West Coast Marine and Coastal Localities:
a Detailed Description of 14 Segments
5.9 Wanganui
(Mikonui River – Abut Head, 50 km)
5.8.1 Summary
The Wanganui segment mostly consists of a coastal plain backed by marine
terraces and broad river flats, interspersed with a number of headlands
that are being eroded into bluffs by wave action. Saltwater Lagoon is a
prominent coastal lagoon and four moderately large rivers flow out to sea
in this segment. The coastal plain and terraces are a mixture of protected
forests, wetlands and farmland with little residential development. The
seabed is mostly of a uniform shelf grading out to fine sediments, with
mostly coarse-grained mixed sand and gravel or cobble beaches, while boulder
reefs provide patches of hard shore. The shelf is broad and shallow in the
northern part of this segment.
The Wanganui coastal and marine area supports marine life that is typical
of such habitats in the central West Coast. Notable features include: accessibility
to the coastline and use of the river mouths; Saltwater Lagoon and other
coastal wetlands; ease of travel along the coast; natural coastal landscapes;
cultural and historic heritage features; and recreational uses.
Existing coastal protection includes several portions of conservation land,
especially Saltwater Lagoon and Abut Head Scenic Reserves and the Kakapotahi
and Saltwater Ecological Areas. There are also three waterways closed to
whitebaiting and several specified areas under the Regional Coastal Plan.
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Saltwater Lagoon, at a time when the outlet is blocked. Photo: T Hume, NIWA |
5.8.2 Natural Features
Coastal Land and Islands
The glacial landforms in the Wanganui segment are typical of the central
part of the West Coast; they include moraine bluffs, shingle riverbeds,
outwash terraces and dunes. Overall,the moraine bluffs are in a largely
unmodified state, whereas the river mouth flats and coastal strip comprise
a mixture of natural landscape (coastal wetlands and podocarp forest) and
areas modified by farming development and introduced vegetation (such as
marram and gorse).
The moraine bluffs which are such a visual coastal landscape feature of
this segment, have been formed by sea erosion of the extensive glacial deposits
of the ice ages. Bold Head, the Wanganui Bluffs, and Abut Head are the most
prominent moraine bluffs within this segment; Bold Head is the most northerly
of these distinctive coastal landforms on the West Coast. Another, The Doughboy/Kokiraki,
a moraine remnant landmark at the mouth of the Wanganui River, has a formed
track to its summit providing an elevated coastal viewpoint.
Coastal dunes in this segment are extensive but substantially modified by
farming and weed infestation. The main exception to this is the Saltwater
Lagoon beach, which has been rated as one of the most biologically valuable
coastal dune systems on the West Coast191.
Coastal Wetlands and Waterways
Shearer Swamp (135 ha) lies mostly outside the coastal marine area but drains
to the sea through Waikoriri Creek lagoon, a ‘hapua’ wetland
that lies in a swale behind the foredune and beach192.
The swamp has been rated a wetland of national importance193.
“With the adjoining Fergusons Bush Scenic Reserve, Shearer Swamp forms
part of an increasingly rare example of a relatively intact succession from
virgin lowland podocarp forest to unmodified inland swamp which eventually
progresses into tidal lagoon. It supports a number of endemic threatened
species including the giant kokopu ... and Australasian bittern... It also
supports whitebait ... and other indigenous [freshwater] fish, as well as
considerable numbers of waterfowl.”
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| Pouerua River mouth, with Hikimutu and Saltwater Lagoons toward the
south. Photo: T Hume, NIWA |
Wanganui River Photo: T Hume, NIWA |
The largest waterways in the Wanganui segment are the Mikonui, Waitaha,
Wanganui and Pouerua Rivers. The Waitaha River has an estimated annual suspended
sediment discharge of 2.8 million tonnes194. Each
of these has river mouth habitats with adjoining tidal and coastal wetlands.
The slow-moving, tannin-stained streams flowing into the Waitaha River (Te
Rahotaiepa River/ Ounatai Lagoon) and the Pouerua River (Hikimutu Lagoon)
are unmodified with good cover of riparian indigenous forests and wetlands.
Te Rahotaiepa Lagoon sometimes has its own outlet separate to the main stem
of the Waitaha River. The Waitaha and Wanganui River mouths have been rated
as habitats of moderate wildlife value195.
