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SC/69B/SH/14
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Resource ID
22156
Access
Open
Document Number
SC/69B/SH/14
Full Title
Preliminary demographic estimates for southern right whales off Australia using the common model and comparison to the South African population
Author
A. Brandao, A. Ross-Gillespie, C. Charlton And D.S. Butterworth
Authors Summary
To come
Publisher
IWC
Publication Year
2024
Abstract
The Common demographic model is applied to the photo-identification data for southern right whales in Australian waters. Given problems with estimating some model parameters because of the scarcity of data, the Base case Common model for the Australian right whale population considers the parameters Sj, ?, and to be fixed to their values for the Base case Delta-loop model for southern right whales off South Africa (Brand?o et al., 2023), while the probabilities PyC are fixed to the average of their estimated values for the model without time-variation in other parameters. For the time-variant Base case model, the number of parous females in 2018 is estimated to be 850, the total population (including males and calves) 2 821, and the annual population growth rate at 5.6%. Comparing estimates of key demographic parameters for populations in Australia and South Africa indicates that the age at which 50% of the female population has reached the age of first parturition (am ) is much lower for the Australian population (4.6 years) than for that of South Africa (8.1 to 8.5 years). However, this difference might be due to the limited number of female calf sighting histories available in the Australian data, as these data inform the estimation of the maturity ogive. The annual population growth rates for parous females are very similar, with a slightly larger growth rate estimated by the South African Base case Delta-loop model (6.5%) compared to the 5.6% for the Australian population. The predicted average apparent calving intervals for the two populations are similar, the Australian population being slightly larger (4.6 years) than the South African one (around 4.0 years) and both being larger than previous estimates for the species. Estimating demographic parameters in this comparative common model framework is essential for undertaking a species assessment for the southern right whale and investigating changes to apparent mean calving intervals and growth rates over time.