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Big crabs produce big trout by Ed Herbst

Monday, 24 November 2014 12:23

 South African fly fishers are fortunate in that the country’s rivers and dams are home to the Potamonautid river crab, the major food source for the otter and water mongoose.

They are also relished by trout. They are, for example, a staple food source at Lakenvlei Dam near Ceres and are regularly found in the stomach contents of the big trout caught by in the Langkloof River in Barkly East by Christo du Plessis.


I was reminded of this when Alan Hobson of the Angler and Antelope in Somerset East sent me a short note and a few photographs:  “Last week I had two well-known fly fishers, Mike Dolhoff and Andrew Parsons, as guests and I took them to Karreerbosch Dam, one of several in the area that regularly produce trout weighing up to 10 lbs.  Mike caught his biggest trout to date, a beauty of eight pounds, together with a five and six pounder. Unfortunately we had to keep the five pounder because it was hooked very deep in the gills.  Its stomach contents confirmed why our trout in the Karoo grow so big, so quickly.  It had no less than eleven whole crabs in its stomach, the biggest of which was nearly 10cm!”


Click in images to enlarge

987 Somerset East 9787 crab

Some of the crabs eaten by Mike Dolhoff’s five-pound trout

 4141 MD 8 lbs

Mike Dolhoff with his eight pound rainbow trout

The presence of the crab in our rivers and dams explains the success half a century ago of the then-favourite patterns, the Walker’s Killer and the Mrs Simpson tied on long shank #8 hooks. The Mrs Simpson is still the favourite of legendary Eastern Cape ichthyologist, Martin Davies of Rhodes University in Grahamstown. Alan Hobson ties his own version of this fly which simply adds a Zonker strip to the original pattern. It is the first fly in his arsenal when he tackles the big barbel in the area and trout are equally susceptible to its charms.

321 Zonker Strip Mrs Simpson

Alan Hobson’s Zonker Strip Mrs Simpson

The late Bob Crass, for many years Scientific Officer for the Natal Parks Board examined the stomach contents of 235 brown trout caught by him in 10 Natal rivers including the Mooi, Yarrow, Loteni and Inzinga. The resulting paper, “Preliminary Report on Trout Food in Natal” was carried in the 1946 Journal of the Natal University College Scientific Society.

He found that mayfly nymphs were the most important trout food, followed by crabs and then dragonfly nymphs. Nearly sixty percent of the trout stomachs examined contained mayfly nymph and a third contained crabs. The figure for beetles and dragonfly nymphs was twenty percent in each case. He found that one crab of the size most commonly captured by the trout took up as much stomach space as 35 mayfly nymphs. This would clearly make the crab a valuable capture to the trout because it would require far less energy expenditure than the capture of three dozen nymphs.

Filled with crabs

The late Dr Douglas Hey, the doyen of South Africa’s professional nature conservators, told me that, as a child, he had to clean hundreds of trout caught by his father Sydney (author of the classic, Rapture of the River) and his friends in the newly stocked rivers of the North Eastern Cape. He said that their stomachs were predominantly filled with crabs and not the indigenous minnows which are allegedly most vulnerable in recently-stocked, previously-virgin waters

About twenty years ago I decided to develop a crab imitation and, like Alan with his Zonker Strip Mrs Simpson, I drew on existing ideas.

 555 Eds Rubber Hackle Crab

The original Soft Hackle Rubber Leg Crab

What does a crab look like when confronted by danger? Normally it raises its claws aggressively and the legs are a blur as it scuttles sideways or backwards. I decided that if I combined the marabou tail of the Woolly Bugger, the palmered marabou of Jack Gartside’s Soft Hackle Streamer and, at the eye of the hook, a few rubber strands to imitate the crab’s legs, I might just have a winner - and so it proved.

A bass a cast

Andrew Ingram took my first prototype to the Bulshoek Dam on the Olifants River below Clanwilliam and, fishing from his float tube, caught a bass a cast. It became so boring that he took it off and replaced it with another fly whereupon his success ratio dropped dramatically.


 In Maclear, Ron Moore fishing the Little Pot River and various dams caught numerous trout weighing a total of 42 lbs on a single fly before it disintegrated. He says it is the most successful fly he has tried in a lifetime of fishing in the area. He cites an occasion on the  LittlePot near the dinosaur footprints when he and neighbour Ginger Jenkins tried a variety of flies from March Browns to Woolly Worms for close on an hour without success. He then tried the rubber-legged apparition and took half a dozen fish in quick succession.

These are hardly conclusive results. When bass are on the prod they will hit anything that moves and the day that Andrew fished the Bulshoek Dam could have been just such a situation. However the one characteristic which this amalgam of existing fly tying techniques and proven materials does have in abundance is movement - and movement more than any other factor is what triggers strikes from predatory fish. The pulsing of the marabou and the flutter of the rubber legs are an often-irresistible combination.

Thank you Jack Gartside.


