ArticlePDF Available

The Origins of the Nile Perch in Lake Victoria

Authors:

Abstract

The ways in which economic, social, and political forces lead to species introductions are an important, if overlooked, aspect of ecology and conservation. The nonnative Nile perch (Lates niloticus) in Lake Victoria, and the ecological changes associated with the species' establishment and expansion there, has elicited tremendous attention from biologists. Yet it has never been clear why, when, or by whom the fish was introduced. Here I outline the history of fishery research and management in East Africa and explore the circumstances that led to the introduction of the Nile perch. The evidence suggests that repeated secretive introductions were made in the mid-1950s by members of the Uganda Game and Fisheries Department as part of a bifurcated effort to improve sport fishing on the one hand and to bolster fisheries on the other. Fisheries scientists affiliated with the East African Fisheries Research Organization opposed the introduction, but were ineffective; I suggest that this failure stemmed partially from their inability to engage effectively with political processes.
Biology in History
780 BioScience • September 2005 / Vol. 55 No. 9
Most ecologists and evolutionary biologists are
familiar with the saga of the introduced Nile perch
(Lates niloticus) in Lake Victoria. The explosion of the lake’s
Nile perch population in the 1980s was monitored closely, be-
cause it coincided both with a fivefold increase in the economic
value of the fishery (Reynolds et al.1995) and with a halving
of the lake’s 500-species haplochromine cichlid flock (Ogutu-
Ohwayo 1990).This reduction in species and functional di-
versity restructured the lake’s ecology; for example, the
disappearance of zooplanktivorous haplochromines coin-
cided with a dramatic sixfold increase in biomass of the zoo-
planktivorous cyprinid Rastrineobola argentea (Wanink 1999).
By the early 1990s, what had been a diverse multispecies
fishery rested on only three species: the nonindigenous Nile
perch, the nonindigenous Nile tilapia Oreochromis niloticus,
and the diminutive R. argentea. Although some of the blame
for the cichlid extinction spasm has been shifted from the Nile
perch to other anthropogenic factors, such as overfishing
and eutrophication (Seehausen et al. 1997), the Nile perch was
certainly a major contributor.
The lucrative fishery that developed for Nile perch has it-
self had diverse impacts. Around the lakeshore, enthusiasm
over the increase in the value of the fishery has been tempered
by concerns about species loss, increased economic stratifi-
cation, and the fact that most Nile perch is exported and lo-
cally unaffordable (Pringle 2005). Ecologically, the intense
fishing pressure on Nile perch has depressed its populations
to the extent that certain species of the remnant cichlid fauna
are resurging (Witte et al. 2000).
These events have spawned hundreds of publications,
making the Nile perch in Lake Victoria one of the best-
studied invasive species in history (for a recent review, see
Balirwa et al. 2003).Yet despite this wealth of knowledge,there
remains confusion about exactly when, why, and by whom the
Nile perch was introduced into Lake Victoria. The literature
offers a range of dates for the introduction, from the 1920s
to the 1960s; tracing the tortuous citation chain to the origins
of these dates reveals a fundamental uncertainty about when
the Nile perch was first introduced.Likewise, the motivations
for this anthropogenic introduction, often ambiguously as-
cribed to a desire to “increase productivity,” have not been
thoroughly explored.
Unlike many introductions , which occur b y acc ident o r are
made quietly by private citizens, the introduction of Nile
perch into Lake Victoria was hotly debated at the highest
levels of the British administration in colonial East Africa. As
today’s ecologists often note, colonial ecologists opposed the
proposal (Fryer 1960).The eventual introduction of the Nile
perch therefore represents the failure of ecologists to com-
municate and implement their vision for Lake Victoria.
Although this failure was at least partially due to the famil-
iar problem of trying to regulate a common resource, I
suggest that there were two additional factors at play.
Robert M. Pr ingle (e-mail: pringle@stanford.ed u) was a Thouron Fellow in
the program in Economic and Social History at the University of Oxford
when this research was conducted; he is now a doctoral student in the
Department of Biological Sciences at Stanford University, Stanford,CA 94305.
Althou gh his cur rent focus is tropica l ecology (esp ecially of Afri can savannas),
he maintains an active interest in history and its applications to ecology and
environmental policy. © 2005 American Institute of Biological Sciences.
The Origins of the Nile
Perch in Lake Victoria
ROBERT M. PRINGLE
The ways in which economic, social, and political forces lead to species introductions are an important, if overlooked, aspect of ecology and
conservation. The nonnative Nile perch (Lates niloticus) in Lake Victoria, and the ecological changes associated with the species’ establishment and
expansion there, has elicited tremendous attention from biologists. Yet it has never been clear why, when, or by whom the fish was introduced. Here
I outline the history of fishery research and management in East Africa and explore the circumstances that led to the introduction of the Nile perch.
The evidence suggests that repeated secretive introductions were made in the mid-1950s by members of the Uganda Game and Fisheries Department
as part of a bifurcated effort to improve sport fishing on the one hand and to bolster fisheries on the other. Fisheries scientists affiliated with the East
African Fisheries Research Organization opposed the introduction, but were ineffective; I suggest that this failure stemmed partially from their
inability to engage effectively with political processes.
Key wo rds : A fri can c ich li ds, exo tic s pec ie s i ntr od uct ion s, ex ti nct ion , i nv asi ve spe ci es, Haplochromis
September 2005 / Vol. 55 No. 9 BioScience 781
The first of these factors stems from the nature of British
colonialism in East Africa and the role of science within it. The
colonial enterprise underwent a transformation in the late
1930s. The Great Depression had highlighted human vul-
nerability and prompted new concern for the welfare of
Britain’s “dependents” in the colonies. Likewise, confrontation
with Nazi Germany had made clear,among other things, the
true ugliness of imperialism. Hence the shift to what histo-
rians have called the second colonial occupation”(Low and
Lonsdale 1976): the paternalistic attempt to guide Africa
through development and into modernity,in which eventual
self-government was a stated aim.But administrators in this
new developmental bureaucracy lacked the patience of their
predecessors for basic ecological research. They wanted im-
mediate results, practical scientific means of running an ef-
ficient transitional empire. The scientists who opposed the
introduction of the Nile perch into Lake Victoria failed to en-
gage effectively with these emergent political trends; as a re-
sult, they were considered too cautious and their research too
pure. They were thus kept to the political margins,where they
found it difficult to influence policy.
The second factor relates to the history of ecology and
evolutionary biology as disciplines. The late 1950s and 1960s
were a particularly fertile time for ecological and evolution-
ary ideas; several conceptual developments of that period
would arguably have enabled fisheries scientists in East Africa
to make a more forceful case against the Nile perch intro-
duction, had the debate taken place a few years later than it
actually did.
Whether or not it was “right” to introduce the Nile perch
into Lake Victoria is a contentious and subjective question
(Pringle 2005). I do not wish to take a stand on that issue here.
Neither am I interested in apportioning blame—or credit—
for the Nile perch’s introduction, the haplochromine extinc-
tions, or the economic growth of Lake Victoria’s fisheries. My
only intention is to shed light on the social, economic, sci-
entific, and political processes that led to these important
events.Thus, although I speak of the failure”of scientists to
prevent the introduction,I do not mean it in a pejorative sense.
It was simply the failure of a stated objective.
The origins of fishery research and
management, 1921–1950
To t h e B r i t i s h i n E a s t A f r i c a , L a k e V i c t o r i a ’ s 7 0 , 0 0 0 s q u a r e k i l o -
meters (km2) seemed capable of supporting outstanding
fisheries. The 1901 completion of the railroad from Mombasa
to Kisumu, which enabled the transport of lake fish to Nairobi
marketplaces, provided an added incentive to maximize fish-
ery production.Yet by 1921 there was concern that fish yields,
especially of ngege (Oreochromis esculentus), were declining.
