An update of the east Australian humpback whale population (E1) rate of increase

A six week land-based survey was conducted at Pt Lookout on the east coast of Australia, in June and July 2007. Over the peak four weeks of the northward migration, an average of 70.7 whales passed per 10h. This was compared with a similar metric from previous surveys at this site yielding a long-term rate of increase of 10.9% per annum (95% CI 10.5 – 11.4%), slightly higher than our previous estimate from a survey in 2004 (Noad et al., 2006). This indicates that the long-term rapid increase in the size of the east Australian population of humpback whales continues without any apparent slowing. Aerial surveys were also conducted concurrently with the land-based surveys during which 249 groups of humpbacks containing an estimated 399 whales were seen from the air. Analysis confirms that only about 3% of groups pass more than 10km of the headland which is consistent with Bryden’s (1985) estimates despite an approximately 15-fold increase in the population over this time. Further, the offshore distribution of whales was characterised with no significant difference being found between the patterns of distribution whether measured from land or air. Approximately 89% of groups passed within 5km of land and the mean distances offshore for both aerial and land-based surveys were less than 2.5km. This supports one of the key assumptions of the land-based counts, that they are not greatly affected by whales missed as a function of increasing distance offshore. An estimate of absolute abundance for 2007 was made by extrapolating from the 2004 absolute abundance estimate. Using the land-based correction factor for groups available but missed estimated in 2004, 2007 absolute abundance is estimated at 9,683 whales (95% CI 8,556 – 10,959)