AERIAL SURVEYS OF SEA OTTERS (Enhydra lutris) 

 IN KACHEMAK BAY, ALASKA, 2008 

BY 

VERENA A. GILL, ANGELA M. DOROFF, AND DOUGLAS M. BURN 

U.S. Fish and Wildlife Service 

Marine Mammals Management 

1011 E. Tudor Road, MS 341 

Anchorage, Alaska 99503 

Verena_Gill@fws.gov 

January 2009 

Prepared for Army Corps of Engineers, MIPR # WC1JUW80880784 
Table of Contents 

List of Tables...................................................................................................................................ii 

List of Figures .................................................................................................................................ii 

ABSTRACT .................................................................................................................................... 1 

INTRODUCTION........................................................................................................................... 2 

METHODS...................................................................................................................................... 3 

Study Area........................................................................................................................... 3 

Survey Methods................................................................................................................... 3 

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

RESULTS........................................................................................................................................ 6 

DISCUSSION ................................................................................................................................. 7 

Recommendations ...............................................................................................................8

ACKNOWLEDGMENTS............................................................................................................... 9 

LITERATURE CITED.................................................................................................................... 9 
ii

List of Tables 

Table 1. Results for the five replicate aerial surveys of sea otters in Kachemak Bay, 

May 2008............................................................................................................... 11 

List of Figures 

Figure 1. Study area of the 2008 sea otter aerial surveys in Kachemak Bay........................ 12 

Figure 2. Survey transects and sea otter sightings for the first replicate of the aerial 

survey of Kachemak Bay conducted 7 May 2008................................................ 13 

Figure 3. Survey transects and sea otter sightings for the second replicate of the aerial 

survey of Kachemak Bay conducted 8 May 2008................................................ 14 

Figure 4. Survey transects and sea otter sightings for the third replicate of the aerial 

survey of Kachemak Bay conducted 9 May 2008................................................ 15 

Figure 5. Survey transects and sea otter sightings for the fourth replicate of the aerial 

survey of Kachemak Bay conducted 10 May 2008............................................... 16 

Figure 6. Survey transects and sea otter sightings for the fifth replicate of the aerial 

survey of Kachemak Bay conducted 13 May 2008.............................................. 17 

Figure 7. Trackline and sea otter sightings for the winter distribution survey, 21-22 

February 2008........................................................................................................ 18 

Figure 8. Trackline and sea otter sightings for the summer distribution survey, 

19 August 2008 ..................................................................................................... 19 

Figure 9. Winter and summer distribution of sea otters in Kachemak Bay, Alaska 2008.... 20 

Figure 10. Distribution of sea otters in Kachemak Bay during the spring abundance 

survey, 7-13 May 2008.......................................................................................... 21 
1

ABSTRACT 

Previous to the 1960s Kachemak Bay had not yet been repopulated with sea otters (Enhydra 

lutris) after the commercial exploitation that lasted from the mid-1700s through the 1800s. In 

the late 1960s there were sporadic reports of single otters moving into the Bay. An estimate from 

limited aerial surveys in 1976 suggests there could have been up to 400 sea otters in the Bay and 

joint bird and otter boat surveys in 1994 estimated about 1000 animals. The first complete 

abundance survey was flown in 2002 and calculated 912 ± 368 sea otters. Five years later 

another complete survey was flown and found 3,724 ± 979 animals. A comprehensive marine 

habitat inventory of Kachemak Bay was undertaken in 2007 and 2008 as part of a feasibility 

study by the Army Corps of Engineers to assess the impact of constructing navigation 

improvements for Homer harbor. Information on current sea otter abundance and seasonal 

distribution in Kachemak Bay was needed as part of this study. To address the first question on 

population abundance of sea otters, five replicate aerial surveys were flown in Kachemak Bay 

over the course of one week in May 2008. Our estimate of the overall sea otter population of 

Kachemak Bay is 3,596 ± 802 animals. The estimated annual rate of increase in Kachemak Bay 

between 2002 and 2008 was 26% per year which exceeds the maximum productivity rate for this 

species. It is therefore likely that immigration from other areas has contributed to the observed 

population increase of sea otters in Kachemak Bay. 

