Whangateau Harbour: Gem of Auckland’s mainland estuaries.
By Roger Grace
The Whangateau Harbour is a small estuary on the east coast out from Warkworth on the way to Leigh, still in good ecological condition compared with other mainland estuaries in the Auckland Region. Because of its small catchment with housing development only on low-lying sandy soils, there is little silt run-off into the estuary.
Wetlands
The southern arm of the harbour has a rich mosaic of salt marsh and seagrass habitats, and is flanked by the Omaha Taniko Wetlands Scientific Reserve, with a world-acclaimed example of an unbroken succession from coastal forest to estuarine vegetation.
NZ Dotterel
In contrast to the muddy estuaries close to Auckland, sand flats in the upper harbour are clean and firm and easy to walk on. They provide extensive feeding areas for the rare NZ dotterel, which breeds on the end of Omaha spit, where they struggle against predators like cats, rats and hedgehogs, and disturbance by people and dogs.
Kayakers
Mangrove areas in the estuary are great for kayaking in shallow water when the tide is in. There is a maze of passages through the mangroves, where you can see dense beds of necklace weed and schools of mullet zipping around in the clear water.
Snorkellers
Because of the small amount of silt entering the harbour, and because of the vast numbers of shellfish which filter the harbour water for food, the water is often amazingly clear and a safe area for families snorkeling in the shallows. Few NZ estuaries offer such opportunities for snorkeling amongst the mangroves.
Cockles
The estuary has many millions of cockles and is known for the best cockle resource in the Auckland Region. The beds have recently been closed for 3 years because in summer 2009 80% of the cockles died from infection by two diseases. It is hoped the closure will give the shellfish a chance to recover and to maintain their ecological role in keeping the waters healthy.
Necklace weed on a reef
Whangateau is a popular place to snorkel and learn about estuarine ecology. Here a bed of necklace weed is attached to a sandstone ledge next to a channel behind Horse Shoe Island. The Whangateau HarbourCare Group is promoting a 50-hectare area as a fish haven for the enjoyment and education of school and community groups.
Parore in necklace weed
The necklace weed bed is a very important nursery for parore. Whangateau supplies most of the parore on the coast from Pakiri to Kawau. The channel is also a nursery for juvenile snapper, and for large numbers of spotties.
Trevally school
Juvenile trevally also occur in the channel, a school of around 200 living there in summer. Such an easy-access estuarine area for snorkeling, in lovely clear water, is very rare and well worth looking after as a no-fishing zone.
Flounder amongst roots
With a policy of no-fishing around Horse Shoe Island and the adjacent channel, we could expect a dramatic increase in the numbers of several fish. Flounder are fascinating to see well-camouflaged on the sand and sometimes among the aerial roots of mangroves.
Flounder face
If you approach very carefully sometimes you can get really close and personal with flounder. This one allowed me within 10cm of its face, my twin flashes producing an eerie green reflection in the eyes! Presently you may see one or two flounder if you snorkel here, but protection would increase numbers and enhance the snorkel experience.
Stargazer buried / stargazer yawning
A strange fish in the harbour is the stargazer. It is an “ambush” predator, lurking below the sand surface. If a crab or small fish comes close, the stargazer lunges forward and swallows the prey in one gulp. A few quick wriggles and the fish disappears again below the sand.
Yellow-eye mullet
Yellow-eye mullet, often called sprats, are common in the estuary, where they form an important link between the harbour and the open coast by providing food for larger predators such as kahawai and kingfish. Mullet feed in shallow water, and schools of juveniles are often seen in summer sheltering among the branches of mangroves.
Mangrove
The mangroves themselves are fun to snorkel around. We have one species in NZ, common in the northern half of the North Island. Mangroves are specialized trees which can live in salt water. They have peg-like breathing roots which stick up out of the sand or mud around the base of the trees.
Necklace weed, leaves, propagules
Mangroves are important in many ways. They provide shelter for juvenile fish, and their fallen leaves are consumed by fungi and bacteria at the beginning of the estuarine food chain. Mangroves spread by dropping green propagules on the water, which float around for a few days then sink. If near the upper shore they put down roots quickly.
Wavelets & seedlings / Seedlings underwater
They soon grow into small seedlings which are alternately inundated and exposed by the tides. If silt gets into the estuary because of poor management of the catchment, some of this silt is trapped by mangroves and encourages further mangrove expansion. This is the mangroves’ response to human abuses of the catchment – nature trying to repair the damage.
Mangrove community / sunrays in mangrove tree
Large, old established mangroves help protect the shoreline from erosion, but also serve as a hard attachment surface for filter-feeding oysters, barnacles and small mussels, which help clean the water and keep the estuary healthy.
Parore juveniles in mangrove
Thousands of juvenile parore settle from their planktonic larval phase into the mangroves. Only 20mm long, they quickly develop the stripes typical of the adults. When the tide drops they move into shallow channels, returning to the mangroves when the tide rises.
Pulled seedling / Chainsawed stump
Some local landowners are upset that mangroves are spreading in front of their properties. Recently 40-year-old mangroves have been chainsawed illegally. The Auckland Regional Council has a new policy recognizing the value of mangroves but also their potential nuisance. Permits can be obtained for pulling seedlings and limited removal of mature trees.
Lone seedling & ripples
The Whangateau HarbourCare Group continues to promote the natural values of this amazing estuary and to seek better long-term environmental outcomes by working with Councils and the local community.
This programme was first presented in this form at a Pecha Kucha event in Auckland on 16th June 2010. Google Pecha Kucha to learn more about this snappy presentation format - 20 slides each shown for 20 seconds.
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