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Executive summary

  1. Over the past 30 years there has been a big increase in sites entered into the New Zealand Freshwater Fish Database (NZFFD). Most of this increase has been at pasture and indigenous forest sites. In the last decade (2000 – 2007) the number of pasture sites sampled was more than the number of sites for all other land-cover classes combined.

  2. Thirty-seven years of freshwater fish and crustacean presence/absence data were obtained from the NZFFD; that was all entries on flowing water dating from January 1970 to June 2007 and consisted of 22,546 sites.

  3. To enable between site comparisons an Index of Biotic Integrity (IBI) was used as it takes into account natural elevational and distance from coast variation in fish communities caused by the largely migratory New Zealand fish fauna.

  4. Clear differences in IBI scores were found in relation to land cover. Sites in native vegetation catchments had significantly higher scores and more species than sites in pasture and urban catchments, while those in tussock land cover had the lowest scores.

  5. Analysis of IBI scores over time revealed a significant reduction in average IBI scores for the past 37 years, especially over the last decade.

  6. Investigation of the temporal trends by land-cover type showed the biggest declines were at pasture, tussock, and urban sites, while exotic forest sites showed no significant change and there was a significant improvement at native forest and scrub sites.

  7. Where data was available for the same reaches sampled repeatedly over time these were analysed for changes. These showed more declines than improvements, although the differences were small. This study identified a shortage of repeatedly sampled sites.

  8. The measures used in this study are only based on presence/absence data, thus the results are inherently conservative because fish species will show reduced abundance long before they become locally extinct.

  9. This analysis highlighted the necessity for a set of long term repeatedly sampled monitoring sites for the whole country and the need to have a consistent sampling protocol.

 

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