Esslinger, George G. (ORCID:0000-0002-3459-0083) Weitzman, Benjamin P. (ORCID:0000-0001-7559-3654) Robinson, Brian H. (ORCID:0000-0001-8588-7162) 20220127 tabular digital data Anchorage, Alaska U.S. Geological Survey, Alaska Science Center Suggested Citation: Esslinger, G.G., Weitzman, B.P., and Robinson, B.H., 2021, Sea otter aerial survey data from lower Cook Inlet, Alaska, 2017: U.S. Geological Survey data release, https://doi.org/10.5066/P9Q4DA3T https://doi.org/10.5066/P9Q4DA3T This dataset consists of three tables related to abundance and distribution of northern sea otters (Enhydra lutris kenyoni) in lower Cook Inlet, Alaska, based on data collected during a series of population-wide aerial surveys in May 2017. The dataset consists of: (1) sea otter counts along strip transects, (2) sea otter counts in Intensive Search Unit (ISU) within the transects, and (3) Transect coordinates. These data were collected to assess changes in the abundance and distribution of sea otters in the waters throughout lower Cook Inlet, Alaska in 2017. Sea otters are a keystone predator, well known for structuring the nearshore marine ecosystem through their consumption of invertebrate prey. To estimate sea otter abundance, the U.S. Geological Survey has designed and conducted multiple aerial surveys in Alaska using a method that adjusts for detection bias. The surveys provide data and a population estimate that federal and state management agencies use for decision making and planning additional research. 20170525 20170530 observed Complete None planned Nearshore waters in lower Cook Inlet, Alaska -154.50 -150.50 60.50 58.83 USGS Metadata Identifier USGS:ASC434 ISO 19115 Topic Category Biota Environment NASA GCMD Earth Science Keyword Thesaurus Animals/vertebrates Mammals Carnivores Otters USGS CSA Biocomplexity Thesaurus Aerial surveys Population density Abundance (organisms) Marine mammals Spatial distribution USGS Thesaurus Wildlife Ecology Population dynamics Ecosystem monitoring None Sea otters Enhydra lutris kenyoni Northern sea otters Geographic Names Information System (GNIS) Alaska Cook Inlet None Mammals Carnivore ITIS Integrated Taxonomic Information System Unknown online database online ITIS-North America Taxonomic details retrieved October 12, 2021, from the Integrated Taxonomic Information System online database https://www.itis.gov https://www.itis.gov Species were identified by skilled observers in the field based on general appearance. Taxonomy is complete for all samples. No voucher specimens were collected. Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Mammalia Subclass Theria Infraclass Eutheria Order Carnivora Suborder Caniformia Family Mustelidae Subfamily Lutrinae Genus Enhydra Species Enhydra lutris TSN: 180547 Subspecies Enhydra lutris kenyoni TSN: 622038 No access constraints. No use constraints. These data are marked with a Creative Common CC0 1.0 Universal License and are in the public domain. It is requested that this USGS data release be cited for any subsequent publications that reference or utilize these data. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. U.S. Geological Survey, Alaska Science Center Mailing and Physical

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Anchorage Alaska 99508 USA 907-786-7000 gs-ak_asc_datamanagers@usgs.gov Sea otter group locations from the 2017 aerial surveys were mapped during the survey and later digitized by Benjamin Weitzman. This survey was funded by the United States Fish and Wildlife Service. Esslinger, G.G. Robinson, B.H. Monson, D.H. Taylor, R.L. Esler, D. Weitzman, B.P Garlich-Miller, J. 2021 document U.S. Geological Survey Open-File Report 2021–1122 online U.S. Geological Survey Esslinger, G.G., Robinson, B.H., Monson, D.H., Taylor, R.L., Esler, D., Weitzman, B.P., and Garlich-Miller, J., 2021, Abundance and distribution of sea otters (Enhydra lutris) in the southcentral Alaska stock, 2014, 2017, and 2019: U.S. Geological Survey Open-File Report 2021–1122, 19 p., https://doi.org/10.3133/ofr20211122. https://doi.org/10.3133/ofr20211122 Prior to conducting an aerial survey, each observer underwent a training program that involved comparing aerial counts with ground-based counts and was able to consistently detect at least 90 percent of the sea otters within Intensive Search Units (ISU). Adult sea otters were distinguished from pups when possible and are identified as separate fields in the data. However, small pups may not have been detected and large pups were sometimes indistinguishable from adults. Therefore, pup counts should be regarded as minimum counts. Groups greater than 20 sea otters typically contain