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

Abstract

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.

Southern right whales (Eubalaena australis) return to a former wintering calving ground: Fowlers Bay, South Australia

“…At Fowlers Bay, the aerial transect was undertaken as part of the longer leg of the aerial surveys from Head of Bight to Ceduna. Because mean calving SRW occupancy periods between 40 and 71 d were recorded at Head of Bight (Burnell 2001, Charlton 2017, and whales are known to depart Head of Bight in September/October (Charlton et al 2019), female and calf pair sightings during the aerial surveys in this study were assumed to have selected Fowlers Bay as their calving or nursing habitat for the season. Unaccompanied adults are highly transient within season, so the aerial surveys captured a snapshot of information on habitats used by unaccompanied adults.…”

“…Despite almost a century of protection since 1935, SRW long term, annual monitoring has been restricted to areas where the largest remnant populations exist (Burnell , Charlton et al . , Rowntree et al . , Bannister et al .…”

“…), spatial ecology (Pirzl ), and fine scale demographics and population trends at the primary aggregation area at Head of Bight (Burnell and Bryden , Burnell , Charlton ; Charlton et al . ), understanding the characteristics of SRW in small established and emerging aggregation areas is prioritized in the Commonwealth SRW Conservation Management Plan to (DSEWPaC ). Such knowledge is required for species conservation management and for setting of population recovery targets.…”

“…From 1993 to 2016 aerial surveys were undertaken annually between Cape Leeuwin, WA, and Ceduna, SA. While there is knowledge of the broad scale distribution and abundance trends (Bannister 2001(Bannister , 2010(Bannister , 2017Bannister et al 2011), spatial ecology (Pirzl 2008), and fine scale demographics and population trends at the primary aggregation area at Head of Bight (Burnell and Bryden 1997, Burnell 2001, Charlton 2017Charlton et al 2019), understanding the characteristics of SRW in small established and emerging aggregation areas is prioritized in the Commonwealth SRW Conservation Management Plan to (DSEWPaC 2012). Such knowledge is required for species conservation management and for setting of population recovery targets.…”

Calving rates, long-range movements and site fidelity of southern right whales (Eubalaena australis) in south-eastern Australia

“…Population demographics and life history parameters are fundamental to the assessment of population viability and rate of increase analyses (Brandão et al, 2011;Brandão et al, 2018;Cooke et al, 2001;Skalski et al, 2005;Zerbini et al, 2010). Population estimates and life-history parameters for the south-western subpopulation, such as calving interval, site fidelity, movement patterns and seasonality, have been quantified from cliff-based surveys and aerial surveys (Bannister, 2018;Burnell, 2001;Burnell, 2008;Charlton, 2017;Charlton et al, 2019a;Pirzl et al, 2009). However, comparative data on the south-eastern subpopulation are lacking.…”