To address the question of sea otter distribution in Kachemak Bay, two additional surveys were 

flown in February and August 2008, respectively. The information from these surveys indicates 

that sea otters in Kachemak Bay have markedly different seasonal distributions although the 

north shore, waters adjacent to the Homer Spit, and the area around Yukon Island and Kasitsna 

Bay remain occupied at all times of the year. The southern fjords are important habitat for otters 

in the winter months when protection from large storms may be a priority. With the relative 

calm of the summer, otters are able to utilize more of the Bay especially areas east of Homer Spit 

where foraging opportunities abound. Information from our distribution surveys corresponds to 

data collected from 44 sea otters that have been radio-tracked in the Kachemak Bay area since 

August 2007. It is unclear if this population is at equilibrium or whether there is capacity for 

more growth so we recommend periodic aerial surveys to monitor the abundance and distribution 

of sea otters in Kachemak Bay. Possible mitigation measures may include limiting harbor 

construction activities to summer months when otters are more widely-distributed. Once the new 

harbor is complete, the additional vessel traffic would likely result in increased disturbance of 

sea otters, and increased risk of injury or mortality from boat. These potential impacts could be 

mitigated by regulating vessel speed in areas of known sea otter concentrations. 
2

INTRODUCTION 

Prior to the mid-1700s, sea otters (Enhydra lutris) occurred in large numbers in coastal areas of 

Japan, Russia (Kamchatka), the United States (Alaska, Washington, Oregon, and California), 

Canada (British Columbia), and Mexico (Lensink 1962, Kenyon 1969). Extensive commercial 

harvests of sea otters occurred from the mid-1700s through the 1800s which drastically reduced 

the population (Bancroft 1959, Lensink 1962, Kenyon 1969) and eliminated them from much of 

their range (Kenyon 1969, Riedman and Estes 1990). Sea otters were subsequently protected by 

the International Fur Seal Treaty in 1911. Sea otter populations were nearly eliminated from 

Cook Inlet in the early 1900s however, a remnant group was thought to remain in Kamishak Bay 

on the west side of lower Cook Inlet (Schneider 1976). In the absence of harvest pressure, the 

population expanded from the 11 remnant groups to re-colonize much of the former sea otter 

range. 

Prior to the 1960s Kachemak Bay had not yet been repopulated with sea otters. In the late 1960s 

there were sporadic reports of single otters, usually old males, moving into the Bay (Schneider 

1976). Sea otters had repopulated the outer Kenai Peninsula in the 1960s and Schneider believed 

it was these animals that were expanding into Kachemak Bay. In 1975 there was an increase in 

sightings in offshore areas west of the Homer Spit and reports from residents began to increase 

(Schneider 1976). In October 1975 Schneider conducted helicopter surveys along the coastline 

of Kachemak Bay and found 11 otters. From February to June of 1976 Schneider flew monthly 

surveys in a Grumman Goose in various areas of Kachemak Bay looking for sea otters and found 

as many as 49 otters. Most of the sightings were in the Seldovia area. Based on his 

observations, Schneider (1976) estimated there were 400 sea otters in the Bay but that it was a 

non-breeding population made up of males seeking new territory. 

It was twenty years before another survey for sea otters was conducted in Kachemak Bay. From 

February to March of 1994 U.S. Fish and Wildlife crews used boats and planes to count marine 

birds and sea otters along the shoreline of Kachemak Bay (Agler et al. 1995). They counted 355 

otters by aircraft and 151 by boat. From this they estimated the population of sea otters in 

Kachemak Bay to be 1,104 ± 592. They also observed mothers and pups which indicated 

reproduction was now occurring in the Bay. 

In 2002 the first complete abundance survey for sea otters in Kachemak Bay was completed and 

estimated 912 ± 368 animals (USGS unpubl. data). Another complete abundance survey was 

flown in 2007 using the same observer and method (Bodkin and Udevitz 1999). This survey 

showed a large increase of sea otters since 2002; 3,724 ± 979 animals. 

A comprehensive marine habitat inventory of Kachemak Bay was undertaken in 2007 and 2008 

as part of a feasibility study by the Army Corps of Engineers to assess the impact of constructing 

navigation improvements for Homer harbor. Current sea otter seasonal distribution and 

abundance data from Kachemak Bay was needed as part of this study. Since the 2007 estimate 

represented such a big increase, another survey was needed to validate the population status in 

the Bay. In addition, as these surveys had been conducted during the summer months, there was 

a need for surveys to document seasonal distribution patterns of sea otters in Kachmak Bay. 
3

Kachemak Bay is located near the western extent of the southcentral Alaska population stock 

(Gorbics and Bodkin 2001). The southcentral Alaska stock extends from Cape Yakataga to Cook 

Inlet and includes Prince William Sound, the Kenai Peninsula coast, and Kachemak Bay 

(USFWS 2008a). The most current Marine Mammal Protection Acts stock assessment report 

(USFWS 2008a) considers this population to be stable at this time. 