active individuals which make it more challenging to obtain accurate counts so photographs are occasionally taken and used to check these counts. Sea otters hauled out on land are typically more difficult to sight but were counted when observed. During the aerial survey, sea otter locations were mapped on paper maps and later digitized into ArcMap (ESRI). Mapped otter locations are approximate and, especially where sea otters were observed in offshore waters devoid of landmarks, may be off by several hundreds of meters. We carried out a standard quality assurance quality control (QAQC) procedure for this data. Entries were checked against field data sheets and data standards for accuracy, missing values, outliers, and inconsistencies. When applicable, data were checked against validated ranges. Attribute values fall within expected ranges. Null values are represented with "." This survey was designed to cover all habitat in lower Cook Inlet, Alaska where sea otters were known to occur in 2017. All planned survey transects are included in the file "seaOtter_aerialSurveyTransectCoords_LCI_esslinger_2017.csv" (included with this data package). However, transects or portions of transects may not have been surveyed if the survey crew encountered: (1) hazardous conditions such as downdrafts, (2) land due to low tide, or (3) sensitive areas such as sea lion rookeries. Transects that were not surveyed are not included in the file "seaOtter_aerialSurveyTransectCounts_LCI_esslinger_2017.csv" Transect coordinate accuracy was not tested quantitatively. Many high density transects intersect with the shoreline on at least one end and the vast majority of these planned intersection points seemed to align well with observed locations during the surveys. However, planned shoreline intersection points may not match ground conditions due to factors such as tidal state (especially on gradually sloping beaches), navigation error, and inaccuracies in the shoreline maps used to design the surveys, mostly resulting from changes in the shoreline from ongoing natural processes such as erosion, sedimentation, or isostatic rebound. Mapped otter locations are approximate and, especially where sea otters were observed in offshore waters devoid of landmarks, may be off by several hundreds of meters. FIELD: Sea otter habitat was divided into two strata, high density and low density, based on distance from shore and water depth. The high density stratum extended from shore to 400 m seaward or to the 40 m depth contour, whichever was greater. The low density stratum extended from the high density line to a line 2 km offshore or to the 100 m depth contour, whichever was greater. The low density stratum was not surveyed in 2017 due to safety concerns over flying a single engine aircraft at low altitude so far from shore. Bays and inlets less than 6 km wide were sampled entirely, regardless of depth. For each aerial survey, the pilot flew an airplane at an airspeed of 29 meters per second and an altitude of 91 meters over pre-determined transects while an observer searched on one side of the plane and recorded sea otter group counts and locations. All sea otter groups observed within 400 meters of each transect were recorded. A group of sea otters was defined as 1 or more sea otters spaced less than 3 otter lengths apart. Adult sea otters were distinguished from pups when possible and identified as separate fields in the data. When large groups of sea otters (≥20) were sighted on transect, they were circled until a complete count was made. Sea otters sighted beyond the confines of designated transect swaths were also counted and mapped, time permitting. We used Intensive Search Units (ISU) to estimate the number of sea otters in small groups (<20) not detected along transect swaths (e.g., due to diving behavior or the presence of kelp canopy). ISUs are 400 meter diameter circles, along the transects, that were searched intensively by periodically flying 5 concentric circles around an initiating group. These ISUs were distributed throughout the survey area in an attempt to accurately represent the full range of observation conditions encountered during the survey. See Esslinger et al. (2022) for additional details of field sampling (cross-referenced publication). Unknown Aerial survey observational data were collected by experienced field observers. Field data were recorded on paper field data sheets for electronic entry at a later time. Unknown Quality Assurance/Quality Control (QAQC): Field data sheets QAQC: the aerial observer and then a data manager review the data sheets for missing, illegible, or confusing entries