Population estimation, distribution, and habitat preference of Irrawaddy dolphins <i>Orcaella brevirostris</i> (Owen in Gray, 1866) in the Brunei Bay, Malaysian waters

Mahmud, Anisul Islam; Jaaman, Saifullah Arifin; Muda, Azmi Marzuki; Muhamad, Hairul Masrini; Zhang, Xuelei; Scapini, Felicita

doi:10.2981/wlb.00383

Cited by 12 publications

(9 citation statements)

References 51 publications

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“…Habitat models were built, validated and projected across a transboundary region to map seasonal distributions of an endangered species of small cetacean. Overall, Irrawaddy dolphins from the Kep Archipelago displayed habitat preferences that were similar to the suite of environmental variables commonly associated with coastal-estuarine Irrawaddy populations (Minton et al, 2011;Mahmud et al, 2018;Jackson-Ricketts et al, 2020). Previous studies have linked Irrawaddy dolphins to shallow areas, close to river mouths, and with changing tidal states; conditions associated with low sea surface salinity and high turbidity (Dolar et al, 2002;Peter et al, 2016b).…”

Section: Discussionmentioning

confidence: 71%

Modeling Seasonal Distribution of Irrawaddy Dolphins (Orcaella brevirostris) in a Transnational Important Marine Mammal Area

Verutes

Tubbs²,

Selmes

et al. 2021

Front. Mar. Sci.

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Fishing activities continue to decimate populations of marine mammals, fish, and their habitats in the coastal waters of the Kep Archipelago, a cluster of tropical islands on the Cambodia-Vietnam border. In 2019, the area was recognized as an Important Marine Mammal Area, largely owing to the significant presence of Irrawaddy dolphins (Orcaella brevirostris). Understanding habitat preferences and distribution aids in the identification of areas to target for monitoring and conservation, which is particularly challenging in data-limited nations of Southeast Asia. Here, we test the hypothesis that accurate seasonal habitat models, relying on environmental data and species occurrences alone, can be used to describe the ecological processes governing abundance for the resident dolphin population of the Kep Archipelago, Cambodia. Leveraging two years of species and oceanographic data—depth, slope, distance to shore and rivers, sea surface temperature, and chlorophyll-a concentration—we built temporally stratified models to estimate distribution and infer seasonal habitat importance. Overall, Irrawaddy dolphins of Kep displayed habitat preferences similar to other populations, and were predominately encountered in three situations: (1) water depths ranging from 3.0 to 5.3 m, (2) surface water temperatures of 27–32°C, and (3) in close proximity to offshore islands (< 7.5 km). With respect to seasonality, statistical tests detected significant differences for all environment variables considered except seafloor slope. Four predictor sets, each with a unique combination of variables, were used to map seasonal variation in dolphin habitat suitability. Models with highest variable importance scores were water depth, pre- and during monsoon season (61–62%), and sea surface temperature, post-monsoon (71%), which suggests that greater freshwater flow during the wet season may alter primary productivity and dolphin prey abundance. Importantly, findings show the majority of areas with highest habitat suitability are not currently surveyed for dolphins and located outside Kep’s Marine Fisheries Management Area. This research confirms the need to expand monitoring to new areas where high-impact fisheries and other human activities operate. Baseline knowledge on dolphin distribution can guide regional conservation efforts by taking into account the seasonality of the species and support the design of tailored management strategies that address transboundary threats to an Important Marine Mammal Area.

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Section: Discussionmentioning

confidence: 71%

Modeling Seasonal Distribution of Irrawaddy Dolphins (Orcaella brevirostris) in a Transnational Important Marine Mammal Area

Verutes

Tubbs²,

Selmes

et al. 2021

Front. Mar. Sci.

