Ms Thomas is one of a small group of concerned people who voluntarily work to try and control what she says is a "burgeoning problem" in the Central Business District, as well as suburbs and rural areas.
She works in co-operation with Trieste Neilson of C.H.A.R.M and Mary Lou Nation of Precious Paws Paradise to trap, de-sex and re-home cats where possible.
"The cats are living in colonies and if you are around Victoria Ave in the early morning hours, you see them scavenging around."
Red Eye Cafe owner Doug Brett says he sees a lot of cats roaming around town when he starts work early in the morning and there are a couple of regulars behind his cafe.
"I think they might have been left behind when some people from upstairs moved out," he says.
"We keep a tin of cat food here and put it out for them."
Staff at Ab Fab Flowers in Victoria Ave also feed the colony of cats living behind their premises.
"They were living under Christ Church in Wicksteed St before and they have moved down here," says staff member Nicole Comp.
"It is good having them there in some ways because they keep rats and mice away."
She says the downside of the feline occupation is that they tend to defecate everywhere.
"They fight a lot as well because there are so many of them."
Ms Neilson has managed to trap two of the female cats in the colony and have them de-sexed.
She says a female cat can have three litters during a breeding season and by the time she has the last kittens, her first ones will have started breeding.
Whanganui District Council compliance team leader Warrick Zander says if stray or unwanted cats are on a residents' property, the landowner has the responsibility of managing or euthanising them.
"We urge landowners to make sure the cats on their property are strays and are not a domestic cat which has gone wandering.
"Once the landowner has made sure the cat does not belong to anyone, the cat should be euthanised humanly, preferably at a veterinary clinic.
"The Council does not financially support people who trap and de-sex cats, but we do provide cat traps to residents."
Mr Zander said the Council and the SPCA are interested in talking about how they can work together on stray cats.
Ms Thomas says it is in the Council's interests to help control urban stray cat populations because it is a bad look for the city.
"These colonies are increasing around Whanganui," she says.
"There is one behind Pak n Save and I believe there is one at the YMCA.
"What we would like the Council to do is fund the cost of more traps because we only have three, or fund the SPCA to co-ordinate efforts to control the problem."
She says Whanganui SPCA manager Francie Flis is very helpful and supportive of their work but the organisation is under resourced.
SPCA central communications manager Jessie Gilchrist, says there is a lack of accurate information due to there being 45 separately run and financed SPCA centres in New Zealand.
"I know that it [funding from councils] does happen in some areas, but I couldn't tell you which centres, how much funding, or if it is tied specifically to desexing."
SPCA delegates voted to form one national organisation in June this year and Ms Gilchrist says the move will make it easier to gather up-to-date information.
