|Auburn University Digital Library|
|Managing Tropical Animal Resources - Crocodiles as a Resource for the Tropics|
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This appendix is adapted from a paper by A. Pooley that detailed the lessons learned from farming crocodiles to restock depleted habitats in Natal, South Africa. The information is presented here not as a blueprint for setting up a farm, but to show prospective farmers some of the points that they must first consider before attempting to rear crocodiles.
Reliable supplies of good water and suitable food are the most important considerations for establishment of a crocodile farm; the area selected must have both. Village farms also need to be close enough to wild crocodile populations for the animals to be obtained easily. Larger farms can be located farther from the source.
For small farms, a natural supply of food should also be readily available in the wild. Areas that have a fishing industry are ideal locations. For large farms, sites near slaughterhouses or fish-processing facilities are ideal.
Other considerations also include the volume of water available throughout the year, the distance over which water must be piped to the ponds, and pumping costs. The quality of the water should be established, with samples tested for salinity and acidity and, where the supply comes from mineral springs, analyzed for harmful chemicals. Chlorinated water must be tested regularly to ensure that the chlorine content is not too high, and the nature of any factory effluents present should be determined. It is important to establish whether fish, frogs, crabs, mollusks, or aquatic insects survive in the water intended for use.
Bacterial analysis is advisable where the water is drawn from a river that drains an area densely populated by humans and livestock. If the water is found to be contaminated, the stagnant pond rearing pen system should not be used, particularly when Salmonella spp. are present in high concentrations.
A filter system has advantages if water is pumped straight from a river carrying a heavy silt load. Apart from enabling farmers to see the animals in the pools, filtered water makes the pools and pipes easier to clean. Filtration can be achieved by drawing water from a deep pit close to the river so that the water collected seeps through sand or mud.
A reservoir or a series of supply tanks is useful as an additional method of filtering water. In the event that pumping equipment fails, such a reserve supply may prove vital to the health and survival of the crocodiles.
The ponds should receive as much sun as possible, particularly during the winter months. A series of winter air temperature recordings would be useful in choosing the site of rearing pens, since valley temperatures are often several degrees lower than the temperatures some 50 to 100 m uphill. Preference should be given to the warmer locations, taking into account the direction of local winds and heavy rains.
Soil types are the next consideration. If soils are sandy and porous, earth ponds are impractical and a concrete lining is required to retain water.
Drainage of the ponds must be carefully considered. Drainage is far easier if the ponds are built on a slight rise. Water from the ponds must not be allowed to stagnate nearby; the drainage system must be efficient. It is recommended that pens be spaced at least 8 m apart and that their drainpipes lead underground at least 10 m before emptying.
Pens with rounded corners are the most successful. Crocodiles frequently choose to lie together in a pile. Square corners allow them to pile up against the angle, smothering those on the bottom and sometimes allowing animals to climb over the fence. With rounded corners, the pile cannot grow very high before the crocodiles slide sideways and the heap collapses.
Experiments in South Africa indicate that natural pools containing rooted vegetation are less prone to become sources of disease than are concrete pools. The surface of the concrete seems to become impregnated with liquid and debris from food and to become a breeding ground for bacteria. For hatchlings and very small juvenile crocodiles, concrete has an added disadvantage; its rough surface can abrade the belly skin when the animals slide in and out of the water, which can foster infection. In 5 or 10 years, even smooth concrete will erode sufficiently to become a problem.
Researchers elsewhere, however, report better results with concrete lined ponds, which they find easier to clean. Concrete pools are useful for summer because they can be scrubbed clean and because the volume of water used is small. Normally they need only be emptied, cleaned, and refilled every third day, and there is no wastage through seepage.
The pools are best built as channels. This provides more bank for basking and enables the pools to accommodate more crocodiles. Because the larger males become belligerent only when they can see each other, floating logs, patches of grass, or channel corners are visual barriers that reduce interactions. The channel system also gives more water edge, and this appears to satisfy the territorial instinct.
Crocodiles are famous for basking in the sun, but they die surprisingly easily of heat prostration. At least one-third of the land area of a farm pen should be shaded with vegetation. The amount of space around each pool is calculated to allow ample basking room for each animal, and an area of shade must likewise be provided.
On land, crocodiles often seek contact with each other (thigmotaxis) and frequently lie piled on top of each other, but this should be a matter of choice rather than of overcrowding. There should be few enough animals in the enclosure to allow every crocodile to get out of the water if it chooses.
