The Tropical Lakes Biodiversity CrisisPaul Hacker, Ryan Haines & Alex Swan
http://www.go2africa.com/location/6482/why-go
Case Study Introduction: Lake Victoria (Witte et al. 2007)
Analysis of Witte et al. (2007) Conclusions from Witte et al. Supporting literature Conclusion Discussion
Outline
Location: Africa - Uganda / Kenya / Tanzania.
Size: 68,800km2
Elevation: 1,134m Age: ~ 1 million years
Dry until 14,000 years ago.
Fish Species: Several 100 species of haplochromine cichlids and Nile Perch.
Case Study: Lake Victoria (Witte
et al. 2007)
http://www.worldatlas.com/aatlas/infopage/lakevictoria.gif
http://www.theasc.com/blog/wp-content/uploads/2011/08/09.-africa_map.jpeg
Haplochromine cichlids (>500 sp.) Difficult to distinguish
Evolved in last 14,000 years (Kitchell et al. 1997).
Monophyletic assemblage Phenotypically similar
Males brightly coloured Females choose males based on
colouration (Witte et al. 2007).
Historic food to local peoples & important part of economy (Kaufman et al. 1997 & Kitchell et al. 1997).
Past studies grouped them together.
Case Study: Lake Victoria (Witte
et al. 2007)
http://www.african-cichlid.com/Nubila8116.jpg
Astatotilapia nubila
http://www.african-cichlid.com/Alluaudi4623.jpg
Astatoreochromis alluaudi
Hypothesis: “The identification of this speciose group to the species level is helpful in unraveling what happened in Lake Victoria and crucial for the proper management of its fishery and biodiversity”
Case Study: Lake Victoria (Witte
et al. 2007)
Haplochromine cichlids are particularly difficult to distinguish between species - need specialists Intraspecific variation Phenotypic plasticity Sexual dimorphism Colour polymorphism
Management implications Managing for 5oo+ species as 1 causes some
problems. Signals may not paint the correct picture.
Species Distinction: Problem
A quick history lesson about human involvement in Lake Victoria before we dive into the data collection by Witte et al.
Case Study: Lake Victoria (Witte
et al. 2007)
Critically threatened due to humans! Collapsing fisheries! (Kaufman et al. 1997 &
Witte et al. 2007).
Lake wide environmental degradation! (Kaufman et al. 1997 & Witte et al. 2007).
“Whole sale loss of fish species”! (Kaufman et al. 1997).
Case Study: Lake Victoria (Witte
et al. 2007)
The Human Problem!
https://global3.memecdn.com/grumpy-cat-strikes-again-human-race_o_1112508.jpg
INTRODUCED SPECIES! EUTROPHICATION! OVERFISHING!
Case Study: Lake Victoria (Witte
et al. 2007)
Causes? http://images1.fanpop.com/images/photos/2200000/home-alone-home-alone-2258019-1024-768.jpg
Nile Perch (Lates niloticus) Introduced in 1950s to
support fisheries (Witte et al. 2007).
“The Saviour” (Greboval 1990).
Yields 4x greater than native sp. (Kitchell et al. 1997).
25,000 tons 175,000 tons between 1978-1990.
150,000 jobs created (Greboval 1990).
Successful predator Grows 1kg in first year (Kitchell et
al. 1997).
Can reach 100kg (220lbs) (Kitchell et al. 1997).
Case Study: Lake Victoria (Witte
et al. 2007)
http://www.busiweek.com/img2/nile-perch-colour.jpg
INTRODUCING SPECIES!!
Human population pressure! (Odada
et al. 2003)
Human untreated waste 30million people live in the rift
valley Water transparency reduction
(Odada et al. 2003)
5m in 1930 1m in 1990s Phosphorous loading in deep
water Nitrogen loading in shallow
waters Periods of anoxic conditions in
shallow water
Case Study: Lake Victoria (Witte
et al. 2007)
EUTROPHICATION!!
https://sp.yimg.com/ib/th?id=HN.608029410971356475&pid=15.1&P=0
Historical problem not improving 1950s overfishing –
Outboard motors & Nylon nets (Kaufman et al. 1997)
84,000 fisherman in 1990/91 (Odada et al. 2004).
122,000 fishermen in 2000 (Odada et al. 2004).
Unrestricted access and lack of enforcement of existing legislation (Odada et al.