If sea otters have indeed increased in Kachemak Bay as indicated by the 2007 survey, resource 

management conflicts can be expected, including disturbance, injury, and mortality of sea otters 

due to increased boat traffic. In order to address these management concerns, a comprehensive 

understanding of sea otter distribution and abundance in Kachemak Bay is needed. This report 

presents the results of an abundance survey for sea otters that was conducted in Kachemak Bay 

during May 2008 and distribution surveys that were conducted in February and August of 2008. 

METHODS 

Study area

The study area is located in Kachemak Bay (59.10°N, 152.00°W by 59.85°N, 150.90°W) on the 

west side of the Kenai Peninsula in lower Cook Inlet, Alaska (Figure 1). Kachemak Bay is 63 

km long and 39 km wide at its entrance between Anchor Point and Point Pogibshi, with more 

than 515 km of shoreline. Homer Spit projects 7.2 km from the northern shore out into the Bay, 

dividing it into an inner and outer Bay. The inner Bay is east of the Homer Spit to the head of 

Kachemak Bay, and the outer Bay is west of Homer Spit to the mouth of Kachemak Bay. Much 

of the area in the region has been designated as wilderness and is part of the Kachemak Bay 

National Estuarine Research Reserve managed by the State of Alaska in cooperation with the 

National Oceanic and Atmospheric Administration. The Reserve manages 1,501 km2 of the Bay 

and 2,658 km2

 of its watershed. The U.S. Forest Service, National Park Service, and U.S. Fish 

and Wildlife Service also have the responsibility to manage lands and trust resources within 

these areas. Homer and Seldovia are the two main communities that reside on Kachemak Bay 

but numerous small settlements exist along the entire shoreline. 

Survey Methods 

Abundance survey 

The purpose of the abundance survey was to estimate the size of the sea otter population in 

Kachemak Bay by counting otters on specific transects and then correcting for those missed. 

Only those otters on transect are counted. The survey methodology followed Bodkin and 

Udevitz (1999), consisting of a stratified random sampling of parallel 400 m-wide strip transects, 

overlaying the study area and oriented perpendicular to the coastline. To allocate survey effort in 

proportion to expected sea otter abundance, we separated the survey area into high and low 

density strata. The entire inner Bay was designated high density stratum while for the outer Bay 

the high density stratum extended from shore to 400 m seaward or to the 40 m depth contour, 

whichever was greatest. In the outer Bay, the low density stratum boundary began at the 

seaward high density stratum boundaries and extended to 2 km offshore or to the 100 m depth 

contour, whichever was greater. Bays and inlets less than 6 km wide were sampled with high 

density strata regardless of water depth. The distance between adjacent transects was 4 km in the 
4

high density stratum and 6 km in the low density stratum, thereby sampling approximately 10 

and 7 percent of the high and low density strata, respectively. 

The survey platform was a Piper PA18 Super Cub (a fixed-wing, single-engine aircraft with 

tandem seating) with a pilot and one observer. Five complete replicate surveys for Kachemak 

Bay were flown (7-10 May, and 13 May, 2008; Figures 2-6). There were two days of poor 

survey conditions between the fourth and fifth replicate surveys. Each survey consisted of a 

systematic random sample of all possible transects, with a different set of transects selected for 

each replicate. 

All otter sightings were digitized into GIS format in real-time using a tablet PC connected to a 

Global Positioning System (GPS). A custom-written ArcPad software (ESRI, Redlands, 

California) application recorded the location, number of otters, and behavior of each otter group. 

The survey methodology includes a survey-specific correction factor to account for otters that 

may be underwater and available for observation, as well as otters at the surface that may not be 

detected. This correction factor is calculated by conducting intensive search units (ISU) to 

estimate a correction factor for the proportion of sea otters that were missed by the observer on 

the strip transects. An ISU consisted of 5 concentric 400 m diameter circles flown within the 

survey strip. Each ISU is initiated by the sighting of a group (≥ 1 sea otter) only when the time 

since the previous ISU was > 1 minute. For each ISU, several variables are recorded: 1) whether 

animals were detected on the strip count or on the subsequent circles within the ISU, 2) location 

of the group within the ISU, and 3) the behavior of each animal (e.g. diving or non-diving). Sea 

otters in the initiating group and those that entered the survey area during the course of 

conducting an ISU are not included in the calculation of the correction factor. However, large 

groups of sea otters (defined as ≥20 sea otters) were observed until an accurate count or photo 

was obtained; these were recorded as complete counts. 