Ideally, only half the available number of pools should be occupied at a time, so that they can be used in rotation. In this system, the animals can be moved to fresh pools every two months (or as necessary), leaving the "used" pools to be drained and dried out to bake in the sun. After two months, the pools will then be clean and ready for use again.
An important requirement is that the pools be at least 60 cm in depth; otherwise, the water becomes too hot in summer. The pool floor should be sloped towards the drain outlet to facilitate cleaning and flushing away uneaten food. Also, the outlet pipe should be 10 cm in diameter, with a stopcock outside the enclosure, so that the pool can be cleaned and emptied efficiently. It is essential to place a screen in the drainpipe to prevent small crocodiles from escaping or being sucked out of the pool during cleaning. After some time, stagnant ponds may become difficult to clean because of the heavy growth of algae on their sides. Hard-bristle scrubbing brushes are needed to dislodge this growth. Small amounts of copper sulfate in the water will help control algae if used regularly.
The entire pond and surrounding apron must be smoothly plastered to facilitate cleaning. It helps to have a water source close to each pool from which a hose pipe can be led to pressure spray and clean the pool and its apron.
An important part of the design is a partly submerged, gently sloping ledge, some 45 cm in width, around the perimeter of the pool. This provides a shallow resting zone for the crocodiles and gives them easy access to the water. The crocodiles rest there when feeding, and the ledge prevents them from scraping their bellies and damaging their claws when they enter or leave the pool.
For small crocodiles it is advisable to roof over the entire pen with wire netting or cries-crossed strands of wire. This protects against predators. Further, young crocodiles can climb vertical wire netting with ease and will escape unless the enclosure is either roofed or has side walls that slope inwards. A skirting board (planking, sheet iron, tin, or plastic sheeting) placed against the wire netting can also prevent this. If wire netting is used for the sides of the pens it should have mesh no larger than 1 cm so that hatchlings will not injure themselves by trying to climb through. While these pools are being cleaned, care must be exercised to prevent crocodiles from falling into the empty pool.
Water can be passed continuously through the pools. The advantage of this is that during hot summer weather, when crocodiles are feeding at their maximum rate, small uneaten food particles, feces, and urine are carried away. Constant dilution of the pond's water also ensures a low bacteria level. However, the pool must be drained and scrubbed clean at least weekly.
Earthen pools are easy and cheap to build and are a "natural" habitat where vegetation can be planted and small live fish introduced; insects, frogs, and other creatures attracted to the dams will be an important addition to the diet and health of the crocodiles. Earthen pools are ideal in climates where low winter temperatures are likely to cause respiratory illness in the young animals. During cold weather the crocodiles burrow into the mudbanks and survive nights of heavy frost.
Because of the animal's burrowing capabilities, it is important to provide a strip of land 4 m wide between the pool's edge and the boundary fence. Otherwise, crocodiles may tunnel beyond the fence line. Fences must be buried at least 1 m deep to intercept the burrows and to prevent predators from burrowing in. Burrowing, however, can be hazardous, because the burrows can collapse and suffocate the animals.
In areas where the soil is porous or sandy, the floor of an earth dam can be sealed with concrete or plastic irrigation sheets. A layer of earth can be used to conceal this artificial floor. The disadvantages of earth pools are that, because of seepage, they require more water than concrete ones and that they require more maintenance because they cannot be efficiently cleaned. Even if the pools are provided with constantly circulating water, they eventually become fouled, particularly during hot weather.
Removing crocodiles from an earth pond can prove difficult, since most will take refuge in their burrows.
Crocodiles are located at night, usually from a boat, by shining a light along the edges of rivers and lagoons. Because of a reflective tapetum, the eyes of crocodiles glow reddish or orange and are visible for a hundred meters or more. If the population has not become exposed to hunting and become wary of people, the animals will not submerge when the light strikes them. Dazzled by the beam, they tolerate a stealthy approach, and small animals can simply be grabbed by hand or scooped up in a net. They can then be transported in sacks to the rearing pens. Larger animals may be noosed or baited into cylindrical screen traps at places they frequent along the water's edge.
Managing a Crocodile Farm
It is a problem to sort the young crocodiles. From one clutch of eggs, some individuals will be aggressive and others may be shy or extremely timid; growth may vary from rapid to very slow, with a few individuals classed as runts.
Larger animals can be so dominant that smaller individuals will not even attempt to feed. If sorting is not done, the smaller, less-aggressive individuals do not get a fair share of the food; they grow slowly and get bitten and harassed by the larger animals. At feeding time, some will flee to the opposite side of the pen and stop feeding altogether. Keeping the young animals sorted into classes of the same size avoids many of these problems.
