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eDNA testing, which is being done in streams and rivers in the Matakana area, is showing mixed results. On the positive side, testing shows that several nationally vulnerable, threatened or at risk species are present in the waterways.
These include four out of the five adult whitebait species – inanga, giant kokopu, shortjaw kokopu and banded kokopu – along with long fin tuna (eel), common, giant and red fin bullies, koura (freshwater crayfish), kākahi (freshwater mussels) and Hochstetter’s frog.
However, biodiversity indicators also show that three sites only have an ‘average’ score, with the lower Matakana scoring ‘poorly’.
A biodiversity indicator is a measurement of the range and proliferation of different native flora and fauna. This means that finding only water fleas, sandfly larvae and tuna shows poor diversity. If mayfly larvae, kākahi, shrimps, caddisflies, dragonfly larvae, snails, pond skaters, bullies, tuna, koura and inanga are present, then the biodiversity score is much higher.
The testing is being carried out by Friends of Awa Matakanakana Catchment Inc (FOAM), a small community group that is monitoring and restoring the Matakana and the Glen Eden catchments, two of the largest rivers in Rodney.
Earlier this year, FOAM teamed up with The Forest Bridge Trust and Ngāti Manuhiri to apply to Wai Tuwhera o te Taiao, Open Waters Aotearoa programme for environmental DNA (eDNA) kits to help identify the range of life in our rivers. They received kits to sample the freshwater near the top and bottom of each river.
eDNA describes the tiny traces of genetic material left behind by living things that pass through soil or water (source: EPA). Unique traces of DNA are shed from skin, scales, feathers, plant pieces, seeds, and poop when a fish, mollusc, mammal, plant or macroinvertebrate lands or passes through the water.
Water samples were collected using special kits that filter and trap the biological matter. DNA collected was extracted in a specialist laboratory to identify the molecules, which then revealed which species were present.
DNA bar codes, known as sequences, have been collated on a national database for reference.
This database is extensive, but not yet exhaustive. For instance, at one of our sites on the Glen Eden, FOAM found freshwater shrimps when searching for macroinvertebrates. The species were not on the database at the time, but they are now.
A wonderful advantage of gathering data this way is that it is a non-invasive way to identify the biodiversity of a waterway with no stress caused to the creatures living in and around the water. Long term, if restoration of a stream is in progress, re-sampling can rapidly show the effectiveness of changes to the native flora and fauna.
The results also revealed the presence of rats, so despite a large commitment to trapping across the region there is a way to go to reach pest-free 2050.
Most of the native fish species listed above have survived in the catchment, but with the threatened habitat and declining water quality, there is a high risk that we will lose these species. For example, kākahi are extremely sensitive to sediment, suffocating as the levels rise. FOAM has measured exceptionally high sediment loads in the Matakana. In addition, many of the native fish have a life cycle that requires travel between salt and fresh water. Poorly designed culverts and dams prevent them from travelling back upstream when they return from the sea, affecting population numbers.
Restoring our freshwater streams and their terrestrial surroundings back to healthy ecosystems is not only good for the fish and the birds, it is significantly healthier for us all. One day, it would be amazing to have eDNA results that reflect this goal.
If you would like to volunteer to do some monitoring, are a landowner on one of the rivers seeking support, would like to help or are just interested in the work we do, please contact us on matakanakana2@gmail.com
by Lyn Hamilton-Hunter