Saltwater Lagoon has been rated as a habitat of high wildlife value196,
and is a Statutory Acknowledgement Area under the Ngai Tahu Settlement Act.
Its character is very dependant on the state of its outlet, which can be
either blocked or opened for extended periods (months or years) by natural
build-ups and breaches of the barrier beach sediments at the mouth. These
natural changes tend to cause little disruption to human activities, and
so the lagoon is one of the few wetlands on the West Coast that frequently
blocks but does not have a history of artificial breaching. The lagoon takes
the form of a coastal lake when the outlet is blocked, but becomes a tidal
flat estuary when the outlet is open. Although these physical changes have
not been studied in detail, it is likely that they have substantial effects
on the natural ecology of the lagoon and its catchments.
Seashore and Marine Areas
A broad shelving area extending into the northern part of the Wanganui segment
is informally known as Bold Head (after the nearby landmark), where depths
of less than 50 metres reach out beyond the 12 Mile territorial limit. In
the south of the segment the seabed shelves off more steeply across the
inner shelf, reaching a depth of about 150 metres at the territorial limit.
The seabed grades from coarse sand and gravel beaches to muddy sediments
offshore. The beaches mostly comprise sand and gravel foreshore, with a
foredune of low to medium height. Beach dynamics are greatly affected by
the mouth and channel movements of the nearby rivers, and shoreline erosion
of up to 8.3 metres per year have been reported197.
The inter-tidal zone is dominated by mixed sand and gravel beaches of variable
width that have generally very low biological diversity.
Rocky shores formed from the eroded ends of Ice Age moraines are mainly
in the vicinity of Wanganui Bluff and Abut Head. Two areas of extensive
moraine boulder ‘ramp’ occur in this segment, at the ‘Mikonui
mussel bed’ and near the mouth of Saltwater Lagoon. These areas are
exposed only at spring low tides and form suitable habitats for greenlip
mussels and other shorelife over several hectares each. Other patchy areas
of moraine boulder shore and reef occur at Bold Head, Opuku Cliff, The Doughboy/Kokiraki
and north of the Pouerua River mouth.
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| From left: Mikonui River and Shearer Swamp Photo: T Hume, NIWA |
Waitaha River Photo: T Hume, NIWA |
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| Ounatai Lagoon. Photo: T Hume, NIWA |
Bold Head Photo: D Neale, DOC. |
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Glacial moraine bluffs at Abut Head Photo: D Neale, DOC. |
Coastal and Marine Wildlife
During the winter months, up to several hundred New Zealand fur seals haul
out in the vicinity of rocky coasts near Whakaikai River and at Abut Head,
dwindling to much lower numbers in the summer198.
A small colony of sooty shearwaters was known to breed in burrows near the
top of The Doughboy/Kokiraki in the mid 1990s199,
but there is no information on its present status.
Marine Fish and Other Species
This coastal region like the whole west coast of the South Island, supports
a rich diversity of fish and invertebrate species that are fished both commercially
and recreationally by a number of fishing methods including trawl, longlining,
trolling, potting and set netting.
Inshore trawl fisheries are multi-species and are primarily based on flatfish
(several species), red gurnard, red cod, giant stargazer, tarakihi and blue
warehou. Other species taken as bycatch include arrow squid, dark ghost
shark, ling, barracouta, jack mackerel, spiny dogfish, rig, school shark,
sea perch, rough skate and smooth skate200.
A coastal reef north of the Mikonui River supports a large population of
greenlip mussels201. Coastal reef fish surveyed
at this site revealed a suite of species typical of moraine shores in central
Westland and similar to those found in the northern West Coast. This is
one of only two known habitats of the mottled clingfish, an intertidal fish
known only from the West Coast region202.
5.8.3 Historical and Archaeological Heritage
Early Maori sites are recorded at Saltwater Lagoon, as well as other sites.
The locality has a significant place in Maori history203,
as a settlement site, mahinga kai and the place where the Crown agent James
Mackay sealed the purchase of Te Tai Poutini (the West Coast) from the chiefs
of Poutini Ngai Tahu in 1860. Remains of goldmining and pack tracks occur
intermittently along the whole coastline204.
