Variation in harbour seal counts obtained using aerial surveys
Variation in harbour seal counts obtained using aerial surveys
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DOI：
10.1017/s002531540999155x
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发表时间：
2010-12-01
影响因子：
1.2
通讯作者：
Boyd, Ian L.
中科院分区：
文献类型：
--
作者：
Cunningham, Louise;Baxter, John M.;Boyd, Ian L.
对斑海豹（Phoca vitulina）的空中调查通常是为了提供种群规模的指数。这可以通过设计或事后分析进行标准化，以减少日期、时间、潮汐和天气对海豹数量的影响。为了从这些数量中确定长期趋势，假设在调查期间，特定地点的海豹平均数量不变，调查窗口的开始和持续时间不因地点或年份而异。本研究使用了重复的陆基和航空调查相结合，以测试在调查期间的计数恒定的假设。这项研究的重点是苏格兰西北部斯凯岛周围的港口海豹数量。根据使用热成像的重复航空调查，这些计数的变异系数估计为15%。陆基计数用于检查协变量对海豹数量的影响，使用广义加法模型。这个网站的特定模型预测，目前的航空调查窗口在英国的斑海豹，这是一个为期三周的换羽期间，是大约一个星期太早，计数变化可以减少测量潮汐周期提前11/2小时。此外，幼犬期表现出更高（虽然更多的变量）丰富的拖出来的海豹比在换羽。
Aerial surveys of harbour seals (Phoca vitulina) are usually carried out to provide an index of population size. This can be normalized, either by design or by post-hoc analysis to reduce the effects that date, time of day, tide and weather might have on the number of seals counted. In order for long-term trends to be determined from these counts it is assumed that the mean number of seals at a particular site does not vary during the survey period, and that the start and duration of the survey window does not vary with location or between years. This study used a combination of repeat land-based and aerial surveys to test the assumption for constancy of counts during the survey period. The study focused on harbour seal abundance at haul-out sites around the Isle of Skye in north-west Scotland. The coefficient of variation in these counts was estimated to be 15%, based on repeat aerial surveys using thermal imaging. Land-based counts were used to examine the effect of covariates on seal numbers using generalized additive modelling. This site-specific model predicted that the current aerial survey window for harbour seals in the UK, which is a three-week period during the moult, is about a week too early and that count variation could be reduced by surveying 11/2 hours earlier in the tidal cycle. Furthermore, the pupping period showed even higher (though more variable) abundance of hauled out seals than during the moult.