size: 5036KB - Crocodile Specialist Group

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with a shift fiom terrestrial to aquatic invertebrates
their diet High water level were
associatedwithincleasedamountsolfoodinthestomachs.Thiswascontrarytowhatwas
e*pecteO as tfte frigft *ater peliod occurs during $e cool season and itx'as.suggested that any
effects of the cool season are masked by the high temperatures ln the zamDez' vallev'
The importance offish in the diet ofcrocodiles increases while they are between 700 mm sVL
and 1300 mm SVL and, when estimated by weight, accounts for 98 % ofthe diet This figure
declinestoaround33%inadultcrocodiles'Therewasnocompellingevidencetosupport
Cott's (1961) tbeory that they frequently eat cl?Lriids lt should be noted that this was the first
.toJV f"eriitg in-large Nile cromdiles that did not require wholesale slaughter in ihe name
of science "'f (Gani and Pooley, 1976). The Mozambican data (taken from a commercial cropping
*iri"tt ttti. rtudy did not initiate or support) confirmed these conclusions and helped
"i"r"ir" io pui"onna"n"" in the smaller sub-adult sample from Lake Kariba Political problems in
Mo)ambique unfortunately meanthat sample was only collecle during a single time of year
but this m;kes the data more comparable with Coft's (1961) data'
DIGESTION
Rates of digestion were investigated in different size classes of crocodiles The el'fbct of
i"rnp".utu."_una integument type of the prey on digestion rate was ascertained,
juvenile
croiodiles. Fish were digested to l0 % of their original volume atier 2 days in the stomacn'
This information was necessary ln oroer rc be able to assign an age to prey items found in wild
crocoalile stomachs and it was used to estimate feeding frequencies
CONDITION
Condition in juvenile crocodiles was significantly affected by water level butnot by season'
-omparisonsi"t*een ttte hot Zambeziv;lley and the cooler Lake Ngezi showed that the Ngezi
uni.uft (iuiog in less than ideal conditions at the edge of their demographic range) wele in
better conditio-n. It is hypothesized that this could be attributed to the presence of crabs in Lake
Ngezi which make up 51 % oftheir diet at this Iocality (Hutton, 1984)'
GROWTH ANID AGEING
Using skeletochronology (Hutton, 1986; Garnes' 1991) itwas shown that crocodiles Srew faster
in thiZarnbezi valley lboth study sites) and matrred some 15 years earlier than in Lake Ngezi'
It appeaied that juve;iles grew slowly for the first two years and then the growth rate increased
untiiabout I . iL uft". *tti"h it declined again. Females matured at between 15 and 20 years
of age. The growth cufles constructeal from t'emurs from Calora Bassa were similar which
sugg-ests thaathey may be a true representation of growth in wild Nile ctocodile's lt was
est]irated that a iemati crocodile in Lake Kariba will spend 6 % of her life as a juvenile, 19
% as a sub-adult ?|Ild75% as an adult. As males gmw quicker they will spend 6 % as
iuveniles. ll % as sub-adults and 83 % as adults (average life span assumed to be 80 years)'
FEEDING FRDQI,'ENCY AND COMPETITION WITH TIIE ARTISANAL FISIIERY
Wild juvenile crocodiles ate small amounts of fbod compared to captive juveniles where they
*erc'lfd ad lib but tte data suggestiat they were more efficient at converting it Using the
feeding frequencies an annual estimate ol fish consumption fiom Lake Kariba was poposed
(mean-= 1i0.14 tonnes; upper estimate 22539 tonnes). This was the first time that this had