Alaska,1969–2003: 

U.S. Geological Survey Scientific Investigations Report 2009–5045, 18 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Study Methods ...............................................................................................................................................3

Glacier Bay.............................................................................................................................................3

Northern and Southern Southeast Alaska .......................................................................................3

Aerial Survey Methods ........................................................................................................................5

Data Analysis.........................................................................................................................................5

Aerial Survey Results....................................................................................................................................5

Glacier Bay.............................................................................................................................................5

Northern Southeast Alaska ................................................................................................................5

Southern Southeast Alaska ................................................................................................................8

Southeast Alaska..................................................................................................................................8

Status and Trends in Sea Otter Populations............................................................................................12

Distribution...........................................................................................................................................12

Northern Population..................................................................................................................12

Maurelle Population..................................................................................................................12

Barrier Population .....................................................................................................................12

Southeast Alaska Distribution .................................................................................................12

Abundance...........................................................................................................................................12

Glacier Bay and Northern Southeast Alaska........................................................................12

Southern Southeast Alaska .....................................................................................................14

Southeast Alaska ......................................................................................................................14

Potential Factors Limiting Population Growth ......................................................................15

Conclusion.....................................................................................................................................................16

Acknowledgments.......................................................................................................................................16

References Cited..........................................................................................................................................16

Figures

Figure 1. Map showing sea otter translocation sites (1965–69) and areas surveyed for

sea otters, Southeast Alaska (SEAK)...................................................... 2

Figure 2. Map showing one of five replicate aerial surveys used to estimate sea otter

abundance in Glacier Bay, Alaska, May 2002 .......................................... 4

Figure 3. Map showing aerial transects used for sea otter survey in northern

Southeast Alaska, July 2002 ............................................................... 6

Figure 4. Map showing aerial transects used for sea otter survey in southern

Southeast Alaska, August 2003 ............................................................ 7

Figure 5. Map showing cumulative distributions of sea otter groups from five replicate

aerial surveys in Glacier Bay, Alaska, May 2002 ....................................... 9

Figure 6. Map showing sea otter group locations from aerial survey in northern

Southeast Alaska, July 2002 ............................................................... 10

Figure 7. Map showing sea otter group locations from aerial survey in southern

Southeast Alaska, August 2003 ............................................................ 11
iv

Tables

Table 1. Numbers of sea otters translocated to Southeast Alaska, 1965–1969 ............... 3

Table 2. Southeast Alaska sea otter population estimates derived from aerial surveys

conducted in 2002 and 2003 ............................................................... 8

Conversion Factors and Datums

Conversion Factors

Multiply By To obtain

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

square kilometer (km2) 0.3861 square mile (mi2)

 Datum

 Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Figure 8. Map showing sea otter distribution from aerial surveys in Southeast Alaska

(SE AK), summers 2002, 2003 ............................................................... 13

Figure 9. Graph showing trends in abundance of sea otters in Glacier Bay National

Park and Preserve, Alaska, 1995–2002 ................................................... 14

Figure 10. Graph showing sea otter population trends in northern and southern

Southeast Alaska (SE AK), 1987–2003, inclusive of Glacier Bay and all other

occupied habitats ........................................................................... 14

Figure 11. Graph showing trends in sea otter populations in Southeast Alaska between

1969 and 2003................................................................................. 15

Figures—Continued
Abstract

Aerial surveys of all known sea otter (Enhydra lutris) 

habitat in Southeast Alaska (SE AK) in 2002-2003 indicated 

a population size of 8,949 otters [Standard Error (SE) = 899] 

at an average density of 0.92 otters per square kilometer. 

These findings on sea otter distribution and abundance were 

compared to results from several previous surveys. Sea 

otters have expanded their range beyond the outer coast of 

SE AK and currently occupy inside waters such as Glacier 

Bay and Sumner Strait. This range expansion, along with 

archeological evidence, supports the hypothesis that sea 

otters are capable of colonizing inside waters in SE AK. 

Inside Glacier Bay National Park and Preserve, in northern 

SE AK, sea otter abundance has increased from 5 in 1995 to 

1,266 (SE = 196) in 2002, more than doubling on an average 

annual basis, indicating immigration and reproduction as 

factors contributing to population growth. In the remainder of 

northern SE AK, the estimated abundance has declined from 

2,295 in 1987 to 1,838 (SE = 307) in 2002. In southern SE 

AK, the abundance of sea otters increased from 2,167 in 1988 

to 5,845 (SE = 821) in 2003. Overall, population growth rates 

for sea otters in SE AK between 1987 and 2003 are much 

lower than rates from previous studies and were unexpected 

given the amount of unoccupied habitat available in SE AK. 

Divergent population trajectories were evident between the 

southern (6.6 percent per year) and northern areas of SE AK 

(2.0 percent per year). These differences suggest variation 

in reproductive or survival rates between the areas. Harvest 

levels between 1989 and 2003 may have had a measurable 

effect on sea otter populations in SE AK. Available data on 

age and sex specific fecundity and survival rates could be used 

to develop age- and sex-structured population matrix models 

to help guide management and conservation of sea otter 

populations.

Introduction 

Prior to the mid-1700s, sea otters occupied nearshore 

coastal waters in the Pacific Ocean from central Baja 

California to northern Japan, including both sides of 

the Alaska Peninsula and the Aleutian Archipelago 

(Kenyon, 1969). Commercial fur harvests between 1741 and 

1911 reduced sea otters to 13 small remnant colonies, mostly 

in the Aleutians, with the species extirpated between Prince 

William Sound, Alaska, and Central California (Riedman and 

Estes, 1990).

