Effects of Human Activities on Coastal Dolphin Behavior
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This dissertation contributes to our understanding of anthropogenic effects on wildlife, a central question in the growing field of conservation behavior. I present three case studies of coastal delphinid species in diverse ecosystems with varied human pressures. I examine how 1) common bottlenose dolphins (Tursiops truncatus) in a narrow congested waterway respond to heavy vessel traffic, 2) Indo-Pacific humpback dolphins (Sousa chinensis) respond to chronic maritime construction and associated vessel activity, and 3) dusky dolphins (Lagenorhynchus obscurus) use distinct patches within a bay that supports shellfish aquaculture. In each study, group focal follows were conducted using non-invasive shore-based theodolite tracking. Data collection included behavioral states, movement patterns and habitat-use patterns. Metrics to evaluate alterations in movement patterns included swimming speed, reorientation rate, and linearity. Data to evaluate alterations in habitat-use included behavioral activity states and track duration among habitat patches. Multivariate generalized additive models identified significant explanatory variables. Dolphin movement and habitat-use patterns were good indicators of response to human activity across diverse species and ecosystems. Bottlenose dolphins avoided tour boats and were attracted to commercial trawlers that may facilitate prey accessibility. Current voluntary dolphin-viewing recommendations do not protect dolphins from behavioral harassment, but dolphins did not abandon the area, which may reflect a lack of ecologically similar habitat nearby. Humpback dolphins avoided areas near chronic construction activity during the day, but some returned at night when human activity decreased. Dusky dolphins used defined patches within the bay in different ways. Mid-bay and nearshore patches reflect areas that may yield greater benefits relative to prey ball herding opportunities, whereas patches near mussel farms reflect areas that may yield greater benefits relative to non-prey ball foraging opportunities. Flexibility in foraging tactics occurred across study sites and species, and allows dolphins to adjust to fluctuating environments with ephemeral and patchily distributed prey. Behaviors are likely influenced by human activity, prey characteristics, and accessibility to alternate habitats that support prey. Integration of data on prey characteristics (e.g., fish species, abundance, and distribution) in future research will enhance our understanding of factors influencing dolphin behavior in these dynamic systems.
SubjectCommon bottlenose dolphin
Indo-Pacific humpback dolphin
Piwetz, Sarah Katherine (2018). Effects of Human Activities on Coastal Dolphin Behavior. Doctoral dissertation, Texas A & M University. Available electronically from