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AERIAL SURVEYS OF SEA OTTERS (Enhydra lutris) IN LOWER COOK INLET, ALASKA MAY, 2017

BY

JOEL L. GARLICH-MILLERa, GEORGE G. ESSLINGERb, AND BENJAMIN P. WEITZMANb

aU.S. Fish and Wildlife Service, Marine Mammals Management 1011 E. Tudor Road, MS 341, Anchorage, Alaska 99503

bU.S. Geological Survey, Alaska Science Center

4210 University Drive, Anchorage, Alaska 99508

USFWS Technical Report MMM 2018-01

September, 2018

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Table of Contents List of Tables .................................................................................................................................. ii

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

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

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

METHODS ..................................................................................................................................... 2

RESULTS ....................................................................................................................................... 4

Western LCI ................................................................................................................................ 4

Eastern LCI ................................................................................................................................. 4

Other Marine Mammal Sightings ............................................................................................... 4

DISCUSSION ................................................................................................................................. 5

Western LCI – Southwest Alaska Stock ..................................................................................... 5

Eastern LCI – Southcentral Alaska Stock ................................................................................... 6

Recommendations for Future Studies ......................................................................................... 7

ACKNOWLEDGMENTS .............................................................................................................. 8

LITERATURE CITED ................................................................................................................... 8

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List of Tables Table 1. Sea otter abundance estimates based on aerial surveys of Western Lower Cook Inlet, May, 2017. .................................................................................................................................... 11

Table 2. Sea Otter abundance estimates based on aerial surveys of Eastern Lower Cook Inlet, May 2017. ..................................................................................................................................... 12

Table 3. Sea Otter abundance estimates based on aerial surveys of Kachemak Bay, May 2017. 13

Table 4. Opportunistic sightings of other marine mammal species during aerial surveys of Lower Cook Inlet, May 2017. .................................................................................................................. 14

Table 5. Estimates of sea otter abundance in Kachemak Bay. ..................................................... 15

List of Figures Figure 1. Map of Lower Cook Inlet showing the boundaries of 3 survey units that were surveyed in May 2017 to estimate sea otter abundance. .............................................................................. 16

Figure 2. Map showing transects from 3 replicate aerial surveys flown to estimate sea otter abundance in Lower Cook Inlet, May 2017.................................................................................. 17

Figure 3. Map showing transects from 4 replicate aerial surveys flown to estimate sea otter abundance in Kachemak Bay, May 2017. .................................................................................... 18

Figure 4. Distribution of sea otters sighted during replicate aerial surveys in Lower Cook Inlet, May 2017. ..................................................................................................................................... 19

Figure 5. Mean relative densities of sea otters encountered during replicate aerial surveys in Lower Cook Inlet, May 2017. ....................................................................................................... 20

Figure 6. Map showing sea otters sighted during a coastal survey along the eastern shore of Lower Cook Inlet on 19 May, 2017 to determine the northern extent of their range. .................. 21

Figure 7. Other marine mammals sighted in Lower Cook Inlet during sea otter aerial surveys in May 2017. ..................................................................................................................................... 22

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ABSTRACT Portions of two stocks of northern sea otters (Enhydra lutris kenyoni) occur in Lower Cook Inlet (LCI), Alaska. Sea otters on the west side of LCI are considered part of the southwest Alaska stock; sea otters occupying eastern LCI are considered part of the southcentral Alaska stock. Information concerning the distributions and abundance of sea otters in LCI is needed to track the status and trends of these populations and address management concerns associated with oil and gas exploration and coastal development in the region. In May 2017, we conducted a series of replicate aerial surveys of sea otters across LCI following the methods of Bodkin and Udevitz (1999). Our abundance estimate for western LCI (southwest Alaska stock) was 10,737 (SE = 2,323) sea otters. Sea otters were not uniformly distributed across western LCI. The highest sea otter densities (up to 8 sea otter/km2) occurred within Kamishak Bay to the west and north of Augustine Island. Sea otter densities were relatively low north of Kamishak Bay. The total abundance estimate for eastern LCI (part of the southcentral Alaska stock) was 9,152 (SE = 1,020) sea otters. The highest densities of sea otters in eastern LCI were found along the north shore of Kachemak Bay and in Port Graham. We also found large numbers of sea otters along the eastern shore of LCI between Anchor Point and Clam Gulch. We recommend conducting a sea otter distribution survey in September, prior to the appearance of sea ice, and again during winter to examine potential seasonal shifts in sea otter distributions in LCI.

