DOI: 10.5061/dryad.r2280gb94
title: Data from: Habitat modeling of Irrawaddy dolphins (Orcaella brevirostris) in the eastern Gulf of Thailand

description: 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 24.93oC with an optimal range between 24.93 and 25.31oC.
 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.
description: Data were collected during line transect boat surveys using the
 following equipment: Depth Temperature Salinity Turbidity Chl <em>a</em> pH 
 Davis Instruments Portable Water Depth
 Sounder Guage YSI Model 30 Handheld Salinity,
 Conductivity, and Temperature System YSI Model 30
 Handheld Salinity, Conductivity, and Temperature System
 Secchi disk Eureka Environmental Manta 2
 Water Quality Multiprobe Eureka Environmental Manta 2
 Water Quality Multiprobe 
 HawkEye Handheld Sonar System Eureka
 Environmental Manta 2 Water Quality Multiprobe Eureka
 Environmental Manta 2 Water Quality Multiprobe
 LaMotte Model 2020 Turbidimeter
     
      
 Eureka Environmental Manta 2 Water Quality Multiprobe
     
 We added distance to river mouths for each
 environmental data point via measurement in ArcGIS. Analyses were carried
 out in R version 2.13.1. We removed outliers and binned both turbidity and
 chlorophyll-<em>a</em> into high, medium, and low using Jenks
 natural breaks classification. We employed hurdle models using a negative
 binomial distribution to analyze the count data (binary data are modeled
 using a binomial distribution). 
description: Data availability was uneven across years, so we separated the
 data into 5 smaller datasets. Datasets 1-4 include all data points for
 each year, so variables with missing values were left out. The fifth
 dataset contains only points for which all variables were measured, so it
 is smaller. Please see Data_Key .docx file for numbers used to indicate
 location and year within datasets. Model Framework Variables Included Collection Year(s) 
 1
 depth, temp, salinity, dist. to river mouth, calves (binary),
 year 2008, 2009, Jan. 2012, Apr.-May 2012, Jan.-Feb.
 2013, Jan.-Feb. 2014 
 2 depth, temp, salinity, turbidity, dist.
 to river mouth, calves, year 2009, Jan. 2012,
 Apr.-May 2012, Jan.-Feb. 2013, Jan.-Feb. 2014  
 3 depth, temp, salinity,
 turbidity, chl <em>a</em>, dist. to river mouth,
 calves Jan.-Feb. 2013, Jan.-Feb. 2014
 4 depth, temp,
 salinity, turbidity, chl <em>a</em>, pH, dist. to river mouth,
 calves Jan.-Feb. 2014 
 5 depth, temp, salinity,
 turbidity, dist. to river mouth, calves, year 2008,
 2009, Jan. 2012, Apr.-May 2012, Jan.-Feb. 2013, Jan.-Feb.2014