WORLD RECORD BASS IN KARIBA?

The possibility of bass infiltrating Kariba has long been a topic for debate, and as interest escalates with increasing catches of bass in the lake - speared and caught on rod and line - it is of interest to look at some of points associated with their emergence in this man-made lake.

There has never really been any doubt that eventually bass would find their way into Kariba, our biggest water impoundment and one of the largest man made water bodies in the world. The northern drainage system of Zimbabwe is home to many of Zimbabwe's prime bass dams, and almost all are linked to the major river systems, many of which find their way into Kariba. Bass have already been identified in most river systems around the country (normally escaping from small and medium sized dams), and have in many cases, been able to establish sustainable populations without any major influence from man. In addition, one cannot rule out the well-wishing Bassing enthusiast who may have released his favourite fish into Kariba, in the hope that one day this 5 000 square kilometre haven would be home to some of the biggest, meanest bass in Africa, and indeed the world. After all, the conditions and general habitat do seem ideal.

Given these facts, there can be no doubt that it is only a matter of time before anglers start catching bass regularly in Kariba. Perhaps the first question that comes to mind is, what effect is this species likely to have on the indigenous tigerfish? Research by the Lake Fisheries Institute in Zimbabwe is on-going, but as far as bass and tigerfish boffins (anglers in this case) are concerned, the two species should be able to co-exist with little immediate effect on the indigenous tigerfish and other species for that matter. Long term alterations in the eco-systems though are certain, and were probably a foregone conclusion when bass were first introduced to Africa in the 1930's.

Tigerfish are primarily an open water fish. Known to shoal, they constantly roam the medium to deep waters (although normally found near the surface) in search of their favourite food, the Kapenta. Juvenile fish are found around marginal structure in shallow water, with some bigger fish roaming on the edge of this, often picking off careless juveniles in acts of cannibalism. Tigerfish are known to cannibalise smaller fish of up to 40% of their own body length. This fact, and a dependency on specific depths by different sized fish, conveniently separates distinct groups with each occupying a niche in the lake, often utilising different links in the food chain, and in some cases forming a link themselves. Apart from other tigerfish, they have few natural predators fast enough or big enough to threaten them, and with the exception of the disastrous effects man continues to have on their populations (i.e. mass poaching, indiscriminate removal by anglers), there is no reason to believe that this balance should change.

The tigerfish has a specific spawning regime that is dependent on flowing water. They are believed to migrate up stream in their natural river environment to spawn, although it is unclear exactly where the act takes place. In Kariba the major rivers such as the Sanyati, Nyaodza and Ume teem with migrating tiger during the summer months, triggered by the faster flowing water of these historic breeding grounds.

In contrast, Largemouth bass are traditionally a lake or dam fish, preferring still waters. Their spawning habits can be likened to many of the indigenous bream species present in Kariba with a preference for shallow (one to two metres) water and a firm, gravel substrate, but will nest on submerged anthills, and among rocks. Spawning is primarily dependent on water temperature (triggered at about 18 degrees centigrade) and to a lesser degree on P.H. levels and light conditions. In Kariba, with its warm climate, it is possible that bass will spawn from as early as June or July, and continue doing so for most of the year subject to other favourable water conditions, like clarity, level etc., laying up to 15 000 eggs at one time, compared to almost a million laid by tigerfish.

Habitat preference, generally speaking, is vastly different to that of the tiger as well. Bass are basically a shy, lazy fish, preferring a shallower depth with plentiful structure. Territorial, they will establish a small home range, normally dominated by a prominent structure feature, from where they lie in wait, attacking unwary prey as it passes by. This need for fairly dense structure and the ambush feeding technique, should be enough to separate bass from tigerfish as far as the food chain is concerned. Juveniles of both species, are likely to be the only fish to compete, and here it is logical to assume the more voracious tigerfish will dominate, picking off the slower, less aggressive bass.