Between 1965 and 1969, the Alaska Department of Fish 

and Game translocated 403 sea otters from Prince William 

Sound and Amchitka Island to 6 areas along the outer coast 

of Southeast Alaska (SE AK) (fig. 1; table 1). Consequently, 

sea otters in SE AK contain a genetically diverse mixture of 

mitochondrial DNA from their source populations (Bodkin 

and others, 1999) and are considered to be a separate stock 

from southcentral and southwestern Alaska stocks based on 

genotypic differences and geographic distribution (Gorbics 

and Bodkin, 2001).

Since the translocations, sea otters have been surveyed 

in SE AK using various types of boats and aircraft (Schneider, 

1975, Jameson and others, 1982; Johnson and others, 1983; 

Simon-Jackson and Hodges, 1986; Pitcher, 1989; Agler 

and others, 1995; and this study). In conjunction with the 

results of his 1987 and 1988 boat-based surveys, Pitcher 

(1989) provided a complete synthesis of SE AK sea otter 

surveys conducted through 1988. Prior to 1994, sea otter 

surveys were essentially censuses or minimum counts made 

from small vessels or from shore, and did not incorporate 

detection probabilities (Udevitz and others, 1995) or provide 

estimates of precision. In 1994, the U.S. Fish and Wildlife 

Service (USFWS) conducted boat-based marine bird and 

sea otter surveys throughout SE AK using strip-transect 

sampling methods and provided the first estimates of precision 

associated with a population survey of sea otters in the region 

(Agler and others, 1995). Beginning in 1999, the National 

Park Service (NPS) funded annual sea otter aerial surveys in 

Glacier Bay National Park and Preserve (Bodkin and others, 

2007). Sea otter counts and locations also were recorded by 

USFWS (J. Hodges, U.S. Fish and Wildlife Service, written 

commun., 2002) during aerial waterfowl surveys in SE AK 

from 1997 to 2002.

The cumulative results of surveys of sea otters in SE AK 

and other translocated populations show that, due to mortality 

and emigration, translocated populations grow slowly during 

the first decade post translocation (Schneider, 1975; Bodkin 

and others, 1999), but increase over time (Pitcher, 1989). 

Status and Trends of Sea Otter Populations in 

Southeast Alaska, 1969–2003

By George G. Esslinger and James L. Bodkin
2 Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003

aktac08-5132_Fig 01

!C

!C

!C

!C

!C

!C

Khaz Bay

Cape Spencer

Biorka Island

Yakobi Island

Barrier Islands

Maurelle Islands

Survey period

Glacier Bay, May 2002

Northern SEAK, Jul 2002

Southern SEAK, Aug 2003

!C Translocation site

ALASKA

BRITISH COLUMBIA

ALASKA

Location

Juneau

Petersburg

Ketchikan

Sitka

Craig

Bartlett

Cove

EXPLANATION

0

0

25

25

50

50

75

75

100 MILES

100 KILOMETERS

Figure 1. Sea otter translocation sites (1965–69) and areas surveyed for sea otters, Southeast Alaska (SEAK).
Study Methods 3

Population growth rate estimates for sea otters in SE AK 

between 1975 and 1988 ranged from 16 to 23 percent (Pitcher, 

1989) and were among the highest reported for expanding sea 

otter populations (Estes, 1990). During this period, sea otters 

expanded their range considerably and reoccupied large areas, 

primarily along the outer coast of SE AK (Pitcher, 1989).

The well documented overharvesting of sea otter 

populations demonstrates the need to monitor population 

status and trends for conservation and management (Kenyon, 

1969). Because otters are harvested in much of their range in 

Alaska, conservation and management needs dictate careful 

evaluation of population status, trends, and harvest. Largescale sea otter mortality events such as the Exxon Valdez oil 

spill (Estes, 1991) and the Aleutian sea otter decline (Doroff 

and others, 2003) underscore the importance of having current 

distribution and abundance data on sea otter populations. 

Recently, a series of aerial surveys have been conducted to 

assess the abundance of sea otters throughout their range in 

Alaska. The survey areas included Prince William Sound, 

Kenai/Cook Inlet, the Aleutian archipelago, Kodiak, and the 

Alaska Peninsula (Bodkin and others, 2002; J. Bodkin, U.S. 

Geological Survey, written commun., 2002; Doroff and others, 

2003; U.S. Fish and Wildlife Service, unpub. data, 2004; and 

Burn and Doroff, 2005). Lacking recent population data for 

sea otters in SE AK, the U.S. Geological Survey (USGS) 

designed and conducted the first comprehensive aerial survey 

of sea otters in SE AK.

Methodology designed specifically to correct for 

detection (Bodkin and Udevitz, 1999) was used to conduct an 

aerial survey of sea otters in SE AK with the goal of obtaining 

accurate and precise population estimates. In this report, we 

present the results of three aerial surveys encompassing all 

habitats known to be occupied by sea otters in SE AK during 

the summers of 2002 and 2003 (fig. 1). We then compare the 

results of our surveys with prior boat-based censuses for all of 

SE AK to evaluate trends in sea otter abundance since the end 

of the translocations in 1969.

Study Methods

We used a strip transect aerial survey method that 

incorporated intensive searches to determine an observer and 

survey specific correction factor for diving sea otters and 

sightability bias (Bodkin and Udevitz, 1999). The survey 

areas were stratified based on depth and distance from shore, 

and transect spacing was varied within strata to match the 

sampling effort with expected sea otter densities (Bodkin and 

Udevitz, 1999; Bodkin and others, 2004). Because of the large 

geographic area involved, separate surveys were designed for 

three regions: (1) Glacier Bay, (2) northern SE AK, and (3) 

southern SE AK (fig. 1).

