Water Sampling

What lives in Cannons Creek?

There are three kinds of fish, longfin eels, and freshwater crayfish, along with a wide variety of plants, insects and bacteria in Cannons Creek.    But there are no signs of possums, rats, cats or rabbits, giving us hope that years of pest control has reduced the numbers of these predators.

This is a short summary of the findings from an eDNA sample taken earlier this year.   To see the full results, go to www.wilderlab.co.nz/explore and search for sample 522958 which will extract the Cannons Creek sample from the many others that have been taken around New Zealand.    It will bring up pictures of the main findings, which you can click through to Wikipedia for further explanation. 

The sampling site, seen from the bridge across Cannons Creek on the Takapu Track. Photos: Janet Tyson.

The free eDNA water sampling kit is offered by Open Waters Aotearoa (Wai Tuwhera o te Taiao), which will be offering another round of sampling kits in August (eDNA@epa.govt.nz).   This is an initiative by the Environmental Protection Authority to encourage people to learn what is living in the waterways around them. 

The incredibly powerful eDNA technology has been used for many purposes, perhaps the most well known being to find traces of Covid in waste-water samples.   Different assays can be used to look for different things, and the sampling kits on offer can give a comprehensive list of everything living that has been in a particular waterway, from large animals like pigs and deer down to insects, plants and bacteria.

For our first survey, we chose the section of Cannons Creek above the bridge that crosses the Takapu Track, closed off since construction began on Transmission Gully.  Our aim was to look for traces of possums and rats, to see how effective our 20 plus years of pest control has been.

The sample kit included a large syringe with a filter at one end.  Our instructions were to draw up water from the creek to fill the syringe, then squeeze it out again through the filter.  This had to be done 20 times, or until the filter was completely clogged with material.

Drawing up water into the syringe (above) then straining it out through the filter (at right).  This should be done 20 times or until the filter is full.

Drawing up water into the syringe (above) then straining it out through the filter (at right).  This should be done 20 times or until the filter is full.

Then it was a matter of capping off the filter, filling in identification and chain of custody details, and sending it to Wilderlab in Miramar for analysis.

Three weeks later we got a comprehensive report which amongst other things showed that the water in that section of Cannons Creek scores Excellent on a measure of ecological health.

It also showed we have three types of fish – the Banded kokopu, the koaro and some galaxids, and the longfin eel or tuna. There are many populations of springtails, insects, worms and snails; a long list of types of bacteria, and a selection of plants with pepper plants and mahoe prominent. Kereru, pukeko, blackbird, and thrush have waded in the water, while freshwater crayfish or koura are living there.   There are also traces of homo sapiens (humans) represented on the Wheel of Life printout  (see below) that accompanied the results.

It should be good news that we did not find any trace of possums, rats, cats, or other predators.  However, Wilderlab cautions us that to be sure, we would need a different sampling kit that can be left in the water for 24 hours.   Land-based animals only enter the water occasionally.

Our sample is one of four that are being taken around Belmont Regional Park to build a picture of its waterways.     So far it is a very good one.