Impact of human activities and environmental variables on habitat use of Heaviside’s dolphin (Cephalorhynchus heavisidii) and bottlenose dolphin (Tursiops truncatus) in Walvis Bay: A passive acoustic monitoring approach
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Date
2025
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University of Namibia
Abstract
The rapid expansion and scope of development along marine coastlines threaten marine
mammals with cumulative effects from human practices. such as vessel strikes, by-catch,
entanglement, debris ingestion, petroleum exploration, underwater shipping noise, and
other noise pollution. This study aimed to understand the impacts of environmental and
anthropogenic factors on the habitat use patterns of two dolphin species; Heaviside’s
dolphins (Cephalorhynchus heavisidii) and common bottlenose dolphins (Tursiops
truncatus) which are a small, localized population, at two key sites in Walvis Bay: Afrodite
Beach and Pelican Point. The specific objectives were to: (a) Investigate the influence of
anthropogenic factors (boat sonar and a period harbor expansion and their associated noise)
on the diel present patterns and habitat use of C. heavisidii at Pelican Point and T. truncatus
at Afrodite Beach. (b) Assess whether environmental factors (time of day, season, moon
illumination, temperature, wind direction and wind speed) influence habitat use of C.
heavisidii at Pelican Point and T. truncatus at Afrodite Beach. (c) Investigate the
interspecific influence of T. truncatus on the habitat use patterns and diel presence of
heavisidii at Pelican Point. (d) Assess the impacts of harbor expansion on the seasonal
distribution and habitat use of C. heavisidii and T. truncatus, comparing patterns of
presence and area usage before and during the development process. The study used data
obtained from the Namibian Dolphin Project and collected using a Passive Acoustic
Monitoring (PAM) over a long-term study period of 2009-2014 (pre construction) and
2015-2018 (during construction). Acoustic data was collected using C-POD hydrophones
with sounds extracted and processed using the C-POD developer software CPOD.exe
v2.033. A hurdle modelling approach was used to investigate sonar, time of day, season,
i
period of study, and environmental parameters predictor variables (water temperature, wind
speed and direction and moon illumination) potentially influencing dolphin presence and
behavior at these sites. The results showed that boat-related noise had a significant impact
on the diel presence ((p ˂ 0.001) at Pelican Point and (p ˂ 0.001) at Afrodite Beach) and
habitat utilization (p= 0.0433 at Pelican Point and p = 0.0153 at Afrodite Beach) of both
species. Environmental elements such as moon illumination (p ˂ 0.001), wind direction (p
= 0.025), wind speed (p = 0.0156), and temperature (p ˂ 0.001) have a significant impact
on their behaviors. Furthermore, inter-species interactions were observed, with T. truncatus
having a considerable influence on C. heavisidii, especially at seasonal time scales. As a
result, the study proposes targeted noise reduction from boats and the incorporation of
seasonal dynamics into conservation planning
Description
A thesis submitted in fulfilment of the requirement for the Degree of Master of Science in Fisheries and Ocean Sciences
Keywords
Habitat use patterns, Cephalorhynchus heavisidii, Tursiops truncatus, Passive acoustic monitoring, Anthropogenic activities, Harbor expansion, Environmental parameters, Namibia, University of Namibia