Otago shags move to Sumpter Wharf

Up to half of the world's Otago shags - Otago's only endemic seabird - now live in Oamaru Harbour.

After a year of substantial growth, the Otago shag colony on Sumpter Wharf was no longer just the largest colony of the species anywhere. The roughly 650 nests on the ageing wharf represented 40% to 50% of the entire species, Dr Chris Lalas, who has monitored the birds since 1977, said.

The number of nests on Sumpter Wharf increased ''hugely'' from last year from about 411 nests to this year's roughly 650 nests - a 58% increase.

Maukiekie Island, at Moeraki, held the largest number of Otago shag nests from the 1980s to 2017, but last year Dr Lalas recorded a 19% increase in nests at Oamaru Harbour, a rise of about 65 nests from about 346 nests.

This year, the number of nests at Maukiekie Island dropped again to about 245 and at Taiaroa Head, the third-largest colony of the species, about 236 nests remain.

The size of the increase in nest numbers at Sumpter Wharf was evidence Otago shags were arriving in Oamaru from elsewhere, Dr Lalas said.

''What they've done - heaven knows why - is that they're emptying out of Otago Peninsula and going north and south. And down south they're on one island that is very difficult to get to, and they're also at Nugget Point.''

But the bulk of the population had now for years drifted north - Otago shags only began nesting on the 200m-long Sumpter Wharf in 2014 after it had been closed to traffic in 2004.

Oamaru Blue Penguin Colony science and environmental manager Dr Philippa Agnew, who is also one of four community representatives on the Waitaki District Council's harbour area committee, said the news was ''very exciting''.

It showed Sumpter Wharf was an important part of prime habitat for seabirds.

''That we've got this many of an endemic species in one area tells us that it's really productive. It's obviously got ideal conditions, particularly here [Sumpter Wharf] it would be in terms of the lack of disturbance, and lack of predation,'' Dr Agnew said.

It could also prove an opportunity for education about the birds, she said.

In July last year, the council approved a $35,000 budget for a dedicated viewing area for the harbour's Otago shag colony.

Dr Lalas' nest counts for the species this year included a broad range of about 1300 to 1630 nests in total because three nesting sites required aerial surveys for accurate counts, he said.

hamish.maclean@odt.co.nz