and correct any issues. Spreadsheet QAQC: tabular sea otter counts are checked against maps showing sea otter group counts and locations, and also checked row by row/cell by cell for accuracy and completeness. Basic descriptive statistics were run on the count data to look for outliers or values inconsistent with the protocol. If outliers or inconsistent values were found, corrections were applied to the data. The descriptive statistics are not part of the dataset, but are used for QAQC. Digitized sea otter sightings were checked by ensuring values entered in the point attribute table matched values recorded by the aerial observer on paper maps, transect count data sheets, and ISU count data sheets. Unknown Transect start and end coordinates are unique for each Survey_Unit, Year, and Replicate combination in the strip transect count data. Sea otter group coordinates are included for each group in the strip transect count data. Point 0.0001 0.0001 Decimal degrees World Geodetic System of 1984 World Geodetic System of 1984 6378137 298.257223563 seaOtter_aerialSurveyTransectCounts_LCI_esslinger_2017.csv Each record (row) represents one group of observed sea otters along a transect. In the case of no otters observed, each row represents one transect. Presented in a Comma Separated Value (CSV) formatted table. Author defined SURVEY_UNIT Up to four character code for the area covered by the survey. Author defined WLCI The WLCI unit comprises Western Lower Cook Inlet. Author defined ELCI The WLCI unit comprises Eastern Lower Cook Inlet. Author defined KBAY The KBAY unit comprises Kachemak Bay. Author defined YEAR Year of survey; this attribute is preferable to the "date" field for sorting transects within a year. Author defined 2017 Survey conducted in 2017. Author defined DATE Date sea otter group was observed, year month day (YYYYMMDD). A "." indicates the date was not recorded by the observer because the record is from an off transect sighting. Author defined 20170504 20170518 Date (YYYYMMDD) OBSERVER First initial and first seven letters of last name of aerial observer. Author defined BWEITZMA Benjamin P Weitzman Author defined REPLICATE Replicate number; used to designate the order surveys were flown when more than one survey was flown in a given year. Author defined 1 4 Replicate number STRATUM Designates the stratum each transect falls within, high density (H). The low density stratum was not surveyed in 2017. Sea otter groups sighted off-transect have a "." in this column. Author defined H High density Author defined . Sea otter sighting was not on a transect, so no stratum is designated. Author defined TRANSECT Sequential integer number assigned to each transect within a survey when survey is designed. Transect number; designates which transect the sea otter group was observed on, if any. Sea otter groups sighted off-transect have a "0" in this column. Author defined 0 76 Integer GROUP Sequential integer number assigned to each group of sea otters along a transect. Group number; used to designate the order sea otter groups were sighted on a given transect. "0" is assigned for otters observed off transect or when no otters are observed along a transect. Author defined 0 77 Integer ADULTS Number of adult sea otters observed in a group. Author defined 0 250 Integer PUPS Number of sea otter pups observed in a group. Author defined 0 12 Integer ISU Intensive Search Unit; indicates an ISU number if a group of sea otters occurred within an ISU. A "0" in this field indicates no ISUs were flown on that transect. An ISU is a 400m diameter circle, located within the transect strip, where the survey plane flew 5 concentric circles to search for sea otters that were not sighted (for example, because they were diving or camouflaged by kelp). These data were later used to estimate the proportion of sea otters not detected on transects and adjust the overall abundance estimate for each survey accordingly. Sea otter groups sighted during the strip count portion of the ISU are indicated with an ISU number in the file "seaOtter_aerialSurveyTransectCounts_LCI_esslinger_2017.csv" and also entered into the file "seaOtter_aerialSurveyISUCounts_LCI_esslinger_2017" (both files included in this data package), linked by the Survey Unit, Year, Replicate, and ISU number. Author defined 0 20 Assigned unit number CC Complete Count; designates whether a group of sea otters was circled until it was completely counted. Author defined 0 No, group was not circled for complete count. Author defined 1 Yes, group was circled for complete count. Author defined GROUP_X Sea otter group longitude in decimal degrees, WGS84. A null