Researchers are diving deep to find out more about the ocean sunfish, the Jabba the Hutt of the fish world, that hang out on the reefs off Bali for just three months each year. They’ve become an intriguing tourist attraction for divers, but is this tourism sustainable?

The sunfish head to the reefs from July to October to seek out cleaner fish—such as longfin bannerfish and emperor angelfish— which help them remove skin parasites and clean up skin lesions.

“It’s a bit like a spa for these gentle giants, which can weigh over 2,000kg,” explains Marianne Nyegaard, a PhD candidate from Murdoch University.

Marianne has spent three consecutive seasons diving with the sunfish, studying their movements. She wants to make sure the diving tourism isn’t disturbing for the fish and that it’s sustainable.

“We’ve deployed eight satellite tags in Bali and sampled 30 fish from the local area for their genetics,” Marianne says.

“Local dive operators have logged thousands of dives enabling us to look at temporal and spatial occurrence patterns of sunfish in the Nusa Penida Marine Protected Area. Our temperature logger array has recovered more than two million data points.”

While Marianne is currently working through her data, she suspects the sunfish are probably more vulnerable to climate change than to the effects of curious onlookers.

The research has involved collaboration between Murdoch University, Aarhus University, the Coral Triangle Center, and RISTEK-DIKTI; and was funded by Seaworld Sea and Rescue Foundation Australia, Graduate Women WA, the PADI Foundation, and the Australian Government.

Credit for banner image: Marianne Nyegaar.