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Invasive Species

Invasive freshwater species pose a significant threat to lakes and rivers. The early detection, control and eradication of invasive species is vital for maintaining water quality and protecting native biodiversity. New methods for the detection of introduced fish species such as brown bulhead catfish and common (koi) carp are currently being developed. Techniques for targeted control of European perch and common carp are also under evaluation.

Research is also being conducted into the spread and ecological impacts of non-indigenous invertebrates.



Invasive Fish

Over one-quarter of the freshwater fish species present in New Zealand have been introduced from overseas. Like all introduced species, they have some impact on native ecosystems, but some cause more problems than others. These invasive fish are most widespread and abundant in the northern half of the North Island where they can have a range of potential adverse effects on freshwater ecosystems. These effects are likely to become more significant and widespread in the face of human population growth and climate change which both have the potential to increase the distribution of these species.

Our research aims to:

  1. Understand the biology and abundance of invasive fish in New Zealand
  2. Quantify their ecological impacts on freshwater ecosystems, and
  3. Develop methods to assist with their control and monitoring.
  • Invasive species
  • Population estimates
  • Ecological effects
  • Control and monitoring methods
  • Management implications

Scent-detection of Pest Fish

LERNZ researchers Grant Tempero and Nick Ling are working with the University of Waikato Scent Detection Research Group to develop a low-cost, rapid screening tool for detecting invasive fish such as common (koi) carp and brown bullhead catfish. This MBIE funded Smart Idea will use an innovative scent-detection system, where water samples are brought into the scent-detection facility, and placed into automated equipment for assessment by detection-dogs under controlled conditions. Protocols employed here remedy common methodological issues in detection dog research, and this is a novel approach to a detection challenge in aquatic environments.

Invasive fish species such as koi carp pose a significant threat to New Zealand's freshwater ecosystems due to their destructive feeding behaviour, large size and ability to reach high densities. In shallow lakes, carp biomass can exceed 400 kg/ha with negative impacts occurring at biomasses above 50 kg/ha (biomass equivalent to 2.5 mg/L in a lake of average depth of 2 m). Currently, boat electrofishing, netting, and environmental DNA (eDNA) are used to survey for carp. These methods are expensive and often ineffective when fish are at low densities. While scent-detection dogs have been used in terrestrial settings for conservation and biosecurity programmes, their ability to detect aquatic invasive species has not been investigated.

PhD student Melissa Collins trained a single dog to use an automated carousel and assess water samples from aquaria containing either no fish (n = 3, negative), goldfish scent (n = 5, negative) or carp scent (n = 9, target). The goldfish samples and six of the target samples were presented to the dog at a standard biomass concentration of 15.5 mg/L. The remaining three target samples (probes) were systematically diluted to determine dogs’ detection thresholds. It was found that the dog could detect carp at a biomass concentration down to 0.46 mg/L (≈9.3 kg/ha) and could effectively discriminate between carp and goldfish samples. This research will produce a novel biosecurity detection system with greater sensitivity and lower costs than current methods. This will allow improved monitoring of freshwater systems, and confer direct benefits to ecosystem health, biodiversity, and biosecurity. This system is of stated interest to end-users such as regional councils. An additional advantage of this technology is its wide-spread applicability to other biosecurity and conservation problems.

Research lead: Nick Ling

Research lead: Grant Tempero

The scent detection of pest fish research programme trains pet dogs from the community to identify the presence of invasive fish  from water samples. The dogs are trained to operate an automated apparatus containing the water samples on a carousel. The dog places its nose in the porthole and sniffs the sample, if negative, the dog hits the lever on the side of the screen and the carousel rotates to present a new sample. If positive, the dog will hold it's nose in the port for 5 seconds and then be rewarded with food (off-screen), as demonstrated by dog in training Harlee.

The testing apparatuses used in this study, A; showing the initial apparatus with opaque plexiglass front panel showing porthole and omnidirectional switch, B; showing the second apparatus with transparent front panel, and C; showing sample segments.

Scent Detection of Invasive Fish

Watch a short video by primary investigator Clare Browne on the use of scent detection dogs in identifying invasive freshwater fish from water samples


Brown Bullhead Catfish in Te Arawa Lakes

Catfish are significant invaders that are widespread in the North Island of New Zealand (Invasive fish management handbook). The North American brown bullhead catfish (Ameiurus nebulosus) was introduced to NZ in 1877 and is recognised internationally as an invasive species. This catfish species is commonly 200–300 mm in length in New Zealand but can grow to 480 mm and more than 2 kg in weight (McDowall 1990). Catfish in NZ present potential adverse ecological impacts on lakes due to their benthic feeding, which can add to nutrients and sediment in the water column. They also prey on and compete with native freshwater crayfish (kōura, Paranephrops planifrons) and other fish (Francis 2019).

Catfish have most likely been in Lake Rotoiti for more than 20 years because in 1995 a juvenile catfish was observed to fall out of a hollow-framed boat trailer after a boat launching. This boat had been parked on its trailer overnight in Lake Taupo at Motuapa, where catfish are abundant, some hours before the boat was driven to and launched in Lake Rotoiti. There were no further confirmed sightings of catfish in Lake Rotoiti until January 2009 when a dead adult catfish 450-500 mm long was found on the shore (Blair and Hicks 2009). In March 2016, catfish were caught first by a weed harvester and then by fyke netting in Te Weta Bay, Lake Rotoiti (Hicks and Allan 2019).

Warm water temperatures in early summer 2017 probably allowed a rapid expansion of catfish abundance through a very successful breeding season (Below); Hicks and Allan 2019). One reason that catfish have high juvenile survival in suitable environmental conditions is that unusually in fish they exhibit parental care, in which parents guard small juveniles.The recruitment to the Lake Rotoiti catfish population from this breeding season was seen in the vast increase of young of the year (juveniles < 100 mm fork length) seen in late summer 2018, when 13,935 catfish were caught, compared with the same season in 2017, when similar netting effort caught only 2,889 catfish.

Temperature anomaly in Lake Rotoiti surface waters from July 2017 to January 2018 compared to the mean of data from 2005-2017. Source: unpublished lake buoy data, Chris McBride, The University of Waikato

Potential catfish habitat (red shading) in Lake Rotoiti. Source: Hamilton et al. (2005).

Research Lead: Brendan Hicks

Brown bullhead catfish, Ameiurus nebulosus. Fork length 415 mm, 1035 g. Photo: Brendan Hicks.

Adult catfish guarding a school of juvenile catfish. Photo H J Bannon.

Length frequencies of catfish (n catfish = 32,738) caught in Te Weta Bay between March 2016 and September 2018 by fyke netting (n net nights = 5,812). Relative frequency scales are normalised the modal length to 1. (Source: Francis 2019).


Invertebrate Invaders

LERNZ research also focuses on invertebrate biological invasions, particularly of zooplankton. Recently completed published work has included examinations of: 1) long-term zooplankton monitoring sampled from the Waikato lakes, which showed that the greatest changes to zooplankton communities through time have come about due to species invasions rather than water quality changes; 2) the effects of non-native willows on zooplankton in New Zealand wetlands, which seemingly had very little effect; 3) zooplankton communities in farm ponds, finding that these were relatively uninvaded by non-native species relative to urban waters, and; 4) the interactions between kākahi (freshwater mussels) and zooplankton, where the mussels were found to have greatest effects on smaller zooplankton species by filtration, but limited effects on larger species (including non-native Daphnia). Research is also conducted on the aquarium trade, recently recording a new parasite within New Zealand, associated with the snail Melanoides tuberculata.

Research lead: Ian Duggan

Parasite associated with the snail Melanoides tuberculata.