Relatively little was known about ferrets at that time.
There were suspicions they spread bovine tuberculosis (Tb), and despite this later being proven, ferrets still have her respect and she believes they are misunderstood.
"If it wasn't carrying Tb, as an animal in the pastoral environment it would do limited damage. In fact, it helps with rabbit control."
Ferrets are also much more prevalent than many landowners think, specifically in areas with high rabbit populations, their primary source of food.
During a typical trapping season, from January to the end of May, Dr Ragg will catch 1200 ferrets.
In one 30-day period in Central Otago, she caught 525 and in a smaller area of East Otago in the same time period, she caught 330.
That was the early 1990s, when Tb was prevalent in Otago, and there was debate about whether ferrets, stoats and wild cats were spreading the disease.
Dr Ragg said research on Tb spread in the Mackenzie had revealed possums could not be the only vector, and further research on a South Otago deer farm infected with Tb found three of four captured ferrets had the disease.
Subsequent research in North Canterbury found a correlation between lower ferret numbers following control programmes and a reduction in Tb infection rates in cattle.
At that time, Tb was rife in Otago and the Animal Health Board's attention was sufficiently piqued to request further research on the role of ferrets as a vector, for which Dr Ragg was recruited.
She started catching ferrets, stoats and wild cats on several Otago properties.
Autopsies were performed to determine if they had Tb.
The results confirmed earlier suspicions that ferrets were not the dead hosts they had previously been considered to be, but were carriers and spreaders of the disease.
"It became apparent very quickly that ferrets had a high prevalence of Tb."
Such has been the success of reducing possum and ferret numbers and Tb, Dr Ragg said ferrets were now considered an indicator species for the presence of the disease.
That survey also unearthed information about ferrets' social organisation, their home ranges, use of habitat, breeding cycle, litter size and the fact animals which were once considered solitary were in fact very social at certain times of the year, during which infection could be spread.
Ferrets will eat Tb-infected carcasses or kill rabbits in their burrows, taking over the burrows and feeding on the carcasses.
Other ferrets will join them and after an inevitable fight they will co-habitat until the food source is gone.
Depending on the season, a female can have between one and 14 young, but Dr Ragg estimated 80% die in the first month and 90% of males die at a young age.
There is high mortality of juvenile ferrets anyway, but as they get older they become obsessed with finding a mate, which results in fighting and little eating, behaviour from which many die.
Dr Ragg said ferrets were not necessarily territorial, and there had been instances where animals with tracking devices attached had travelled 56km in the Mackenzie, and another instance where one was found at Naseby - 24km from where it was initially caught and a tracking device attached.
"Initially, when there was a high prevalence of Tb, the ability of ferrets to move was quite alarming, because they were moving Tb all around the place.
"Now Tb is low, it is not such a concern," she said.
Typically, ferrets do not kill indiscriminately like stoats, although rogue individuals can and do.
They are clumsy climbers, which means they do not pose the same threat to birds as stoats and weasels.
Ferrets are instinctively drawn to vegetative cover.
In their northern European homeland, they are preyed on by aerial predators.
If a farmer has rabbits, they are likely to have ferrets living close by in scrubby areas such as shelter belts, pasture margins and stream banks.
"When you are thinking about trapping ferrets, you have got to think about rabbits, sunny faces and areas where rabbits are going to be; [these are] are good places for ferrets."
"They also make use of farm and forestry tracks.
They are mostly visible when juveniles leave the nest, typically in late summer and early autumn, the time Dr Ragg is contracted by TB Free New Zealand to trap the mustelids.
Ferrets and Tb
- Dispelling some myths about ferretsFerrets are quite social animals at certain times of the year.
- Because of this interaction, they spread bovine tuberculosis.
- 80% of ferrets will die in the first month after birth.
- If you have high rabbit numbers, you will have high ferret numbers.
- They are not necessarily territorial, with reports of ferrets travelling 56km.
- Weasels are small and stoats slightly bigger.
- Ferrets are larger than stoats, with adult males weighing up to 2kg prior to mating.