Skip to main content.

Our rivers: trends in fish communities

As part of its National Environmental Reporting Programme, the Ministry for the Environment reports on the health of fish communities in our rivers. This is the first time this data has been analysed and reported at a national level.

The Index of Biotic Integrity (IBI) was used to analyse 22,546 records from the New Zealand Freshwater Fish Database between January 1970 and June 2007.

Key findings

  • On average, IBI scores in rivers surrounded by indigenous forest were 10.9 per cent higher (better) than rivers surrounded by pasture and 9.8 per cent higher than rivers in urban areas.
  • At a national scale, average IBI scores for all sites decreased (worsened) by 8.3 per cent between 1970 and 2007.
  • The biggest decreases in IBI were in rivers surrounded by pasture (11 per cent) and in rivers in urban areas (9.9 per cent).

Average index of biotic integrity (IBI) score for all sites, grouped by River Environment Classification land cover class

Read table of data of this graph

Graph showing average Index of Biotic Integrity (IBI) score for all river sites monitored between 1970 and 2007, grouped by River Environment Classification land-cover type.

Land cover type Average IBI
Tussock 17.98
Pasture 29.68
Urban 30.33
Exotic forest 30.47
Bare 31.40
Indigenous forest 36.22
Scrub 36.51

All landcover classes

Read table of data of this graph

Graph showing average Index of Biotic Integrity (IBI) score for all river sites monitored between 1970 and 2007 by decade.

Decade Average IBI score
1970-1979 32.86
1980-1989 32.11
1990-1999 31.64
2000-2007 27.91

Pasture

Read table of data of this graph

Graph showing average Index of Biotic Integrity (IBI) score for river sites with pasture land-cover type monitored between 1970 and 2007 by decade. Land-cover type defined using River Environment Classification

Decade Average IBI score
1970-1979 33.57
1980-1989 31.79
1990-1999 31.28
2000-2007 27.63

Urban

Read table of data of this graph

Graph showing average Index of Biotic Integrity (IBI) score for river sites with urban land-cover type monitored between 1970 and 2007 by decade. Land-cover type defined using River Environment Classification

Decade Average IBI score
1970-1979 33.36
1980-1989 33.96
1990-1999 29.67
2000-2007 26.74

This information supports the Government’s New Start for Fresh Water work programme and other freshwater policy initiatives.

For more information go to Temporal and Land-cover Trends in Freshwater Fish Communities in New Zealand’s Rivers, 1970–2007.