The ex-girlfriend of a man accused of stabbing a young sea-lion to death said he spoke repeatedly about killing the animal.

Kelly Cormier had been dating 54-year-old Graeme Mark Lowery - whose name suppression lapsed this morning - for only a few weeks, after the pair met through the dating app Tinder in October 2016.

She said the defendant heard a marine mammal interfering with his fishing nets while he was urinating from the deck of his Portobello home one night.

Lowery allegedly vowed to kill the animal responsible.

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"It wasn't just one conversation. He went on about it for like a week or 10 days or something," Ms Cormier said.

Defence counsel Judith Ablett-Kerr QC pressed her in cross-examination.

"I'm going to suggest to you you know the message you want to give this jury and it becomes inflated," she said.

"What you're doing is exaggerating what he said and the number of times he's supposed to have said it."

Cormier denied any embellishment to her testimony.

Lowery is on trial at the Dunedin District Court facing one charge of wilfully ill-treating an animal and another of preventing the course of justice, after he threatened to tell an investigating police officer's wife that the man was having an affair.

The court heard the brief relationship between Lowery and Cormier ended the day before the alleged killing of Rua the sea lion on November 5, 2016.

The woman said her then boyfriend had invited her to a pub but spent the night talking to his friends without buying her a drink.

The spat, Cormier said, came to a head outside the premises.

"He screamed bloody murder," she told the jury. "He screamed and he roared and he called me nasty nasty names."

Lowery allegedly said she was no longer welcome at his house and that she could walk back to Dunedin.

Cormier spent the night at a local resident's home and never saw the defendant again.

She called him a "big, overbearing, awful, loud, angry man", and two weeks later, after hearing about Rua's death, she contacted police.

Why, Ablett-Kerr asked.

"Because I thought it was the right thing to do; because I thought I had relevant information as to who killed the sea lion," Ms Cormier said.

She acknowledged she was aware of a reward being offered but said her actions were nothing to do with a financial incentive.

"I don't think I'd put myself through all this drama for it," she said.

Lowery's daughter Carmen, who gave evidence yesterday, also spoke out against the man.

She maintained the reward had no bearing on her decision nor any grudge she may have against her father.

The trial, before Judge Michael Crosbie and a jury of nine women and three men, continues.