The Bennetts Stream restoration project began five years ago, as part of a wider biodiversity projectfocused on improving sites of ecological interest across the irrigation scheme’s 44,000-hectare command area.
Waimakariri Irrigation Limited biodiversity project lead Dan Cameron said 10 threatened Canterbury mudfish were visually identified at Bennetts Stream in January, followed by two tadpole shrimp in September.
He said it raised several interesting questions regarding their role in the ecosystem and how it would shape the restoration project’s future.
“It was a huge surprise to find Canterbury mudfish at the site as there are no known records of this species north of the Waimakariri River, apart from at Coopers Creek near Oxford.
“Unfortunately, a couple of months after we found the mudfish the stream went dry, and water only started flowing through this ephemeral stream again this month.
“We didn’t find any mudfish when we did our recent trapping exercise, so we don’t know yet whether the mudfish we found in January are still here.
“We are not sure if they could be a remnant population or if they were translocated here through a natural process such as a flood.”
The recent discovery of rare tadpole shrimps at the restoration site has prompted Cameron to consider further investigations to understand what other species could be living in Bennetts Stream and how their lifecycles interact with the unique nature of an ephemeral stream ecosystem.
Tadpole shrimps are classified as “living fossils” as they are an ancient species with the oldest fossil ever discovered, dating back to the Upper Carboniferous period (approximately 300 million years ago).
Found only in New Zealand and Australia, they are known as shield shrimps due to the shell-type structure that wraps around their body.
Waimakariri Irrigation Limited biodiversity project lead Dan Cameron, WIL board director Tim Wells and Waimakariri District Council ecologist Kate Steel at the Bennetts Stream site where Canterbury mudfish and tadpole shrimp have been discovered.
Tadpole shrimp require a specific habitat that dries up and must remain dry for some time for their lifecycle to be completed.
The eggs of the tadpole shrimp hatch once a waterway or pond is refilled with water.
Cameron said tadpole shrimp have been found in Hawke’s Bay and Canterbury.
“There have been limited numbers of tadpole shrimp recorded in Canterbury, so the discovery of both tadpole shrimp and Canterbury mudfish means that we will need to broaden our knowledge about the role they play in this ecosystem.”
Waimakariri Irrigation Limited is carrying out a biodiversity restoration project at Bennetts Stream which is a tributary of the Eyre River, located near Oxford in North Canterbury.
Waimakariri Irrigation Limited board director and local farmer Tim Wells started working on the Bennetts Stream project in 2019 with a focus on removing gorse and blackberry and carrying out native planting.
He said the impetus for the project was in response to Plan Change 7 (PC7).
“WIL created a solutions package in response to Plan Change 7 which focused on biodiversity restoration within the area covered by our irrigation scheme, along with Managed Aquifer Recharge (MAR) and Targeted Stream Augmentation (TSA),” he said.
“I identified this site as a good way for farmers and the irrigation cooperative to make a difference as the stream is surrounded by WIL shareholder properties.
“We want to be part of the solution to the water quality issues that we have here in Waimakariri.”
The next step in the project is environmental DNA (eDNA) sampling which will help confirm if Canterbury mudfish are present and provide a more detailed picture of the different types of species living in Bennetts Stream.
“We will take samples from the stream and analyse these to determine traces of DNA in the samples,” Cameron said.
“We can then understand more about what is living in the stream from species of fish right down to small invertebrates, microorganisms and algae.
“This will help us to decide which actions to take next and will also help to determine a long-term plan for the site.”
Cameron said that ultimately, the project wanted to create a self-sustaining site with thriving indigenous biodiversity, but wanted to spend more time understanding this ecosystem first.
“We need to determine how all of the different elements at this site impact each other so we can create a long-term plan to enhance and preserve this special space for future generations to enjoy.”
