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).
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.
Any thoughts or findings of your own?