Freshwater Crayfish (Kōura)

Freshwater Crayfish (Kōura)
Exploring the ecology and conservation of New Zealand's native freshwater crustaceans
Native Freshwater Crustaceans of Aotearoa
Freshwater crayfish, known in Aotearoa New Zealand as kōura (Paranephrops planifrons in the North Island and Paranephrops zealandicus in the South Island), are native freshwater crustaceans that typically grow between 60 and 120 millimetres in length.
They have hard, jointed exoskeletons, long antennae, and strong front claws used for feeding and defence. Their colour varies from dark green and brown to bluish tones, allowing them to blend into streambeds and lake margins.
Habitat and Behaviour
Kōura are found in rivers, streams, lakes, wetlands, and farm dams throughout much of New Zealand. They prefer cool, clean freshwater environments with plenty of shelter such as rocks, submerged logs, macrophytes, and undercut banks.
Nocturnal Activity
Kōura are most active at night
Daytime Shelter
Spend the day hiding in burrows or beneath debris to avoid predators
Life Cycle and Development
The life cycle of Paranephrops species begins when females carry fertilised eggs beneath their tails through winter. In spring, the eggs hatch into tiny juvenile crayfish that remain attached to the female for several days before becoming independent.
Juveniles grow by moulting their exoskeleton multiple times as they increase in size. Growth is slow, and kōura may take several years to reach maturity.
Morphology and Feeding Adaptations
Morphologically, kōura are well adapted to benthic life. Their strong claws allow them to tear apart food and defend territory, while their fan-shaped tail enables rapid backward escape when threatened.
Omnivorous Diet
They are omnivorous scavengers, feeding on aquatic plants, algae, insects, worms, dead fish, and organic detritus. This flexible diet allows them to survive in a wide range of freshwater habitats.
Ecological Importance
Ecologically, kōura play a vital role in freshwater ecosystems. As both predators and scavengers, they help recycle nutrients by breaking down organic matter and controlling invertebrate populations.
Food Web Connections
They are also an important food source for native fish such as eels, kōkopu, and trout, linking different levels of the freshwater food web.
Sediment Health
Their burrowing behaviour helps oxygenate sediments and redistribute nutrients.
Threats to Kōura Populations
Despite their ecological importance, kōura populations are declining in many areas. Habitat degradation from sedimentation, pollution, river modification, and wetland drainage reduces the availability of clean, sheltered environments they depend on.
Introduced Species
Introduced species such as trout, perch, and catfish prey on kōura and compete for food.
Overharvesting
Overharvesting and illegal collection have also contributed to local population declines.
Climate Change and Water Quality
Climate change poses additional risks by increasing water temperatures and altering flow regimes, which can reduce oxygen levels and disrupt breeding cycles.
Agricultural runoff containing nutrients and chemicals further degrades water quality, making habitats unsuitable for kōura survival.
Conservation and Future Protection
In conclusion, kōura (Paranephrops spp.) are a keystone species in New Zealand's freshwater ecosystems. Their role in nutrient cycling, food webs, and sediment health highlights their ecological importance.
Protecting water quality, restoring habitats, and managing invasive species are essential to ensure the long-term survival of New Zealand's native freshwater crayfish.