The basic requirements of juvenile crocodiles are essentially the same as for
hatchlings but by the time they are a year old crocodiles are generally able to withstand
harsher conditions. This is important from the farmer's point of view because as his
animals grow, and the scale of operations increases, he will naturally look for ways of
cutting costs.
If inexpensive heating is available, such as from a hotspring or industrial
source, it will be a great advantage but heated pools will not be essential
in most areas within the crocodiles' natural range. A cold spell is less likely
to do any permanent harm to juveniles although if crocodiles become too cold
to feed they become more susceptible to illness and, of course, if food intake
is reduced growth will be slowed. However, if temperatures are usually adequate
and the animals are properly cared for, disease should not be a major problem
and juvenile crocodiles can be kept together in much larger numbers than would
be safe with hatchlings. This permits the use of larger enclosures but crocodile
size segregation is still necessary so that two or three pens are needed as
a minimum.
Local climate is a prime consideration.
In selecting a site for outdoor pens it may be possible to create a warmer environment (by
a few degrees) simply by making the most of aspect, windbreaks, building materials and
design.
Shelter from cooling winds is usually easy to arrange. If no sheltered site exists, a belt
of trees and bushes makes a most effective windbreak. More quickly, a belt of sugar cane
or bamboo can be established until the trees grow. As a general rule a good windbreak
(which filters the wind rather than blocking it solidly) will reduce windspeed by 50% for
a distance of about 7 times the height of the barrier. There is no significant effect
beyond a distance of about 20 times the barrier height.
Windbreaks should not be so close that they prevent early morning and evening sun from
reaching the pens.
Because air sinks as it cools the coldest air will collect, on still nights at the bottom
of hollows and valleys. Even within the tropics and near sea level there may be a few
degrees' difference between a valley bottom and a point 30 metres or so higher up. Where
there is a possibility of different night temperatures it will be worth leaving
maximum-minimum thermometers out overnight before selecting a site.
For hatchlings the water need not be deeper than about 15 cm but, because water retains
heat relatively well, it can be worth having deeper water just to maintain a higher
temperature during the night. In Zimbabwe farmers on the shore of Lake Kariba pump lake
water continually through the hatchling pools at night (Blake, 1982).
One disadvantage in having a simple sloping floor is that food and other dirt
tends to collect in the water. Another, small disadvantage is that the water
edge, where crocodiles like to lie, is restricted to one side of the pool. If
pens are not to be subdivided by removable partitions it is better to have,
in each pen, a central pool with sloping sides and dry land all around. In pens
of 2 x 2 m a square pool of 1.25 x 1.25 m or a circular pool of about 1.5 m
diameter would be appropriate. The circular pool permits a slightly larger water
surface without the land becoming too narrow all around. On the other hand the
perimeter of the circular pool is a little less than that of the square one.
The pool should have a smooth, rounded rim raised about 4 cm above the surrounding land to
help keep the water clean. The land area can be concrete, which is easy to keep clean, but
the hatchlings should not be forced to lie on concrete. Concrete is a heat sink which will
conduct heat from the hatchlings' bodies. Wooden boards should be provided for the
hatchlings to lie on. Alternatively (in addition to wooden boards) the land area can
consist of sand a few centimetres deep. The top layer can then be skimmed off and clean
sand added as a routine cleaning operation.
A compromise between unheated, outdoor enclosures and an indoor complex might make
economic sense if night temperatures are only occasionally too low. Hatchling pools can be
kept warmer at night if copper pipes are run through the concrete floors at the time of
construction. Hot water can then be circulated through the pipes. The cost of heating
might be as much, or more, than that needed to heat an indoor unit; the saving would be on
construction costs. The same system of heating, of course, can also be used indoors but
the heater, if other than electrical, should be located outside the room. Reptiles should
not be subjected to smoke or fumes from kerosene or gas.
Another possibility, if electricity is available, is that of using brooders. At their
simplest these are like large metal lamp shades fitted with light bulbs and supported
above the boards where the hatchlings lie. The bulbs must be low wattage (e.g. 25W) and
have a wire mesh guard beneath them so that hatchlings piling up do not touch the hot
bulb. Such brooders have been used, apparently with some success, in Papua New Guinea and
Burma. They certainly offer scope for experiment. Disadvantages are that they only warm
the area immediately below them and rising heat goes to waste. Larger brooders, suspended
higher above the pools and basking boards, with insulated tops (e.g. sheets of styrofoam
above the metal) and hotter bulbs might be more effective. Sometimes young crocodiles are
more willing to feed during the night and brooders which encourage them to do so, instead
of keeping them huddled together on a small board, are obviously preferable. Different
designs could be tested above thermometers in the proposed situation before a particular
scheme is adopted.
