Lake Wairarapa

Forest and Bird, Volume 16, Issue 1, 1 February 1985, Page 19

Lake Wairarapa

by

Scientist technician, Wildlife Service

Peter Moore

— a wetland of international Importance

A: least 90 percent of the former ponds and swampland of the lower Wairarapa region have been drained, a casualty of a century of European settlement and agricultural development. Today Lake Wairarapa itself has come under threat. In 1964 the Wairarapa Catchment Board began the Lower Wairarapa Valley Development Scheme, in which it was proposed to drain more than 5,200ha of lake and wetlands and to protect a further 16,200ha of farmland from flooding. Several parts of the scheme have been completed; the final stage of development, the ‘polder scheme’, proposed to ‘reclaim’ some lake bed, creating 1,700ha of lowlying farmland and protecting 900ha of land adjacent to the lake, by building a system of banks along the eastern side of the lake. This development would eliminate most of the lake’s shallow water and marshland, the single most valuable wildlife habitat in the wetlands. The Wildlife Service has sought to reserve the remaining wetland areas since

the early 1970’s. Although large areas were lost, including the 386ha Te Hopai Lagoon, the other large pond complexes adjacent to Lake Wairarapa, the old Ruamahanga channel and part of Allsops Bay have now been set aside from development, giving a total reserve area of 817ha. While the Crown owns the largest part of the remaining wetlands, most of the lake shore itself is unprotected. Over the past decade, members of the Ornithological Society, Wellington Acclimatisation Society and Wildlife Service have compiled a list of birds and made a few counts of individual species inhabiting the lake, but up to 1982 there was no detailed information on seasonal variations in bird numbers, activity or habitat use, nor on what parts of the wetlands were important to birds. Therefore, the Wildlife Service began a detailed study of the habitat requirements of wetland birds in late 1982 and over the next year I spent 136 days observing birds in the Lake Wairarapa wetlands. The results of this study have now been published. Wide open spaces Lake Wairarapa is one of the largest lakes in the North Island, being 18 long, up to 6 km wide and covering 7,800 ha, but is nowhere more than 2.5m deep at normal water levels. The two sides of the lake are noticeably different. The western shore is narrow and shelves quickly into relatively deep water whereas sediment brought by the main rivers to the eastern shore has created large areas of shallow water and frequentlyexposed flats, with an intricate system of backwaters, channels and pools. The lake’s water levels vary by up to 30cm (occasionally by 1m in floods) daily and seasonally because of rain in the catchment, control of the outlet and local effects

of wind. Because of these water changes the vegetation cover ranges from bare sandflats to turfs of native plants, mostly less than 5cm tall, and finally to rushland dominated by the introduced jointedleaved rush (Juncus articulatus), which is mostly less than 15cm tall. This marshland (turfs and rushes) covers nearly 400ha, and up to 600ha (or 1km across) of sandflats can be exposed at low water levels. Even at normal water levels, the eastern shore leaves a lasting impression of wide open spaces with anyone who visits it. The main pond complexes lie adjacent to the eastern shore of the lake in J K Donald Reserve, Boggy Pond Reserve and Matthews Lagoon Reserve. They have a wide variety of pond types, ranging from permanent water to seasonally dry ponds, and from natural to managed ponds. Raupo commonly borders the ponds, as do large areas of willow forest. Unfortunately, there are few native trees remaining. Some swampland borders the lake in the south-west at Allsops Bay. Pasture surrounds most of the lake and separates it from all the pond complexes except J K Donald Reserve. Abundant birdlife Eighty species of birds have been recorded from the Lake Wairarapa wetlands in the last decade. This is much more than other purely freshwater system such as the Whangamarino wetlands (56 species) or the Ahuriri River (55 species). Of the 57 wetland species at Lake Wairarapa (i.e. ignoring the terrestrial birds), 24 species are permanent residents and at least 15 species are regular visitors. The remainder visit the area only occasionally. Waterfowl, the main group of birds, include both native and introduced species. In some years they are very abundant; for example, in the autumn of 1978 waterfowl

Despite the recent fervent debate between developers and conservationists over the fate of Lake Wairarapa and its adjacent wetlands, this area is little known by the public. Few people, therefore, appreciate the importance of this system to wildlife, particularly birds. In this article Peter Moore remedies this deficiency by describing the bird life of the Lake Wairarapa wetlands and explaining why the area has such high value for wildlife. This account complements the description of the area’s vegetation by Colin Ogle and Tom Moss in the February 1984 issue of Forest and Bird.

