A wayward scientific instrument has completed a remarkable year-long journey across the Tasman Sea, delighting the Aussie researchers who thought it had been lost for good.

The device, called an acoustic doppler current profiler, or ADCP, had been deployed 100m below the ocean surface off the coast of Bondi Beach and broke from its moorings at some point between last October and January.

It was part of an array used by University of New South Wales (UNSW) scientists monitoring the East Australian Current, measuring ocean dynamics, including speed, temperature and pressure.

When UNSW researchers discovered it had gone missing - probably during a storm - they were faced with the prospect of losing years of valuable data.


Ten months later, that disappointment turned to joy and surprise when Foxton man Rusty Kuiti phoned to say he'd come upon it while out fishing on Waitarere Beach.

"We were very happy," UNSW researcher Stuart Milburn said.

He promptly sent his father, Mike, down from Thames to pick it up with his ute.

"It was quite an event down there, because a lot of people turned out to see the handover ... it was a bit of a laugh."

For his discovery, Kuiti was rewarded with a case of beer.

"It's great to have the instrument back, because it contains a long-term data stream covering a number of years - and that gap in the data had been a real loss."

Associate Professor Moninya Roughan, a UNSW oceanographer currently based at Auckland University, said the instrument was in "remarkably good shape" considering its rough trip across the Tasman.

The fact it had been adrift for a year suggested the journey had been a lot longer than the 2246km between Sydney and Foxton - but she wasn't surprised it had ultimately ended up on a New Zealand beach.

"I would've thought the probability was high, but it's a long and perilous crossing, the Tasman Sea."

She explained the East Australian Current flows down the east coast of Australia, eventually heading eastwards toward New Zealand.

"Much like the Bledisloe Cup, it goes to New Zealand and never comes back."

While her colleagues had lost instruments in the past, this was the first that had popped up on the other side of the ditch.

Because the device didn't have GPS tracking, it would have only measured temperature on its course to New Zealand, and what data it collected on the way was of little to no scientific value, Milburn said.

"But we really won't know until we get it back; it's certainly of interest, so it might be a good student project for someone."