There are two species of kōura or freshwater crayfish in Aotearoa.
Common name: Freshwater crayfish
Scientific names: Paranephrops planifrons and Paranephrops zealandicus
Māori names: includes kōura and kēwai
About this species
There are two species of kōura in New Zealand, both belonging to the family Parastacidae. Paranephrops planifrons is found in the North Island and in the northwest of the South Island and Paranephrops zealandicus is distributed along the eastern side of the South island and on Stewart Island. P. planifrons is separated from P. zealandicus by the Southern Alps.
Kōura are a valued mahinga kai species and considered a delicacy by Māori. In the past they were a staple food item, and prized in some areas for their use as a bartering tool. The Te Arawa and Taupō lakes were considered the most productive kōura fisheries in New Zealand. In the past, the kōura fishery was actively managed by a combination of rāhui (where all fishing was halted in a particular area for a specified period of time, or where limits were placed on the use of particular methods) and ownership rights (based on ancestral fishing grounds). Occasional releases of kōura were made into waterways to boost populations and selective harvesting (e.g., return of gravid females to the lake) ensured the long term viability of the populations.
Impacts on kōura
Catchment land use
Kōura are found in native forest, exotic forest, and pastoral waterways, but very rarely in urban streams because of chemical pollution, increased flood flows from stormwater inputs, and degradation of habitat. Kōura densities can be lower in pasture streams compared to native forest streams. Kōura tend to live longer in native forest streams because of cooler water, but grow faster in pasture streams with warmer water temperatures and more abundant invertebrate food.
Kōura survival can be affected by high water temperatures, particularly for the southern species, P. zealandicus, where survival in laboratory experiments decreased as constant water temperatures exceeded 16ºC, with 50% survival at 21ºC after 12 weeks. The northern species, P. planifrons, can tolerate higher temperatures, but optimum temperatures are likely to be less than 23ºC. Kōura are rare in low calcium waters such as Lake Tikitapu, and kōura (P. zealandicus) survival in laboratory tests increased with water calcium concentrations above 10 mg/L. Kōura in lakes can be affected by periods of anoxia, e.g., they are now absent from Lake Okaro as this lake has no oxygen in its bottom waters during summer. Kōura may also be affected by pollutants such as heavy metals or by toxins from cyanobacterial blooms.
Habitat cover (e.g., large wood, undercut banks, cobbles, and boulders) is extremely important as it provides shelter from predation and cannibalism. Kōura prefer pools and areas of slow or no flow. Deep habitat (pools in streams) may act as a refuge from terrestrial predators and collect leaves and other foods. At times of heavy flooding, forested streams with stable habitat from riparian vegetation (e.g., stable banks, tree roots, and pools) provide a better refuge for kōura populations than pasture streams dominated by unstable cover items such as cobbles and macrophytes.
Crayfish are vulnerable to predation from introduced species that they have not evolved with (e.g., trout, catfish, and perch). Kōura make up a large proportion of catfish diet in Lake Taupō (up to 80% in some areas). Anecdotally, the introduction of perch to a Northland lake has dramatically decreased crayfish populations. In some South Island streams, brown trout were the main factor affecting kōura abundance, particularly for kōura sized 7-20 mm.
References and further reading
Kōura, freshwater crayfish
- Allibone, R., Horrox, J., Parkyn, S. 2001. Stream classification and instream objectives for Auckland’s urban streams. NIWA Client Report ARC00257.
- Barnes, G. E. 1996. The biology and general ecology of the brown bullhead catfish (Ameiurus nebulosus) in Lake Taupo. Unpubl. MSc thesis, University of Waikato.
- Brown, L. A. 2009. Habitat determinants and predatory interactions of the endemic freshwater crayfish (Koura, Paranephrops planifrons) in the Lower North Island, New Zealand. Palmerston North, Massey University. Masters of Science in Ecology. 76 p.
- Hicks, B. J., McCaughan, H. C. 1997. Land use, associated eel production, and abundance of fish and crayfish in streams in Waikato, New Zealand. New Zealand Journal of Marine and Freshwater Research 31(5): 635-650.
- Hammond K. S., Hollows, J. W., Townsend, C. R., Lokman, P. M. 2006. Effects of temperature and water calcium concentration on growth, survival and moulting of freshwater crayfish, Paranephrops zealandicus. Aquaculture 251(2-4): 271-279
- Hopkins, C. L. 1967. Breeding in the freshwater crayfish Paranephrops planifrons White. New Zealand Journal of Marine and Freshwater Research 1: 51-58.
- Jowett, I., Parkyn, S. M., Richardson, J. 2008. Habitat characteristics of crayfish (Paranephrops planifrons) in New Zealand streams using generalised additive models (GAMs). Hydrobiologia.
- Landman, M. J., Van Den Heuvel, M. R., Ling, N. 2005. Relative sensitivities of common freshwater fish and invertebrates to acute hypoxia. New Zealand Journal of Marine and Freshwater Research 39(5): 1061-1067.
- Nisikawa, U., Townsend, C. R. 2000. Distribution of the New Zealand crayfish Paranephrops zealandicus in relation to stream physico-chemistry, predatory fish, and invertebrate prey. New Zealand Journal of Marine and Freshwater Research 34: 557-567.
- Olsson, K. 2003. The influence of introduced brown trout (Salmo trutta) on the distribution and abundance of native crayfish (Paranephrops planifrons) and galaxiids (Galaxias spp.) in New Zealand streams. Honours thesis in Environmental science, Department of Ecology, Limnology, Lund University, Sweden.
- Parkyn, S. M., Collier, K. J., Hicks, B. J. 2002. Growth and population dynamics of crayfish Paranephrops planifrons in streams within native forest and pastoral land uses. New Zealand Journal of Marine and Freshwater Research 36: 847-861.
- Parkyn, S. M., Collier, K. J. 2004. Interaction of press and pulse disturbance on crayfish populations: flood impacts in pasture and forest streams. Hydrobiolgia 527: 113-124.
- Parkyn, S., Kusabs, I. 2007. Taonga and mahinga kai species of the Te Arawa lakes: a review of current knowledge – koura. NIWA Client Report HAM2007-022.
- Shave, C. R., Townsend, C. R., Crowl, T. A. 1994. Anti-predator behaviours of a freshwater crayfish (Paranephrops zealandicus) to a native and an introduced predator. New Zealand Journal of Ecology 18(1): 1-10.
- Whitmore, N., Huryn, A. D., Arbuckle, C. J., Jansma, F. 2000. Ecology and distribution of the freshwater crayfish Paranephrops zealandicus in Otago Implications for conservation. Science for Conservation 148. 42 p.