The Waitomo caves are a delicate ecosystem. Photo / File
The Waitomo caves are a delicate ecosystem. Photo / File
The Waitomo caves, famous for their glowworms and stalactite and stalagmites formations, are struggling with an invasive visitor - the fish species koi carp.
Koi carp, which look like large goldfish, are considered a pest in New Zealand and pose a risk to native species and freshwater habitats.
NIWA Principal Scientist for Natural Hazards and Hydrodynamics Dr Graeme Smart and hydrometric technician Carl Fischer were alerted to the undesirable invaders lurking in the cave system, last year.
“It’s a delicate ecosystem... People were worried because they may be competing for food sources in the caves, which could severely impact the glowworms and other native animals. Waitomo caves have vast spiritual, environmental, and economic importance, so it’s a problem that needs resolving, and quickly,” says Smart.
The Waikato Regional Council proposed to build a fish barrier downstream of the caves to stop the carp from migrating upstream, however, as the caves can flood, anything that raises flood levels, such as a fish barrier, could be a problem.
That’s why the Discover Waitomo Group tasked NIWA with measuring water levels through the cave system to help determine the best course of action.
Koi carp are on NIWA's most-wanted list. Photo / Supplied
Fischer and Smart thought this was going to be a straightforward exercise, but it turned out to be a bit more complicated because none of their GPS-operated surveying equipment worked in a cave.
“So, we went back to the good old-fashioned way of doing things. Which meant getting our feet wet,” says Smart.
Smart and Fisher instead used a so-called level traverse which involves linking water levels measured inside the cave to water levels at the cave inlet and exit. The shortest way to do this was through the visitor centre.
“We had this situation where people were happily sipping their lattes, and we were nestling in saying ‘excuse me, we just need to insert this tripod beside your table, not to worry, pardon me’,” Smart says.
To better understand why the caves need protecting, Smart went on a guided tour.
NIWA hydrodynamics and hazards scientist Dr Graeme Smart measuring water surface levels into the cave system. Photo / NIWA
“The guide zig-zagged the boat through the cave, and above you is the most beautiful light show, twinkling like the night sky... It’s nature at its finest.”
The NIWA team is now evaluating the findings. It’s likely that computer modelling will be undertaken to assess the possible impacts of a fish barrier.
Local Māori have long known about the Waitomo Caves, but they were not explored until 1887 when Māori Chief Tane Tinorau and English surveyor Fred Mace went on s mission.
Tane Tinorau wanted to share these natural wonders and opened the caves to tourists in 1889. Today, the Waitomo Glowworm Caves host thousands of visitors per year and are owned and protected by the Ruapuha Uekaha Hapū Trust and Department of Conservation.
Koi carp, prized in places like Japan because of their ability to survive in extreme conditions and live long lives were released into New Zealand waters around 60 years ago. Their appetite means they are destroying indigenous species and freshwater habitats at an alarming rate.
