The state environment department said in a recent release that marine park rangers had been patrolling Michaelmas Reef off the coast of Cairns on September 9, 2022, when they spotted the couple.
The pair had taken their kelpie dog to the small islet of Michaelmas Cay on a boat before letting it jump ashore.
The cay is one of the most important seabird breeding areas in the Great Barrier Reef.
The couple were charged with entering a restricted area and bringing a dog into a national park.
They appeared in court in late June and pleaded guilty.
A man was fined $300 and ordered to pay $551.40 for court costs.
A woman was fined $200 and ordered to $450 for court costs.
The total came to $1501.40.
“In general, if part of a national park is closed, it is closed for good reason, either to keep people safe or to protect the environment,” Parks and Wildlife Service principal ranger Dan Schaper said.
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“We also don't allow pets into national parks because they can carry diseases or injure protected wildlife.
“In this case, Michaelmas Cay provides critical habitat and breeding grounds for sea birds, which nest all year round on the coastal outcrops and can be easily disturbed by people and especially by domestic animals.
“If disturbed, adult birds could abandon their chicks and eggs, leaving them vulnerable to predatory birds and sun exposure.”