A few years later, when the Sage “Ought Weight” arrived, I decided to tie a smaller version using chickabou feathers and legs of smaller diameter rubber strands.    It proved to be exceptionally successful on Basie Vosloo’s Birkhall stretch of the Sterkspruit River in Barkly East.  I fished it across and down with appropriate twitches to lure trout away from their holding places in the undercut banks and they responded with sometimes startling alacrity. The rivers and streams in Barkly East, Rhodes and Maclear carry a heavy load of leaves and twigs because of the willow and other trees on the banks. The fish thus ignore items in the drift which are inert and the manipulated fly – lifts, or twitches – is essential for success. Flies with innate movement created by mobile hackles, tails or body material that are easily animated by the rod tip or the line hand enhance the potential of a strike.

The arrival of # 18 jig hooks from Dohiku (available from Upstream in Cape Town, Allen ( available by mail order from the African Fly Angler) and Mouche (available through Gordon van der Spuy) led me to relook this pattern because it is less likely to get snagged on the river bed than conventional hooks. It is a design more than a pattern and the objective is to get the maximum movement. Soft, mobile materials are accordingly used.

Orange hot spot

The Pheasant Tail Nymph with an orange hot spot has become a religion for local anglers and Alan says there might be some reason for this.  The legs and pincers of the Potamonautid crab are tipped with orange and, when it is in berry, the orange eggs glow through the abdomen. This, he says, might well be a trigger point which results in takes.

I use a 2mm orange slotted tungsten bead and this and the jig hook result in it fishing head down and hook point up. If you need more weight attach a strand of fine lead wire on top of the hook shank and this will cause it to sink more horizontally.

Tying Instructions - Filoplume version

1 Attach the 2mm slotted tungsten bead to the hook and tie in tail of marabou or fur from a Zonker strip

2 Tie in copper wire rib and a filoplume feather along with an ostrich feather and two strands of peacock herl. The peacock herl and ostrich feather separate the turns of filoplume feather and prevent it from matting together. At the same time they provide their own subtle movement and shine.

3 Palmer the feathers forward to a position a few millimetres behind the bead,  rib with copper wire and tie off.  Leave a gap between the feather body and the hook eye for the rubber legs

4 Take two strands of barred fine, Tentacle rubber, fold them around the thread and attach them to the top of the hook shank. Do the same on the bottom of the hook shank and splay the eight rubber strands around the hook shank with thread wraps. If any of them are too close together and likely to mat, snip them out. (As an alternative you can use translucent “Bait Cotton” which salt water anglers use to tie soft baits like shrimp to the hook. This material can be mottled in different colours with a permanent marker.)


5674 PB210499

Two versions of the author’s rubber hackle crab pattern. The authors version is  above  and the Gartside version is below it.

Keep in mind that the movement of flies like this will be enhanced if you use Lefty Kreh’s Non-slip Mono Loop knot.


Given the many close-copy crab imitations developed for bonefish and permit it is somewhat surprising that such patterns are not often fished in South African rivers and dams. Giordano (Zamps) Zamparini who fishes the rivers in Magoebaskloof (Polokwane) has however produced an outstanding imitation – utilising a felt wad bought from gun shops that cater for black powder marksmen. A chapter written by him about this fly will be included in the book on indigenous South African fly patterns which Peter Brigg and I are compiling and which we hope to have published next year. Zamps says the crabs are born in early spring and this pattern is exceptionally effective at that time.

 6745 Basic Craimitation 1

Zamps Zamparini’s Powder Wad Crab

Platanna tadpole

The other staple in the diet of trout caught in Somerset East is the platanna tadpole and the HOT Fly (Hobson’s Original Tadpole) and other patterns developed by Alan - such as his justly-famous Mottled Dragon - can now be purchased from him and they are produced by Julihana Johannes, a talented local fly tyer who he has trained.

 321 Alan Julihana

Alan Hobson and Julihana Johannes who will now be tying Alan’s patterns for customers

 It was a Zonker Strip Mrs Simpson which brought him the record for the heaviest rainbow trout ever caught in a South African river, the 14 lb 6 oz fish caught in the Little Fish River on 8 November 2013.

 6768 Alan Hobson  Little Fish River

Alan Hobson’s record trout – tadpoles, crabs and dragonfly nymphs on the menu.

A year ago I wrote about the exceptional barbel fishing at Darlington Dam near Somerset East in my article on this website, “Barbel on Beetles”.


 8989 Andrew Parsons 10 kg

Andrew Parsons with a typical Somerset East barbel – they grow to twice this size!

Well, that venue is no longer available because the area where he fished has now been incorporated in the Addo National Park. Alan told me with a chuckle that he has found another dam, Lake Arthur near Cradock with equivalent fishing and that when Mike Dolhoff and Andrew Parsons visited it they caught, in three hours, about twenty barbel between them weighing up to 10 kgs. He says that there are several similar dams close to Somerset East and the barbel, which are not indigenous to the Eastern Cape, gained access to the province when the Orange River Project in the 1960’s diverted water from the Vaal River in the Great Fish and Sundays Rivers.


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