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 ancestors of marine mammals once roamed the land and independently committed to an aquatic lifestyle. These macroevolutionary transitions have intrigued scientists for centuries. Here, we generated high-quality genome assemblies of 17 marine mammals (11 cetaceans and six pinnipeds), including eight assemblies at the chromosome level. Incorporating previously published data, we reconstructed the marine mammal phylogeny and population histories and identified numerous idiosyncratic and convergent genomic variations that possibly contributed to the transition from land to water in marine mammal lineages. Genes associated with the formation of blubber (NFIA), vascular development (SEMA3E), and heat production by brown adipose tissue (UCP1) had unique changes that may contribute to marine mammal thermoregulation. We also observed many lineage-specific changes in the marine mammals, including genes associated with deep diving and navigation. Our study advances understanding of the timing, pattern, and molecular changes associated with the evolution of mammalian lineages adapting to aquatic life.

Background: Populations of Indo-Pacific humpback dolphins (Sousa chinensis) in China were known to be distributed from the Beibu Gulf near the border with Vietnam to the mouth of the Yangtze River. According to existing studies, the waters around Hainan Island, China, were not considered to be part of the humpback dolphins' distribution. Results: In 2014, for the first time, we recorded humpback dolphins in waters southwest of Hainan Island.