OPINION: How multi-trophic aquaculture (IMTA) could transform a major NZ primary industry

By Dr Leo Zamora, Cawthron Institute

Momentum is building behind calls for multi-trophic practices to be embraced by New Zealand’s aquaculture industry. Multi-trophic practices is an overarching term used to describe an approach to marine farming and aquaculture that incorporates multiple species of marine animals and plants rather than focusing on a single species. A number of other terms are used to describe these practices, including integrated multi-trophic aquaculture (IMTA), co-culture, polyculture, polyfarming, ecological intensification and aquaponics.

A recent scientific review by NIWA, Tisbe Ltd. and Cawthron Institute highlighted the potential of IMTA for New Zealand’s aquaculture industry. It summarised research findings and outlined opportunities for such practices to promote the sustainable growth of the industry as well as the constraints preventing their uptake at commercial scale. 

A critical step to overcoming the technical, regulatory and economic hurdles facing adoption of IMTA practices in New Zealand is continued investment in research that supports industry innovation. Why is this research a good investment for the aquaculture industry? Below I have outlined five reasons why IMTA is an attractive opportunity:

1)     IMTA could increase returns and provide diversification on existing farming space to reduce risk

There are an array of native species in New Zealand with commercial potential, be it for direct consumption or as a source of high-value bioactives. Species that could be included in IMTA systems must be compatible species that do not compete for resources (i.e. space or food). Species that could be considered include seaweeds, shellfish such as scallops and geoducks, and deposit-feeders like sea cucumbers. Diversification to farm complementary species enables farmers to reduce their business risk profile by expanding their product portfolio should product demand change.

2)     IMTA’s inherent flexibility allows for implementation in coastal, land-based, and open-ocean farming systems

The growth of the aquaculture sector will depend in part on the development of both land-based and open ocean farming. Land-based operations have optimal control and understanding of nutrient flow, and therefore the efficiency of IMTA practices can be better harnessed when compared to coastal operations. In the open ocean environment, IMTA practices could maximise space and resources when farming species that can thrive in high energy farming sites. For example, seaweed could be used to dampen wave energy and assist the farming of shellfish.

3)     There is no need to add extra food into IMTA farming systems because they rely on natural nutrient flow cycles in the water column and the seafloor

By selecting compatible species from different trophic levels (i.e. using different food sources), nutrients can circulate from one species to the next with most of the system being supported by primary producers like phytoplankton and seaweeds. When finfish like salmon are part of the operation, there is no need for the addition of extra food if a lower trophic compatible species is selected.

4)     IMTA systems can help reduce environmental impacts

By maximising nutrient utilisation in IMTA systems, the overall environmental footprint of the operation is reduced. Moreover, depending on the spatial scale that you are working on, there is no need for the species to be in direct contact, enabling large-scale (i.e. regional level) ecosystem-based management principles. By selecting the appropriate complementary extractive species (e.g. seaweeds, sea cucumbers) with a well-defined ecosystem function, their farming can provide further environmental services.

5)     IMTA systems align well with Māori principles for the management of natural resources

IMTA practices can clearly benefit from indigenous knowledge (mātauranga Māori) for the consideration and selection of complementary species in a particular area. An IMTA approach aligns with kaitiakitanga principles and practices more so than the traditional single species approach to aquaculture. Done correctly, IMTA can enable environmentally sustainable economic opportunities for iwi to be realised and our aspirations for a blue economy sector.

In summary, because IMTA systems are inherently flexible and more efficient in their use of natural resources, their widespread adoption in New Zealand could offer wide-ranging economic, environmental and cultural benefits.

With the Government setting an aquaculture industry revenue target of $3bn by 2035, Cawthron’s intent is for our IMTA/coculture research findings to support the diversification of farmed species to create new opportunities and maximise returns on existing operations.