Marine mammal diversity and spatio-temporal dynamics in a hyper-urbanised tropical environment

The mesoscale distribution of marine mammals remains obscure within Southeast Asia, where coastal spaces are subject to long-term, extensive, and ongoing anthropogenic encroachment. Consequently, many populations here face high extinction risks, especially where conservation management strategies are absent or misaligned. To address this issue, we conservatively curated marine mammal records along Singapore's hyper-urbanised waters from scientific and grey literature, natural history museum archives, and citizen science datasets. We present 124 validated, time-stamped, and georeferenced records of seven species from 1820 to 2024—a majority of which (87.9 %; n = 109) were Sousa chinensis , Dugong dugon , and Tursiops aduncus occurrences (in order of frequency). This dataset, which serves as the longest record of marine mammals in Singapore to date, was used to identify occurrence hotspots and evaluate their spatio-temporal dynamics using historical maps and remotely sensed data. Dugong dugon occurrences in Singapore were most commonly observed as single individual strandings along the Sungei Johor Estuary, where two international shipping channels meet. Along with declining reported pod sizes—most evidently over the past three decades—overlapping occurrence hotspots of Sousa chinensis and Tursiops aduncus were observed within the Southern Islands. Over the assessed period, Sousa chinensis occurred in areas more associated to anthropogenic activity, which are also farther from coastal habitats. Our results add to the growing body of knowledge on the continued use of anthropogenically impacted spaces by marine mammals and are utilised to provide key recommendations for conservation and research in Singapore. The findings also applicable for areas facing similar levels of anthropogenic stress, where small and elusive marine mammal populations persist.