A rare albatross endemic to New Zealand's subantarctic islands could be lost within a few decades if urgent action isn't taken to stop its slide to extinction, Conservation Minister Eugenie Sage says.

Sage, who has been visiting the remote, windswept islands south of New Zealand, said there was a risk the critically endangered Antipodes Island wandering albatross could become functionally extinct within just 20 years.

The population, which breeds almost exclusively on Antipodes Island, has experienced an alarming decline in the past 13 years, with very high mortality of females and reduced breeding success.

Under the current rate of decline, fewer than 500 pairs will remain within the space of two decades.

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"In 1994-96, there were 5180 pairs breeding each year on Antipodes Island," Sage said.

"By 2015-17, there were only an estimated 2900 pairs breeding there each year."

More research was underway to better understand the situation but, if nothing changed, their future was "very grim", she said.

The decline co-incided with a change in foraging behaviour, with females in particular travelling much further than they formerly did, taking them into international waters northeast of New Zealand and as far east as Chile.

Females were dying in large numbers, which had led to a very skewed sex ratio in the population, with many males now unable to find a partner.

"The main known human cause of adult mortality is bycatch in fisheries," Sage said.

"Wandering albatrosses are known to be highly susceptible to bycatch, particularly in pelagic longline fisheries such as those targeting tuna.

"Reduced food, squid and fish, and alteration in the birds' foraging locations due to changing ocean temperatures and wind speed may be the cause of reduced breeding success in recent years."

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New Zealand was working with international organisations such as the Agreement on the Conservation of Albatrosses and Petrels (ACAP) and Regional Fisheries Management Organisations to highlight the concern for Antipodes Island wandering albatrosses when they leave New Zealand waters and to try and ensure fisheries' bycatch risks are appropriately managed, even on the high seas.

In New Zealand waters, a National Plan of Action has been developed to reduce seabird bycatch.

New Zealand vessels were required to use bird-scaring lines and daytime line setting among other methods, to minimise any chance of accidentally hooking and drowning seabirds.

"Further research on the diet and foraging patterns of Antipodes Island wandering albatrosses can help better understand what is happening to these birds," Sage said.

"The rapid collapse of the Antipodes Island wandering albatross population means we need urgent international action to prevent this magnificent species sliding into extinction."

Such action could include protecting important seabird feeding areas to reduce albatross deaths on hooks in pelagic longline fisheries for tuna and swordfish, she said.

"Gaining a better understanding of the birds' diet will help us identify how fishing may be influencing the availability of prey, and could potentially allow for fisheries management to improve the availability of prey species for the Antipodes Island wandering albatross."