Cruise tourism was the fastest growing segment of global tourism prior to the COVID-19 pandemic. Annual cruise ship visits to Akaroa Harbour, Aotearoa New Zealand, more than quadrupled to approximately 80 per year following earthquake damage to nearby Lyttelton Port in 2011. Akaroa Harbour is a core habitat for endangered, endemic and taonga Hector’s dolphins (Cephalorhynchus hectori; Pahu), and a shift in their summer distribution away from the cruise anchorages was observed between 2011 and 2019. Implementation of COVID-19 restrictions in 2020 prevented cruise ship visits, but the industry returned in a limited capacity in 2022 (to approximately 15 visits p.a.). To determine the distribution of Hector’s dolphins under varying levels of cruise ship tourism before, during and after the COVID-19 pandemic, I analysed 703 sightings from 4,377 kilometres of active survey effort using kernel density estimation and generalised additive models (GAMs). The middle harbour, closest to the cruise ship anchorage sites and a previously documented core habitat for the dolphins, continued to be only minimally encompassed within core habitat after 2019. Encounter rates and the contribution of the harbour to core habitat, however, were highest over COVID-19, lower for the low cruise ship period (2022/23-2023/24) and lowest over the high cruise ship period (2018/19-2019/20). Lower encounter rates of Hector’s dolphins throughout Akaroa Harbour on days when a cruise ship was present provided evidence for avoidance of key habitat in response to cruise vessels. I sought to develop baseline data on the impacts of cruise ships on the marine environment to elucidate the most likely mechanisms of short- and long-term shifts in the distribution of dolphins. I utilised high resolution multibeam and macrofaunal data collected as part of the Iongairo project. Additionally, I collected data on turbidity and sound levels during the summer of 2023/24 using both boat-based and moored systems. Depressions in the seabed up to 0.9 m deep were observed at the designated cruise ship anchorage sites, covering a cumulative area of 1.2 km2 and remaining visible for over seven years. No impacts on benthic diversity were discernible, likely due to poor selection of control sites. The use of contour plots, interpolation and GAMs revealed that turbidity levels were elevated for 20 hours after anchoring and potentially up to 6 km from anchoring sites. Cruise ships introduced noise largely in the 100 Hz to 1 kHz frequency range at source levels of 139.5 to 168.2 dB re 1 μP a at 1 m while propulsion was on. While permanent shifts in hearing threshold were considered unlikely, temporary threshold shifts and changes to the behaviour of Hector’s dolphin were predicted up to 674 m and 14 km from the cruise ship respectively. My findings suggest that short-term avoidance of Akaroa Harbour by Hector’s dolphins may be attributable to increased ambient sound levels, while long-term abandonment of previously documented core habitat may be due to the degradation of benthic communities. This thesis presents suggestions for management of the cruise ship industry in Akaroa Harbour and further afield, and emphasises the importance of taking precautionary measures to prevent long-term and irreversible consequences on the marine environment.
Rose Bunney Ursem (Thu,) studied this question.
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