Glacier Bay

The survey in Glacier Bay was designed to ensure 

consistency with previous surveys conducted by USGS 

(Bodkin and others, 2007). The 2002 survey comprised five 

replicate aerial surveys with randomly selected combinations 

of high- and low-density stratum transects that varied among 

replicates (fig. 2). Transects in the high density stratum 

were spaced at what was considered maximum intensity 

(1,200 m) to increase precision of the population estimate 

while minimizing the probability of double-counting moving 

animals. For each replicate survey, approximately 67 percent 

of the sampling effort was allocated to the high-density 

stratum and 33 percent to the low-density stratum.

Northern and Southern Southeast Alaska

Designing an aerial survey for estimating sea otter 

abundance in SE AK required some understanding of their 

distribution. Approximate sea otter distribution in SE AK 

was determined by reviewing results of previous surveys 

(Simon-Jackson and Hodges, 1986; Pitcher, 1989; Agler and 

others, 1995; Garza and Lorrigan, 1999) and by consulting 

with local biologists, researchers, sea otter hunters, and nature 

tour operators. The selected survey area boundaries included 

all areas where groups of sea otters were known to occur or 

could easily emigrate. Areas where sea otter sightings were 

rare or where distances of sightings from known occupied 

habitat were great (for example, Juneau and Skagway) were 

not included. Excluding Glacier Bay, the survey area included 

12,994 km of shoreline (fig. 1).

The SE AK surveys were modeled on the basis of earlier 

aerial designs used for surveying sea otters in Prince William 

Sound, Glacier Bay, Cook Inlet, Kenai Peninsula, and Kodiak 

Island waters (Bodkin and Udevitz, 1999; Bodkin and others, 

2002; J. Bodkin, U.S. Geological Survey, written commun., 2002). 

Table 1. Numbers of sea otters translocated to Southeast 

Alaska, 1965–1969.

[Data from Burris and McKnight, 1973]

Release site

Year

1965 1966 1967 1968 1969 Total

Cape Spencer 0 0 0 25 0 25

Yakobi Island 0 0 0 30 0 30

Khaz Bay 23 20 0 93 58 194

Biorka Island 0 0 0 48 0 48

Maurelle Islands 0 0 0 51 0 51

Barrier Islands 0 0 0 55 0 55

Total 23 20 0 302 58 403
4 Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003

aktac08-5132_Fig 02

Gustavus

Icy Strait

EXPLANATION

High density stratum

Low density stratum

Not surveyed

Survey area boundary

High density transect

Low density transect

Dundas

Bay

Glacier

Bay

0

0 2 4 8 KILOMETERS 

2 4 8 MILES

Figure 2. One of five replicate aerial surveys used to estimate sea otter abundance in Glacier Bay, Alaska, May 

2002.
Aerial Survey Results 5

These surveys were developed with the aid of geographic 

information system software (ArcView and ArcInfo, ESRI, 

Inc. Redlands, Calif.) and required environmental data such 

as shoreline and water depth in digital format. Depth is a 

key variable in the creation of survey strata and, at the time 

of survey design, large sections of SE AK lacked digital 

bathymetric coverage. These digital data gaps made it 

necessary to digitize the 20- and 50-fathom depth contours 

from georeferenced digital images of National Oceanic 

and Atmospheric Administration (NOAA) nautical charts 

(Maptech, Amesbury, Mass.) using ArcView. Although digital 

shoreline data were available from several sources, those 

data matched the bathymetry poorly. Consequently, we also 

digitized the high-tide line from digital NOAA nautical charts. 

We used existing digital bathymetric data for Glacier Bay and 

part of Sumner Strait.

The northern and southern SE AK area transects were 

designed to be flown without replication due to logistical 

constraints. We allocated our sampling effort based on earlier 

testing (Bodkin and Udevitz, 1999), focusing 84 percent of 

our effort in the high density stratum and 16 percent in the 

low density stratum (figs. 3 and 4). Transect spacing varied 

by survey area according to expected sea otter densities and 

logistical constraints (table 2).

Aerial Survey Methods

For all three surveys, we used a Bellanca Scout, a twopassenger tandem, float-equipped, single-engine airplane, 

which allowed equal visibility out both sides of the aircraft. 

Survey conditions were generally limited to periods with wind 

velocities less than 18–28 km/h and sea conditions without 

whitecaps. Along each 400-m wide transect strip we recorded 

the number of individual sea otters observed and mapped their 

location. Intensive search units (ISUs) were used to estimate 

the proportion of animals that remained undetected during 

the strip counts. Detailed survey methodology is available in 

Bodkin and Udevitz (1999).

Data Analysis

Detection adjusted strip counts were used to calculate 

population estimates for each stratum sampled, and those 

were combined to provide population size estimates and 

associated sample variance estimates. Independent rates of 

population change over time were estimated for each of the 

three regions, and for SE AK as a whole, from the exponential 

function, Nt = N0ert, where Nt = population estimate in year 

t, N0 = population estimate in some earlier year 0, and r = 

annual rate of increase (Estes, 1990). A linear regression 

was fitted to log-transformed values using PROC GLM in 

SAS 9.1 (SAS Institute, Cary, N.C.) for the relatively limited 

time span (1999–2002) over which aerial surveys were 

conducted in Glacier Bay. A non-linear regression was fitted 

to the exponential model with the least-squares (Marquardt) 

method using PROC NLIN in SAS for the more extended 

period (1969–94) of population growth recorded for SE AK 

as a whole. Because ISUs also afford the aerial observer 

enough time to differentiate pups from independent (nonpup) otters, the pup:independent ratio was used as an index of 

reproduction for each area.

