THE critically endangered Mary River Cod is among the first Australian native fish to be saved from extinction in the Bremer River.

Fisheries biologists yesterday electronically tagged and released 100 Mary River Cod at the site of the state's longest fish ladder at Berry's Weir at Yamanto.

It was the first time the fish ladder had been put to the test since its construction in October and it has already proved successful with fish as small as 15mm making their way to the top overnight.

Catchment Solutions fisheries biologist Matt Moore and Ipswich City Council waterways health officer Phil Smith look over the tag and release of fish at the fish ladder at Berry's Weir.
Catchment Solutions fisheries biologist Matt Moore and Ipswich City Council waterways health officer Phil Smith look over the tag and release of fish at the fish ladder at Berry's Weir. Rob Williams

Catchment Solutions fisheries biologist Matt Moore said the Mary River Cod was once found in the Bremer River catchment but became extinct in the 1930s through habitat degradation and bush fires depleting oxygen.

He said the fish ladder would support the fish, and other native Australian fish species, to re-populate in south east Queensland waterways.

"In the Bremer we have a lot of fish the migrate between the sea and fresh water to complete their life cycle. They spawn in the estuary and the juveniles migrate up, species like Australian Bass, long-finned eel, sea mullet and fresh water mullet," Mr Moore said.

"So what we've done is a series of pools called a fish way or a fish ladder, a set of under water stairs where fish use their speed. Australian fish are really lazy, they're not big jumpers like in the northern hemisphere so they use their speed to go in between the gaps where there is a bit of velocity, they go really fast and they they rest in the pool and get their energy back and go again.

SEQ Water senior scientist David Roberts and Catchment Solutions senior aquatic ecologist Trent Power enter the data from the tag and release at Berry's Weir fish ladder on Thursday.
SEQ Water senior scientist David Roberts and Catchment Solutions senior aquatic ecologist Trent Power enter the data from the tag and release at Berry's Weir fish ladder on Thursday. Rob Williams

 

"As the fish have to migrate to complete their life cycle, it meant the barrier was restricting a lot of fish from getting up stream so the diversity and variety of species that live up stream was significantly reduced and the abundance of them was also reduced. What starts to happen is we get the proliferation of pest fish."

The 2.4m fish ladder made the most of new construction technology which meant it was the largest, made up of 33 pools, as well as the cheapest in the state.

The fish ladder will help support the regeneration of endangered fish species, limit pest fish numbers as well as re-populate local waterways for commercial and recreational fishermen.

"This size would have cost in excess of $1 million so by creating the rock ramp, it looks aesthetically pleasing like it belongs in a river and as we've proven already with the trap up the top and catching many species and a high number already, it works. Fish as small as 15mm have already got through so if the little tiny baby fish can get through then the bigger fish can get through easy," Mr Moore said.

"By putting the fish ladder in it allows predatory fish to migrate up stream and become more resilient and healthier native fish populations and help keep the pest numbers at bay."

The fish ladder was designed and constructed by environmental consultants Catchment Solutions.



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