Two citizen-science investigations profiling heavy metal exposure in seabirds using their feathers have both indicated that the southern end of Cockburn Sound, and in particular Mangles Bay, may be providing the conditions for mercury bio-accumulation in the marine food-chain.
According to Dr Nic Dunlop, Environmental Science & Policy Coordinator with the Conservation Council (WA) , ‘ both the Little Penguins that forage at the southern end of Cockburn Sound and Caspian Terns that fish in that area when breeding show elevated levels of mercury in their feathers’.
‘Some individuals of both seabirds have mercury levels (as measured in feathers) above the level considered safe for marine birds of 5 mg/kg’.
‘Mercury concentrations bio-magnify in top predators like seabirds which prey on fish species that are also consumed by humans. Whilst mercury concentration in the seabirds may be becoming problematic, the levels in their prey are probably within health limits for human consumption at the present time’.
‘Mercury is a ubiquitous and rapidly increasing contaminant on both global and local scales. To be transferred through food chains elemental mercury must be converted to organic forms (methyl-mercury). This ‘methylation’ process is carried out by bacteria in low oxygen environments with significant quantities of decaying organic matter. The seagrass meadows at the southern end of Cockburn Sound are poorly flushed and over-supplied with nutrients and covered with excessive algal growth. The result is potentially ideal conditions for mercury methylation’.
The proposed Mangles Bay Marina Project could elevate the mercury contamination hazard in at least two ways. Firstly, the dredging program may release methyl-mercury into the water column causing a spike in contamination in fish and other marine life. Secondly, the settling organic matter in the dredged channel, and in the poorly-flushed, blind-ending canal development, is likely to further enhance the conditions for mercury methylation by bacteria in the long-term.
This would present a threat to the commercial & recreational fisheries in Cockburn Sound and to the local aquaculture industry.
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Press Release, May 29, 2013