Port Phillip Baykeeper » dredging

Radionuclides dumped in the Bay… is that OK?

BayKeeper — Thu, 15 Oct 2009 12:12:08 +0000

Opponents of the Port Phillip Bay Channel Deepening project vigorously opposed dumping of more than 3 million m3 of contaminated sediments from the Lower Yarra River in the Bay. But CDP proponents claimed the toxic sediments would be contained underwater within in a 6km2 clay walled area.

After dredging and dumping had started, Baykeeper learned of evidence suggesting uranium and thorium had entered the Yarra from a CSIRO research facility at 506 Lorimer Street Fishermens Bend between1945 to 65. These contaminants are most likely still under the wharf, but river currents, tidal movements, and turbulence from ships may have shifted them in all directions.

Radionuclides remobilised by dredging and dumping could well be introduced into the food chain; and Thorium is believed to cause liver cancer. I called for dredging to stop until the risk had been assessed.

Extract from 1989 Radiation Survey of 506 Lorimer Street

No testing for radionuclides in Yarra sediments has been conducted, despite repeated submissions to the Channel Deepening Community Liaison Group (convened by Port of Melbourne Corporation).

Now, on completing the Channel Deepening, PoMC propose to conduct maintenance dredging in the Yarra, and more dumping in the Bay… What do you reckon? Is that OK?

DOLPHINS LIVING DANGEROUSLY!

BayKeeper — Tue, 29 Sep 2009 13:19:05 +0000

Dolphins have a reputation of being smarter than your average mullet. After all, you can’t get to the top of the food chain on good looks alone. But being big in fishworld has its downside. You have to do what it takes to find a feed…. sometimes in dodgy waters.

Dolphins at work (pic: Andrew McCutcheon)

My notes on dolphins in the north of the Bay (recorded between 1988 and 2009) show almost all occurred between June and December, with two thirds between July – September. The two pictured here were snapped in the Yarra just north of Westgate Bridge in early September 2009, while the Coza Zaanen was dredging just 200m downstream.

One theory, which seems to make sense, is that dredging creates a short term smorgasbord for predator species, as smaller marine organisms that normally live in the seabed are thrown up into the water column. The problem is that these same organisms have often swallowed heavy metals and other toxins that have been flushed into the river from stormwater drains.

Due to the gradual accumulation of toxins, it takes time for animals to be affected. Meanwhile, perhaps the Dolphins are also wondering why all the Yellow-eyed Mullet disappeared during the EPA’s 2009 Lower Yarra Fish Study?

THE CASE OF THE MISSING ANCHOVY

BayKeeper — Mon, 03 Aug 2009 12:11:52 +0000

Anchovy are an important prey item of Little Penguins and numerous fish species in Port Phillip Bay. They’re also great on pizza!
So Channel Deepening through their spawning habitat in Hobsons Bay and the Yarra is cause for concern, as is disposal of contaminated dredged sediments in the Bay. In response to these concerns, a Baywide Anchovy Survey is being conducted over several years.

Anchovy larvae comprised 74.5% of total fish larvae sampled in PPB during November to January of 2007-08. Curiously, just 6 months later, the Baywide Anchovy Study Sub-Program conducted during June-July 2008 recorded no Anchovy in the 0+ (first year) age class.

The Goomai grab-dredge in the Yarra

Explanations cited for the failure to find first year Anchovy are:

1. Anchovy of 0+ years of age occur in regions of PPB not sampled;

2. Fish of this size may not have been sampled due to loss through the net;

3. A recruitment failure may have occurred beyond the larval stage.

If anchovy recruitment from the 2007- 2008 season has failed, the effects on penguin foraging would initially be absorbed by the presence of the 1+, 2+, and 3+ year classes. Increased penguin preying on older age class Anchovy is likely to reduce the mature (reproductive) Anchovy population. Combined with the absence of the 0+ age class Anchovy, this is likely to impact on Anchovy recruitment in subsequent seasons.

The degree of impact of the dredging program on penguin prey species such as Anchovy, like many other aspects of the project, will often take more than a year or two to show up. The results of the 2009 Anchovy surveys are sure to be really interesting.