What is happening to these rare Marlborough Sounds seabirds?

They're one of the country's rarest seabirds, living only in the Marlborough Sounds - but there are concerns the king shag is in trouble.

A recent census saw bird numbers drop by a quarter. Now a crucial tagging programme is underway which could help find out why.

Eleven king shag chicks and one adult have been tagged for the first time on Pohuenui Island in Tawhitinui Bay as part of a joint effort between the Department of Conservation and Marine Farming Association.

Kingshags living in the Marlborough Sounds
Kingshags living in the Marlborough Sounds. Source: Supplied

"It was thought to be quite a sensitive bird, and so there was a lot of reluctance to do any banding of it but we really needed to learn more about it," explains DOC seabird scientist Graeme Taylor.

Three years ago an aerial survey, commissioned by King Salmon, was carried out which counted a total of 830 birds in the area. This year that total dropped by 200 birds.

"While we are concerned there's been such a big decline, we would certainly like to get a longer term trend data, at least another three or four years to see whether this is part of a steady decline down which would be terrible if it is or whether they just fluctuate in numbers," says Mr Taylor.

It's also possible human activity in the Sounds is to blame.

Marine farms do occupy space and underneath them the habitat may not be suitable for king shags so that has been one of the main concerns in the marine consent hearings".

Other factors could include siltation of the Sounds from run off from land, disturbance of colonies from boating, ocean acidification and climate change.

Marine Farming Association president Jonathan Large says the problem at the moment is "we don't know if we are causing a problem or not".

Which is why they've spent two years collaborating with a number of groups including the Department of Conservation, Ministry for Primary Industries, Marlborough District Council, Iwi and Wildlife Management International.

Together they form the King Shag Working Group.

"What we wanted to try and ascertain is some really good scientific data around not only how many birds are around but also where those birds are interacting, how far their flights are, where we see them,” explains Mr Large.

Local eco-tourism operators will be watching with interest, having tried to raise the king shag's profile.

"I've been watching these birds daily for ten years every day," says E-ko Tours operator Paul Keating.

"Really the significance they hold for us, both nationally and locally, we should put a lot more effort into making sure they are sustainable for the future and their numbers don't decrease".

The king shag is one of the country's rarest seabirds - but how much do we actually know about it? Source: 1 NEWS