INTRODUCTION Intensive commercial hunting in the early 1900s led to the extirpation of northern sea otters from most areas of Cook Inlet, Alaska (Schneider 1976). Commercial sea otter hunting ended with the passage of the International Fur Seal Treaty in 1911, and sea otter numbers in LCI have subsequently rebounded. Lensink (1960) postulated that a small remnant population of otters may have persisted through the era of commercial hunting in the remote waters of Kamishak Bay on the west side of LCI (Fig.1). Sea otters reportedly began to re-colonize the east side of LCI in the 1960s, possibly moving into the region from the outer coast of the Kenai Peninsula (Schneider 1976). By the mid-1970s, sea otters had begun to expand their range into Kachemak Bay (Schneider 1976, Fig. 1). A 2002 aerial survey of eastern LCI found sea otters distributed throughout Kachemak Bay and scattered individuals as far north as Clam Gulch (Bodkin et al. 2003, Fig. 1).

The expansive breadth of Cook Inlet is considered a natural boundary separating the southcentral Alaska and southwest Alaska stocks of northern sea otters (Gorbics and Bodkin 2001). Sea otters in eastern LCI are considered part of the southcentral Alaska stock which includes the coastal waters of eastern Cook Inlet, the Kenai Peninsula coast, and Prince William Sound. The most recent Marine Mammal Protection Act Stock Assessment Report considers this sea otter stock to be stable or growing (USFWS, 2014). Sea otters occupying western LCI are considered

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part of the southwest Alaska stock, which extends from western LCI to the western end of the Aleutian archipelago. The southwest Alaska stock experienced a precipitous decline in abundance during the late 1990s and early 2000s (Doroff et al. 2003, Estes et al. 2005) and was listed as threatened under the Endangered Species Act (ESA) in 2005. However, the decline in sea otter abundance across the range of the southwest Alaska stock was not uniform. The most significant declines were reported in the western (Aleutian) portion of the range, while other areas within the southwest stock boundaries, such as the Kodiak archipelago and Katmai coast were relatively unaffected (USFWS 2013). The prevailing hypothesis is that killer whale (Orcinus orca) predation may have been a primary driver in the decline of sea otters along the Aleutian chain (Estes et al. 1998, USFWS 2013). Sea otters in western LCI were last surveyed in 2002 and their current status and trend is unknown.

Emerging conservation and management concerns for sea otters in LCI include an increase in disease related mortality (Gill 2006) and potential impacts associated with expanding oil and gas exploration and resource development. Information concerning recent trends in abundance is needed to evaluate the impacts of disease related mortality on sea otter populations in LCI. Information on sea otter distributions is needed to help mitigate potential interactions and impacts associated with oil and gas exploration and development in the region. Here we present results of aerial surveys for sea otters in LCI in May, 2017.

METHODS Our study area encompassed both the western and eastern portions of LCI. The Western LCI Survey Unit extends from Cape Douglas at the mouth of Cook Inlet up the western shore of Cook Inlet to Tuxedni Bay, including the waters of Kamishak Bay (Fig.1). The Eastern LCI Survey Unit extended from Cape Elizabeth to Clam Gulch on the eastern shore of LCI (Fig.1). We also defined a separate Kachemak Bay Survey Unit (a subunit of eastern LCI) to facilitate comparisons with previous aerial survey efforts for this region (Fig.1). We made a concerted effort to fly each Survey Unit continuously to minimize potential for double-counting individuals that moved across boundaries during surveys.

Survey methods followed protocols described in Bodkin and Udevitz (1999). Transect lines were flown at an altitude of approximately 300 feet (91 meters) and speed of approximately 70 knots (130 km/hr). The survey platform was a fixed-winged float plane (American Champion Scout) with tandem seating for a pilot and one observer. Survey protocols called for periodically conducting intensive search units (ISUs) within transects to estimate the proportion of sea otters not detected on strips. An ISU consisted of 5 concentric 400 m diameter circles flown within the survey strip, during which time any additional sea otters not observed on the initial strip count were recorded. For each survey replicate, strip counts were extrapolated for the area not surveyed and by the correction factor generated from ISUs to obtain an adjusted population size estimate. Other marine mammal sightings also were recorded opportunistically, however these

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species were often overlooked when sea otter densities were high and no effort was made to develop an abundance estimate for other species.