Predictions are that bass will slot into the food chain, utilising a parallel link with tigerfish, but not necessarily conflicting with it. Bream, especially species such as the Happy (because of its more streamlined shape), are likely to form the major part of the adult bass' diet. The spawning of kapenta in shallows (normally between September and March), will provide a sustained food supply for juvenile bass produced some months before, but is likely to be ignored by bigger fish in preference to the many and prolific bream species inhabiting the same areas.

So what can be deduced from all this? Certainly the bass will do well in Kariba. The highly stable conditions afforded by such a large water body are ideal for any species, and well-suited to bass. The marginal (relatively speaking) fluctuations in water level will serve to release nutrients that support the lower levels of the food chain depended on by growing bass, and the suitable water temperatures will have a significant effect on bass viability and prolong growth periods. The recent All-Africa record bass of 7,995kg taken from Zimbabwe's Lowveld (where conditions are very similar to Kariba) is evidence of what Africa is capable of, and especially so in the warmer climes of low lying altitudes. The accompanying table of past Zimbabwe (and some All-Africa) record fish demonstrates the steady climb in weights, especially after the introduction of the faster growing Florida strain in the 1980's. This healthy initial food source (kapenta) coupled with a prolific supply of bigger bream for growing fish, and conditions which support longer sustained growth, could mean world record bass!

Although bass could take as long as 20 years to establish a viable angling population in Kariba, its potential growth rate of up to two kilograms a year (with a suitable food supply) will produce some big fish. Because of the sheer size of Kariba, and varying conditions throughout its waters, it is expected that bass will initially colonise certain areas close to their point of entry, and later move throughout the lake seeking conditions considered ideal. As most highveld rivers drain into or close to the eastern basin of Kariba, and it is believed that significant numbers have been released by anglers here, this area will likely be the first to produce significant catches of bass. Other species such as tigerfish will limit bass presence in some areas, as will the lack of significant structure in others. The limited life span of most bass (not more than about 10 years) will mean a slow colonisation of Kariba, with viable populations tending to dominate those areas first colonised, in preference to roaming the vast waters of virgin territory.

The advent of floating bream cages for commercial rearing of the Niloticus bream (another alien fish) in the eastern basin has seen a change in the environment in very short time. Escapees from the cages have colonised the nearby Antelope Island archipelago with a resultant increase in big tigerfish (as evidenced by the recently broken world record in excess of 16kg), and a change in even land based creatures (like fisheagles). It is quite likely that bass which are known to have been released close-by will take advantage of this group of islands with its suitable and varied structure forms and water depths.

It is possible also that bass as we know them in Africa, could mutate in Kariba over a period of time, adapting to the big water lifestyle. The tigerfish, historically a river fish, has changed considerably since Kariba was built, growing bigger and heavier than ever before, with a shift in feeding habits, and some suggest even breeding habits (it is thought by some that tiger may now spawn in the lake itself). American bass experts believe that in order to grow record breaking fish, it is necessary to indulge in a bit of genetic engineering, as ideal conditions are not enough. The practice of introducing record strain fish and continuously varying genetic strains (i.e. introducing fresh blood) is necessary to grow big fish. This may happen naturally in Kariba, given the high number of prime bass dams that eventually feed into the lake.

While there have been a growing number of reports of bass catches in the lake - fish often taking drifted fillet baits set for tigerfish - it is likely that more have not been caught simply because they are not being targeted. It is not unlikely either that some bass anglers have indeed targeted and caught bass, but have kept their discovery under wraps till such time as a viable population emerges which is capable of sustaining an active bass fishing industry in Kariba.

Until such time as we are catching bass on a regular basis in Kariba, one can expect their presence to seemingly come and go. We have seen bass populations apparently decline in inland dams soon after their introduction, only to be amazed at their sudden re-appearance years later in greater numbers and sizes than previously. In spite of being an exotic (imported) species, the bass is hardy, adaptable and able to withstand extremes of conditions many indigenous fish succumb to. They even have an uncanny knack of avoiding nets (partially because of their habitat), which will protect them from decimation by poachers on the scale seen with tigerfish in past years.

