The pair then spent two years developing a passive trapping program for the National Parks and Wildlife Service, which has seen over 1000 horses taken from the park to be tamed and rehomed.

Later, the horses were shown to be direct descendants of Walers bred for service in the First World War and were recognised as a breed - Guy Fawkes Heritage Horses - which are highly regarded for their resilience and endurance.

Related: Attuned to the wild side

This week, Invasive Species Council CEO Andrew Cox used the 20-year anniversary of the mass shooting to declare that the subsequent ban on aerial culling has created an environmental crisis, as "horse populations in parks are without effective control".

"After the 2000 cull Guy Fawkes River National Park had less than 100 horses and yet despite a trap and removal program it is now home to about 1800 horses and rising," he said.

"The ban on aerial culling has been an abysmal failure for the some 11 NSW National Parks with feral horse populations. In almost all parks there has been an exponential growth in feral horse numbers and escalating damage.

"It's time to reflect on the anniversary of the Guy Fawkes incident and accept the reality of what it has meant for the NSW National Parks system."

However, Erica Jessup from the Guy Fawkes Heritage Horse Association said the problem is how the National Parks & Wildlife Service runs the trapping program.

"Our horses are in strong demand. For many years demand has far outstripped supply. We have a waiting list for horses to be purchased.

"We have worked hard to have a viable management plan, stud register and well organised association and the only singular problem is the fact NPWS do not make the horse trapping program a priority."

She said this calendar year the Guy Fawkes Heritage Horse Association has received a single colt from the NPWS trapping program.

Erica explained that she and her husband Graeme were the original contractors who did trial trapping for NPWS in 2004-2005. They were capturing horses above the breeding rate, which is roughly 20 per cent per year.

Later on, NPWS took the job back in house, and according to Erica the number of horses being removed went into a decline and has never been above the annual breeding rate since.

"In 2012 Caring for Country (Aboriginal youth employment scheme) were awarded funds to trap horses in the northern end of the park. They were very successful until their funding was cut," Erica said.

She said aerial culling will not work in the Guy Fawkes River NP.

"There are no flat open areas of land big enough in the GFRNP to be able to get horses moving out as required for aerial culling, which is why last time they did this they chased them with the choppers up steep ridges and shot them when the exhausted horses couldn't climb any higher.

"This has been discussed many times with the NPWS and the Horse Reference Group, which was set up to oversee the management of the horses in the GFRNP.

"We highlighted to the NPWS the growing welfare problem in the park over the last few years of the drought, pleading with them to go and trap some horses as there were hundreds of hungry horses waiting to be easily trapped. They did nothing."

Erica said she wouldn't be surprised if up to 1000 horses died of starvation in the last months of 2019. During a trip inside the park since the fires she counted eight horses in an area where there would normally be 200.

The Northern Tablelands office of National Parks & Wildlife Service, which manages Guy Fawkes River NP, was approached for comment on its trapping program.

They confirmed that nearly 1,100 horses have been removed from the park since 2004 under the Guy Fawkes River National Park Horse Management Plan 2006 and said aerial shooting was not being considered.

"A survey of wild horses in Guy Fawkes River National Park is currently underway and will guide control efforts," a spokesperson said.

However, the spokesperson did not respond to a question about why the number of horses they've trapped has been in decline for years or why only one horse has been removed from the park in 2020.

Erica believes NPWS simply doesn't have the necessary resources to handle the trapping program adequately.

Like Andrew Cox, she would prefer to see horses out of the national park.

"We want to reduce the population to zero, but we want it done humanely," she said.