Nutrition and Feeding
Despite the crocodilian's reputation as a man-eater, small wild crocodiles live mainly on invertebrates and larger ones live mainly on fish. Papua New Guinea's farmers feed a varied diet of locally caught fish, crab, shrimp, frogs, snails, grasshoppers, beetles, and slaughterhouse waste. Whole animals minced up should be used, if necessary, because crocodiles require a diet of bone, intestine, scales, and other tissues to provide calcium and minerals. Bones in chopped fish must be minced thoroughly for hatchlings or very young crocodiles, or they should be fed very small fish supplemented by tadpoles or insects. One village in Papua New Guinea has shown remarkable success in rearing hatchlings on a diet of chopped fish and live freshwater shrimp.
Fish is an excellent food for the bulk feeding of a large captive population. Whole fish chopped into pieces, including the livers and hearts, forms a balanced diet that may be supplemented by meat, if available, to make up bulk. Small whole fish are particularly suitable; the crocodiles derive calcium from the bones and scales, plus roughage to facilitate digestion, while the flesh, liver, and heart are rich in nutrients and protein The main difficulty usually lies in harvesting enough fish to meet the crocodiles' demands.
Any method of supplementing the diet with live creatures is recommended. For instance, a light can be left burning in each pen about 15 cm above the water for attracting insects. Various types of insect traps may also be used.
Crocodiles also can be fed on a variety of wastes such as offal or noncommercial fish. Ideally, a large-scale farm should be located near a poultry slaughterhouse. (Cattle offal is also satisfactory, but it is not nutritionally adequate as a sole ration for crocodiles.) Even crocodile offal itself can be fed back to crocodiles. However, the use of offal will necessitate dietary supplements to assure sufficient phosphorus and calcium. These minerals are generally provided by feeding bones to the crocodiles.
Crocodiles usually consume their food in the water, but they can also be fed on land. They will eat daily, but are able to remain active for weeks without food. If they are fed in the water of a farm pen, the water will become polluted unless there is considerable flow to carry away the debris. In extreme cases, the pools become septic. To ensure the health of the growing animals, constantly flowing water is far superior to standing water. (The Samutprakan Crocodile Farm in Thailand feeds some of its animals in water, but the small feeding pools are separate from the large regular breeding pools and at a lower level to prevent their overflowing into the breeding pools.)
It is important to feed pieces of food small enough to be swallowed without difficulty. Large fish should be cut into elongated rather than square pieces, since the bones can cause damage during swallowing. Similarly, whole live fish should not be so large that the dorsal fin may cause damage to the reptile's throat and gullet.
It is important to know the amount of food that each group of animals will consume at each meal. By feeding at the same time each day, it is easy to calculate how much is required. Moreover, the crocodiles become accustomed to a routine and the food is consumed while it is still fresh. In the hot summer months the animals will devour a full meal every 24 hours, but the feeding rate slackens with the onset of colder weather. It is then wise to start reducing frequency and quantities until food is required only every second or third day, depending on the climate. Generally, young crocodiles will refuse food when the air or water temperature falls below 60°F (15.6°C). Even in midsummer sudden cold spells may occur; at such times, it is usually futile to feed the animals or try to coax them to eat until the weather warms up again.
During hot weather conditions it is preferable to feed late in the afternoon or evenings, mainly to avoid placing the food on a hot cement surface. The food should be spread out around the edge of the pool under the shaded area so that the animals do not have to climb over one another to reach it.
In cemented pens the area where the food is laid out should be cleaned and scrubbed two hours after feeding time and any uneaten food removed from the water with a hand net. In earthen pools, the food should be placed at a different spot along the bank at each feeding. A useful aid to hygiene is keeping a few predacious fish, such as barbel (Clarias spp.), in each pool to clean up scraps of uneaten food.
Twenty-five crocodiles are considered the maximum manageable number per unit; staying within this limit reduces competition for food, bullying and fighting, and the number of injuries. A low stocking rate also results in a more even average growth rate. Most important is the fact that the overall health of the crocodiles is better than in a more crowded pen; disease problems are fewer and the symptoms easier to detect in a small group. If the units are spaced 8 m apart, there is also less danger of infectious disease spreading to other pens. The cleaning of pens is facilitated, and the disturbance caused by capturing crocodiles to be moved to other units is minimized. Housing 500 crocodiles in groups of 25 will require 20 separate pens, and an additional two pens should be provided to allow for intensive care of sick, injured, and weaker animals.
