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Status of our freshwater species

New Zealand has a diverse range of native freshwater plants, fish, and invertebrates, many of which are endemic (found nowhere else in the world), while some have very localised distributions.

Our freshwater environment supports approximately 53 known resident native freshwater fish species (Goodman et al, 2014), and 630 known native freshwater invertebrate taxa (Grainger et al, 2014), and 559 freshwater-dependant plant and algae taxa (Gerbeaux et al, 2016).

More than half our known fish species migrate between the sea and fresh water to complete their life cycles, meaning they can be severely affected by barriers to migration in rivers and streams (McDowall, 2010). In addition, 21 freshwater fish species, including trout and salmon, have become naturalised after being deliberately or accidently introduced to New Zealand through human activities (Collier & Grainger, 2015).

Many New Zealand bird species live around our wetlands, rivers, and lakes, including threatened iconic and taonga species – kāki (black stilt), whio (blue duck), and the kōtuku (white heron). Other native animals live in, or depend on, our freshwater ecosystems, such as the at-risk Hochstetters frog. Wetland and riparian environments are also home to a range of native plants – these include taonga species which Māori use in rongoa (medicine), raranga/ahatu (weaving), and mahinga kai.

This section focuses on information we have on our freshwater fish, invertebrates, plants, and algae.

Six of the 11 freshwater species for which we have data have declined in abundance over the past 39 years

The presence of a fish species at a site can be affected by changes in catchment land cover, land use, in-stream habitat, fish passage (routes for moving up and down rivers and streams), pests, and contaminants.

National-scale information on the abundance, distribution, and trends in freshwater fish is currently limited. To overcome this limitation, trends in abundance of freshwater fish were analysed using data from the New Zealand Freshwater Fish Database (NZFFD). However, anyone can enter information in the NZFFD (ie there are no set sites or methods used for capturing fish), which means there are sampling differences across sites and time.

To reduce the impact of sampling differences on the trends in the abundance of fish species over time, NZFFD data was standardised using generalised linear models to take into account the different number of samples between years and the differences in sampling (Crow et al, 2016). These models estimate the probability that a species will be present for each year of the 1977–2015 period.

There were enough data to assess trends in abundance for 10 fish species and for kōura (freshwater crayfish). Of the 11 freshwater species, trends for six species were declining and two were improving, over 39 years from 1977 to 2015 (Crow et al, 2016). The six fish species that had declining trends were four native species (longfin eel, kōaro (a whitebait species), Canterbury galaxias, and common bully) and two exotic species (rainbow trout and brown trout). Two species had improving trends over the 39 years (upland bully and shortfin eel). For the other three species (redfin bully, torrentfish, and kōura), the trend was indeterminate, meaning there are insufficient data to determine a trend. For each of the eight species where a trend could be determined, the trends were improving or declining less than 0.5 percent a year.

For more detail see Environmental indicators Te taiao AotearoaTrends in freshwater fish [Stats NZ].

Many freshwater species are under threat

Conservation status refers to the threat classification of resident native freshwater plants, fish, and invertebrate taxa. The Department of Conservation (DOC) developed the New Zealand Threat Classification System to provide a national system similar to the International Union for Conservation of Nature and Natural Resources Red List (see Appendix: New Zealand Threat Classification System for a description of the threat classification categories).

Experts assign a threat of extinction status through a DOC-led process, based on criteria of abundance, distribution, and trends. The criteria are used to monitor the status of individual species and report on the state of native biodiversity (Townsend et al, 2008). We looked at the conservation status of freshwater plants and animals for which we had sufficient information on taxonomy, distribution, and abundance (ie plants and animals that were taxonomically indeterminate and data deficient were excluded from this analysis). This means we only report on 39 of 53 fish species (39 excludes one extinct species), 435 of 630 invertebrate taxa, and 537 of 559 freshwater-dependent plant and algae taxa (537 excludes one extinct plant).

Around three-quarters of our known native freshwater fish are threatened with, or at risk of, extinction

We have one known extinct freshwater fish, the once widespread and common New Zealand grayling. Of New Zealand’s remaining 39 known native freshwater fish species, 72 percent were either threatened with extinction (12 species) or at risk of extinction (16 species) in 2013 (Goodman et al, 2014; see figure 26 and Appendix: New Zealand Threat Classification System). Native freshwater fish species listed as threatened with, or at risk of, extinction include taonga species – such as īnanga, shortjaw kōkopu, giant kōkopu, kōaro (all are whitebait species), kanakana/piharau (lamprey), and tuna (longfin eel). Most at risk or threatened freshwater fish are at risk of a ‘high ongoing decline’ or a ‘predicted decline’ in population size (see Human activities are degrading some ecosystems for more information on the pressures on our freshwater species).

