Heterogeneity in food-web interactions of fish in the Mwanza Gulf, Lake Victoria : a quantitative stable isotope study
Cornelissen, Ilse J.M. ; Vijverberg, J. ; Beld, A.M. ; Helmsing, N.R. ; Verreth, J.A.J. ; Nagelkerke, L.A.J. - \ 2018
Hydrobiologia 805 (2018)1. - ISSN 0018-8158 - p. 113 - 130.
Haplochromines - Nile perch - Population-level metrics - Trophic level - Tropical lake
Stable isotope analyses and derived population-level metrics were used to quantitatively analyse spatial and seasonal heterogeneity in the fish trophic dynamics in relation to environmental variables in Mwanza Gulf, Lake Victoria (Tanzania). The fish community in Lake Victoria, including the top predator Nile perch, is generally omnivorous with a heavy reliance on invertebrates. This is in contrast to findings based on stomach content analyses of Nile perch, which showed a stronger reliance on fish. We tested two hypotheses: (1) during the rainy seasons multiple carbon sources influence the food-web structure inside the Gulf, leading to increased carbon ranges and trophic diversity. (2) During dry periods, the food-web structure mainly relies on pelagic primary production, reducing carbon ranges and trophic diversity. Carbon sources indeed varied seasonally and spatially, affecting the fish community at the highest trophic levels. With the onset of rains, carbon sources became spatially highly differentiated with enriched δ13C values of fish in shallow water inside the Gulf and depleted δ13C values in open waters. Metrics associated with niche size correlated significantly with seasonally varying environmental variables, while δ13C ranges correlated with spatially varying environmental variables.
Zooplankton, fish communities and the role of planktivory in nine Ethiopian lakes
Vijverberg, J. ; Dejen, E. ; Getahun, A. ; Nagelkerke, L.A.J. - \ 2014
Hydrobiologia 722 (2014)1. - ISSN 0018-8158 - p. 45 - 60.
fresh-water zooplankton - top-down control - trophic relationships - subtropical lake - nutrient state - body-size - sri-lanka - shallow - reservoirs - food
Fish and zooplankton populations of nine Ethiopian freshwater lakes were quantitatively sampled along a North–South gradient. Differences in altitude and latitude resulted in a temperature gradient from North to South. We tested three hypotheses: (1) the degree of zooplanktivory decreases with water temperature, i.e. from North to South; (2) the degree of zooplanktivory increases with the abundance of large-bodied zooplankton; and (3) the pattern of zooplanktivory in eutrophic Ethiopian water bodies differs from other tropical and temperate water bodies. Proportions of zooplanktivory in the fish communities did not show a geographical trend, but mainly depended on fish species, zooplankton density and the availability of large-bodied cladocerans. The degree of zooplanktivory in eutrophic Ethiopian water bodies differs from other eutrophic water bodies, both temperate and tropical. In Ethiopia, the degree of zooplanktivory can be both low and high, in contrast with other tropical water bodies where zooplanktivory is generally low and with temperate eutrophic water bodies where it is generally high. As a result, predation pressure on zooplankton by fish varies dramatically amongst Ethiopian water bodies.
The composition of fish communities of nine Ethiopian lakes along a north-south gradient: threats and possible solutions
Vijverberg, J. ; Dejen, E. ; Getahun, A. ; Nagelkerke, L.A.J. - \ 2012
Animal Biology 62 (2012)3. - ISSN 1570-7555 - p. 315 - 335.
