Improving Fish and Shellfish

Date: 11/03/2016

The  article below describes the importance of the Kaipara Harbour as a habitat for juvenile snapper. It raises some key questions, questions which MHRS has raised about the Manukau. Why are 98% of juvenile snapper on the West Coast coming from the Kaipara and only 2% from the Manukau? What has destroyed the snapper habitat in the Manukau and can it be restored? 

We believe the situation in the Manukau differs from the Kaipara on key points but there is little good science. What is the effect of the daily discharges of suspended solids, high concentrations of nitrates, contaminants from urban stormwater and large volumes of fresh water from the Mangere Treatment Plant into the Manukau? Are these discharges contributing to sedimentation and rapid growth of mangroves in the harbour? How are these discharges affecting not only juvenile snapper habitat but also bird feeding grounds and shellfish beds? 

What is the effect of the spread of mangroves on juvenile snapper habitat, by trapping sediment in the harbour and replacing biodiverse ecosystems with what essentially is a mangrove monoculture? 

How can the quality and abundance of shellfish be improved and people reassured that shellfish are safe to eat? 

MHRS supports further research into the hydrodynamics and ecosystems of the harbour as being led by the Manukau Harbour Forum. We have also worked with NIWA for over 18 months researching mangrove growth and will continue to support further scientific research.

MHRS has a goal that the water quality of the harbour be improved so that it is safe to eat the fish and shellfish and swim anywhere in the harbour.

 

The Kaipara is called the 'last harbour standing'

Manukau & west coast harbours were once important nurseries for west coast snapper. But their seagrass meadows have virtually gone.

Young west coast snapper "hot spots" in the Kaipara Harbour are being investigated as concerns about their feeding grounds continue.

"The Kaipara is the major harbour for west coast juvenile snapper habitats, so it is a really key place," NIWA Auckland marine ecologist Mark Morrison says.

"We know it's under stress from sedimentation and other land-based impacts that degrade key habitats."

These habitats include seagrass meadows and horse mussel beds, which have now largely disappeared from most harbours in northwest New Zealand, Auckland Council marine scientist Jarrod Walker says.

They are thought to have been smothered by silt from roading and building sites, and from farming and forestry. The effects of plankton blooms caused by nutrients washed off the land may also have contributed, he says.

Kaipara is the "last harbour standing" as a snapper nursery on the west coast, Dr Walker says. Delwyn Dickey, Rodney Times  Read More