A series of replicate aerial surveys were flown over the LCI study area between the dates of May 4th–19th, 2017. Three replicate surveys were flown over the entire survey area; a fourth replicate was flown over the Kachemak Bay Survey Unit in an effort to improve the precision of the resulting abundance estimate for this region. Each replicate survey involved flying a series of parallel 400 m-wide strip transects oriented perpendicular to the coastline. Each survey replicate consisted of a random sample of all possible transects, with a different set of transects selected for each replicate.

For the Western and Eastern LCI Survey Units, transect lines extended out from shore to a water depth of 40 meters, an area defined by Bodkin and Udevitz (1999) as a high density stratum (Fig. 2). The distance between adjacent transects was set at 7 km thereby sampling approximately 5 percent of this habitat during each replicate survey. An area typically defined as a low density stratum (water depths 40–100 m; Bodkin and Udevitz 1999), was not surveyed in the Western and Eastern LCI Survey Units in 2017 due to safety concerns over flying a single engine aircraft at a low altitude so far from shore. Previous aerial survey efforts have found very few sea otters occupy these habitats in central Cook Inlet.

For the Kachemak Bay Survey Unit, the distance between adjacent transects was set at 4 km, thereby sampling approximately 10 percent of the survey area during each replicate survey. Although Kachemak Bay includes considerable amounts of habitat with water depths greater than 40 m, the entire area was treated as a high density stratum because large groups of otters were commonly spotted beyond the 40 m bathymetric contour in Kachemak Bay during prior aerial surveys (Fig. 3).

All sea otter sightings were digitized in ArcMap 10.4.1 (ESRI, Redlands, CA). Sea otter counts were converted to point themes with each point representing a count location. To depict the relative density of sea otters across LCI, points were combined across all Survey Units to account for the continuous distribution of sea otters across the study area. The kernel density function in ArcGIS (ESRI, Redlands CA) was used to calculate kernel density estimates (KDE) for each replicate survey. The KDE parameters were set to a 200 m pixel size and 7,500 m kernel smoothing radius to account for potential sea otter movements based on an approximation of sea otter home ranges from other areas (Tarjan and Tinker 2016). Once a rasterized KDE surface was created for each replicate survey, replicates were averaged together using the Map Algebra tool to calculate a mean sea otter density map. The averaged KDEs represent smoothed values of relative estimated sea otter density as number of otters per square kilometer.

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RESULTS

Western LCI Abundance estimates for three replicate surveys flown in the Western LCI Survey Unit (Fig. 1) ranged from 9,665 to 11,600 sea otters (Table 1). The mean estimate of the three replicate surveys (total abundance estimate for western LCI, southwest Alaska stock) was 10,737 (SE = 2,323). The average estimated density of sea otters in the Western LCI Survey Unit was 2.25 sea otters/km2; however, distributions were not uniform across this region. Most sightings occurred between Cape Douglas and Chinitna Bay (Fig. 4). Highest sea otter densities (up to 8 sea otter/km2) occurred within Kamishak Bay, to the west and north of Augustine Island (Fig. 5). Sea otters were relatively scarce north of Chinitna Bay, and no sea otters were observed north of Chisik Island (Fig. 4).

Eastern LCI Abundance estimates for two replicate surveys flown in the Eastern LCI Survey Unit (encompassing all high density habitat areas outside of Kachemak Bay, Fig. 2) were 3,800 and 2,528 otters respectively (mean = 3,164, SE = 685). A third replicate survey of the Eastern LCI Survey Unit contained only one usable ISU and was excluded from this abundance estimate (Table 2). The average estimated density of sea otters in the Eastern LCI Survey Unit was 1.89 sea otters/km2. Abundance estimates for four replicate surveys flown in the Kachemak Bay Survey Unit ranged from 4,856 to 7,422 otters, with a mean abundance estimate of 5,988 (SE = 756) (Table 3). The average density in Kachemak Bay was 6.37 sea otters/km2. The total abundance estimate for eastern LCI (Kachemak Bay and Eastern LCI Survey Units combined) was 9,152, SE = 1,020.