rift-valley lakes - fresh-water ecosystems - species flock pisces - reproductive segregation - cyprinidae - tana - barbs - strategies - diversity - example
Fish populations of nine Ethiopian freshwater lakes were quantitatively sampled with a standardized protocol, using multi-mesh gill nets. In total, 27 species were identified, but only 14 species were common. Based on the common species, the fish communities showed large differences in their species composition, except for Lake Abaya and Lake Chamo which were similar. Most fish species were observed in only one or two lakes. Compared with the information reported in literature the present study generally underestimated the species richness. The empirical model of Amarasinghe and Welcomme (2002) for African lakes was used to estimate fish species richness, which was compared with species presence reported in literature. Biodiversity in the two northern highland lakes is low, but not lower than the model estimate. Lake Tana has a high biodiversity which is close to what is estimated by the model, but three Rift Valley lakes have low biodiversity, lower than estimated by the model. There are also strong indications for the Rift Valley lakes that species richness was higher in the past because the species richness reported in the older literature was generally much higher than those observed by us in the present study and those reported in the more recent literature. Threats like overfishing, high sediment load and degradation of habitats were identified. It is recommended that Ethiopia should develop guidelines for fishery legislation and implement it through an enforcement agency. Moreover, catchments management should be practiced to save the water bodies and their fish communities
Spawning migrations of the endemic Labeobarbus (Cyprinidae, Teleostei) species of Lake Tana, Ethiopia: status and threats
Anteneh, W. ; Getahun, A. ; Dejen, E. ; Sibbing, F.A. ; Nagelkerke, L.A.J. ; Graaf, M. de; Wudneh, T. ; Vijverberg, J. ; Palstra, A.P. - \ 2012
Journal of Fish Biology 81 (2012)2. - ISSN 0022-1112 - p. 750 - 765.
The reproductive biology of the only known intact species flock of large cyprinids, the 16 Labeobarbus species of Lake Tana (Ethiopia), has been extensively studied for the past two decades. Seven species of Labeobarbus are known to migrate >50 km upstream into tributary rivers for spawning during the rainy season (July to October), whereas eight other species are absent from these rivers and probably developed a new strategy of lacustrine spawning (macro-spatial segregation). One species (L. intermedius) probably spawns in the lake as well as in the rivers. Between the early 1990s and 2000s, the riverine spawners showed a decline of 75% in both biomass and number in both fishery independent surveys and in commercial catches. Reproductive migration makes fishes vulnerable to fisheries and other threats like habitat modifications. Lacustrine spawners are probably more resilient as they are not known to form spawning aggregations that can easily be exploited by fishermen. In addition, upstream rivers and catchments around Lake Tana are highly degraded by erosion and recently subjected to intensive habitat modification for irrigation and hydroelectric power generation. This article reviews results of field studies on the Labeobarbus spawning migration from Lake Tana to spawning rivers, giving emphasis on segregation and homing. It also summarizes existing and emerging threats which form potential causes for the decline of the migratory Labeobarbus species. Knowledge gaps on the reproductive biology are identified for further investigation
Growth, biomass, and production of two small barbs (Barbus humilis and B. tanapelagius, Cyprinidae) and their role in the food web of Lake Tana (Ethiopia)
Dejen, E. ; Vijverberg, J. ; Nagelkerke, L.A.J. ; Sibbing, F.A. - \ 2009
Hydrobiologia 636 (2009)1. - ISSN 0018-8158 - p. 89 - 100.
species flock - seasonal-variation - fish - zooplankton - model
Growth, biomass and production of two small barbs (Barbus humilis and Barbus tanapelagius) and their role in the food web of Lake Tana were investigated. From length–frequency distribution of trawl monitoring surveys growth coefficient, F' values were estimated at 3.71–4.17 for B. humilis and 3.70–4.14 for B. tanapelagius, respectively. Values for B. humilis were confirmed in pond experiments. Mean biomass of the small barbs was 13.3 kg fresh wt ha-1, with B. humilis being most abundant in the littoral and sub-littoral zones, whereas B. tanapelagius was most abundant in the sub-littoral and pelagic zones. The two small barbs had a production of 53 kg fresh wt ha-1 year-1. Although their P/B ratios of about 4.0 were relatively high for small cyprinids, both their biomass and production were low in comparison with other small fish taxa in other tropical lakes. Of the zooplankton production only about 29% was consumed by the small barbs. However, they did not utilize calanoid copepods, which were responsible for approximately 57% of the zooplankton production and it is likely that small barb production was food limited during certain periods of the year. Piscivorous labeobarbs consumed about 56% of the small barbs production annually, but additionally, Clarias gariepinus, and many bird species were also preying on them. Therefore, limitation of Barbus production by predation during certain periods in the year cannot be excluded
|Lake Tana: Source of the Blue Nile
Vijverberg, J. ; Sibbing, F.A. ; Dejen, E. - \ 2009
In: The Nile. Origin, Environments, Limnology and Human Use / Dumont, H.J., Springer Science + Business Media B.V. (Monographiae Biologicae 89) - ISBN 9781402097256 - p. 163 - 192.
Structure of microcrustacean zooplankton communities in five tropical Asian water bodies.
