The Lake Victoria Species Survival Plan represents an organized effort by North
American zoos and public aquariums to conserve as much of the diversity of the
endemic cichlids therein as possible. Captive breeding of endangered species
plays an important role in these efforts. Unfortunately much of the cichlid
species diversity (representing many entire trophic groups) had already gone
extinct in Lake Victoria before founder populations could be secured for the
program. Therefore, only a handful of species representing relatively few trophic
groups and specializations are now being protected from extinction in breeding
programs. Periodically, species in the program are reviewed as to the priority
they should be given. To do so, the status of a species in the wild must be
considered, using updated information collected during recent field efforts.
The major limiting factor in the program is the number of participating institutions
and the aquarium space each can make available.
Much of the existing debate concerning the future direction of LV-SSP activities
centers around the best ways to maintain genetic integrity of the fishes in
the program. Species kept in aquaria or ponds will over time become genetically
distinct from wild founder stocks, a situation that is not particularly surprising
given the very different selection pressures operating on captive fishes. One
option that would maintain these fishes under natural selection pressures and
eliminate the need for costly, labor-intensive efforts in North America and
Europe is to locate and protect satellite lakes that still support important
taxa. Satellite lakes are small, isolated bodies of water left behind when water
levels in the Lake Victoria basin dropped to present levels. Provided these
lakes are granted protection from environmental degradation and overexploitation,
they could serve as sanctuaries for native cichlids as well as other endemic
flora and fauna of the basin. Ugandan and American researchers have recently
discovered that one of these satellites, Lake Nawampasa, is home to haplochromine
taxa representing trophic specializations that have been extirpated from Lake
Victoria. This provides an incredible opportunity, at the very least, to secure
founder stocks for these taxa, and at best, to preserve a natural "living
museum" that grants a second chance to fishes already thought lost forever.
Because of its importance to the LV-SSP, and the fact that Lake Nawampasa is
already under exploitation pressures from ornamental fish exporters, a reconnaissance
of this lake was a priority of my trip to Uganda.
This year's field work (1995) began at the British Museum of Natural History
in London during a lengthy stopover on my way to Entebbe (Uganda). Here I met
up with Dr. Mark Chandler of the New England Aquarium in Boston to study preserved
specimens of Haplochromis species that we were unfamiliar with but expected
to encounter in Lake Victoria and Lake Nawampasa. Admittedly, the viewing of
preserved specimens became more meaningful only once we were able to compare
them with live fishes from the lake.
After arriving in Entebbe, we drove eastward for three hours along the north
shore of Lake Victoria to the Fisheries Research Institute (FIRI) in Jinja.
Once we were settled in a comfortable guest house (only a 10-minute walk from
FIRI), work plans were established for the next fortnight. The first week would
be spent sampling in the Napoleon Gulf of Lake Victoria near Jinja; the second
would be consumed in building aquaria at FIRI and collecting fishes in Lake
The first week afforded us an opportunity to observe the many changes that
have taken place in the lake ecosystem over the last three decades. Hillsides
surrounding the Napoleon Gulf are being deforested to produce charcoal fuel.
This increases run-off of silt into the lake, which in turn causes increased
turbidity. More importantly, the increased inflow of nutrients has resulted
in significant eutrophication. The introduced water hyacinth (Eichhornia crassipes)
is now common in almost all areas of the gulf, a clear indication of the increased
nutrient levels in the lake. Aside from being an indicator of nutrient levels,
water hyacinth acts as a barrier to the exchange of oxygen at the air-water
interface in areas where it collects as a result of wind. Unfortunately, this
often happens to be in smaller bays and along shorelines, typically the most
productive habitats for haplochromine cichlids.
In a 6-m wooden canoe fitted with an outboard motor, we visited Mark's five
study sites in the Napoleon Gulf, reflecting the major habitats represented:
papyrus shorelines; intermediate zones with mixed rock and sand substrates;
and fringing swamps. Dr. Chandler's research requires regular sampling of these
sites with gill nets. At each site, one net is set along the shoreline in shallow
water; a second is set parallel to the first about 20 meters offshore; and a
third is set ca. 200 meters offshore parallel to the first two. Nets are composed
of five panels, each with a different mesh size, for sampling fishes of varying
sizes. At each site, temperature, dissolved oxygen, and Secchi disk (water transparency)
measurements were taken. The nets are left in position for twelve hours but
are checked twice during this period, once after about eight hours and then
a second time just before they are moved to the next site. As the nets are checked,
any haplochromines caught are identified, measured, and recorded. For less commonly
encountered species or fishes that we could not positively identify, tissue
samples and photographs were also taken. The relatively-abundant characoid Brycinus
sadleri, Nile perch (Lates niloticus), and introduced tilapias, particularly
the Nile tilapia (Oreochromis niloticus), were measured and counted, then set
aside by the Ugandan crew for further studies of a culinary nature!
