Document ID: chunk:federal_register_of_legislation:F2024L00930:reg:2:p7
Version: federal_register_of_legislation:F2024L00930
Segment Type: reg
Provision Reference: reg 2 (pt 7/48)
Character Range: 81160–84016

activities may impose further demands on the whale's limited energy stores and affect the body condition of lactating females and the reproductive viability of offspring. There is a significant energetic cost to the mother in the late stages of gestation (i.e. last trimester), and calf growth rate has been observed at the Head of the Bight and found to be dependent on the maternal body size and condition of the mother (Christiansen et al. 2018, Christiansen et al. 2022). The proportion and duration of time calves spend nursing increases with increased calf size throughout the breeding season, and lactating females can lose up to 25 percent of their initial body volume (Christiansen et al. 2018, Nielsen et al. 2019). Behavioural disturbance from human activities can also incur energetic costs to southern right whales, associated with changes in more energetically expensive behaviours. For example, southern right whales off the coast of Argentina were found to decrease their proportion of time spent resting and increase the proportion of time spent travelling in the presence of tourism swim with interactions, with mothers and calves being most sensitive to the presence of swimmers (Lundquist et al. 2013).
Southern right whales have a single calf on average every three years, with a maximum of up to five-year intervals. Post-partum ovulation does not typically occur in right whales and no published record exists of a female right whale giving birth in consecutive years. Calving intervals shorter than three years are considered rare but have been recorded in instances where a mother loses a calf, and calving intervals observed to be greater than five years are not considered likely but rather a consequence of missed intervening calving's (Bannister 1990, Cooke et al. 2001, Brandão et al. 2011, Charlton et al. 2022). Based on the predominant 3-year calving cycle, females form breeding cohorts, in which it is assumed that the year following calving is a rest year followed then by a mating year (Burnell 2001, Cooke et al. 2001, Brandão et al. 2018). This assumption is supported by observations that identify that reproductively mature females that calve in Australian waters are almost never recorded on the Australian coast between calving years (Bannister 1990, Burnell & Bryden 1997). At the Head of Bight, the mean calving interval for breeding females during 2015-2021 has been observed to increase from three to four years (Charlton et al. 2022). The factors associated with this increase are unknown but may have been influenced by factors such as climate change (Pirzl 2008)Pirzl et al. 2009).

     2.4.3      Mortality and survivorship
Reliable estimates of mortality rates are generally unknown for Australian southern right whales, although concerted effort to compile stranding records in South Australia has been