Plus

Plus

Return of the croc to Jaffna
By Charles Santiapillai and S. Wijeyamohan
A recent survey carried out in the Jaffna peninsula, in and around the Thondamanaru lagoon confirmed the presence of crocodiles. It appears that crocodiles are among those species that benefited from the 18-year armed conflict in the area. The conflict seems to have favoured the return of the crocodiles following the displacement of many people from the area. It is one of the few instances where war may have helped improve biodiversity.

Crocodiles did occur in the distant past in the Jaffna peninsula. In 1672, the Dutchman Reverend Phillipus Baldaeus observed them in the fens, ponds, and lakes of the Jaffna peninsula. In the 19th century, Sir Emerson Tennent referred to the still waters and tanks of the northern provinces "teeming with crocodiles".

But with increased urbanization, crocodiles began to decline both in range and number in the peninsula and for some time, they were generally believed to have become locally extinct there for several decades. An island-wide survey of the crocodiles carried out by Rom and Zai Whitaker in 1977 could not find any in the Thondamanaru lagoon, although they mentioned that Chundikulam Sanctuary, noted for its birds, might harbour occasional crocodiles moving in from the tanks and water holes.

Species
Two species of crocodile are found in Sri Lanka: the 'freshy' or marsh or freshwater crocodile (Crocody-lus palustris) and the 'salty' or estuarine crocodile (C. porosus). Both are listed on Appendix I of CITES, and so their international trade is banned. In Sri Lanka, the two species would meet the IUCN criteria for being ‘endangered’ and ‘critically endangered’ respectively.

Since the survey of crocodiles by Rom and Zai Whittaker, it was not possible to determine the status of the crocodiles in the Jaffna peninsula for almost two decades on account of the armed conflict. However, with the declaration of a ceasefire, it was possible to travel to the north and carry out surveys. Our preliminary survey of the Thondamanaru lagoon in the Jaffna peninsula confirmed the presence of both species of crocodile. Locals refer to them by their vernacular names Chaanakan (the 'freshy') and Semmookan (the 'salty'). Both species were recorded from the northern extension of the Chundikulam Sanctuary, while freshwater crocodiles was known to be present in Pallai. Two crocodiles were killed in early January at Naharkoil. Crocodiles were also recorded from places such as Varani, Ampan, Maruthankerni, Maanviluntha kooru, Mulliyan and from the extensive mangroves along the Thondamanaru lagoon.

Ecology
Although crocodiles are excellent predators, they are often indiscriminate and opportunistic feeders. They hunt at night, waiting half-submerged for land-bound prey such as spotted deer, wild boar, or even a buffalo calf to disturb the water surface. They have specialized sensory organs known as dome-pressure-receptors on their faces that can detect tiny disruptions in the surface of water. Prey varies from crabs, prawns or shrimps in the case of hatchlings, to fish, aquatic birds and large terrestrial herbivores in the case of adults. Before a croc can attack a large herbivore in water, it needs to rotate its head sideways by 45 degrees. This is achieved by making the rest of the body rigid through the contraction of the longitudinal muscles along the back and tail. This results in 'tail-arching' which allows the head to be swung efficiently. The muscles that help close the jaws are strong and extremely powerful, while those that are involved in opening them are weak.

Crocs can hear over a wide range of frequencies, and are among the few reptiles that have a voice. They have also good eyesight and their vision is greatly enhanced by a layer of guanine crystals behind the retina, known as the retinal tapetum, which reflects any light that reaches it, and so intensifies the image, making it easy for crocs to see even under low light intensity. Furthermore, in a croc that is 5 m long, the two eyes are separated by only 7 cm. Such close placement of the eyes makes it possible for crocs to have binocular vision - a feature that helps estimate depth.

Crocs have a very good sense of smell. They have no salivary glands and their fleshy tongue is immobile since it is attached along its length between the lower jaws. Despite its size, a croc usually cannot eat larger prey whole given its small stomach. This is why it often stashes its prey underwater or in a swampy area, and returns at intervals to feed. Prey is swallowed in large pieces.