Although the highest densities of sea otters in eastern LCI were found along the north shore of Kachemak Bay and in Port Graham (Fig. 5), we found greater than expected numbers of sea otters along the eastern shore of LCI between Anchor Point and Clam Gulch (Fig. 4). We elected to fly an additional distribution survey along the eastern shore of LCI to approximate the northern extent of sea otter distribution up the eastern shore of Cook Inlet. The survey consisted of flying one coastal transect, approximately 500 m from and parallel to the shoreline at an altitude of 500 feet (152.4 m), between Homer and Kenai and a second strip, approximately 2 km further offshore on the return. We observed sea otters distributed along the eastern coastline of LCI to approximately 10 km south of Kenai (Fig. 6). A transect was also flown over the shallow habitats surrounding Kalgin Island, however no sea otters were sighted in this region. A distribution survey along the western shore of Cook Inlet was deemed unnecessary, as the northern edge of distribution appears to have been captured within the western LCI survey block.

Other Marine Mammal Sightings Other marine mammals observed during our surveys of LCI included: harbor seal (Phoca vitulina), Steller sea lion (Eumetopias jubatus), harbor porpoise (Phocoena phocoena),

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humpback whale (Megaptera novaeangliae), killer whale (Orcinus orca), and minke whale (Balaenotptera acutorostrata) (Fig. 7; Table 4). Harbor seals and harbor porpoises were distributed primarily in the western LCI survey unit (Fig. 7). It should be noted that the dearth of other marine mammal sightings in Kamishak Bay likely can be attributed to a focused effort on counting large numbers of sea otters.

DISCUSSION

Western LCI – Southwest Alaska Stock Historic information on sea otter distribution and abundance in western LCI is limited. Based on anecdotal reports from fishermen and biologists, Schneider (1976) estimated that there were between 500–1,000 sea otters in western LCI in the mid-1970s, with a core area of abundance centered near Augustine Island in Kamishak Bay. The first abundance survey for sea otters in western LCI occurred in 2002 generating an abundance estimate of 6,918 (SE = 368) (Bodkin et al. 2003). Our 2017 survey effort of this same region produced an abundance estimate of 10,737 (SE = 2,323) otters. Comparisons of these two point estimates suggest an average annual growth rate of approximately 3% over the past 15 years, although large overlapping confidence intervals preclude firm conclusions regarding population trend.

Notwithstanding the large variance associated with these abundance estimates, it does not appear that sea otter abundance in western LCI has declined appreciably since the early 2000’s as has been the case in other sub-regions of the ESA listed southwest Alaska Stock. LCI is geographically isolated from the Aleutian archipelago where the most significant population declines have been reported (USFWS 2013) and the western LCI population of sea otters appears to operate under different ecological conditions and demographic drivers.

Heatmaps created from the averaged KDEs showed stark patterns of distribution across the western LCI survey unit, and a broad range of densities. Sea otter densities were quite high to the west and north of Augustine Island, but extremely low to the north of Kamishak Bay (Fig. 5). It should be noted that although sea otters were primarily concentrated in offshore regions of Kamishak Bay during our May 2017 survey, recent environmental monitoring studies indicate that sea otters also use other parts of Kamishak Bay (Pebble Partnership 2011). Therefore, our heat map should not be interpreted as a representation of the full extent of useable sea otter habitat in this region.

Our 2017 survey effort of western LCI suggests that despite significant population growth over the past 40 years, there has been very little range expansion beyond Kamishak Bay. We are not aware of any physical or ecological features limiting sea otter distribution in western LCI to Kamishak Bay. Although winter sea ice has been described as a limiting factor restricting sea otter distributions in other parts of their range (Kenyon 1969), the sea ice in upper Cook Inlet is discontinuous, and sea otters are known to tolerate broken sea ice conditions in other regions (Schneider and Faro 1975). Little is known about the factors influencing the productivity of prey

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resources across western LCI, which likely responds to complex forcing from hydrology, oceanography, and sediment loading. While a recreational razor clam fishery persists on intertidal beaches of Western LCI to the north of Kamishak Bay, it is unknown to what degree sea otters prey upon razor clams, or what other invertebrate resources are available in subtidal zones. Given our lack of knowledge on the potential for seasonal movements of sea otters in this area, it is also possible that sea otters occupy these northerly areas of western LCI seasonally or will emigrate further north in the future.

