Ecological Services of Grey Mullet Lost Through Fishing

The humble grey mullet may have been an important vector in transporting sediment through our estuaries.  They were in huge abundance 100 years or so ago, but now are present in just a shadow of their former numbers.

When grey mullet were in huge numbers they would have been an important vector in transporting sediment through our estuaries, by swallowing mud in the upper estuary and releasing it near the estuary mouth.  Unfortunately there are so few left that this service is no longer effective

When grey mullet were in huge numbers they would have been an important vector in transporting sediment through our estuaries, by swallowing mud in the upper estuary and releasing it near the estuary mouth. Unfortunately there are so few left that this service is no longer effective

There are historic photos of clinker dinghies in the Kaipara Harbour, loaded to overflowing with mullet, many huge by todays standards and upwards of 70 cm long.

In my youth I saw a few schools of grey mullet while snorkeling, but then they “disappeared from the face of the earth”. Only in the last eight or so years have they been starting to come back, and I now frequently see adult grey mullet in the mangroves of Whangateau, and juveniles are seen in the lower reaches of the Brick Bay stream. A couple of years ago I saw a school of around 200 grey mullet, swirling around like a school of kahawai, in the Whangateau 100 metres or so below the Ti Point wharf.

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Risk of Spreading Marine Pests from Sandspit by Dredge Spoil Dumping at Sea

NZ Hydrographic Chart number NZ531

NZ Hydrographic Chart number NZ531

It is understood that dumping of most dredgings from the proposed Sandspit marina is likely to be at the eastern Great Barrier Island site designated for disposal of marina maintenance dredgings from various Auckland marinas.

I am not in possession of the actual coordinates for the disposal site, but I understand it is east of Great Barrier Island and north of Cuvier Island, in a clear “indentation” in the boundary line for the 12-nautical-mile outer limit of the Territorial Sea in this area (see chart NZ531). This is the closest point of “open sea” to Auckland, where many rules and regulations of the Territorial Sea do not apply.

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Marine Pest Species at Sandspit, Northern New Zealand

The invasive Asian paddle crab Charybdis japonica brandishes its nippers in a defiant stance in front of the Sandspit Yacht Club.  This aggressive crab has the potential to alter the ecology of natural shallow reefs in sheltered areas by competing with native species and changing the trophic balance.  It is now established at Auckland, Sandspit, Mahurangi and Whangarei harbours.

The invasive Asian paddle crab Charybdis japonica brandishes its nippers in a defiant stance in front of the Sandspit Yacht Club. This aggressive crab has the potential to alter the ecology of natural shallow reefs in sheltered areas by competing with native species and changing the trophic balance. It is now established at Auckland, Sandspit, Mahurangi and Whangarei harbours.

By Roger Grace Ph.D.
Independent Marine Biologist
gracer@xtra.co.nz
January 2014

Contents

  1. Summary
  2. Introduction
  3. Non-indigenous marine species recorded at Sandspit
  4. Observations and recent surveys
  5. Discussion of each non-indigenous species
    1. Parchment worm (Chaetopterus sp.)
    2. Asian date mussel (Musculista senhousia)
    3. Pacific oyster (Crassostrea gigas)
    4. Asian paddle crab (Charybdis japonica)
    5.  Clubbed tunicate (Styela clava)
    6. Australian droplet tunicate (Eudistoma elongatum)
  6. Biosecurity risk for marina development plans
    1.  Biosecurity Management Plan
    2. Dumping Permit
    3. NZ Coastal Policy Statement
  7. Conclusions
  8. References

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