During the first year, when animals are graded frequently, they will often be moved from one pen to another. Recording the number of animals housed in each pen will make it possible to keep track of numbers and movements.
Reproduction is impossible when crocodiles are kept in large groups composed of different species and sizes and in more or less unnatural enclosures.
Healthy, sexually mature pairs of crocodiles are usually not enough to start a breeding program. Genetic diversity to maintain a long-term breeding group must be considered, and certain environmental factors are vital for success. The distinct size and age classes of a free-living population must also be taken into consideration. Optimal sex ratios for breeding in enclosed compounds must be determined and adhered to. If a breeding unit is not based on regard for the animals' basic needs for space, nesting sites, and retreats, the larger specimens will disturb, injure, and often kill smaller specimens.
Diseases and Parasites
Disease symptoms may be easily overlooked if the observer is not familiar with the behavior of crocodiles under a variety of conditions. It is essential to know how they normally walk, swim, sleep, feed, and bask in relation to the time of day, the air and water temperatures, and the amount of sunlight or rain, by day, by night, and at different seasons of the year. Caretakers should notice the appearance of feces from healthy animals to be able to detect evidence of diarrhea, and to identify misaligned teeth and weakened limbs to detect nutritional deficiencies. Eggs are critically dependent on specific temperature and moisture requirements if the embryos are to develop normally.
It is often difficult to determine the cause of illness or death, and even if the ailment has been correctly diagnosed, it is not easy to capture and administer drugs to large numbers of sick animals. Some animals may be injured during the handling process. Emphasis on preventing disease, rather than curing it, is the best way of ensuring a healthy crop.
Almost inevitably, the water in the pools will harbor concentrations of bacteria such as salmonella. If strict hygiene is observed, however, the bacterial level will not be harmful.
It is recommended that whenever possible animals found newly dead should be dissected and vital organs such as the brain, heart, lung, liver, spleen, kidney, and stomach removed for veterinary research. Blood slides should also be taken and feces samples collected. The various specimens must be carefully labeled, frozen as quickly as possible, and packed on ice in a vacuum flask for immediate dispatch to the nearest veterinary research institute or pathologist. Alternatively, dying animals may be sent live for research purposes.
It is helpful for the handler to become thoroughly acquainted with the animal's internal anatomy, in order to distinguish between healthy and diseased organs. This knowledge, coupled with the symptoms noted before the animal dies, and the veterinary report, will be useful in future diagnosis and treatment.
One problem for the crocodile farmer is a roundworm (nematode) parasite that burrows into the belly skin. When the burrow collapses it produces an undulating track across the belly and throat scales that ruins the hide. These parasites have been found in crocodiles from Latin America, Africa, Australia, Papua New Guinea, and Asia. They seem more prevalent in some areas and some farms than in others. The organism has been identified, but no treatment or control has been discovered. It is, however, believed that damp, muddy conditions foster the nematode, and that to reduce it pens should have areas of dry land where the animals can bask.
Killing, Skinning, and Tanning
Some farmers kill the crocodiles themselves, but many rear the animals and then sell them to a larger concern that is better equipped to deal with the skins. Killing is done most quickly and humanely by catching the crocodile with a noose and severing the spinal cord just behind the skull.
Many hides are ruined or severely damaged during skinning. Even a single hole resulting from a slip of the skinning knife may reduce a hide's value by 25 percent.
After skinning, the hides are normally coated with about 0.5 cm of coarse salt and rolled up. Within 48 hours they are unrolled and resalted. If the hide is not sufficiently salted, it may become infected with bacteria or fungi that cause the epidermis of the scales to decay or slip. Although this layer is removed during tannage, scale slip is a symptom of rot and usually causes damage to the finished hide product. If the decay is intense, the salted hides may become reddish or brown in color. This is called "red heat."
Although salt remains the universally used preservative for raw hides, the reptile leather industry has developed chemical fixatives that are used in addition to salt for preserving hides for tanning. Most of these pretannage fixatives are liquid and require soaking the hide in a vat, which may not be feasible in remote areas.
A pretanned hide is called a crust. It is green-gray (chrome tanned) or tan (vegetable tanned) and is stiff. The hide is dyed and glazed to its final finish. To increase the workability and to remove as many of the osteoderms as possible (if they are present), the underside of the hide is shaved to an even thickness. The shaving is done by craftsmen. If they shaved too much, the hide will be thin and weak, especially over the suture between the scales.