A man charged by police after claims he tossed a quokka into the ocean off Rottnest Island has been given a spent conviction for animal cruelty.

Bevan Denis Hames, 37, who has a degree in zoology, has defended his actions with the Perth Magistrate's Court accepting he placed, rather than threw, the marsupial in the water.

The quokka was able to swim to shore from a jetty near the Rottnest Hotel about 10:00pm on Friday.

Hames, who is from Christchurch in New Zealand, pleaded guilty to animal cruelty and was granted a spent conviction and fined $2,000.

Hames' lawyer Nick Terry told the court his client had no idea he was doing anything wrong, and wanted to show his friends at the pub that quokkas were surprisingly good swimmers.

Mr Hames told his friends that quokkas swam in a similar way to doggy paddle.

Quokkas are found in abundance on Rottnest Island and are a major drawcard for tourists, but are no longer common on the mainland.

Mr Terry told the court his client apologised for and regretted the ill-treatment of the animal, and had a "proven passion for animals and animal welfare".

Quokkas are a major tourist attraction on Rottnest Island. ( Flickr: Eirik Luka )

He described it as a "momentary lapse of judgment" that was not a malicious act.

Mr Hames rejected the allegation he threw the quokka into the water, saying he placed it into the water and it jumped from his hands.

The court accepted Mr Hames knew no harm would come to the animal by putting it in the water close to the shore, and it was not done in an "experimental" way.

Threatening emails sent to Hames

Magistrate Steven Heath said there would have been a "substantially different outcome" for Mr Hames if the quokka had been hurled, as previously reported.

Authorities say they have not noticed any increase in acts of cruelty against quokkas. ( Flickr: Finn Pröpper )

The court heard since the story went "viral", Hames and his colleagues had received threatening emails, and it had been devastating for his family.

Another man was fined after allegedly helping Hames catch the quokka.

The 38-year-old from Noosa Heads in Queensland was issued with a $200 Rottnest Island Authority (RIA) infringement notice and was evicted from the island.

The case comes after a 21-year-old man was fined last week after admitting to the ill-treatment of a quokka. He had filmed a man allegedly attacking the animal on the island last month.

The man who was recorded in the video is due to reappear in court in May.

In 2015, two French backpackers were fined after one of them set fire to one of the animals.

The RIA said there had not been any discernible increase in incidents of quokka harm.