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Cockles and tuatua 'alive alive oh'


Friday 10 January 2014

The last of our tuatua and cockle surveys took place on beaches and in the Avon-Heathcote Estuary/Ihutai just before Christmas 2013. The Christchurch City Council commissioned this monitoring programme, which measures pathogen levels (bacteria and viruses) in shellfish. This programme started in 2008, originally in response to the decommissioning of the sewage discharge into the estuary, with the plans to replace it with an ocean outfall. Monitoring was due to finish in 2010 but got extended through to December 2013 to measure the effects of earthquake-related sewage discharges.

This is important information not only from an ecological point of view, but also in terms of public safety. Basically our monitoring meant that every time we found a high result of pathogens, the safety signs advising against collecting shellfish for food went up. It’s the perfect synergy of science and signs, making our lives safer!

This long-term monitoring programme has given us plenty of experience that can be applied to any situation involving storm water and sewage discharges and its effect on food safety. It also represents one of the few long-term data sets in New Zealand on shellfish pathogen levels.

27 March 2014 update

Following the one-in-100 year rain event in early March, the EOS team decided to do an additional round of cockle monitoring that they funded themselves, to see what effect such an unprecedented event could have on E. coli levels. Levels at both of the river mouth sites were high when compared to past March rounds so there is some noticeable effect from the storms. 

"But even this March level was still below the December levels, which seem to be high every year,” said EOS estuary technician Nick Hempston.

“The low human virus levels in the December samples indicate that this contamination is coming from a non-human source, which could point to waterfowl."

"Unfortunately we could not extend to paying for the virus tests for the extra March round that we did, but it would be reasonable to expect that virus levels may have been elevated due to the sewer overflows during the storm.

“The cockles can be kept frozen indefinitely on the off-chance that we can get external funding to have them tested at a later date." 

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spacerEOS Ecology's Nick Hempston and Amber Sinton collecting cockles.
Collecting tuatua in Avon-Heathcote Estuary/Ihutai. grey-BR

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