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“…Dolphins will change direction to avoid noisy areas (Noor et al 2013) and swim further from ship traffic. Anthropogenic activities are also a threat to the Irrawaddy Dolphin population in Brunei Bay (Mahmud et al 2018).…”

Section: Discussionmentioning

confidence: 99%

Historical and new records of the Irrawaddy Dolphins, Orcaella brevirostris (Owen in Gray, 1866) (Cetacea, Delphinidae) from the east coast of South Sumatra, Indonesia

Fauziyah¹,

Agustriani²,

Rozirwan³

et al. 2022

CheckList

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Irrawaddy Dolphin, Orcaella brevirostris (Owen in Gray, 1866), has been reported in the waters of Berbak Sembilang National Park, Indonesia, since 1990. We used interview techniques, direct observations, and secondary data from the literature to show that this dolphin occurs on the east coast of South Sumatra from October to February. An Irrawaddy Dolphin bycatch was recorded on 26 January 2021 in a gillnet. There have been historical sightings of fewer than six individuals of Irrawaddy Dolphins between 1990 and 2013 in the estuaries of Bogem, Bungin, Ngirawan, Terusan Dalam, Betet Island, Banyuasin, Lalan, and Tanjung Carat to Makarti Jaya. We map the geographic distribution of Irrawaddy Dolphin in South Sumatra.

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“…Cherdsukjai & Kittiwattanawong, 2013; Minton et al, 2013; Hines et al, 2015a; Kreb et al, 2020). Published scientific studies on cetacean abundance in Malaysia are sparse and have mostly been conducted in east Malaysia (Minton et al, 2013; Teoh, Jaaman & Palaniappan, 2013; Zulkifli Poh et al, 2016; Mahmud et al, 2018). The geographically closest Irrawaddy dolphin study to Matang is on the west side of Penang Island, approximately 80 km north of Matang, where 32 to 43 individuals were estimated in a small study area of 80 km 2 (Rodríguez‐Vargas et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Abundance estimates of three cetacean species in the coastal waters of Matang, Perak, Peninsular Malaysia

Kuit

Ponnampalam²,

Hammond

et al. 2021

Aquatic Conservation

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1. The paucity of baseline data on coastal cetaceans due to a lack of research in developing countries frequently precludes assessment of their status and informed management actions for conservation.2. This study provides the first abundance estimates of Indo-Pacific humpback dolphins, Irrawaddy dolphins, and Indo-Pacific finless porpoises in the coastal waters of Matang, Peninsular Malaysia. 3. Boat-based surveys covering 1,152 km 2 of coastal waters with 4,108 km of survey effort were conducted between 2013 and 2016 to collect data for line transect analysis of Irrawaddy dolphins and finless porpoises. Photo-identification data of humpback dolphins were concurrently collected for mark-recapture analysis. 4. Estimates of abundance from four sampling strata totalled 763 Irrawaddy dolphins (CV = 13%, 95% confidence interval (CI) [588, 990]) and 600 Indo-Pacific finless porpoises (CV = 27%, 95% CI [354, 1,016]). 5. The annual abundance estimates of humpback dolphins ranged between 171 (95% CI [148, 208]) in 2014-2015 and 81 (95% CI [67, 98]) in 2015-2016, likely due to the presence of offshore individuals that moved in and out of the study area. The estuarine strata were inhabited by 68 (95% CI [63, 73]) inshore humpback dolphins in 2013-2014 to 87 (95% CI [78, 97]) dolphins in 2014-2015. 6. As an International Union for Conservation of Nature important marine mammal area, the productive coastal waters of Matang are shown to support a high density of small coastal cetaceans, and the results serve as an important baseline for future studies to identify population trends for conservation management plans.

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Population estimation, distribution, and habitat preference of Irrawaddy dolphins Orcaella brevirostris (Owen in Gray, 1866) in the Brunei Bay, Malaysian waters

Abstract: BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Cited by 12 publications

References 51 publications

Modeling Seasonal Distribution of Irrawaddy Dolphins (Orcaella brevirostris) in a Transnational Important Marine Mammal Area

Modeling Seasonal Distribution of Irrawaddy Dolphins (Orcaella brevirostris) in a Transnational Important Marine Mammal Area

Historical and new records of the Irrawaddy Dolphins, Orcaella brevirostris (Owen in Gray, 1866) (Cetacea, Delphinidae) from the east coast of South Sumatra, Indonesia

Abundance estimates of three cetacean species in the coastal waters of Matang, Perak, Peninsular Malaysia

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