Sex ratio, pregnancy status and blubber testosterone concentrations of humpback whales (Megaptera novaeangliae) on foraging grounds in the Southwestern Atlantic

Understanding the demography of animal populations is fundamental to conservation biology. Key parameters such as sex ratio and reproductive success are important contributors for assessing current population health, forecasting population trends, and assessing impacts of conservation management interventions (Mills 2007). For long-lived and slow-reproducing species such as baleen whales, small changes in reproductive parameters can strongly influence population trajectories (Caswell 2001; Heppell et al. 2000). Many baleen whale species and populations were heavily exploited during the 19th and 20th century whaling and are still recovering (Allison and Smith 2023; Jackson et al. 2020; Stewart et al. 2025). For exploited populations undergoing recovery, accurate demographic information is essential for assessing population status and informing management decisions.