They are small and round and look like furry footballs - and they are being kicked to death by young Australians for "fun". The quokka, a species of miniature wallaby found only in Western Australia, has become the renewed target of a sadistic "sport" called quokka soccer.

Since last Sunday, eight quokkas have been found dead on the seven mile-long island of Rottnest, apparently kicked or beaten to death.

The animals were found on a cricket oval near Thomson Bay Settlement, one of the few villages on Rottnest, a resort island in the Indian Ocean 12 miles west of Fremantle. Quokka soccer began in the 1990s when day-trippers from the mainland began kicking and killing the animals - a protected species - for fun.

Incidences of quokka killings tailed off and it had been hoped that the cruel craze was over but last November it re-emerged in a variant form: quokka hockey.

A 16-year-old schoolboy was given a formal caution after he admitted that he hit one of the rabbit-sized marsupials with a stick.

The police on the island are now investigating the latest attacks and say that a number of visitors have come forward with information which they hope will lead to an arrest.

Senior Constable Michael Wear, of the island's small police force, said: "Quokka soccer was well known in the 1990s. People would just walk along and boot them for no reason. It happened quite a lot but since then we've had very few attacks.

"It's disgraceful. They're very cute little things. They're round and furry and about the size of a soccer ball. Like kangaroos the females keep their joeys in pouches."

Apart from a small colony in the south of Western Australia, Quokkas are found nowhere else in the world. Rottnest supports a population of about 10,000.

The animals are naturally inquisitive and - disastrously for their own survival - largely fearless."They wander down the streets and into cafes and restaurants," Constable Wear said. "You can get right up to them."

In 1996, in response to the cruelties of quokka soccer, the Western Australian government imposed a fine of A$10,000 (£4,000) for anyone caught harming the small herbivores.

The dead quokkas discovered last week were found by maintenance workers who alerted the island's wildlife rangers.

Sallyann Gudge, one of the rangers, said: "I've shed many a tear over the last few days. We are all really shocked and upset about the whole thing. I just don't understand human beings sometimes. I hope and pray that this sort of thing doesn't happen again."

Rottnest ("rat's nest") was originally named by a Dutch explorer, Willem de Vlamingh, who discovered the island in 1696 and mistook the quokkas for giant rats. The island was settled by the British in 1831 and was used as a penal colony for Aborigines between 1838 and 1902.

Known as "Rotto" by locals, its sandy beaches and turquoise bays make it a popular weekend getaway destination for people from Perth and Fremantle.

Private cars are not allowed, and the island's 500,000 annual visitors get around by foot or by bicycle. The quokkas are one of the island's main attractions.