Aerial Survey Results

The surveys were conducted over a 2-year period because 

of the size and shoreline complexity of the area involved. The 

surveys for Glacier Bay (fig. 2) and for northern SE AK, from 

Icy Point to Cape Ommaney, were conducted in 2002 (fig. 3). 

The survey for southern SE AK, from Kake to Cape Chacon, 

was conducted in 2003 (fig. 4). Because about 80 km of 

unoccupied habitat separates the northern and southern SE AK 

survey regions, little, if any, movement of individuals between 

years was expected to influence the survey results, which are 

summarized below.

Glacier Bay

The survey of Glacier Bay was conducted between May 6 

and 18, 2002. Replicate surveys took between 6 and 8 hours 

to fly and ranged from 297 to 343 km in total transect length. 

Five replicate surveys yielded a population size estimate of 

1,266 sea otters (SE = 196; table 2; fig. 5). The density of sea 

otters in the surveyed portion of Glacier Bay was 2.3/km2 and 

the pup:independent ratio was 0.14.

Northern Southeast Alaska 

The survey of northern SE AK was conducted between 

June 30 and July 13, 2002. This survey was based at Bartlett 

Cove in Glacier Bay for transects north of Khaz Bay and 

at Sitka to access areas south of Khaz Bay. It took about 56 

hours of flight time to survey 2,148 km of transect. Weather 

conditions greatly affected how many hours per day we flew 

on 11 survey days (range = 0.6 to 8 hrs/d) and precluded 

surveying on 3 days. Upon completion of the northern SE AK 

survey, survey area boundaries were adjusted to reflect sea 

otter distribution during the survey and accurately estimate sea 

otter densities (fig. 6). The 2002 population size estimate for 

northern SE AK was 1,838 sea otters (SE = 307, table 2). The 

density of sea otters in northern SE AK was 0.48/km2 and the 

pup:independent ratio was 0.22.
6 Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003

aktac08-5132_Fig 04

Hoonah

EXPLANATION

High density stratum

Low density stratum

Survey area boundary

High density transect

Low density transect

Sitka

Juneau

Pelican

Angoon

Chichagof

Island

Baranof

Island

Admiralty

Island

Gustavus

Chatham Strait

Icy Strait

Cross Sound

Kuiu

Island

Cape Ommaney

Icy Point

0

0

20 40 60

20 40 60

80 MILES

80 KILOMETERS

Figure 3. Aerial transects used for sea otter survey in northern Southeast Alaska, July 2002.
Aerial Survey Results 7

aktac08-5132_Fig 04

EXPLANATION

High density stratum

Low density stratum

Survey area boundary

High density transect

Low density transect

Prince of

Wales Island

Craig

Kake

Hydaburg

Petersburg

Wrangell

Ketchikan

Kuiu

Island

Baranof

Is

Dall

Is

DIXON ENTRANCE

Chatham Strait

Strait

S

u

mner

Cape Chacon

Kasaan

0

0

20 40 60

20 40 60

80 MILES

80 KILOMETERS

Figure 4. Aerial transects used for sea otter survey in southern Southeast Alaska, August 2003.
8 Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003

Table 2. Southeast Alaska sea otter population estimates derived from aerial surveys conducted in 2002 and 2003. 

[Stratum refers to stratification of sea otter habitat into areas of high and low sampling effort. The Glacier Bay population estimate was derived from five 

replicate surveys, whereas, northern and southern Southeast Alaska (SE AK) population estimates were derived from single surveys. Small groups (<30 sea 

otters) were adjusted with a correction factor, whereas, large groups were unadjusted. Abbreviations: m, meter; km, kilometer; km2, square kilometer; <, less 

than]

Aerial 

survey 

year

Region Stratum Group 

size

Transect Area 

sampled 

(km2

)

Stratum 

area 

(km2)

Sea 

otter 

count

Correction 

factor

Corrected 

population 

size

Standard 

error

Proportional 

standard 

error

Spacing 

(m)

Sampled 

(km)

