River and stream water quality and ecology - Greater Wellington ...

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River and stream water quality and ecology in the Wellington region: State and trends (c) Cautionary notes Given that the state analysis period spans 20 years (1990 to 2010), it can be expected that in some cases the REC landcover class may not accurately reflect the dominant landcover at the time some of the earlier fish surveys were undertaken (the same is true for landcover classes used in the trend analysis carried out in Section in 7.2). In addition, there are several potential limitations in using fish data from the NZFFD that should be borne in mind when interpreting the results of the analyses undertaken: 7.1.2 Results Not all catchments in the Wellington region have been surveyed equally (in terms of the number of records and also the type, methodology and effort of each individual survey). NZFFD data have been collected using a range of survey methods and while backpack electric fishing has been used to undertake the majority of surveys in the Wellington region (>70% of all records), other methods have also been used (eg, spotlighting and netting/trapping). Different fishing methods have different biases in terms of both the habitat they can be used effectively in and the range of species they are likely to catch (Joy & David in prep) 27 . For example, the predominance of backpack electric fishing – which is only suitable for use in wadeable rivers and streams – indicates that larger/deeper rivers are likely to be under-represented in NZFFD data. Furthermore, the ‘catchability’ of different species using this method is also widely variable, suggesting that the presence of some species (eg, large galaxiids and pelagic species) may be under-represented. Many surveys undertaken target specific species, such as those that are rare or considered threatened, and as such these species might be overrepresented in the NZFFD records. (a) RSoE data A summary of species caught, along with relevant site information, from the five RSoE sites fished between 2009 and 2011 is presented in Table 7.2. The five sites surveyed ranged from being located relatively close to the coast (Kaiwharawhara Stream at Ngaio Gorge and Whareroa Stream at Queen Elizabeth Park) to 90 km inland (Beef Creek at Headwaters) and are located across the four REC landcover types represented in the RSoE network (indigenous forest, exotic forest, pasture and urban). Across these five sites, a total of 11 indigenous as well as one introduced (brown trout) species were caught. Indigenous species diversity at each site ranged from two (Tauanui River at Whakatomotomo Road and Beef Creek at Headwaters) to eight (Whareroa Stream at Queen Elizabeth Park) species and the total number of fish caught at each site ranged from 23 (Beef Creek at Headwaters) to 318 (Totara Stream at Stronvar). Longfin eels were the only species caught at all five sites. IBI scores ranged from 28 (‘poor’, two sites) to 48 (‘very good’) (Table 7.2). 27 Different biases associated with different sampling methodologies should also be kept in mind when interpreting the RSoE site data presented in this section. WGN_DOCS-#1100598-V3 PAGE 91 OF 160
River and stream water quality and ecology in the Wellington region: State and trends Table 7.2: Summary of fish community data and relevant site information for five RSoE sites, based on one-off fish surveys undertaken in a 150 m long stream reach between 2009 and 2011 RS12 RS18 RS44 RS49 RS52 Whareroa S at QE Park 1 Kaiwharawhara S at Ngaio Gorge Totara S at Stronvar Beef Ck at Headwaters Tauanui R at Whakatomotomo Rd Year surveyed 2011 2011 2009 2009 2009 Elevation (m) 2 21 200 148 150 Distance inland (km) 1 2 31 90 29 Dominant landcover Pasture Urban Exotic forest Indigenous forest Indigenous forest IBI score 48 34 40 28 28 IBI class Very good Fair Good Poor Poor Species caught and abundance Longfin eel 19 15 78 3 4 Shortfin eel 11 14 ― ― ― Bluegill bully ― 10 ― ― ― Common bully 1 ― ― ― ― Cran’s bully ― ― 156 ― ― Giant bully 9 ― ― ― ― Redfin bully 14 40 83 ― ― Upland bully ― ― 1 18 289 Inanga 5 ― ― ― ― Giant kokopu 15 ― ― ― ― Smelt 1 ― ― ― ― Brown trout ― ― ― 2 3 Species richness 8 4 4 3 3 Total fish caught 75 79 318 23 296 1 Data provided courtesy of Dr Mike Joy (Massey University). The lowest IBI scores (28) were recorded at two sites with upstream catchments dominated by indigenous forest (and are classed as ‘reference’ sites): Beef Creek at Headwaters and Tauanui River at Whakatomotomo Road. Both of these are tributaries of the Ruamahanga River, are located at moderately high elevations (~150 m) and range from 30 to 90 km inland from the coast. The low IBI scores at these two sites are in contrast to the excellent results for water quality, periphyton and monitoring indicators, as well as the excellent habitat present at both sites (Table 7.3). The reason for the poor IBI score at the Tauanui River site is not known. In the case of Beef Creek, an instream barrier downstream of the monitoring site may affect fish access to the site. Whareroa Stream at Queen Elizabeth Park shows the opposite pattern to the Beef Creek and Tauanui River sites. This site is located on the lower reaches of a pastoral catchment and typically records amongst the poorest water quality and macroinvertebrate health of the 55 RSoE sites; despite this, its IBI score (48) places it in the top 10% of all NZFFD fish records for the Wellington region. This likely reflects the close proximity of this site to the coast, along with the absence of instream barriers to restrict access to diadromous species. Overall, the fact that habitat quality at the Whareroa Stream site was also classed PAGE 92 OF 160 WGN_DOCS-#1100598-V3
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observed trends were unclear. The p
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