Dying Cockles in Marine Reserve Report

A report of an recent field inspection of the Okura Marine Reserve by Coastal & Freshwater Ecologist Treffery Barnett has fallen into our hands.

The news about cockles is bad.

Okura Estuary cockle bed showing mass mortality of cockles. Site near Okura River Road
boat ramp. Note anoxic area on photo right with surface sheen of decayed organic material.

Keep Okura Green Inc (KOG) requested a site visit by an ecologist of the Okura Estuary after complaints by local residents and visitors using the Marine Reserve of a strong persistent smell of rotting fish or shellfish.

A site visit was carried out at low tide on Monday 2nd April 2018. The intertidal area of the estuary was inspected from the boat launching ramp at the end of Okura River Road, to approximately 500m upstream of the ramp.

Several large beds of cockles, tuangi (Austrovenus stutchburyi) were observed between the boat ramp and mid-estuary and additional cockle beds are known to be present seaward of the boat ramp.

Cockles are an edible shellfish that burrow into muddy sand and can be found in estuaries, mudflats and intertidal beaches, usually in areas without excess sediment loadings from the adjacent land.

The extent and health of the beds were examined. A recent mass mortality event had occurred, as event by the number of recently opened shells, often with the remains of adductor muscles still attached, and a strong odour of decomposition both in the recently opened shells and throughout the bed (Photo 1). In addition to the odour, the recently opened shells were easily distinguished from older shells in the bed by colour and lustre of the internal surface of the bivalves.

Download the full report here: MEMO April 2018 Shellfish mortality

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