2002 Glacier 

Bay

High – replicate 1 Small 1,200 226 90 272 98 1.60 472 – –

High – replicate 2 Small 1,200 228 91 272 73 1.75 381 – –

High – replicate 3 Small 1,200 229 92 272 72 1.38 294 – –

High – replicate 4 Small 1,200 202 81 272 84 1.44 408 – –

High – replicate 5 Small 1,200 214 86 272 58 1.36 250 – –

Low – replicate 1 Small 2,400 111 44 277 43 1.60 432 – –

Low – replicate 2 Small 2,400 111 44 277 21 1.75 230 – –

Low – replicate 3 Small 2,400 114 45 277 23 1.38 193 – –

Low – replicate 4 Small 2,400 96 38 277 22 1.44 230 – –

Low – replicate 5 Small 2,400 113 45 277 20 1.36 166 – –

High – replicate 1 Large 1,200 226 90 272 158 – 476 – –

High – replicate 2 Large 1,200 228 91 272 298 – 890 – –

High – replicate 3 Large 1,200 229 92 272 175 – 521 – –

High – replicate 4 Large 1,200 202 81 272 188 – 635 – –

High – replicate 5 Large 1,200 214 86 272 63 – 200 – –

Low – replicate 1 Large 2,400 111 44 277 28 – 176 – –

Low – replicate 2 Large 2,400 111 44 277 21 – 132 – –

Low – replicate 3 Large 2,400 114 45 277 0 – 0 – –

Low – replicate 4 Large 2,400 96 38 277 34 – 247 – –

Low – replicate 5 Large 2,400 113 45 277 0 – 0 – –

1,266 196 0.15

2002 Northern 

SEAK1

High Small 1,500 1,407 563 2,089 297 1.16 1,282 182 0.14

Low Small 5,000 325 130 1,732 4 1.16 62 36 0.58

High Large 1,500 1,407 563 2,089 133 – 494 245 0.50

1,838 307 0.17

2003 Southern 

SEAK1

High Small 2,000 1,729 692 3,418 473 1.69 3,958 590 0.15

Low Small 5,000 305 122 1,902 8 1.69 211 97 0.46

High Large 2,000 1,729 692 3,418 339 – 1,675 564 0.34

5,845 821 0.14

Southeast 

Alaska 8,949 899 0.10

1

Numbers for this region are derived from high and low density strata that were reduced post-survey to reflect actual sea otter distribution during the survey.

Southern Southeast Alaska

The southern SE AK survey, conducted between July 

31 and August 12, 2003, included 2,640 km of transect in 77 

hours of flight time. Although predominately sunny weather 

permitted surveying on 12 of 13 days, windy conditions 

greatly limited survey time on most days (range = 1.5 to 

8 hrs/d). The survey area was reduced post-survey to closely 

match actual sea otter distribution and ensure accurate 

otter density estimation (fig. 7). The 2003 southern SE AK 

population was estimated to be 5,845 sea otters (SE = 821, 

table 2). The density of sea otters in southern SE AK was 

1.01/km2 and the pup:independent ratio was 0.26.

Southeast Alaska

Based on these three surveys, the estimated population of 

otters for the entire region in 2002–03 was 8,949 (SE = 899), 

at a density of 0.92 individuals/km2.
Aerial Survey Results 9

aktac08-5132_Fig 05

Gustavus

Icy Strait

EXPLANATION

High density stratum

Low density stratum

Not surveyed

Survey area boundary

Sea otter groups

1 - 50

51 - 100

101 - 155

Dundas

Bay

Glacier

Bay

0

0 2 4 8 KILOMETERS 

2 4 8 MILES

Figure 5. Cumulative distributions of sea otter groups from five replicate aerial surveys in Glacier Bay, Alaska, 

May 2002. (See figure 2.)
10 Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003

aktac08-5132_Fig 06

Hoonah

EXPLANATION

High density stratum

Low density stratum

Reduced survey boundary

Survey area boundary

Sea otter groups

1 - 20

21 - 40

41 - 67

Sitka

Juneau

Pelican

Angoon

Chichagof

Island

Baranof

Island

Admiralty

Island

Gustavus

Chatham Strait

Icy Strait

Cross Sound

Kuiu

Island

Whale Bay

Necker

Iss

Cape Ommaney

Icy Point

Khaz

Bay

0

0

20 40 60

20 40 60

80 MILES

80 KILOMETERS

Figure 6. Sea otter group locations from aerial survey in northern Southeast Alaska, July 2002. Also shown are 

strata that have been reduced from the area surveyed to reflect sea otter distribution and estimate abundance (see 

figure 3).
Aerial Survey Results 11

aktac08-5132_Fig 07

EXPLANATION

High density stratum

Low density stratum

Reduced survey boundary

Survey area boundary

Sea otter groups

1 - 20

21 - 35

36 - 51

Prince of

Wales Island

Craig

Kake

Hydaburg

Petersburg

Wrangell

Ketchikan

Kuiu

Island

Baranof

Is

Dall

Is

DIXON ENTRANCE

Chatham Strait

Strait

S

umner

Maurelle

Islands

Sea Otter

Sound

Cape

Felix

Cape

Muzon

Cape Chacon

Kasaan

0

0

20 40 60

20 40 60

80 MILES

80 KILOMETERS

Figure 7. Sea otter group locations from aerial survey in southern Southeast Alaska, August 2003. Also shown are 

strata that have been reduced from the area surveyed to reflect sea otter distribution and estimate abundance (see 

figure 4).
12 Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003

Status and Trends in Sea Otter 

Populations

Sea otter populations can be described on the basis of two 

characteristics: distribution, or their spatial occurrence and 

extent of their range; and abundance, the actual numbers and 

trends in numbers of otters present.

Distribution

The results of the 2002–03 aerial surveys indicate that 

sea otters in SE Alaska were not evenly distributed across 

the region, but generally occurred in three spatially discrete 

sub-populations: (1) the northern population, (2) the Maurelle 

population, and (3) the Barrier population (fig. 8). The scarcity 

of otters in areas between these three concentrations was 

likely a historical consequence of commercial fur harvests and 

translocations, but also probably reflected limited dispersal 

between these areas.

Northern Population

The northern sea otter population extended along the 

outer coast from Icy Point in the north to Whale Bay in 

the south (fig. 8). Increases in abundance and changes in 

distribution had occurred since Pitcher’s 1987 survey (Pitcher, 

1989), with population expansion north into Glacier Bay and 

south to Whale Bay. 

Maurelle Population

An 80 km gap between Whale Bay and Kuiu Island 

separated the northern population from the Maurelle 

population (fig. 8). Since Pitcher’s 1988 survey (Pitcher, 

1989), the Maurelle population had expanded northward, up 

the western side of Kuiu Island, further into Sumner Strait, 

and Sea Otter Sound. On the southern end of this population, 

sea otters expanded from the Maurelle Islands southward to 

Cape Felix (fig. 7).

Barrier Population

The Maurelle population and the Barrier population 

were separated by a 75 km gap between Cape Felix and 

Cape Muzon (fig. 7). In contrast to the other two SE AK 

populations, the Barrier population expanded its distribution 

only slightly since 1988 (Pitcher, 1989).

