title: Threshold of long-term survival of a coastal delphinid in anthropogenically degraded environment: Indo-Pacific humpback dolphins in Pearl River Delta.
abstract: Defining demographic and ecological threshold of population persistence can assist in informing conservation management. We undertook such analyses for the Indo-Pacific humpback dolphin (Sousa chinensis) in the Pearl River Delta (PRD) region, southeast China. We use adult survival estimates for assessments of population status and annual rate of change. Our estimates indicate that, given a stationary population structure and minimal risk scenario, ~2000 individuals (minimum viable population in carrying capacity, MVPk) can maintain the population persistence across 40 generations. However, under the current population trend (~2.5% decline/annum), the population is fast approaching its viability threshold and may soon face effects of demographic stochasticity. The population demographic trajectory and the minimum area of critical habitat (MACH) that could prevent stochastic extinction are both highly sensitive to fluctuations in adult survival. For a hypothetical stationary population, MACH should approximate 3000-km2. However, this estimate increases four-fold with a 5% increase of adult mortality and exceeds the size of PRD when calculated for the current population status. On the other hand, cumulatively all current MPAs within PRD fail to secure the minimum habitat requirement to accommodate sufficiently viable population size. Our findings indicate that the PRD population is deemed to become extinct unless effective conservation measures can rapidly reverse the current population trend.
authors.affiliation: The Swire Institute of Marine Science and School of Biological Sciences, Faculty of Science, The University of Hong Kong, Cape d'Aguilar, Shek O, Hong Kong.
authors.forename: Leszek
authors.initials: L
authors.lastname: Karczmarski
authors.affiliation: The Swire Institute of Marine Science and School of Biological Sciences, Faculty of Science, The University of Hong Kong, Cape d'Aguilar, Shek O, Hong Kong.
authors.forename: Shiang-Lin
authors.initials: SL
authors.lastname: Huang
authors.affiliation: The Swire Institute of Marine Science and School of Biological Sciences, Faculty of Science, The University of Hong Kong, Cape d'Aguilar, Shek O, Hong Kong.
authors.forename: Stephen C Y
authors.initials: SC
authors.lastname: Chan
mesh_terms: D063147:Animal Distribution; D000818:Animals; D002681:China; D003247:Conservation of Natural Resources; D004289:Dolphins / Q000502:physiology*; D056727:Endangered Species / Q000639:trends*; D011156:Population Density; D011157:Population Dynamics / Q000639:trends