Murdoch University researchers have released a new report, which counters recent claims that the Swan-Canning Estuary is 'dead'.
Dr Chris Hallett, from the Centre for Fish, Fisheries and Aquatic Ecosystems Research at Murdoch University, said the condition of the estuary remained generally good to fair.
“The results are consistent with our previous monitoring, which has indicated an overall improvement in the ecological condition of the Swan-Canning Estuary since the mid 2000s,” he said.
A Fish Community Index was used to rate the health of the estuary from A (very good) to E (very poor), comparing the result to a 30-year historical data set. The Swan River Trust established an annual monitoring regime using this index.
Scientists sampled and assessed more than 30,000 fish from 40 species during the first half of 2013. The fish were collected at 48 locations throughout the estuary.
“The health of upper Swan and Canning estuary habitats was deemed slightly poorer at times, compared to the 2012 data,” Dr Hallett said.
“We put this down to the presence of low oxygen conditions in the deeper waters of the upper estuary zones during autumn of this year.”
Dr Hallett said these events have been shown to have a short-term impact in the estuaries.
“Trends over the last five to eight years show that the system is fairly resilient to the algal blooms and low oxygen events that periodically affect parts of the estuary,” he said.
“Our research indicates that the majority of fish species are able to avoid low oxygen areas by moving closer to shore, where oxygen levels are higher. The fish tend to return to deeper waters when oxygen levels return to normal.”
This behaviour has been credited with reducing the extent of fish kills following a major algal bloom in the Swan-Canning Estuary in 2004.
“This avoidance behaviour is well documented among fish species in other estuaries across the world.”
The full report can be viewed here.