Tucked on the south side of Te Pātaka o Rākaihautū (Banks Peninsula) is the peaceful and unique Akaroa Harbour, home to the world’s smallest, and one of New Zealand’s most at threat dolphins, the Hector’s dolphin.
DOC is working alongside local tour operators, Rūnanga, researchers and the regional council to study the impacts of cruise ships, dolphin tourism and general vessel traffic in the Akaroa Harbour.
Researcher Will Carome describes how they detected dolphins underwater to further examine potential causes for the observed shifts in Hector’s dolphin distribution during the last decade.
I leaned over the bow, bracing my knees against the gunwales, as our research boat bounced in strengthening seas. Lindsay, PhD student and leader of our field work, deftly manoeuvred our research vessel Grampus toward a hi-vis orange buoy, the white-caps of an approaching southerly looming behind her. I hauled the buoy aboard, affixed a one-metre section of PVC pipe to the buoy’s anchor line, and splashed both buoy and pipe into the water before heading north to safety.
A specialised dolphin detector
This PVC pipe housed a specialised sound recorder, called a T-POD, and we were on a mission to get this device in the water and recording before the weather arrived. In short, T-PODs are dolphin detectors. They listen to the surrounding ocean with a hydrophone (an underwater microphone) and, with the help of an algorithm, tell us when they hear dolphins.
Hector’s dolphins use high-frequency clicks to communicate and find food. If we tune in, we can listen for when they are around, even when we’re not on the water.
How do Hector’s dolphins respond to boats?
In previous installments, we learned that the distribution of Hector’s dolphins at Akaroa has shifted during the last decade and boat traffic has likely increased. By combining tracking of boats with detection of dolphin clicks, we can look closer into whether boat traffic may be having an influence on where the dolphins go.
We moored the T-POD within the field of view of our automated camera, off Nine Fathom Point. This gave us high-resolution data on when dolphins were present, that could be examined in relation to variations in boat traffic.
At the same time, we measured multiple aspects of boat traffic, as well as environmental variables, from GPS tracks and the automated camera.
Disruption and opportunity
It wasn’t just southerlies that kept us off the water. Our 2019 – 2020 field season was cut short as the March 2020 Level 4 Lockdown came into effect. Fortunately, we serviced the T-POD just in time. With it being illegal for most boats to be on the water, I crossed my fingers in isolation, hoping the batteries lasted. How would the dolphins respond to a quiet harbour?
Statistical modelling revealed that there were fewer detections of dolphins at Nine Fathom Point on days with more dolphin tour trips, more motor vessel traffic, and when one or more cruise ships was present in the harbour.
Our findings suggest that Hector’s dolphins at Akaroa Harbour have been displaced by boat traffic. This lends support to the hypothesis that increasing cruise ships, and related tourism activity, have contributed to the shift in dolphin distribution seen during the last decade.
How can we work together toward changes that promote mutual flourishing for coastal people and wildlife?