What weird and wonderful creatures lurk beneath north-west Australia's deep blue sea?

A crew of CSIRO scientists studying marine life on the north-west shelf are finding out, and have seen some strange things during their voyage.

The research vessel Investigator set sail from Broome on October 11 and is due to dock in Fremantle on November 9.

The team is investigating recovery rates of fish and marine life that live on the seafloor, including sea sponges and soft corals, after heavy trawling in the 1970s and 80s.

CSIRO senior research scientist John Keesing and the RV Investigator. ( Supplied: CSIRO )

Since then, some parts of the north-west shelf have been closed to trawling but other areas remain open.

Scientists will compare their findings with data collected 35 years ago.

Tens of thousands of photographs will give researchers a glimpse of life up to 100 metres below the ocean's surface.

What quirky things have they seen?

A sea cucumber nicknamed the Christmas bauble. ( Supplied: CSIRO )

Sea sponges weighing in at up to a whopping 100kg, and a sea cucumber that might be mistaken for a Christmas tree bauble, are some of the unusual marine life that have been discovered.

CSIRO principal research scientist John Keesing said a family of 30 catfish living inside a massive cup sponge had surprised and amazed the crew.

"When you're sampling from the seabed you find all sorts of extraordinary things," he said.

CSIRO scientists discovered 30 catfish living inside a sea sponge. ( Supplied: CSIRO )

"A very large goblinfish … which has a very big, ugly head and short body… was living inside a dead trumpet shell.

"You find not just extraordinary animals, but extraordinary associations between two different types of animals, or animals and their seabed habitat."

Dr Keesing said scientists had been impressed by the size of some of the sea sponges, because trawl nets towed by fishing boats tended to rip them off the seabed.

"What happened in the 1970s was foreign fleets used to use a very large net to trawl between two ships … and that dislodged a lot of that habitat," he said.

Dr Keesing said removing large swathes of seafloor habitat was like clearing a forest, and it had caused a reduction of large fish such as red emperor.

CSIRO's findings are expected to be published within the next year.