258
13. Nile Perch Population Dynamics in Lake Vi ctoria:
and our experience in building it sugges t that active adaptive management of the fishery must rep lace passivity and indecision if the goals of
fishery managers, conservatio nists, and eco nomists are to be met.
73.7.7. The Lake and Its Fishes
Circa twelve thousand years ago, a valley between the great rifts of East
Africa refilled with water, and the great Lake Victoria rose again in its most
recent incarnation (Stager et al. 1986). This largest of all tropical lakes has an
evolutionary history whose details have yet to be reconstructed . What we do
know is that through a combination of rep eated invasions and bursts of speciation there arose an almost entirely endemic flock of abo ut 500 species of
haplochromine fishes (Fryer and lies 1972; Greenwood 1981; Kaufman 1997;
Kaufman and Ochumba 1993; Lowe-McConnell 1995; Ribbink 1988).
The Lake Victoria haplochromine species flock mirrors the cichlid flocks
of Lakes Malawi and Tanganyika in its general features, but the Lake Victoria basin itself is much younger than either Malawi or Tanganyika. Armed
with an array of feeding modalities and their versatile ph aryngeal jaws
(Kaufman and Liem 1982; Liem 1973), the haplochromines have dominated
Lake Victoria in terms of species diversity and biomass, for at least the last
12,000 years and most likely throughout most of the lake's existence (Fryer
and lies 1972; Greenwood 1981).
But more than forty years ago, the story of Lake Victoria took a drastic
tum . In an attempt to convert the relatively small haplochromine cichlids
into a larger fish with export value, Nile perch (Lates niloticus) was introduced (Anderso n 1961; Hamblyn 1961). The plan ultimately worked. In the
mid 1980s Nile perch populations exploded, correlated with precip itous declines in haplochromine diversity and standing stocks (Goldschmidt et al.
1993; Kaufman 1992; Kaufman 1993; Kaufman and Cohen 1993; Kaufman et
al. 1997; Kaufman and Ochumba 1993; Kaufman et al. 1993; Kudhongania et
al. 1992; Ogutu-Ohwayo et al. 1997; Seehausen et al. 1997; Witte et al. 1992),
Drastic changes in the lake and its food web have since bee n observed
(Bootsma and Hecky 1993; Goldschmidt et al. 1993; Gophen et al. 1995;
Hecky et al. 1994; Ligtvoet and Witte 1991; Livingston 1980; LoweMcConn ell 1994; Moreau 1995; Moreau et al. 1993; Ogutu-Ohwayo et al.
1997). Commercial and artisanal fisheries have shifted focus to exploiting primarily Nile perch, Nile tilapia (Oreoc hromis n iloticus), and a pelagic minnow
known locally as omena or dagaa (Rastrineo bola argentea) (Kudhongania et
al. 1992; Pitcher and Hart 1995; Witte and Densen 1995). All other fisheries
have been virtually eliminated excep t for the occasional capture of the native
food fishes, some so highly valued that fishermen refuse to sell them.
Nile perch has fulfilled its bestowe d expec tations of deve loping a produc tive export fishery, but the sustainability of the fishery, and the survivability of seve ral hun dred endemic fishes, are both very much in question.
Through little fault of their own, managers in the fisheries, forestry, and
13. Nile Perch Population Dynamics in Lake Vi ctoria:
and our experience in building it sugges t that active adaptive management of the fishery must rep lace passivity and indecision if the goals of
fishery managers, conservatio nists, and eco nomists are to be met.
73.7.7. The Lake and Its Fishes
Circa twelve thousand years ago, a valley between the great rifts of East
Africa refilled with water, and the great Lake Victoria rose again in its most
recent incarnation (Stager et al. 1986). This largest of all tropical lakes has an
evolutionary history whose details have yet to be reconstructed . What we do
know is that through a combination of rep eated invasions and bursts of speciation there arose an almost entirely endemic flock of abo ut 500 species of
haplochromine fishes (Fryer and lies 1972; Greenwood 1981; Kaufman 1997;
Kaufman and Ochumba 1993; Lowe-McConnell 1995; Ribbink 1988).
The Lake Victoria haplochromine species flock mirrors the cichlid flocks
of Lakes Malawi and Tanganyika in its general features, but the Lake Victoria basin itself is much younger than either Malawi or Tanganyika. Armed
with an array of feeding modalities and their versatile ph aryngeal jaws
(Kaufman and Liem 1982; Liem 1973), the haplochromines have dominated
Lake Victoria in terms of species diversity and biomass, for at least the last
12,000 years and most likely throughout most of the lake's existence (Fryer
and lies 1972; Greenwood 1981).
But more than forty years ago, the story of Lake Victoria took a drastic
tum . In an attempt to convert the relatively small haplochromine cichlids
into a larger fish with export value, Nile perch (Lates niloticus) was introduced (Anderso n 1961; Hamblyn 1961). The plan ultimately worked. In the
mid 1980s Nile perch populations exploded, correlated with precip itous declines in haplochromine diversity and standing stocks (Goldschmidt et al.
1993; Kaufman 1992; Kaufman 1993; Kaufman and Cohen 1993; Kaufman et
al. 1997; Kaufman and Ochumba 1993; Kaufman et al. 1993; Kudhongania et
al. 1992; Ogutu-Ohwayo et al. 1997; Seehausen et al. 1997; Witte et al. 1992),
Drastic changes in the lake and its food web have since bee n observed
(Bootsma and Hecky 1993; Goldschmidt et al. 1993; Gophen et al. 1995;
Hecky et al. 1994; Ligtvoet and Witte 1991; Livingston 1980; LoweMcConn ell 1994; Moreau 1995; Moreau et al. 1993; Ogutu-Ohwayo et al.
1997). Commercial and artisanal fisheries have shifted focus to exploiting primarily Nile perch, Nile tilapia (Oreoc hromis n iloticus), and a pelagic minnow
known locally as omena or dagaa (Rastrineo bola argentea) (Kudhongania et
al. 1992; Pitcher and Hart 1995; Witte and Densen 1995). All other fisheries
have been virtually eliminated excep t for the occasional capture of the native
food fishes, some so highly valued that fishermen refuse to sell them.
Nile perch has fulfilled its bestowe d expec tations of deve loping a produc tive export fishery, but the sustainability of the fishery, and the survivability of seve ral hun dred endemic fishes, are both very much in question.
Through little fault of their own, managers in the fisheries, forestry, and