Evaluation of koi carp as a fertiliser for establishing native sand binders on coastal dunes in the Waikato region – first year trials

TR 2016/28
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Report: TR 2016/28

Author: David Bergin & Michael Bergin (Environmental Restoration Ltd)

About this report

Exotic koi carp (Cyprinus carpio) have become a major pest in freshwater systems of the lower Waikato since introduction. They contribute to poor water quality destroying native plant and fish habitat. Waikato Regional Council have been trapping large numbers of carp and "digesting" them into a nutrient-rich dry powdery substance that has potential uses in environmental restoration including as a fertiliser in Beachcare planting projects.

Beachcare groups in the Waikato region are involved in planting tens of thousands of the native sand binding species spinifex (Spinifex sericeus) and pingao (Ficinia spiralis) on foredunes. Planting trials were established at three Waikato beaches comparing application of koi carp fertiliser in the form of pellets with the current standard practice of NPK slow-release fertiliser tablets.

Based on growth performance up to 8 months after planting, results indicate that koi carp fertiliser gives a similar boost to growth of sand binders as the commonly used slow-release fertiliser tablets. The substantial boost in growth by koi carp compared to non-fertilised plants is consistent with previous research. There was only a small increase in growth performance for spinifex with higher rates of fertiliser and there may be a small difference in the slow-release effect between koi carp and tablet fertiliser. A second series of planting trials is recommended to confirm and refine results.

These results have implications for two streams of Waikato Regional Council activities; the Beachcare Programme and the koi carp capture and digestion experiment. Koi carp fertilizer could eventually replace standard fertilizers in the Beachcare planting projects.

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Evaluation of koi carp as a fertiliser for establishing native sand binders on coastal dunes in the Waikato region – first year trials [PDF, 2.8 MB]