Aerial Survey Counts of Harbor Seals in Lake Iliamna, Alaska, 1984-2013 (NCEI Accession 0123188)

This dataset provides counts of harbor seals from aerial surveys over Lake Iliamna, Alaska, USA. The data have been collated from three previously published sources (Mathisen and Kline 1992; Small 2001; ABR Inc. Environmental Research and Services 2011) and newly available data from the NOAA Alaska Fisheries Science Center and the Newhalen Tribal Council. The survey years range between 1984 and 2013. Counts are reported as summed totals across all identified waypoints in the lake for each survey date.

The NOAA National Marine Mammal Laboratory (NMML) (Alaska Fisheries Science Center, Seattle, Washington, USA) conducted aerial surveys of Iliamna Lake between 2008 and 2013. Surveys were conducted as part of annual harbor seal survey effort and in collaboration with local community participants and researchers at the University of Alaska. Surveys were flown using high wing, twin engine aircraft (Aero Commander 680, 690 or a de Havilland Twin Otter). Survey altitude was generally 330 m and at an aircraft speed of 120 kts. Surveys were performed seasonally for most years between 2008 and 2013. Surveys were timed so that one survey was conducted while the lake was mostly frozen (Late March/early April), one during pupping (mid July), and often several during the August molt, when the greatest number of seals typically haul out on shore. Surveys were flown, weather allowing, in the mid- to late-afternoon, when the number of seals hauled out was expected to be highest. Aircraft flight track was recorded by GPS and all seals sighted were digitally photographed using a high resolution digital SLR camera with a telephoto zoom lens (up to 400mm). Time, date, latitude, longitude, and altitude were automatically saved into the image metadata or georeferenced post survey using the GPS track and software.

The total number of seals hauled out were counted from the digital photographs and recorded for each identified site. Pups were determined by their smaller size, and close proximity (less than 1 body length; either nursing or laying right next) to a larger seal. Pups were no longer recorded beyond about mid-August when many have been weaned and cannot reliably be distinguished from other non-adult seals. In 2009, a collaborative effort between NMML and researchers from the Newhalen Tribal Council (Newhalen Tribal Council 2009) provided 10 additional surveys and similar techniques were used. The raw survey count data from these surveys was provided to NMML. Aerial surveys were authorized under a Marine Mammal Protection Act General Authorization (LOC No. 14590) issued to the NMML.

Between 2005 and 2007, ABR, Inc. Environmental Research and Services conducted a series of aerial surveys for harbor seals in Iliamna Lake (ABR Inc. Environmental Research and Services 2011). In addition, earlier counts from surveys conducted by ADFG (Small 2001) and a 1991 census by Mathisen and Kline (Mathisen and Kline 1992) were incorporated into the dataset to expand the historical reach. Geographic coordinates were provided (or, when not provided, determined based on descriptions or physical maps) for each survey site and these sites were compared and merged with locations identified by NMML. In some cases, sites in very close geographic proximity were combined into a single site.

The iliamna_totalcounts file provides counts (n=96) and observed weather conditions for each survey date. Both total number of adult seals (adulttotal) and total number of identified pups (puptotal) are provided when available. puptotal is recorded as NA when adults and pups were not distinguished. In these cases, the adulttotal value is presumed to include pups. In addition to the seal count information, each record includes observed weather variables (airtemp (in ranges of degrees F), windspeed (in ranges of miles per hour), winddirection (cardinal), and descriptive categories for skycondition and precip). The datetime values correspond to local Alaska time.

本数据集提供了美国阿拉斯加州伊利亚马纳湖（Lake Iliamna）上空航空调查所得的斑海豹（harbor seal）数量统计数据。数据整合自3项已发表的研究成果（Mathisen与Kline 1992；Small 2001；ABR公司环境研究与服务部2011），以及美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）阿拉斯加渔业科学中心与纽哈伦部落委员会（Newhalen Tribal Council）的最新公开数据。调查年份跨度为1984年至2013年，统计值为每次调查当日湖中所有已识别航点的海豹总数之和。

美国国家海洋哺乳动物实验室（National Marine Mammal Laboratory, NMML，隶属于美国华盛顿州西雅图市阿拉斯加渔业科学中心）于2008年至2013年间开展了伊利亚马纳湖的航空调查。该调查为年度斑海豹调查工作的一部分，由当地社区参与者与阿拉斯加大学的研究人员协作完成。调查使用上单翼双引擎飞机（机型为Aero Commander 680、690或德哈维兰双水獭（de Havilland Twin Otter））执行，飞行高度通常为330米，航速120节（kts）。2008年至2013年的多数年份均按季节开展调查：调查时间分别设置为湖面大部分封冻时段（3月末/4月初）、斑海豹产崽期（7月中旬），以及通常海豹上岸休憩数量最多的8月换毛期，该时段通常会开展多次调查。调查选择在午后中晚期进行，此时上岸休憩的海豹数量预计达到峰值，且仅在天气允许的情况下执行。飞行轨迹由全球定位系统（Global Positioning System, GPS）记录，所有目击到的海豹均使用搭载长焦变焦镜头（最大焦距400mm）的高分辨率数码单反相机进行数字化拍摄。拍摄时间、日期、纬度、经度与飞行高度会自动保存至图像元数据中，或在调查结束后通过GPS轨迹与配套软件完成地理配准。

研究人员从数字化照片中统计上岸海豹的总数量，并为每个已识别的栖息地记录统计结果。幼崽通过体型更小、与成年海豹距离极近（小于1倍体长，处于哺乳或紧贴成年海豹状态）来识别。8月中旬之后，多数幼崽已断奶，无法与其他非成年海豹可靠区分，因此不再单独记录幼崽数量。2009年，NMML与纽哈伦部落委员会的研究人员开展合作（纽哈伦部落委员会2009），新增10次调查并采用了相同的调查方法，该批次调查的原始统计数据已提交至NMML。本次航空调查依据授予NMML的《海洋哺乳动物保护法（Marine Mammal Protection Act）》通用授权（批准号LOC No.14590）实施。

2005年至2007年间，ABR公司环境研究与服务部针对伊利亚马纳湖的斑海豹开展了一系列航空调查（ABR公司环境研究与服务部2011）。此外，数据集还纳入了阿拉斯加鱼类与狩猎部（Alaska Department of Fish and Game, ADFG）于2001年开展的早期调查统计结果（Small 2001），以及Mathisen与Kline于1991年完成的普查数据（Mathisen与Kline 1992），以拓展数据集的历史时间跨度。每个调查站点均提供了地理坐标，若未提供坐标，则通过调查描述或实体地图确定其位置；这些站点与NMML识别的点位进行了比对合并，部分地理距离极近的站点会被整合为单个站点。

iliamna_totalcounts文件包含了96次调查的统计值（n=96）与每次调查当日记录的天气状况。若可区分，则同时提供成年海豹总数量（adulttotal）与已识别幼崽总数量（puptotal）；若未区分成年海豹与幼崽，则puptotal记为NA（缺失值），此时adulttotal默认包含幼崽数量。除海豹统计信息外，每条记录还包含观测到的气象变量：气温（airtemp，以华氏度区间表示）、风速（windspeed，以英里每小时区间表示）、风向（winddirection，以方位角表示），以及天空状况（skycondition）和降水（precip）的描述性分类。datetime字段对应阿拉斯加当地时间。