numbered at least 47,500 along the eastern shore. In 1983 the maximum on the eastern shore was about 20,000, witha further 5,000 in other parts of the wetlands. While the sight of thousands of birds in a flock and the roar of beating wings as they take to the air are most impressive, the presence of such large numbers makes counting them a daunting task. Waders are the second largest group, comprising residents, internal migrants and Arctic migrants. They number more than 1,600 throughout autumn and winter. The greatest numbers and diversity of species in the wetlands are found along the eastern shore of the lake, particularly to the north of the Oporua Floodway. Waterfowl The wetlands are important to native waterfowl such as the New Zealand shoveler, which in autumn 1983 rose to a peak of around 3,600 birds. Spectacular rafts of shoveler and other ducks were a feature of the eastern shore at this time. They were largely restricted to shallow water zones and used a narrower range of habitats than the introduced waterfowl.

Paradise shelduck are also abundant, having increased dramatically since hunting stopped in 1968. In January 1983 there were about 1,900 shelduck present, mostly in moulting flocks in Allsops Bay; the majority later moved to the eastern shore before leaving the wetlands in winter. More than 500 grey teal were present at times, often flocking on the eastern shore or favouring secluded ponds near Matthews Lagoon. The other native, the grey duck, was once numerous but now may number as few as 220. The two introduced species, mallard and black swan, are the most numerous birds, and much of my time in 1983 was spent counting them. Mallards fluctuated widely in numbers — from 15,500 in autumn to fewer than 600 in spring. They fed and loafed in shallows of the lake and ponds except in the hunting season, when they spent most of the day far out on the lake, in safety. Even though black swan numbers have more than halved at the lake since 1977, the 3,000 to 5,000 birds present constitute an important part of the declining national total. Nesting colonies have also disappeared in this period because of wetland drainage and human

disturbance, leaving only solitary nests scattered throughout raupo swamps. Cygnets are reared in the ponds before their parents take them to the lake. Cygnet numbers have dropped from nearly 2,000 in 1977 to 400 in 1983. Swans grazed vegetation in a wide range of habitats from pasture to deep water. Another introduced species, the Canada goose, had a small resident population which increased to 50 birds in winter. The waterfowl breed at pond margins near the lake, the ducks usually constructing nests in Carex, grass clumps or on sheltered mounds at the base of willows, surrounded by water. One small pond in Donald reserve had black swan, grey teal, shoveler and mallard nesting close together. Waders Native waders predominate at the Lake Wairarapa wetlands. In 1983 there was a resident population of at least 300 pied stilts rising to more than 1,200 in autumn and winter. Wherever there was shallow water suitable for wading, pied stilts were sure to be found, including pond margins when water levels were low in summer and

autumn. Most stilts were on the eastern shore, feeding on small invertebrates at the lake edge and in the numerous pools, backwaters and channels of the shore. They moved seasonally in response to changing water levels and food supply, with more than 600 flocking at times. I found small breeding colonies of stilts on short rushland at pond margins and near the lake. Banded dotterels did not breed at Lake Wairarapa but spent much of the year there, peaking at 350 in autumn. They were largely confined to the eastern shore and used fewer habitats than pied sults, foraging in flocks on saturated or partially-flooded native turf flats. The other native waders are _ less numerous. Black-fronted dotterels can be quite hard to find but are scattered round the lake shore, with up to 60 flocking in winter of 1983. Variable and South Island pied oystercatchers are also present. Spurwinged plovers are not very dependent on the wetlands, often feeding and breeding on semi-developed pasture, although flocks of up to 70 frequently visited the lake. One of the most fascinating groups of birds at Lake Wairarapa is the migratory waders from the Northern Hemisphere. There is always that chance of finding something quite out of the ordinary, such as the lesser yellowlegs that I saw in January 1983. Total numbers of migrants are lower at Lake Wairarapa than in some estuaries, since fewer than 100 godwits or knots visit the lake. However, there are some species, such as least golden plover (more than 70 birds) and sharp-tailed sandpiper (up to 80), which regularly visit in nationally high numbers. Few pectoral sandpipers and greenshanks reach New Zealand each year but one or two of each turn up regularly at Lake Wairarapa. Some of the migrant species show very specific preferences for different areas and habitat types at Lake Wairarapa, and these preferences can change seasonally. Young shag cacophony Some of the most conspicuous breeding birds in the wetlands are shags. They nest in colonies in willows bordering some of the ponds, the largest colonies being at Matthews Lagoon. The black shag predominates, with 230 breeding birds nesting after late July 1983. Sixty little shags arrived about a month later and occupied many of the same trees as black shags. At least some of the 23 little black shags nested in one colony, so that all three species shared the same tree. A constant feature of spring at the pénds was the cacophony of young shags begging for food. The amount of fish needed to sustain this level of breeding must be immense. The three species differed in their habits: black shags mostly flew individually to the lake to dive for fish, little black shags fished in small flocks, and little shags kept mostly to the ponds. Several species inhabit the ponds and swamps and are rarely found elsewhere. Although the numbers of dabchick (about 25) and the elusive bittern (about 15) seem low, they are nevertheless important components of their national population. The FEBRUARY 1985