value "." indicates when there were no otters observed. Author defined -154.0847 -151.0227 Decimal degrees (WGS84) GROUP_Y Sea otter group latitude in decimal degrees, WGS84. A null value "." indicates when there were no otters observed. Author defined 58.8708 60.2461 Decimal degrees (WGS84) seaOtter_aerialSurveyISUCounts_LCI_esslinger_2017.csv Each record (row) represents one ISU conducted along a transect. Presented in a Comma Separated Value (CSV) formatted table. Author defined SURVEY_UNIT Up to four character code for the area covered by the survey. Author defined WLCI The WLCI unit comprises Western Lower Cook Inlet. Author defined ELCI The WLCI unit comprises Eastern Lower Cook Inlet. Author defined KBAY The KBAY unit comprises Kachemak Bay. Author defined YEAR Year of survey; this attribute is preferable to the "date" field for sorting transects within a year. Author defined 2017 Survey conducted in 2017. Author defined DATE Date sea otter group was observed, year month day (YYYYMMDD). A "." indicates the date was not recorded by the observer because the record is from an off transect sighting. Author defined 20170504 20170517 Date (YYYYMMDD) OBSERVER First initial and first seven letters of last name of aerial observer. Author defined BWEITZMA Benjamin P Weitzman Author defined REPLICATE Replicate number; used to designate the order surveys were flown when more than one survey was flown in a given year. Author defined 1 4 Replicate number STRATUM Designates the stratum each transect falls within, high density (H). The low density stratum was not surveyed in 2017. Sea otter groups sighted off-transect have a "." in this column. Author defined H High density Author defined ISU Intensive Search Unit; indicates the number of a particular ISU. Sequential integer number assigned to each ISU within a survey. An ISU is a 400m diameter circle, located within the transect strip, where the survey plane flew 5 concentric circles to search for sea otters that were not sighted (for example, because they were diving or camouflaged by kelp). These data were later used to estimate the proportion of sea otters not detected on transects and adjust the overall abundance estimate for each survey accordingly. Sea otter groups sighted during the strip count portion of the ISU are indicated with an ISU number in the file "seaOtter_aerialSurveyTransectCounts_LCI_esslinger_2017.csv" and also entered into the file "seaOtter_aerialSurveyISUCounts_LCI_esslinger_2017" (both files included in this data package), linked by the Survey Unit, Year, Replicate, and ISU number. Author defined 1 20 Assigned unit number TRANSECT Sequential integer number assigned to each transect within a survey when survey is designed. Transect number; designates which transect the sea otter group was observed on, if any. Sea otter groups sighted off-transect have a "0" in this column. Author defined 3 76 Integer GROUP Group number, sequential integer number used to designate the order sea otter groups were sighted in a given ISU. A group was defined as 1 or more sea otters spaced less than 3 otter lengths apart. Author defined 1 9 Integer STRIP_ADULTS Number of adult sea otters observed in a group while flying the strip count portion of an ISU. When the observer asked the pilot to initiate an ISU, the plane temporarily departed the transect flight path to circle the initiating sea otter group 5 times. Any adult sea otters sighted prior to the first quarter turn of the first circle are included in the "Strip_Adults" count. Author defined 0 17 Integer STRIP_PUPS Number of sea otter pups observed in a group while flying the strip count portion of an ISU. When the observer asked the pilot to initiate an ISU, the plane temporarily departed the transect flight path to circle the initiating sea otter group 5 times. Any sea otter pups sighted prior to the first quarter turn of the first circle are included in the "Strip_Pups" count. Author defined 0 4 Integer CIRCLE_ADULTS Number of adult sea otters observed in a group while flying the circle count portion of an ISU. When the observer asked the pilot to initiate an ISU, the plane temporarily departed the transect flight path to circle the initiating sea otter group 5 times. Any adult sea otters sighted after the first quarter turn of the first circle are included in the "Circle_Adults" count. Author defined 0 17 Integer CIRCLE_PUPS Number of sea otter pups observed in a group while flying the circle count portion of an ISU. When the observer asked the pilot to initiate an ISU, the plane temporarily departed the transect flight path to circle the initiating sea otter group 5 times. Any sea