Habitat modeling of Irrawaddy dolphins (Orcaella brevirostris) in
the Eastern Gulf of Thailand
DOI: 10.1002/ece3.6023
Justine Jackson-Ricketts1, Chalatip Junchompoo2, Ellen M. Hines3, Elliot L. Hazen4,
Louisa S. Ponnampalam5, Anoukchika Ilangakoon6, Somchai Monanunsap7
1Department of Ecology and Evolutionary
Biology, University of California Santa Cruz,
Santa Cruz, California
2Department of Marine and Coastal
Resources, Marine and Coastal Resources
Research and Development Center, The
Eastern Gulf of Thailand, Rayong, Thailand
3Estuary & Ocean Science Center, San
Francisco State University, Tiburon,
California
4NOAA Southwest Fisheries Science
Center, Environmental Research Division/
Department of Ecology and Evolutionary
Biology, University of California Santa Cruz,
Monterey, California
5The MareCet Research Organization, Shah
Alam, Malaysia
6Maharagama, Sri Lanka
7Department of Marine and Coastal
Resources, Southern Marine and Coastal
Resources Research Center, Songkhla, Thailand
Abstract
Aim: The Irrawaddy dolphin (Orcaella brevirostris) is an endangered cetacean found
throughout Southeast Asia. The main threat to this species is human encroachment,
led by entanglement in fishing gear. Information on this data-poor species’ ecology
and habitat use is needed to effectively inform spatial management.
Location: We investigated the habitat of a previously unstudied group of Irrawaddy
dolphins in the eastern Gulf of Thailand, between the villages of Laem Klat and
Khlong Yai, in Trat Province. This location is important as government groups plan to
establish a marine protected area.
Methods: We carried out boat-based visual line transect surveys with concurrent
oceanographic measurements and used hurdle models to evaluate this species’
patterns of habitat use in this area.
Results: Depth most strongly predicted dolphin presence, while temperature was a
strong predictor of group size. The highest probability of dolphin presence occurred
at around 10.0 m with an optimal depth range of 7.50 to 13.05 m. The greatest number
of dolphins was predicted at 24.93°C with an optimal range between 24.93 and 25.31°C.
Dolphins are most likely to occur in two primary locations, one large region in the center
of the study area (11o54′18′′N to 11o59′23′′N) and a smaller region in the south
(11o47′28′′N to 11o49′59′′N). Protections for this population will likely have the greatest
chance of success in these two areas.
Main Conclusions: The results of this work can inform management strategies within
the immediate study area by highlighting areas of high habitat use that should be
considered for marine spatial planning measures, such as the creation of marine
protected areas. Species distribution models for this species in Thailand can also assist
conservation planning in other parts of the species’ range by expanding our understanding
of habitat preferences.
Ellen Hines, PhD
Associate Director and Professor of Geography & Environment
Estuary and Ocean Science Center
San Francisco State University
3150 Paradise Dr. Tiburon, CA 94920
415 338 3512, ehines@sfsu.edu
http://eoscenter.sfsu.edu/content/ellen-hines