New Zealand has 22 introduced freshwater species in its waterways (a high
figure given that New Zealand only has 36 native freshwater species). Some
introduced species, like trout, are highly valued by anglers, but others
pose significant threats to native freshwater ecosystems. Introduced fish
can:
- Stir up sediment and make water murky
- Increase nutrient levels and algal concentrations
- Contribute to erosion
- Feed on and remove native aquatic plants
- Prey on invertebrates, native fish and their eggs
- Compete with native species
Of the 22 introduced species, koi carp, gambusia (also known as mosquito
fish), rudd and catfish are considered to pose the most significant threats.
New Zealand Biodiversity Strategy funding since 2000 has enabled the
Department of Conservation to gather much more information about the spread
of pest fish in New Zealand waterways. This information is providing a sound
basis for identifying and controlling priority infestations, and further
restricting the spread of pest fish species through direct management and
increased public awareness.
A pest fish survey of the North Island was carried out over the summer of
2001/02. This complemented a similar survey carried out in the South Island.
As a result of these surveys further evidence was found of the spread of
pest fish in the North Island with some significant new populations
confirmed. Koi carp and Gambusia were located at 12 new South Island sites.
Monitoring at 19 Nelson locations where Gambusia and koi carp were
eradicated in the 2000/01 year suggest this work has been successful.
Further eradication attempts were made at four priority sites in 2001/02.
Publicity material produced to support this work, pest fish information
and links are available on the Department of Conservation’s
website. |
