Abstract:

To continue an annual series of aerial surveys off the southern Australian coast between Cape Leeuwin WA and Ceduna SA since 1993, an aerial survey was undertaken as planned over six days, 2-6 September, 2015. For comparison with previous results, counts were obtained of 462 individuals including 97 calves of the year. From 3679 photographic images obtained, 377 have been selected for computer-assisted ‘matching’ with those (some 6600 images of 2175 individuals) already available in the catalogue, and 126 data sightings sheets have been added to the sightings database, currently totalling 3670 sightings sheets.

The 2015 counts were considerably lower than in recent years, particularly for cow calf pairs, which were the lowest recorded since 2007.

Regression analysis of log number against year for the period 1993-2015 gives increase rates, for all animals of 0.0563 (95% CI 0.0380, 0.0747) (exponential rate) or 5.79 (95% CI 3.87, 7.75) (percent), and for cow/calf pairs 0.0588 (0.0324, 0.0852) or 6.06 (3.29, 8.89) respectively.

Current population size, for this the ‘western’ Australian subpopulation, is estimated at 2266.

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