A river that runs backwards

So we all know that New Zealand is unstable. Literally. As anyone from Christchurch will assert. So it shouldn’t really come as a surprise that with all this up-ing and down-ing and to-ing and fro-ing of the land, that a river has changed direction. No, I don’t mean there is a river that runs uphill, but rather that the land under a river has shifted enough to make it turn around. That’s pretty crazy stuff. Like, at some stage in our geological history, the Nevis River has just stopped and then carried on in the other direction. Cooler still is that it is part of this river system: (Although the pillars of the Kings weren’t there the last time I checked).  Image

Picture from here

So how do we know this?

It’s thanks in part to these guys who I wrote about in my last blog:

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This story involves 3 rivers:

–       The Nevis (which changed direction)

–       The Kawarau (which the Nevis now runs into)

–       The Mataura (which the Nevis used to run into)

(and I suppose I should mention that the Nokomai stream is the part of the Nevis which continued flowing the same way)

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And the story involves this fish: Image

Photo from here

If there were an award for the best naming of a species, this would certainly be a contender: Galaxias gollumoides , aka the Gollum fish. There is even another very closely related species called the Smeagol fish.

Zoologists at the University of Otago have found that the Gollum fish in the Nevis have relatives in the Mataura River (to the south) but not in the Kawarau River, which the Nevis currently flows into. This supports the geologists’ evidence that in the Pleistocene (2 million-ish years ago) the Nevis used to run south through a valley between the Garvie Range and the Remarkables Range (the jagged mountains behind Queenstown).

As the mountains on either side grew, they pinched off the valley the Nevis was in. At the same time, erosion blocked off the Nevis, and caused it to run back the other way.  This isolated the Gollum fish in the Nevis from the Mataura river where it used to run. The Nevis population has since diverged from the Mataura population, but is still closely related. Image

Species that today are found in the Kawarau are not found in the Nevis, yet are found in other tributaries to the Kawarau.

P.S. If you want a closer look at the Nevis River, then this is a good way to do it!Image

Photo from here

“You ate my babies and didn’t even know it” – NZ’s Galaxy Fish

This is the Bacon Street Creek on the Otago Peninsula:

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I spent half my childhood in this creek, going on “expeditions” on the walk home from school – building dams, catching tadpoles and going “mining” in the pipe. For all the hours I spent in the creek I never had a clue there was something else living there.

These guys:

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Photo from here

This is a giant kokopu, a species of galaxiid, which are native freshwater fish. The name is kind of strange, but someone thought their patterned skin looked like stars in the galaxy, so they named the fish after it. I took the liberty to simplify it further to “Galaxy Fish”.

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A lot of kiwis have never even heard of galaxiids, but have eaten their babies!

There are 5 species of galaxiids (there are about 28 altogether) that go out to sea just after they hatch from their eggs. They spend their larval stage eating plankton, before swimming back into rivers as whitebait.

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Photo from here

If the whitebait manage to run the gauntlet through the nets, then they go way upstream to grow up.

Of those that don’t make it past the nets and end up in your fritter, 80% are probably inanga, while the other four are giant kokopu, banded kokopu, koaro, and shortjaw kokopu.

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Wikimedia commons

Galaxiids are on the whole endangered. Some are as rare as Kakapos, but we don’t really know that much about them. Part of the reason is that they are so secretive, but also because they are not a sexy species to protect – we all love to help save cute fluffy things like kiwis, but what about the slimy galaxy fish?  Image

But what they lack in sexiness, they make up for in awesomeness:

They can climb better than you –

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Photo from here – Koaro whitebait climbing a barrier designed to stop fish from moving upstream.

They can also tell us about New Zealand’s history. In my next post, I’ll talk about how these fish have helped us figure out the mystery of a river that flows backwards, and how they stopped a whole valley from being flooded.

But these little fish are in trouble, mostly because of trout, which eat and out-compete them.

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Wikimedia commons

Trout are pretty neat too, and we like them because they bring the tourists here who in turn bring their big fat wallets. Because of the trout fishing industry, the organisation Fish and Game make sure our rivers are clean and healthy for the fish.

We don’t want to get rid of trout at all, but just from the small streams that aren’t worth fishing for trout in.

In Otago, there are heaps of really little streams with galaxiids in them. The streams are tiny and have changed course over time, splitting up populations of galaxiids and causing them to diverge into different species. Some of these species are super rare, so it would be a shame if trout got in and wiped them out. They’ve already invaded most streams, but it’s worth the effort to take care of the rest.

Galaxy fish are awesome.

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