Foraging and feeding ecology of Platanista: an integrative review

Abstract

1.Limited visual perception in aquatic environments has driven the evolution of diverse sensory modalities in aquatic mammals. Dolphins largely use echolocation for prey capture in the face of limited visual and olfactory cues. Multiple foraging modes exist, although an understanding of how sensory systems are adapted to environmental and prey characteristics is limited. This is especially true for animals with extreme sensory specialisation, such as South Asian river dolphins of the genus Platanista. This taxon is effectively blind and retains plesiomorphic traits from its once-diverse ancestors. Distributed in murky rivers of the Indus-Ganga-Brahmaputra basins, it is thought to use mainly echolocation for feeding on fish and shrimp. 2. We hypothesised that foraging modes used by Platanista differ according to prey position in the water column (at the river surface, mid-column, and bottom) and are mediated by ecomorphology, acoustics, prey characteristics, and habitat features. 3. To test this, we combined a detailed review of the literature (anatomy-physiology-morphology studies, observations in captivity) with preliminary field observations and acoustics studies to investigate foraging mode selection. 4. Platanista displays peculiar foraging and feeding behaviours, including side swimming, rotational feeding, and grasp-suction feeding. Feeding is restricted to small prey with low body depth. At the river surface and bottom, echolocation-based foraging may not be efficient due to acoustic reflection or reverberation effects. 5. Platanista uses echolocation clicks to scan and detect prey at distances of about 20 m across the river mid-column, possibly switching to passive listening at the surface, and electroreception at the bottom, to maximise prey capture rate and feeding success. 6. Platanista is remarkable for its ability to persist in some of the most intensively used and abused river basins of the world. Using echolocation, electroreception, and passive listening might reduce overall foraging costs and contribute to the adaptability of the taxon.

Seasonal flow dynamics exacerbate overlap between artisanal fisheries and imperiled Ganges River dolphins

“…Specific fish sizes have been previously reported as GRD-preferred prey regardless of species 10 , 52 , 58 . We considered fish in the range of 3–15 cm total length as preferred fish size regardless of species.…”

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

“…Increasing pressure from artisanal fisheries heightens the potential for river dolphin and fisheries interactions, mainly through direct competition for certain fish size‐classes as well as habitat and diel activity overlap. Conflicts between Ganges dolphins and artisanal fishing increased dramatically in recent years across the GBMK Basin (Kelkar et al, ; Kelkar, Krishnaswamy, Choudhary, & Sutaria, ; Paudel, Levesque, Saavedra, Pita, & Pal, ). Although by‐catch data were not available for the Ganges dolphin, this is considered one of the prime consequences of the direct fisheries–dolphin interaction (Read, ), which further threatens their survivorship of the Ganges dolphins, especially young calves.…”

“…We found 85 publications comprised of journal articles (n = 61), review articles (n = 4), notes (n = 2), proceedings articles (n = 16), and book chapters (n = 2) related to the Ganges dolphin population (n = 20), biology (n = 12), ecology (n = 7), anthropogenic threats (n = 12), echolocation and communication (n = 14), phylogenetics (n = 6), evolution (n = 2), biochemistry (n = 8), anatomy (n = 3) and disease (n = 1). We did not find publications devoted to interactive evolutionary potential of the Ganges dolphin; however, two partially dealt with the integrative evolutionary potential of the Ganges dolphin (Kelkar et al, 2018;Smith & Reeves, 2012).…”

“…The few previous conservation studies of the Ganges dolphin examined habitat components (Khanal et al, ; Smith & Reeves, ), feeding and foraging behaviors (Kelkar et al, ), and flow regimes (Choudhary et al, ; Khanal et al, ). Critically, these previous efforts did not integrate ecological, demographic, and environmental factors that might accelerate extinction risk before genetic deterioration (Lande, ).…”

The range of atlanto‐occipital joint motion in cetaceans reflects their feeding behavior

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