Last updated 12:57 23/07/2013
Captain Brent Thomas of the Sealord vessel Aukaha, a 45-metre Nelson-based fishing trawler, said people often asked him if earthquakes could be felt at sea. Now he knows.
A noise and a shudder like a massive explosion beneath the 1200-tonne trawler turned out to be Sunday evening's 6.5-magnitude earthquake beneath Cook Strait.
"I've worked in the strait for 20 years and I've been fishing for Sealord for 24 years, and I've never felt anything like it.
"I'd never felt an earthquake at sea before," said Mr Thomas who reckons they must have been positioned pretty well near the epicentre of the quake that struck just after 5pm.
Passengers on the Cook Strait Interislander ferry, which was crossing the area on Sunday, were alarmed by the shaking felt on the vessel.
An Interislander spokeswoman said the captain of the Arahura thought at first he had hit something.
Mr Thomas said they were in Cook Strait fishing for hoki and conducting research on hoki stocks. They were preparing to fish when the quake hit.
"The whole boat was shuddering. It felt like a massive explosion had gone off beneath us."
Mr Thomas said he stopped the boat, turned up the radio, and began checking everything but could not explain what it might have been, so he carried on.
"It was like a loud, shuddering steel noise.
"I would have sworn something had gone through the propeller, like a log, or a net.
"I shut down the pitch, then we were dumbfounded to learn it was an earthquake.
"The ship was almost jumping out of the water. You never stop learning, but that's what it's all about, I guess," Mr Thomas said.
Alison Sykora of Sealord Group said the company had three vessels in the area at the time, including the Thomas Harrison and Otakau. The company made sure all those on board were able to contact families as needed.
Mr Thomas said the aftershocks kept coming. He knew from spending a long time at sea there were always earthquakes, but until Sunday he had not known they could have been heard or felt.
A Nelson family sailing from Samoa to Tonga in 2009 when the 8.1-magnitude earthquake struck and generated a devastating tsunami, felt the quake rattle their 23-tonne steel yacht.
Pat and Clare Holmes and two of their three children were sailing over the Tonga Trench, which drops to 10 kilometres at its deepest point, and felt a long shuddering which turned out to be the massive quake.
"We were very close to Tongatapu - about 40 nautical miles east of the island. We were sailing along and all felt this strange vibration in the boat.
"It went on for a while. My wife Clare thought it might have been a whale rubbing up against us and I thought a part of the rigging had broken."
Mr Holmes recalled the water suddenly looking "odd", with patches of calm in what had been sea conditions typical of those stirred up by a 12-knot breeze.
"It was just an unusual noise and then it stopped dead. I was still puzzled when it started up again and I knew then it was an earthquake," Mr Holmes said.
It was not long after they heard on the yacht's VHF radio that yachts were clearing out of northern Tonga, where the tsunami struck and killed many people.
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