The final phase of a four-year study into spinner dolphins that reside off the Kona Coast, Hawaii Island, has shown that human activity could be affecting numbers of the marine mammals, known for their aerial acrobatics.

Spinner dolphins are small dolphins found in tropical waters around the world and are known for leaping and spinning along a longitudinal axis.

Dolphins seeking a human-free rest might avoid their preferred habitats, which could also negatively affect their eating and mating habits, according to Murdoch researchers.

Dr Julian Tyne is a researcher with the Aquatic Megafauna Research Unit at Murdoch University who has been studying their population, the importance of resting bays and how to implement a management strategy to reduce the intensity and number of human-dolphin interactions.

Dr Tyne has completed three years of field work with researchers from Duke University to assist the National Oceanic and Atmospheric Administration (NOAA) in developing effective management strategies.

Human interaction with dolphins a concern

For more than a decade, interactions between humans and Hawaiian spinner dolphins in their resting bays have been a concern for members of the general public, managers, scientists, policymakers, and tour operators.

Hawaiian spinner dolphins are an easy target of wildlife tourism due to their predictable daytime resting behaviour and presence in coastal areas.

Spinner dolphins need sheltered bays for rest and protection from predators so they can recover the energy they’ve lost after spending the night time foraging for food, but Hawaii Island attracts thousands of visitors, and swimmers, kayakers and boats actively seek  out the dolphins in these sheltered bays for close-up encounters.

However, repeated interactions with humans can lead to changes in many aspects of animal behaviour, inducing physiological stress and changes in behavioural patterns and habitat use, Dr Tyne said.

“Their predictable presence in the bays make it relatively easy to find them,” Dr Tyne said. “This has raised concerns about the effect of their repeated exposure to humans.”

Dolphins exposed to human activity for 80% of daylight hours

“A 50-yard ‘no approach’ rule has been released by NOAA for public comment as a potential mitigation approach, but it will be difficult to enforce. We found the spinner dolphins were exposed to human activity for more than 80 per cent of the day time.”

During the study, dolphins were exposed to human activity within 100m for 82 per cent of daytime hours, with 10 minutes between exposure times. They spend 62 per cent of their day time resting, and despite high levels of human exposure, the researchers did not observe an effect on dolphin resting behaviour.

“I was surprised at just how much human activity they were exposed to – there are fewer dolphins than there were 20-30 years ago, so the activity could be having a negative impact on the dolphin numbers.

“There was simply not enough control data for us to show conclusively the impact of long-term human-dolphin interaction.”

Chronic levels of exposure to human activities could lead to rest deprivation, displacement from preferred habitats and, ultimately, negative population-level effects.

Dr Tyne’s results will have implications for new proposed legislation in Hawaii aimed at reducing dolphin exposure to human activities.

Images supplied by Dr Julian Tyne