By Sarah-Jane O'Connor 01/02/2016

Numbers of the Antipodean wandering albatross have continued to fall, according to New Zealand researchers who visit the birds’ main breeding island every summer.

The population has been monitored since 1994 and in a brief report to New Zealand’s Department of Conservation (DOC) in December, scientists Graeme Elliott and Kath Walker warned that the population has continued to drop.

During the 1990s, Elliott and Walker found that the albatross population was increasing, presumably thanks to a decrease in long-line fishing

But in about 2006 there was a notable decline in the breeding population which has continued for the past decade.

Every year when they visit the birds, Elliott and Walker search a 29-hectare study area and attempt to identify every pair of breeding adults – any unknown birds are hopefully banded for future surveys. All the nests are labelled, mapped and the results of the previous year’s breeding noted, plus new chicks are banded.

That work gives estimates on survivorship, productivity, recruitment and attendance on the breeding grounds. Additionally, an annual census of nests in three areas on the island gives an estimate of population trends.

Wandering albatross can live for over 40 years but do not start breeding until about 10 years of age and then only breed every two to three years – that means they are particularly susceptible to high mortality rates, such as through by-catch.

The Antipodean wandering albatross (Diomedea antipodensis antipodensis) is endemic to the Antipodes Islands – located about 850 kilometres south-east of New Zealand’s Rakiura/Stewart Island. About 99% of all breeding occurs on Antipodes Island, with some remaining pairs nesting on Campbell Island and the Chatham Islands.

It is one of two sub-species of Antipodean albatross – the second, Gibson’s, nests on the Auckland Islands.

Mark-recapture work has shown that between 1995 and 2004 the number of breeding adults on Antipodes Island increased by 7% a year. But since then, the numbers have dropped by 9% per annum for females and 5.2% per annum for males. By 2013, the female breeding population was 40% what it had been in 2004.

Tracking data has also found that birds are foraging over a much greater area of the ocean than they were before the population drop and are visiting areas they had hardly been to before. Female birds are foraging in more northern waters, which may go some way to explaining the difference in survival rates if females are more exposed to long-line fisheries by-catch.

Elliott and Walker, who are currently on Antipodes Island for the annual population monitoring, wrote that they needed to secure funding to continue the work. Since 2012, the pair has funded the annual monitoring themselves, with support from DOC and the New Zealand Navy.

They recommended that changing oceanic conditions would need to be investigated to see if that was partly behind the decreasing population and that further studies should be made of the fisheries by-catch of D. antipodensis females, both in and outside of New Zealand’s Exclusive Economic Zone.

Featured image: an Antipodean albatross chick tests its wings. Kath Walker.