UC Santa Cruz

Using the IUCN Red List, we identified a total of 1256 freshwater fish species (sharks not included) across all categories that occur in Indonesia, with 553 being endemic to the archipelago. Of all freshwater fish species, 212 (16.9%) were classified as Threatened (Critically Endangered, Endangered, or Vulnerable) and 257 (21%) were Data Deficient. Of endemic freshwater fish species, 189 (34.2%) were Threatened. We found the major drivers of threat included habitat destruction, exploitation, pollution, and invasive species. We found that across the major Indonesian islands, Papua, Sumatra, and Kalimantan islands maintained the largest number of threatened endemic freshwater fish. To help guide conservation efforts for highly threatened (Critically Endangered and Endangered) endemic Indonesian freshwater fish, we calculated a Threatened Species Index (TSI) based on extinction probability, irreplaceability, and evolutionary distinctiveness. We found the Mbuta Rainbowfish (Pelangia mbutaensis) (TS Score: 23.34) and Vogelkop Blue-Eye (Pseudomugil reticulatus) (TS Score: 12.18) to have the largest TS scores. Additionally, we calculated a Site Prioritization Index (SPI) to identify water bodies critical for highly threatened endemic fish that also contained a threatening nonnative invasive fish as potential candidates for invasive eradication. Of the 47 water bodies meeting our criteria, we identified Lakes Matano (SI = 327.58), Lake Mahalona (SI = 327.57), and Lake Towuti (SI = 327.56) in Sulawesi as significant conservation sites based on the top 3 highest SI scores, emphasizing the importance of targeted efforts. Despite challenges, such as data limitations, our approach provides a replicable framework that can be applicable globally.