Legal status of Rudd, Catfish, Goldfish – fact sheet

New Zealand has a total of about 36 native freshwater fish species, and a further 22 species (equivalent to 38% of all freshwater fish species) have been introduced from overseas. Like all introduced species, they have some impact on New Zealand's native ecosystems, but some cause more problems than others

The contribution of lakes to greenhouse gas emissions – fact sheet

Greenhouse gases such as carbon dioxide (C0₂) , methane (CH₄) and nitrous oxide (N₂0) trap heat in the atmosphere. Lakes can play an important role in regulating these gases at global scales. Total carbon uptake by lakes is of the same magnitude as that of oceans or forests, despite lakes occupying <1% of the Earth's area. In lakes, GHGs are mostly produced in the bottom sediment as products of organic matter decomposition. Geothermal activities - of importance to some Rotorua lakes - may also contribute substantial amounts of C0₂ and CH₄

Invasive fish and nutrients – fact sheet

Invasive fish such as koi (or common) carp (Cyprinus carpio) are large fish as adults (typically 1-3 kg) and can exist at high biomass (commonly 1000-2000 kg/ha). Because of their large size, high biomass, and suctorial feeding behaviour that disturbs the lake bed, koi carp have the potential to contribute a significant amount of plant nutrients (nitrogen (N) and phosphorus (P)) to lake waters. To estimate the potential of koi carp to inhibit lake restoration, we estimated the rates of excretion relative to other processes contributing nutrients to lakes

Exclusion and removal of pest fish from Lake Ohinewai – fact sheet

Many of the shallow lakes in the lower Waikato River floodplain have significantly degraded water quality as a result of nutrient and sediment enrichment from non-point sources. Pest fish species such as koi carp, goldfish, and catfish have exacerbated lake decline by resuspending lake sediments and uprooting submerged macrophytes. This this resulted in a collapse of submerged macrophytes and progression from clear-water oligotrophic state to a eutrophic (algal-dominated) state

Flocculation and sediment capping – fact sheet

Sediment capping and flocculation are in-lake techniques designed to reduce internal nutrient loads from the bottom sediments of lakes. These loads are roughly equivalent in magnitude to external loads. Case studies of the Rotorua lakes (Figure 1) show that with careful design and management, sediment capping and flocculation can reduce nutrient concentrations and the likelihood of algal blooms. Relevant actions can include: (i) reducing bioavailable phosphorus in stream inflows through continuous addition of the active material to the stream, (ii) removing bioavailable phosphorus, and flocculation and sedimentation of nutrients, and (iii) altering sediment composition so that nutrients are more efficiently retained within the bottom sediment

Pest fish detection using environmental DNA – fact sheet

Molecular tools using DNA sequencing can improve pest fish management by ensuring accurate identification of fish, especially larval fish, without the need for specialist taxonomic knowledge. DNA is made of four chemicals; guanine (G), adenine (A), thymine (T), or cytosine (C), joined together as a string (Figure 1). The order of the chemicals is unique to each species and can be used as a DNA "barcode" to identify organisms. It is relatively simple to obtain DNA sequences for a reference gene such as the widely accepted "barcode gene" cytochrome C oxidase subunit 1, and compare the sequence to a voucher specimen sequence in genetic databases such as GenBank and the Barcode of Life database BOLD

Applying citizen science to freshwater ecosystem restoration – fact sheet

Citizen science describes the diverse ways in which the public participates in scientific investigations. Participation covers a spectrum from sending observations to a project coordinator to designing, implementing protocols, analysing and sharing findings. The popularity of citizen science both for educational and scientific purposes has grown in recent decades. Community volunteers now participate in diverse programmes that investigate the effects of climate change on biota, evolutionary processes, invasive species ecology, and changes in water and air quality (Figure 1)