7.1 Capture of Young, Wild Crocodiles

As mentioned in section 4, losses of eggs in the wild can be substantial so that collection of young crocodiles is generally less productive in terms of size of harvest. But young crocodiles may be easier to locate than nests, they may be collected at different times of the year and under certain circumstances it may be preferable to collect live young rather than eggs. In Papua New Guinea, for example, villagers living in remote, flooded regions can collect and safely transport young crocodiles with minimal facilities.

If eggs were collected the losses would almost certainly be much heavier.

Crocodiles may be located in daylight but capture must be done at night. The usual practice is to work from a boat, at least 30 meters offshore, and to scan the water margin with a powerful torch. At night crocodiles commonly lie near the shore with eyes and nostrils above water. The eyes shine red or orange in the torch beam and (with the crocodiles presumably dazzled) it is possible to approach quietly to within touching distance. Small crocodiles can then be seized or netted.

For small crocodiles hand nets can be used in two ways. In deep water, or around rocky shores, an ordinary scoop net fitted on a pole can be slipped into the water and slowly brought up under the crocodile. The net must have an open mesh and the rim should be at least 60 cm in diameter. The disadvantage of this technique is that little crocodiles are often lying among water plants and the net cannot be moved easily through the water.

In the shallows and among water plants it is better to have a net which can be plunged down over the crocodile to trap it in the mud at the bottom. This method has proved successful for catching C. porosus in Australia and the net shown in Fig. 4 was described by Webb & Messel (1977).

7.2 Transport

Small crocodiles travel well for short periods in damp jute sacks (gunny bags). For transport by boat or road the sacks should be laid flat and kept in the shade. To avoid suffocation the bags must not be piled one on top of another, nor should any bag contain more crocodiles than can comfortably find floor space. Crocodiles of more than about 70cm in length should have a bag to themselves and should never be placed in the same bag as very small animals. Ten or fifteen hatchlings could be carried together, especially if the bag is lightly filled out with soft, leafy branches. This helps to prevent them from piling into one corner. Tying the jaws of crocodiles for transport in containers is not necessary. It could possibly interfere with the animal's temperature regulation and in the case of accidental escape the crocodile could not survive.

There are obvious constraints in the use of sacks for transport. The crocodiles are very much at risk from rough handling and in boats or other vehicles floor space soon becomes limiting. In Papua New Guinea, in order to minimize transport time and stress on long journeys, it is usual to accommodate crocodiles in temporary holding pens until enough have been assembled (a few hundred) to make up a load for a light aircraft. Tens of thousands of young crocodiles have been transported by air within Papua New Guinea and deaths or injuries in transit have been rare. This extremely good record has been attained by using strong cardboard boxes which were developed and manufactured specially for the purpose. One design is shown in Fig. 5.

Boxes of identical design but bigger have been used for crocodiles up to a metre long. When new the boxes are surprisingly rigid and will support the weight of a mediumsized person. They can be disassembled and folded flat for storage. They weaken and eventually disintegrate when wet and the compartments may have to be thrown away after one use. The outer cover can usually be used again. Waterproofed cardboard may have a longer life but the inner surfaces become scratched and moisture still penetrates. Crocodiles are normally carried one to each compartment. Wooden boxes can be used where weight is not important.

For hatchlings the cardboard boxes made for transporting day-old chicks are suitable but as they are not divided into compartments they should be very loosely filled with soft hay.

7.3 Marking and Tagging

It may be useful to mark crocodiles so that a record can be kept of their origins and date of capture. Marking is essential in growth trials when progress of individuals has to be monitored.

Fig 4. Steel framed handnet for capture of young crocodiles (after Wells& Messel, 1977)


Fig 5. Cardboard transport box for young crocodiles (by courtesy of Mainland Holdings, Papua New Guinea)



For short-term requirements a spot of quick-drying, waterproof paint is the simplest. If crocodiles can be kept out of water and away from each other (to prevent smudging) for about 30 minutes they can be numbered with a water-based acrylic paint (as sold for exterior timber) which will last for weeks. It takes about half an hour to dry.

More permanent markings, which can be seen at a distance, have to be made on tags which are then attached to the animal. Metal clip-on tags, such as ear-tags used for cattle, can be punched through a large tail scute without any risk of infection or even discomfort to the crocodile. They usually stay in place but occasionally get torn out. Anchor tags are made by the Floy Tag and Manufacturing Co., 4616 Union Bay Place, Seattle, Washington 98105, U.S.A. The anchors can be pushed through the skin of the neck, just behind the bony platform of the skull. Nylon coated vinyl tags are attached to the anchor and are conspicuous on land and visible even in shallow muddy water. They are said to be effective for 3 years but, like other tags, they may occasionally be lost (De Vos, 1982).

A less conspicuous numbering system but a very useful one if crocodiles have to be re-caught for examination (e.g. weighing/measuring in growth trials) is based on branding or cutting the tail scutes. A system described by Webb (in Messel & Butler,1977) uses the raised scutes of the tail for counting.

The point between the double row and single row of tail scutes is considered to be zero (Fig. 6). Counting down the tail from this point, the single scutes represent thousands on the left side and hundreds on the right side. Counting forwards, the double scutes represent tens on the left and units on the right. Brand marks are made between the scales directly under a scute. if the skin between two scales is lightly touched with a hot soldering iron it will burn and heal to leave a permanent scar.

A simpler system, which limits numbering to a thousand or so, can be followed by using the single scutes themselves to represent hundreds. The double scutes, left and right sides, then represent tens and units respectively (Fig. 7). The scutes can be marked by clipping off the tops or punching holes in them with a leather punch. This will last for several months. The last few singles scutes should not be used as tail tips often get bitten off.

If scutes are cut off at the base with a very sharp blade they will not grow again and the marks will be permanent. This makes a small wound which bleeds and though there is an obvious risk of infection, in practice, the wounds seem to heal without trouble. Nonetheless, it seems unwise to wound or brand hatchlings when the main aim is to get them to settle down and begin feeding.

7.4 Weighing and Measuring

By far the quickest way to weigh hatchlings is to fit a light box (plastic is ideal) on a spring balance and then zero it. The box must have smooth sides to stop the crocodile from scampering out. Bigger animals are most easily weighed by suspending them in a sack from a spring balance of the hook type. For speed the sack can be formed into a shallow sling which cradles the animal tightly while being suspended. The crocodile's jaws must be tied and this is most quickly done with a rubber band - narrow sections of bicycle inner tybe are suitable. The binding must never pass over the raised area where the nostril open or the crocodile will suffocate.

For comparison of crocodile sizes two measurements are commonly used. Total length is simply snout Lip to tail tip and can be measured with a steel tape while the crocodile lies on its belly. On farms where a large number have to be measured it may be worth making a wooden trough with the sides marked in centimetres. The crocodile is then laid in the trough, snout against one end, and the length read off.

The disadvantage with total length is that tail tips are so frequently lost. A more reliable measure is snout-vent length. This is less convenient to record because the crocodile must be held on its back. The measurement is taken from the snout tip to the front (anterior) extremity of the vent slit (cloaca). Belly width, as used in measuring skins, varies with a crocodile's breathing and is not recommended for comparing the size of live crocodiles.

Fig 6. Method of Numbering by Branding Scute Rows on Tail (after Webb in Messel & Butler, 1977)

Fig 7. More limited method of numbering by clipping or punching raised scutes. Single row represents hundreds. Double row represents tens on left; units on right. Number illustrated by punch holes = 213

To avoid being bitten when picking up young crocodiles in pens it is customary to throw a wet sack over the animal's head. The jaws can then be held through the sack while an assistant fits the rubber band.