5.8.4 Recreation and Tourism
Fishing and other recreational activities are dispersed throughout the Wanganui
segment, especially near river mouths and access points. The Harihari coastal
walk is an especially popular access route to the coast between the Wanganui
River mouth, The Doughboy/Kokiraki and the Pouerua River mouth – for
fishing, whitebaiting, and beachwalking. Several baches occur near the mouth
of the Pouerua River, and whitebaiters’ baches and other structures
occur along the banks of the Wanganui River. Whitebaiting occurs on each
of the main rivers (Wanganui, Pouerua, Waitaha and Mikonui) as well as the
smaller creeks in the area. While greenlip and blue mussels are present
at several locations (most notably the bed near Saltwater Lagoon) the extent
of gathering is not documented.
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| Kaihinu Photo: D Neale, DOC. |
The Hokitika beachfront area. Photos: D Neale, DOC. |
-1.jpg) |
Hokitika from sea Photos: D Neale, DOC. |
5.8.5 Commercial Use
This area – as for most of the inshore West Coast – is fished
by commercial fishers using a variety of methods, the most common being
bottom trawl205. Vessels in this area mostly operate
out of Greymouth, but also Westport, Nelson and other ports.
Six mining licenses exist on the coastal strip from the Waitaha River to
Wanganui Bluff, one at the Wanganui River mouth and five from Pouerua River
to Saltwater Lagoon.
5.8.6 Other Public Uses and Facilities
The main public access points to the coastal marine area in this segment
are at Donoghues, Greens Beach, and the Harihari coastal walkway. Access
across private land is also possible in other locations such as Bold Head
Road and the Waitaha River mouth north bank. Public access to the more isolated
parts of this segment is mostly by walking or beach vehicle from those points,
or by boat. Coastal foot travel is restricted by the tide at several points,
especially at Abut Head and the major river mouths.
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Mananui Photo: D Neale, DOC. |
While isolated residences occur in places and the inland settlement of
Harihari is nearby, there are no heavily settled coastal areas in this segment.
There are Resource Management Act coastal permits issued in this segment206
for:
- whitebait stands (Waitaha, Wanganui and Pouerua Rivers);
- stream outlet opening (Waikoriri Lagoon);
- stone and gravel extraction (several locations);
- blacksand goldmining (Greens Beach to Saltwater beach).
Extensive parts of the coastal strip and adjoining wetlands are within conservation lands, especially:
- in the vicinity of Shearer Swamp, Bold Head (including Kakapotahi Ecological Area).
- between the Waitaha River and Saltwater Lagoon (including Saltwater Lagoon Scenic Reserve and Saltwater Ecological Area surrounding it).
- Abut Head (including Abut Head Scenic Reserve).
- The largest blocks of private coastal land occur in the vicinity of Mikonui River, Waitaha River and parts of Abut Head.
Several waterways in this segment are closed to whitebaiting:
- Ounatai Lagoon (a tributary of the Waitaha River)
- Oneone Creek (a tributary of the Wanganui River)
- Hikimutu Lagoon (a tributary of the Poerua River)
Saltwater Lagoon Scenic Reserve is an extensive water body which is closed to commercial eel fishing (on account of its protected land status)208.
The Wanganui marine area lies within Fisheries Statistical Area FSA 34, which is part of the Challenger Fishery Management Area (FMA 7). The adjoining land area is within the Westland District.
The operative West Coast Regional Coastal Plan recognises:
- Coastal Protection Area; CPA8 Saltwater Lagoon
- Culturally Significant Area; CSA14 Mikonui
- Coastal Recreation Area; CRA13 Harihari Coastal Walkway
- Marine Mammal and Bird Sites; MMB12 Wanganui Bluff, MMB13 Abut Head.
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Coastal gold mining near Ross Photo: D Neale, DOC. |
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| Totara Lagoon beach Photo: D Neale, DOC. |
Wadeson Island recreation area, in the upper tidal reach of Hokitika River Photo: D Neale, DOC. |
191 Johnson 1992
192 Hart & Single 2004
193 Cromarty & Scott 1995
194 Hicks & Shankar 2003
195 Coker & Imboden 1980
196 Coker & Imboden 1980
197 Gibb 1978
198 Neale & Best 1999
199 J. Reid pers comm 1999
200 Stevenson & Hanchet 2000
201 Stark & Asher 1993
202 Roberts et al 2005
203 Ngai Tahu Settlement Act 1998
204 Hooker 1986, 1990
205 Booth et al 2005
206 www.wcrc.govt.nz “Maps on the Web”, June 2006
207 Whitebait Fishing (West Coast) Regulations 1994
208 Tai Poutini Tuna 1999