Abundance of the endangered Indus River dolphin Platanista minor

Freshwater dolphins are among the world’s most endangered mammals, with all populations classified as Endangered or Critically Endangered on the IUCN Red List. The Indus River dolphin Platanista minor, functionally endemic to Pakistan, has one of the most restricted ranges of any cetacean and, due to fragmentation by irrigation dams, exists as 6 subpopulations. We estimated the abundance of the 3 largest subpopulations in 2011 and 2017 using Huggins conditional likelihood mark-recapture models applied to visual sightings from tandem survey vessels. Favourable survey conditions and the narrow river channel resulted in high detection rates: of 559 dolphin groups recorded across both years, 72.3% of groups and 83.3% of individuals were matched between vessels. The total species abundance was estimated at 1665 individuals in 2011 (CV = 17%, 95% CI = 1499-3017) and had increased to 1987 by 2017 (CV = 13%, 95% CI = 1886-3552)—a 19.4% rise over 6 yr. In 2017, subpopulation estimates were 188 (CV = 8%) between Chashma and Taunsa barrages, 660 (CV = 6%) between Taunsa and Guddu and 1139 (CV = 9%) between Guddu and Sukkur. Although abundance monitoring is resource intensive, even at 5 yr intervals, it is essential for assessing species status. The long-term dataset gained from continued multi-decade monitoring provides invaluable insight, with its value increasing over time. Given their continued isolation and vulnerability, sustained monitoring and conservation interventions remain critical to ensure the species’ long-term survival.