A shark species described as "rabbits of the sea" are having an unwelcome population boom in Taranaki waters.
Some recreational fishermen in Taranaki are increasingly finding their favourite spots spoilt by spiny dogfish – a small shark species which grows up to a metre long.
The scavenger sharks, also known as spiky dogfish, are regarded by both recreational and commercial fishermen as unwanted by-catch.
Oakura Surfcasting and Kayak Fishing Club secretary Garry Harrison said Taranaki waters had become inundated with spiny dogfish.
"I went out yesterday and there were plagues of them," Mr Harrison said.
He said he had caught about 40 spiny dogfish while fishing in about four metres of water off Urenui on Sunday.
Some club members believed the set-net ban to protect maui's dolphin was largely responsible for the population explosion.
"Banning the set nets has by far increased the number of sharks out there," Mr Harrison said.
A set-net exclusion zone of 4200 square kilometres is in place along the North Island's West Coast to protect maui's dolphins from getting entangled.
Former Urenui crayfisherman of 44 years Murray Wells said he had certainly noticed an increase in the sharks.
"There seems to be more of them around than there used to be," Mr Wells said.
"Five years ago we never ever had spikies."
But longtime Taranaki commercial fisherman Rob Ansley said it was unlikely the set-net ban had had any effect on the number of dogfish.
However, he does believe some fish species on the West Coast were experiencing considerable population growth because of extensive fishing restrictions and quotas.
"All fish species are increasing because there's nowhere near the commercial pressure out there as there used to be," Mr Ansley said.
New Plymouth Sportfishing & Underwater Club president Lee Drummond said every year club members were seeing greater numbers of spiky dogfish caught.
He attributed the increase in numbers to a lack of commercial demand for the scavengers.
"If there's no pressure on them they're left to breed."
New Plymouth man Dan Govier, who has a masters in marine biology, said he was aware of the spike in spiny dogfish numbers but didn't believe the set-net ban was responsible because it had only been in place for a short time.
As a keen recreational fisherman he had experienced the boom first-hand.
"The spiky dog numbers have been increasing so much each year for a number of years," Mr Govier said.
That was because the sharks had no natural predators and there was no commercial market for them, he said.
"They've got no pressure on them so they're just going to keep booming and that's the way it is."
There was no way of knowing when the population growth would plateau, he said.
"I don't think it will be a good place where it ends up."
- © Fairfax NZ News
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