Eastern LCI – Southcentral Alaska Stock Sea otters reportedly began re-colonizing the east side of LCI in the 1960s, establishing themselves first in Port Graham (Schneider 1976), and later, throughout Kachemak Bay (Bodkin et al. 2003, Gill et al. 2009). The first complete abundance survey for sea otters in Kachemak Bay was carried out in 2002, and abundance estimates for Kachemak Bay have increased substantially over the past 15 years (Table 5). Our 2017 estimate (5,988, SE = 756) was not appreciably different from results of the last (2012) survey (Table 5), suggesting that sea otters in Kachemak Bay may be approaching an equilibrium density. Because sea otter habitats and distributions in Kachemak Bay are contiguous with habitats in the Eastern LCI Survey Unit (Fig. 4), it is possible that reproductive rates within Kachemak Bay remain elevated and approximately equal to mortality plus net emigration rates to areas outside of the Bay.

We found large numbers of sea otters to the north of Kachemak Bay (Fig. 4). Although sea otters have been sighted in this region for many years (e.g. Schneider 1976, Bodkin et al. 2003) the number of sea otters occupying this region appears to have increased since the last survey in 2002. Gill et al. (2009) reported significant seasonal shifts in sea otter distributions within Kachemak Bay. They found sea otters were more broadly distributed across Kachemak Bay during the summer months and retreated to more sheltered regions of the Bay in winter. It is possible that the otters observed along the eastern shore of LCI during our May 2017 survey behave in a similar fashion and only occupy this region on a seasonal basis; however fall and winter distribution surveys are needed to evaluate this hypothesis.

In the early 2000’s, residents of Homer, Alaska began reporting increasing numbers of stranded sea otter carcasses along the southern shore of Kachemak Bay. In 2006, an Unusual Mortality Event (UME) was declared, triggering an investigation to determine the cause and significance of the mortalities. Investigators found that the most commonly diagnosed causes of death were pathological conditions associated with bacterial (Streptococcus spp.) infections (Gill 2006). Although the cause and etiology of strep related illness in eastern LCI remain unknown, the number of sea otters in eastern LCI appears to have grown significantly over the past 15 years (Table 5), suggesting that disease related mortality has not been a significant factor limiting population growth. As sea otter numbers increase, competition for resources, disease events, and other density dependent processes may play a bigger role in structuring abundance and distributions. Future monitoring of various metrics of population status are needed to better understand sea otter ecology in Kachemak Bay. For example, observations of foraging sea otters

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can be used to estimate energy intake rates, an indicator of population status relative to carrying capacity (Monson and Bowen 2015, Tinker 2015, Coletti et al. 2016).

In June 2017, the Bureau of Ocean Energy Management held a federal lease sale (Cook Inlet Oil & Gas Lease Sale 244) offering 224 blocks in LCI for leasing. Exploration activities are expected to occur in the summer of 2019. The lease sale area overlaps with considerable swaths of high density sea otter habitat in both the eastern and western sectors of LCI (Fig. 4, Fig. 5). Our survey results suggest that interactions with sea otters during exploration activities are most likely to occur in lease sale blocks situated near Kamishak Bay and along the eastern shore of LCI. It should be noted that our density maps are based upon sea otter distributions observed during our May 2017 survey, and that seasonal shifts in sea otter distributions are likely to occur. For example, a series of wildlife surveys conducted in winter (November-February) 2004–2006, noted large concentrations of sea otters in Iliamna and Iniskin Bays to the northwest of Kamishak Bay (Pebble Partnership 2011), while relatively few sea otters were observed in this region during our survey. Therefore, these density maps are unlikely to represent the full extent of useable sea otter habitat across the study area.