One observer,assistant surgeon E. J. H. Oorloff, complained
that Africans were overfishing the lake with the aid of imported
equipment—“the better class of natives use English nets”—
and recommended that a closed season be implemented
(Oorloff 1921). However, administrators were hesitant to
regulate fishing, principally because their ignorance of fish
biology left them unsure whether “any good results would
accrue from putting fishermen to the hardship of a general
close season” (Caldwell 1923); it was suggested that museum
experts be recruited to survey “the finny denizens of our
premier pool” (Anonymous 1923).
To t h a t e n d , M i c h a e l G r a h a m a n d E d g a r B a r t o n W o r -
thington traveled from Britain in 1927 and spent a year
steaming around Lake Victoria. Their work resulted in Gra-
ham’s (1929) The Victoria Nyanza and Its Fisheries. In that
book, Graham recommended that a permanent fisheries re-
search institute be erected to continue scientific study of the
lake. This led to the construction in 1947 of a research labo-
ratory in Jinja, Uganda, which became home to the East
African Fisheries Research Organization (EAFRO). Crucially,
however, an earlier warning by Worthington—that “it would
be a mistake to separate administration from research in the
matter of fisheries” (Worthington 1940)—was ignored. “I
suppose difficulties are bound to go on,” Worthington had
written,“so long as fisheries in Uganda are directly under the
Game Department, while in Kenya they are ? [sic] Agriculture,
and in Tanganyika are directly under the Administration”
(Worthington 1940). Ultimately, however, research and ad-
ministration were indeed separated; the Lake Victoria Fish-
eries Service was created as an interterritorial administrative
body distinct from EAFRO in 1948.
In 1950, the East African High Commission implemented
the Lake Victoria Fisheries Act.The act initiated several con-
servation measures, one of which was the stricture that “any
person who introduces, puts or places into Lake Victoria any
fish, or the spawn thereof, of a species other than that in
Lake Victoria...shall be guilty of an offense against this Act.
Significantly,EAFRO and Lake Victoria Fisheries Service per-
sonnel were exempt from these provisions. And although a
1953 amendment to the 1950 act extended its legislative
reach one mile up “each river and stream entering Lake Vic-
toria,” the rest of East Africa’s inland water remained under
territorial control.
These provisions reflected a growing debate over whether
fishery productivity might be increased by introducing non-
indigenous species into Lake Victoria. Colonial officials were
frustrated that Africa’s largest lake contained relatively small
fish, mostly cichlids of the genus Haplochromis. Hap-
lochromine cichlids were widely utilized by local fishermen,
but the British disdained them, labeling them “trash fish.In
The Victoria Nyanza and Its Fisheries, Graham (1929) wrote,
“It has been suggested to me frequently that Lake Victoria
would be improved if its fish fauna contained some of the Lake
Albert species, such as the Nile perch (Lates) or the Tiger fish
(Hydrocyon)” (p. 23). Graham conceded that this was a rea-
sonable idea, but he urged caution: “In the ngege fishery of Lake
Victoria we have an extremely valuable established fisher y for
a very desirable fish. The introduction of a large predatory
species from another area would be attended with the utmost
danger,unless preceded by extensive research into the prob-
able effects of the operation” (Graham 1929, p. 23).
Biology in History
Biology in History
782 BioScience • September 2005 / Vol. 55 No. 9
Of course, the introduction of nonindigenous fish was a
common practice in colonial East Africa. Beginning in the
1890s, colonial administrators stocked dozens of Kenya’s
rivers with trout, both to entertain themselves and to entice
prospective settlers.Later, in an attempt to stem tilapia declines,
EAFRO blessed the introduction of four nonindigenous
tilapiines (Oreochromis leucostictus, O. niloticus, Tilapia ren-
dalli, and Tilapia zillii) in 1953. Although legal under the
1950 Fisheries Act’s exemption of fisheries officials, these
tilapia introductions were controversial. The British Mu-
seum’s Ethelwynn Trewavas, who saw her opportunity to
map Africa’s ichthyogeography slipping away, had complained
that people were moving tilapia around the continent “in a
slap-happy fashion” (Trewavas 1952). Much later, one-time
EAFRO director Peter Jackson lamented the introductions as
“woolly-headed” and “useless” (Jackson 2000). At the time,
however, the move was rationalized by EAFRO’s “seemingly
paradoxical conclusion that under tropical conditions the
more animals, particularly herbivorous animals, living in a
lake, the more animals that lake can support”(EAFRO 1953).
However, the introduction of a large predatory fish was
viewed with considerably more skepticism by fishery biolo-
gists. Because of the possibility that the Nile perch might
ruin Lake Victorias important tilapia fishery, Worthington
(1929) echoed Graham’s caution, urging that “the recom-
mendation made by Mr. Graham that no such project be put in
hand must be endorsed here [italics in original] until extensive
research has been carried out into the effects of the intro-
duction. He later suggested an experimental introduction into
nearby Lake Nabugabo and concluded that “if the introduc-
tion is effected and a natural balance is struck between the Nile
Perch a nd the Lake Na bugabo fish es, the i ntroduction o f the
Nile Perch into Lake Victoria may be considered” (Wor-
thington 1932).
The cautious stance of Graham and Worthington found
support in other quarters. Kenya fish warden Hugh Copley
(1940) wrote that
the question of a predatory fish in Lake Victoria is an inter-
territorial matter and any introduction should take place
only after a most exhaustive and searching investigation. It
has always been a worry to myself having [American]
Black Bass in Lake Naivasha, for it is always possible some
irresponsible person will take this fish and stock a dam
having an outflow (possibly during the season of heavy
rains) to some stream with an ultimate access to Lake Vic-
toria, and thereby introducing a predatory fish whether it
was advisable or not.
This memo captures the essence of the management
dilemma that took shape in the years following World War II.
First, the lake was shared by three territories,and different as-
pects of its administration fell to different organizations, all
of which were disjunct from fisheries research. Second, try-
ing to regulate the species composition of a lake the size of Vic-
toria in an era obsessed with bolstering production was a
monumental job.It implied both monitoring the numerous
rivers and swamps that abutted the lake and policing a 3500-
km shoreline to prevent any unilateral introductions.
Fisheries management in a developmental
empire: 1948–1963
The consecutive ravages of depression and war brought food
supply to the fore of the colonial mind. EAFRO, which owed
its existence to the beneficence of the High Commission and
the Colonial Office, was often pressed to aid in the under-
taking. In 1948, EAFRO director Robert Beauchamp received
an inquiry from the East African Industrial Research Board
in Nairobi about the prospects for an industry, based on the
lake, to “make fishmeal to supplement the animal protein ra-
tion which is deficient to the [tune] of some 1,000 tons per
annum” (EAIRB 1948). Beauchamp’s lukewarm response
prompted chastisement from an official at the Colonial De-
velopment Corporation in London, who urged that “if we keep
bashing at these problems, I think we will find some field for
commercial development!” (CDC 1949). In one extreme at-
tempt to boost production, London-based colonial fisheries
adviser C. F. Hickling (1953) recommended that the fishery
be totally deregulated: “It is possible to exterminate stocks of
game, hence the need for game sanctuaries; but it is in fact im-
possible to exterminate stocks of fish except in a few special
cases.... It would seem a wise principle to assume that a fish-
ery is in a sound condition, requiring no regulation, unless
the contrary can be proven.
EAFRO’s reluctance to throw its weight behind such “prac-
tical” measures, and the tendency of its scientists to work on
problems that had no immediate economic application, was
almost its undoing. In 1954,Worthington received a letter from
the High Commission. “Sir,” it began,“I have the honour to
address you on the question whether or not there still exists
an economic need for fisheries research in the East African ter-
ritories” (EAHC 1954). Copley (1954), frustrated at the po-
litical naïveté of the EAFRO scientists, begged Worthington
to give him something with which he could justify further re-
search to his superiors:
Literally I stand between the Kenya Government with-
drawing its support from Jinja, and Jinja, if you
understand me. The Kenya Government would withdraw
their support tomorrow morning with the greatest of plea-
sure.... Tanganyika would do so the next day. What one is
fighting for is to get all these Governments to believe
that...a lot of the work has practical application NOW; if
we cannot, then good-bye to Jinja.
