Naturalists, Explorers and Field Scientists in South-East Asia and Australasia

Abstract

Irrawaddy dolphins, Orcaella brevirostris , in the Kuching Bay, Sarawak, Malaysia have been subjected to pressure from cetacean-fi sheries interactions, dol- phin watching tourism and coastal development. However, very little information is known about their ecology and factors driving their habitat preferences. To obtain critical information on the distribution, habitat preference and range pattern of Irrawaddy dolphins in Kuching Bay, Sarawak, systematic boat-based surveys were conducted between June 2008 and October 2012. The results showed a statistically signifi cant relationship between Irrawaddy dolphins’ distribution and different cat- egories of salinity, tide levels and distance to river mouths. Kruskal-Wallis tests confi rmed that the presence of Irrawaddy dolphins in Kuching Bay had statistically signifi cant relationships to habitat parameters of salinity (chi-square = 4.694, p = 0.03). Fisher’s exact test indicated that Irrawaddy dolphins were statistically more likely to be present in waters within a 6 km radius of river mouths. The distri- bution of dolphins was also affected by tide levels as Mann-Whitney U -tests proved a statistically signifi cant difference in dolphin distribution between tide levels lower than 2.0 m and tide levels higher than 2.0 m (p = 3.153 × 10 −11 ). The representative range and core area of photo-identifi ed Irrawaddy dolphins estimated using fi xed kernel range was 246.42 km 2 and 37.22 km 2 , respectively, with core area located in the Salak Estuary. The results obtained in this study refl ect dry season distribution only, and may differ during the wet season. Nonetheless, these results highlight the importance of shallow coastal waters and the overlap of Irrawaddy dolphin critical habitat with that of human activities in Kuching Bay. Conservation efforts are required to minimise the effects of the pressures exerted on these animals and their habitats.