Recommendations for Future Studies Cook Inlet poses a unique set of logistical and safety related challenges for any field effort to estimate sea otter abundance. Given that sea otters are spread throughout a vast expanse of open water, exposed to strong winds and tidal currents, often tens of kilometers from shore, the sea conditions need to be almost perfect in order for: 1) sea otters to be sighted, and 2) a single engine float-equipped aircraft to land safely in the event of an emergency. In our experience, nearly perfect weather conditions are uncommon in Cook Inlet. We recommend future survey efforts consider the potential advantages of having observers survey from a twin-engine aircraft or explore the use of a camera-equipped aircraft (manned or unmanned) flown at higher altitudes.

Anecdotal reports indicate potential for seasonal shifts in sea otter distribution in LCI, possibly in response to winter storms or sea ice. We recommend conducting a distribution survey in September, prior to the appearance of sea ice in Cook Inlet, and again during winter to evaluate seasonal shifts in distributions. Studies of distributional shifts could also be used to evaluate the influence of physical drivers like strong tidal currents or seasonal sea ice cover and extent on sea otter habitat use in LCI.

In Kachemak Bay, sea otters may be approaching an equilibrium density; however future studies addressing population status with multiple metrics are needed to confirm this hypothesis. Given the lack of basic knowledge regarding sea otter food resources in LCI, we recommend foraging studies to investigate the prey types being consumed and the size of prey consumed. In addition to identifying important sea otter foraging areas and prey species, these studies can provide

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energy intake rates, a metric which has proven useful in gauging sea otter population status in many other regions (Tinker 2015, Coletti et al. 2016).

LCI is an area ill-suited to the use of traditional VHF telemetry methods. To learn more about the demographics of sea otters here, we recommend exploring the use of newer technology which has the potential to reveal patterns in movements, reproduction, survival, and mortality without the need for attaching and monitoring VHF tracking devices. The life history transmitter, an implanted device developed to study juvenile Steller sea lion survival rates and causes of mortality through the transmission of sensor data to satellites post-mortem (Horning and Mellish 2009), has recently been modified to also record reproductive events and has been deployed successfully in harbor seal pups (Horning et al. 2017) and sea otters.

ACKNOWLEDGMENTS We thank Taj Shoemaker of North River Air for his excellent piloting skills during the course of the survey. Thanks also to Jose de Creeft of Northwind Aviation for establishing fuel caches in support of our survey effort of western LCI. We are also grateful to Dan Esler, Kimberly Klein and James MacCracken for their thoughtful and constructive review of this report.

The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

LITERATURE CITED Bodkin, J.L., D.H. Monson, and G.G. Esslinger. 2003. Results of the 2002 Kenai Peninsula and

Lower Cook Inlet Aerial Sea Otter Survey. Unpublished U.S. Geological Survey Report.

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.

Coletti, H.A., J.L. Bodkin, D.H. Monson, B.E. Ballachey, T.A. Dean. 2016. Detecting and inferring cause of change in an Alaska nearshore marine ecosystem. Ecosphere 7(10):1-20.

Doroff, A. M., J. A. Estes, M. T. Tinker, D. M. Burn, T. J. Evans. 2003. Sea otter population declines in the Aleutian archipelago. J. Mammalogy. 84(1):55-64.

Estes, J.A., M.T. Tinker, A.M. Doroff, and D.M. Burn. 2005. Continuing sea otter population declines in the Aleutian archipelago. Marine Mammal Science. 21:169-172.

Estes, J.A., M.T. Tinker, T.M. Williams, and D.F. Doak. 1998. Killer whale predation on sea otters linking oceanic and nearshore ecosystems. Science 282:473-476.

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Gill, V.A., A.M. Doroff, and D. Burn. 2009. Aerial Surveys of Sea Otters Enhydra lutris in Kachemak, Alaska 2008. U.S. Fish and Wildlife Service report for Army Corps of Engineers. MIPR # WC1JUW80880784. 21pp. Available at: https://www.fws.gov/alaska/fisheries/mmm/seaotters/pdf/kachemak_bay_2008_survey_report.pdf

Gill, V.A. 2006. Marine Mammal Unusual Mortality event initiation protocol for northern sea otters. Unpublished USFWS report. 11pp. Available at: https://www.fws.gov/alaska/fisheries/mmm/seaotters/UME_Initiation_Request.pdf

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.

