Ogutu-Ohwayo R., Natugonza V., Musiguzi L., Kitabona J.

National Fisheries Resources Research Institute (NaFIRRI),

P. O. Box 343, Jinja, Uganda. .

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The Response of Inland Aquatic Ecosystems,

Fisheries Productivity and Livelihoods to

Climate Variability and Change:

Lessons from Africa

Vulnerability of fisheries resources Africa is endowed with aquatic

ecosystems which are important

sources of food, employment and

income.

The diversity and quantity of fish in

these systems has decreased due to

over-exploitation, pollution, invasive

species, habitat degradation, and climate

variability and change.

However the response of aquatic

ecosystems, resources and livelihoods to

climate variability and change has

received limited attention.

We review literature from Africa to

demonstrate how aquatic ecosystems,

productivity, fisheries and livelihoods

respond to increasing variability and

change in climate to guide policy. 2

We predict that:

Lake area, depth, circulation, stratification, loading and

recycling of nutrients and oxygen will shift between states with

variability and change in climate.

In turn, the composition and abundance of aquatic organisms,

including fishes will shift to those that can persist, adjust or

exploit the changed conditions.

This will make it necessary for communities to adapt to build

their resilience in order to sustain livelihoods;

Existing policies will have to be adjusted and additional ones

put in place to address the changes and support adaptation.

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Theory of Change

Temperatures of the deep African Great lakes increased by

0.2-1.5oC over the 20th century and those around shallow

lakes increased by 0.02°C - 0.03°.

Wind speed over the lakes has changed depending on

geographic location and changed the mixing dynamics and

stratification regimes of the lakes.

Rainfall has varied resulting into episodes of floods and

droughts and changes in lake levels, depths and area.

The changes appear to have intensified around 1980s.

The changes have contributed to changes in mixing

dynamics, productivity of the lakes, and affected livelihoods

making it necessary for communities to adapt to build

resilience so as to sustain livelihoods.

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Changes in Climate Variables

Changes in Temperature and Windspeed

The temperature over Lake Victoria increased consistently after

1980s while wind speed increased since 1976 to around 2000

and decreased (MacIntyres 2013) suggesting that some climate

factors will shift between states with similar changes in

productivity processes.

Temperatures around Lake Wamala increased consistently by

0.02 to 0.030C annually since 1980s and rainfall was generally

above average since the 1990s in line with global predictions

and those for the East African region

Changes in Temperature and Rainfall

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Area and Depth of the Lakes

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The area of Lake Chad decreased by 90% & depth from 7 to

1.5m; Area of Wamala from 250-100 km2 & depth from 4.5-1.5;

The area of Lake Chilwa has varied and in some cases virtually

dried up and; The depth of deep African lakes has manifested

decreasing trends with changes in climate variables.

Chad Wamala

Decrease in Depth of Deep African the Lakes

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The depth of African lakes Kyoga, Albert & Edward (Swenson &

Wahr 2013) and Victoria and Kyoga has decreased.

Decrease in Diversity of Fishes

Shrinking of Lake Chad was accompanied by a decrease in the

number of fish species from about 40 to 15 (Leveque, 1995).

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Fluctuations in rainfall around Lake Wamala were closely

associated with changes in fish catch.

Fish Catches

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Fluctuations in lake level of Lake Chilwa were closely

associated with changes in fish catch (Allison et al., 2007).

Fish Catches

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Life History Parameters of Nile tilapia

The changes in area

and depth of Wamala

were accompanied by

changes in mean

length and size at first

maturity of the Nile

tilapia before 1980 and

after 2000

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The mean weight of Kapenta in Lake Kariba decreased with

increasing temperature especially after 1980s and appears to

have increased after around 2000 (Ndebere-murisa et al.,

2011).

Weight of Fish

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Physical and Chemical Conditions and

Productivity

Paleolimnologic observations show that the deposition of P,

biogenic Si, and organic carbon increased more rapidly after

1980s and was later followed by increases overall fish catches

(Hecky et al 2010).

The concentration of P in

Lake Victoria doubled;

dissolved silicon

decreased ten times;

Chla increased fivefold;

thermal stratification and

anoxia increased and

water transparency

decreased during 1990s

(Hecky 1993)

The concentration of Chl a in Lake Victoria which increased from

around 1985 to 2000 decreased thereafter around 2000 while

water transparency improved (Sitoki et al 2010). This was

attributed to changes in mixing dynamics (Marshall 2013) which

supports our prediction that productivity processes will shift

between states with changes in some climate variables such as

wind speed.