Vijverberg, J. ; Amarasinghe, P.B. ; Chitapalapong, T. ; Pagulayan, R.C. ; Ariyaratne, M.G. ; Pamanian, E.R.J. ; Silva, E.I.L. ; Nagelkerke, L.A.J. - \ 2008
In: Aquatic Ecosystems and Development: Comparative Asian Perspectives. / Schiemer, K, Simon, D, Amarasinghe, U.S., Moreau, J, Germany, Netherlands : Margraf Publishers and Backhuys Publishers - ISBN 9789057822018 - p. 153 - 172.
|Adaptive radiation of Labeobarbus species in Lake Tana
Sibbing, F.A. ; Graaf, M. de; Dejen, E. ; Nagelkerke, L.A.J. ; Vijverberg, J. ; Osse, J.W.M. - \ 2008
In: Abstracts of the 4th International Conference of the Pan African Fish and Fisheries Association. - Addis Ababa, Ethiopia : - p. 76 - 76.
Lake Tana, Ethiopia: The Source of the Blue Nile
Vijverberg, J. ; Dejen, E. ; Sibbing, F.A. - \ 2007
SIL-news 2007 (2007)51. - p. 12 - 12.
Seasonal variation in primary production of a large high altitude tropical lake (Lake Tana, Ethiopia): effects of nutritient availability and water transparency
Wondie, A. ; Mengistu, S. ; Vijverberg, J. ; Dejen, E. - \ 2007
Aquatic Ecology 41 (2007)2. - ISSN 1386-2588 - p. 195 - 207.
barbs barbus - turbid waters - species flock - cyprinidae - reservoir
Primary production rates, chlorophyll and phytoplankton biovolume were measured monthly from April 2003 to November 2004 in Lake Tana, a large tropical lake in the highlands of Ethiopia. The lake is characterised by low nutrient concentrations, and a low water transparency due to high silt load of the inflowing rivers during the rainy seasons (May¿November) and daily resuspension of sediments in the inshore zone. The mean chlorophyll-a concentrations varied seasonally and ranged from 2.6 mg m¿3 to 8.5 mg m¿3 (mean: 4.5 mg m¿3) in the offshore zone. Primary production was measured using the light¿dark bottles technique. We incubated only at three depths, i.e. 0.6, 1.2 and 1.8 m. Therefore, we may have missed a substantial part of the depth production profile and probably also frequently missed P max. Gross primary production in the openwater averaged 2.43 g O2 m¿2 d¿1 and ranged between 0.03 g O2 m¿2 d¿1 and 10.2 g O2 m¿2 d¿1; production was significantly higher in the inshore zone. The highest production rates were observed in the post-rainy season (Oct¿Nov), which coincided with a bloom of Microcystis and higher chlorophyll levels. This seasonal high production is probably caused by a relatively high nutrient availability in combination with favourable light conditions. The gross primary production rates of L. Tana are among the lowest compared with other tropical lakes. This will be partly the result of our underestimation of gross primary production by often missing P max. Another cause is the oligotrophic nature of the lake in combination with its relatively low water transparency. The gross primary production per unit chlorophyll in the openwater zone was in the same range as in 30 other tropical lakes and reservoirs. The higher primary production in the inshore zone is probably the result of the daily water column mixing (Z mix ¿ Z t) in this area, enhancing nutrient recycling. A large proportion of the annual primary production is realised in one of the four seasons only. This productive post-rainy season is relatively short (2 months) and therefore efficiency of transfer of matter between the first and second trophic level of the Lake ecosystem will be poor.
Predicting and testing resource partitioning in a tropical fish assemblage of zooplanktivorous 'barbs': an ecomorphological approach
Dejen, E. ; Vijverberg, J. ; Graaf, M. de; Sibbing, F.A. - \ 2006
Journal of Fish Biology 69 (2006)5. - ISSN 0022-1112 - p. 1356 - 1378.
