Spatial and temporal extinction dynamics in a freshwater cetacean

Abstract

Geographical range contraction is a fundamental ecological characteristic of species population decline, but relatively little investigation has been conducted into general trends in the dynamic properties of range collapse. The Yangtze River dolphin or baiji (Lipotes vexillifer), probably the first large mammal species to have become extinct in over 50 years, was believed to have experienced major range collapse during its decline through progressive large-scale range contraction and fragmentation. This range-collapse model is challenged by a new dataset of 406 baiji last-sighting records collected from across the baiji's historical range during an interview survey of Yangtze fishing communities. Although baiji regional abundance may have varied across its range, analyses of the extensive new sighting series provide comprehensive evidence that baiji population decline was not associated with any major contraction in geographical range across the middle -lower Yangtze drainage, even in the decade immediately before probable global extinction of the species. Extinction risk in baiji was therefore seemingly not related to evidence of range collapse. Baiji apparently underwent large-scale periodic and seasonal movements across their range, and we propose that range contraction and fragmentation may not be general biogeographic characteristics for declining populations of mobile species in connected landscapes.

Can local ecological knowledge be used to assess status and extinction drivers in a threatened freshwater cetacean?

“…Further interview data show that porpoises may undergo seasonal upstream-downstream movements, possibly in response to the annual high-low water cycle. Although mtDNA genetic structuring shown by porpoise samples from the middle-lower Yangtze has been interpreted to suggest these animals may not move far (Zheng et al, 2005), informant data have previously demonstrated that baiji formerly also made large-scale upstream-downstream movements (Zhang et al, 2003;Turvey et al, 2010b). Seasonal movements may also explain the slight spatial shift in peak porpoise abundance along the river shown between informant weekly sighting data and autumn 2006 boat-based survey data.…”

Population status and habitat occupancy of endangered river dolphins in the Karnali River system of Nepal during low water season

“…Loss of the Ganges river dolphin from Nepal would be disturbing considering the previous loss of the Yangtze river dolphin (Turvey et al . ). Predictions for loss of the Ganges River dolphin have been made previously.…”

At the Heart of the Industrial Boom: Australian Snubfin Dolphins in the Capricorn Coast, Queensland, Need Urgent Conservation Action

“…Moreover, the most cautionary example is that of the recent (functional) extinction of the Yangtze River dolphin ( Lipotes vexillifer ) [52], which represents the first known cetacean extinction in recent history.…”