Effects of the Louisiana crayfish
invasion and other human impacts
on the African Clawless otter in the
Ewaso Ng’iro ecosystem
Otter density is significantly higher in the Burguret river
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Burguret
Ewaso Ng'iro.
8
Otters per Km. of river
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Mordecai O. Ogada ,
Department of Zoology
Kenyatta University, Nairobi, Kenya
Email: mordyogada @yahoo.com
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The Study Area.
Thanks for your support!
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Month
Prof. P. Aloo-Obudho& Prof. R. O.Okelo
Whitley Laing/ Rufford Foundation
Wildlife Conservation Society
Mpala Wildlife Foundation
Columbus Zoo & Aquarium
Lincoln Park Zoo
KenyattaUniversity Biological Sciences Dept.
Crayfish
-Invaded Ecosystem…
(Here atMpala)
‘Pristine’ Ecosystem…
(at BurguretRiver)
• Availability of food (crab exposure) does
not change significantly with river level.
• Otter diet is relatively constant (97.25100% crab content in faeces).
• No significant seasonal change in otter
territorial behaviour/ marking.
Dry Season. Low
water level due to
Drought, Water
Extraction
Crayfish exposed
to Herons, genets,
baboons, etc
(Otters’ niche
invaded)
Otters experience food
stress & Territorial
Behaviour breaks
down.
Rainy Season. High water
level. Otters’ niche reestablished. Territorial
marking resumes.
Dietary Trends…
Crayfish percentage in faecal pellets closely tracks river
level when analyzed by LOWESS curve, showing that
fewer crayfish are available to otters in the Lower Ewaso
Ng’iro when river levels are low.
Territorial marking…
Percentage of aggregated
faecalpellets is significantly higher
(t=5.030,p<0.0004, n= 2)
in the Burguretriver
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The Major Species Involved…
90
300
crayfish%
80
River Level
• Aonyx capensis -
The African clawless otter is highly
dependent on crustacean prey, because its lack of claws makes
it very difficult to catch fish
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60
• Potamonautes neumannii
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• Procambarus
E.Ngiro
Burguret
clarkii - The Louisiana crayfish has
invaded the lower Ewaso Ng’iro , supplanted the crab, and now
forms >60% of the otters’ diet there. It hasn’t invaded the
Burguret river due to low water temperatures there.
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- The freshwater crab is the
otters’ natural prey. It forms most (>97%) of the otters’ diet in the
the Burguret river.
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250
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month
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0
0
100
200
300
Pellet collection number
400
500
600