Damage to sand dunes along the Manawatu-Wanganui coastline is risking the extinction of katipo spiders in some areas, researchers say.
"Katipo populations at some sites like Wanganui South and Castlecliff have been more severely affected than at other sites," said researcher Jess Costall.
"Perhaps these populations are at risk of local extinction."
New katipo spiders may have to be moved into these areas to bolster the local populations, she said in a paper published in the New Zealand Journal of Zoology.
These sites had low numbers of juveniles, which could be because the female spiders were distributed so thinly the males were having problems finding mates.
Ms Costall said the decline of those populations was not due to high number of the South African spider Steatoda capensis -- which is competing for the same ecological niche on beached driftwood and sand-dune vegetation.
There were much greater numbers of the South African spider at Himatangi and Foxton, where there were healthy populations of the katipo, scientifically known as Lactrodectus katipo.
She said there was a need for increased monitoring of the species, and reduction and reversal of damage being done to sand dunes by vehicles, dumping, grazing by hares, and the spread of exotic plants with dense growth.
Ms Costall and her co-author, Russell Death, called for continued monitoring of the katipo population along the Manawatu-Wanganui coastline.
She found that artificial retreats could be put down and checked at intervals for katipo occupation -- an approach which took less time than the traditional searching for spiders on driftwood and in dune vegetation.
Ms Costall said katipo -- like many coastal species -- would be highly vulnerable to future rising sea levels, and the coastal dunes in which they lived had already been destroyed for use as farmland or forest plantations. "Rising sea levels would further reduce the little suitable katipo habitat we have left," she said . "Katipo have never successfully established further inland, so it seems they are dependent upon coastal dunes for their survival."
The katipo is New Zealand's only native poisonous spider.