By week's end it was Mark's impression that there were fewer haplochromines
at the sites we sampled than in previous years. The lake's rising turbidity
increases the efficiency of Nile perch predation on the visually-oriented cichlids
better adapted for life in clear water. However, the effects of water hyacinth
on dissolved oxygen levels in inshore habitats may be beneficial to cichlids
in that haplochromines can take advantage of the cover in these habitats despite
the low oxygen, whereas Nile perch are intolerant of such oxygen levels. This
would explain the significantly higher numbers of cichlids caught in the shoreline
gill nets as opposed to the nets offshore. While there is little doubt that
the lake is still responding to environmental changes and fishing pressures,
it is certain that the diversity of haplochromine taxa that once flourished
in the lake is now greatly reduced.
Part of FIRI's commitment to conserving the cichlid biodiversity of the region
is the development of aquaria and pond aquaculture for education and captive
breeding purposes. I suggested using the more secure indoor aquaria to display
and breed Lake Nawampasa cichlids and the outdoor ponds to rear offspring. By
this arrangement, valuable brood stock can be protected; reproduction can be
carefully controlled; and juveniles would have the requisite space for proper
At the start of our second week, we made a trip to Kampala, the capital, to
order and pick up glass needed for the planned exhibit aquaria to be built and
housed at FIRI. A room (6 m x 4 m) with a sink, drainage, electrical power,
and windows (to control ambient light) accomodated a metal stand constructed
to hold twelve 150-l aquaria. The arrangement of these tanks permits further
expansion as resources become available and husbandry skills develop. A primary
aquarist or technician and a back-up person will staff the aquarium room for
weekends, holidays, and other times when the primary person is not around. To
make the facility complete, a supply of such tools as buckets, nets, siphon
hoses, fish foods, medications, and resource books are needed. While we were
setting up this facility, we also made plans and took the initial steps to construct
concrete lined rearing ponds on the "back lawn" at FIRI. They were
designed to operate on a gravity flow system and would be built above ground
to facilitate husbandry work.
Lake Nawampasa is small (ca. l square kilometer) and very shallow with a maximum
depth of only three meters. The lake is accessible by dirt road although a 4-wheel
drive truck is required to negotiate the route given its poor condition. There
is a village alongside the lake whose residents are primarily involved in ranching.
The area around the lake has little relief so the lake (which is surrounded
by tall fringing grasses) is difficult to locate from a distance. One almost
needs to get wet feet to know where the lake actually starts!
Perhaps the dominant (certainly the most impressive) physical feature of Lake
Nawampasa is the extensive fringe of submerged and emergent macrophytes in the
littoral zone, which provides habitat and food for an abundance of resident
cichlids. The dominant submerged macrophyte appeared to be Ceratophyllum sp.
(hornwort), although Nymphaea sp. and Potamogeton sp. were also readily observed
in the clear, shallow waters. In places the submerged macrophytes were so dense
that it made travel in the canoe difficult, in contrast to the inshore zones
of the Napoleon Gulf of Lake Victoria where I observed no submerged macrophytes.
The latter condition is due at least in part to the presence of the introduced
Tilapia zilli, which has been described as "a goat with fins" based
on its habits of foraging on vegetation.
The water of the littoral zone appeared clear and was not stained despite abundant
plant debris on the bottom. The substrate in this zone was predominantly a combination
of mud and plant debris. The littoral zone conditions contrasted sharply with
the turbid, seemingly macrophyte free, open waters of offshore areas.
Geological conditions around Lake Nawampasa are dramatically different from
the lateritic soils found in the Jinja area of Lake Victoria. Lake Nawampasa
is situated on an ancient shield, responsible for the grey, sandy soils, which
also makes its presence known by the occasional massive rock outcrop. It was
not surprising to find dissimilar water chemistry from the values observed at
Jinja. When tested with a Tetra Laborett kit, the pH of Lake Nawampasa was 7.3
(range: 7.07.5) with a KH of 11 DH. Dissolved oxygen levels were near saturation
at most sites where measurements were taken, but this could depend on the amount
of exposure to wind and the density of submerged macrophytes.
During our second week, we made two trips to Lake Nawampasa with our Ugandan
colleague, S. B. Wandera. Our objectives were to survey the habitat and collect
founder stocks for specific Haplochromis taxa not represented in the LV-SSP
captive breeding program. On the first trip we arrived late in the afternoon;
while some of the FIRI crew set up camp, we had a local take us onto the lake.
The canoe we used seemed to have been designed to float at the expense of any
ability to keep out water and lacked all but the absolute minimum of stability.
However we did manage to complete our work on (rather than in) the lake! Several
inshore and offshore sites were identified and sampled using unbaited minnow
traps. Also at these sites, temperature and dissolved oxygen measurements were
taken. The following morning the minnow traps were checked and removed. The
only fish found in the traps were juvenile cichlids less than 3 cm TL. The first
trip ended with an unfortunate accident that resulted in the demise of the fish
captured from the lake. The plug in the transport cooler came out during the
3.5 hr drive back to Jinja along less than perfectly level roads. Luckily, our
second trip later in the week was far more successful.
When we arrived at the lake for the second time, we were greeted by young men
eager to fish for us. The local fishermen were very productive. In no time at
all, they brought us shallow, plastic tubs containing not more than a few liters
of water and up to thirty adult cichlids. The tubs were at times covered with
a waterlily leaf to maintain water temperature. Despite this, temperatures in
the tubs rose very quickly with an obvious effect on dissolved oxygen content,
evidenced by the fish "gasping" at the surface.