Southeast Alaska Distribution

The historical range of sea otters in SE AK included the 

outer coast, but the extent to which otters occupied inside 

waters is not well known. Kenyon (1969, p. 183) states, 

“There is no record that sea otters occurred in the inland 

passages of Southeastern Alaska . . .” and Kvitek and others 

(1991) suggested that paralytic shellfish poisoning toxins 

sequestered by butter clams (Saxidomus giganteus), an 

important sea otter prey, may limit sea otter distribution to 

the exposed outer coast of SE AK. Pitcher (1989), however, 

pointed out that sea otters occur in the inside waters of Prince 

William Sound, an area with habitat qualities similar to those 

of the inside waters of SE AK. Sea otter bones excavated from 

aboriginal Tlingit middens at Daxatkanada, Young Bay, and 

Port Houghton (fig. 8) indicate sea otters were a human food 

source that may have been obtained locally from inside waters 

(de Laguna, 1960; Swanson and Davis, 1982; Davis, 1985).

Sea otters have become well established in some inside 

waters such as Glacier Bay and Sumner Strait (fig. 8). This 

inside range expansion is a significant development because 

it demonstrates that sea otters are capable of colonizing inside 

waters in SE AK and are likely to extend their distribution into 

other inside waters in the future.

Abundance

Comparisons of the results of our 2002–03 surveys of 

otter populations in Southeast Alaska with those of earlier 

surveys show that population growth trends differ across the 

three survey areas. These differences can be explained, at least 

in part, by several factors that potentially control population 

growth. 

Glacier Bay and Northern Southeast Alaska

The lower (southern) part of Glacier Bay currently 

supports some of the highest sea otter densities ever recorded 

in SE AK. Studies in this region have documented the 

dramatic increase from 5 otters in 1995 to 1,266 in 2002 

(fig. 9; J. Bodkin, U.S. Geological Survey, written commun., 

2003). Although Glacier Bay sea otters are not completely 

isolated from nearby populations in Icy Strait and Cross 

Sound (fig. 6), the population trajectories in Glacier Bay 

differ dramatically from trajectories elsewhere in SE AK and 

warrant independent evaluation. The annual rate of increase 

for sea otters within Glacier Bay has been 44 percent per year 

since systematic aerial surveys were implemented in 1999. 

Because this rate of increase exceeds the reproductive capacity 

of the species (Estes, 1990), it is reasonable to conclude 

that immigration is contributing to the high growth trend in 

Glacier Bay. In contrast to the rapid increase in Glacier Bay 

alone, the combined 2002 population size estimate for Glacier 

Bay and northern SE AK (3,104) is only 35 percent greater 

than Pitcher’s 1987 count (2,295; Pitcher, 1989), indicating 

relatively slow population growth overall (2.0 percent 

per year) for this period (fig. 10). This is in contrast to the 

previously documented growth rate for SE AK of 18 percent 

per year between 1975 and 1987 (Estes, 1990).
Status and Trends in Sea Otter Populations 13

aktac08-5132_Fig 08

"/

"/

"/

Young Bay

Daxatkanada

Port Houghton

EXPLANATION

Northern population

Maurelle population

Barrier population

Sea otter groups

1 - 25

26 - 50

51 - 155

"/ Midden site

!C Translocation site

ALASKA

BRITISH COLUMBIA

ALASKA

Location

Hoonah

Sound

Kuiu

Is

Juneau

Petersburg

Ketchikan

Sitka

Craig

Idaho

Inlet

Port

Althorp

Whale Bay

Glacier

Bay

Sumner Strait

Icy

Point

0

0

25

25

50

50

75

75

100 MILES

100 KILOMETERS

Figure 8. Sea otter distribution from aerial surveys in Southeast Alaska (SE AK), summers 2002, 2003. Maurelle 

and Barrier populations were treated as one population (southern SE AK) for trend analysis. Midden sites 

containing sea otter bones indicate potential historical distribution.
14 Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003

Southern Southeast Alaska

Although the Maurelle and Barrier populations were 

spatially distinct, the data were combined for the analysis 

of sea otter population growth in southern SE AK because 

the Barrier Island population was too small to provide an 

independent estimate of abundance given the sampling design 

used. The abundance of sea otters within the southern SE AK 

survey area had increased at an annual rate of 6.6 percent 

since Pitcher’s 1988 count of 2,167 (Pitcher, 1989) (fig. 10). 

Although this rate is more than 3 times greater than the rate 

observed in northern SE AK, it is less than one-half of the 

14 percent annual growth observed between 1969 and 1994 

(fig. 11).

Southeast Alaska 

In 1994, Agler and others (1995) conducted a boat-based 

systematic survey of all marine waters in SE AK to estimate 

populations of marine birds and mammals. Their survey 

differed from Pitcher’s (1989) surveys in that Agler and others 

counted all marine birds and mammals and systematically 

sampled a small proportion (less than 3 percent) of all 

habitat, whereas Pitcher counted only sea otters, surveyed 

only occupied sea otter habitat, and attempted to census the 

population (with no correction). Because Agler and others 

included all of SE AK and their sampling effort was low, 

incorporating these data required treating SE AK as a single 

geographic unit. However, because Agler and others sampled 

132_Fig 09

ESTIMATED POPULATION SIZE 

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

Average rate of increase

from 1999 to 2002 = 44%

1995 1996 1997

YEAR

1998 1999 2000 2001 2002

Figure 9. Trends in abundance of sea otters in Glacier 

Bay National Park and Preserve, Alaska, 1995–2002. 