2004)
Case Study: Lake Victoria (Witte
et al. 2007)
OVERFISHING!!
https://c2.staticflickr.com/4/3087/2331808854_31e2549c7b_z.jpg?zz=1
Timeline: The decline of cichlids and the rise of the Nile Perch.
Case Study: Lake Victoria (Witte
et al. 2007)
1920s: Eutrophication began (Hecky 1993).
1950s: Introduction of Nile perch (Witte et al. 2007).
Needed to support fishery due to overfishing of cichlids. 1980s: Nile Perch Boom & Blue-green algal bloom! (Witte et al.
2007).
Haplochromines vanished from sublittoral and offshore areas. 1990s: Overfishing = Decline in Nile Perch (Witte et al. 2007 & Kitchell et
al. 1997).
Slow recovery in some cichlids 1998 Nile Perch harvest half of 1990 catch.
Eutrophication still a problem.
IMPORTANT: Most studies categorize cichlids as one.
Methods (Witte et al. 2007)
What was caught?Haplochromine cichlids
Eleven Stations monitored for 26 years (1979-2005)
Transect 5km wide, depth ranges from 2- 15m
Witte et al. (2007)
Trawling samples Small
Bottom (headrope: 4.6m, cod-end mesh: 5mm) Surface (beam: 4.5m, cod-end mesh: 5mm)
Large The gulfs (headrope: 18-25m, cod-end mesh:
20mm)
Methods (Witte et al. 2007)
http://anw.inl.nl/article/trawler#s=0&l=&lp=
Witte et al. (2007)
Rocky shores fished Gill nets Local traps Angler rods baited with worms
Adults and Sub-adults Approx >4cm long
Methods (Witte et al. 2007)
https://photosundari.wordpress.com/2012/01/17/960/
http://www.oldeastafricapostcards.com/?page_id=2338
Total number of haplochromine species in Lake Victoria is still debated…
... So Witte et al. (2007) must consider all data!
Methods (Witte et al. 2007)
http://etims.net/?p=6052
Species Discovery and Description 3 periods of study
1. 1888-1938 61 species: little to no ecological data
2. 1956-1969 104 species: littoral studies and species
descriptions
3. 1975- present Estimated 500+ species
Results (Witte et al. 2007)
Species Discovery/ Distribution
Results (Witte et al. 2007)
Species Discovery/Description
Witte et al. (2007)
15 groups have been identified Number of species per group different
Highest number of individuals = piscivores Highest biomass = detritivores Habitat type determined distribution
Multiple habitat types means many sampling stations
Results (Witte et al. 2007)
Trophic Groups
Many different communities Communities differ vastly based on
substrate Bottom: Sand (75) > Mud (49)
Causes of differences Food availability Abiotic conditions:
light effects feeding efficiency Dissolved oxygen
Results (Witte et al. 2007)
Haplochromine Communities
Witte et al. (2007) analyze the data
Results (Witte et al. 2007)
Is the biodiversity Crisis in Lake Victoria Real?
http://register.eau.ac.th/
There has been an overall decline in haplochromines!!! 80 species disappeared from 1972-1990… BUT scientists disagree
Can we determine extinction based on extirpation? NO, disagreements over causes or severity
Luckily, Witte et al. (2007) attempt to analyze the full picture coupling their findings with the historical
Results (Witte et al. 2007)
Is the biodiversity Crisis in Lake Victoria Real?
1987 reported decreases (Barel et al. 1985, Coulter et al. 1986)
>90% sublittoral 70% littoral 40% rock dwellingNOT NECESSARILY CORRECT! What does the data ACTUALLY indicate? Nile perch have inverse distribution Abiotic factors can not be ruled out
Results (Witte et al. 2007)
Impacts on Communities
1. Large size species declined faster than small Piscivores, molluscivores, insectivores
2. Interspecific differences Number of individuals = same, species composition
is different Zooplanktivores: H. pyrrhocephalus better adapted
to low-light than H. heusinkveldi Spawning and diet effected
Gills surface area increased 70% in H. pyrrhocephalus between 1970-1990.
