Freshwater species

Fish
Most of our 29 native fish species are small, well-camouflaged creatures that stay close to the beds of rivers. Only three species grow to more than two kilograms in body weight – two eels, the giant kokopu (a fourth large fish – the grayling – is extinct). Only eight native species are considered common – eels, torrentfish, various bully species and the common river galaxiids.

Although they live in freshwater, many native species have a marine stage in their life-cycle.

Fishy facts:

• 29 species of native freshwater fish have been identified, and more continue to be identified
• One species, the grayling, became extinct early in the 1900s
• 10 freshwater fish species are considered threatened
• Nearly 90 per cent of the freshwater fish species are endemic (i.e. they are not found anywhere else in the world)
• About 20 alien species of freshwater fish have been introduced since European settlement – including trout, salmon, koi carp, catfish, tench, rudd and perch – and these tend to dominate the fish communities

Invertebrates
New Zealand has about 450 formally identified insect species and at least 200 other kinds of invertebrate (such as, crustaceans, molluscs and various worm phyla) in its streams and other freshwater habitats.

Freshwater habitats

New Zealand has more than 70 major river systems and numerous streams. A few rivers include significant channels within cave systems. Only two complete river systems still lie within unmodified catchments and remain free of introduced species.

• More than 770 lakes and innumerable ponds cover around 3400 square kilometres
• The 30 or so large deep lakes have generally high water quality, and some support almost intact native ecosystems.
• Many of the shallow lakes (around 700) are degraded by nutrient enrichment and oxygen loss – a few are now incapable of sustaining fish life.
• Invasive exotic plant species are extensive in most lakes.

Wetlands represent some of the most diverse ecosystems, but few remain – swamps, bogs and marshes now cover only 1000 square kilometres – less than 10 per cent of the original wetland area in New Zealand. While many of the remaining wetlands are degraded to varying degrees, some are large and have internationally significant biodiversity values, as do some remaining geothermal areas. Examples include wetlands at Farewell Spit and the Firth of Thames, both of which have been listed under the Ramsar Convention as wetlands of international importance.