A shipping alert was sent out last week and maritime authorities have been monitoring the iceberg flotilla as it drifted north from Antarctica toward New Zealand's South Island.

"It looks like they've all disappeared east of New Zealand," oceanographer Mike Williams, with New Zealand's National Institute of Water and Atmospheric Research, told The Associated Press. He said it would be unlikely they would be seen anywhere near the coastline.

The nearest one, measuring about 330 to 660 feet (100 to 200 meters) long, was 160 miles (260 kilometers) southeast of New Zealand's Stewart Island a week ago.

Australian glaciologist Neal Young said satellite imaging shows no sign of any icebergs northeast of Auckland Islands, 250 miles (400 kilometers) south of New Zealand.

"If ice is there, it's below 500 feet (150 meters) in length," the smallest size detectable on satellite images, Young said.

Williams said melting and erosion by waves would have made many of the icebergs quite small by now, and that it was unlikely scientists will spot them again on satellite.

Large numbers of icebergs last floated close to New Zealand in 2006, when some were visible from the coastline - the first such sighting since 1931.

Scientists say the current flotilla of icebergs likely split off Antarctica in 2000 when parts of two major ice shelves - the Ross Sea Ice Shelf and Ronne Ice Shelf - fractured. The Ross Sea Ice Shelf is the size of France and is also widely believed to be the origin of the 2006 icebergs.

Icebergs are routinely sloughed off as part of the natural development of ice shelves.

The latest appearance of the bergs in waters south of New Zealand depends as much on weather patterns and ocean currents as on the rate at which icebergs are calving off Antarctic ice shelves.

Rodney Russ, expedition leader on board the Spirit of Enderby eco-tourism vessel east of New Zealand, said they had earlier spotted two big icebergs north of Macquarie Island and also sighted two fishing boats working south of Auckland Islands.

"Traffic in this part of the world is pretty light at all times of the year. We're probably one of the only vessels that ply this area regularly," he told The AP in a telephone interview.

While the vessel has a fully ice-strengthened hull, it has up to three sailors on permanent watch in iceberg-affected ocean, a constant radar scanning and also uses powerful searchlights during the short, six- to seven-hour nights, he noted.

"It would be a foolhardy captain who would come down here and not step up the (iceberg) watch and increase the lookouts," Russ said.

©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.