Horning, M., M. Haulena, J.F. Rosenberg, and C. Nordstrom. 2017. Intraperitoneal implantation of life-long telemetry transmitters in three rehabilitated harbor seal pups. BMC Veterinary Research 13:1-14.

Horning, M. and J. A. Mellish. 2009. Spatially explicit detection of predation on individual pinnipeds from implanted post-mortem satellite data transmitters. Endangered Species Research 10:135-143.Kenyon, K.W. 1969. The sea otter in the eastern Pacific Ocean. North American Fauna 68:1-352.

Lensink, C.J. 1960. Status and distribution of sea otters in Alaska. Journal of Mammalogy 41(2):172-182.

Monson, D.H. and L. Bowen. 2015. Evaluating the Status of Individuals and Populations: Advantages of Multiple Approaches and Time Scales. Pages 121-158. in S.E. Larson, J.L. Bodkin and G.R. VanBlaricom editors. Sea Otter Conservation. Elsevier, Amsterdam Netherlands.

Pebble Partnership 2011. Pebble Project Environmental Baseline Studies, 2004-2008, Technical Summary. Chapter 44. Marine Wildlife - Cook Inlet Drainages. Available at: http://www.arlis.org/docs/vol2/Pebble/2004-2008%20EBD/CH44%20Marine%20Wildlife%20CI.pdf

Riedman. M. L. and J. A. Estes. 1990. The sea otter (Enhydra lutris): behavior, ecology, and natural history. U.S. Fish and Wildlife Service Biological Report 90(14).

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.

Schneider, K.B. and J.B. Faro 1975. Effects of sea ice on sea otters (Enhydra lutris). Journal of Mammalogy 56:91-101.

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Tarjan, L.M. and M.T. Tinker. 2016. Permissible home range estimation (PHRE) in restricted habitats: a new algorithm and an evaluation for sea otters. PLoS ONE. 11(3): e0150547.doi:10.1371/journal.pone.0150547.

Tinker, M. T. 2015. The use of quantitative models in sea otter conservation. Pages 257-300 in S.E. Larson, J.L. Bodkin and G.R. VanBlaricom editors. Sea Otter Conservation. Elsevier, Amsterdam Netherlands.

U.S. Fish and Wildlife Service. 2013. Southwest Alaska Distinct Population Segment of the Northern Sea Otter (Enhydra lutris kenyoni) - Recovery Plan. U.S. Fish and Wildlife Service, Region 7, Alaska. 171pp.

US Fish and Wildlife Service. 2014. Northern sea otter (Enhydra lutris kenyoni): Southcentral Alaska Stock - Stock Assessment Report. Available at: https://www.fws.gov/alaska/fisheries/mmm/stock/stock.htm

Williams, P.J., M. B. Hooten, G. G. Esslinger, J. N. Womble, J. L. Bodkin, and M. R. Bower. In review. The rise of an apex predator following deglaciation.

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Table 1. Sea otter abundance estimates based on aerial surveys of Western Lower Cook Inlet, May, 2017.

Number of Transect Area Stratum Number

Proportional

Replicate Group sea otters spacing sampled area of Correction Abundance Standard standard Density survey size counted (km) (km2) (km2) ISUs factor estimate error error (otters/km2)a

1 Small 341 7 223 4,762 9 1.44 10,455 4,511 0.43 2.20

Large 23 7 223 4,762 - - 491 475 0.97 0.10

Total

364

10,945 4,536 0.41 2.30

2 Small 336 7 272 4,762 5 1.67 9,798 3,995 0.41 2.06

Large 103 7 272 4,762 - - 1,802 1,117 0.62 0.38

Total

439

11,600 4,148 0.36 2.44

3 Small 257 7 263 4,762 9 1.43 6,672 2,347 0.35 1.40

Large 165 7 263 4,762 - - 2,993 2,302 0.77 0.63

Total

422

9,665 3,287 0.34 2.03

10,737 2,323 0.22 2.25 a Sea otter density estimates include areas of unoccupied habitat.

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Table 2. Sea Otter abundance estimates based on aerial surveys of Eastern Lower Cook Inlet, May 2017.

