Distribution of a Coastal Delphinid Under the Impact of Long-Term Habitat Loss: Indo-Pacific Humpback Dolphins off Taiwan's West Coast

For the Indo-Pacific humpback dolphin, Sousa chinensis, an obligatory shallow water inshore species, the degradation of coastal habitats can have major consequences for population persistence and distribution. Off Taiwan's west coast (TWC), these animals are predominantly seen in two areas separated by a stretch of coast with only sporadic sightings, suggesting that either (a) only two sectors of TWC offer sufficiently suitable habitat for the dolphins or (b) a recent environmental change limits the population connectivity. We measured the extent of habitat destruction due to land reclamation off TWC since 1972 using a habitat integrity index (HII) and applied general linear models (GLMs) to compare HII with sightings of dolphins per unit effort (SPUE). While early Landsat data reveal extensive continuity and diversity of coastal habitats, by 2013, a total area of over 222 km(2) was lost to land reclamation (23 % of dolphin habitat and 40 % of dolphin foraging habitat). GLM analysis showed a significant relationship between HII and SPUE; the lower HII the lower SPUE, indicating that off TWC, the current discontinuous distribution of humpback dolphins is likely due to a different extent of habitat degradation rather than natural patchiness of their environment. We emphasize that the history of coastal habitat alteration must be considered when interpreting cetacean distribution from survey data and formulating habitat management decisions, especially in areas experiencing extensive anthropogenic coastal change.