Distribution survey 

The purpose of the distribution survey was to count every otter in Kachemak Bay to provide a 

comprehensive picture of otter distribution across the Bay rather than a population estimate. The 

survey area was divided into two segments: 1) nearshore waters adjacent to the coastline; and 2) 

a series of parallel transects across the bay. The transects were located at equally-spaced interval 

to prevent double-counting of otters on adjacent transects, while ensuring complete coverage of 

the area. Unlike the abundance survey methods, no effort was made to correct for otters not 

detected by observers. 

The survey platform was a Cessna 206 (a fixed-wing, single-engine aircraft with four seats; two 

in front and two in back) with a pilot, two observers, and a data recorder. All otter sightings 

were recorded using the same tablet PC, GPS, and ArcPad application as the abundance surveys. 

Two distribution surveys were completed in 2008; 21-22 February (Figure 7) and 19 August 

(Figure 8). Due to reduced daylight in February the survey was divided over two days; one to fly 

the coastline and one to fly the transects across the Bay. In August both the coastline and 

transect were surveyed in one day. 
5

Data Analysis 

Abundance survey 

To correct the estimates of sea otter abundance a correction factor is calculated from the ISUs 

that had 2 or more groups of sea otters. Bodkin and Udevitz (1999) suggest that at least 30 

usable ISUs during a survey are needed to calculate a reasonable correction factor from a single 

replicate. Although 35 useable ISUs was flown during the Kachemak Bay survey a malfunction 

occurred in the ArcPad program and the data was not properly recorded. Therefore the 

correction factor used (3.1) was calculated as an average from previous surveys flown by VAG 

in Kodiak (Doroff et al. in prep) and Yakutat (Gill and Burn 2007). Complete counts were not 

considered in the calculation of the correction factor, nor was the correction factor applied to 

these large groups. 

The variance in each replicate includes the variance associated with sea otter density between 

transects and the variance of the correction factor calculated from the ISUs (Bodkin & Udevitz 

1999). Finally, we calculated an overall population estimate as the mean and the variance of the 

five replicate surveys. All resulted presented are ± standard error. 
6

RESULTS 

Abundance survey 

The corrected population estimates ranged from 1,437 to 5,691 for the five replicate surveys in 

Kachemak Bay (Table 1). Estimates from the five replicates varied widely primarily due to the 

number of large groups observed and to the number of otters seen in low density strata. Both of 

these variables have a significant effect on the final corrected estimate. The mean estimate of the 

five replicate surveys was 3,596 ± 802. 

The corrected population estimate for the first replicate survey was 3,422 ± 919 which is similar 

to the mean estimate and standard error of the five replicate surveys. The corrected population 

estimate for the second replicate was 2,344 ± 729. The third replicate survey had the highest 

corrected population size of 5,691 ± 1,247. The corrected estimate for the fourth replicate was 

5,085 ± 1,363. The third and fourth replicates had the highest corrected estimates because of the 

presence of more sea otters in both high and low density strata. Additionally, several large 

groups ranging in size from 20-43 otters were observed during these replicates resulting in a 

higher corrected population estimate than the other replicates. The corrected estimate for the 

fifth replicate had the lowest corrected population size of 1,437 ± 593. This low estimate is due 

to the fact that no large groups were observed at all during this replicate and no otters were 

observed in the low density strata. Immediately after completing this replicate, the lead author 

noted that the distribution of otters differed markedly from the previous four replicates because 

of the number of single otters scattered and feeding. A pilot tracking radio-tagged sea otters on 

the same day in Kachemak Bay also noted that it was hard to find them because of their dispersal 

(J. DeCreft pers. comm.). It is presumed after the two-day storm that interrupted the survey, 

otters were taking advantage of the calm weather for intensive foraging. The scattering of otters 

across the Bay made it more likely to entirely miss animals on transect since it is easier to spot 

even a very small group than it is a single animal. 