Results (Witte et al. 2007)
Impacts on Trophic Groups
Morphological selection and creation of “new species” has occurredWhy?1. Populations in all areas understudied2. Anatomy of coloration changes due to
environmental changes3. Creation of hybrids4. Genetic changes have taken place in small
surviving populations5. Combination of the above
Results (Witte et al. 2007)
Adaptive Responses in Recovering Species
Haplochromines can not be considered as a homogeneous unit
Adaptive responses to water conditions have played a role in population dynamics Low- light adaptations advantageous Zooplanktivourous diet advantageous
Conclusion (Witte et al. 2007)
What do we already know?
Need a credible list on extinction to be able to implement rigorous regulations and criteria
Currently the number of unknown extinctions is likely high
Causes of haplochromine populaiton changes Nile Perch Eutrophication Fishing
Conclusion (Witte et al. 2007)
What do we already know?
Knowledge of haplochromine cichlids is important for management Biodiversity Fish production
The studies in the 70s and 80s were integral in identifying crisis the extent of the crisis is still unknown
Conclusion (Witte et al. 2007)
Why do we need to know more?
Future Management Focus on Nile perch important, but not
comprehensive Eutrophication needs to be halted and reversed
if possible Areas of refuge need to be created
Each habitat type needs to be represented Key issue in managing the lake:
KNOWLEDGE OF CICHLIDS
Conclusion (Witte et al. 2007)
What’s next?
Compared the densities and diversity of cichlids over different substrate types before and after environmental damage of Lake Victoria
Anthropogenic Environmental Damage Nile Perch—disruption of the food web
Algal blooms Eutrophication
Decreased water transparency and Dissolved Oxygen (DO)
Case Study #1: Witte et al 2013
Eutrophication and introduction of Nile Perch to the lake coincided with the disappearance of cichlid species.
Debate on what the cause of cichlids declining is. Eutrophication or Nile Perch?
This study looks at the effects of eutrophication as a possible cause for the decline of cichlids.
Case Study #1: Cont’d
Case Study #1: Cont’d
Significantly more DO and light at the bottom of sand sites.
Significantly higher mean number of species in the sand sites.
Mud sites had significantly more detritivores but significantly less insectivores and mollusc shellers.
Case Study #1: Cont’d
Mud sites saw a significant decline in haplochromine catch and diversity.
Case Study #1: Cont’d
Mud substrate sites had lower frequency of brooding females overall and in months with predicted high turbidity levels.
Months with low DO (Feb-April) affected the frequency of brooding females regardless of substrate type.
Human impacts have caused about 70% decline in the loss of species in Lake Victoria.
Nile Perch strongly affected haplochromine densities and forced them into different, less ideal habitats.
However, results of their study suggest that water transparency affects species diversity the most.
Case Study #1: Cont’d
Ethiopia is currently facing fish biodiversity crisis.
Diversity of ichthyofauna is unknown, like Lake Victoria.
Environmental degradation at accelerated levels.
Case Study #2: Getahun & Stiassny 1998
Threats to freshwater fauna: River/Stream alterations (dams and irrigation) Deforestation Introduction of invasive species
Interestingly, fish as a food source is not a major threat in Ethiopia.
Case Study #2: Cont’d
Case Study #2: Cont’d
81% from Cyprinidae. Most diverse family. Cichlids comprise
largest part of inland commercial fishery.
Vulnerable freshwater ecosystems are not well protected
Diversity of fish is underestimated Fish faced with considerable threats
HIPPO Need more studies to establish baseline of
fish diversity knowledge Need to alleviate environmental degradation
Case Study #2: Cont’d
Case study of rapid speciation and adaptive radiation of haplochromines in Lake Victoria is unprecedented
However, Lake Victoria is a case study in anthropogenic mass extinction >50% of endemic fishes disappeared 1980-
1986 Examine the dynamics of haplochromine
volatility Find ways to manage and conserve
Case Study #3: Kaufman et al 1997
Case Study #3: Kaufman et al 1997
East Africa has greatest concentration of freshwater fish species on earth. Around 2000 species 8% of global fish species
Haplochromines very diverse group. Traditionally lumped together
as one unit Increased taxonomic
distinction has provided a clearer picture of cichlidae family
Haplochromines are relatively young 12,000 years old
Where does 600+ species of fish with broad trophic variation come from in such a short amount of time? Re-invasion of Lake Victoria from outside the
basin Intra-lacustrine radiation Not mutually exclusive
Case Study #3: Kaufman et al 1997
Re-invasion of Lake Victoria from other Lakes Great Rift Lakes are connected Most likely from Edward-George Lake System Haplochromines do exist in Lake Kyoga and Edward-
George Lake System Rescue effect would have to flow both ways
From Lake Victoria to Edward-George Lake System and vice versa
Could only be possible if flooding was great enough to create more lacustrine connectivity between these lake systems
Case Study #3: Kaufman et al 1997
Lacustrine Radiation Rapid physical change of the lake could create new
habitat (Volcanic eruptions and fluctuating water levels).