As far as the scientists were concerned, their various in-
vestigations needed no special justification. Administrators,
however, expected scientists in the colonies to be responsive
to political and economic imperatives. In one revealing
episode, Colonel S. P. Fearon of the High Commission dis-
patched a directive to EAFRO director Beauchamp:“You will
undertake a fishing survey of the deeper waters of the Lake,
it instructed, and “you will exercise the strictest economy”
(Fearon 1955).This wording was so dictatorial that even the
Colonial Office blanched, but Fearon would not budge:
We ar e m e re l y t r y i n g t o l a y d o w n w ha t t h e Co u n c il e x p e ct s
Beauchamp to do, both for his benefit and the Council’s....
To d a y t h e s u c c e s s f u l s c i e n t i s t i s a m a n c o m m a n d i n g a
handsome salary with a host of lesser scientists beneath
him and a large, expensive and complicated organization
to manage.... The scientist of today, in fact, cannot expect
to have his cake and eat it. He must either accept the
restrictions which the expenditure of public money entails,
or he must be content to remain a scientist pure and sim-
ple. (Fearon 1955)
Thus, EAFRO scientists were not in a particularly strong
position to influence policy when the idea of introducing Nile
perch was revisited in the 1950s. Despite considerable effort,
the British had not been able to discover a commercial value
for the “trash” haplochromines. Graham (1929) had sug-
gested that they might be made into fertilizer; others posited
that their function was simply to die,thereby enhancing the
fertility of the lake (Greenwood 1966). Still others suggested
that they were vermin, in that some preyed on economically
valuable tilapia fry, and should therefore be exterminated
(Provincial Commissioner, Nyanza 1939).
The impetus for the revival of the Nile perch introduction
proposal was the Uganda Game and Fisheries Department
(UGFD), which brought together two men who advocated the
idea for different reasons. Bruce Kinloch, chief game warden
from 1950 to 1960, was a devoted big-game hunter and sport
fisherman, and he worked hard to expand the range of the
Nile perch, a “fine sporting and very edible fish” (UGFD
1951, Kinloch 1972). Kinloch’s chief fisheries officer Don
Rhodes believed, according to a contemporary, “that any-
thing whatsoever was justified if it could conceivably
advance the weal of the common man” (Jackson 2000).
Yet UGFD was hamstrung by “certain influential and
conservative-minded quarters” at EAFRO, which opposed
any Nile perch introductions (Kinloch 1972).
However, when the Owen Falls Dam was constructed in
1954, putatively sealing off Lake Victoria from the Nile, UGFD
came into sole regional jurisdiction over the upper Nile and
the attached Lake Kyoga. Within the year, UGFD officials
and local African fish guards had transferred a handful of Nile
perch from the base to the top of Murchison Falls (which
separates Lake Albert from the upper Nile). In 1955, UGFD
officer John Stoneman led a “proper” stocking expedition,
transferring 47 Nile perch from Butiaba on Lake Albert to the
Victoria Nile below the dam, and 100 more to Lake Kyoga at
Masindi Port (Kinloch 1972).
After these steps had already been taken, the debate over
whether to stock Lake Victoria grew louder, with the lines
drawn between EAFRO and UGFD. At a 1955 meeting, Kin-
loch requested consideration of the issue, arguing that al-
though the Nile perch would probably affect “various species
of fish which were of little or no commercial value, it would
have minimal impact on tilapia (EAIFAC 1955). Opposition
from EAFRO hinged on the argument that the outcome of the
“exp eriment” w ith Nile perch i n Lake Kyog a sho uld be kn own
before an introduction into Lake Victoria could be considered.
Adopting a different tack, UGFD employees seized on a
paleontological study showing that a congener of the Nile
perch (Lates sp.) had occurred,and gone extinct, in the Lake
Victoria region during the Miocene (Greenwood 1951). Thus,
UGFD officials began calling for the reintroduction of the Nile
perch, while also alluding to “vague reports”that Nile perch
had already been seen in Lake Victoria near Port Bell (EAIFAC
1957). In face of stubborn resistance from EAFRO, UGFD of-
ficer Alec Anderson agreed to a hiatus on stocking operations
within Uganda,although he grumbled that he would prefer
to see some such device as an electrical fence installed rather
than that there should be a complete prohibition on stock-
ing”(EAIFAC 1957).Anderson also engaged in a debate in the
East African Agricultural Journal with EAFRO scientist Geoffrey
Fryer. Fryer (1960) appealed to the “common-sense” princi-
ple of trophic inefficiency (Lindeman 1942) and argued that
to assume Nile perch would feed only on Haplochromis species
to the exclusion of tilapia was “wishful thinking.” Anderson
(1961) countered that Nile perch certainly would feed on “les
indesirables Haplochromis,”which is [sic] generally regarded
as a [sic] ‘trash fish’ of very little value.
EAFRO,perhaps recognizing that the Nile perch question
would not disappear, had belatedly begun to arrange for a
study of Nile perch biology, which they had long stated was
a prerequisite for considering the introduction. This work was
not begun until 1959 (EAFRO 1960),in part because of bud-
get constraints (themselves due to niggardly funding from the
High Commission, which had decided in 1958 to disband the
Lake Victoria Fisheries Service and distribute its duties to the
three territories). And almost before the work could get un-
der way, Nile perch began turning up in Lake Victoria. The
1960 EAFRO annual report stated that the need for the Nile
perch study had become all the more urgent,“since during the
year it became apparent that Nile perch had already gained
access to the lake by some means” (EAFRO 1960). In Octo-
ber of 1961, a Nile perch caught near Mwanza, Tanganyika,
was brought to fisheries officials there by an engineer who,hav-
ing worked for years on Lake Albert, was familiar with the fish
(Mwanza Fisheries Officer 1961).
These discoveries transformed the debate, and nobody
objected when Don Rhodes said in 1962 that “in view of
the evidence that Nile perch were already breeding in Lake
Victo ria and spreading rapidly, [I] would therefore like to stock
more fish immediately as these become available at Port Bell,
Kaazi, and Entebbe to satisfy the long-standing demands of
important sporting and commercial efforts in these areas”
(UFD 1962). Thereafter, the anthropogenic dispersal of Nile
perch did indeed spread rapidly (figure 1). Thirty-five were
introduced into Lake Victoria at Entebbe Harbor in May
1962; by November 1963,that total had reached 339. In 1963,
Nile perch were stocked “in the Kagera River, Lake Salisbury,
September 2005 / Vol. 55 No. 9 BioScience 783
Biology in History
Biology in History
784 BioScience • September 2005 / Vol. 55 No. 9
Lake Saka, Lake Nabugabo, Lake Kijanebalola, and various
dams” (UFD 1962/1963). Fishery officials in Kenya intro-
duced eight more Nile perch (from Lake Turkana) at Kisumu
in 1963.
It remains impossible to say with absolute certainty that
somebody within UGFD introduced Nile perch directly into
Lake Victoria before 1960. However, the available evidence
points strongly in that direction (although both Kinloch and
Rhodes denied having done so personally in interviews with
the author). Kinloch’s 1972 memoir and numerous official
documents from the time certainly evince a steadfast resolve
to spread Nile perch and a disdain for those who opposed the
idea, as does a report by American economist James A. Crutch-
field (1959), who worked closely with UGFD during his
tenure as a Fulbright fellow.
