Long‐term changes in the distribution and core habitat use of a coastal delphinid in response to anthropogenic coastal alterations

Abstract

1. The influence of anthropogenic habitat loss on animal distribution and core habitat use can be particularly strong in animals with narrow habitat selectivity, such as the Indo-Pacific humpback dolphin (Sousa chinensis), a delphinid species that specifically inhabits coastal and estuarine waters. 2. This study measured the extent of habitat loss in the waters around Xiamen City, China, where intense environmental changes and coast utilization have occurred in the past 40 years. The extent of occurrence and the core habitat of the humpback dolphin were measured based on sighting records from censuses conducted in different years. 3. A Landsat image series revealed a permanent 119.95 km 2 loss of coastal waters to land reclamation, coastal modification and harbour construction from 1973 to 2013. The distribution of the humpback dolphin showed a significant shift from inshore to offshore waters and away from artificial shorelines. Though the extent of occurrence appears to change minimally, a significant shift in the core habitat from the original coastal habitats into mid-channel waters was observed in the eastern Xiamen Bay. 4. These results imply multiple consequences of anthropogenic coastal alterations for the humpback dolphin: the elimination of vital habitats, changes in habitat use preferences, and the partitioning of the social structure of the population.5. The need to adjust current protected area designations along with adequate measures to restore habitat quality and population connectivity, both locally and regionally, are considered.

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

“…If as a result the movement route of humpback dolphins was displaced to offshore waters, humpback dolphin sightings may be substantially reduced and hence the importance of the affected waters could be overlooked. In the worst‐case scenario, social interactions of the humpback dolphin between sectors G and L will decrease (Chen et al, ), as has already happened in other locations like Hong Kong waters (Dungan et al, ), Xiamen Bay (Wang et al, , ) and the western Taiwanese coast (Chang, ; Karczmarski et al, ). If this condition persists, humpback dolphins in the northern Beibu Gulf may become more prone to population fragmentation that would increase local population vulnerability (Huang et al, ).…”

“…The construction associated with reclamations, embankments and harbours concurrently alters oceanographic features in neighbouring waters, including water current patterns, sediment‐erosion dynamics and benthic structure, as has been observed around the reclamation sites in western Taiwan (Karczmarski et al, ). These changes, along with the significant reduction in local productivity and biodiversity (Fraschetti et al, ; Lin, Xue, & Lu, ; Wu, Fu, Lu, & Chen, ) and shifting faunal composition (Fraschetti et al, ; Gedan, Silliman, & Bertness, ; Ryu et al, ), can lead to intense habitat deterioration and degradation (Karczmarski et al, ; Liu & Mou, ; Wang et al, ). In the northern Beibu Gulf, the Landsat data implied a change in water flow characteristics around the greatly extended seaward land‐reclamations or embankments in sectors C, E and L, and also intense environmental degradation at the land–sea interface from sectors H to L. Numerically decreasing SPUF in sectors E, I, J and L, as well as the apparently fragmented social structure between sectors G and L (Chen et al, ) imply that changes in habitat quality and function that alter the regional preferences of the dolphins to these sectors may already have been occurring and could become worse in the future.…”

“…All downloaded Landsat scenes were processed into false‐colour images by ArcMap 9.3 (ESRI, ), using the RGB231 (R: red, G: green, B: blue) band composite for the Landsat 1–4 Multispectral Scanner (MSS) data, the RGB742 band composite for the Landsat 5 Thematic Mapper (TM) data and Landsat 7 Enhanced Thematic Mapper Plus (ETM+) data, or the RGB753 band composite for the Landsat 8 Operational Land Imager (OLI) data (Chander et al, ; Merem & Twumasi, ). These band composite images allowed clear contrasts between aquatic and terrestrial objects and between urban and vegetated landscapes (Chen et al, ; Karczmarski et al, ; Kerr & Ostrovsky, ; Wang et al, ). The earliest Landsat image over the study site dated back to 1973 (Landsat 1 MSS) and hence was referenced as the baseline image for identifying habitat loss.…”

“…Unlike most other marine species, the humpback dolphin exclusively uses coastal and estuarine waters (Jefferson & Karczmarski, ; Jefferson & Rosenbaum, ; Jutapruet et al, ) for virtually all life functions (Würsig, Parsons, Piwetz, & Porter, ). Human‐induced changes in habitat structure and status in some coastal waters have shifted the distribution patterns, habitat use and social structure of humpback dolphins (Dungan, Hung, Wang, & White, ; Huang & Karczmarski, ; Karczmarski et al, ; Wang et al, ; Wang, Wu, Zhu, & Huang, ). In countries where coastal and estuarine waters have been massively altered to accommodate land reclamation or port facilities along with rapid urbanization and industrialization in the past decades, such as in China (Chen et al, ; Huang & Karczmarski, ; MacKinnon et al, ), the baseline shift can be substantial.…”

“…Current information cannot distinguish whether these are less important habitats that the dolphins seldom visit, or if there are some other likely habitats which represent information gaps due to insufficient survey effort (as in Li et al, ). In Chinese waters, many of the humpback dolphin habitats have been damaged or destroyed to accommodate artificial landscapes such as land reclamation, embankments or harbours, often without implementation of adequate mitigation and compensation measures (Chen et al, ; Huang & Karczmarski, ; Karczmarski et al, ; Rao, Lin, Kong, Jin, & Peng, ; Wang et al, ), while the likely impact of these anthropogenic activities on humpback dolphin habitat status is often not fully addressed in current environmental impact assessment programmes. The actual risk to population viability due to habitat degradation and deterioration can easily be underestimated (Huang et al, ), especially in some of the larger ‘populations’.…”