Guide to restoring kōura (freshwater crayfish) in lakes, rivers and streams
Habitat degradation and the introduction of exotic plant and fish species have adversely affected kōura populations throughout New Zealand. However, there are a number of measures that we can use to restore kōura populations in lakes, rivers and streams.
The importance of Kōura
Freshwater crayfish are endemic to New Zealand where they are known locally by the Māori name kōura (and less commonly kēwai). New Zealand has two species of freshwater crayfish, the northern kōura, Paranephrops planifrons, which occurs in the North Island and the West Coast of the South Island, and the southern kōura, P. zealandicus, which occurs in the east and south of the South Island. Koura are a taonga species and an important traditional food source for Maori, particularly in the central North Island.
Kōura are an important component of freshwater ecosystems and a source of food for freshwater fish and humans. They are considered a keystone species in freshwater ecosystems and have various ecological functions, acting as shredders, detritivores and predators, which in turn influence other macroinvertebrate fauna. Furthermore, kōura increasingly feature as indicator species because of their important role in aquatic ecosystem food webs and their iconic and heritage values.
Kōura are one of the original inhabitants of Aotearoa. They have a very ancient lineage that diverged from their Australian relatives about 109 million to 160 million years ago. Because their entire life cycle requires freshwater, kōura are evidence that there has been continuous freshwater in Zealandia ever since our part of Gondwanaland broke up 60 million to 80 million years ago. As far as our evolutionary history goes, kōura are as significant as tuatara, wēta and kiwi.
Historically, kōura were an important food for Māori, particularly in the central North Island lakes where large numbers were harvested for consumption and trade. Today, kōura are considered a ‘taonga’ species and support important customary fisheries in some North Island lakes (e.g., Rotomā, Rotoiti, Tarawera and Taupō) where large populations are still present. Nevertheless, over the past century or so, kōura populations have declined due to habitat degradation, introductions of exotic fish and plant species as well as reduced concentrations of dissolved oxygen in the bottom waters of lakes due to eutrophication (nutrient enrichment).
Today, there is increasing interest in restoring lake, rivers and stream habitats with many restoration projects being carried out around New Zealand. However, factors other than habitat can reduce kōura numbers, and there is little guidance for conservation groups and local authorities on what practical steps are needed to restore kōura and increase stocks. This guide provides an overview of the steps involved in kōura restoration, along with a range of research-based information, tools and links.
NIWA contact: Dr John Quinn
External people involved: Dr Ian Kusabs - Fisheries Consultant Ngati Tuwharetoa, Te Arawa
How do we restore kōura?
There are three main steps to restoring kōura waterways.