Distribution survey 

The information from the two distribution surveys indicates that sea otters in Kachemak Bay 

have marked seasonal distributions. However, there do appear to be areas that are occupied at all 

times of the year; the Homer Spit, the north shore of both the inner and outer Bay, and the area 

around Yukon Island and Kasitsna Bay (Figure 9). Waters adjacent to the Spit are especially 

preferred in winter (Figure 7) while the entire inner Bay is heavily used in the summer (Figure 

8). The protected waters of the southern fjords are densely occupied in the winter, especially 

around Seldovia, compared to the summer. As a comparison the distribution of sea otters during 

the five abundance surveys conducted in May were also mapped (Figure 10). Although this was 

not a distribution survey and only sea otters on transect were recorded it provides another 

snapshot of their distribution in Kachemak Bay albeit a coarser depiction. By May it appears 

that otters had already have moved out of the southern fjords and into their summer habitat to 

utilize the northern shore feeding areas. 

 

The distribution of sea otters observed on the two distribution surveys and the five replicate 

abundance surveys corresponds to data collected from 44 radio-tagged sea otters that have been 

tracked from August 2007 to present within the Kachemak Bay area (USFWS unpubl. data). 
7

DISCUSSION 

The estimate of the overall sea otter population of Kachemak Bay is 3,596 ± 802 animals. The 

previous abundance survey was conducted in 2007 and estimated a similar number of sea otters; 

3,724 ± 979 animals. The only other complete aerial survey of sea otters in Kachemak Bay was 

flown in 2002 when the population was estimated to number 912 ± 368 animals. All three 

abundance surveys (2002, 2007, and 2008) were flown using the same methodology. 

Additionally, the 2002 and 2007 surveys were flown by the same observer. 

Other sources of information suggest that the sea otter population in Kachemak Bay has grown 

significantly since 2002. Over the past several years, the number of stranded sea otters 

recovered from Kachemak Bay has dramatically increased (USFWS unpubl. data). Larger 

numbers of stranded sea otters could be a result of either an increase in otter mortality, an 

increase in population size with a constant rate of mortality, or some combination of both factors. 

However, local residents and avid beachcombers in the area had never observed stranded sea 

otters prior to 2000. In 2006 a sea otter Unusual Mortality Event focusing on Kachemak Bay 

was declared because of large number of animals dying from one syndrome from 2002 to 2006 

(Gill et al. in prep). It is clear from the increasing trend in otter numbers from 2002 to 2008 that 

this mortality event has had no negative impact on population growth. 

The annual rate of increase between the 2002 and the 2008 aerial abundance surveys was 26 % 

per year which exceeds maximum net productivity rate (RMAX) for sea otters, which is estimated 

to be 20% (Estes 1990). Therefore, some portion of the observed population increase must be 

the result of immigration. The source of immigration could be movement of otters from the 

outer Kenai Peninsula coast and from across Cook Inlet in Kamishak Bay. The number of sea 

otters in Kamishak Bay is estimated to be 6,918 (USFWS 2008b) and the number in Cook Inlet 

and along the Kenai Peninsula (excluding Kachemak Bay) is 1,761 (USFWS 2008a). Schneider 

(1976) believed the source population for Kachemak Bay came from the outer Kenai coast and 

predicted a continued movement of animals into Kachemak Bay from the Peninsula. Also both 

Schneider (1976) and Agler et al. (1995) believed there was movement across Cook Inlet 

between Kachemak and Kamishak Bays. The distance between the two Bays (80 km directly 

west of Kachemak Bay across lower Cook Inlet) is not outside the swimming capability of a sea 

otter, particularly a female or young male, looking for new resources (Reidman and Estes 1990). 

Schneider (1976) predicted Kachemak Bay would eventually support high densities of sea otters 

which he believed would make it a key area for this species because of its easy public access for 

wildlife viewing. A possible reason for the large increase of sea otters in Kachemak Bay since 

2002 is a recent increase in the Tanner crab (Chionoecetes bairdi) population. Crab are a 

preferred prey item for sea otters (Bodkin et al. 2007) because of their high calorific value. The 

sport, personal use, and subsistence fishery (sport fishery) for Tanner crab in Kachemak Bay was 

closed from 2002 to 2008 because of a lack of legal-sized crab (Charles Trowbridge ADFG pers. 

comm.). However, beginning 15 July 2008 the Alaska Department of Fish and Game (ADFG) 

re-opened the sport fishery in Kachemak Bay and lower Cook Inlet because crab numbers had 

recovered enough to support a harvest. But tanner crab numbers have not recovered enough to 

reopen the commercial fishery which has been closed since 1994 in all fishing districts of the 
8

Cook Inlet Management Area. The increase of this valuable prey resource since 2002 may have 

increased sea otter reproduction (see von Biela et al. in press) as well as driven immigration into 

the Bay. A continued increase in Tanner crab abundance may facilitate further sea otter 

population growth in Kachemak Bay. 

