The number of New Zealand’s freshwater fish listed as threatened has increased since we first started keeping track of them in 1992.
A new study comparing land use changes and freshwater fish distribution from 1970 to 2017 has found that more species were in decline in sites surrounded by pasture than those in areas covered by native bush.
The toll from intensive agriculture on NZ’s native fish is pretty high, say the authors, with three-quarters of freshwater fish listed as threatened or at risk, compared to the global average of 37 per cent.
In this study, temporal and land cover-related trends were analysed for data on freshwater fish distribution, comprising more than 20 000 records for the 47 years from January 1970 to January 2017 from the New Zealand Freshwater Fish Database.
The analysis included individual species abundance and distribution trends, as well as an index of fish community integrity, namely the Index of Biotic Integrity (IBI).
Of the 25 fish species that met the requirements for analysis to determine changes in the proportion of sites they occupied over time, 76% had negative trends (indicating declining occurrence).
Of the 20 native species analysed for the proportion of sites occupied over time, 75% had negative trends; 65% of these were significant declines and more species were in decline at pasture sites than natural cover sites.
The average IBI score also declined over the time period and, when analysed separately, the major land cover types revealed that the IBI declined at pasture catchment sites but not at sites with natural vegetation catchments.
The authors thank all the contributors to the New Zealand Freshwater fish database and to NIWA for maintaining the database.