(J. Bodkin, U.S. Geological Survey, written commun., 

2003.) Error bars represent 95 percent confidence 

intervals.

aktac08-5132_Fig 10

ESTIMATED POPULATION SIZE 

YEAR

4,000

3,000

2,000

1,000

5,000

6,000

7,000

8,000

1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

Annual rate of increase

Southern SE AK = 6.6%

Annual rate of increase

Northern SE AK = 2.0%

Figure 10. Sea otter population trends in northern and 

southern Southeast Alaska (SE AK), 1987–2003, inclusive 

of Glacier Bay and all other occupied habitats. Count 

data for 1987 and 1988 are from Pitcher (1989). See figure 

11 for data prior to 1988. Error bars represent 95 percent 

confidence intervals.

such a small proportion of sea otter habitat, and because their 

survey area included more unoccupied than occupied habitat, 

we have relatively less confidence in the accuracy of their 

sea otter population estimate of 8,180 (95 percent confidence 

interval = 1,894–14,466). Nonetheless, no other estimates of 

SE AK sea otter population size were made between 1988 and 

2003.

Another limitation of the 1994 population estimate from 

Agler and others (1995) is that it does not include a correction 

factor to account for undetected otters. Udevitz and others 

(1995) estimated that 30 percent of the sea otters present along 

surveyed transects were not detected during a survey using 

similar methods conducted in Prince William Sound, Alaska. 

Trends in sea otter abundance in SE AK since 1969, including 

the uncorrected estimates from Agler and others (1995), 

suggest a population rapidly increasing at an annual rate of 

14 percent through 1994 (fig. 11). To allow comparability 

with our detection-adjusted 2003 estimate, a correction factor 

was applied to the Agler and others (1995) estimate. The 

correction factor was based (conservatively) on the 70 percent 

detection rate estimated by Udevitz and others (1995); based 

on the corrected estimate, the SE AK population apparently 

declined at an annual rate of -3 percent between 1994 and 

2003 (fig. 11).

In the absence of the 1994 data (Agler and others, 

1995), estimates of population growth rates for sea otters in 

SE AK between 1987 and 2003 (2.0–6.6 percent per year) 

are substantially lower than rates reported in earlier studies, 

which range from 15.7 to 23.3 percent per year (Pitcher, 

1989; Estes, 1990; Bodkin and others, 1999). Further, for any 
Status and Trends in Sea Otter Populations 15

recovering population (Estes, 1990; Bodkin and others, 1999), 

the growth rates reported here are among the lowest, including 

those reported for California (4.4–7.8 percent per year; Estes, 

1990). The inclusion of the 1994 survey results does not 

modify the finding of a reduced rate of change in the SE AK 

sea otter population, but it does influence our understanding 

of the magnitude of the change. When the 1994 uncorrected 

estimate is included in the trend analysis, the emergent pattern 

is one of continued increase in growth rates through the mid 

1990s, followed by a period of apparent stability. Although 

population growth of sea otters would be expected to reach an 

asymptote as population size approaches carrying capacity, the 

reduced growth rate and the decline were unanticipated given 

the amount of unoccupied habitat available in SE AK and the 

continued growth observed in the Glacier Bay population.

Potential Factors Limiting Population Growth

Ultimately, sea otter population growth in SE AK is being 

limited by one or more of the following population processes: 

reproduction, emigration, or mortality. Reproduction, 

estimated by the proportion of pups (to total number of 

individuals) detected in ISUs, ranged from 0.14 to 0.26 and 

08-5132_Fig11

1965 1970 1975 1980 1985 1990 1995 2000 2005

COUNT OR ESTIMATED POPULATION SIZE (1994 AND 2003) 

YEAR

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

Annual rate of increase =14%

corrected -3%

not

corrected

Figure 11. Trends in sea otter populations in Southeast 

Alaska between 1969 and 2003. (1969, Estes and others, 

1989; 1975, Schneider, 1975; 1983, Johnson and others, 

1983; 1988, Pitcher, 1989; 1994, Agler and others, 1995; 

2003, this study.) The 1994 estimate was not corrected for 

detection when calculating the growth rate from 1969–94, 

but was corrected using a 70 percent detection rate 

(Udevitz and others, 1995) to calculate a rate of change 

from 1994–2003. Dashed curves approximate a 95 percent 

confidence interval for the expected values associated 

with the 1969-94 regression line. Error bars indicate 95 

percent confidence intervals and are associated only with 

the “not-corrected” estimate in 1994.

is consistent with growing populations elsewhere (Estes, 

1990; Riedman and Estes, 1990). Rates of emigration to 

SE AK are difficult to assess, but is likely insignificant given 

what is known about the magnitude and frequency of sea 

otter movements and the extreme distances required for 

emigration to other populations (Kenyon, 1969; Riedman and 

Estes, 1990). That leaves mortality as the process most likely 

responsible for reduced, or negative, population growth. 

Possible factors contributing to mortality include lack 

of food, pollution (or other habitat degradation), disease, 

predation, and direct human-caused mortality (boat strikes, 

legal and illegal take). Our own studies in Port Althorp, Idaho 

Inlet, and Glacier Bay, in northern SE AK (fig. 8) suggest 

that food may be a limiting resource in areas of long-term 

occupation by sea otters, but recently occupied or unoccupied 

areas tend to have abundant prey resources (Bodkin and 

others, 2007). High densities of sea otters in newly occupied 

areas seem to support this observation, and because the 

majority of sea otters in SE AK now live in such areas, 

we would expect food to be limiting for a relatively small 

proportion of the population. Significant levels of mortality 

resulting from starvation, pollution or disease are usually 

accompanied by observations of moribund animals or large 

numbers of carcasses (Bodkin and others, 2000; Ballachey 

and others, 2002), but no such reports of “die-offs” have been 

documented in SE AK.

