Mussel Country
The sheltered Firth of Thames waters were once clearer and supported much more marine life thanks to abundent mussel beds which carpeted much of the seafloor in the Firth and along the Coromandel coast.
The self-replenishing mussel reefs were the engine room of one of the country's most productive shallow-water ecosystems. The mussels themselves supported a commercial dredging industry from the early 1900s. In 1961, 2800 tonnes were taken. But within eight years the industry had collapsed thanks to over-dredging and poaching.
The reefs have never recovered, and the barren seafloor offers stark illustration of how quickly human greed and ignorance can destroy a resource. The greenlipped mussels we get from the Firth today grow on ropes beneath pontoons which effectively privatise surrounding waters and bays and raise visual pollution complaints.
Mussels helping revive water quality
Water quality remains the most significant concern facing the 4000sq km gulf, this concern dating back over 100 years when mining and land clearing hugely affected it.
Environmental reports in recent years show the health of the gulf is declining for a myriad of reasons, and it’s ability to assimilate current nitrogen loads is a growing concern.
Nitrogen comes from a range of sources, including human wastewater overflows, storm water and from all types of farming, horticulture or cattle farming. The Firth of Thames is adjacent to dairy farming areas and an estimated 2000 dairy farms are in its catchment.
Much of the nitrogen load delivered to the Hauraki Gulf via the Firth is converted to atmospheric nitrogen by the natural process of denitrification. Nutrients can also be 'exported' from the system via the annual harvesting of around 30,000 tonnes of shellfish from a growing number of mussel and oyster aquaculture operations in the Firth.
Mussels obtain food by filtering microscopic algae out of the water column, filtering out sediment and other particles at the same time.
Today there are over 100 mussel farms operating in the Firth of Thames, generating more than a third of New Zealand’s mussel harvest.
