Scientists tag Fiordland's broadnose sevengill sharks to monitor climate change impacts

Sharks are one of the scariest creatures in our oceans, but also one of the most important as they're a crucial part of the ecosystem.

A Kiwi-led team of scientists has been catching and tagging broadnose sevengill sharks in Fiordland to monitor how climate change is affecting them.

"There was a lot of excitement and a lot of anxiety around this, as it was the first trip to do this work, but we had such a great team on the boat," said project leader Alice Rogers from Victoria University.

Rogers is a lecturer in fisheries science at Victoria University, but twice a year you'll find her in the deep south working with the Southern Fiordland Initiative who are helping her find the sharks.

"We have to fish for the shark essentially, once we've caught a shark we bring it alongside the boat. We keep it in the water so that it's got water constantly moving across its gills, then we attach a tag, and the tag is this transmitter that stays with the shark for up to 10 years or so," she said.

"They were up to 2.5 metres [long] some of the females we caught, but it was nice to see they were a very calm and relaxed animal," said Rogers.

Tagging a shark.
Tagging a shark. Photo credit: Supplied

The project is funded by the Save Our Seas Foundation, and the team of researchers have tagged 11 sharks with small tube-like transmitters that will collect data about the shark's temperature and depth.

To get the information from the tag, scuba divers have anchored 29 acoustic receivers on the seafloor.

"If the shark swims within around 400m from those receivers the information in its tag will be transmitted to that receiver," said Rogers.

The transmitters that are attached to the sharks.
The transmitters that are attached to the sharks. Photo credit: Supplied

The most common shark in Fiordland is the broadnose sevengill (notorynchus cepedianus). Rogers said they are a fundamental part of this place, and without them it would look, feel and function very differently.

"When you've got a top predator like that that controls all the other animals, if it suddenly goes somewhere else, or if it turns up and there are more of them... it's really important for us to understand that," she said.

Scientists already know that fishing activity is reducing a number of different shark populations globally, but little is known about the impact of climate change.

Rogers wants to know how a changing climate and more frequent extreme weather events are going to affect sevengill sharks in Fiordland.

"Will their movement patterns differ? Might they escape to deeper waters to avoid heat stress in the shallows? Does their behaviour change in the short term, when floods hit or droughts strike?"

One of the sharks.
One of the sharks. Photo credit: Richard Kinsey / Supplied

Her team of experts includes scientists from NIWA, who have also supplied the acoustic receivers, and Ross Dwyer from the University of the Sunshine Coast who is doing similar work over in Australia. Dwyer said he didn't hesitate to join the Fiordland project when Rogers asked.

"It's an amazing place to be able to conduct this research, to see how these animals respond to the warming temperatures, and see what their capacity is to be resilient to these warming seas," he said.

"What an incredibly magical place, hands down one of the most beautiful places I've been to."

They're worried the sharks could be sensitive to marine heatwaves, but are hoping they'll find cooler temperatures in the fiords.

"We don't know, and that's why this research is so important. The sevengills are the tip of the iceberg, there are lots of other species that live in these sensitive ecosystems that we know very little about," said Dwyer.

And the broadnose sevengill shark is especially interesting for Rogers.

"Their closest ancestors date back to the Jurassic, which is really cool, they're kinda like the dinosaur of sharks," she said.

They'll return to Fiordland every six months to gather data from the receivers, as they piece together how our warming world is changing this magnificent ecosystem.