As anglers, we can only view these developments with positive excitement. Bass in Kariba are likely to have a revolutionary effect on sport angling and in particular bass angling. Tourism on an unprecedented scale (supported by international bass fishermen) will boom with world attention shifting from the great lakes of America, the home of Big Bass, to Africa. The many tourism industries that revolve around fishing in Kariba will benefit, and those associated industries such as the boat manufacturers, tackle suppliers and fishing safari operators in Zimbabwe and many other African states will undergo a transformation previously unseen.

We must accept that in spite of the very positive aspects of this exotic fish in Kariba, there are likely to be some negative ones also. It is probable that there will be some alteration to the ecosystem, even if we do not notice it. A decline in certain species or a shift in the food chain that will only be evident in future lifetimes. Truthfully, we do not know what the long-term ramifications could be, and in the interests of protecting our indigenous identification, should not actively stock Kariba with bass. As outlined, this will happen naturally, and like it or not, the bass is a part of Zimbabwe. Be that as it may, relocating exotic fish without permission is an offence, and should not be encouraged by anglers, especially in view of the possible disastrous effects indiscriminate stocking could have, as with the piranha in some parts of the United States.

In conclusion, let me paint a picture. The sun is just creeping over the horizon, painting the silhouettes that golden orange, synonymous with Africa. The dark shadows of grazing buffalo and elephant come to life as the growing sun picks them out along the shoreline. You've just run 30 kilometres from the houseboat, which in turn cruised 100 kilometres to get you to your favourite hot-spot. The famous forests of dead Mopani stand ghostly, even in the growing light, and as you pick out the watchful gaze of a resident fisheagle, the gentle tap tap transmitted through your favourite graphite rod tells you your hot-spot is still productive.

Your power driven strike sends a grazing herd of impala, not twenty yards way, into panicked flight. Distracted only momentarily, you look back just in time to catch sight of the fish, gills flared, head shaking, as it tries to throw your bait. A short battle ensues with all concentration focused on keeping the fish away from the unforgiving petrified forest. As you boat the fish, the fisheagle throws its head back in the spiritual cry of Kariba, applauding your skilful efforts in subduing your prey.

With the sun already prickling the skin on your bare back, you slide the fish gently over the side of the boat, releasing it back to the clear emerald water. You can't help feeling a brief pang of disappointment as she swims away, another ten pounder, one of three caught in two days. You cast again, targeting the tree where you caught the seventeen pounder last week, tensed with anticipation, you pray for that magical twenty pound bass...

This is bass fishing on Kariba!

The "Eastern Basin" area of Lake Kariba

TABLE OF ZIMBABWE BASS RECORDS

Date/Time                    Place                                    Angler            Weight/Length/Girth

*1953                        Mushandike,Masvingo              J.Erwing         3,771kg -  

*08/10/70                  Muturikwe, Masvingo               A.Hodgeson    3,997kg -

*--/08/77                   Muturikwe, Masvingo               G.Banks         4,040kg -

--/--/87                      Two Trees, Mhangura              M.Williemse    4,290kg -

30/08/87                    Private Dam, Shamva             H DuPlessis     4,915kg -

18/03/89 4pm             BlackmoreVale, Cheg.             J.VanDiepen   4,947kg 57cm51cm

25/01/90 6.30pm        Chiredzi                               D.Duncan         5,150kg 66cm51cm

21/06/90 2,30pm        Two Trees, Mhangura            R.McNeilage     5,500kg 67cm50cm

09/12/90 2,30pm        BlackmoreVale, Cheg.              E. Smit         5,610kg -

10/10/94 3,30pm        Biri River, Selous                M. Draga          6,275kg 67cm53cm

21/09/96 12,45pm      Priv. Dam, Centenary               B.Buckby      6,500kg 61cm57cm

05/07/98 11,15am      Manyame Dam, Darwendale      N.Mkondo     7,295kg 67cm56cm

08/08/01 12pm           Private Dam, Lowveld             R. Patel          7,995kg 67cm54,5cm

*These fish were the original Northern strain, a smaller, slower growing fish first introduced in 1932. The introduction of the faster growing Florida strain in 1981, and its cross breeding with the original strain, can account for the larger record fish from the late eighties onward.

“Ant” Williams