River Cetaceans and Habitat Change: Generalist Resilience or Specialist Vulnerability?

Table 2

Details on the conservation status, behavior, and ecology of riverine populations of the facultative freshwater cetaceans. Information for the Yangtze finless porpoise from [30, 31]; tucuxi from [32–34]; Irrawaddy dolphin from [2, 35–38]. VU: vulnerable.

Species/subspecies	IUCN Red List status and justification	Group sizes or aggregations	Seasonal movements	Habitat preferences	Observations of sociality	Prey
Yangtze finless porpoise	EN—Population <2,500 mature individuals with a continuing decline and all individuals in a single subpopulation.	3–6 but occasionally as many as 20 in the Yangtze	Indirect evidence from changes in density that some porpoises move upstream during the high-water season.	Nearshore waters in the Yangtze.	Little socializing observed on the surface. Chasing observed in captivity.	Opportunistic feeder on wide variety of demersal fishes, cephalopods, and crustaceans.
Amazon and Orinoco tucuxi	DD—Lack of basic information (e.g., abundance, population structure, bycatch rates).	Generally 1–6 with a mean in the Amazon of 3.3 and maximum of 30.	May enter lake systems during high water but generally avoids flooded forests.	Similar to boto, tucuxis show a distinct preference for river junctions.	Group feeding observed.	A wide variety of fishes (at least 28 species), mostly small schooling species.
Irrawaddy dolphin	VU—At least a 30% reduction in the rangewide population size over three generations (45–48 years) inferred from increasing bycatch and habitat degradation. Five geographically isolated populations (including three riverine) are CR.	2–6 but up to 15 when two or more groups come together.	Some evidence of range expansion into smaller tributaries during high-water season. Seasonal movements in response to changes in freshwater flow in the Sundarbans Delta. Apparent small home ranges and individual fidelity to confluences in the Mahakam River.	Deep pools of large rivers and nearshore marine environments (including appended lakes or lagoons) with freshwater inputs.	Fission-fusion group dynamics with frequent social interactions. Cooperative feeding, both intraspecific and with cast-net fishermen, reported in the Ayeyarwady River.	At least seven fishes (two Pangasiidae and five Cyprinidae) and various shrimps in the Mekong. Probably many more based on catches of cooperative fishermen in Ayeyarwady River.