River wildlife values high

Press, 23 September 1983, Page 22

River wildlife values high

Five Canterbury rivers have outstanding wildlife values, according to a report from the New Zealand Wildlife Service.

Nine other braided rivers in the area have either high or moderate wildlife values, according to “The Wildlife and Conservation of Braided River Systems in Canterbury.”

The five rivers classified as outstanding were the Ashley, the Waimakariri, the Rakaia, the Ashburton and the Rangitata. The report is based on surveys on 14 braided river systems in Canterbury, gathered between 1974 and 1981 by the Wildlife Service’s Fauna Survey Unit. The surveys were instigated in response to threats of river development for hydro-electric purposes and irrigation abstraction.

The authors, Mr C. F. J. O’Donnell and Mr S. M. Moore, stress that the surveys were for the primary identification of the rivers’ values only, and more detailed research could follow.

The braided river systems in Canterbury were unique, not only to New Zealand, but to the world, said the report. Riverbed habitats were used for breeding by more than 40 riverbed and wetland birds and each river was sufficiently distinctive in its characteristics, to provide for a “unique combination” of wildlife.

Although there were other braided rivers in Southland, Central Otago, Westland, Nelson and Marlborough,’ these were characteristically shorter, less braided and had more single channel sections.

The surveys concentrated mainly on the bird species present, which were the

major form, of wildlife inhabiting the riverbeds. The habitats of many of these birds were under threat from modifications to the rivers, such as irrigation abstraction, recreation activities, dam impoundments and the introduction of plant species. “Historical indications are that population size and distribution of various species, particularly the endemic riverbed specialists, have been greatly reduced” from human activities on some rivers, the report says.

Rivermouth habitats were likely to be influenced by upstream modifications to flows, such as irrigation abstraction, earthworks and hydro-electric development.

The Rakaia river was especially important for its large wrybill population. Three quarters of all wrybill recorded on the river surveys to date were breeding on the Rakaia River. Although most of the population was above the gorge, the numbers of wrybill on the middle section and below the main South Road bridge were still higher than any other river in Canterbury.

The rivermouth of the Ashley was rated as one of the most valuable estuaries in Canterbury, and was the only place in New Zealand where red-capped dotterel (an Australian species) had bred. “The mouth represents an uncommon habitat combination with the richest

species combination of all rivermouths discussed in this report.”

The Waimakariri river had the second largest number of wrybill after the Rakaia. Numbers of most birds were similar to those on other rivers, although, considering the large size of the habitat involved, more were expected. A total of 50 species was recorded on the Ashburton river, with black-fronted tern and black-billed gull being more numerous than on all the other riverbeds. The black-fronted dotterel had only three confirmed breeding sites in the South Island to date, and one of these was on the Opihi river. This river was the only known site in New Zealand where white-winged black tern had attempted to breed.

Extensive areas on many riverbeds had become unavailable to wetland bird species due to the introduction of plant species, particularly lupin, gorse, broom and willow, said the report. Lack of nesting space caused by vegetation encroachment may now be a major limiting factor to the breeding of riverbed species,” the report concluded. It has, in its recommendations, suggested that a feasibility study be carried out to see if spraying of riverbed weeds was possible.

A serious threat to riverbed wildlife habitat in

Canterbury would be the abstraction of river waters for irrigation. This could lead to a loss of acquatic habitat causing a lack of invertebrate food for birds. Increased plant encroachment would ensue, giving a further reduction of available habitat for wetland birds.

Nesting birds would be subjected to more flooding through the increased impact of flash floods, breeding wader birds may suffer because of an increase in the distance between their nests and the water and river works could disturb nesting birds. The damming of braided rivers for hydro-electric power generation could increase the vulnerability of bird nests at lower riverbed levels. Downstream areas could dry up during critical low flow periods, and the downstream geomorphology would be changed due to impounding shingle and other sediment.

During the crucial breeding season, many recreational activities could disturb or threaten riverbed birds, causing destruction of nests, disturbance of sensitive birds, or a modification of the critical feeding habitat.

Most of the well-known river recreation activities have been included in the report’s list — four wheel drive vehicles, trail bikes, jet boaters, rafters, canoeists, anglers, picnickers,

walkers, hunters, and bird watchers, including the survey personnel themselves could disturb the birds. Other threats to wildlife on the rivers include rats and hedgehogs. which caused significant damage by taking chicks, eggs and adult birds. Black-backed gulls and their predatory habits were also a worry. Sewage and industrial effluent, intensive stocking with sheep and cattle, burning of riverbed vegetation and poisoning of rabbits could disturb the birds. The Wildlife Service desired early consultation from local authorities who were planning significant river control, dam or water abstraction works, the recommendations state. The authorities would be advised of the wildlife values of the Canterbury rivers, and should formulate and pursue reservation proposals for braided river systems.

The Wildlife Service would seek preservation of areas with wildlife communities which were vulnerable to habitat modification.