Its Not Over Yet! The Cockle Die-Off Continues

The new cockle die-off event is still in progress, with rotting cockles beginning to create a stink on the Omaha side of the harbour.

A dead and gaping cockle still embedded in the sand is slowly spreading its shells apart as the muscles which hold the shells together gradually fail.

A dead and gaping cockle still embedded in the sand is slowly spreading its shells apart as the muscles which hold the shells together gradually fail.

Following the massive die-off of 80% of the Whangateau cockles in 2009, a new cockle die-off event was first noticed on 28th March 2014. Mahurangi College students were carrying out a regular monitoring of the Horseshoe Island shellfish transects when unusually large numbers of recently dead cockles were noticed by Karen Tricklebank and Roger Grace.

Large numbers of open shells, or “cluckers”, are spread over the sand surface south of the Omaha jetty and boat ramp.

Large numbers of open shells, or “cluckers”, are spread over the sand surface south of the Omaha jetty and boat ramp.

Karen sent off samples to Ministry of Primary Industries in Wellington. Soon we should have the definitive answer about just what is killing the cockles this time round.

The signs were there for a repeat of the 2009 event – several days in a row with mid day low tide, hot weather with no wind or clouds – which apparently stressed the cockles. Last time this allowed naturally occurring protozoan parasites and a bacterium to multiply rapidly to a point where they actually killed the cockles.

A freshly gaping cockle lies among a few dead cockle shells.

A freshly gaping cockle lies among a few dead cockle shells.

Although we have not had similar weather and tide conditions in the past few weeks, it appears that the damage caused by the pathogen is still taking its toll of cockles and they are continuing to die.

We will probably carry out another monitoring session about late May when hopefully the cockle deaths have ceased and we can assess the magnitude of the die-off.

The accompanying photos were all taken on 2nd May 2014 south of the boat ramp on the Omaha side of the estuary.

A gaping cockle lies rotting and stinking on the sand surface.

A gaping cockle lies rotting and stinking on the sand surface.

Fresh “cluckers” are common, with the flexible hinge springing the dead shells apart once the flesh and muscles have rotted out or been consumed by scavengers.

Fresh “cluckers” are common, with the flexible hinge springing the dead shells apart once the flesh and muscles have rotted out or been consumed by scavengers.

Sick cockles lying on the surface can be prized open with fingernails.  This would not be possible if the cockle was healthy and strong.

Sick cockles lying on the surface can be prized open with fingernails. This would not be possible if the cockle was healthy and strong.

A small topshell continues to graze on the green algal film on the shell of a gaping and dead cockle.

A small topshell continues to graze on the green algal film on the shell of a gaping and dead cockle.

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