Shifts in Chl a and Water Transparency

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Changes in Invertebrates Communities

The zooplankton in Lake Victoria

changed from dominance of

larger calanoid copepods and

cladocerans before 1950s to

smaller cyclopoid copepods

during 1990s; and benthic

invertebrates from chironomids

and chaoborid midges and the

prawn (Caridina nilotica)

(Ndawula ,1993)

There have also been a

shift in the contribution of

small pelagic clupeids in

lakes Victoria, Kyoga and

Albert to contribute up to

80% of the fish catches

after 1980s in line with the

predictions by FAO that

climate change will shift

fisheries to small and

faster growing

opportunistic species.

Shifts in Fish Species Composition

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Water hyacinth

infestation occurred

suddenly and

increased rapidly in

lakes Victoria and

Kyoga in 1980s and

attained peak cover in

1998 after which its

biomass collapsed

suddenly during the

last half of 1998.

Appearance of Aquatic Weeds

Warming of surface waters of

Lake Tanganyika was

accompanied by changes in

mixing dynamics and plankton

composition but was unlike

Victoria followed by a 20%

decrease in primary

production and a 30%

decrease in fisheries yield

(O’Reilly et al., 2003)

suggesting that the impacts of

climate change will vary

between aquatic systems

depending on the influence of

climate variables on mixing

regimes.

Primary Production and Fisheries Yield

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In Lake Wamala changes in climate factors were associated with

loss of gear, damage to landing sites and loss of lives and affected

fish catches and consumption;

Flooding of Lake Chilwa in 1991 resulted in death of >500 people

and the decline in catches to zero deprived fishers on fishing

opportunities, income and livelihoods.

On Lake Kariba, the decline in mean weight of Kapenta and catch

per unit effort related to climatic factors affected the benefits of

fishers from fishing and interfered with fishing operation.

On Lake Tanganyika, the 30% reduction in fish yield reduced

catches for fishers, loss of revenue and interference with fishing

operations.

On Lakes Victoria and Albert there has been an increase in less

valuable clupeids

Impacts on Livelihoods

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In Lake Wamala fishers adapted by reverting to non-fishery

activities, increasing time and changing fishing ground and target

species;

More innovative fishers on Wamala diversified to growing high

value crops such as oranges, pineapples and tomatoes which

resulted into higher incomes than they used to get from fishing.

On Lake Chilwa people adapted to flood by shifting homes to

higher ground, seeking off-farm employment, and diversifying their

food sources to include wild animals;

On lakes Victoria and Kyoga fishers increasingly shifted from

gillnets to mosquito seine nets with increase in small pelagic fishes.

Mitigation measures on Lake Wamala included protecting

wetlands, planting trees and mulching garden

Adaptation and Mitigation Measures

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Increase in unsustainable fishing practices use of illegal gears

and fishing practices.

Degradation of critical aquatic habitats cultivating and grazing up

to lake shores and farming lake floors.

Excessive use fertilizers and pesticides which can degrade the

fish habitat, cause fish kills and can even render the fish

unsuitable for human consumption.

Challenges accompanying adaptation

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. On Lake Chilwa the main constraints included:

Increased population;

Reduced opportunities for off-farm activities;

Limited access to improved crop varieties; and

Poor social services, and

On Lake Wamala they included:

Limited credit facilities, awareness, and land;

Limited availability of appropriate planting materials;

Lack of affordable irrigation facilities;

Inadequate law enforcement; and

High dependence on only fishing as a source off

livelihood

Constraints to adaptation

The policies interventions that need to be implemented

support adaptation and mitigation include:

Controlling human population increases;

Controlling nutrient loading;

Managing wetlands, river banks and lake shores;

Managing emerging fisheries, and invasive species;

Managing land use, land use change, and agricultural

practices;

Promoting aforestation and reforestation;

Promoting adaptation and mitigation measures; and

Incorporating climate change in existing policies

Policy Interventions

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Evidence from literature suggests that the changes in climate

are accompanied by shifts in aquatic productivity processes,

fisheries and livelihoods.

The changes became more pronounced after 1980s but shifted

around 2000 supporting our prediction that aquatic productivity

processes will shift between states with climate variables.

The impacts are also location specific.

There is need to examine the direction and consequences of the

increasing variability and change in climate on aquatic

productivity processes, fisheries, and livelihoods of specific

aquatic systems, and to develop and promote appropriate

adaptations and mitigations strategies and policies that integrate

climate science in management of the resources.

Conclusion and Recommendations

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