Southern right whale (Eubalaena australis), seasonal abundance and distribution at Head of Bight, South Australia

Abstract

© 2019 John Wiley & Sons, Ltd.

Seasonal trends in the distribution and relative abundance of southern right whales (SRWs) Eubalaena australis, were assessed in Australia's largest calving aggregation ground at the Head of the Great Australian Bight, in the Commonwealth Marine Reserve, South Australia. Annual cliff-based surveys were undertaken between June and October from 1992 to 2016. SRWs were primarily distributed in a 15 km by 2 km area within the 10 m depth contour (with 95% of whale sightings made within a 10 km2 area). The distribution of SRWs at Head of Bight varied within an individual season but was consistent among the years. The composition of SRW sightings was 70% female–calf pairs and 30% unaccompanied whales. Peak abundance occurred between mid-July and end-August for female–calf pairs and unaccompanied whales (juveniles or adults not accompanied by a calf), earlier than previously reported. A mean of 16% (range 8–28%, SD = 6.5, 95% CI = 0.15) of calving females were present at the site in mid-June and a mean of 37% (range 13–61%, SD = 15.8, 95% CI = 0.37) remained at the site at the end of September. Based on nearest-neighbour distances of 150 m, the area occupied by 95% of SRWs at Head of Bight could reach carrying capacity at 68 female and calf pairs. Results suggest that the primary aggregation area at Head of Bight may have reached saturation capacity and that habitat expansion can be expected as the population increases. This study provides information on SRW seasonal trends in distribution and abundance, timing of arrival and departure from the site and peak abundance periods relevant to application to conservation and marine park management. As management requirements increase with a growing population, there is a need to complete an Australia-wide assessment of SRW connectivity and habitat expansion.