Shane Mensforth

As I write this editorial in late May, a major section of the SA coast is suffering one of the most catastrophic events in recent memory. Literally thousands of sharks, rays, marine crustaceans, molluscs and scale fish are dying and washing ashore. Both coasts of Gulf St Vincent, Fleurieu Peninsula and Kangaroo Island’s north and east coasts have been affected, and to this point at least, things look like getting worse before they get any better.

Scientists have suggested the possible cause to be a micro-algal bloom, most likely brought on by unseasonable weather patterns and elevated sea surface temperatures. Our unusually warm autumn, compounded by next to no rainfall and protracted periods of little or no wind, are being blamed for the toxic algae infestation, which has had dire consequences. Never before in my life have I witnessed anything quite like this, and to say I’m worried would definitely be an understatement.

Naturally, the press has had a field day with all of this, and particularly its likely link to an alarming increase in great white shark activity. At one stage, quite early in the piece, there seemed to be a new white shark story on TV news bulletins daily. First up there were consistent sightings on beaches south of Adelaide, then the stranding and ultimate death of a 2.5m shark at Henley South, followed by others on both sides of Gulf St Vincent. Never before had so many small to medium great whites been seen with such regularity in such shallow water.

On Easter Sunday son Brett shot drone footage of a 3.5m great white shark at Port Vincent, which has since been viewed more than 300,000 times on YouTube. This shark swam into the marina at Vincent, travelled right up to the boat ramp boarding pontoons and then made its way southward to the swimming beach along the town foreshore. If you haven’t seen this video, check it out here. It’s well worth a look.

That shark swam almost the entire length of the beach, occasionally venturing within 15m of the shore and in less than a metre of water. Just a few hours before, dozens of kids had been splashing around in exactly the same location, which is quite alarming when you think about it. The drone footage clearly shows eagle rays darting out of the shark’s path as it made its way leisurely through the shallows before eventually heading away from the coast with the approach of dusk. It’s some of the most impressive white shark video I’ve ever seen and, judging by the reaction it has received via YouTube, hundreds of thousands of others around the world obviously agree.

Theories as to why larger sea creatures like sharks and rays have fared so badly through this algal bloom and resultant reduced water quality are many and varied. Being apex predators, great whites regularly feed on rays, particularly in our gulfs.

It has been suggested that an accumulation of toxins consumed from eating algae-affected ray flesh might be messing with the sharks’ metabolism, causing them to become disoriented and ultimately expire.

Another theory is that the algae itself is directly affecting the shark’ gills and maybe even their nervous system, causing them to become lost and eventually strand in the shallows. At this stage PIRSA have conducted autopsies on two great whites, neither of which has provided any conclusive information. This seems strange to me, but I guess we can only go by what we’ve been told by the people who should know.

Theories as to origin and cause of the toxic algae bloom are also rife, varying from highly plausible to downright absurd. The now fully operational desalination plant at Hallett Cove has featured regularly in the theorists’ hypotheses, and there is quite a bit of research data to link desal’ waste water with algal blooms. I’m sure this is one possibility at least being considered and investigated by Government departments.

My favourite theory concerns the recent presence of Chinese submarines in SA’s offshore waters. I really got a chuckle out of this one!

The most likely explanation, of course, is that we are smack in the middle of a once-in-a-lifetime natural event brought on by environmental factors well beyond our control. There’s not much we can do other than sit back and let Mother Nature sort it all out. Hopefully, by the time you read this we will have experienced some heavy weather and a decent amount of rain – the factors most scientists agree will start to turn things back in the right direction. Exactly how much damage has been done to our sealife over the period of the algal disaster is yet to be seen. Will the Goolwa cockle population ever make a full recovery? In time will our white sharks resume normal activities? How long will it take for our decimated ray and smaller shark populations to recover? And what long term damage, if any, will this disaster have had on our scale fish populations?