They were inseparable in life, so it is perhaps not surprising that they went together in death.

When one of Natureland Zoo's two male otter old-timers died last week, his longtime companion was unable to carry on life alone.

It is believed Daz, 19, and Chip, 16 - both having lived to ripe old ages for otters - died of heart attacks within an hour of each other.

"The biggest consolation for us was that we weren't left with one lonely otter. As much as we hated what had happened," said zoo operations manager Gail Sutton.

The pair had been residents of the Nelson zoo for 15 years and had lived largely healthy lives until they recently fell ill, she said.

"About two weeks ago they were a bit off-colour. And so we ran tests on them, and with the vets we decided to give them a course of antibiotics just in case there was something going on."

The pair were taken from the outdoor enclosure they shared and were housed in a warmer quarantine area.

Their treatment appeared to soon bring them back to their "busy, growly, bitey selves".

But on the day last week when they were due to be taken back to their enclosure, they were found dead.

"The keeper who opened the door and found them just looked at them and burst into tears.

"The bottom line is that when one of them had a heart attack, it just set the other one off and he followed through."

The zoo is hoping it will be able to find new otters to fill its enclosure, in a bid to continue raising awareness of the threats they face in the wild.