status of the more secretive swamp inhabitants, our small native rails, is more uncertain. Spotless crake appear to be well established, especially around Boggy Pond. Because they are so elusive, one of the most exciting experiences of my study was the chance to watch and photograph a marsh crake. The resulting picture in this article is believed to be the first coloured photograph of this species to be published in New Zealand. Both spotless and marsh crakes moved seasonally in response to changes in water levels. I found crakes wading at the water’s edge in young raupo, but at high water they were in mature raupo, where they walked on fallen leaves covering the water’s surface. Their large relative, the pukeko, was in all swamps, venturing on to farmland in the wetter months. Of gulls, the Southern black-backed gull is the most numerous, with up to 500 birds in 1983 based at two breeding colonies on shingle deltas of the western shore. Black-billed gulls breed elsewhere but more than 200 were present in autumn and winter, usually flying over the lake in search of fish. A few Caspian terns also used the lake for much of the year. Up to 100 white-faced herons occupy the wetlands, using a variety of habitats from pasture to the lake edge. Some pairs nest in tall trees on farmland near the lake. Most important in southern North Island The Lake Wairarapa wetlands have already lost some of their original values. Banded rails and fernbirds were once present but have disappeared as a result of wetland drainage. Even though no major development yet occurred on the shore itself, drains have been dug across it, stopbanks and fences built, and stock have been given access to the flats, causing pugging of the fragile marshland. Despite this deterioration, the wetland complex is a unique and valuable area for wildlife. It is the most important wetland in the southern North Island and is clearly a wetland of international importance, satisfying several criteria for identification of such wetlands, as outlined by the International Union for the Conservation of Nature and Natural Resources. For example, it regularly supports more than 10,000 waterfowl, and at least seven species have more than one percent of their national populations at Lake Wairarapa. It is a complex freshwater system. The many varieties of birds present are a result of the varied habitats available to them, since each species has different niche requirements. Many of the values of the area are a result of the close proximity of different wetland types, giving nearly a continuum of habitats from lake to ponds. Furthermore, the large size of the wetland has led to large numbers of birds. The large, nearly unmodified lake with its wide expanse of eastern shoreline has considerable aesthetic value. Space and wind, birds, and sparse, short plants combine to give a landscape character of unusual quality for this region.

What lies in store There is still much of value to wildlife and to man at Lake Wairarapa. Any development of the eastern shore of Lake Wairarapa would harm wildlife, including both native and international migratory species, and therefore the Wildlife Service strongly recommends the retention of the wetlands. Furthermore the deterioration that has already occurred can be reversed by suitable wetland management. When talking of conservation it is often difficult to argue in economic terms. Reservation, however, need not mean an economic ‘loss’ to the region. The lake can still be used as a storage vessel to protect farmland from flooding and there is some room for use of stock as a management tool to maintain habitat diversity. There is also a valuable game-bird resource. Controlled public use should be encouraged, with information centres, nature walks and observation hides. Combined with development of the National Wildlife Centre at Mount Bruce, this would extend the region’s tourist potential as well as provide jobs. Multiple-use of the Lake Wairarapa wetlands is possible, while at the same time the wetland and wildlife values are conserved for the benefit of our future generations. we

Footnote In October 1984 the Wairarapa Catchment Board ruled out the ‘polder scheme’ as a viable option for the development of lake Wairarapa because of a lack of finance. Instead, it proposed that lakeside banks be constructed to protect farmland from flooding. This would still eliminate some _ wildlife habitat, including about 100ha of semideveloped ponds, marshland and willows between Boggy Pond and the lake.