otter pups sighted after the first quarter turn of the first circle are included in the "Circle_Pups" count. Author defined 0 6 Integer BEHAVIOR Behavior is defined as "whatever the otter was doing before the plane arrived" and recorded for each group as either diving (D), non-diving (N), or hauled-out (H). A null value "." indicates the behavior was not recorded by the observer. Diving otters include any individuals that swim below the surface and out of view, whether traveling or foraging. If any individual(s) in a group are diving, the whole group is classified as diving. Non-diving otters are animals seen resting, interacting, swimming (but not diving), or hauled-out on land or ice. Author defined D Diving, out of view Author defined N Not Diving Author defined seaOtter_aerialSurveyTransectCoords_LCI_esslinger_2017.csv Each record (row) represents one transect endpoint, describing a pool of possible survey transects. Not all transects in this transect coordinate file were surveyed. Transects listed in the strip transect counts file were surveyed. Presented in a Comma Separated Value (CSV) formatted table. Author defined SURVEY_UNIT Up to four character code for the area covered by the survey. Author defined WLCI The WLCI unit comprises Western Lower Cook Inlet. Author defined ELCI The WLCI unit comprises Eastern Lower Cook Inlet. Author defined KBAY The KBAY unit comprises Kachemak Bay. Author defined YEAR Year of survey; this attribute is preferable to the "date" field for sorting transects within a year. Author defined 2017 Survey conducted in 2017. Author defined REPLICATE Replicate number; used to designate the order surveys were flown when more than one survey was flown in a given year. Author defined 1 4 Replicate number STRATUM Designates the stratum each transect falls within, high density (H). The low density stratum was not surveyed in 2017. Sea otter groups sighted off-transect have a "." in this column. Author defined H High density Author defined TRANSECT Sequential integer number assigned to each transect within a survey when survey is designed along with a letter indicating which end (E = east, W = west). For example, transect 1 in the otter data spreadsheets is designated here by endpoints 001E and 001W. Author defined 001 078 Integer X_COORDINATE Sea otter group longitude in decimal degrees, WGS84. Author defined -154.2496 -150.9067 Decimal degrees (WGS84) Y_COORDINATE Sea otter group latitude in decimal degrees, WGS84. Author defined 58.8690 60.2822 Decimal degrees (WGS84) The information contained in these datasets includes strip transect counts, ISU counts, and transect coordinates from sea otter aerial surveys conducted in lower Cook Inlet, Alaska. Author defined U.S. Geological Survey USGS ScienceBase Team Mailing and Physical

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Denver Colorado 80225 USA 1-888-275-8747 sciencebase@usgs.gov The U.S. Geological Survey, Alaska Science Center is the authoritative source of these data, distributed by ScienceBase (a USGS Trusted Digital Repository). Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data for other purposes or on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. CSV Tabular data in CSV format; FGDC metadata in XML and HTML formats. https://doi.org/10.5066/P9Q4DA3T None Gulf Watch Alaska Mailing and Physical

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Anchorage Alaska 99508 USA (907) 278-8012 https://gulfwatchalaska.org Gulf Watch Alaska is the long-term ecosystem monitoring program of the Exxon Valdez Oil Spill Trustee Council for the marine ecosystem affected by the 1989 oil spill. Gulf Watch Alaska is an alternative distributor of these data. The USGS Alaska Science Center is the authoritative source and distributor of these data. To facilitate discovery and access, the data are also available through Gulf Watch Alaska via the Alaska Ocean Observing System (AOOS) - Gulf of Alaska Data Portal. The USGS Alaska Science Center is not responsible for the accuracy, maintenance, or integrity of any alternative source of these data. CSV https://gulf-of-alaska.portal.aoos.org/#metadata/7867a791-8b05-4a8c-8065-eb6e1b425f5f/project/folder_metadata/39919016 None The Alaska Ocean Observing System (AOOS) - Gulf of Alaska Data Portal is accessible at: https://portal.aoos.org/gulf-of-alaska 20250411 U.S. Geological Survey, Alaska Science Center Mailing and Physical

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Anchorage Alaska 99508 USA 907-786-7000 gs-ak_asc_datamanagers@usgs.gov FGDC Biological Data Profile of the Content Standard for Digital Geospatial Metadata (CSDGM) FGDC-STD-001.1-1999