The Waikato River and its catchment area is a place of life – a wide biodiversity of plants and animals. The river, the surrounding land and the connected tributaries, wetlands and lakes and the animals and plants in them are inextricably linked. Pressures on the environment affect the species that interact with it.
Biodiversity from a historical cultural perspective
Historical biodiversity in and around the lower region of the Waikato River is disclosed by accounts from iwi who live there. A few generations ago, the river ran clear and provided an abundance of food (mahinga kai) for Māori. Tuna (eels), īnanga (whitebait), pōrohe (smelt), kōura (freshwater crayfish), kaeo/kākahi (freshwater mussels), kanae (mullet), waterfowl and wild vegetables (such as watercress and pūhā) were harvested from the river and its associated wetlands and lakes. For Māori, it is important to supply visitors with a variety of kai from the river (this concept is called manaaki tangata). Tuna, in particular, is king among the kai, and to a large extent, the mana of Māori is reliant on the ability to provide such kai. Today, Māori are unable to use the river in such a way any more. Mahinga kai has either vanished or is not fit to eat.
The ecology of the river now
The Waikato River currently supports 19 species of native fish and 13 species of introduced fish. These occur in different sections of the river and in different combinations. Our focus is on the section of the river north of Karāpiro and out to the river mouth.
The river just north of Karāpiro is characterised by a deep main channel with some gently sloping shelves and beaches. The riparian fringe of mainly willow trees limits aquatic growth to where sunlight can penetrate. This limits habitat for the growth of invertebrates and as a cover for fish. Human population pressures have led to a degradation of tributaries in and around urban areas. Gully networks in Hamilton, however, do provide good riparian cover in many places, and the threatened giant kōkopu and longfin eel are still found there. Urban development increases the amount of stormwater issuing into the river. Several discharges from sewage treatment plants and industry occur along this section.
Contributing waters from the Waipā River are highly turbid (from land use activities). Turbid water limits upstream migration of some galaxiid fish such as the banded kōkopu – the juveniles avoid highly turbid water as they swim upstream searching for habitat in small forested streams (such as at Mt Pirongia). Fish access to and from the river is limited by poorly designed road culverts leading to tributaries.
Prior to drainage and flood protection development, the low-lying plains adjacent to the river north of Huntly flooded frequently, causing flows into lakes (such as Waikare and Whangape) and wetlands (such as Whangamarino and Opuatia). This provided a buffer during peak flows in the river. Flood control measures restrict the natural flow of water across these areas. The threatened black mudfish is present in the wetlands, but the habitat area has declined due to drainage activities. The floodplain originally provided eel-feeding habitat during periods of flooding.
These lower areas are heavily colonised by exotic fish, such as gambusia, catfish and koi carp. Koi dominate the biomass. Downstream of Huntly, invertebrate communities are dominated by the freshwater shrimp (Paratya curvirostris). Mysid shrimp, once common, are low in numbers.
The influence of tidal water levels in the river reach as far upstream as Rangiriri, but saltwater intrudes only as far as Glenbrook. Several fish species that mainly live in saltwater are found in this area, such as the black flounder. Īnanga (the main whitebait species) spawn in this section, and the young hatch in spring to join the other whitebait species (banded kōkopu, shortjaw kōkopu, giant kōkopu and kōaro) moving upstream. Floodgates and grazing of riverside vegetation limit īnanga spawning habitat.
Scientists can assess the ecological health of the river catchment by using the Macroinvertebrate Community Index (MCI). The MCI reflects invertebrates’ sensitivity to pollution.
Data from 2006 from monitoring over an 8-year period suggested that most catchment areas had stable MCI values. Overall, declines were greater in small lowland streams with highly developed catchments.
Fish presence can also be used to assess ecological health using the predictive Fish Index of Biotic Integrity. Results from 2007 indicated that 75% of tributaries were in poor condition, 21% were in moderate condition and 4% were in excellent condition.
Historical data also indicates declining whitebait and eel catches. Land clearance and wetland drainage have markedly reduced the distribution of species with specialised habitat requirements. The decline in native species is also the decline of mahinga kai for Māori.
Since the Waikato-Tainui River Settlement in 2008, the management of the river has been shared by iwi, councils and government agencies. Each has different roles, responsibilities and priorities, and they are all working together for the restoration, health and wellbeing of the Waikato River.
Nature of science
Science knowledge is produced within a society and culture. For example, scientists are increasingly investigating issues of concern in their environment such as pressures on the environment that affect the ecology and health of the river. Research projects such as whitebaiting, koi carp entrapment and glass eel observation have developed from such investigations.
Read about the Macroinvertebrate Community Index and its use.
Read this report to get an understanding of the Fish Index of Biotic Integrity. This index was developed for the Waikato region.