I just finished my 'Freshwater Conservation' module of my masters degree and I want to talk about it.
I haven't written much about my masters course so here's a quick run-down of what I'm doing: I'm studying Conservation Biology at the University of Cape Town. It's a dream come true and I love it so much.
It's very intense and challenging, as to be expected with a masters programme, but it really is great. It's not like conventional uni in the sense that the modules run back-to-back, rather than side-by-side. So each module is 1-3 weeks, and that's all you do in that time. Then it's over and on to the next. This is great because you can fully immerse yourself in it, but obviously it has it's pitfalls: namely that each module is over quick and every week is just as intense as the last.
So last week was 'Freshwater Conservation'. Most of my experience is in terrestrial ecology/conservation and I knew very little about freshwater conservation. I had studied rivers in my geography degree (anyone who has studied geography in the UK knows how much the lecturers love rivers), but very little on the ecology. I was interested to learn more but wasn't expected to love the module as much as I did.
The best thing about studying conservation in a global biodiversity hotpot (the fynbos) is the field trips. We have at least one per module which is awesome. This module however went above and beyond, with a two night stay studying the Witte River, in Bainskloof (about 1.5 hours from Cape Town).
Whether you study an environmental science or not, I think we can all agree that getting out of the classroom is always preferable to staying in it. This is definitely true of conservation. People studying conservation are doing it because they love nature, but studying nature seems to involve a lot of time in front of a computer screen. It is so essential to go back to nature every now and then (or you know, as much as humanly possible) to remind yourself why you care, and to just give yourself a break. For me, fieldwork is the perfect middle ground.
The trip to Bainskloof essentially gave us an introduction into some field work sampling techniques involved in freshwater conservation and research, some of the problems facing these systems.
We set fyke nets in the river to see what's living there. My simple explanation of fyke nets is: they are big nets, cylinder or cone-shaped, that sit at the bottom of the river (when you attach them to something like a rock) with a wide opening. The have two 'wings' that fan out of the front and guide the fish in. 'The fish can get in but can't get out' is the basic principle. (The fish technically can get out but they don't know that. )
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| Fyke nets |
The Witte River has a natural barrier (essentially some rocks at a slightly higher elevation to the river below tightly packed so fish can't just swim through), and so we set nets above and below it. There have been a number of invasions on the river: species that are not naturally found here have been brought here and introduced and are now damaging the ecosystem. The most notable ones are species of catfish, trout, and bass, as these predate on the indigenous fish. These fish are only found downstream of the barrier (for now) and so there is refuge upstream for indigenous fish. We set the nets above and below the barrier to compare. The nets don't harm the fish and are a standard sampling technique.
Below the barrier we only caught invasive fish: sharp-toothed catfish and small-mouthed bass. This was disappointing and worrying. There is a possibility that some poor indigenous fish did swim into the net, and were then predated on by these invasives. However, when we were swimming around in these areas and laying the net, we did not see a single native fish.
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| Above: Sharp-tooth catfish Below: Left: Smallmouth bass. Right: Sharp-tooth catfish. |
Above the barrier, it could be a completely different river. There are fish everywhere. It's amazing. They are much smaller but there are hundreds of them.
There is also a lot more algae. This is because the native fish - eg red-finned minnows and cape kurper - feed on the invertebrates (animals without a backbone - insects mostly) which feed on the algae. By having the indigenous fish there to control the herbivore populations, the algae has more opportunity to grow. Below the barrier, this isn't happening, and so there is a notable different in algae growth (and slippery-ness of the rocks).
I don't think I've ever seen such a clear contrast with my own eyes before due to invasive species. There are so many fish above the barrier, and basically none below. It's shocking.
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| Above the barrier! |
The fish were introduced for various reasons (mostly angling) and some were more recent than others. Some were about 100 years ago, but the catfish are a much more recent invasion. Furthermore the catfish are much better colonisers, and there is fear they will be able to cross the barrier. They can cope out of water for a fair amount of time and can essentially walk on slippery surfaces.
The good news is, we only found indigenous fish above the barrier! This is hopeful, as it suggests the invasive predators have not managed to move upstream, and so this area is still acting as a refugium for the native species. Hopefully it'll stay this way.
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| Photo: Conor Eastment |
We did catch an eel (long-finned eel) which is native and a natural predator for the indigenous fish. This was quite exciting! The invasive predators could also be a problem for the eels if they do cross the barrier, as they would be in competition now for food.
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| Long-finned Eel. |
We also did some invertebrate sampling. Invertebrates (insects and such) can indicate how healthy an ecosystem is. Some insects are more sensitive than others, to variables like water quality. Therefore, if you have sensitive insects in your stream, it suggests your water quality is high. Equally if you have insects with low sensitivity that can essentially survive anywhere, it might indicate that your stream is not very healthy.
This kind of sample is really easy to do. We caught the invertebrates in a net by just moving it around the aquatic vegetation, or holding it downstream and allowing the river to do the work for us. Using an ID kit, we could ID the insects and calculate the score of river health. Anyone can do this using miniSASS: a citizen science toolkit for monitoring stream health. Read more: here.
I made a video about the trip as well which you can find here: https://youtu.be/k9mVn5rCx1g.
I made a video about the trip as well which you can find here: https://youtu.be/k9mVn5rCx1g.
Bainskloof is really beautiful. It's worth a visit for sure. Great place to relax, swim, and just enjoy being in nature for a while.
