2. Freshwater ecological values in the Waitaki Catchment
2.1 Overview
2.1.1 Biological groups covered in GIS layers
The coverage of GIS data for the diversity of biological groups is generally very good for the Waitaki River Catchment and the freshwater ecology GIS layers include species records and habitat data for freshwater invertebrates, freshwater fish, lizards, birds, threatened plants and weed plants. Description of the diversity and spatial extent of these groups is given in the following sections. While many of the major taxonomic groups are represented in the GIS layers, groups not represented include algae, bryophytes (mosses and liverworts), fungi, frogs and bats.
There is little spatial information available for freshwater algae, bryophytes or fungi in New Zealand in general, or in the Waitaki River Catchment in particular. At the time of writing, Landcare Research (a Crown Research Institute) was preparing a "Moss Flora of New Zealand" publication as part of their Moss Flora project, but this information was not readily available at the time of writing. Most up-to-date information for the lower catchment on freshwater algae is held by the National Institute of Water and Atmospheric Research (NIWA). Although there is the potential for rare algal taxa to be present, the Project Aqua field surveys and literature review found no rare taxa in the lower catchment (Biggs et al., 2003). In general, understanding of taxonomy and biodiversity of freshwater algae in New Zealand is still poorly developed. Little is known of freshwater fungi in New Zealand.
None of the three native frog species found on mainland New Zealand (all belonging to the genus Leiopelma) are found within the Waitaki River Catchment (Hitchmough, 2002). There are no historic or recent records of either long-tailed bats (Chalinolobus spp.) or short-tailed bats (Mystacina spp.) occurring within the Waitaki River Catchment (O'Donnell, 2001; Lloyd, 2001).
2.1.2 Life stages represented in GIS layers
The importance of a given freshwater body to species of interest may vary according to whether it is used for feeding, dispersal, breeding, or over-wintering. Freshwater fish, numerous native bird species, and many insects with aquatic larval stages depend on freshwaters to complete important parts of their life history.
Life history information is presented in GIS format for salmonid fish (introduced salmon, trout and charr) and native birds. The New Zealand Freshwater Fish Database (NZFFD) records information of native and introduced fish, however information on the life history status is patchy, so was not used as part of this project. O'Donnell (2000) identified the locations of significant feeding, breeding, roosting and over-wintering habitat for native birds (including riparian areas, lakes and rivers) in Canterbury in a GIS format. In the Waitaki River Catchment, there are large areas of open water and braided riverbed that form important habitat to a variety of native birds. For example, Fig. 2 shows that the braided riverbeds and deltas of the upper Waitaki catchment are primary breeding habitat for one of New Zealand's rarest birds, the black stilt (Himantopus novaezelandiae). The GIS layer from O'Donnell (2000) includes similar life history and habitat information for seven bird guilds and seven threatened bird species found within the Waitaki River Catchment.
Most salmonid fish species undertake migrations associated with spawning or downstream migration of juveniles within river catchments. The timing and habitat requirements of migrating salmonids depend on the developmental stage and species of interest. Langlands and Elley (2000) summarised salmonid habitat values, including spawning habitats, in the Canterbury region (including the Waitaki Catchment) in a GIS format. For example, Fig. 3 shows that brown trout spawning habitat occurs throughout the Waitaki Catchment, from the mainstem and tributaries below Lake Benmore, to the glacial lake tributaries in the upper catchment. The relative value of salmonid habitats, based on the assessment of Langlands (2000), is also presented in the GIS layer.
2.1.3 Spatial distribution of ecological information and values within the Waitaki River Catchment
Overall, the spatial coverage of the Waitaki Catchment with freshwater ecological GIS data is variable, and depends on the biological group of interest (see discussion below). All sub-catchments and major tributaries have some ecological information included in the GIS data, however the upper catchment (above Lake Waitaki) has a greater proportion of ecological data than the lower catchment, reflecting either greater ecological values or greater sampling effort in the upper catchment.
One of the major constraints in using the GIS data provided is that it will not be updated automatically when new records are added to the original data source. This will not greatly affect GIS layers such as the Department of Conservation Natural Significance layer, where much of the information is based on historic surveys. However, for groups such as the freshwater fish, new records are constantly being added, such that the spatial distribution of fish in the GIS layers may be misleading if the data is not updated regularly. Therefore, the 'life' of the ecological data presented in this report and associated GIS layers may be as short as 12 months for groups such as the freshwater fish, but will be longer for other layers.