lake tana ethiopia - species flock - sri-lanka - growth - tanapelagius - cyprinidae - reservoirs - humilis - overlap - shifts
Morphometrics on 25 critical feeding structures predicted conspicuous specializations in Barbus tanapelagius (pursuit hunting for zooplankton), Labeobarbus brevicephalus (surface dwelling pump-filter-feeder on zooplankton) and Barbus pleurogramma (particulate feeding on tough, benthic food), whereas for Barbus humilis intermediate values predicted few constraints and specializations in feeding. These potential niches, set by fish size and structural constraints, were tested by comparing gut contents collected during a 24 months sampling programme on Lake Tana, Ethiopia. Zooplankton dominated the diet of B. tanapelagius (75% of gut volume) and L. brevicephalus (39%). The guts of B. pleurogramma and juveniles of the large labeobarbs showed an array of benthic food types, whereas B. humilis had the widest food niche, both zooplankton (40% of gut volume) and benthic invertebrates. Although the pelagic species showed the largest spatial overlap, their size, feeding modes and utilization of zooplankters differed: L. brevicephalus preyed predominantly on the larger zooplankton (Daphnia sp.) and B. tanapelagius also on smaller species (e.g. Bosmina sp. and cyclopoid copepods). The spatial segregation between B. tanapelagius (pelagic) and the juvenile labeobarbs (littoral) indicated the possibility for a small pelagic barb fishery without negative effects on the labeobarb stocks. The ecomorphological approach using the 'Food-Fish Model' appeared to predict competitive positions and resource partitioning appropriately, and is of major importance to evaluate food web interactions
Spatial and temporal variation of cestode infection and its effect on two small barbs (Barbus humilis and B. tanapelagius) in Lake Tana, Ethiopia
Dejen, E. ; Vijverberg, J. ; Sibbing, F.A. - \ 2006
Hydrobiologia 556 (2006)1. - ISSN 0018-8158 - p. 109 - 117.
ligula-intestinalis l - roach - plerocercoids - aggregation - cyprinidae - l.
Pseudophyllidean cestodes as Ligula have a complex life cycle with cyclopoid copepods as first intermediate host, zooplanktivorous fish as second, and piscivorous birds as final host. We studied the effects of diet, season and habitat occupation on the prevalence of plerocercoid larvae of the tapeworm Ligula intestinalis in two closely related small barbs and the effects of the parasites on the barbs life histories in Lake Tana (Ethiopia) during 1 year. In all affected barbs L. intestinalis caused retardation in gonad development, maturation at reduced size and lower absolute fecundity. Infection rate, averaged over all habitats was significantly higher in B. tanapelagius (10%) than in B. humilis (6%). Below a threshold of 48 mm the infection rate was zero for both barbs, this coincided with a very low proportion of copepods in their diets, increasing up to 90 and 55%, respectively, for their largest size class (81¿90 mm). The relatively high infection rate in B. tanapelagius is explained by its obligatory zooplanktivorous feeding behaviour, ingesting a relatively high proportion of infected cyclopoid copepods. This is in contrast with B. humilis, which is a polyphagous species, feeding both on zooplankton and benthic invertebrates. Significant seasonal effects in infection rates were observed. In both barb species infection rates were lower during the breeding season. Only for B. tanapelagius a significant negative correlation was observed between rain fall and infection rate, probably caused by an increased turbidity that decreases feeding efficiency on zooplankton. Habitat type had also a significant effect on infection rate. Barbus humilis showed a much higher infection rate in shallow clear water (10%) than in shallow turbid water (3%), whereas B. tanapelagius showed much higher infection rates in the shallow sublittoral (13%) than in the deeper pelagic (7%). Most likely, birds predate more efficiently on barbs in shallow clear waters than in shallow turbid and deep waters.
Effects of predation and food on the population dynamics of the raptorial cladoceran Leptodora kindtii
Vijverberg, J. ; Koelewijn, H.P. ; Densen, W.L.T. van - \ 2005
Limnology and Oceanography 50 (2005)2. - ISSN 0024-3590 - p. 455 - 464.
neusiedler-see austria - shallow eutrophic lake - invertebrate predation - natural-population - foraging behavior - feeding-behavior - seasonal-changes - daphnia-hyalina - focke crustacea - zooplankton
We assessed the trophic status of Leptodora kindtii in the food web of a shallow, eutrophic lake in which 0+ age group fish were the main predators. The mean biomass of 0+ fish during three successive years varied from 0.39 g dry wt m(-2) in the first year to 0.05 g dry wt m(-2)in the second year to 2.49 g dry wt m(-2) in the third year. In the years with high fish biomass, densities of small-bodied (<1-mm) cladocerans (e.g., Bosmina spp., Chydorus sphaericus) were relatively high, whereas in the year with low fish biomass, densities of large-bodied Daphnia galeata were high, and densities of small-bodied cladocerans were lower. During the three study years, the predation pressure of juvenile fish and biomass and production of Leptodora were negatively correlated. Despite the low 0+ fish biomass in the second year, the Leptodora population densities were high only during the first part of the growing season. The elevated Leptodora mortality in July coincided with the lowest observed densities of small-bodied cladocerans, preferred prey items of Leptodora, and with an abundance of large-bodied Daphnia, the preferred food for 0+ fish. We conclude that the population dynamics of Leptodora during the growing season is predominantly regulated by direct predation effects.
