THE EXTENT OF THE LOUISIANA RED SWAMP CRAYFISH (Procambarus clarkii) INVASION AND ITS EFFECT ON THE AFRICAN CLAWLESS OTTER (Aonyx capensis) THROUGHOUT ITS RANGE IN KENYA 

This project is concerned with the distribution, status and conservation of the African clawless otter (Aonyx capensis) and will also examine the affect of the introduction of the Louisiana red swamp crayfish (Procambarus clarkii) and other exotic species, such as the brown trout (Onchorhynchus mykiss).  It will  also investigate the possible existence of the Congo clawless otter (Aonyx congicus) in Western Kenya.   

It has already been established that the spread of the crayfish has negatively affected the African clawless otter in riverine habitats.  Over extraction of water in the dry season exposes the otters’ niche to other predators, i.e. crayfish are being eaten by monitor lizards, herons, genets and baboons. Crayfish have therefore had a negative effect on otters by exposing them to competition that is absent in habitats where they live on crabs.                                                      

In August 2004 evidence of crayfish invasion was found in water below 14^oC, which was previously thought to be the threshold below which crayfish could not survive. This indicates that the geographical spread of crayfish is beyond what was previously thought, and new habitats are being invaded as they adapt to colder water.  The African clawless otter is highly sensitive to fluctuations in the abundance and availability of crustacean prey.  

In addition, the exact identity of the otter species in western Kenya is uncertain as this forms part of the Congo rainforest and it is indeed possible that the Congo clawless otter (Aonyx congicus) may be present.   

This project is especially important to conservation outside protected areas because the nature of otters demands that they occupy linear habitats (rivers) around which human activities are concentrated because of our need for water.  It will also highlight the extent of otter habitats in Kenya and provide more accurate information for targeting conservation and research efforts. 

Geographic Location:    Rift Valley, central, and northeastern Provinces, Kenya                                    

 Project Objectives 

1.      To determine the geographical extent to which the Louisiana red swamp crayfish (Procambarus clarkii) and other exotic fauna have invaded freshwater ecosystems and affected clawless otter populations in Kenya. 

2. To determine the species of clawless otters present in Kenya and make a case for their protection and prudent management of aquatic ecosystems in Kenya, and other parts of Africa. 

This study will investigate the effects of invasions of crayfish on otter populations and recommend ways in which these can be minimized, including stiffer regulations on the activities of sport fishermen, who are behind most of these introductions. 

The project will also incorporate the exploration of unknown areas of otter range. Foremost among these is the Lorian Swamp in eastern Kenya. This is where the Ewaso Ng’iro river ends, and was identified as a priority area by the Africa meeting at the 9^th International Otter Colloquium. It will also investigate two wetland areas in western Kenya to verify whether they are inhabited by A. capensis or the Congo clawless otter A. congicus. These are the Saiwa Swamp and the Kingwal Swamp. These are both fragments of the eastern arc of the Congo rainforest.  This is further confirmed by the presence of two Congo basin species, the sitatunga antelope (Tragelaphus spekei) and De Brazza’s monkey (Cercopithecus neglectus). The Saiwa swamp is a protected area, and otters have been reported to exist there by the Kenya Wildlife Service, but they are unable to confirm the species. Information is highly deficient on the range of A. congicus, and according to Kingdon (1997) this does not extend beyond the Albertine rift in western Uganda.  

Methods 

Otter prey species will be sampled using funnel-mouth traps already used in a previous study at Ewaso Ng’iro. These are made using ¾ inch size wire mesh reinforced with binding wire.  They are weighted with stones, placed on the bottom of the river, baited with meat and secured to the riverbank. Water in swamp sites (< 50cm deep) will be sampled using scoop nets every 0.5 km in a transect along the longer aspect of the swamp. This will be interspersed with trap sampling wherever it is deep enough. Traps will be emptied, moved and rebaited every 24 hours.  

The aquatic fauna caught in the traps will be counted, measured and weighed. This will be compared to the proportion found in otter faeces collected in the same area. The composition, abundance, and frequency of the faecal samples in the study area will be an additional indicator of fluctuations in the distribution of the otters and their prey. 

Sampling sites will be assessed for vegetation, substrate composition, water depth and simple chemical composition in order to examine the possible effects of abiotic factors on otter prey distribution.  

Otters will be live-trapped in Tomahawk, single-door, rigid live traps baited with fish (Wilson et al. 1996), weighed, measured, marked and released. Trapped animals will be anaesthetized using etorphine hydrochloride by means of a pole syringe and the clinical effects will be reversed using the specific antagonist diprenorphine. The anaesthetized animal will be marked and released:  two marks will be made on each animal, one on the back of the head and one at the base of the tail. These are the most visible sites when an otter is running or swimming away from the observer. The two spots are washed first with ethyl acetate to remove the natural oils from the fur, and then the marks will be made using ‘ABRO’ brand automotive spray paint. This mark will last at least six months. This method is preferable to plastic rings and ear tags, because the otters could easily remove these, and the plastic rings could get caught in riverbank vegetation. 

The three motion sensor cameras will be moved from holt to holt in order to confirm and extend our estimates of otter home range sizes obtained from observation and trapping.  

More emphasis will be placed on spraint collection and camera trap photography as indicators than trapping and marking of otters. This is because repeated trapping at latrine sites could cause the otters to abandon them, thus depriving the study of a valuable data source.  

Sightings of otters and locations of spraints will be recorded using a Global Positioning System (GPS).  Spraints will be collected and returned to the laboratory where they will be dried, sorted and their contents identified. Using antennule base size, the size distribution of prey will be compared to the size distribution obtained from trapping, to see if otters selectively take different sizes (ages) of prey. A mathematical relationship between the antennule base size and overall weight of live caught crayfish was formulated in a previous study and this can also be used to deduce the mass of crayfish being taken by otters at the various field sites.

Project Outputs:

     1.      Scientific papers and a report indicating the extent of the threat to otters from the invasion of Louisiana crayfish and other exotic fauna.

2.      Conservation recommendations – Recommendations will be made for ways to minimize the effects of introductions of crayfish and other exotic species.  Most of these introductions are by sport fishermen and it will be necessary to impose stiffer regulations on their activities and to ensure that these are enforced.

3.      Benefits to indigenous people - The Kingwal swamp is on community-owned land and the recent (2002) discovery of a population of sitatunga antelope in the area has raised tourism interest in the area. Already, local youth are forming groups to initiate projects like swamp walkways and market it as an ecotourism destination. It also has a high density and diversity of wetland birds. The confirmed presence of otters there would raise the interest level of both tourists and the Kenya Wildlife Service and help the local people gain from tourism enterprises.

4.      Public awareness – Part of the project will include giving talks to school children in schools around the study areas so that local people will learn to appreciate the importance of otters and wildlife in their own area.         

5.      Education/Training - Students in the University of Eastern Africa, Baraton Biological Sciences Department will also be trained to do aquatic biology studies under this project. This university borders the Kingwal swamp.   

Budget  (please include a detailed budget for the entire project): 

 Personnel:  This project will be carried out by Mordecai Owidi Ogada MSC, Mpala Research Centre, PO Box 555 Nanyuki, Kenya