Figure 26

the conservation status of freshwater fish and invertebrates in 2013
Click to enlarge view

This graph shows the conservation status of freshwater fish and invertebrates in 2013. Visit the MfE data service for the full breakdown of the data.

Of the 12 freshwater fish species listed as threatened, two (Otago longjaw galaxias and Canterbury mudfish) are in the highest threat category (nationally critical), meaning they are at a high risk of extinction. Both species are considered likely to become extinct if current conservation management ceases (Goodman et al, 2014).

No improvements in conservation status for native freshwater fish occurred for species that can be directly compared between the two assessment periods (2009 and 2013). Declines in conservation status were observed for four species – Central Otago roundhead galaxias, Canterbury galaxias, black mudfish, and lamprey (kanakana/piharau), an important taonga species (see The conservation status of lamprey (kanakana/piharau); Goodman et al 2014).

The conservation status of lamprey (kanakana/piharau)

The lamprey (kanakana/piharau) is a unique freshwater fish species. Like the tuatara, it is often described as a living fossil that has remained unchanged for hundreds of millions of years. It is a jawless fish, with a distinctive sucking disk mouth. The lamprey migrates into rivers to spawn, and the juvenile lamprey spends four years in rivers and streams before migrating out to sea. The lamprey is a taonga, and is a traditionally important mahinga kai species. It is threatened with extinction (Goodman et al, 2014).

The conservation status of lamprey

Source: Robert Holdaway

For more detail see Environmental indicators Te taiao AotearoaConservation status of freshwater fish and invertebrates [Stats NZ].

About one-third of our known native freshwater invertebrates are threatened with, or at risk of, extinction

Freshwater invertebrates include many organisms such as crustaceans, molluscs, worms, and freshwater insects. In 2013, 34 percent of our known native freshwater invertebrates were threatened with extinction (66 species of 435) or at risk of extinction (82 species) (Grainger et al, 2014; see figure 26). The South Island kōura (freshwater crayfish) and all three species of freshwater mussel (kākahi/kāeo) are included in the at risk or threatened categories.

Forty-two invertebrates (10 percent) are in the highest threat category (nationally critical).

Of the invertebrates that can be directly compared between assessment periods (2005–13), three invertebrates had a decline in conservation status.

For more detail see Environmental indicators Te taiao AotearoaConservation status of freshwater fish and invertebrates [Stats NZ].

Almost one-third of our known native freshwater-dependent plants are threatened with, or at risk of, extinction

Freshwater-dependent plants include vascular plants, mosses, hornworts and liverworts, and green algae that live in and round freshwater. We have one known extinct plant,Stellaria elatinoides, thought to have been naturally uncommon and succumbed to over-collection and weed competition in its tussock and lake margin habitats (Norton et al, 1997). Of the remaining 537 plant taxa, 71 plant taxa (13 percent) are threatened with extinction, of which there are 34 plant taxa in the highest category, threatened – nationally critical (Gerbeaux et al, 2016). A further 97 plant taxa (18 percent) are at risk of extinction. None of the common weaving plants (eg kiekie, pingao, raupo) are threatened with, or at risk of, extinction.

Our knowledge of our native freshwater biodiversity is limited

An additional 14 fish, 197 invertebrates, and 22 freshwater-dependant plants do not have generally accepted or formalised taxonomy, or we lack sufficient information on their distribution and abundance to assign a conservation threat classification. This means the current number of species threatened with, or at risk of, extinction may be under-reported.

Biodiversity loss has wider ecosystem impacts

Declining ecosystem health and the resulting degradation and loss of habitat of some freshwater bodies are affecting New Zealand’s freshwater biodiversity. Our freshwater algae, plants, fish, and invertebrates interact resulting in complex ecosystems. Invertebrates perform important ecosystem services such as grazing on periphyton (algae) and breaking down leaves and wood (Mcintosh, 2000). They also provide food for our native fish and birds and some provide food to humans (eg kōura (freshwater crayfish) and kākahi (freshwater mussel)). Changes to invertebrate communities through habitat loss (eg when sediment clogs spaces between pebbles) can affect the ability of our native fish to feed, and the availability of freshwater resources for food, and recreational and customary uses.

The loss or decline of a single species can have detrimental effects on other species and the wider ecosystem. For example, a decline in numbers of the at-risk kōaro may also negatively affect the at-risk kākahi (freshwater mussel), which use the kōaro as a host during the parasitic larval stage of their life cycle (Phillips et al, 2007). In turn, a decline in kākahi numbers could potentially result in less nutrients and sediment being filtered from the water, which in turn may alter the water quality and habitat for other freshwater species.