Why fishermen believe shark numbers are increasing in New Zealand waters

An underwater videographer and spearfisher says he is seeing more sharks in New Zealand waters than 10 years ago.

Whangaparāoa’s Luke Potts dives off the coasts of north Auckland’s Te Arai, Leigh and Cape Rodney about once a week, and posts spearfishing demonstration videos to his Youtube channel Aquatic Rehab Spearfishing.

Potts said this season he has seen more sharks than ever before, sometimes between six and 12 per dive, a gradual increase he also noticed looking back at video footage from 10 years ago.

“It’s unavoidable” he said, adding that he will almost always see a shark when diving off the east coast, anywhere from Tauranga to the top of the North Island.

Spear fisher and underwater videographer Luke Potts believes there are more sharks in New Zealand waters this year than there were 10 years ago.

Aquatic Rehab Solutions/Supplied

Spear fisher and underwater videographer Luke Potts believes there are more sharks in New Zealand waters this year than there were 10 years ago.

His comments have been echoed by commercial fishers in Tauranga who say legislation banning shark-finning has protected the species, making sightings – particularly of great whites – more common in the Bay of Plenty than previously.

Last week 19-year-old Kaelah Marlow was killed at Bowentown, near Waihi beach in the Bay of Plenty, in a suspected shark attack.

Coromandel and Bay of Plenty beaches have been on high alert in the week since, with “continuous shark sightings” reported in waters near Pauanui.

Bay of Plenty fishing captain Dan Harvey says he’s seeing more sharks daily. He says that’s likely due to legislation banning shark finning.

Shark finning involved fisherman harvesting the fins and dumping the animal’s body at sea which allowed them to rapidly harvest animals.

The practice can devastate shark populations.

“Aside from a few dodgy cash deals people used to do on the side, the ban has taken away the shark fin market in New Zealand,” he said.

“No one targets sharks any more. The meat is not valuable and, without finning, there is no market for them.”

Dan Harvey unloads his boat at the only public wharf in Tauranga able to take his catch. There is only room for one truck at a time to use the facility.

Matt Shand/Stuff

Dan Harvey unloads his boat at the only public wharf in Tauranga able to take his catch. There is only room for one truck at a time to use the facility.

Harvey says increased shark numbers will likely be spotted near beaches where people swim – and that people need to be more aware of that when in the water.

The Ministry of Primary Industries’ acting director of fisheries management Arthur Hore said it is difficult to assess shark numbers given the migratory nature of the species.

“However, we do think that since the ban on shark finning came into effect in 2014, some shark populations are likely to have improved,” he said.

Potts added that the sea seemed warmer sooner than usual and that he had witnessed a higher presence of sharks much earlier in the season – of the opinion 99 per cent were bronze whalers.

At times, it had been tricky to catch kingfish, as the sharks had learnt to recognise spearfishers’ catch were the source of an easy meal. Sometimes at least two sharks would be vying for Potts’ yield.

“They all know where all the foods going to be, once they get a feed they learn.”

He didn’t know for sure why he had seen more sharks, but wondered if numbers were returning to normal levels since sharks were killed by a processing factory which operated off Kawau Island between 1900 and 1902.

Divers think bronze whalers have learned to hang around spearfishers for an easy feed.

Aquatic Rehab Solutions/Supplied

Divers think bronze whalers have learned to hang around spearfishers for an easy feed.

“If they really gave them a big towel up, they [shark populations] really could have dipped.”

Potts, who has spent “hundreds” of hours interacting with sharks, said people shouldn’t panic about them.

“To me, seeing a shark is just about as normal as seeing the reef.”

Department of Conservation marine scientist and shark expert Clinton Duffy said there was nothing to indicate a population boom among sharks, adding that there was no reason fewer sharks were being killed this year compared to others.

A regular spearfisher off Auckland wonders whether shark populations are returning to normal levels seen before a shark fishery started at Kawau Island in the early 1900s.

Aquatic Rehab Solutions/Supplied

A regular spearfisher off Auckland wonders whether shark populations are returning to normal levels seen before a shark fishery started at Kawau Island in the early 1900s.

The number of shark sighting reports were also “very typical”.

However, he had heard of bronze whalers being able to recognise the potential for an easy feed when spearfishers were around.

Duffy said bronze whalers moved closer to the shore to give birth around October until around February.

There was “no good data” on the abundance, or lack thereof, of sharks for experts to examine critically, as such studies were of low economic value.

“They don’t attract much research funding.”

National Institute of Water and Atmospheric Research (NIWA) marine biology technician Warrick Lyon said it was unlikely there had been a “sudden” increase in sharks this year as any increase would happen gradually over several years.

This was because sharks took more than seven years to reach sexual maturity and produce offspring.

“To get a change in population that big can take years.”

He says fishing changes could lead to increases, among other factors.

“If a species of fish used to be caught by commercial fishers and it is no longer, than there should be an increase in some places,” he said.

Warmer sea temperatures could also speed up shark gestation. While human bodies stay within a certain temperature range, a shark’s physiological and inner workings relied on water temperature.

For example, sharks in warmer waters could grow babies and give birth after eight months, while it may take 11 months for sharks in cooler waters, Lyon said.

He suggested that Potts might be diving in “really sharky spots”, as the ocean was a naturally variable environment and it was hard to say whether a shark would be in a certain spot at any one time.

“If it’s [a good spot] for a spear fisherman, then it’s good for a shark,” Lyon added.

“Sometimes there can be a lot of sharks somewhere and then you can go the next day and there won’t be any there.”

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