The Tropical Lakes Biodiversity Crisis Paul Hacker, Ryan Haines & Alex Swan

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.


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”


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.


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).


et al. 2007)

The Human Problem!

https://global3.memecdn.com/grumpy-cat-strikes-again-human-race_o_1112508.jpg

INTRODUCED SPECIES! EUTROPHICATION! OVERFISHING!


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).


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


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)


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.


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)


http://anw.inl.nl/article/trawler#s=0&l=&lp=

Witte et al. (2007)

http://anw.inl.nl/article/trawler#s=0&l=&lp

http://anw.inl.nl/article/trawler#s=0&l=&lp

Rocky shores fished Gill nets Local traps Angler rods baited with worms

Adults and Sub-adults Approx >4cm long


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!


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


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


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


Haplochromine Communities

Witte et al. (2007) analyze the data


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


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


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.


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


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


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


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


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


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.


Mud sites saw a significant decline in haplochromine catch and diversity.


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.


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.



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 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


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


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


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


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.


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.

Documents

The Tropical Lakes Biodiversity Crisis Paul Hacker, Ryan Haines & Alex Swan