New habitat allows for species radiation to occur. Isolation of sub-lakes and lagoons on a decadal time
scale could allow for species radiation Lagoons and isolated lakes are hostile to lacustrine taxa Rapid adaptation would be needed to survive Haplochromines are volatile and could potentially adapt
that quickly
Case Study #3: Kaufman et al 1997
Haplochromines have faced previous extinction cycles and are quite resistant to it
If the extinction wave in the 80’s has passed, then the existing flock could be the basis for future lacustrine radiation
Find ways to conserve haplochromines via: Decreasing habitat degradation Increased speciation distinction knowledge Increased studies of haplochromine populations now that
Nile Perch has decreased sufficiently to allow for a recovery effect.
Case Study #3: Kaufman et al 1997
Tropical lakes are all facing anthropogenic changes.
Species distinction plays an important role in identifying biodiversity loss Historically not properly studied and
understood Must know more for correct management
Actions going forward Halt environmental degradation Enforce international fishing regulations
Conclusion
Questions?
1. Should management strategies target restoring the original ecosystem or sustaining the current equilibrium?
2. If you were to manage Lake Victoria, what aspect of the lake would you focus on first?
3. Will the international aspect of management preclude success? Or does economic development of surrounding countries play a more significant role in management practices?
Discussion
4. How integral are regulations in solving this crisis? Will they work?
5. Is gathering data on individual species (500+) realistic? Should energy be better spent elsewhere?
Discussion
ReferencesBarel C.D. N., R. Dorit, P.H. Greenwood, G. Fryer, N. Hughes, P.B.N. Jackson, H. Kanawabe, R.H. Lowe-McConnell, M. Nagoshi, A.J.
Ribbink, E. Trewavas, F. Witte and K. Yamaoka. 1985. Destruction of fisheries in Africa’s lakes. Nature 315: 19-20.
Coulter, G.W., B.R. Allanson, M.N. Bruton, P.H. Greenwood, R.C. Hart, P.B.N. Jackson and A.J. Ribbink. 1986. Unique qualities and special problems of the Afican Great Lakes. Environmental Biology of Fishes 17: 117-118.
Getahun, A., and M. L. J. Stiassny. 1998. The freshwater biodiversity crisis: the case of the Ethiopian fish fauna. Ethiopian Journal of Sience 21: 207-230.
Greboval, D. 1990. Socio-economic issues for planning in support of fisheries management. In CIFA report of the 5th session of the Sub-committee for the Development and Management of the Fisheries of Lake Victoria, Mwanze, Tanzania, 12–14 September 1989. FAO Fisheries Report 430: 75–97.
Hecky, R. E. 1993. The eutrophication of Lake Victoria. Verhandlungen der Internationalen Vereinigung fu¨r Theoretische und Angewandte Limnologie 25: 39–48.
Kaufman, L.S., L.J. Chapman, and C. A. Chapman. 1997. Evolution in fast forward: haplochromine fishes of the Lake Victoria region. Endeavour 21: 1997.
Kitchell, J.K., D.E. Schindler, R. Ogutu-Ohwayo, and P.N. Reinthal. 1997. The Nile Perch in Lake Victoria: interactions between predation and fisheries. Ecological applications 7: 653-664.
Odada, E.O., D.O. Olago, K. Kulindwa, M. Ntiba, and S. Wandinga. 2004. Mitigation of environmental problems in Lake Victoria, East Africa: casual chain and policy options analyses. A Journal of the Human Environment 33: 13-23.
Witte, F., J.H. Wanink and M. Kishe-Machumu. 2007. Species distinction and the biodiversity crisis in Lake Victoria. Transactions of the American Fisheries Society 136: 1146-1159
Witte, F., O. Seehausen, J.H. Wanink, M.A. Kishe-Machumu, M. Rensing, and T. Goldschmidt. 2013. Cichlid species diversity in naturally and anthropogenically turbid habitats of Lake Victoria, East Africa. Aquatic Sciences 75: 169-183.