So many management factors are involved that it is difficult to offer general
guidelines on pen size and stock density. At the lower end of the scale, pens
of less than 10 x 10 m would scarcely be worthwhile for commercial rearing.
In Papua New Guinea village pens of this size, and with earth pools, have proved
adequate for 100 animals in their second year. At the other extreme the writer
has seen saltwater crocodiles of 1-1.5 m long. all apparently healthy, being
kept in such crowded conditions that they could not all be out of the water
at the same time without some lying on top. Of others. In the environmental
chambers mentioned in section 6.3.3 the stock density was reduced to a minimum
of 0.3 square metres per animal when the alligators reached one year old. This
density was maintained until the alligators reached the age of 3 years. They
were then removed from the chambers.
The state of being crowded does not, in itself, appear to be harmful to juvenile
crocodiles provided that size segregation, proper feeding and, above all, cleaning can be
maintained. There are enormous advantages in having more sophisticated facilities even
though crocodiles can be reared to culling size (1.5 to 2m) in simple village pens.
Because cost is so often a limiting factor, a range of possibilities will be discussed.
Fences must be proof against climbing and burrowing. A smooth fence need not be higher
than 1.3m but boards or a triangle of wire netting should be fixed across the corners to
form an overhang. This will prevent escapes in the event of pile-ups which are usually in
the corners and often occur during catching operations or other major disturbance in the
pens. To prevent escapes by digging, especially when soil is very wet, fences should be
sunk to a depth of 50 cm.
Fences can be of wood or wire netting or they can be walls of brick, concrete block, sheet
metal or a combination of any of these materials as available.
In Papua New Guinea the fences of village pens are usually palisades with the wooden
stakes sunk in the ground and lashed together at the top. The most serious disadvantage of
wooden fences is their poor durability. In the tropics many timbers will be destroyed by
termites or will rot at the base within two or three years. Preservatives which penetrate
the wood are effective but treatment is so expensive that it will usually be cheaper to
use wire netting. Wood preservatives which are merely painted on are not very effective
and there is the possibility of contamination of soil and water.
In short, fences of durable hardwood are perfectly satisfactory but if the wood needs
preservative it should not be sunk into the ground. The obvious compromise is to sink a
durable footing of logs, brick or concrete so that a fence of lighter material can be
erected upon it. Only the main posts of the fence will then need to be set in the ground.
The simplest way of protecting the top of a post from rot, where water soaks into the end
grain, is to fit a cap of galvanised sheet metal.
The problem of durability below ground applies also to wire netting. The life of a wire
netting fence will be very much increased if the bottom is attached to a raised
foundation. An excellent system is to build a foundation wall of concrete block, concrete
or brick and raise it to about 30cm above ground level. Wire netting (or other material)
can then be set upon this. Crocodiles not accustomed to wire netting will often patrol the
fence and injure themselves by pushing their snouts through the mesh. A low foundation
wall reduces this problem.
Young crocodiles can easily climb wire netting though escapes can be prevented with a 20cm
overhang. Another disadvantage of wire netting is that crocodiles are often disturbed by
people or vehicles which they can see outside the pen.
Walls of brick or concrete block need no special attention. They are permanent and
completely effective provided that the walls are not so high, or the enclosures so small,
that air circulation is restricted. In Papua New Guinea large numbers of crocodiles up to
2m long are contained by walls of concrete block only 6 blocks high (about 1.4 m) and
there is no overhang except at the corners. The enclosures measure 30 x 30 m and can
easily accommodate 800 crocodiles up to culling size. On occasions they have held many
more than that.
Earth pools have been used in different parts of the world with varying success. In
southern Africa, where low winter temperatures are a major problem, earth pools enable
Nile crocodiles to burrow into the bank. Wild crocodiles also do this and inside their
tunnels the air temperature can be 8-10°C higher than that of the river water (Pooley
& Cans, 1976).
To set against this advantage, earth pools can present a number of problems. Needless to
say, in very porous soil they will not hold water and attempts to line them with clay or
plastic sheets can lead to endless maintenance work. Very often pools will hold water only
if they are made much deeper than one would otherwise need. Yet if the sides are too steep
the crocodiles have difficulty climbing out and they cannot use the water margin for
basking. To slope the sides gently from a deeper pool than planned may increase its
diameter so much that the pool comes too close to the fence. For this reason the size of
an enclosure can often be decided only after a satisfactory pool has been excavated.
