UC Santa Cruz

Baleen whale populations in the Southern Ocean are recovering after intense commercial whaling in the 20th century. Along the Western Antarctic Peninsula (WAP), this recovery is occurring in one of the planet's most rapidly changing marine ecosystems. Understanding how climate-driven changes influence the population dynamics of whales in this region is critical for understanding what conservation and management actions must be prioritized to maintain the structure and function of this marine ecosystem. This is even more important as this region has seen extraordinary increases in industrial krill fishery pressure, which overlaps in both time and space with whales foraging in this region, as well as increased human presence in the form of ecotourism. Thus, to begin understanding the dynamics of whale recovery under continued environmental change, we need to study these whales' demography and population dynamics. My dissertation aimed to examine and describe the demographics and population dynamics of two species of Southern Hemisphere baleen whales (Antarctic minke whales and Southern Hemisphere humpback whales) in the context of a rapidly changing ecosystem. To do this, I used one of the most extensive, non-lethal tissue archives of these two species, collected as part of the National Science Foundations (NSF) Palmer Station long-term ecological research (LTER) project. I found that on average, Antarctic minke whales reproduced each year and estimated that two-thirds of females along the WAP were sexually mature. More importantly, these data represent the first non-lethal approach to studying this species. Furthermore, I found that broad-scale environmental variation affecting krill abundance and availability along the WAP adversely impacted humpback whale pregnancy rates. This indicates that continued warming along the WAP that results in subsequent changes in the distribution and abundance of prey may adversely affect the recovery of this humpback whale population. Lastly, I found that blubber cortisol levels were not significantly different between male and female humpback whales but were significantly different across different demographic groups of females and across months. Blubber cortisol levels also significantly decreased in 2021, a year when human presence along the WAP was greatly reduced due to the COVID-19 pandemic. These findings provide a critical baseline of cortisol levels for whales in a rapidly changing region and show direct relationships between cortisol levels and human presence. These are some of the first non-lethal quantitative observations of the demography and population dynamics of recovering whale populations in the Antarctic and provide a critical reference point for future work as the Antarctic climate continues to change and populations continue to recover from whaling.