What El Nino might reveal about great white sharks in NZ

New Zealand’s El Nino summer could give us a clearer understanding of what attracts great white sharks to areas such as Tauranga Harbour, shark scientist Dr Riley Elliott says.

He said the previous three summers had been La Nina – a climate pattern bringing prominent easterly winds and warmer water – and the sharks had been “really apparent”.

That had been a bit unexpected because the conditions should have meant less food around for them.

He said it would be “interesting” to see how the switch to El Nino’s westerlies and cooler waters this summer would impact the sharks’ distribution.

Elliott said the El Nino pattern “pushes our coastal water offshore and pulls up deep water from the bottom [like a] conveyor belt system”.

This was predicted to create “lots of upwelling and food productivity”, meaning “greater fish life” and more food for the sharks.

“Māori legends say east is least, like when the wind is blowing east the fishing is the least … so west is best.

“It will be interesting to see if La Nina, which bought us warm water — which is very important to baby sharks that can’t regulate their body temperature — if that was a major driver or is it food, and the habitat.

“Basically, there is a lot of unknown in the ocean.”

Great White App

Last summer Elliott’s interactive Great White App allowed the public to track four satellite-tagged sharks, most famously 2.75m female Daisy, as they moved around, often in the Bay of Plenty.

Daisy’s tag, like the others, came off as expected after about five months.

A great white shark identified as Daisy and tagged by scientist Riley Elliott.

Elliott said thanks to public sponsorship he had funding for new trackers but had not yet tagged a new cast of characters for the app, with waters warming later due to El Nino.

Like all fish species, the sharks tended to go offshore during winter and were not likely to return until coastal water temperatures reached about 20C.

“When reports of great whites become more common, new tagging efforts will be made.”

He said one of the biggest takeaways from last summer’s tracking was seeing sharks such as Daisy swimming “right in front of the surf club” during the busy school holidays and “nothing happened”.

“[It] is like ripping off the Band-Aid and looking under the bed and realising the boogeyman isn’t there, you know, it’s just, it’s just a fish.”

The wider research project aimed to better understand the species’ breeding grounds and population.

A protected species, great white sharks continue to be tracked for research in New Zealand. Photo / Clinton Duffy

Another takeaway was seeing how “highly mobile” the tracked sharks were, moving all around the coasts.

Elliott said it suggested the Waihī area was not “shark town” as it may have seemed, although Tauranga Harbour was an important nursery area for great whites.

A swimmer was fatally attacked by a great white shark off Waihī Beach in January 2021 and locals reported an increase in great white sightings in recent years.

Elliott said the combined great white population of Australia and New Zealand was thought to be about 2000 to 5000.

“When you break it down, that’s only 200 to 500 adults and, of them, only about 50 will be mating every year,” with about 250 babies being born.

New Zealand shark scientist Dr Riley Elliott says it will be interesting to see if an El Nino summer impacts the distribution of great whites.

Signs of the big fish in the Bay of Plenty were indicators of a “very healthy ecosystem” that locals “should be proud of”.

Elliott said people should not be afraid of sharks in the water but use the “golden rule” to stay safe.

He said sharks were “very polite predators” and swimmers should “avoid overlapping with food”.

“The golden rule is don’t swim where people are fishing and don’t fish where people are swimming.

“Just go and enjoy the summer and more importantly, focus on swimming between the flags and wearing a lifejacket.”

How you can help with shark research

Elliott said it was important for people to report great white shark sightings to him and the Department of Conservation.

DoC marine technical adviser and shark scientist Clinton Duffy said DoC was interested in “receiving details of sighting of any protected fishes including great white”.

He said both the west and east coasts of the top half of the North Island were “considered a nursery area for great white sharks”.

“It’s common for great whites to develop preferences for certain sites and return regularly, so although we can’t predict what sightings will occur this summer, people should expect to see great white sharks, among others.

Department of Conservation marine technical adviser and shark scientist Clinton Duffy. Photo / Clinton Duffy

“We also appreciate being notified promptly if anyone comes across a dead white shark.

“Both types of information help us better understand the distribution of the species, particularly differences between juveniles and adults.

“Access to dead specimens gives us a chance to study things such as their diet, age and growth, reproduction and threats.”

Staying safe in the water

To keep yourself safe from sharks, avoid swimming or diving:

• at night
• near seal colonies
• near large schools of fish
• in areas where marine life is actively feeding
• in areas where people are fishing or discarding fish remains
• near whale stranding or burial sites.

Source: Clinton Duffy, Department of Conservation

Michaela Pointon is an NZME reporter based in the Bay of Plenty and was formerly a feature writer.