The cost of reproduction is a key parameter determining a species' life history strategy. Despite exhibiting some of the fastest offspring growth rates among mammals, the cost of reproduction in baleen whales is largely unknown since standard field metabolic techniques cannot be applied. We quantified the cost of reproduction for southern right whales Eubalaena australis over a 3 mo breeding season. We did this by determining the relationship between calf growth rate and maternal rate of loss in energy reserves, using repeated measurements of body volume obtained from un manned aerial vehicle photogrammetry. We recorded 1118 body volume estimates from 40 female and calf pairs over 40 to 89 d. Calves grew at a rate of 3.2 cm d −1 (SD = 0.45) in body length and 0.081 m 3 d −1 (SD = 0.011) in body volume, while females decreased in volume at a rate of 0.126 m 3 d −1 (SD = 0.036). The average volume conversion efficiency from female to calf was 68% (SD = 16.91). Calf growth rate was positively related to the rate of loss in maternal body volume, suggesting that maternal volume loss is proportional to the energy investment into her calf. Maternal in vestment was determined by her body size and condition, with longer and more rotund females investing more volume into their calves compared to shorter and leaner females. Lactating females lost on average 25% of their initial body volume over the 3 mo breeding season. This study demonstrates the considerable energetic cost that females face during the lactation period, and highlights the importance of sufficient maternal energy reserves for reproduction in this capital breeding species.

The duration and timing of coastal residence of individually identified southern right whales at a principal aggregation area on the southern Australian coast differed markedly between females with calves and unaccompanied whales. The mean residence period of females that calved within the aggregation area was 70.9 days, with mean residence mid‐points of 20 August in 1993 and 22 August in 1994. In contrast, unaccompanied adults remained resident for an average of only 20.4 days with mean residence mid‐points of 27 July and 11 August in 1993 and 1994, respectively. Whales have been sighted at this aggregation area from mid May to late October (approx. 160 days), although the effective calving season (95‐100% of calves born) lasted only 88 days in 1993 and 96 days in 1994. The mean birth date based on first sighting with neonatal calf, and corrected for sightability bias, was 15 July in 1993 and 17 July in 1994, with 100% of calves born before 31 August 1993 and 23 September 1994. The time between birth and dispersal from the aggregation area, at or just prior to the commencement of the southward migration, was highly variable. Calves bom before the mean calving date averaged 80 days within the aggregation area, twice as long as those born after the mean (40 days). The large number of calves estimated to be less than 14 days old at first sighting, combined with the sighting of 26 pregnant females prior to parturition, suggests the majority of births occurred within, or very near to, the aggregation area.

Between 1991 and 1997 right whales were studied on their wintering grounds on the southern coastline of Australia, predominantly at theHead of the Great Australian Bight, where over 350 individuals have been identified. The observed mean inter-calf interval for females was3.33±0.10 years (±SE, n = 57) at the Head of the Bight and 3.64±0.13 years (±SE, n = 117) in the wider Australian population. Wheninter-calf intervals of six or more years were excluded, the mean intervals became 3.28±0.09 years (±SE, n = 56) and 3.28±0.06 years (±SE,n = 107), respectively. Inter-calf intervals of two years were recorded following the early death of a neonate on two separate occasions andthe implications of these ‘shortened’ intervals and of calvings that were not observed are discussed. The mean age at which yearlings wereobserved to be fully weaned was calculated to be 365±8 days (±SE, n = 18) from the estimated birth dates of individual calves andsubsequent associations, or lack of them, between the yearlings and their cows the following year. A total of 108 movements greater than200km in length were made by individual whales. The mean within-year movement was 730±84 km, made over 34±4 days (±SE, n = 18),whilst the mean between-year movement was 1,036±45km (±SE, n = 87), made over a mean interval of 3.3±0.3 years (±SE, n = 90). Thenumber and direction of coastal movements observed suggest that the right whales off southern Australia comprise a single populationwhich may undertake an almost circular, anti-clockwise migration to the south of the Australian continent. A significantly greaterproportion of females displayed a level of between-year fidelity to the Head of the Bight aggregation area (92%, n = 61) than did males(68%, n = 19) or whales of unknown sex (63%, n = 8).

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Animal body size and growth patterns play important roles in shaping the life history of species. Baleen whales include the largest animals on the planet, with somatic growth costs expected to be substantial. We used unmanned aerial vehicle photogrammetry and long-term individual sighting histories from photo identification (1991-2019) to estimate the cost of somatic growth for southern right whales (SRWs) Eubalaena australis. A Richards length-at-age growth model was developed, based on 161 calves, 20 yearlings, 1 juvenile and 23 adults, ranging in age from newborn to 27 yr. Predicted lengths were 4.7 m at birth, 12.5 m at minimum age of first parturition (6 yr) and an asymptotic length of 14.3 m. A volume-at-age curve was estimated from the body volume versus length relationship, and converted to a mass-at-age curve, using data on body tissue composition of North Pacific right whales E. japonica (n = 13). The energetic cost of growth was estimated using published estimates of tissue lipid and protein concentrations. The cost of growth for SRWs (in MJ d-1) was 2112 at birth, 544 at 4 mo, 314 at 1 yr (~weaning age), 108 at 5 yr (minimum age of sexual maturity), 51.5 at 10 yr and 5.2 at 30 yr. The cumulative cost to age 30 was 764.3 GJ, but varied widely (458-995 GJ) depending on the tissue energy content. Our estimates represent a healthy SRW population, and provide a baseline to investigate individual and population level impacts of anthropogenic disturbance (including climate change).