After getting his PhD in pancakes, refusals and eats, Professor LeRoy Botha runs us through the equations involved in catching the spotted grunter on fly.

For most of the past two years, I’ve had less time for fishing than I used to, and, oh boy, did the grunter rub it in. The few times I snuck onto the flats in 2022 and early 2023 were catastrophically testy, to say the least. I’m going to talk about all of that, soon, but in the meantime, let me say this to the one friend who alluded to the idea that my more recent success (I use that word quite liberally here) with these damn fish, is down to a so-called purple patch on our home estuary. To that, sir, I say, how dare you? Have you no idea the mountain of self-inflicted bullshit grunter math I had to climb to get out of the bogus mindset that had me flailing like a shot dog on those flats?

spotted grunter on fly

I suppose it’s not a big deal. It’s part of the grunter life. Grunter math is rarely cut-and-dried, if it even checks out at all. Take this example, with the disclaimer that this obviously isn’t science, just good old grunter math based on believing what I can see with my own eyes:

Call me childish, but I’m unashamed to say that my quest for a 69cm grunter, sight-fished on the flats, is rather top-of my current fly fishing goals. Much Like Pete on a quest for an Atlantic permit, I’m again constantly tweaking fly designs, engineering against the latest environmental or behavioural curve-ball. Word is that permit math is not dissimilar at all to grunter math, Pete (see Monk Mode for more on that).

When targeting trophy fish, the age-old trick is to increase your fly size. So naturally, I’ve wondered hard about supersizing flies like Shawn for said home waters, and ended up with a somewhat surprising preliminary conclusion, backed by data visually obtained from the grunter flats.


An introductory grunter math problem may look something like this: Pomadasys commersonnii can be divided into fish under 50cm, and those above. If a sub 50cm fish is a grunt, and above 50cm is even grunter, are you a gruntist?

spotted grunter on fly

Today, however, the problem is much more advanced: find x if x+y = 69cm grunter, and y = not being a douche. Show your work.


Were one to assume the known variables (y and 69cm grunter) are sort of done and dusted, respectively, one could simplify the question and rephrase: Will a really big grunter eat a standard-sized Shawn, in all its proven gruntishness? Or do you need to upsize your offering in order to draw their attention at all?

To answer that, we once again turn to the source: El Google. We asked Google about the energy expenditure versus nutritional gain per unit effort, as it pertains to crustacean eaters, given what we know a grunter will go through to get a prawn in his belly.

This cutting-edge research seems to suggest that prawns and shrimps are splendidly nutritious snacks. They are somewhat high in cholesterol, but that is only a problem for Karen grunts. We know that the average grunter will skoffel really hard for a prawn he doesn’t even know he’ll get. That’s high effort for low reward, right?

Wrong! Probably.

Turns out, a shrimp contains up to ten times as much protein as a fish of the same size. The inferences aren’t that much of a stretch:

On the question of whether we should be focusing on imitating sprat-type baitfish, given that we do, every now and again, see evidence of grunter eating them? Probably not gonna do much. For a grunter, hunting fish is indeed high effort for low reward. They probably only do it for a laugh.

And do you need a big fly to catch a big grunter? Well, dammit. Also probably not. Probably. Because every shrimp or prawn is worth a grunter’s time. Probably.

In conclusion, oh boy. X, for now, equals same-old Shawn, size wise. But maybe add a weed guard, and always pay attention:

spotted grunter on fly
“They say you should tie your Shawn so it really stands out over the substrate.”

Speaking of fly engineering. We’ve put our old favourite Shawn hook through as much as he can take. So I hunted down a new one, capable of making a small Shawn that works right, and yet is able to literally pull its weight. The Ahrex NS110 in sizes 10 and 8 have stood head and shoulders above the rest. If someone in SA would start stocking them, you’ll make a few grunter nerds very, very happy. I must also mention the barbless Hanak 950BL in size 8, used to perfect effect around these parts by a talented cat called Joburg De Jagter.

“Ahrex NS110 for the win!”

Lastly, I’ve noticed that the more you tweak the fly, the more stable your success rate seems to be. This checks out: We’re fishing to finite populations of resident fish. It’s not the tweaks that count, but the fact that you’re doing them. Keep it fresh. Grunter math never works out the same way twice.

12 thoughts on “GRUNTER MATH”

    • James, I’m sorry. I should feel bad. My analogies are bad. My math’s worse. But that’s kind of the point. All of this just to say that the more I fish for grunter, the more I realise that intuition in the moment is all you’ve got. And if you read between the lines you’ll see that all I’m trying to illustrate is that grunter are slowly robbing me of my sanity. Thanks for the comment, man!

    • Cheers, Mark! I did a full review of the rod in The Mission 32, loved it then, still do now. It’s a fun bass rod, but it is clearly made for lighter flies and stalking flats fish. Really does a great job, as long as y is done.

  1. I’m going to Knysna this weekend and will definitely try my hand at my first grunt/grunter! I’ll be using a 9wt which is probably not ideal but new sticks & line are a whack of dosh hey. A lotto win tonight would change the game so will hedge R5 on that…

    From what I have gathered one should not hold ones breath when attempting to become a gruntist, but I’ll damn well try!

  2. I did not know that factoid about protein content of shrimps vs fish, but all of a sudden, a shitload more observations and stuff is much more clearer! Buy a donkey.

    • Cheers Ed! Thanks for the comment! I was also rather struck when I found that info, hey. Much clarity, indeed!

  3. Hi Leroy. What do you like about the Ahrex streamer hook? I’ve been tying on the Ahrex #8 and #10 light stinger, and fairly happy..

    • Howzit, Jared! We must go fish! I haven’t tied on the light stinger, but my guess would be “too light” for what I’m trying to do. It’s very similar to the #6 B10S which has opened too many times on grunter reaching 60+ cm. Since I’m looking for a fish nearer 70cm, I needed a small, black hook, at least heavier wire than the B10S, and happy with being used in the salt. Also, I believe the bent-in point on the B10S causes missed takes, so I wanted a hook with a point parallel to the shank. The NS110 fits all those criteria and has landed 60cm+ grunters with zero sign of opening, and a noticeably better eat-to-hookup ratio. Shot for the comment, man!

      • Hey man, yeah would love to go on a mission soon!
        Thanks for the notes on the hooks makes sense, fortunately haven’t had any of the hooks open yet on the larger fish yet, but its not like I’m smashing load of fish so the sample size isn’t huge haha, I’ve been focusing on tying smaller lighter flies for delicate presentation. have also caught a number of large grunts on the Ahrex NS150 curved shrimp #10 ( the wire is thicker than the light stinger but the gape is quite tight) also bought the Ahrex SA250 shrimp #8 but these hooks just feel slightly too big to me.


Leave a comment



Subscribe to our newsletter and get all the latest to your inbox!