Tampa Bay 1987-1994 Manatee Distribution Survey Observations

Aerial distribution surveys are used by marine mammal biologists from FWC and other agencies to determine the seasonal distribution of manatees. Most surveys are conducted from small, four-seat, high-winged airplanes (Cessna 172 or 182) flying at a height of 500-1000 ft at a speed of 70-90 kts. Small helicopters may be used instead of fixed wing aircraft in urban areas or where waters are particularly opaque and hovering may be required. Flights are usually three hours (west Tampa Bay) and four and half hours (east Tampa Bay) long and are most commonly flown every two weeks for five and half years. The surveys are designed to maximize the manatee counts by concentrating on shallow nearshore waters around the state where manatees and their primary food source, sea grasses, are located. Flight paths curve parallel to the shoreline, and the airplane circles when manatees are spotted until a count of the number of animals in each group is obtained. Offshore waters are usually not surveyed. Dolphin and sea turtle sightings are recorded opportunistically. All aerial data are recorded on paper maps and entered into a GIS shapefile for spatial analysis. GIS is a computer software system for representing data spatially and for conducting spatial analyses. Surveys of Tampa Bay were flown twice a month from November 1987 to May 1994. FWC staff members were observers for these flights. The survey area includes the largest estuary in Florida, which borders Pinellas, Hillsborough, and Manatee counties on Florida’s west coast. Tampa Bay consists of mostly shallow water (average 3m) with Egmont Channel (27m) and the main dredged shipping channels (13m). Five rivers enter the Bay: Hillsborough, Alafia, Little Manatee, Manatee, and Braden rivers. The area includes large expanses of seagrass in Boca Ciega Bay and Anna Maria Sound. Many undeveloped areas under state or federal management were part of the study area, including Egmont Key, Passage Key, and Pinellas national wildlife refuge.佛罗里达鱼类与野生动物保护委员会（FWC）及其他机构的海洋哺乳动物生物学家会开展航空分布调查，以确定海牛（manatee）的季节性分布情况。大部分调查会乘坐小型四座高翼飞机（赛斯纳172或182）开展，飞行高度为500至1000英尺，飞行速度为70至90节（kts）。在城市区域或水体透明度极低、需要悬停的场景中，可使用小型直升机替代固定翼飞机。飞行时长通常为3小时（坦帕湾西部）或4.5小时（坦帕湾东部），调查周期一般为5.5年，且每两周开展一次飞行。本次调查以最大化海牛统计数量为目标，重点覆盖全州范围内海牛及其主要食物来源海草（sea grass）栖息的浅海近岸水域。飞行轨迹呈与海岸线平行的曲线形态，当发现海牛时，飞机会盘旋直至完成对每一群海牛的个体计数。远海海域通常不在调查范围内。偶遇海豚与海龟时，会记录其观测信息。所有航空观测数据均会记录在纸质地图上，并录入地理信息系统（GIS）形状文件以开展空间分析。地理信息系统（GIS）是一种可对数据进行空间可视化并开展空间分析的计算机软件系统。1987年11月至1994年5月期间，坦帕湾的调查每月开展两次飞行观测，本次飞行观测的观察员均为FWC的工作人员。调查区域涵盖佛罗里达州最大的河口湾——坦帕湾，其位于佛罗里达西海岸，毗邻皮尼拉斯、希尔斯伯勒与马纳蒂县。坦帕湾以浅水环境为主（平均水深3米），仅埃格蒙特航道（水深27米）与主要疏浚航运航道（水深13米）为深水区。共有五条河流注入坦帕湾：希尔斯伯勒河、阿拉菲亚河、小马纳蒂河、马纳蒂河与布雷登河。该区域内的博卡谢加湾与安娜玛丽亚湾拥有大面积海草床。诸多由州级或联邦级管理的未开发区域均纳入本次研究范围，包括埃格蒙特基岛、帕萨奇基岛与皮尼拉斯国家野生动物保护区。