Abstract
AbstractThe migrations of humpback whales on the African east coast were monitored between 1988 and 1991 at Cape Vidal, South Africa. Shore‐based surveys of the northward migration were undertaken each winter, and a survey of the southward migration was undertaken in 1990, from an approximately 60‐m‐high vantage point on a headland. Independent‐observer surveys were carried out in both 1990 (22 d) and 1991 (51 d) to determine the proportion of the population within the survey area that were being missed by observers using a single mark‐release model. Results were stratified into three distance intervals from the shore and three sighting condition intervals; there were constant sighting probabilities from the south tower under different sighting conditions, while those from the north tower increased slightly as sighting conditions improved. Sighting probabilities from both towers were highest in the intermediate distance interval and decreased in both the inshore and offshore regions.
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