Meanwhile in Tanzania – the ‘Prawn Walk’ demystified (sort of)

The Prawn Walk
Mud Prawn bank

Everyone has heard of the great Wildebeest Migration through Tanzania’s Serengeti and up into Kenya. This spectacular phenomenon is actually more than ‘just’ a wildebeest migration as includes (in far lesser numbers) zebra, as well as Thompson’s and Grant’s gazelles follow the trek for better grazing and water. As spectacular as it is in sheer size, it is fairly predictable, if rain dependant (not unlike the sardine run, but lets not confuse things). Typically by now (August to October) the herds are massing in far northern Tanzania and preparing to move into Kenya, where they will graze in the Maasai Mara reserve until October before heading south once more.

Mud prawns (Upogebia Africana) – that favourite food of our beloved Spotted Grunter, among others – also migrate, in big numbers. But that, very unfortunately, is where the similarity ends. Tied to variables uncountable, you simply cannot predict, time or pinpoint the mythical ‘prawn walk’.

Lemming-like behaviour, some have called this mass ‘up-and-swim-away,’ but is it?

Obliviously ignorant, I witnessed my first ‘walk’ at age 16 on the Gamtoos River in the Eastern Cape. What I saw that day near two decades ago now is with me still. A regretful memory, but so we learn.

We were – five fairly proficient bait fisherman – teenage school boys on a camping and fishing trip, way more intent on getting into the (long since warm) beers we’d manage to swindle (and then muggle out of sight of our parents) into the overnight gear.

It was mid-tide on the flood, a few days after Springs and we needed bait, so, armed with pumps and buckets we hurriedly boarded our trusty craft – a racing-style pontoon rubber duck – and sped off for the mud flats near the mouth. The water was muddy brown, not uncommon for this river.

As we neared our target bank (raced up to, would be an apt description) an older gentleman with light stick in hand off the back of his cabin boat, motioned for us to slow down. It wasn’t grumpy gesture, but as we got right up near he put his finger to his mouth, school prefect-style directing us to be quiet. ‘What did this old ballie know?’  We thought, ‘he didn’t own the river, what was he doing fishing so shallow anyway?’

A regretful memory, as I mentioned.

Old Man River then proceeded to lift what must’ve been at least six kilograms of river slab – one of the biggest Spotted Grunts I’d seen up until then. Biggest still, perhaps.

Coming in to the bank like cowboys and jumping off around knee deep I immediately noticed the prawns swimming around in the water column – just below the surface, everywhere! We proceeded to pump, scoop and grab a bucket or two worth before whirl-winding back off the bank and further up river where (we thought we knew) the big Cob, Steenies and Grunter lurked. Our departure was much to the old man’s relief, I’m sure. And he most probably boated a few more similar-sized specimens. (If you’re out there sir, our humblest apologies. We simply knew no better).

mud prawn flat
Will they stay or will they go now

I do know now – at least I know what that was. The ‘prawn walk’ – as far as the smart okes in lab coats can tell us – is a mini migration in search of a better place to live. There have been scant few studies on mud prawns, let alone on their migration habits (in fact, during extended and extensive searching I’ve yet to come across any).

From what I’ve pulled together from various resources (including a few legit old-man-river-like characters) is that they bug out in search of a new bank to setup home when a particular bank becomes too crowded, the mud the wrong texture, consistency or make-up, a reduction in food source, water quality, tidal flow…etc etc. It is that simple and that complicated all at the same time.

In the Hermanus of my youth there was a sign on the way out of town (just past the caravan park) toward the Klein River estuary that read ‘Prawn Flats.’ Back then I imagined it not in the terms of a ‘flat’ as we think of it now, rather in terms of a block of flats, as in apartments. I still kind of like that analogy, and I imagine them (the prawns) getting fed up with the landlord because he’s refused to fix the plumbing or something and just upping and moving out to find a new ‘block of flats’.

 

In terms of timing it happens (usually) in early Spring (August – October) – the cycle we’re heading into now. However, with all the mentioned variables and environmental elements at play, it simply is impossible to predict – when, on what particular bank and even on what river it may take place is anyone’s guess. Ian Kitching and Peter Coetzee have experienced first-hand the bonanza it can be when it comes off here in the Southern Cape.

If we could predict it, I imagine it to create a similar phenomenon to the ‘Salmon Fly’ hatch on the Deschutes or the Barbel run in the Okavango. Ja, better then perhaps it remains such a mystery.

I will forever continue to make (a very amateur) study of their cycles on estuary systems I frequent, hoping to crack a pattern. Or just luck into a walk…

Demystified, okay, not quite, but meanwhile, in Tanzania, the Wildebeest trudge on.

*Hit this for a cool animated model showing the Migration.

And, learn more about the humble mud prawn here and here.

Any thoughts or findings of your own?

4 thoughts on “Meanwhile in Tanzania – the ‘Prawn Walk’ demystified (sort of)”

  1. Craig says:

    Witnessed a sand crab migration in Langebaan lagoon last November. They were all on or near the surface on the outgoing tide (at night). Moving house or going to spawn somewhere I do not know.

  2. Sam16 says:

    Then there is the amazing red crab migration on Christmas Island! I know these monster coconut crabs also migrate at some point in time. Horseshoe crabs migrate once a year on the east coast of the USA. We still have a lot to learn when it comes to crustaceans and their habits. I just hate it when these damn river crabs snip your fly line when you are focussed on catching yellow fish! 😁

  3. Leonard Flemming says:

    Excellent post Jazz! I haven’t witnessed a prawn walk – for some reason they have always occurred the week before or after my visits; but, I have waded around estuaries at night a few times now and the mud prawns have always been out and about (swimming around my legs, crawling over my bare feet etc.). Grunter and kob also actively hunt at night and I believe there’s merit in targeting both species at night (besides just looking for prawn walks)…Check out http://feathersandfluoro.com/?p=7560#.V6L51Pm7iko for proof of a big grunt that came out on fly at night. Interestingly, I’ve also ‘bumped’ into steenbras on the prawn flats at night and almost picked them up with my bare hands in my red torch light.

  4. wildwillfisher says:

    Cool post! Mudprawns = number one popular critters. Think about it, Colton said imitation is the sincerest form of flattery. The mudprawn is being imitated to death by fly fishermen!

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