The sight of lifeless silvery fish will become more common, according to one marine biologist who believes La Nina will exacerbate mass fish kills in Australia.
According to Dr Leonardo Guida, a shark scientist and conservationist at the Australian Marine Conservation Society, scenes like the photo above will become more common.
“I suspect these fish kills will increase in the future,” he said, adding that climate change and wet weather is a leading cause of die-offs.
“With climate change it’s quite likely, almost a guarantee, we will see more severe weather events, which can ultimately lead to fish deaths.
“Already we’ve seen some pretty horrible examples.”
Guida explained floodwater can decrease the amount of oxygen available in riverine and marine environments as it can generate bacteria and algal blooms.
“In the context of floods you get massive run-off of water,” he said.
“Animal waste, chemicals, nutrients from fertilisers can get pushed into ecosystems and that can then cause algal blooms, which use up oxygen in the water – reducing the amount of oxygen for other marine life like fish.
“Because of flooding – whether it’s from nutrients, fertilsers, animal waste or decaying plants and animals – marine life is getting choked of oxygen.”
Guida pointed to the Lake Macqurie fish kill observed last weekend and admitted he was “surprised” to see a white-spotted eagle ray among the deceased.
Although it has not been formally confirmed he suspects recent wet weather and flash flooding contributed to the die-off.
The NSW Environment Protection Authority (EPA) is ramping up efforts to determine the cause of the mass kill.
In a statement issued it said heavy metals were an “unlikely” cause of death – signs point towards oxygen depletion.
“The Department of Planning and Environment labs tested for a full suite of metals and found levels below the ANZECC marine water quality guidelines (where guidelines are available),” a statement read.
“A decrease in oxygen content in water is a natural event that can cause rapid fish deaths.
“Residents are warned to stay out of the water until a cause is determined.
Areas at risk of fish-kills
The entire coast of Australia is at risk of marine and riverine die-offs, Guida said.
With the east coast at the mercy of La Nina, the west coast is experiencing another weather phenomenon; a negative Indian Ocean Dipole, which is fuelling marine heatwaves.
Locals described a coral spawn and fish die-off near Exmouth around Ningaloo Reef in March as “different to anything they’d seen before,” Guida said.
“We saw a coral die-off and a fish kill,” Guida said.
“It’s not definitive but one of the causes they suspect is because of the marine heatwave there were alterations in water currents and temperature.
“What supposedly happened is the coral spawn hadn’t been able to dissipate as effectively and essentially created coral spawn slicks that were trapped close to the coast
“You had this massive concentrated die-off of coral spawn that used up oxygen in the water as they decay leading to the subsequent fish kill.”
Guida said the modification of river systems, wetlands and coastal regions are a “compounding factor” for mass fish kills and called for greater environmental protections around waterways.
“Coastal ecosystems are under more pressure than ever,” Guida said.
“We need to have stronger environmental laws that support the protection and recovery of these ecosystems so they are more resilient to future impacts.
“That way we can have a healthier future.”