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 7. Fish – state and trends As outlined in Section 2.4.2, fish monitoring using a standardised survey approach has only been trialled at five of the 55 RSoE sites to date. This section summarises the results of this monitoring and compares these against RSoE water quality, periphyton and macroinvertebrate monitoring results. To help provide a more complete picture of the fish health in the Wellington region’s rivers and streams, the second part of this section presents an analysis of state and trends in freshwater fish communities using data extracted from the New Zealand Freshwater Fish Database (NZFFD). Administered by NIWA, this database provides a large amount of information on the distribution of freshwater fish within the Wellington region and NZFFD data has previously been used successfully at both regional and national scales to analyse spatial and temporal trends in freshwater fish populations (Joy 2009; Joy 2011). 7.1 State 7.1.1 Approach to analysis The Index of Biotic Integrity (IBI) was calculated for each site (using both RSoE and NZFDD fish data) to help facilitate inter-site comparisons and provide an indication of overall fish community condition. The IBI is a combination of six metrics that was developed specifically to assess the condition of New Zealand’s fish fauna and takes into account the fact that many species exhibit diadromous life histories (ie, often migrate between the ocean and freshwater at some point in their lifecycle). The IBI compares the species found at a site with those expected to be at a site, while taking into account natural changes that occur with distance inland and elevation. For full details of the IBI see Joy and Death (2004) and Joy (2004). IBI scores were generated for each site in a Microsoft Excel spreadsheet macro using a version of the IBI calibrated for the Wellington region (Joy 2004). IBI scores can range from 0 (no fish present) to 60, with a score of 60 indicating that all fish expected to be present were found. Interpretation of IBI scores was undertaken using the classes recommended in Joy (2004) and outlined in Table 7.1. See Section 4.1.1 for interpretation of the box plots presented in this section. Table 7.1: Attributes and suggested thresholds for interpretation of IBI scores for the Wellington region from Joy (2004) IBI score Integrity class Attributes 52–60 Excellent 48–51 Very good 38–47 Good Comparable to the best situations without human disturbance; all regionally expected species for the stream position are present. Site is above the 97 th percentile of Wellington sites. Site is above the 90th percentile of all Wellington sites; species richness is slightly less then best for the region. Site is above the 70th percentile of Wellington sites but species richness and habitat or migratory access reduced some signs of stress. 30–37 Fair Score is just above average but species richness is significantly reduced habitat and or access impaired. 18–29 Poor Site is less than average for Wellington region IBI scores, less than the 50th percentile, thus species richness and or habitat are severely impacted. 2–17 Very poor Site is impacted or migratory access almost non-existent. 0 No native fish Site is grossly impacted or access for fish is non-existent. WGN_DOCS-#1100598-V3 PAGE 89 OF 160
River and stream water quality and ecology in the Wellington region: State and trends (a) RSoE sites Over 2009 to 2011, four RSoE sites (Beef Creek at Headwaters, Kaiwharawhara Stream at Ngaio Gorge, Tauanui River at Whakatomotomo Road and Totara Stream at Stronvar) were surveyed following standardised fish monitoring protocols documented in David et al. (2010); in brief, this involved fishing 150 m of suitable stream reach using one-pass backpack electric fishing. Additionally, a 150 m reach of the Whareroa Stream at Queen Elizabeth Park was also surveyed in 2011 using 10 fyke nets and 20 minnow traps 26 . The use of nets and traps at this site follows ‘best practice’ recommendations for surveying freshwater fish communities in deep streams (typically >0.6 m) characterised by a soft-bottomed substrate, poor water clarity and low velocities (Joy & David in prep.). (b) NZFFD records Given the limited RSoE fish data available, the current state of freshwater fish communities in the Wellington region was assessed using NZFFD records for the period 1990 to 2010. This 20-year period was chosen to provide sufficient data for analysis. However, it must be recognised that, in some cases, NZFFD records from the earlier part of this period may no longer accurately represent the current state of the fish communities in the river or stream surveyed. All fish survey records for the Wellington region were downloaded from the NZFFD in April 2011. The ‘sampling locality’ for each record was screened prior to any analyses being undertaken and all records with sampling localities that were clearly not river or stream type environments (eg, lakes, wetlands, etc.) were excluded from the dataset. NZFFD records were plotted on a map to provide a spatial representation of fish surveys across the region. A list of species, both indigenous and introduced, was compiled and the ‘frequency of occurrence’ of each species in the region was calculated (ie, the number of records for a species divided by the total number of records in the NZFFD). IBI scores were calculated for all records and the range of scores compared between different catchments. Comparisons between catchments were limited to those that had sufficient records (in this case arbitrarily defined as n ≥ 15). Given the large variation in the number of records between catchments, along with the significant range of catchment sizes assessed, no in-depth analysis was undertaken other than summarising the range of IBI scores for each catchment. Relationships between IBI scores and landcover were examined following a similar approach to Joy (2011). Each NZFFD record was assigned a River Environment Classification (REC) landcover class (see Appendix 2) of indigenous forest, exotic forest, pasture or urban. Because the data were not normally distributed, differences between IBI scores for different landcover types were examined using a Kruskal-Wallis One Way Analysis of Variance on ranked data. These tests were performed in SigmaPlot (Version 11.0) with a statistically significant difference set at p
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River and stream water quality and
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DISCLAIMER This report has been pre
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observed trends were unclear. The p
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5. Periphyton - state and trends 57
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Figure 2.1: RSoE monitoring sites a
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2.4.2 Biological variables River an
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