An unusual feature of the stomach is the presence of stones or gastroliths, which help in digestion by tearing up the parts of prey swallowed. The digestive enzymes are so strong (low pH levels) in the stomach that they can digest even bones. But their activity depends on ambient temperature. If the outside temperature is too low, crocs may stop feeding completely. At low temperatures, food will rot before it can be digested and assimilated. Crocs are efficient in converting what they eat - about 22% on a fish diet - and can go for long periods without feeding, during which they rely on the fat stored in the tail. They can also feed on carrion. Teeth may be lost but they are replaced throughout life.

Reproductive behaviour
Crocs are polygynous, with single males mating with a number of females. Dominant saltwater crocs occupy well-defined territories from which other males are excluded. Such territories may include the nesting sites of several females. Stimulus for ovulation is the onset of the rainy season. Mating always takes place in water and is preceded by courtship. 4-6 weeks after mating, the female would start laying 10-50 hard-shelled eggs. Freshwater crocs are 'hole nesters' in that the females excavate a hole into which they would deposit their eggs, like turtles. Saltwater crocs are 'mound nesters" since they construct a mound using earth and vegetation, in the centre of which the female would deposit her eggs.

Freshwater crocs are also 'pulse nesters' - all the females within a population would nest within a few weeks. Saltwater crocs are said to be 'prolonged nesters' since nesting may go on for 6 months. Since sex is determined by temperature in crocodiles, females select their nest sites with great care. Often, a number of 'trial nests' are made to reduce the risk of predation. As hatching time approaches, the young crocs would produce a cheeping sound to alert the mother who would come to excavate the nests and carry the newly hatched young in her mouth to water.

Most eggs fail to survive to produce hatchlings due to desiccation, infertility, flooding, predation or inadequate gas exchange. Out of 1000 eggs that hatch, only 8 crocs would survive up to 5 years of age! But crocs, like elephants, continue to grow all their lives. When they reach a certain length, they expand in bulk. Although parental care is rare among reptiles, female crocodiles are very protective of their nests. Maternal behaviour includes nest defence, nest opening, manipulation of eggs to release hatchlings, and mouth transport of eggs and the young.

Conservation
That the crocodiles have managed to survive in the Jaffna peninsula points to their tenacity and ability to bounce back if and when conditions in their environment improve. The 18-year civil war may have been a blessing in disguise to the crocodiles since most of the people were moved from the peninsula and resettled in the Vanni region. This reduction of human pressure enabled the crocodiles to return and recolonize the Thondamanaru lagoon. It also reduced the hunting pressure on crocodiles.

Today, the Thondamanaru lagoon and its mangroves represent the last stronghold of the crocodiles in the Jaffna peninsula. More intensive surveys are needed to identify clearly the range and number of the two species of crocodiles in the Jaffna peninsula if they are to be conserved.

One difficulty in surveying wildlife in general and the crocs (and birds) in particular is that the use of binoculars is prohibited by the military. This greatly restricts the ability to identify species at a distance. Though ordinary fishermen are using GPS to catch fish in the sea the military has banned the use of binoculars in the peninsula.

Crocodiles in Sri Lanka have a poor image and hence their long-term survival in the wild will depend on the attitude and tolerance of the local people. Rural people are often intolerant of large and dangerous predators in their backyard. Thus there is a need to provide incentives to the local people to maintain crocodiles and their habitats in the wild.

Crocodiles have declined both in range and number since they were indiscriminately hunted in the past for skin and meat. Intensive inland fishing has also led to the decline of freshwater crocs in some areas, and crocs also get entangled in fishnets and drown. Contrary to the popular belief, crocs are beneficial to reservoir fishery. They do control a number of avian predators of fish such as storks, darters and pelicans.

Conserving crocodiles needs relatively large, diverse and undisturbed wetlands, since crocodiles increase in size from hatchlings to adults through several orders of magnitude. Reclamation of swamps, draining of coastal wetlands, conversion of mangroves to prawn farms, and the removal of riverine forests are some of the threats faced by crocodiles.

Mangroves are especially important for the protection of hatchlings which seek shelter among the roots of Rhizophora spp, where they are safe from predators. Mangroves in the Jaffna peninsula are extensive and they support a variety of wildlife. They provide support for the marine food web, nurseries for valuable fish and crustaceans, and habitat for plants and animals.

As "keystone species", crocodiles are important for the maintenance of ecosystem structure and function. They should also be regarded as "flagship species" for the conservation of the mangroves in the Jaffna peninsula.

Back to Plus