Most compelling, however, is the testimony of two
Africans who worked for UGFD in the 1950s. On 25
February 1978—shortly before the Nile perch boom—John
Ofulla Amaras published the following in a letter to the
East African Standard: “Please take note that Nile perch...were
stocked in Lake Victoria and Kioga [sic] from Lake Albert in
August, 1954. ..by mys elf assisted by fi sh scouts at that time
Augustino Kyomya, Benwa Magadu, Peter Karakaba and
others—under the directive of the then Senior Fisheries Of-
ficer, Mr. Alex [sic] M.Anderson.”
Figure 1. Map of the Lake Victoria region, showing the range expansion of the Nile perch in East Africa during the 1950s and
1960s. Dots show locations and years of deliberate introductions: (1) Murchison Falls; (2) Masindi Port; (3) the upper Nile
below the Owen Falls Dam; (4) Port Bell; (5) Entebbe Pier; (6) Lake Nabugabo; (7) Lake Kijanebalola; (8) the Kagera River;
(9) Lake Saka; (10) Lake Salisbury; (11) Kisumu. Arrows indicate entry of Nile perch into Lake Victoria; question marks indi-
cate uncertainty. The asterisk shows the point of origin of Nile perch introduced into the Ugandan waters of Lake Victoria, at
Butiaba on Lake Albert; the Nile perch introduced at Kisumu in 1963 came from Lake Turkana in northern Kenya (not
shown). The fish icon represents the point of furthest advance, near Mwanza, Tanganyika, by 1961.
Amaras, a Kenyan, was indeed a UGFD fisheries assistant
from 1954 to 1955 (UGFD 1955); in a 2003 interview with the
author,he claimed that multiple introductions of Nile perch
from Lake Albert had been made into Lake Victoria at Port
Bell and Entebbe Pier over several months in 1954 (these are
the same locations subsequently proposed by Don Rhodes in
1962). Peter Karakaba, named in Amaras’s letter, also stated
in a 2003 letter to the author that Nile perch had been in-
troduced directly into Lake Victoria, although he gave the date
as 1955. Former UGFD officer John Stoneman, in an inter-
view with the author, remembered Amaras’s having been in-
volved in the stocking of Lake Victoria, which would mean
that the introduction took place in either 1954 or 1955, as
Amaras was dismissed from UGFD in October 1955 (UGFD
1955).
It is unlikely that any existing evidence could conclusively
prove whether the initial introduction into Lake Victoria it-
self was intentional or accidental. UGFD officials have always
maintained that Nile perch must have entered the lake through
the turbines in the Owen Falls Dam when the dam was shut
down for cleaning, a claim that many scientists considered im-
plausible (Jackson 2000). In any case, it made little practical
difference whether the Nile perch was introduced directly into
the lake or into a river behind a penetrable dam.
Conclusions
Although a number of factors and individuals clearly con-
tributed to the Nile perch’s introduction, it is perhaps most
interesting historically to ask why EAFRO’s research biologists
failed in their attempts to prevent it.This is neither a criticism
nor an attempt to downplay the considerable importance of
EAFRO’s basic research during these years—much of it con-
ducted under difficult conditions. It is merely an attempt to
learn from history.
It is true that it would have been difficult for EAFRO to pre-
vent determined UGFD officials from transferring Nile perch
at least to the source of the Nile. However, it is possible that
if they had made a stronger attempt to push their agenda
through political channels from the beginning, the interter-
ritorial organizations of research and administration might
have been fused, as originally advocated by E. B. Worthing-
ton. Such an arrangement would have provided scientists
direct control over policy. Alternatively, EAFRO might have
been afforded a stronger intraterritorial role,such that mov-
ing Nile perch from Lake Albert to Lake Kyoga or the upper
Nile would at least have required EAFRO oversight.
A third possibility is that more funding would have been
forthcoming if EAFRO had more skillfully manipulated ad-
ministrative sentiment within the High Commission. As
early as Graham’s 1929 survey, EAFRO scientists had main-
tained that “extensive research” was required before Nile
perch introductions could be considered.Yet they were slow
to undertake such a study, and by the time they did, they found
it difficult to obtain funding from an administration convinced
that their work was too esoteric. It is tempting to speculate
what would have happened if, as Worthington suggested in
1932, an experimental introduction had been made into
Lake Nabugabo. What ultimately happened in Lake Nabugabo
was similar to what happened in Lake Victoria, with ap-
proximately 50 percent of indigenous fishes disappearing
from open waters (Chapman et al. 2003). This is hardly the
“natural balance” that Worthington (1932) was looking for.
However, it is not clear that even this would have pro-
vided EAFRO biologists with a compelling argument against
further introductions. Biologists such as the British Mu-
seum’s Ethelwynn Trewavas and Humphrey Greenwood val-
ued haplochromine cichlids as evolutionary curiosities, but
the argument that these cichlids had some intrinsic value was
never raised in fishery policy discussions.Instead, biologists
such as Fryer (1960) appealed principally to economics, ar-
guing that the Nile perch would devastate valuable established
fisheries. This turns out not to have been the case—indeed,
the Nile perch vastly increased the economic value of every
lake where it was introduced. To modern biologists, who
generally believe that biological diversity is a good in itself, the
term “trash fish” sounds odd, even offensive. But modern ecol-
ogy’s preoccupation with diversity and its benefits only really
began in the late 1950s (e.g., Hutchinson 1959). While EAFRO
biologists clearly believed that species were interesting things
to study, they would have found it hard to articulate policy
arguments based on the value of biodiversity. Simply, no
such “value” had yet been attributed to biodiversity.
Similarly, the study of biological invasions was in its
infancy in the 1950s (Elton 1958) and later drew heavily on
the observations that predator–prey, parasite–host, and
mutualist–mutualist relationships are coevolved (Ehrlich
and Raven 1964), and that invasive species can exploit or dis-
rupt those relationships.Whereas Fryer (1960) and others at
EAFRO clearly recognized that the introduction of a non-
indigenous apex predator could endanger fisheries, their
arguments could have been much stronger in,say,1970 than
they could possibly have been in the period 1954–1960.
It might be argued that no amount of cogent scientific rea-
soning would have made a difference—that government
agencies like UGFD tend to introduce nonindigenous species
regardless of scientific concerns, and that such introduc-
tions, once proposed, are so difficult to prevent as to be almost
inevitable. However, the history of the Nile perch in Lake
Victoria also offers an instructive example of applied sci-
ence being used to forestall such an introduction.In the late
1980s, it was proposed to introduce the Nile perch into still-
water bodies of tropical Queensland,Australia.After a detailed
study of the thermal tolerances of Nile perch, and careful
scrutiny of the consequences of the introductions in Lakes
Victoria and Kyoga, it was concluded that the introduction
“would be potentially disastrous for Australian aquatic fauna....
Consequently, the agency responsible for the evaluation
program has abandoned the concept of introducing the Nile
perch to Australia” (Barlow and Lisle 1987). The Nile perch
remains classified as a noxious species in Queensland.
It is also possible that the secretive introduction of a hand-
ful of fish would have been inadequate to establish the Nile
September 2005 / Vol. 55 No. 9 BioScience 785
Biology in History
Biology in History
786 BioScience • September 2005 / Vol. 55 No. 9
perch in Lake Victoria, and that the legally sanctioned mass
introductions after 1960 were crucial to its subsequent suc-
cess. A growing literature suggests that multiple introductions
can increase the genetic diversity of invading populations and
lessen the probability of stochastic extinction (Kolbe et al.
2004).
Incipient conflicts between biodiversity and economic or
infrastructural development persist today in various mani-
festations: new roads, new dams,new species introductions.
Thus, ecologists and evolutionary biologists might profitably
take several lessons from this story. The first is that there is an
important role for scientists who are willing to grapple with
policy,and with politics. While science itself should obviously
be apolitical, the systems that scientists study (and the eco-
nomic, legal, and social matrix in which they must operate)
are politically contested arenas. Thus,scientists who desire the
persistence of the systems they study (and the unfettered
ability to study them) are justified in being advocates in
matters on which their science can be brought to bear.
