Thirroul man Peter Armstrong filmed the dead Indo-Pacific bottlenose dolphin floating in the ocean on Tuesday, its tail still stuck in the shark net.

It was not the first time a dolphin had died in the Thirroul net in recent years.

A spokesperson for the Department of Primary Industries (DPI) said the carcass had been removed by its contractors on Wednesday morning.

"The 2.2m Indo-Pacific Bottlenose dolphin was removed from the net as part of regular Shark Meshing Program protocols," the spokesperson said.

"Biological samples were taken from the dolphin for analysis and the carcass was towed out to sea and disposed of as per Management Plan procedures.

"The Shark Meshing Program is actively managed to minimise the impact on marine animals while protecting swimmers at some of NSW's most popular beaches.

"As part of the NSW Shark Meshing Program, frequent inspections are carried out by contractors to minimise the impact on non-target species. These inspections are combined with a range of technology including dolphin 'pingers' and whale 'alarms' to deter marine mammals from the nets."

Mr Armstrong said the dolphin was showing signs of decomposition, but the DPI said its rules were that nets should be checked every three days at a minimum.

"The Management Plan states 'Weather conditions permitting, nets must be inspected no earlier than 12 hours and within 72 hours of the previous inspection'," the DPI spokesperson said.

The Mercury's question about whether this net had been in fact checked on time did not receive an answer.

Statistics from the 2022-23 summer netting season showed eight dolphins were among the non-target species caught in NSW shark nets - all were dead when found.

Only one of these was in the Illawarra - caught by the net at Thirroul Beach.

It was an Indo-Pacific Bottlenose Dolphin, a protected species common to the entire Australian coastline.