Stephanie Plön

Sperm whales ( Physeter macrocephalus ) are predominantly oceanic cetaceans exhibiting marked habitat diversity, ranging from nomadic populations to resident units associated with small oceanic islands. Understanding spatial structure and population parameters at a regional scale is essential for effective conservation and management. The Mascarene region represents a critical yet understudied sperm whale habitat in the Western Indian Ocean. This study provides the first population assessment of sperm whales in the Mascarene region and of the resident subpopulation off Mauritius. A mark–recapture approach based on photo‐identification was applied over a 17‐year period (2008–2024). Results demonstrate the presence of female and immature sperm whale groups representing all three habitat specializations: nomadic, regional residents, and island specialists. The Mascarene population is estimated at approximately 144 individuals, including an average of 26 resident sperm whales off Mauritius. However, analyses reveal increased mortality in the 2020s, threatening regional population viability. Moreover, the resident subpopulation shows instability in age structure, with a decline in adult females that may lead to its collapse. Given the global rarity of this island‐associated ecotype, these trends may have significant ecological and socioeconomic implications, underscoring the need for urgent, targeted conservation measures in the region.

The striped dolphin, Stenella coeruleoalba , is an oceanic species found worldwide in tropical to warm‐temperate waters. Globally, populations are threatened through direct fishing, bycatch, and pollution. Little is known about the life history of this species in South African waters, and an understanding of basic life history parameters is critical for conservation and management. Age and growth were determined for 61 animals stranded along the southeast coast of South Africa between 1972 and 2012 by counting the number of growth layer groups (GLGs) in longitudinal tooth sections. A von Bertalanffy growth curve was fitted to the data, indicating that physical maturity was reached around 231 cm and 21 years in males and 224 cm and 18 years in females. Analyses of the gonads of 48 individuals showed that males reached sexual maturity between 8 and 12 years of age and between 209 and 224 cm total body length, while females reached sexual maturity between 7 and 8 years and between 213 and 216 cm total body length. Maximum age estimates were 21 years for males and 20.2 years for females. Overall, the life history of the species off southeastern South Africa is similar to that reported for populations elsewhere, with minor geographic variations.

Mammalian gut microbiomes are essential for supporting digestion, nutrient absorption and overall host health. While diet and phylogeny are the two main in

Marine mammals as indicators of Ocean Health provide a powerful narrative for inter-, multi- and transdisciplinary research. Collaborating researchers from the global north and south from various disciplines define and position OceanHealth as a transdisciplinary discourse among existing disciplines and propose a new solution-focused knowledge field, Ocean Health Science. This systemic approach advocates transformative thinking with the goal to heal and nurture our global Ocean and the potential for big science, encouraging the global community to take a shared stewardship responsibility.

The current state of marine mammal populations reflects increasing anthropogenic impacts on the global Ocean. Adopting a holistic approach towards marine mammal health, incorporating healthy individuals and healthy populations, these taxa present indicators of the health of the overall Ocean system. Their present deterioration at the animal, population and ecosystem level has implications for human health and the global system. In the Anthropocene, multiple planetary boundaries have already been exceeded, and quiet tipping points in the Ocean may present further uncertainties. Long and short-term monitoring of marine mammal health in the holistic sense is urgently required to assist in evaluating and reversing the impact on Ocean Health and aid in climate change mitigation.

Sirenia , an iconic marine taxon with a tropical and subtropical worldwide distribution, face an uncertain future. All species are designated ‘Vulnerable’ to extinction by the IUCN. Nonetheless, a comprehensive understanding of geographic structuring across the global range is lacking, impeding our ability to highlight particularly vulnerable populations for conservation priority. Here, we use ancient DNA to investigate dugong ( Dugong dugon ) population structure, analysing 56 mitogenomes from specimens comprising the known historical range. Our results reveal geographically structured and distinct monophyletic clades characterized by contrasting evolutionary histories. We observe deep-rooted and divergent lineages in the East (Indo-Pacific) and obtain new evidence for the relatively recent dispersal of dugongs into the western Indian Ocean. All populations are significantly differentiated from each other with western populations having approximately 10-fold lower levels of genetic variation than eastern Indo-Pacific populations. Additionally, we find a significant temporal loss of genetic diversity in western Indian Ocean dugongs since the mid-twentieth century, as well as a decline in population size beginning approximately 1000 years ago. Our results add to the growing body of evidence that dugong populations are becoming ever more susceptible to ongoing human action and global climate change.