Ta k i ng t h i s r e a s o ni n g o n e s t e p f u r t h e r, i t i s n o t u n r e a s on a b l e
for scientists to consider how they might position them-
selves to exert political influence if and when it becomes
necessary.
By the same token, this story highlights the importance of
both applied and basic research: a thorough and persuasive
argument against the introduction of the Nile perch would
have required both empirical data on the probable effects of
the introduction and a cogent theoretical framework to
express generally why the introduction of nonindigenous
species can be ecologically disastrous.
Acknowledgments
I am deeply indebted to those who discussed these events with
me: John Amaras, Peter Karakaba,Bruce Kinloch,Rosemary
Lowe-McConnell,Don Rhodes, John Stoneman, and Robin
We l co m m e . Jo h n Ba l i r w a a n d t h e st a f f s o f R h od e s Ho u s e L i -
brary, the Public Record Office, and the Kenya National
Archives kindly helped me locate archival material. Financial
support was provided by the Thouron family and by St.
John’s College, Oxford. Finally, I am grateful to Dave Ander-
son, William Beinart, Kai Chan, Paul Ehrlich, John Fay, and
Jessica Shors for advice and help with the manuscript.
References cited
Anderson AM. 1961. Further observations concerning the proposed intro-
duction of Nile perch into Lake Victoria. East African Agricultural and
Forestr y Journal 2 6: 195–201.
Anonymous. 1923. Letter to Kenya game warden, 9 December 1923. Nairobi:
Keny a Nat iona l Arc hives Fil e KP /4/7 /18.
Balirwa JS, et al. 2003. Biodiversity and fishery sustainability in the Lake
Victo ria Bas in: An u nexpected m arriag e? BioS cience 53: 703–715 .
Barlow CG, Lisle A. 1987. Biology of the Nile perch Lates niloticus (Pisces:
Centropomidae) with reference to its proposed role as a sport fish in
Aust rali a. Bi olog ical Cons erva tion 39: 269– 289.
Caldwell K. 1923. Letter to Colonial Secretary, Nairobi, 3 December 1923.
Nairo bi: Keny a Natio nal Arc hives File K P/4/7/ 17.
[CDC] Colonial Development Corporation. 1949. Letter to EAFRO direc-
tor, 6 December 1949. Jinja (Uganda): Fisheries Resources Research
Institute File FSH/1.
Chapman LJ,Chapman CA, Schofield PJ, Olowo JP, Kaufman L, Seehausen
O, O gut u-O hwayo R. 2 003 . Fi sh fau nal res urg enc e i n L ake Nabu gab o, E ast
Africa. Conservation Biology 17: 500–511.
Copley H. 1940. Letter to Kenya game warden, 10 May 1940. Nairobi: Kenya
Nati onal Ar chives File K P/6/7 /100.
———. 1954. Letter to E. B. Worthington, 26 May 1954. Oxford (United
Kingdom): Edgar Barton Worthington Papers File 3/10/5, Rhodes
House Library.
Crutchfield JA. 1959. Repor t to the Government of Uganda on Fish Marketing
in Uganda. Rome: Food and Agriculture Organization of the United
Nations.
[EAFRO] East Africa Fisheries Research Organization. 1953. Report on
Fisheries Research. Nairobi: Kenya National Archives File VF/5/9/2/5.
———. 1960. Annual Report. Kampala (Uganda): Uganda Argus.
[EAHC] East Africa High Commission. 1954. Letter to E. B. Worthington,
27 March 1954. Oxford (United Kingdom): Edgar Barton Worthington
Pape rs Fi le 3/1 0/69, Rhod es Hou se Lib rary.
[EAIFAC] East Africa Inland Fisheries Advisory Committee.1955. Meeting
minutes, 22 August 1955. Nairobi: Kenya National Archives File
KL/24/31/1/1.
———. 1957. Meeting minutes, 7 July 1957. Nairobi: Kenya National
Archives File KL/24/31/25.
[EAIRB] East Africa Industrial Research Board. 1948. Letter to EAFRO
director, 19 March 1948. Jinja (Uganda): Fisheries Resources Research
Institute File Res/E.15/22.
Ehrlich PR, Raven PH. 1964.Butterflies and plants: A study in coevolution.
Evolu tion 18 : 586–6 08.
Elton CS. 1958. The Ecology of Invasions by Plants and Animals. London:
Methuen.
Fearon SP. 1955. Letters to EAFRO director (4 Novembe r 1955) and London
Colonial Office (2 December 1955). Kew (United Kingdom): Public
Record Office Fi le CO/927/562.
Fryer G. 1960. Concerning the proposed introduc tion of Nile perch into Lake
Victo ria. Eas t Afric an Agric ultura l Journal 2 5: 267– 270.
Graham M. 1929. The Victoria Nyanza and Its Fisheries: A Report on the
Fishing Survey of Lake Victoria, 1927–1928, and Appendices. London:
Crown Agents for the Colonies.
Greenwood PH. 1951. Fish remains from Miocene deposits of Rusinga
Island and Kavirondo Province, Kenya. Annals and Magazine of Natural
History 4: 1192–1201.
———. 1966. The Fishes of Uganda. Kampala (Uganda): Uganda Society.
Hickling CF. 1953. Memorandum on fisheries legislation. Oxford (United
Kingdom): Edgar Barton Worthington Papers File 3/10, Rhodes House
Library.
Hutch inson GE. 1 959. Ho mage to San ta Ros alia; or, why are t here so man y
kinds of animals? American Naturalist 93: 145–159.
Jackson PBN. 2000. Freshwater fishery research organ izations in central
and eastern Africa.Transactions of the Royal Society of South Africa 55:
1–81.
Kinloch B. 1972. The Shamba Raiders. London: Collins and Harvill.
Kol be JJ , Glo r RE , Sch ett ino LRG, L ara AC, L arso n A, L oso s JB . 200 4. Ge net ic
variation increases during biological invasion by a Cuban lizard.Nature
431: 177–181.
Lindeman R. 1942. The trophic-dynamic aspect of ecology. Ecology
23: 399–418.
Low DA, Lonsdale JM. 1976. Introduction: Towards the new order, 1945–1963.
Pages 1–63 in Low DA,Smith A,eds. The Oxford History of East Africa.
Oxford (United Kingdom): Clarendon Press.
Mwanza Fisheries Officer. 1961. Letter to EAFRO director. Jinja (Uganda):
Fisheries Resources Research Institute File RS/7/57.
Ogutu-Ohwayo R. 1990. The decline of the native fishes of Lakes Victoria and
Kyo ga ( Ea st A fr ica ) a nd t he im pac t o f i ntroduced species, especially the
Nile perch, Lates niloticus, and the Nile tilapia, Oreochromis niloticus.
Environmental Biology of Fishes 27: 81–96.
Oorloff EJH. 1921. Letter to Nyanza senior commissioner, 5 September
1921. Nairobi: Kenya National Archives File KP/4/7/1.
Pringl e RM. 2005. The Nile pe rch in Lake Victoria: Lo cal responses and adap-
tations. Africa 75. Forthcoming.
Provincial Commissioner, Nyanza. 1939. Letter to East Africa High
Commission, 28 December 1939. Nairobi: Kenya National Archives
File KP/6/7/87.
Reynolds JE, Grebova l DF, Mannini P. 19 95. Thirty years on: The d evelop-
ment of the Nile perch fishery in Lake Victoria. Pages 181–214 in Pitcher
TJ, Hart PJB, eds. The Impact of Species Changes in African Lakes.
London: Chapman and Hall.
Seehausen O,van Alphen JJM, Witte F. 1997. Cichlid fish diversity threatened
by eutrophication that curbs sexual selection. Science 277: 1808–1811.
