Over the summer months, Department of Conservation (DOC) and Marlborough District Council continued their decades-long efforts to eradicate Common Cordgrass (Spartina Anglica) from Motuweka/Havelock Estuary. Spartina is an introduced grass that lives in intertidal areas with soft sediment, spreading through seed as well as underground rhizomes.
Spartina displaces native species of salt marshes and mud flats, also causing accelerated sedimentation in estuaries. It was previously introduced to the estuary in the 1950s for agriculture, to reclaim the wetland and use its large roots to stabilise stopbanks and muddy areas for grazing stock. Due to its root mass, this invasive grass can change the estuary dynamic for our native habitats, says Phil Clerke, Senior Biodiversity Ranger for DOC.
“Department of Conservation has a vested interest in the estuary, from protected birds that call the estuary home to juvenile fish that nurse in its waters,” said Mr Clerke.
A joint programme between Council and DOC began in 2004 with the aerial spraying of the main infestations, centred in the Pelorus Sounds around Havelock and Kaituna estuaries. Scattered infestations were also spread across the heads of many bays and inlets in the Marlborough Sounds.
Spartina is an invasive species of regional significance, says Council Biosecurity Manager Liam Falconer.
“Biodiversity in estuaries has been impacted, and we’ve seen major improvements since removing tens of hectares of Spartina throughout the region,” Mr Falconer said.
Today, all infestations of Spartina have been managed to very low levels. In early 2025 the DOC team only found one plant during annual monitoring, and again one plant was found over the 2026 season. Council and DOC jointly fund the operation, where DOC has concluded that eradication is not only feasible, but could be achievable well within a decade at the current levels of funding and management.
Collaboration is at the heart of this programme and why it has been so successful, said Mr Falconer.
“There’s been a strong commitment from dedicated DOC staff that have been involved in the programme for many years. This work is very physical and in tough conditions. Council recognises the effort the DOC field teams have put into delivering results,” Mr Falconer said.
