Factors affecting the persistence of endangered Ganges River dolphins ( Platanista gangetica gangetica)

Abstract

The Ganges–Brahmaputra–Meghna and Karnaphuli (GBMK) River Basin in Nepal, India, and Bangladesh is among the world's most biodiverse river basins. However, human‐induced habitat modification processes threaten the ecological structure of this river basin. Among the GBMK’s diverse flora and fauna of this freshwater ecosystem, the endemic Ganges River dolphin ( Platanista gangetica gangetica; GRD) is one of the most charismatic species in this freshwater ecosystem. Though a >50% population size reduction has occurred since 1957, researchers and decision‐makers often overlook the persistence (or evolutionary potential) of this species in the highly fragmented GBMK. We define the evolutionary potential as the ability of species/populations to adapt in a changing environment by maintaining their genetic diversity. Here, we review how evolutionary trap mechanisms affect the dynamics and viability of the GRD (hereafter Ganges dolphin) populations after rapid declines in their population size and distribution. We detected six potential trap mechanisms that might affect the Ganges dolphin populations discretely or in combination: (a) habitat modification; (b) occurrence of finite and geographically restricted local populations; (c) ratio of effective to estimate population size; (d) increasing risk of inbreeding depression in genetically isolated groups; (e) at‐risk behavioral attributes; and (f) direct fisheries–dolphin interactions. Because evolutionary traps appear most significant during low water season, they adversely affect demographic parameters, which reduce evolutionary potential. These traps have already caused local extirpation events; therefore, we recommend translocation among populations, including restoring and preserving essential habitats as immediate conservation strategies. Integrative evolutionary potential information based on demographic, genetic, and environmental data is still lacking. Thus, we identify gaps in the knowledge and suggest integrative approaches to understand the future of Ganges dolphins in South Asian waterways.

Abstract

The Ganges–Brahmaputra–Meghna and Karnaphuli (GBMK) River Basin in Nepal, India, and Bangladesh is among the world's most biodiverse river basin. The endemic Ganges River dolphin ( Platanista gangetica gangetica; GRD) is one of the most charismatic species in this freshwater ecosystem, which lost 50% of its population size since the last decades. Here, we review how evolutionary trap mechanisms affect the dynamics and viability of this species after rapid declines in their population size. We detected six potential trap mechanisms representing demographics, genetics, environment, and behavioral factors and suggest integrative approaches to understand the future of GRD in South Asian waterways.