Tre w a v as E . 1 95 2 . L et t e r to E . B . Wo r th i n gt o n , 2 1 M a rc h 1 9 5 2 . O x f or d
(United Kingdom):Rhodes House Library.Edgar Barton Worthington
Pape rs Fi le 3/8 /19.
[UFD] Uganda Fisheries Department. 1962. Meeting minutes, 24 April
1962. Jinja (Uganda): Fisheries Resources Research Institute File RS/7/82.
———. 1962/1963. Annual Report. Kampala (Uganda): Makerere Univer-
sity Library Africana Collection.
[UGFD] Uganda Game and Fisheries Department. 1951. Annual Report.
Kampal a (Uganda) : Makerere Universi ty Library Africana Coll ection.
———. 1955. Annual Report. Kampala (Uganda): Makerere University
Library Africana Collection.
Wanink JH. 1999. Prospects for the fishery on the small pelagic
Rastrineobola argentea in Lake Victoria. Hydrobiologia 407: 183–189.
Witt e F, M aku BS, Wanin k JH, See hausen O, Ka tunzi E FB, Goud swaar d
PC, Goldschmidt T.2000. Recovery of cichlid species in Lake Victoria:
An examination of factors leading to differential extinction. Reviews in
Fish Biology and Fisheries 10: 233–241.
Wo rt h i n g to n EB . 19 2 9 . A Re p o r t o n th e Fi s h i n g S u r ve y of L a k es A lb e r t a n d
Kyo ga, Mar ch to Jul y, 1 928 . L ond on: Cr own Ag ent s f or th e C olo ni es.
———. 1932.A Report on the Fisheries of Uganda: Investigated by the Cam-
bridge Expedition to the East African Lakes, 1930–31. London: Crown
Agents for the Colonies.
———. 1940. Letter to Kenya game warden, 22 April 1940. Nairobi: Kenya
Nati onal Ar chives File K P/6/7 /100.
September 2005 / Vol. 55 No. 9 BioScience 787
Biology in History
... Non-native fishes introduced into Victoria (1954/1955 for cichlids and 1962-1963 for Lates niloticus), Kyoga (1954Kyoga ( /1955 for both cichlids and L. niloticus), and Nabugabo (1960 for cichlids and 1963 for L. niloticus). Note that for L. niloticus in Lakes Victoria and Nabugabo, the stated years refer to the official years of introduction, but unreported introductions most likely happened much earlier starting in the mid-1950s (Pringle 2005). Also, for Lake Nabugabo, the year of introduction of cichlids is not certain; the only available information shows that non-native cichlids were already in the lake by 1960 (Bwanika et al. 2006(Bwanika et al. ) 1961(Bwanika et al. -1964 Heavy rains increase lake levels, submerge aquatic macrophytes and expand open waters over Lake Kyoga and in shallow inshore areas of Lake Victoria Mid 1960s ...
... The large piscivorous L. niloticus and four other species, O. niloticus, O. leucostictus, C. zillii, and C. rendalli, were introduced into the Lake Victoria region in the 1950s and 1960s (Ogutu-Ohwayo and Hecky 1991;Pringle 2005). Introduction of L. niloticus was primarily intended to feed on haplochromine cichlids, which were abundant in this lake, and convert them into a suitable commercially important table and recreational fish. ...
Chapter
Lakes Victoria, Kyoga, and Nabugabo (“the Lake Victoria region”) are remarkable for hosting one of the largest assemblages of cichlid fishes among the African inland lakes. Here, we review the role and severity of anthropogenic and environmental stressors on the cichlid communities in the Lake Victoria region to understand the mechanisms leading to the persistence and resurgence of some of the cichlid fishes. Our review suggests that (1) the native Oreochromis species populations primarily collapsed due to overfishing and that the introduced species and habitat change suppressed their ability to recover; (2) without primary triggers associated with change in the environment and habitat conditions, particularly eutrophication and associated anoxia and reduced water transparency, Nile perch (Lates niloticus) predation alone may not have caused the massive loss of species diversity; and (3) the resurgence of haplochromine cichlids is due to a combination of general improvement in the environment and reduction in L. niloticus abundance, with additionally possibly some rapid ecological adaptations. We conclude that environmental stressors will likely continue to shape the ecosystems in which the remaining endemic cichlid fish diversity continue to evolve, clearly involving genetic exchange between species. If water clarity can be improved again, it is possible to maintain a diverse assemblage of endemic species.
... Separated from Lake Victoria about 5000 years ago (Stager et al., 2005), Lake Nabugabo is a small satellite lake (surface area = 33 km 2 , mean depth = 3.13 m, Nyboer and Chapman, 2013) with a unique composition of fish species, such as a small number of haplochromine cichlid species that are endemic to Lake Nabugabo and nearby satellite lakes (Trewavas, 1933;Greenwood, 1965;Kaufman and Ochumba, 1993) and four species of mormyrid weakly electric fishes (Ogutu-Ohwayo, 1993;Chapman et al., 2002). In the years following the introduction of the predatory Nile Perch in the 1960s (Ogutu-Ohwayo, 1993;Pringle, 2005), Lake Nabugabo suffered a dramatic decline or disappearance of several native species from the waters of the main lake (Ogutu-Ohwayo, 1993;Chapman et al., 2003). The lake is surrounded by an extensive wetland area (Lwamunda Swamp), which is dominated by the emergent grass Miscanthidium violaceum that transitions to water lilies (Nymphaea lotus and N. carulea) or hippo grass (Vossia cuspidata) at the lake edge (Chapman et al., 1996a;Chrétien and Chapman, 2016). ...
Article
Full-text available
To understand animal ecology, observation of wildlife in the natural habitat is essential, but particularly challenging in the underwater realm. Weakly electric fishes provide an excellent opportunity to overcome some of these challenges because they generate electric organ discharges (EODs) to sense their environment and to communicate, which can be detected non-invasively. We tracked the EOD and swimming activity of two species of mormyrid weakly electric fishes (Marcusenius victoriae and Petrocephalus degeni) over diel cycles in the laboratory, and we recorded EODs and environmental dissolved oxygen (DO) concentration and temperature over several months in a naturally hypoxic habitat in Uganda. Under laboratory conditions, both species showed increases of activity and exploration behavior that were closely synchronized to the onset of the dark phase. In the wild, fish preferred structurally complex habitats during the day, but dispersed toward open areas at night, presumably to forage and interact. Nocturnal increase of movement range coincided with diel declines in DO concentration to extremely low levels. The fact that fish showed pronounced nocturnal activity patterns in the laboratory and in the open areas of their habitat, but not under floating vegetation, indicates that light intensity exerts a direct effect on their activity. We hypothesize that being dark-active and tolerant to hypoxia increases the resistance of these fish against predators. This study establishes a new technology to record EODs in the field and provides a window into the largely unknown behavior of mormyrids in their natural habitat.
... The Nile perch (np; Lates niloticus) is a freshwater fish introduced into Ugandan waters of Lake Victoria from Lake Turkana in Northern Kenya and now widely distributed in the Nile basin (Pringle, 2005); over time, given its high market demand, this fish species has attracted commercial interests from aqua-culturists in several parts of Uganda, as well as in other parts of East Africa. However, the capture Nile perch fishery is threatened by its extinction due to a lack of knowledge for its sustained exploitation. ...
