Increasing urbanisation and more intensive farming are killing New Zealand's freshwater fish species by degrading water quality, says the author of a report published this week by the Ministry for the Environment.
Dr Mike Joy, a senior lecturer in the ecology group of the University's Institute of Natural Resources, reviewed 22 500 records of fish communities nationally and found they show significant decline over the past 40 years.
The most dramatic impacts are in waterways adjoining pastoral and urban sites. "These fish communities are like miners' canaries," Dr Joy says. "They have a strong message for us – our freshwater ecosystems are in dire straits and more than half of our native freshwater fish species are classed as being at risk of extinction.
"These fish are long-lived species and their demise is indicative of long-term declines in the condition of their habitats.
"The causes are the intensification of agriculture and increased urbanisation eading to increases in sediment and nutrients inputs into rivers and treams. These changes are revealed in the chemical measures monitored nationally by NIWA and shown in a separate report released at the same time."
Dr Joy has previously issued specific warnings about the declines in eel populations and in the native fish species that make up whitebait.
Editor's Note: Original news release can be found here. Dr Mike Joy's report may be read here, and the NIWA report on water quality trends is here.