Abstract
The Indo-Pacific humpback dolphin (Sousa chinensis) has been reported to prefer estuary habitats. This study explored the environmental factors affecting a critically endangered population off the coast of Yunlin, Taiwan. We measured dolphin sighting rates and estuary characteristics affected by the watershed, including seven physical factors (watershed rainfall, watershed runoff, estuarine turbidity, pH, salinity, temperature, and dissolved oxygen) and two biological factors (estuarine net primary production and chlorophyll a concentration), at the Hsinhuwei River estuary in Taiwan. Dolphin activity was measured by sighting rate and behavioral indices for feeding and traveling between 2017 and 2018. We observed that when the maximum net production increased alongside rising temperatures in spring, both the dolphin sighting rate and foraging activity increased. This trend was maintained until heavy rainfall or increased river runoff occurred during late summer, which resulted in high turbidity in autumn and winter. Turbidity was significantly negatively correlated with dolphin activity (sighting rate and foraging). Furthermore, we found that dolphin traveling positively correlated with the chlorophyll a concentration and maximum net production factors, which could attract dolphins expecting more abundant prey fish in the estuary supported by the high primary production. This study provides empirical evidence on how estuary characteristics affected by the watershed can affect the sighting rate and behavioral activities of Indo-Pacific humpback dolphins.
Highlights
Knowledge of the spatial distribution patterns of species is crucial for their conservation (Ferrier, 2002; Rushton et al, 2004) as it improves our understanding of the relationship between environmental factors and animal activities
A total of 20 single-species (S. chinensis) dolphin groups were sighted on the nearshore transect line, with no sightings on the offshore line
The physical factors consist of rainfall, runoff, turbidity, temperature, salinity, pH, and dissolved oxygen, and the biological factors refer to maximum net production (NPm) and chlorophyll a concentration
Summary
Knowledge of the spatial distribution patterns of species is crucial for their conservation (Ferrier, 2002; Rushton et al, 2004) as it improves our understanding of the relationship between environmental factors and animal activities. Lin et al (2015) found that their activity pattern in the Hsinhuwei estuary significantly varied with the amount of rainfall They suggested that dolphin activity may be related to estuary productivity. Pan et al (2016a) demonstrated that primary production in the Hsinhuwei estuary was higher than in two other nearby locations This means that the area could support larger numbers of invertebrates and predatory fish, allowing for a larger population of IndoPacific humpback dolphins in the estuary. This study empirically explored the seasonal variation in and the association between environmental factors affected by the watershed and activity levels of Indo-Pacific humpback dolphins in the Hsinhuwei estuary
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