Port Phillip Baykeeper » dredging

Cart-rut shells alive and well in Brighton

BayKeeper — Fri, 11 Nov 2011 23:32:25 +0000

A Baykeeper shoreline shell survey found a large Cart-rut shell (Thais orbita) at Holloway Bend earlier this year, suggesting the species may still live in the area. This species was central to the ban on use of Tributyltin (TBT) as an anti-foulant on vessels less that 25m in Victoria in 1989.

Cart-rut shell: worse for wear but there!

International studies had shown TBT caused female shellfish to grow penises. A high incidence of the condition (known as imposex) had been recorded at Brighton Harbour in the early 1990s, but had reduced after the ban. We were delighted this week to receive photos of several “fist-sized” Cart-rut Shells on a reef offshore of Brighton.

Cart-rut shells on Brighton reef (pic: Steven Putt)

10 years after the ban was introduced, Marine Pollution Bulletin (Volume 42 # 10) reported that the relative penis size index (RPSI) of female Thais orbita in Port Phillip Bay had generally reduced. But the RPSI had increased at Williamstown, indicating that TBT from large vessels, ship maintenance activities, and release from historically contaminated sediments, continued to pollute the area.

The study concluded that while the ban remained, TBT pollution would only threaten ports areas and be unlikely to impact more widely in the Bay. Unfortunately, their study was restricted to a limited number of sites and they didn’t consider the practice of dumping dredged sediments from the Port of Melbourne into the Bay.

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?