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Natural Barriers

This is an important positive message about fish passage.

We are seeing an increase in the use of the term “natural barrier”, particularly when prioritizing remediation of man-made structures/barriers.

As it happens, many species of fish have evolved to navigate what humans might think are impossible features.

There are now a number of effective fixes that are very low cost, thereby eliminating the need to prioritize in the first place.

All structures in waterways need to allow for fish passage regardless of what is above or below them.

Please watch and share this short video

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Amazing Climbing Koaro

This is a short video by Tim Olley showing larger bodied koaro (Galaxias brevipinnis) “climbing” up a natural feature.

Larger bodied fish tend to use a burst swimming action unlike the juveniles that typically “flip-flop” further out at the edges of the splash zone.

Smaller fish tend to be able to climb steeper slopes.

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Climbing Eels

This rare footage shows both small and larger eels trying to navigate a natural feature. 
You will see that larger bodied specimens are unable to utilise the wet margins or splash zones. 
Remediation techniques should offer a range of options to give migrating fish choices to best suit their needs.

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How Fish Swim – Video Showing How Fish Utilize Small Eddies And Boundary Layers

When designing new structures or considering remediation for existing ones, it is important to consider the swimming ability of the fish likely to pass through or over the structure.

This short video shows that small or juvenile fish operate at a very fine resolution not able to be easily measured or observed.

You will see in the video fish riding very subtle pressure waves within complex or nature-like flows that can have a different velocity and/or direction in the same location. 
It also shows fish climbing vertically when the conditions allow.

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Heads-up 2020

Things to look forward to in the coming months:

More of our short form videos are in the pipeline.

A number of “Lessons Learned” are to be completed and shared.
Watch for “Fish pass fail and subsequent remediation” 
“Installation of baffles to restore fish passage in a very long culvert”

“Before and after” slides showing remediation projects.

Academic papers to be published showing effectiveness of flexible baffles.

Don’t forget that World Fish Migration Day is May 16th.

Here is a great video that Sjaan Bowie of the NZ Fish Passage Advisory Group and the NZ Dept of Conservation shared showing what she organized for World Fish Migration Day and also shows members of the public how baffles improve fish passage up a pipe.

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Fish Pass Opens Up Duck Creek In Auckland

For the landowners along Duck Creek, restoring the stream to its former glory has been a labour of love. First, the mature pine trees along the banks were removed, then native seedlings planted and other weed species managed. The icing on the cake was to remediate a perched, box culvert on the stream that was preventing migratory native fish from accessing wetland habitat upstream. 

The landowners made two previous attempts to create fish passage up the culvert but high flows during flood events destroyed their hard work.  Thanks to funding from Auckland Council Healthy Waters, and through the Whitebait Habitat Restoration Project managed by the Whitebait Connection, this barrier has now been fixed.

Riffle Restoration was employed to remediate the culvert by installing a fish ‘ladder’ and muscle rope on the downstream edge, which allows climbing and strong swimming species to navigate their way upstream. Baffles were also placed inside the culvert, to create resting places for tired fish.

A fish survey undertaken since the fish ladder was installed found juvenile banded kōkopu and bully species above the culvert, and whitebait resting behind the baffles in the culvert. This is great news for the landowners, the Whitebait Connection and the fish, who now have 2kms of extra waterway to explore.

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Magical Climbing Fish

Hi all

Below is a short video that Tim has put together showing juvenile whitebait (galaxiid) climbing up into a perched culvert.

We are often able to imitate the conditions that allow fish to do this by fitting rubber ramps and/or mussel-rope, however little is known about the limitations with respect to gradients, flow, height, substrate etc.