Finding kōura (freshwater crayfish) in the Kakahu River was one of the highlights of recent eDNA monitoring and biomonitoring for Opuha Water Ltd.
The South Canterbury irrigation company’s most recent water quality report focuses on eDNA sampling and biomonitoring undertaken in the river.
eDNA is material that is left behind by organisms as they move through their environment. This material can be skin, hair, scales, mucus and faeces.
The process can identify thousands of species of fish, insects, crustaceans, birds, mammals, amphibians, plants, fungi, bacteria and other organisms.
In the report, Opuha Water Ltd (OWL) freshwater specialist Jared Panther said finding kōura eDNA is significant as local anecdotal reports had suggested the threatened species was no longer present in the Kakahu.
“But it was found upstream and downstream of the OWL discharge point into the Kakahu River, including upstream and downstream of the gorge.
“Kōura are more active at night and usually seek shelter from predators during the day, which is one reason why they are not easily observed in waterways during daylight hours.”
Panther said the eDNA for freshwater mussels, longfin eel, shortfin eel, upland bully, common bully, Canterbury galaxias, torrent fish and brown troutwas also detected upstream and downstream of the discharge point.
OWL publishes its quarterly water quality reports for Lake Opuha and the wider scheme catchment to share with the community the results of the company’s extensive water quality monitoring programme.
Key findings of the Kakahu River studies included from the eDNA monitoring thatKōura, freshwater mussels, longfin eel, shortfin eel, upland bully, common bully, Canterbury galaxias, torrent fish and brown trout were all detected in the Kakahu River with the ecological health of the river rated as either average or poor using the eDNA method.
From the biomonitoring themacroinvertebrate community index (MCI) scores in the Kakahu River were similar to the eDNA findings, with waterway ratings of good and fair.
The quantitative macroinvertebrate community index (QMCI) scores in the river were higher upstream of the discharge point compared with downstream.
Longfin eel, shortfin eel, upland bully, common bully and trout were caught in the river with these fish identified upstream and downstream of the discharge point.
SLR Consulting concluded that the collective biomonitoring results from the survey and previous surveys do not indicate any consistent patterns or significant adverse effects of the consented discharge on the freshwater communities of the Kakahu River.
“The levels of periphyton [material that grows on the surface of rocks on the bottom of a stream or river] cover in the Kakahu River remained below guidelines set by the Ministry for the Environment and Environment Canterbury for thick mats and long filamentous algae.
“There was an increase in periphyton cover at the sampling site immediately downstream of the discharge point, relative to other sites, which could be due to a localised effect of the discharge but could also be due to other factors such as river works undertaken at the start of the irrigation season.
“However, there were no patterns evident in periphyton cover at the other downstream sites, which indicates there are no wider impacts of the discharge on the periphyton community.”
There were no significant statistical differences in the MCI scores between the site immediately upstream of the Opuha discharge and all downstream sites in the river.
“Comparing the 2024 survey with the previous two surveys, there are no consistent patterns in macroinvertebrate community diversity, abundance or quality that would indicate any significant adverse effects of the discharge.
“Attributing a discharge effect is difficult, as different habitats in the Kakahu will naturally give rise to different macroinvertebrate scores.
“High abundance and diversity of fish at sites downstream of the discharge indicate that the discharge is not adversely affecting the fish community,” Panther said.
The full report can be viewed here.
