NCYWGOrange-Vaal Largemouth Yellowfish
Labeobarbus kimberleyensis
report by Pierre de Villiers
Introduction
The Orange-Vaal river system is the largest in South Africa. The Vaal originates on the grassy plains of the Mpumalanga highveld whereas the Orange river springs up in the sub-alpine Lesotho mountain kingdom. The two rivers meet near Douglas in the Northern Cape from where the Orange river winds its way to the Atlantic Ocean at Oranjemund. The river system harbours what is perhaps South Africa's finest freshwater gamefish, the Orange-Vaal Largemouth Yellowfish, Labeobarbus kimberleyensis.
Largemouth yellowfish are sensitive to changes in water quantity, quality and habitat destruction and utilisation pressure and for this reason are often used by river health authorities as a sensitive indicator species. What this means is that the presence and condition of these fish play a vital role in allowing river managers to gauge the success or failure of management interventions or programmes such as river rehabilitation and catch-and-release regulations. moreover the largemouth yellowfish is a classic angling species that provides an angler with a superb fight once hooked. The initial run is unsurpassable as a freshwater angling experience. The catch-and-release ethic for this premier gamefish is now firmly established among fly and artlure anglers and is a great boost to its conservation.
Biology and Ecology
The largemouth yellowfish is South Africa's largest
Labeobarbus species and attains an impressive 22kg in mass.
Not surprisingly, it is partial to large rivers like the Orange and
Vaal, extending down to the estuary at Oranjemund and well into the
larger tributaries.
It favours large pools and adapts well to weirs and dams as these
provide excellent habitat and an abundance of food.
It
is a top predator, preying on smaller fish, crabs, frogs and
insects. in common with other yellowfish species, the
largemouth is a slow grower with a low egg to body mass ratio
(fecundity). It only becomes sexually active at a fork length
of 45cm when it is approximately 8 years old.
The eggs, like those of the smallmouth, are relatively large and
have a double "shell" to survive spawning in rough rapids and riffle
water. Whereas the spawning requirements of this species are
known the exact spawning times and places still need to be
identified. Indeed, to date, very few spawning fish have been
observed which makes the natural breeding cycle a bit of a mystery.
On the other hand, largemouth yellowfish have been spawned and
reared successfully and consistently at the Gariep State Hatchery in
the Free State province.
Status
Although there is no scientific evidence suggesting that the Orange-Vaal largemouth yellowfish is increasing in numbers, its conservation status has recently been changed from "Vulnerable" to "Near Threatened". This change was motivated by anglers' catches which have shown that largemouth yellows are more widespread and abundant across their distribution range than previously recognised. Down listing does not mean that a "free-for-all" approach to managing largemouth yellowfish should now ensue. This is arguably our premier freshwater gamefish in South Africa and being a top predator it is never as plentiful as its cousin, the smallmouth yellowfish. For this reason the Yellowfish Working Group (YWG) has recommended that largemouth yellowfish should be protected by a "no take" policy. This will hopefully be legislated in the near future.
Threats
Largemouth yellowfish face essentially the same threats as smallmouths as they occupy the same rivers and share similar habitats. These threats have already been covered in the preceding pages on smallmouth yellowfish and only those aspects of specific relevance to largemouths will be discussed below.
Over abstraction of water during the dry winter months often result in natural over-wintering pools being sucked dry. In certain places such as highly degraded rivers, the building of dams and weirs has been somewhat beneficial to largemouth inasmuch as they created huge "pools" that support large numbers of fish. With the onset of flooding during early summer, the fish can then migrate from these sanctuaries to upstream spawning sites. On the negative side, dams and weirs act as serious barriers to fish migration, fragmenting populations and inhibiting normal genetic exchange.
Inadequate fisheries management is a problem because of inconsistencies in provincial fisheries regulations and policies - in some provinces, notably Free State, largemouth yellowfish must be released when caught whereas in some other provinces there is a catch limit of up to 10 fish.
Angling for this premier species has always been popular with trophy hunters who target specimens of over 10kg for the awesome sport they provide. Unfortunately not all big fish are released, which is a tragedy as the bigger fish tend to be those females that are the most productive breeders - egg quantity is directly related to fish size. Wading through potential spawning habitat during spawn time is a contentious matter, the effects of which still need to be determined. This can only be done once scientists have determined when and where largemouths spawn so that anglers can adapt their tactics to minimise their impact on the fish.
Conservation and Utilisation
The Orange-Vaal River Yellowfish Conservation and Management Association (OVRYCMA) is an association of interested and affected people who want to conserve the valuable yellowfish resource of this river system more effectively.
Legislative matters dealing with conservation as well as the National River Health Programme have been dealt with in the pages on smallmouth yellowfish and need not be repeated here.
The largemouth yellowfish is not a well studied species and it is
essential that in future we have a much better understanding of its
biology and ecology. Fortunately, several exciting research
projects are under way addressing aspects of its biology. A
number of largemouth and smallmouth yellows have been tagged and
released in OVRYCMA as well as NCYWG territory and researchers are
currently monitoring their movements by sophisticated telemetric
methods.
Another important scientific study seeks to compare genetic and
morphological characteristics of largemouth and smallmouth
yellowfish throughout their natural distribution range.
On a different track, a socio-economic study is being conducted to
make stakeholders aware of the value of the yellowfish resource in
their domain.
Largemouth
yellowfish is a highly valued angling species. Although the
main angling pressure within the Orange-Vaal system is on the
smallmouth yellowfish, anglers increasingly want to catch the larger
and more challenging largemouth. Capture techniques for
largemouth yellowfish are continually being improved with new flies
and lures appearing almost every month. Skilful bait anglers
on the other hand have always had great success in taking largemouth
on crabs and fish baits. It is gratifying therefore that
organised angling has become so supportive of planned and
implemented measures to conserve these two premier angling species.
Subsistence fishers tend to target the more abundant smallmouth yellowfish and sharptooth catfish, but as they mostly use worms, crabs, fish baits and the like, it is not rare for them to catch largemouth. These fish are not released as they represent a good family meal. Ideally all anglers should be taught to identify largemouth yellowfish and educated about the need to release them once caught.
The Free State Department of Tourism, Environmental and Economic Affairs has provided yellowfish juveniles to stock dams. Largemouth yellowfish that were introduced into Sterkfontein Dam in 1994 have prospered to the extent that fish of over 4kg are now being caught. Hatcheries should be discouraged as a means to conserve this species - effective river management for obvious reasons being the preferred method of conservation.
This report is an excerpt from
the WRC Report TT302/07 and emanates from a project entitled
"Status of Yellowfish Populations in South African Waters".
The complete report is obtainable from the Water Research Commission
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