Feral weed creeps in
  |  First Published: May 2005

The feral aquatic plant Caulerpa taxifolia is creeping its way up Sydney Harbour.

I found a chunk of it on my anchor in Rose Bay and after consultation with DPI Fisheries, confirmed that this was a new outbreak. The next-closest stand is about 2km across the Harbour at Clifton Gardens.

The long-term impacts of Caulerpa are unknown but experience with long-term outbreaks in the Mediterranean have shown a definite drop in biodiversity.

It’s not all bad news, though, as early studies have shown that some species will happily use Caulerpa as a hatchery or nursery area after the weed has overtaken native seagrasses.

Furthermore, Caulerpa has a similar effect of stabilising sand drift to the aquatic vegetation that it replaces. Caulerpa is native to Australia and is a good example of a situation where just because something is native doesn’t mean that it can’t cause problems elsewhere in the country.

In a country as big as Australia, environments , local adaptations and species diversity can be as varied as that between South America and Siberia.

So the potential to go feral for something imported from Western Australia to the east coast is as great as it is for something imported from OS.

Caulerpa is used extensively by aquarists because it is one of the few aquatic vegetations that will thrive in saltwater aquaria. As a result, cold-water strains evolved as an adaptation to the widely varying conditions found in the individual aquariums kept throughout Australia and the world.

In other words, once it found its way back into the wild it had evolved to handle a range of environments well outside its normal boundaries.

A representative from the aquarium industry claims that he was unable to give me the current figures on what the industry is worth annually but according to one study (Mckay 1977), it’s the worlds biggest fishery, valued at $4 billion in 1971 and $80 million in 1973 in Australia alone. Imagine what it is worth now !

I accept the fact the aquarium industry cannot be held responsible for what individuals do with their fish and plants after they have purchased them but as the industry is the window through which most of this stuff enters the country, I feel it should be contributing at least part of the cost of the clean-up .

The aquarium industry currently contributes nothing and in more than 20 years of keeping aquariums myself and having hundreds of visits to retail aquarium shops, I have never received any information relating to the dangers and responsibilities of keeping exotic fish and plants.

In the short history of the aquarium industry in Australia already at least four exotic fish have escaped and proliferated in Queensland waters alone.

An average of 8 million aquarium fish are imported into this country every year. Among these millions of plants and fish imported are many considered to be ‘sleepers’ – that is, they have great potential to go feral should they escape.

Ironically, these species never receive the esteemed title of ‘noxious’ until they actually go feral, despite their great potential.

There is clearly a lot of cleaning up to be done within the aquarium industry. A good alternative is to keep native fish, of which Australia boasts some beauties, particularly amongst the rainbow fish and blue eye family.

To help avoid the spread of Caulerpa inspect all fishing gear, boat hulls, trailers and particularly anchors before moving on to a new spot and especially before moving to a new river. It can live for a week in a damp anchor well. Have a look at www.fisheries.nsw.gov.au/thr/species/fn-caulerpa.htm


On other fronts the fishing in the Harbour has been very good, especially for big kings.

April, May and in some years even June are prime season for larger kings although you won’t get them in the same numbers as the smaller earlier-season fish.

The best spot at the moment is Middle Harbour with the stretch from Seaforth to Bantry Bay the best. As usual, you will need fresh squid, which have been very prolific this year.

It’s also the time when you can start to expect a few jewfish and flathead mixed in with your kings and it’s time to start chasing them upstream on soft plastics.

There have been some big tailor in Middle Harbour although they are not very lure-friendly unless you are trolling deep off a downrigger.

Down lower there are some very big salmon and a few straggler Watson’s leaping bonito.

Your best shot at surface action is frigate mackerel that should stay until the end of May.

There are still a few of the smaller kings in the lower reaches.

A good tip for this time of year is to switch to smaller baits and lures. A cube trail of small squares of squid will get them going. Every now and then, slip a small (No 4) hook into one of the cubes and float it back unweighted.

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