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.

Coastal and estuarine waters are important ecosystems with high primary and secondary productivity, but they are prone to the impacts of habitat loss caused by anthropogenic activities. For species exclusively inhabiting coastal and estuarine waters, such as the Indo‐Pacific humpback dolphin, Sousa chinensis, irreversible habitat loss can have dramatic implications for population viability. A Landsat image database was used to determine the extent of coastal changes along the northern Beibu Gulf, where a large humpback dolphin population is found. The results were compared with the standardized sighting gradient (SPUF) determined from a questionnaire survey of fishermen and likely core habitats identified by application of a global digital elevation model. Both SPUF and likely core habitat results indicated a continuous distribution of the humpback dolphin along the northern Beibu Gulf. Landsat images revealed that 129.6 km2 of coastal waters were permanently lost in the past 40 years, 60 km2 within the likely core habitats. Although this may be considered small, the impact of such habitat loss could be substantial in some local habitats. The humpback dolphin population in the northern Beibu Gulf should be regarded as one management unit, with two or more social subunits. Immediate systematic surveys are needed to fill information gaps on true distribution range and habitat‐use patterns. Habitat protection actions for dolphins in the northern Beibu Gulf should include both core and linking habitats, including enacting protected areas in core habitats, mitigating anthropogenic impacts in likely habitats, restoring both coastal waters and surrounding landscape quality, effective treatment of industrial sewage discharge, and comprehensive environmental impact assessments for the planning of coastal development projects.

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Population decline among Asian horseshoe crabs in Asia is increasingly reported, but knowledge of their population and ecological status in China is limited. We conducted community interviews in 30 fishing villages around Beibu Gulf in Guangxi, China, to collect distribution information about the potential spawning/nursery grounds of Tachypleus tridentatus and Carcinoscorpius rotundicauda, and any imminent threats to their populations. Based on the results from 400 respondents we identified 45 potential spawning/nursery grounds distributed widely along the shores of Beibu Gulf. We visited 10 of these sites and verified the presence of juvenile horseshoe crabs by field surveys. Nearly all respondents reported an overall depletion in horseshoe crab populations from these 45 sites, which they attributed mainly to unsustainable fishing practices. Respondents who reported having seen horseshoe crab mating pairs on shores were mostly older people, which may suggest a considerable reduction in horseshoe crabs coming to the shores to spawn in recent years. The mean daily harvest of adult T. tridentatus offshore, as indicated by fishers, has declined from c. 50–1,000 in the 1990s to 0–30 individuals during 2011–2016. Our Wisdom of Crowds approach, supported by confirmatory field surveys, is a cost-effective method for assessing the population status of horseshoe crabs, and the level of threat they face. Similar approaches with other species are likely to be particularly valuable in the Asia–Pacific region, where well-structured population monitoring is largely unaffordable.

Understanding which food sources are nutritionally important at nursery grounds is critical in the conservation of the dwindling populations of horseshoe crabs in Asia. We used δ 13