Article
The Nile perch (np; Lates niloticus) is a freshwater teleost species with a potential for aquaculture in freshwater surroundings. However, wild-caught breeders have persistently failed to spawn spontaneously in captivity. Cloning of the gonadotropin subunits and analysing seasonal variation in reproductive hormone levels for a 1-year period were done to gain knowledge on the physiological basis underlying the reproductive biology of np. The β-follicle-stimulating hormone (FSH-β) and β-luteinizing hormone (LH-β) subunits and their common α-glycoprotein (Gph-α) subunit were cloned using 3’ and 5’ RACE-PCR. The nucleotide sequences of the npgph-α, npfsh-β, and nplh-β subunits were 664, 580 and 675 nucleotides in length, encoding peptides of 124, 120 and 148 amino acids, respectively. The deduced amino acid sequence of each mature subunit showed high similarity with its counterparts in other teleost. Sequence analysis showed that npFSH-β is more similar to higher vertebrate FSH-βs than to higher vertebrate LH-βs. Heterologous immunoassay was calibrated to analyse pituitary LH levels. While the LH immunoassay showed parallelism of npLH with that of tilapia (ta), no parallelism for FSH was found. Levels of pituitary LH were higher in females at gonadal stages of vitellogenic oocytes, mature secondary oocytes and mature tertiary oocytes with migrating nucleus than in pre-vitellogenic oocytes and early and late perinucleolus oocytes. Using competitive steroid ELISA, variations in the levels of the steroid hormones 11-ketotestosterone (11-KT) in males and E2 in females were characterized in relation to month and reproductive index of Nile perch. Our findings show that in females, gonadosomatic index and plasma E2 were highly correlated (R² = 0.699, n = 172) and peaked from September to November while in males, the gonadosomatic index and plasma 11-KT peaked from October to November. In female fish, both steroid hormones were detected in the plasma but greatly varied in concentrations. E2 in particular, increased with the developmental stage of the gonads. The levels of steroid hormones, E2 and 11-KT in females and males respectively increased with fish size (total lengths) and suggest that females mature at a body length of 40–59 cm than their counter part males that mature at a total length of 60-70 cm. Taken together, we describe seasonal endocrine differences in wild-caught adult Nile perch which could potentially be exploited to manipulate the reproductive axis in cultured breeders.
... Patterns in the ITS-1 region differed in the slender specimens between Lake Victoria and Lake Albert. Mitonuclear The haplotype sharing between studied locations supports the co-introduction of D. lacustre with L. niloticus to 449 Lake Victoria from Lake Albert (Pringle 2005). This agrees with host data provided by Hauser et al. (1998), which 450 confirmed the presence of L. niloticus from Lake Albert in Lake Victoria and excluded the successful 451 establishment of introduced Nile perch from Lake Turkana. ...
Preprint
Full-text available
The Nile perch ( Lates niloticus ) is a notorious invasive species. The introductions of Nile perch into several lakes and rivers in the Lake Victoria region led to the impoverishment of the trophic food webs, particularly well documented in Lake Victoria. Along with the introductions of the Nile perch, its parasites were co-introduced. Dolicirroplectanum lacustre (Monogenea, Diplectanidae) is a gill parasite of latid fishes ( Lates spp.) inhabiting several major African freshwater systems. We examined the intra-specific diversification of D. lacustre from L. niloticus in Lake Albert (native range) and Lake Victoria (introduced range) by assessing morphological and genetic differentiation, and microhabitat preference. We expected reduced morphological and genetic diversity for D. lacustre in Lake Victoria compared to Lake Albert, as a result of the historical introductions. Dolicirroplectanum lacustre displays high morphological variability within and between African freshwaters. Mitonuclear discordance within the morphotypes of D. lacustre indicates an incomplete reproductive barrier between the morphotypes. The diversification in the mitochondrial gene portion is directly linked with the morphotypes, while the nuclear gene portions indicate conspecificity. Based on our results, we reported reduced genetic and morphological diversity, potentially being a result of a founder effect in Lake Victoria.
... s0130 Case study 2: Nile Perch in Lake Victoria-Good intentions gone wrong p0165 Perhaps the best-known example of biodiversity impacts from a freshwater invasive species is the introduction of Nile perch to Lake Victoria (Africa) in 1954 (Pringle, 2005). This introduction was intended to augment fisheries in the lake, and thus to provide an extra source of protein, jobs, and income for locals. ...
Chapter
Invasive nonindigenous species cause massive impacts to freshwater biodiversity and to the provisioning of ecosystem services from lakes, rivers, and wetlands. These impacts affect whole ecosystems, economies, human health, and recreational opportunities. The number and total impacts of invasive species will likely continue to increase despite increased management efforts. Other factors, including global climate change, will affect the distribution and impacts of invasive freshwater species and in many cases will make those impacts more severe.
... The Nile perch had been evolving to thrive in a similar niche to many of the cichlids for a much longer time and, as a result, proved a much more efficient hunter than many of the predatory cichlids, outcompeting them for food, as well as directly preying on other cichlid species. The result was that hundreds of species of cichlid became extinct (Pringle 2005). ...
Thesis
In this thesis, I inspect some key assumptions which tend to underpin mainstream accounts of natural selection, noting where those assumptions break down and taking this as a basis for fresh analysis. First, I examine the assumption that natural selection inherently involves struggle or competition. I show selection can take place without zero-sum competition and that competition is not essential for selection to positively facilitate novel adaptations. Moving on to fitness, I address the assumption that biological fitness should be measured as a function of the number of elements of some set of entities (offspring, gene copies or otherwise). Noting cases where selection seemingly acts in terms of persistence and somatic growth, and with these alternative fitness metrics not reducible to one another, I suggest a pluralist stance. Subsequently extending this rationale to the temporal dimension, I show that attempting to measure fitness over any single time frame often fails to capture the action of selection. In later chapters, I explore the possibility of uniting my multiple fitness metrics via a single “common currency” metric. I rule out metrics based around resource or energy consumption, as per Van Valen and others, as unworkable. However, I find some potential in conceptualising the various aspects of fitness in terms of negative entropy. This fails to deliver a quantifiable common currency metric, but does address conceptual issues and allows for the unification of our account of biological fitness with the popular thermodynamic definition of life. The need to buttress earlier arguments necessitates a concluding analysis of the Darwinian population concept. Contra complacent assumptions that they are readily defined, I find that there are no clear means to bound Darwinian populations in many cases. I also argue that analysis of the Darwinian population concept has been confounded by the conflation of pragmatic groupings, assembled for comparative inference, with causally bound Darwinian populations.
Article
The introduction of Nile perch, Lates niloticus, into Lake Victoria resulted in a massive increase in fish catches, but with significant ecological costs. These included the near extirpation of the 500+ endemic haplochromine species and the eutrophication of the lake. A proposal to introduce Nile perch into the artificial Lake Kariba (Zambia/Zimbabwe) is of concern, therefore, because of potentially adverse impacts on its fisheries and biodiversity. It is very unlikely that Nile perch would improve the fisheries in Lake Kariba, as it did in lakes Victoria and Kyoga, because this lake is oligotrophic and much less productive. The principal fishery in Lake Kariba is already in difficulty, owing to overfishing, and Nile perch could reduce catches further. The biomass of other native fish species is very low and would be unlikely to support a significant Nile perch population. Lake Kariba has already experienced a major loss of biodiversity as river‐adapted fish species have not been able to adapt to lacustrine conditions. The non‐native Nile tilapia, Oreochromis niloticus, has also replaced the endemic tilapia species in the middle Zambezi system and the Nile perch could bring about a further loss of biodiversity. The ecological costs of its introduction into Lake Kariba would not be justified by an increase in fishery productivity, and the possible introduction of Nile perch should be forcefully rejected.
Article
Fishing pressure can have strong impacts on fish populations, driving declines in abundance and, occasionally, changing life history traits. However, much of our current understanding of these phenomena derives from studies conducted decades or even centuries after the onset of fishing. Newly established fisheries provide an excellent opportunity to understand this critical early phase. Temporal trends in catch data and life history traits of the cyprinid fish Rastrineobola argentea (Pellegrin), now the target of a burgeoning artisanal fishery in Lake Nabugabo, Uganda, were analysed. Results showed that the R. argentea fishery intensified and became more selective during the first decade since its establishment (2008–2019), while catch-per-unit-effort of R. argentea (fisheries-independent abundance) at repeatedly sampled sites in the lake decreased over this same time period. Size-adjusted egg volume and ovary mass increased significantly over the time period, which may reflect a density-dependent response to a fisheries-induced population decline.
