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Set Adrift To Sydney

By Chris Doyle on December 24, 2012 in Other

Photo: George Evatt

The East Australian Current, or the EAC, was immortalised in the animated film ‘Finding Nemo’ as nature’s superhighway – a way for bodacious sea turtles and colourful clownfish looking for estranged loved ones to transport themselves down the Australian coastline to Sydney Harbour. Despite being a Hollywood film, this captivating storyline, which enchanted children and adults the world over, is based somewhat surprisingly on some sound scientific truths.

Some species of tropical fish do certainly travel south using the EAC and many of them do end up in Sydney. Unfortunately for the fish, however, there is no happy Hollywood ending. Not yet, at least.

About this time every year, tropical fish that usually live among the colourful coral reefs of northern Australia suddenly turn up in Sydney. Up to 80 species of fish are known to frequent Sydney in the summer months, including ghost pipefish (pictured), damselfish, butterflyfish and even the odd clownfish (yes, even Nemo too!). And just like Nemo’s dad, who rode the EAC to find his lost son, these fish have hitched their own ride on the EAC.

The EAC moves vast volumes of water along Australia’s east coast, beginning in northern Queensland and continuing as far south as Tasmania. As the water moves, tiny fish larvae, which hatch out on coral reefs in their millions in early summer, get caught in the current. While some of these larvae manage to make their way back to the reef after a few days or weeks, for others it is the beginning of a journey that will see them ending up thousands of kilometres from home.

Scientists have estimated that fish take up to thirty days to travel to Sydney in the EAC. Of course, Sydney is not the only stop-off point for the fish. Many settle out of the current further north and don’t even reach Sydney, while others continue on further south. However, Sydney is a particular hotspot, with the rocky reefs of Camp Cove and Clovelly being particularly attractive to some species.

The EAC has increased in speed considerably over the past twenty years and scientists anticipate it will continue to increase in the future. This is likely to result in even more fish making the journey down south. But by travelling far away from home, these young adventurers are potential pioneers for their species, discovering new areas of prime real estate to spread to.

The problem, however, is that the fish don’t always make it to areas where they can survive. Coming from coral reefs, they are used to living in warmer, tropical waters. And in Sydney, where the summer water temperatures are at least tolerable, the vast majority of these vagrants will die once the winter chill sets in.

Scientists have noticed that many species are now surviving in Sydney longer than in previous years. This is thought to be due to a recent period of warmer-than-usual winter temperatures. If this trend of increasing water temperature continues, as scientists predict will happen as a result of climate change, then these species may soon be able to survive the Sydney winter and establish themselves here permanently.

For these tiny adventurers, and for those of us too stingy to afford a trip to the reef, this may be the happy ending they were hoping for. But for scientists, it is an early indicator that a period of environmental change is already upon us.