It is not clear whether the population of sea otters in Kachemak Bay is at equilibrium or whether 

there is capacity for more growth. Based on density estimates from this survey there are 5.1 

otters/km2 in the Bay which is comparable to other populations in south central Alaska (USGS 

unpubl. data). Although the 2007 and 2008 estimates from Kachemak Bay are similar, the data 

are not sufficient enough to speculate that the population has reached carry capacity. Another 

survey in a few years is needed before this could be considered.

The seasonal distribution patterns of sea otters observed in Kachemak Bay indicate the north 

shore of both the inner and outer Bay are utilized year round. An extensive shallow shelf 

extending from this shore provides good foraging habitat for these typically shallow divers. The 

waters around the Spit are also used throughout the year, although more so in the winter. The 

protection the Spit provides in any wind direction may be crucial for resting animals throughout 

the year, especially mothers with pups in the summer months. The Spit is also a location where 

many sick and dying otters haul out (USFWS unpubl. data). The protected waters around Yukon 

Island and Kasitsna Bay are also used extensively year round, which tends to be an area that 

mothers and pups inhabit (USFWS unpubl. data). Schneider (1976) and Agler et al. (1995) also 

observed that the Yukon Island area, Seldovia, and the north shore were heavily utilized areas. 

The southern fjords and sheltered bays are important habitat for otters in the winter months when 

protection from large storms is a priority. Both Schneider (1976) and Agler et al. (1995) 

commented on the preference for these areas during their respective winter surveys. With the 

relative calm of the summer, otters are able to utilize more of the Bay especially males (USFWS 

unpubl. data) in the mid-inner Bay where foraging opportunities abound. It is clear that weather 

conditions, foraging opportunities, and gender dictate where sea otters reside throughout the year 

and their seasonal habitat use should be taken into consideration with any activities in Kachemak 

Bay that may impact them. 

Recommendations

This survey method provides a means of comparing population abundance over time and is 

readily repeatable over longer time intervals (e.g. every 5-10 years). There was considerable 

variability in the abundance estimates in the replicate surveys used to estimate abundance. Sea 

otters are highly mobile and large groups of animals can influence the variation among transects 

considerably. For example, the high estimates of 5,691 and 5,085 otters on the third and fourth 

replicates, respectively, were the result of large groups and otters in low density habitat. In 

contrast there were no large groups or otters observed in low-density habitat, resulting in the 

lowest estimate of 1,437. These numbers suggest that a single replicate using this survey method 

is unsuitable for estimating the sea otter population in Kachemak Bay. In order to estimate 

population size with acceptable accuracy and precision, multiple replicates should be conducted. 

We also suggest that for future surveys of Kachemak Bay all habitat be considered high density 

stratum since numbers were similar between the two strata during this survey. This should help 
9

in decreasing the variability between replicates. Another opportunity to decrease variability 

between replicates would be to increase the percentage of habitat sampled. However, since the 

goal is to complete a replicate in one day, that may not be feasible. 

We recommend periodic aerial surveys to monitor the abundance and distribution of sea otters in 

Kachemak Bay to establish a population trend. The development of new harbor facilities in 

Homer may affect sea otters in several ways. Possible mitigation measures to minimize 

disturbance may include limiting harbor construction activities to summer months when otters 

are more widely-distributed. Once the new harbor is complete, the additional vessel traffic 

would be result in increased disturbance of sea otters, and increased risk of injury or mortality 

from boat. These potential impacts could be mitigated by regulating vessel speed in areas of 

known sea otter concentrations. 

