Abundance of irrawaddy dolphins (Orcaella brevirostris) and Ganges River dolphins (Platanista gangetica gangetica) estimated using concurrent counts made by independent teams in waterways of the sundarbans mangrove forest in Bangladesh

Brian D. Smith*, Gill Braulik, Samantha Strindberg, Benazir Ahmed, Rubaiyat Mansur

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

55 Citations (Scopus)

Abstract

Independent observer teams made concurrent counts of Irrawaddy dolphins Orcaella brevirostris and Ganges River dolphins Platanista gangetica gangetica in mangrove channels of the Sundarbans Delta in Bangladesh. These counts were corrected for missed groups using mark-recapture models. For Irrawaddy dolphins, a stratified Lincoln-Petersen model, which incorporated group size and sighting conditions as covariates, and a Huggins conditional likelihood model, which averaged models that individually incorporated group size, sighting conditions, and channel width as covariates, generated abundance estimates of 397 individuals (CV = 10.2%) and 451 individuals (CV = 9.6%), respectively. For Ganges River dolphins, a stratified Lincoln-Petersen model, which incorporated group size as a covariate, and a Huggins conditional likelihood model, which averaged the same models described above, generated abundance estimates of 196 individuals (CV = 12.7%) and 225 individuals (CV = 12.6%), respectively. Although the estimates for both models were relatively close, the analytical advantages of the Huggins models probably outweigh those of the Lincoln-Petersen models. However, the latter should be considered appropriate when simplicity is a priority. This study found that waterways of the Sundarbans support significant numbers of Irrawaddy and Ganges River dolphins, especially compared to other areas where the species have been surveyed.

Original languageEnglish
Pages (from-to)527-547
Number of pages21
JournalMarine Mammal Science
Volume22
Issue number3
DOIs
Publication statusPublished - 1 Jul 2006

Keywords

  • Abundance estimation
  • Chapman's modified Lincoln-Petersen mark-recapture estimator
  • Correction factors
  • Ganges River dolphins
  • Huggins conditional likelihood model
  • Irrawaddy dolphins
  • Orcaella brevirostris
  • Platanista gangetica

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