Article
Over the course of the twentieth century, Lake Victoria faced an unprecedented decline: From a symbol of biodiversity, Africa’s largest lake evolved into a highly degraded habitat. What were the underlying mechanisms of this? Common explanations focus on the introduction of the Nile perch in the 1950s and 1960s and the consequential damage to the lake. This article argues, however, that this introduction must be read against the background of the long-term schemes of resource utilisation deployed by the institutions of the British Empire. The introduction of the Nile perch was not an isolated event but was embedded in a longer process of exploring, utilising and modifying the lake. In this process, the colonial institutions deliberately ignored the many well-founded scientific warnings of an introduction in favour of a modification of the lake. Thus, this modification, presented as legitimate, symbolically reflects the effort of the institutions of the British Empire to control and optimise natural resources and stands in a long series of interventions in natural habitats. Overall, this multi-perspective analysis of Lake Victoria’s modification contributes to questions of nature utilisation in colonial contexts and sheds light on the general relationship between man and nature.
Chapter
For fishes, the availability of dissolved oxygen (DO) can affect performance and fitness traits and influence distribution patterns. Hypoxia occurs naturally in habitats characterized by low mixing and/or light limitation such as dense wetlands and profundal zones of deep lakes. In addition, human activities are increasing the frequency and extent of aquatic hypoxia through eutrophication and pollution. Thus, it has become increasingly important to understand consequences of hypoxia for fishes and mechanisms that facilitate persistence in low-DO habitats. With strong specialization in some cichlid species and high levels of intraspecific variation in others, cichlids have been a key group for exploring strategies for dealing with hypoxia. These include behavioral responses (e.g. aquatic surface respiration), evolution of mechanisms to maximize oxygen uptake and delivery, metabolic depression, use of anaerobic metabolism, and air breathing in a few species. Despite the diversity of strategies that have permitted some cichlids to persist under extreme hypoxia, low DO can incur potential costs such as smaller body size. Such costs may be offset by benefits of hypoxic habitats such as reduced predation risk. This review details the mechanisms used by cichlids for tolerating hypoxia and the costs and benefits of hypoxia tolerance.
Article
Full-text available
Introduced into Lake Victoria in the 1950s, the Nile perch has gained fame for prompting rapid regional economic growth and for driving scores of endemic fish species into extinction. This study uses oral and archival data to trace the historical development of the Nile perch fishery on Lake Victoria. Particular emphasis is placed on local responses and adaptations to (1) the Nile perch itself; (2) the abrupt integration of the Lake Victoria fishery with the global economy; and (3) the ecological changes that the Nile perch has precipitated. I also attempt to situate Lake Victoria's history in the larger debate about environment and African livelihoods. Because so much of Lake Victoria's species diversity has been lost within one generation – biologist E. O. Wilson (1992) has called this process ‘the most catastrophic extinction episode of recent history’ – the lake is an ideal case study with which to examine ‘local’ perceptions of biodiversity. The data suggest that species diversity is important and highly resolved in the worldviews of Lake Victoria's fishermen; yet, although the will for conservation is present, poverty obstructs its realization. These findings are discussed in relation to other work on indigenous environmental knowledge and ecological ethics. I argue that ‘intrinsic’ valuation of species diversity and ecological processes may be more widespread in rural societies than has traditionally been assumed by natural and social scientists, and that the preponderance of social studies highlighting oppositions between Western science and ethno-science, and between conservation concerns and local livelihoods, may have blinded us to synergies between them. More effort is needed to understand fully the nuances in these complex local ecological worldviews, perhaps via ‘social histories of extinction’ that explore the local consequences of species loss.
Chapter
Accounts of the introductions of the large centropomid piscivore, Nile perch, Lates niloticus, into the waters of Lake Victoria have been provided by a number of writers (see Reynolds and Gréboval, 1988, for a fuller review). There is a surprising vagueness in many of these accounts when it comes to the actual sequence of events and the main actors (or villains, depending on one’s point of view) involved. There is no doubt that the fish was placed into Lake Victoria at some point during the series of Nile perch transplantations to the Upper Nile-Lake Kyoga-Owen’s Falls Dam stretch of Nilotic waters, conducted by officials of the Uganda Game and Fisheries Department between 1954 and 1957 (Kinloch, 1972). Stock was captured from Lake Albert and the Nile below Murchison Falls. Unlike the earlier introductions of non-indigenous tilapiines beginning in 1953 (Welcomme, 1966;1967), the first placement of perch into Lake Victoria seems to have been carried out surreptitiously. It came as a surprise when the fish was discovered in waters close to Jinja (map, Chapter 2, Fig. 2.2) in May 1960, even as debate about whether the introduction ought to be carried out was continuing (EAFFRO, 1960; Fryer, 1960; Hamblyn, 1960; Anderson, 1961; Beadle, 1981). Two official‘deliberate’ introductions of Nile perch to Ugandan waters were later conducted in 1962 and 1963 (Gee, 1965).
Article
This review contributes to an historical record of research agencies in Southern, Central and Eastern Africa 1947-72, with a brief addendum on Lake Victoria to accommodate current interest. On-site, as opposed to expeditionary, research into African fish and fisheries development began in those areas where fisheries already existed. Funds were made available in an effort to provide food supplies to offset shortages caused by World War II. The East African Freshwater Fisheries Research Organisation (EAFFRO) serving Kenya, Tanganyika (now Tanzania) and Uganda, and based at Jinja, Uganda, was started with British Colonial Development and Welfare (CDW) funds in 1947. When further CDW funds became available, creation of the Joint Fisheries Research Organisation (JFRO) to serve Northern Rhodesia (now Zambia) and Nyasaland (now Malawi) was proposed in 1950, to be based at Samfya. This was approved in late 1950. The author (soon to become its officer in charge) was recruited into it in September 1951. The third Central African country, Southern Rhodesia (now Zimbabwe), lacked large fisheries and declined to participate. The review covers early attempts at fish farming, the JFRO Survey of Northern Lake Nyasa (now Malawi), the pre-impoundment research on the pristine Middle Zambezi (the first elucidation of this river's ecology), and the ensuing research on the new Kariba Dam as it filled. Research and discoveries on Lake Tanganyika and other Central African waters are described, as is a celebrated controversy regarding the role of the tigerfish Hydrocynus vittatus as a predator, and an account of ill-considered fish introductions in East African fresh waters. The author's experience as director of EAFFRO and as manager.of the FAO Victoria Fisheries Research Project is described.
Article
Much as Rachel Carson's "Silent Spring" was a call to action against the pesticides that were devastating bird populations, Charles S. Elton's classic "The Ecology of Invasions by Animals and Plants" sounded an early warning about an environmental catastrophe that has become all too familiar today-the invasion of nonnative species. From kudzu to zebra mussels to Asian long-horned beetles, nonnative species are colonizing new habitats around the world at an alarming rate thanks to accidental and intentional human intervention. One of the leading causes of extinctions of native animals and plants, invasive species also wreak severe economic havoc, causing $79 billion worth of damage in the United States alone. Elton explains the devastating effects that invasive species can have on local ecosystems in clear, concise language and with numerous examples. The first book on invasion biology, and still the most cited, Elton's masterpiece provides an accessible, engaging introduction to one of the most important environmental crises of our time. Charles S. Elton was one of the founders of ecology, who also established and led Oxford University's Bureau of Animal Population. His work has influenced generations of ecologists and zoologists, and his publications remain central to the literature in modern biology. "History has caught up with Charles Elton's foresight, and "The Ecology of Invasions" can now be seen as one of the central scientific books of our century."-David Quammen, from the Foreword to "Killer Algae: The True Tale of a Biological Invasion"
Article
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.