Had it not been for the donkeys of Santorini, few people would have associated overweight tourists with animal welfare or heard of the law Greece is about to pass.

The island’s volcanic beauty lures millions of tourists each year, but the donkey population paid a heavy price for a record number of visits last year.

Describing the vertiginous climb from Santorini’s port to Fira, the island’s clifftop capital 400 metres (1,300ft) above sea level, Evangelia Konsta, a spokeswoman for the council, said: “Cruise passengers basically have three ways of ascension.

“They can go by foot, cable car, donkey or mule. When there are thousands arriving every day, and no more than five cable car cabins with the space for six people at most, the choice is limited to two options. In the heat, not everyone is so keen on the first.”

The demands of carrying cruise ship passengers up 600 steps have resulted in more equines sustaining spinal injuries, saddle sores and exhaustion than ever before.

Frequent reports of abuse and neglect led animal welfare groups to visit the island in August.

Under international pressure, the Greek government has acted. Legislation put forward by the agriculture ministry will make it illegal for owners to burden animals with “any load exceeding 100kg (15st), or one-fifth of [their] weight”. Although tourists have not been directly mentioned, the regulation has been interpreted as a ban on overweight holidaymakers mounting the creatures.

It is expected to be enshrined in an equine passport law requiring individual identification of all donkeys, horses and mules, due to be ratified by parliament in the coming weeks.

The measure, part of a revived code of conduct aimed at improving the welfare of all equidae, cannot come soon enough for those concerned about animal welfare.

Paul McGlone, the chief executive of the UK-based Greek Animal Welfare Fund, said: “Greece has good laws but all too often fails to implement them.

“It’s not only [donkey] owners in this case who need to be responsible, who have to say ‘you appear to be too heavy. I am sorry, but my animal has limits’. Tourists, too, also need to make an informed decision.”

A petition entitled “Stop animal abuse of donkeys and horses in Santorini” was signed by nearly 109,000 people.

Aware of the depth of feeling, Santorini’s mayor, Nikos Zorzos, has embraced the legislation, with tenders being announced for the construction of new shades and troughs for the animals – a demand of welfare groups who will visit again later this year.

Zorzos, a former teacher with green leanings, has spent most of his seven years at the helm of local government dealing with the effects of overtourism.

In 2017, the island attracted 2.4 million tourists. More than 700,000 were from cruise ships. Although Santorini is less than 76 sq km in size, with the infrastructure of a rural outpost, more than 25,000 people live there permanently. On the back of the increase, more mules and donkeys have been brought in from France.

Zorzos said: “We welcome any measure that will improve the animals’ welfare. There are around 300 donkeys down at the port, but elsewhere too, they have always played a role in our island’s economic and social development. Santorini was practically built with donkeys.”

Alleged abuse filmed this summer appears to have caused concern. “Like human beings, there are good and bad [donkey] owners … We are talking about an isolated few,” he said. “The majority know that as working animals and the source of their income, they need to be cared for.”

With the surge in visitors putting “unbearable” strain on the island’s services, the mayor has limited the number of passengers who can disembark from the huge cruise ships that arrive every day.

“By 2020, this measure will be fully enforced,” Zorzos said. “And life will become more tolerable for all, including our donkeys and mules.”