Effect of temperature on development and growth of the raptorial cladoceran Leptodora kindtii under laboratory conditions
Vijverberg, J. ; Koelewijn, H.P. - \ 2004
Freshwater Biology 49 (2004)11. - ISSN 0046-5070 - p. 1415 - 1422.
foraging behavior - lake - bythotrephes - predator - prey - reproduction - population - tjeukemeer - daphnia
1. Leptodora is a key species in many temperate freshwater systems, but so far its role in the food web could not be properly evaluated because detailed information about its secondary production was lacking. As we wanted to estimate the secondary production of Leptodora, we measured its development and growth rates in the laboratory. 2. Employing improved methods to estimate growth and instar durations, we cultured Leptodora kindtii in the laboratory at four constant temperatures (15, 17.5, 20 and 25 °C). Growth in length and development times of eggs and instar stages were assessed. 3. Growth rates at 15, 17.5 and 20 °C were similar, but at 25 °C growth was distinctly faster. At 17.5 °C we observed seven juvenile instar stages before the first adult instar stage was reached.
Temporal and spatial distribution of microcrustacean zooplankton in relation to turbidity and other environmental factors in a large tropical lake (L. Tana, Ethiopia)
Dejen, E. ; Vijverberg, J. ; Nagelkerke, L.A.J. ; Sibbing, F.A. - \ 2004
Hydrobiologia 513 (2004)1-3. - ISSN 0018-8158 - p. 39 - 49.
barbs barbus-humilis - aquatic organisms - suspended clay - population-dynamics - community structure - reservoir - reproduction - cladocerans - abundance - dispersal
The spatial and seasonal distribution of microcrustacean zooplankton of Lake Tana (Ethiopia) was monthly studied for 2 years. Concurrently, various environmental parameters were measured and related to zooplankton distribution. Canonical Correspondence Analysis (CCA) was used to estimate the influence of abiotic factors and chlorophyll a content in structuring the zooplankton assemblage. Among the environmental factors, zooplankton abundance correlated most strongly with turbidity. Turbidity was negatively correlated with species abundance, especially for Daphnia spp. and to the least extent for Diaphanosoma spp. Analysis of variance (ANOVA) was used to determine spatial (littoral, sublittoral and pelagic zone) and temporal (four seasons) variation in zooplankton abundance. We observed significant temporal differences in zooplankton abundance, with highest densities during dry season (November-April). Only cladocerans showed significant differences in habitat use (highest densities in the sublittoral zone).
Reproductive strategies of two sympatric 'small barbs'(Barbus humilis and B. tanapelagius, Cyprinidae)in Lake Tana, Ethiopia
Dejen, E. ; Sibbing, F.A. ; Vijverberg, J. - \ 2003
Netherlands Journal of Zoology 52 (2003)2-4. - ISSN 0028-2960 - p. 281 - 299.
dynamics - fish
The reproductive strategies of two species of 'small barbs' (12,000 fish). Both species have a long breeding period (from March to September), and the distinct bimodal size-frequency distributions of eggs suggest multiple spawning for both species. Absolute fecundity increased exponentially with fish size, and was significantly higher for B. humilis than for B. tanapelagius. Egg size was similar. Relative fecundity was significantly higher in B. humilis. In most habitats B. tanapelagius reached first maturity at a smaller size (58.5 mm) than B. humilis (64.5 mm). However, in shallow habitats with clear water B. humilis females are much smaller at first maturity (48.3 mm), possibly due to high tapeworm infection rates. The range of fecundity in small barbs from Lake Tana (172-339 eggs per gram) was low compared with small lacustrine cyprinids and clupeids from other African lakes. The reproductive strategies of the two barbs were discussed in relation to their feeding potential, food availability, parasite infection rate and risk of predation