Long‐term habitat loss in a lightly‐disturbed population of the Indo‐Pacific humpback dolphin, Sousa chinensis

Abstract

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.

Abundance and residency dynamics of the Indo‐Pacific humpback dolphin, Sousa chinensis, in the Dafengjiang River Estuary, China

“…Recent studies indicated the Dafengjiang River Estuary is one of the core habitats for humpback dolphins in the northern Beibu Gulf (Chen et al, ; Huang et al, ; Wu et al, ). The movement analysis based on LIR values presented a fluid habitat‐use dynamics.…”

“…Besides the Dafengjiang River Estuary, the Hepu Dugon Reserve is another core humpback dolphin habitat in the northern Beibu Gulf (Chen et al, ; Huang et al, ; Wu et al, ). Recent studies report different results between distribution gradients (Huang et al, ; Wu et al, ) and interhabitat communications (Chen et al, ). A cross‐matching of photo‐ID databases between the Dafengjiang River Estuary and Hepu Dugong Reserve study areas (Chen et al, ; Wang et al, ) and genetic comparison based on stranded carcasses (Alves et al, ; Parra et al, ), would help to clarify the above inferences.…”

Food risk trade‐off in the Indo‐Pacific humpback dolphin: An exploratory case study

“…Despite being highly subject to human‐derived disturbances, i.e. heavy shipping (Jefferson, ; Ross, Dungan, Hung, & Jefferson, ), pollution from rivers (Gui et al, ; Ross et al, ; Yeung et al, ), noise pollution (Ross et al, ; Wang et al, ), and habitat loss (Wu et al, ), estuaries have been identified as its preferred habitat (Jefferson, ; Jefferson & Hung, ; Wang et al, ). It is an interesting and important issue for species conservation to know why IPHDs favour an environment so affected by human activities.…”

Occurrence of Bryde's whales, Balaenoptera edeni, in the northern Beibu Gulf, China

“…; Wu et al . ). For the Bryde's whale in the northern Beibu Gulf, this study aimed to identify sites of occurrence of Bryde's whales based on citizen science information from collaborative fishermen, LEK information from questionnaire interviews and records from authors’ opportunistic surveys to provide preliminary knowledge of the Bryde's whale in the waters around Weizhou and Xieyang Islands before conducting systematically designed field surveys.…”

“…To develop these baselines, however, field surveys generally need to be conducted for several years (as in Chen et al 2010Chen et al , 2016Jutapruet et al 2015;Xu et al 2015;Wang et al 2017;Wu et al 2017a). Local ecological knowledge (LEK) based on questionnaire surveys can provide qualitative, and sometimes quantitative, information on occurrence and distribution gradients of charismatic animals (Turvey et al 2010(Turvey et al , 2013Logan et al 2015;Wu et al 2017b). For the Bryde's whale in the northern Beibu Gulf, this study aimed to identify sites of occurrence of Bryde's whales based on citizen science information from collaborative fishermen, LEK information from questionnaire interviews and records from authors' opportunistic surveys to provide preliminary knowledge of the Bryde's whale in the waters around Weizhou and Xieyang Islands before conducting systematically designed field surveys.…”