New Zealand’s native fish are doing their best to climb up ramps in a NIWA laboratory so scientists can learn how to
better help them navigate our tricky waterways.
Hamilton-based hydroecologist Dr Eleanor Gee and her team have rigged up six ramps - each at different angles and
sporting two different surface types - one smooth, the other textured - to test how adept the fish are at making their
way to the top. The idea is to simulate their upstream migration.
She’s using young fish of the whitebait species kōaro and banded kōkopu at the moment and plans to move on to redfin
bullies. "These species are known to be climbers and all migrate as part of their lifecycle."
Kōaro in particular are known to be excellent climbers and able to penetrate further inland than other whitebait species
after spending their larval life in the sea.
Migrating native fish face a range of issues in our waterways, including manmade barriers such as dams, weirs and
culverts that prevent them reaching their preferred freshwater habitats.
"What we’re trying to do is find out the limits of the known climbing fish by testing them on ramps of varying
steepness. Ultimately, we’d like to look at whether larger or older fish find it more difficult. We know some small fish
can climb near vertical slopes, but they probably can’t do that their entire lives so we want to find out at what stage
they stop."
Dr Gee says the ability to climb is not a particularly common strategy for fish but it allows the fish to migrate
further upstream than other species they may compete with. However, more than one-third of New Zealand’s native
freshwater fish migrate from the sea upstream, and that includes a number of species in decline.
"The shortjaw kōkopu is a nationally threatened species and is also a climber, so it’s important to find as much as
possible about climbing so we can manage them in the best possible way."
Interestingly, not all climbing fish climb in the same way. Kōaro and banded kōkopu use an alternating limb movement,
like swimming freestyle, while bullies go for a bilateral movement which is more like breast-stroke, moving both limbs
in the same direction at the same time. "It’s pretty impressive watching them shuffle their way up these structures."
They can also climb a long way with some known to surmount significant waterfalls depending on the steepness and the
type of substrate available.
The insight Dr Gee gains from the experiments will be used to update the New Zealand Fish Passage Guidelines first
introduced in 2018. The guidelines set out the recommended practice for designing infrastructure in streams that enable
fish to pass through and were developed to help waterway managers, engineers, environmental officers, iwi and
communities understand and implement better management of fish passage in New Zealand.
New freshwater management rules require all regional councils to identify barriers to fish passage and come up with a
plan for mitigating them.
So far the experiment is providing plenty of challenges for the 100 or so fish roped in to help. "I’ve seen a kōaro get
up reasonably quickly and then experience a slippery ride to the bottom, and I’ve had a few naughty children who have
decided to climb off the ramp, but it is a really fun experiment to do."
"For me personally a lot of what drives me professionally is the contribution I can make to the public knowledge and
understanding of these species. People care a lot about these treasured animals."