There is a greater amount of ecological data available for the larger tributaries and sub-catchments within the Waitaki Catchment compared to the smaller headwater streams. The greatest diversity of stoneflies (Plecoptera) in New Zealand is typically found in small headwater streams (Quinn and Hickey, 1990). However, there is little ecological information for small headwater streams in the Waitaki. Thus, there are pockets of biodiversity, such as headwater streams, that are not covered in the GIS layers. Generalised Environment Canterbury GIS data coverage of wetland bird, vegetation, and salmonid habitat is restricted to the larger rivers and lakes such as the Hakataramea River. Similarly, information on distribution of threatened plants, lizards and birds is biased, as records do not include where threatened species were searched for and not found. The NZFFD is good in this regard, as records include sites where fish sampling occurred but no species were found. For example, in the upper Maraewhenua River Catchment (Fig. 4) and the headwaters of the Otematata River no fish have been recorded at some sampling locations.
The NZFFD has the best spatial coverage and most up-to-date records for any of the biological groups considered. Based on a search of the NZFFD in October 2004, there are 712 freshwater fish records, including 26 species in the Waitaki Catchment. Although the Department of Conservation threatened plant GIS data indicated that there were a total of 714 threatened plant species, including 78 species, within the Catchment, no distinction is made between terrestrial and aquatic species, so the actual number of threatened wetland plants is likely to be considerably less than this.
The distribution of threatened native fish and salmonids within the Catchment were modeled, in an effort to fill gaps where ecological data may be scarce. Fish distributions were modeled by combining fish species location records from the NZFFD with habitat information contained in the River Environment Classification (REC), a GIS-based river management tool created by NIWA. Details of the modeling process are described later in this report. However, in general, the modeling process was successful in extrapolating the potential locations of certain fish species throughout the Catchment.
2.2 Assessing ecological values within the Catchment
2.2.1 Overview
In general, ecological values include measures of biodiversity, habitat quality/integrity, and the presence of key species of interest, such as rare and endangered species or species of recreational interest (eg, trout and salmon). This section provides an assessment of the freshwater ecological values of the Waitaki River Catchment, under the categories of threat status, biodiversity, salmonid habitat and habitat quality and ecological pressures. Where species are described as being threatened with extinction, the threat classification follows that of Molloy et al. (2002), as shown in Table 2.1 below.
Table 2.1 Classification of New Zealand native resident species according to threat of extinction (after Molloy et al. , 2002)
| Degree of threat of extinction | Threat category |
|---|---|
|
Acutely threatened |
Nationally critical |
|
Nationally endangered |
|
|
Nationally vulnerable |
|
|
Chronically threatened |
Serious decline |
|
Gradual decline |
|
|
At risk |
Range restricted |
|
Sparse |
Threatened species
Threatened plant and animal species occur throughout the Waitaki Catchment, as shown in Fig. 5. Appendix 2 lists the species recorded in the GIS data layers. Differences amongst groups in their spatial representation most likely reflect historic differences in sampling effort and reporting for the groups. Thus, the distribution of threatened species depicted in the GIS layers is probably quite accurate for birds and plants, patchy for lizards and native fish, and poor for freshwater invertebrates.
One of the three gecko species and four of the six skink species recorded in the Waitaki are threatened. Of these threatened lizards, only the jewelled gecko (Naultinus gemmeus), the green skink (Oligosoma chloronoton) and the long-toed skink (O. longipes) are commonly found in riparian areas, river terraces, or river islands. Threatened lizards are sparsely distributed mainly throughout the upper catchment
There are 714 records of threatened plants, including 78 species, within the Waitaki River Catchment. The most threatened wetland plant species recorded in the catchment is sneezeweed (Centipeda minima), which has a nationally critical threat status. Sneezeweed is a small herb typically found at the margins of wetlands and lakes, and has been recorded in the upper Waitaki catchment in the Ben Omar Swamp (near the Ahuriri River), on the southern shore of Lake Pukaki, and from an unnamed tributary of the Pukaki River. Two species of native broom, Carmichaelia kirkii (nationally endangered) and C. vexillata (in serious decline), are the most commonly recorded threatened plant species in the Waitaki Catchment. Both broom species are sparsely distributed throughout the upper catchment, although there are a cluster of C. kirkii records from tributaries of Lake Benmore in the Ben More range. Both C. kirkii and C. vexillata occur on river banks and terraces, and recent alluvium, and C. kirkii is sometimes found in wetlands.
Six of the 26 freshwater fish species recorded from the Waitaki River Catchment are threatened with extinction. The most threatened of these fish taxa are the lowland longjaw galaxias (Galaxias cobitinus), whose threat status is regarded as nationally critical, and Canterbury mudfish (Neochanna burrowsius), which is nationally endangered (Hitchmough, 2002). Lowland longjaw galaxias are typically found at river margins and most records are from the upper catchment (although there is a single record from the Hakataramea River). In contrast, Canterbury mudfish are typically found in still or sluggish waters, with plenty of aquatic weeds, and have only been found in small tributaries close to the mouth of the Waitaki River. The Waitaki River marks the southern limit of Canterbury mudfish records in New Zealand.