Draining a deep pool can be impossible. if such a pool has to be emptied it can only be
done by pumping.
Burrowing can also be a problem despite the benefits during very cold periods.
In Papua New Guinea both the freshwater and saltwater species (which, incidentally,
do equally well in the same freshwater pools) sometimes tunnelled so extensively
that pools were half filled with soil, drains became blocked, fences were weakened
and occasionally crocodiles were suffocated when tunnels collapsed. Tn other
districts the same species did no serious tunnelling. The difference in behavior
seemed not to be related to stock density, crocodile size or temperature. Possibly
it was connected with soil type.
Tunnelling can be prevented by protecting the sides of the pool with logs, Large rocks
(preferably concreted in place) or concrete.
It is important to avoid having sharp or jagged rocks round the rim of a pool.
Scratches on the crocodiles' belly skins will reduce their value. Rough surfaces can be
smoothed with a cement mortar.
Water edge is important for basking crocodiles and should be maximised. In this
regard a circular pool has the least satisfactory shape. In a small pen with
an earth pool there is not much choice except to square the pool and protect
the sides. In bigger enclosures, on level ground, the water edge can be increased
by digging the pool in the form of a channel with loops or meanders. But this
will not be practicable if the channel has to be dug as a deep trench in order
to hold water.
A most successful enclosure, in terms of crocodile growth rates and the apparent
contentment of the crocodiles, had a pool about 0.8 deep, 3 m wide and 60 m long in the
form of a rounded "W". The pen measured 22 x 25 m and had a palisade fence of
pressure treated wood 1.3 m high. The pool had an earth floor but the sides were protected
by rocks concreted in place. Water level was maintained by a constant trickle system.
Trees were planted within the enclosure to provide shade. More than 600 yearling
crocodiles were stocked in this pen though the numbers were reduced in the second and
third years.
A serious problem arises if earth pools are allowed to become foul. Even if the pools can
be drained there will be a layer of polluted mud at the bottom and there is no practical
way of cleaning it except by allowing it to dry in the sun. This will not get rid of
disease organisms but exposure to the air will allow organic matter to break down so that
the water will be wholesome when the pond is refilled. Muddy water is not, in itself,
harmful and a number of organisms, which may be potentially injurous, seem to do no harm
in healthy pens. The obvious precaution is to avoid overcrowding (see also 8.6) and remove
all uneaten food.
It may help to keep a few freshwater turtles (terrapins) in the pool to eat scraps which
fall to the bottom. This is quite a common practice and the terrapins seem to remain
healthy.
In rearing pens these need never be deeper than about 75 cm and if pens can be located
on a slight gradient the main drain can be run into a fairly shallow ditch at ten or so
meters from the pens.
The simplest method of pool construction is to dig the pool, lay a 10 cm drainpipe and
line the pool sides with steel mesh. If the sides are sufficiently sloped a layer of
concrete about 75 mm thick can be applied without the need for any supporting framework.
A mix of 1:2:3 (cement: damp sand: coarse aggregate by volume) will be suitable and a
fairly stiff consistency is needed both for application and to produce a strong concrete.
At application the concrete must be firmly rammed through the wire mesh and smoothed with
a trowel. As each section is finished it must be covered, ideally with plastic sheets, to
keep it damp for several days while the concrete cures. Concrete which is allowed to dry
out during this period will be weakened as will concrete which is too sloppy to start
with. Concreting is a skilled business and professional advice should be sought if large
pools are involved. The risk of subsidence and cracking will need to be assessed and with
long channels the levelling will have to be very accurate.
If the available land slopes too much for a single channel pool then provision should be
made for having two or more pools and also for subdividing the pen. Where pools are on
different levels within one pen crocodiles tend to crowd into the lowest pool and leave
the higher one virtually unused.
The 30 x 30 m pens mentioned at the end of section 8.1 each had two channel pools as shown
in Fig. 8. The channels have sloping sides and are 60 cm deep at centre. They should never
be less than 60 cm. If one pool is allowed to empty overnight all crocodiles will have
vacated it by the morning. The pool can then be cleaned and scrubbed, if necessary, with
minimum disturbance to the crocodiles in the other pool. This is the greatest advantage of
a two-pool system.
If two straight pools are positioned along opposite walls with a single strip of land
in the middle there will, of course, be less water edge for basking but it will prevent
crocodiles from piling in corners. With crocodiles approaching slaughter size this can be
a serious consideration.
