Project Title: Abundance estimates of the east Australian humpback whale population
Chief Investigators: Dr Michael Noad and Dr Douglas Cato
This is the final report under the agreement between the Commonwealth and the University. The project has progressed largely as detailed in the original funding proposal attached to the funding agreement. Fieldwork, both land-based and aerial, proceeded with only minor delays and all of the anticipated data (except acoustic survey data) have been collected and analysed on time and within budget. The land-based data indicate that the long-term pattern of rapid increase in the size of the east Australian population of humpback whales continues without any apparent slowing. The average number of whales passing Point Lookout per 10h over the peak four weeks of the northward migration was 70.7 whales. When placed in the context of long-term trends, it slightly increases the long-term rate of population growth to 10.9% (95% CI 10.5-11.4%).
During the aerial surveys, 249 groups of humpbacks containing an estimated 399 whales were seen from the air. Extra transects were flown directly off Pt Lookout for matching with the land-based survey with 117 groups spotted from the air in this area. Analysis confirms that only about 3% of groups pass more than 10km of the headland which is consistent with Brydens (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 passing within 5km of land and mean distances offshore for both aerial and land-based surveys less than 2.5km. Matching groups seen from the air and land, however, revealed that 29.1? 6.1% of groups were missed from land. This is much higher than anticipated and requires further analysis.
Estimates of absolute abundance for 2007 were 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 8,740 10,729). Using the higher correction factor derived from the 2007 aerial surveys, 2007 absolute abundance is estimated at 12,599 whales (95% CI 9,874 16,076). Further analyses of existing data are required to resolve the discrepancies in the land-based and aerial/land estimates of groups missed. Also we recommend that the next survey at Pt Lookout adopt a triple-platform methodology including both land-based double counts and aerial surveys.
The only aspect of the project which has fallen behind schedule and remains incomplete is the acoustic survey component. The autonomous logger placed off Pt Lookout has not yet been recovered due to poor weather over the summer of 2007/08 restricting recovery opportunities and the inshore movement of the East Australian Current preventing safe recovery when the attempts have been possible. This component of the project, however, is part of a longer term study using acoustic recordings gathered over many years and the delayed recovery of the recorder should not greatly affect this longer term programme.
