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River Level

crayfish%

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.

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Otte

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Ewaso Ng'iro.Burguret

Otter density is significantly higher in the Burguret river

Effects of the Louisiana crayfish invasion and other human impacts on the African Clawless otter in the

Ewaso Ng’iro ecosystem

Mordecai O. Ogada ,

Department of Zoology

Kenyatta University, Nairobi, Kenya

Email: mordyogada @yahoo.com

Thanks for your support!

• Prof. P. Aloo-Obudho& Prof. R. O. Okelo

• Whitley Laing/ RuffordFoundation

• Wildlife Conservation Society

• Mpala Wildlife Foundation

• Columbus Zoo & Aquarium

• Lincoln Park Zoo

• KenyattaUniversity Biological Sciences Dept.

‘Pristine’ Ecosystem…(at Burguret River)

• Availability of food (crab exposure) does not change significantly with river level.

• Otter diet is relatively constant (97.25-100% crab content in faeces).

• No significant seasonal change in otter territorial behaviour/ marking.

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Burguret

E.Ngiro

Territorial marking…Percentage of aggregated faecal pellets is significantly higher (t=5.030, p<0.0004, n=2)

in the Burguretriver

The Major Species Involved…

• Aonyx capensis - The African clawless otter is highly dependent on crustacean prey, because its lack of claws makes it very difficult to catch fish

• Potamonautes neumannii - The freshwater crab is the otters’ natural prey. It forms most (>97%) of the otters’ diet in the the Burguret river.

• Procambarus 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.

Crayfish-Invaded Ecosystem… (Here at Mpala)

Dry Season. Lowwater level due toDrought, Water

Extraction

Crayfish exposedto Herons, genets,

baboons, etc(Otters’ niche

invaded)

Otters experience foodstress & TerritorialBehaviour breaks

down.

Rainy Season. High waterlevel. Otters’ niche re-established. Territorial

marking resumes.

The Study Area.