Parasites and bacteria implicated in the mass cockle deaths in the Whangateau Harbour. Closure of the shellfish beds is anticipated to allow them to recover.
A report from MAF Biosecurity has implicated coccidia and mycobacteria as the likely cause of the massive die-off which occurred this summer. The role of heat and very low tides is not clear but may have made the cockles more susceptible to infection.
Coccidia are normally present in shellfish but in this case they have massively infected the gills. It is likely that the mycobacteria, which are not normally found in shellfish, have taken the opportunity to parasitise the cockles. Researchers were working with frozen and preserved cockles which made their task more difficult and they have done a fantastic job in view of the fact that they did not receive the samples until April.
Neither of these organisms present a risk to humans but there would certainly be a risk to anyone eating dead or dying cockles which have started to decompose.
The greatest impact on the cockle population was on the larger sizes with a reduction in densities of between 80 and 84%. This is a significant event as these cockles are the filters which keep the Harbour water clean and clear.
Meetings have been held between scientists, MAFBNZ, MAFish, RDC, ARC, Ngati Manuhiri and representatives of local groups to determine how best to proceed. At the latest meeting (Friday, 21st August) agreement was reached on the need to close the cockle fishery until recovery can be achieved. This process will take about 3 months and it is hoped to have the fishery closed by Christmas. It was agreed that the pipi beds should also be closed as they have been drastically reduced by over fishing. A community group will be set up to decide when recovery is sufficient to allow a return to harvesting.