Concrete pools should have a broad concrete apron for basking. Otherwise they should have
a raised, rounded lip to prevent surrounding soil from being carried into the water where
it may block the drain. The entire floor can be concreted if high stock densities are to
be carried but spaces should be left to plant bushes and trees or else permanent shelters
must be constructed.
The best shade plants are woody types with a low, spreading canopy. Crocodiles can
crawl underneath them without flattening new growth. A low canopy offers some seclusion as
well as shade and should be arranged to overhang the water as well as land. Cassava or
Tapioca bushes (Manihot esculenta) do well in crocodile pens but need to be cut back and
re-started from cuttings fter a year or so as they become spindly.
in large enclosures low, spreading trees can be planted but very big trees near concrete
pools and fence foundations can cause trouble if they produce massive roots near the
surface. Trees should be evergreen. Very small leaves and fruits are difficult to keep out
of the water and drains. Larger leaves are less trouble when they fall.
Inside the pens bushes close to the fence must be checked often to make sure there are no
branches which could help small crocodiles to climb out.
A hard-wearing, low growing grass such as couch (Cynodon dactylon) will make a good ground
cover but under conditions of high density the grass may not, survive. On the other hand,
healthy grass and bushes are a sign that all is well with the soil and the crocodiles are
not overcrowded.
If it is intended to maintain a high density of crocodiles the best plan will be to
concrete the entire floorspace so that hosing and scrubbing can be carried out on
occasions. In this event low shelters of thatch or other roofing material must be
constructed in addition to having raised boards on the pen floor and over the pools.
Whether the shade is natural or artificial it should cover about half the total area when
the sun is overhead.
In small pens it is practicable to present food on boards or sheets of corrugated iron
which can be carried away for cleaning. But where several hundred crocodiles are involved
this becomes a significant chore. An alternative is to build a concrete feeding surface at
the time the pools are constructed.
A good design is a long shallow channel, not more than 10 cm deep and spoon shaped in
section. The channel must be skimmed smooth with cement and should have a slight fall
along its length so that a 10 cm} drainpipe can be led from one end to the main drains.
Thorough cleaning can then be done with a hosepipe and a long-handled broom. Feeding
surfaces, whatever their form, should always be placed a few metres away from the pools.
Where both pools and feeding surfaces are in the shape of long channels they should be
parallel to each other.
Birds, especially kites (Milvus migrans) can be a nuisance by swooping down and carrying
off food. This can be stopped by erecting a wire netting or other barrier about 80cm above
the feeding surface. The birds can not then swoop directly upon the food and are not
prepared to go under the barrier.
With hatchlings, which are kept in small groups, one pen will come to contain the smallest, weakest individuals. This will happen as a result of size segregation.
With older crocodiles, which may be kept together in large numbers, a special pen must
be built for the relatively few animals which are thought to be ill or in need of special
attention. The hospital pen need only be a smaller version of the standard rearing pen but
water must drain directly away from it and all other pens to avoid the spread of disease.
If possible the hospital pen should also stand apart from the main block of pens and it
must have its own feeding boards and cleaning brushes.
The slaughter of crocodiles will be covered in a separate section but it is appropriate
here to mention the use of small isolation pens for the capture of animals prior to
slaughter.
Where large numbers of crocodiles are involved slaughtering may have to be continued over
a period of weeks or months. The process of catching crocodiles every day in large
enclosures can cause such disturbance that the animals become unsettled and stop feeding.
This may not be important if all animals in a pen are to be killed but when this is not
the case then the less disturbance the better.
In large enclosures it will be useful to build a small annexe or to fence off a section
with a doorway from the main pen. if the crocodiles are accustomed to entering this
section (a feeding board can be located there) it will be possible to isolate a few
crocodiles at a time by closing the door on them - a drop door with a rope is easy to
arrange. This system does not completely solve the problem of disturbance because it is
not selective and crocodiles may still have to be caught in the main pen. Nevertheless it
is an advantage to be able to take a proportion of the cull with minimal disturbance to
the rest of the stock.
Remarks in section 6.3.3 are relevant here and will not be repeated. Because of the greater volumes of water involved pipes of less than 40 mm are rarely useful in rearing pens. A trickle system (with a standing drainpipe) is a great advantage in maintaining water levels in earth pools. With any pool it is labour saving because at moderate stock densities, with a continuous trickle, pools need not often be emptied for cleaning. It is not satisfactory to have water from one pen trickling into another. Where a trickle system can be arranged, either from a large reservoir or stream, it should be piped in and out of each pen separately.