Number of Transect Area Stratum Number

Proportional

Replicate Group sea otters spacing sampled area of Correction Abundance Standard standard Density survey size counted (km) (km2) (km2) ISUs factor estimate error error (otters/km2)

1 Small 65 7 96 1,677 1a 1.25 1,417 - - 0.84

2 Small 130 7 89 1,677 9 1.55 3,800 1,189 0.31 2.27

3 Small 134 7 94 1,677 6 1.05 2,528 679 0.27 1.51

3,164 685 0.22 1.89 a The highlighted replicate survey was not used in calculating mean sea otter abundance for eastern Cook Inlet because there was only one usable ISU.

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Table 3. Sea Otter abundance estimates based on aerial surveys of Kachemak Bay, May 2017.

Number of Transect Area Stratum Number

Proportional

Replicate Group sea otters spacing sampled area of Correction Abundance Standard standard Density survey size counted (km) (km2) (km2) ISUs factor estimate error error (otters/km2)

1 Small 232 4 95 940 8 1.60 3,684 878 0.24 3.92

Large 135 4 95 940 - - 1,340 842 0.63 1.43

Total

367

5,024 1,217 0.24 5.34

2 Small 340 4 89 940 12 1.27 4,530 1,253 0.28 4.82

Large 31 4 89 940 - - 326 315 0.97 0.35

Total

371

4,856 1,292 0.27 5.17

3 Small 313 4 83 940 10 1.93 6,791 1,625 0.24 7.22

Large 56 4 83 940 - - 631 551 0.87 0.67

Total

369

7,422 1,716 0.23 7.90

4 Small 413 4 89 940 10 1.45 6,343 1,727 0.27 6.75

Large 29 4 89 940 - - 307 283 0.92 0.33

Total

442

6,650 1,750 0.26 7.07

5,988 756 0.13 6.37

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Table 4. Opportunistic sightings of other marine mammal species during aerial surveys of Lower Cook Inlet, May 2017.

Survey Unit Replicate

Harbor Seal Phoca vitulina

Steller sea lions Eumetopias

jubatus

Humpback whale Megaptera

novaeangliae

Killer whale Orcinus

orca

Harbor porpoise

Phocoena phocoena

Minke whale Balaenotptera acutorostrata

Western LCI 1 11 3 3 0 28 0

2 22 3 1 2 71 0

3 201 1 1 0 122 0

x̅ 78 2 2 1 74 0 Eastern LCI 1 0 0 0 8 0 0

2 0 0 1 0 0 1

3 0 0 2 0 0 1

x̅ 0 0 1 3 0 1 Kachemak Bay 1 1 0 0 0 0 0

2 2 0 0 0 0 1

3 0 0 0 0 0 1

4 1 0 0 0 0 0

x̅ 1 0 0 0 0 1

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Table 5. Estimates of sea otter abundance in Kachemak Bay.

Year

Survey area

(km2) Abundance

estimate Standard

error Density

(otters/km2) Source

2002 1,590 912 368 0.57 USGS unpublished data

2007 1,590 3,724 979 2.34 USGS unpublished data

2008 965 3,596 802 3.72 Gill et al. (2009)

2012 1,001 5,926 672 5.92 USGS unpublished data

2017 940 5,988 756 6.37 This study

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Figure 1. Map of Lower Cook Inlet showing the boundaries of 3 survey units that were surveyed in May 2017 to estimate sea otter abundance.

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Figure 2. Map showing transects from 3 replicate aerial surveys flown to estimate sea otter abundance in Lower Cook Inlet, May 2017.

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Figure 3. Map showing transects from 4 replicate aerial surveys flown to estimate sea otter abundance in Kachemak Bay, May 2017.

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Figure 4. Distribution of sea otters sighted during replicate aerial surveys in Lower Cook Inlet, May 2017.

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Figure 5. Mean relative densities of sea otters encountered during replicate aerial surveys in Lower Cook Inlet, May 2017.

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Figure 6. Map showing sea otters sighted during a coastal survey along the eastern shore of Lower Cook Inlet on 19 May, 2017 to determine the northern extent of their range.

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Figure 7. Other marine mammals sighted in Lower Cook Inlet during sea otter aerial surveys in May 2017.

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