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SC/69A/SH/13
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Resource ID
20057
Access
Open
Document Number
SC/69A/SH/13
Full Title
Southern right whale (Eubalaena australis) residency, site fidelity and date of calving in South Australia (1991–2022)
Author
C.M. Charlton, R. Ward, B. O’Shannessy, F. Christiansen, A. Morrison, R.L. Brownell Jr, R.D. Mccauley And S.R. Burnell
Authors Summary
Residency, site fidelity and date of calving for southern right whales (Eubalaena australis) was assessed using 32 years of photo-identification mark-recapture data. Females with newborn calves spend up to four months residing in the wintering aggregation area, while unaccompanied adults are more transient with much shorter residency periods. The mean within-year residency of females with calves decreased across decades from 71 days (range 2–118) during 1992–1994 to 53 days (range 2–99) during 2016–2021. Mean residency for unaccompanied adults of 20 days (2–93) during 1992–1994 was recorded compared with 14 days (range 2-58) during 2016–2021. Site fidelity (individuals returning to the same site across years) was 58.4% of reproductive females (n = 524), compared with 92% reported for this population in the early 1990s (n = 61). Calving site fidelity was displayed for 44.7% (n = 524) of the total reproductive females observed, or 76.5% of the females that showed fidelity to the site (n = 234). Females returned to the study site to calve up to 11 times while the mean number of calves recorded for all reproductive females was 3 (SD = 1.96). A third of the reproductive females were observed in non-calving years. Site fidelity was 21% of non-calving females, sighted on average 1.47 times (SD=1.13, range 1-13) at HOB. Results highlight that inter-seasonal movement across the core use area in Australia is likely and an updated Australian-wide assessment is needed. The timing for calving for females that arrived pregnant at the site was consistent across three decades at HOB. The mean date of calving was 24 July (SD = 14.6). The HOB dataset provides the only known aged animals in Australia with evidence of natal site fidelity (n = 24).
Publisher
IWC
Publication Year
2023
Abstract
Residency, site fidelity and date of calving for southern right whales (Eubalaena australis) was assessed using 32 years of photo-identification mark-recapture data. Shore based count and photo-identification studies were undertaken annually at a significant reproductive area for southern right whales, at the Head of the Great Australia Bight (HOB), South Australia, between 1991 and 2022. Females with newborn calves spend up to four months residing in the wintering aggregation area, while unaccompanied adults are more transient with much shorter residency periods. The mean within-year residency of females with calves decreased across decades from 71 days (range 2–118) during 1992–1994 to 53 days (range 2–99) during 2016–2021. Mean residency for unaccompanied adults of 20 days (2–93) during 1992–1994 was recorded compared with 14 days (range 2-58) during 2016–2021. Site fidelity (individuals returning to the same site across years) was 58.4% of reproductive females (n = 524), compared with 92% reported for this population in the early 1990s (n = 61). Calving site fidelity was displayed for 44.7% (n = 524) of the total reproductive females observed, or 76.5% of the females that showed fidelity to the site (n = 234). Females returned to the study site to calve up to 11 times while the mean number of calves recorded for all reproductive females was 3 (SD = 1.96). Australian wintering grounds are clearly important for reproductive females and unaccompanied adults. A third of the reproductive females were observed in non-calving years. Site fidelity was 21% of non-calving females, sighted on average 1.47 times (SD=1.13, range 1-13) at HOB. Results highlight that inter-seasonal movement across the core use area in Australia is likely and an updated Australian-wide assessment is needed. The timing for calving for females that arrived pregnant at the site was consistent across three decades at HOB. The mean date of calving was 24 July (SD = 14.6). The HOB dataset provides the only known aged animals in Australia with evidence of natal site fidelity (n = 24). The probability of calves being resighted at HOB was greater six years after birth, supporting the theory that calves disperse to other areas and return to their site of birth at sexual maturity. Results highlight the importance of wintering aggregation areas and coastal connective habitat for behaviours critical to survival. As southern right whales recover from whaling and populations grow, habitat dispersal and increased inter and intra-seasonal movement into and out of primary reproductive areas has occurred. Conspecific attraction and spatial pressures may enhance movement out of the area and subsequently reduce the residency periods as population size continues to increase. Ongoing research into population demographics, coastal movement and connectivity are a national priority in Australia. Increased legislative protection across the marine park network in the coastal waters of Australia is needed for the management and recovery of the endangered southern right whale in Australia. This study highlights the importance of reproductive areas and the need to protect coastal habitats for their survival and recovery.