ACKNOWLEDGMENTS 

We thank Paul D. Anderson (Migratory Bird Management, USFWS), for his excellent piloting 

skills during the course of the abundance survey, and Russ Oates (Migratory Bird Management, 

USFWS) for facilitating this arrangement. Thanks to the Koyukuk National Wildlife Refuge for 

use of their airplane during the abundance survey and to Brad Scotton and Kevin Fox (USFWS, 

Refuges) for their assistance with the logistics of this loan. Thanks to Jose DeCreft (Northwind 

Aviation) for his superior piloting during both of the distribution surveys. Ori Badajos (ADFG) 

assisted during the February survey, and Dana Jenski (Marine Mammals Management, USFWS) 

and Sebastian Carrasco (UC Davis) assisted during the August survey. George Esslinger and 

Heather Coletti (USGS) assisted in data preparation and computer support for the survey design. 

LITERATURE CITED 

 

Agler, B.A., S.J. Kendall, P.E. Seiser, and D.B. Irons. 1995. Estimates of Marine Bird and Sea 

Otter Abundance in Lower Cook Inlet, Alaska During Summer 1993, and Winter 1994. 

Minerals Management Service Technical Report: MMS 94-0063. 124 pp. 

Bancroft, H. H. 1959. History of Alaska, 1730-1885. Antiquarian Press Ltd. N. Y. 755 pp. 

Bodkin, J. L. and M. S. Udevitz. 1999. An aerial survey method to estimate sea otter abundance. 

Pages 13-26 in G. W. Garner, S.C. Amstrup, J. L. Laake, B. F. J. Manly, L. L. 

McDonald, and D. G. Robertson editors. Marine Mammal Survey and Assessment 

Methods. A. A. Balkema Publishers, Rotterdam Netherlands. 

Bodkin, J.L., D.H. Monson, G. G. Esslinger. 2007. Activity Budgets Derived From Time– 

Depth Recorders in a Diving Mammal. Journal of Wildlife Management 71(6): 2034–

2044. 

Doroff, A.M, D.M. Burn, M.T. Tinker, R.A. Stovall, and V.A. Gill. (in prep). Northern 

Sea Otter Population Trends in Southwest Alaska: Temporal Dynamics at the Edge of a 
10

Large-Scale Decline in Abundance. 

Estes, J. A. 1990. Growth and equilibrium in sea otter populations. Journal of Animal Ecology 

59:385-401. 

Gill, V.A. and D. Burn. 2007. Aerial Surveys of Sea Otters Enhydra lutris in Yakutat 

Bay, Alaska 2005. U.S. Fish and Wildlife Service, Marine Mammals Management 

Technical Report: MMM 2007-01. 18pp. 

Gill, V.A et al. (in prep). The first baseline pathologic and demographic study of northern 

sea otter carcasses in Alaska. Targeted for Marine Mammal Science.

Gorbics, C. S., and J. L. Bodkin. 2001. Stock structure of sea otters (Enhydra lutris kenyoni ) in 

Alaska. Marine Mammal Science 17(3): 632-647 

Kenyon, K. W. 1969. The sea otter in the eastern Pacific Ocean. North American Fauna. 68:1-

352. 

Lensink, C. J. 1962. The history and status of sea otters in Alaska. Ph.D. thesis, Purdue 

University, West LaFayette, Ind. 188 pp. 

Riedman, M. L. and J. A. Estes. 1990. The sea otter (Enhydra lutris): behavior, ecology, and 

natural history. U.S. Fish and Wildl. Ser. Biol. Report 90(14). 126 pp. 

Schneider, K.B. 1976. Assessment of the distribution and abundance of sea otters along the 

Kenai Peninsula, Kamishak Bay, and the Kodiak Peninsula. Final Report for the Alaska 

Department of Fish and Game, Anchorage, AK. 72pp. 

United States Fish and Wildlife Service. 2008a. Sea Otter (Enhydra lutris): southcentral 

Alaska stock. Marine Mammal Protection Act Stock Assessment Report. 6pp. 

United States Fish and Wildlife Service. 2008b. Sea Otter (Enhydra lutris): southwest 

Alaska stock. Marine Mammal Protection Act Stock Assessment Report. 7pp. 

Von Biela, V.R, V.A. Gill, J.L. Bodkin, and J. M. Burns. (in press). Evidence of 

phenotypic plasticity in the average age at first reproduction of northern sea otters 

(Enhydra lutris kenyoni) in Alaska. Journal of Mammology. 
Table 1. Results for the five replicate aerial surveys of sea otters in Kachemak Bay, May 2008. 

