Monitoring the sounds of an endangered dolphin species may provide clues to ensuring their survival, a new University of Otago – Ōtākou Whakaihu Waka study shows.
Published in the New Zealand Journal of Marine and Freshwater Research, the research is the first to use acoustic monitoring to study Hector's dolphins in Porpoise Bay, Southland, an important habitat for the species.
It reveals new insights into when, where and how the dolphins use the bay, and highlights the need to monitor swimmer-dolphin interactions to mitigate potential impacts on foraging activity.
Only a small number of Hector's dolphins use the bay during summer, which previous research estimated to be about 63 individuals.
Max Harvey
Lead author Max Harvey, who completed the study as part of his Master of Science in the Department of Marine Science, says the endangered Hector's dolphins have a highly fragmented population structure.
"Low abundance and limited gene flow between some subpopulations suggest they are highly vulnerable to local extinction," he says.
"By understanding how they utilise important habitat, we can implement strategies to prevent this from happening."
Researchers deployed two echolocation detectors in the inner and middle of the bay between January and August 2020 to record dolphin clicks during all hours of the day.
They discovered that during summer the dolphins preferred the sheltered inner bay in the south-west corner.
Their foraging increased throughout the day, peaking in the afternoon in the inner bay, before moving towards the middle of the bay.
"Increased foraging activity during daylight hours and around high tide likely reflects greater prey-capture opportunities during these periods," Mr Harvey says.
One unexpected result was detecting dolphins in the bay during winter.
"This suggests the bay provides important winter habitat for at least some Hector's dolphins in the Catlins Coast subpopulation, not just during the busy summer tourist season.
"While it may seem harmless, one of the key pressures on these dolphins is recreational swimmers actively seeking out groups close to shore, which may contain vulnerable mother-calf pairs."
During the summer, the bay is popular with swimmers, who can disrupt the dolphins' usual activities.
"Hector's dolphins are small (about 45kg) and give birth to proportionately large calves (about 8-10kg) in relatively cool waters, so the energetic cost associated with nursing their young is likely to be high," he says.
"Being a small-bodied marine mammal with high metabolic rates, they must forage almost continuously to satisfy their high energetic demands.
"If nursing or foraging behaviours are disrupted by human activities, such as swimming directly towards dolphin groups from shore, mother-calf pairs may experience reduced energetic intake."
Encouraging people to follow dolphin-friendly guidelines and continuing long-term monitoring in Porpoise Bay are key to protecting this important hotspot for Hector's dolphins.
"Entering the water at least 50 metres away from dolphin groups and not swimming with groups containing calves are the best ways we can ensure the dolphins can use the bay on their own terms.
"We need to encourage visitors to the bay to be custodians and care for this beautiful part of Aotearoa New Zealand and its unique wildlife."