Four or five species of threatened native birds are known to occur at any one time on the Waitaki River mainstem, Lake Benmore, Ahuriri River, and the glacial lakes and their major tributary inflows, outflows and deltas (O'Donnell, 2000). The black stilt (Himantopus novaezelandiae) is the most threatened bird species within the Catchment, and only about 100 individual black stilts exist. Black stilts feed and breed along braided rivers and river deltas (Fig. 2), and the Waitaki River Catchment is their principal habitat. Crested grebe (Podiceps cristatus australis), which are also listed as nationally critical, breed and feed on the glacial lakes in the upper catchment, and on Lakes Benmore, Aviemore, and Waitaki further down the Catchment.
Biodiversity
Biodiversity can be measured in the Waitaki Catchment at a variety of taxonomic levels. For example, by overlaying all the freshwater ecological GIS layers, it is clear that there are a diverse assemblage of biological groups (eg, plants, birds and fish) within the Catchment. Clusters of ecological data coincide with areas where more intensive research has been carried out, such as the Department of Conservation Project River Recovery area in the Mackenzie Basin area, and around Mount Cook village in the upper catchment.
Species richness (the number of species found at a given location) is a commonly used measure of biodiversity within a given habitat type or location. Fig. 6 shows that while there are many records of threatened fish species throughout the Catchment, there are only six sites (all below the glacial lakes) where more than one threatened fish species has been found at a site. In contrast, four or five threatened bird species are known to co-occur throughout the Catchment, including most of the large lakes and braided river habitat. Similarly, freshwater invertebrate data, while limited in its spatial extent, shows relatively high species richness (over 20 taxa per site) at a number of sites throughout the Catchment. Caddiflies (Trichoptera) have the greatest diversity within an individual taxon in the Catchment.
Salmonids
There are approximately 350 individual NZFFD records of brown trout (Salmo trutta) from the Waitaki Catchment, making it the most commonly recorded fish species within the Catchment (total of 1851 records, from October 2004 search of the NZFFD). Rainbow trout (Oncorhynchus mykiss) and chinook (or quinnat) salmon (Oncorhynchus tshawytscha) are also commonly found within the catchment. While rainbow trout and brown trout occur throughout the Waitaki Catchment, chinook salmon are mostly found downstream of the Waitaki dam in the mainstem and in tributaries such as the Hakataramea River. Chinook salmon, brown trout and rainbow trout, are all important sports fish within the Catchment. The only New Zealand records of sockeye salmon (O. nerka) are from the upper Waitaki catchment, upstream of the Waitaki dam. Although sockeye salmon are virtually extinct within New Zealand outside of commercial salmon farms, they are known to spawn in Larch Stream at the head of Lake Ohau (Mark Webb, Fish and Game, pers comm.).
Habitat quality and ecological pressures
Fields in the salmonid, bird and vegetation GIS layers include information on habitat intactness and threats to the biological groups of interest. For example, Fig. 7 shows that a significant proportion of native bird habitat within the Catchment is threatened by a variety of factors such as introduced predators and reduced water quality.
The location and density of permits to abstract water provide an additional measure of pressure (water abstraction) on freshwater ecosystems. For example, there is a greater amount of ecological data (considering all point data combined) and fewer water permits in the upper catchment compared to the lower catchment, where there are more water permits and less ecological data (Fig. 8). However, two points must be made before making inferences from this pattern. First, while some layers indicate whether a species was present or absent (eg, the fish layers), others do not. Therefore, the absence of data does not necessarily infer that the ecological values are low. It may simply mean that no detailed collections have been made in the location. Secondly, it is likely that there is additional ecological value information contained in the ecology polygon layers (eg, the bird or salmonid layers) and the REC fish layers.
2.2.2 Examples
To show how GIS data can be used to help assess different freshwater ecological values against water demand, an example is given from the Hakataramea River Catchment. Fig. 9 shows that while there are water permits throughout the Hakataramea River Catchment, including the mainstem and tributaries, most threatened species records are concentrated along the mainstem. In contrast to threatened species records, brown trout are found both within the mainstem and tributaries of the Hakataramea River (Fig. 10). Because threatened species and brown trout distributions differ within the Hakataramea River, management of freshwater resources for instream habitat will vary depending on whether the focus is on tributaries (where brown trout have been found, but threatened species records are uncommon) or on the mainstem (where trout, other salmonids, and threatened species occur).