Replicate 

Survey 

Stratum 

Group 

Sizea

Sea 

Otters 

Counted 

Area 

Sampled 

(km2) 

Density 

(otters/km2)

Stratum 

Area 

(km2) 

Uncorrected 

Population 

Size 

Correction 

Factor 

Corrected 

Population 

Size 

Standard 

Error 

High Small 76 68.71 1.11 704.70 779 3.1 2,416 1 

Low Small 25 20.06 1.25 260.40 325 3.1 1,006 

Total All 101 88.77 1.18 965.10 1,104 3.1 3,422 919 

Small 53 68.36 0.78 704.70 546 3.1 1,694 High 

Large 50 68.36 0.73 704.70 515 

Low Small 3 18.02 0.17 260.40 43 3.1 134 

2 

Total All 106 86.38 0.56 965.10 3.1 2,344 729 

Small 114 68.09 1.67 704.70 1,180 3.1 3,658 High 

Large 92 68.09 1.35 704.70 

Low Small 27 20.15 1.34 260.40 349 3.1 1,081 

3 

Total All 233 88.24 1.45 965.10 2,481 3.1 5,691 1,247 

Small 107 74.95 1.43 704.70 1,006 3.1 3,119 High 

Large 70 74.95 0.93 704.70 658 

Small 24 20.19 1.19 260.40 310 3.1 960 

4 

Low 

Large 27 20.19 1.34 260.40 348 

Total All 228 95.14 1.22 965.10 3.1 5,085 1,363 

5 High Small 50 76.00 0.66 704.70 464 3.1 1,437 

Low Small 0 19.66 0.00 260.40 0 3.1 0 

Total All 50 95.66 0.66 965.10 464 3.1 1,437 593 

11

a Small groups (<20) were used to generate the corrected population estimate and large groups (≥20) were treated as 

complete counts and added into the total estimate. 
Homer

Seldovia

Anchor Point

Comm

Low de

High d

Figure 1. Study area of the 2008 sea otter aerial surveys in Kachemak Bay

Homer Spit

Coal Bay

Sadie Cove

Kasitsna Bay

Yukon Island

Tutka Bay 0 

5 

Inner Bay

Outer Bay

12 
Homer

Seldovia

Anchor Point

Sea otters on t

1

2 - 4

5 - 10

11 - 20

21 - 50

Low dens

High dens

Figure 2. Survey transects and sea otter sightings for the first replicate of the aerial survey of Kachemak Bay con

0 10 5 

13
Homer

Seldovia

Anchor Point

Sea otters on t

1

2 - 4

5 - 10

11 - 20

21 - 50

High dens

Low dens

Figure 3. Survey transects and sea otter sightings for the second replicate of the aerial survey of Kachemak Bay c

0 5 

14
Homer

Seldovia

Anchor Point

Sea otters on 

1

2 - 4

5 - 10

11 - 20

21 - 50

High den

Low den

Figure 4. Survey transects and sea otter sightings for the third replicate of the aerial survey of Kachemak Bay con

0 10 5 

15
Homer

Seldovia

Anchor Point

Sea otters o

1

2 - 4

5 - 10

11 - 20

21 - 50

High de

Low den

Figure 5. Survey transects and sea otter sightings for the fourth replicate of the aerial survey of Kachemak Bay co

0 5 

16
Homer

Seldovia

Anchor Point

Sea otters on 

1

2 - 4

5 - 10

11 - 20

21 - 50

High den

Low dens

Figure 6. Survey transects and sea otter sightings for the fifth replicate of the aerial survey of Kachemak Bay con

0 15 

17
Homer

Seldovia

Anchor Point

Sea otte

Figure 7. Trackline and sea otter sightings for the winter distribution survey, 21-22 February 2008

0 5 

18
Homer

Seldovia

Anchor Point

Sea otter 

1 - 

4 - 

10 

20 

39 

Tra

Co

Figure 8. Trackline and sea otter sightings for the summer distribution survey, 19 August 2008

0 15 

19
Homer

Seldovia

Anchor Point

Winter 

1 

4 

10 

20 

39 

10

Summ

1 

4 

10 

20 

39 

Figure 9. Winter and summer distribution of sea otters in Kachemak Bay, Alaska 2008

0 15 

20
Homer

Seldovia

Anchor Point

Sea ott

1

2 - 

5 - 

11 

21 

Tra

Figure 10. Distribution of sea otters in Kachemak Bay during the spring abundance survey, 7-13 May 2008

0 10 5 K

21