Studies on the distribution and habitat charac-density estimate, MODIS teristics of the Indo-Pacific humpback dolphin (Sousa chinensis) indicate a general preference Introduction toward estuarine environments. However, quantitative connections between this preference Studies on the distribution and habitat characterand estuarine characteristics are seldom investi-istics of animals identify the dynamic function of gated. Distribution of the humpback dolphin in animal habitat use as it relates to the accessibility the northern Beibu Gulf, China, was evaluated of prey, social interactions, predator-prey interacthrough systematically designed surveys and tions, and inter-habitat-patch mobility (Wilson was compared to oceanographic characteristics et al., 1997; Karczmarski et al., 2000; Heithaus, from on-board measured and remotely sensed 2001; Davis et al., 2002; Braulik et al., 2012; variables. The humpback dolphins' core distri-Wang et al., 2015, 2016). Baselines for such data bution zone, measured by the 50% kernel den-provide further insights into practical habitat prosity estimate (50% KDE), was confined to the tection and management planning (International Dafengjiang River Estuary in a 50.23 km 2 area, Union for Conservation of Nature [IUCN], 2001; with a steep-edged underwater sand bar below Wilson et al., 2004; Cañadas et al., 2005; Garaffo and locally high chlorophyll-a concentration. The et al., 2011; Zhao et al., 2013; Wang et al., 2016). surface salinity distribution showed an eco-cline Relevant studies can be especially important in environment in which riverine runoff mixes with protecting key habitat for coastal cetacean species, sea water in the 50% KDE. We found significant such as the Indo-Pacific humpback dolphin (Sousa relationships between distribution probability and chinensis), which frequently interact with anthrotwo oceanographic variables: (1) water depth and pogenic activities (Jefferson, 2000; Ross et al., (2) chlorophyll-a concentration. This associates 2010; Dungan et al., 2012; Würsig et al., 2016). the distribution preference of humpback dolphins The Indo-Pacific humpback dolphin (known with regional productivity and biodiversity peaks as the Chinese white dolphin in Chinese waters) that may facilitate prey aggregation. As hump-is known to specifically rely primarily on coastal back dolphins inhabit comparable environments waters shallower than 20 m deep (Jefferson, 2000; in other locations throughout their range, the Jefferson & Karczmarski, 2001; Hung, 2008; Ross oceanographic features of the 50% KDE may help et al., 2010; Jutapruet et al., 2015). The taxonomy to provide proxies to identify other key habitats of the humpback dolphins was recently revised, over a broader spatial scale.

The mammalian intestinal microbiome is critical for host health and disease resistance. However, the cetacean intestinal microbiota remains relatively unexplored. By using high-throughput 16S rRNA gene sequencing, we analyzed intestinal bacterial samples from an Indo-pacific humpback dolphin (Sousa chinensis) stranded near the Pearl River Estuary in China. The samples included 3 anatomical regions (foregut, midgut, and rectum) and 2 anatomical locations (content and mucus). Our analyses revealed that the dolphin intestinal bacteria contained 139 operational taxonomic units (OTUs), dominated at the phyla level by Firmicutes (47.05% in the content; 94.77% in the mucus), followed by Bacteroidetes (23.63% in the content; 1.58% in the mucus) and Gammaproteobacteria (14.82% in the content; 2.05% in the mucus). The intestinal bacteria had a small core community (15 OTUs, accounting for 99.74% of the reads), some of which could be potentially pathogenic to both human and dolphins. As an alternative to sampling the dolphin intestinal bacteria, fecal sampling could be used. Additionally, function potentials such as, xenobiotics biodegradation, beta-lactam resistance, and human disease-related pathways, were detected in the dolphin intestinal bacteria. These findings provide the first baseline knowledge of the intestinal microbiome of the Indo-Pacific humpback dolphin, which may offer new insights into cetacean conservation by using microbial surveillance.

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