Killer whale (Orcinus orca) predation has been cited as 

the major cause of recent sea otter declines in the Aleutian 

archipelago (Estes and others, 1998; Doroff and others, 

2003), but this predation does not appear to be a limiting 

factor in SE AK for three reasons. First, even though SE 

AK has higher densities of potential human observers when 

compared to the Aleutians, we are not aware of any confirmed 

sightings of killer whales consuming sea otters in SE AK 

(Straley and Trites, 2005). Second, mammal-eating killer 

whales are thought to have increased sea otter depredation in 

the Aleutians because preferred prey populations of harbor 

seals (Phoca vitulina) and Steller sea lions (Eumetopias 

jubatus) had been significantly depressed in that region (Estes 

and others, 1998). With few exceptions, SE AK pinniped 

populations appear healthy and generally increasing in 

abundance (Calkins and others, 1999; National Research 

Council, 2003; Small and others, 2003). Third, for killer 

whale predation to be a significant source of mortality in SE 

AK, such predation would need to be spatially “patchy” (for 

example, restricted to areas outside of Glacier Bay, where 

increases in abundance exceed theoretical limits), a pattern 

not consistent with the broad geographic ranges of transient 

killer whales (Goley and Straley, 1994), and in contrast with 

the spatially uniform declines associated with killer whale 

predation in Southwest Alaska. Depredation by other potential 

predators, including sharks or terrestrial carnivores (Riedman 

and Estes, 1990), cannot be ruled out as a source of mortality, 

but no evidence exists to implicate predation as a cause for 

reduced growth rates in Southeast Alaska sea otters.
16 Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003

Sea otters are harvested by legal subsistence hunting 

in most of Alaska. Hunters reported harvesting 2,311 sea 

otters from northern SE AK and 1,702 from southern SE 

AK between 1989 and 2003 (U.S. Fish and Wildlife Service, 

unpub. data, 2006). In the north, the average annual reported 

harvest was 154 animals (range 35 to 526). This represents a 

minimum annual harvest of 8 percent of the estimated 1,838 

sea otters outside of Glacier Bay National Park and Preserve, 

where no hunting is permitted. In the north, 30 percent of the 

reported harvest was female and 70 percent was male. In the 

south, the average annual reported harvest was 121 animals 

(range 10 to 277). This represents a minimum annual harvest 

rate of about 2 percent of the southern population, and 34 

percent of this reported harvest was female and 66 percent was 

male.

Samuel and Foin (1983) used a Leslie matrix population 

model to explore a range of harvest rates for Alaskan sea 

otters. With a series of 25-year simulations, they determined 

that 2–4 percent harvest rates are sustainable, but that 8–10 

percent harvest rates result in continual population declines. 

However, because their model constrained average annual 

population growth to 4.6 percent, rates of change less than this 

would require reduced harvests to attain stability in population 

size. It would therefore seem that pre-existing harvest levels 

may have been sufficient to limit population growth in some 

regions of SE AK, particularly in the north. Because we have 

no estimates of illegal harvesting, this conclusion is likely 

conservative. The recent availability of age- and sex-specific 

fecundity and survival rates could be used to develop age- and 

sex-structured population matrix models (Caswell, 2001) 

and better understand the potential impact of hunting under a 

variety of specific population growth and harvest scenarios.

Conclusion

Southeast Alaska supports a relatively large and 

geographically isolated sea otter population resulting from 

multiple translocations nearly 30 years ago. Discontinuities in 

the present-day distribution appear to reflect range expansion 

over time from the translocation sites along outer coast 

habitats. Colonization of new habitat includes inside waters 

greater than 75 kilometers from the outer coasts. Population 

growth rates appear divergent among areas and lower than 

historical post-translocation rates, with the exception of 

Glacier Bay, where unprecedented growth is resulting from 

immigration and reproduction. Causes of reduced population 

growth outside of Glacier Bay are uncertain, but hunting 

appears to be a substantial cause of mortality. Development 

of age- and sex-structured population models, which would 

incorporate the estimates of rates of population change 

reported here as well as recently available data on age- and 

sex-specific fecundity and survival rates, would help guide 

the management and conservation of sea otter populations in 

Southeast Alaska.

Acknowledgments

Support for this project was provided by the U.S. 

Geological Survey Alaska Science Center, U.S. Fish and 

Wildlife Service Marine Mammals Management, and Glacier 

Bay National Park and Preserve. We thank Patrick Kearney 

(Cordova Air Service) for safely piloting the surveys, Heather 

Coletti (USGS) for helping to digitize bathymetry, and the 

following for their contributions to the survey: Janet Doherty 

(NPS), Angela Doroff (USFWS), John Haddix (USFWS), Jack 

Hodges (USFWS), Rikk Kvitek (California State University 

Monterey Bay), Mike Miller, the Alaska Sea Otter and 

Steller Sea Lion Commission, and the Sitka Marine Mammal 

Commission. We also thank the U.S. Forest Service in Craig, 

Alaska, for providing lodging and logistical support. Tony 

DeGange, Gary Drew, Kim Kloecker, Dan Monson, Karen 

Oakley, Tim Tinker, and Mark Udevitz provided helpful 

comments on earlier drafts of this report.

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For more information concerning the research in this report, contact the 

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Esslinger and other—Status and Trends of Sea Otter Populations in Southeast Alaska, 1969–2003—Scientific Investigations Report 2009–5045