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Crocodylus novaeguineaeNew Guinea crocodile

By Vi Tran

Geographic Range

New Guinea crocodiles are found in Papua New Guinea (mainland only) and in the Papua Province of Indonesia. This species has been divided into two genetically and morphologically distinct populations (northern and southern), divided by the main cordillera (central highlands) of New Guinea. Both forms are widespread and locally common, with the northern form being found in the Sepik and Ramu River systems and the southern form being found in the Fly and Bamu Rivers and their associated tributaries and lakes in the southwest region of the island, and the tidal forest zone of the Gulf of Papua in the south. (Bolton and Laufa, 1982; Cox, 2010; Hall, 1989)

Habitat

New Guinea crocodiles inhabit freshwater lakes, swamps, and marshes. Larger crocodiles usually occupy main river channels, while juveniles and smaller individuals tend to inhabit nearby grassy wetlands. Seasonal changes in water levels have marked effects on population density and distribution. (Burgin and Pernetta, 1983; Cox, 2010; Montague, 1983)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • Range elevation
    0 to 600 m
    0.00 to 1968.50 ft

Physical Description

This species is a small to medium-sized crocodile with maximum verifiable lengths of 3.5 m for males and 3 m for females. They have relatively narrow snouts and are brown to gray in color, with dark brown to black bands on their bodies and tails; banding is more visible on younger animals. These crocodiles have 66-68 teeth, of which 5 pairs are pre-maxillary, 13-14 are maxillary and 15 are mandibular. (Britton, 2012; Cox, 2010; Hall, 1989)

Northern and southern populations of New Guinea crocodiles differ slightly in morphology. The premaxillary symphysis (a fibrocartilaginous joint) of Southern populations is longer than the maxillary symphysis, while northern populations exhibit premaxillary symphyses that are shorter than the maxillary symphysis. Southern populations have 4-6 post-occipital scales on the neck, while northern populations always have 4 post-occipital scales. Relative skull measurements, however, are comparable between similar-sized individuals of both populations. (Burgin and Pernetta, 1983; Hall, 1989)

New Guinea crocodiles can be morphologically distinguished from saltwater crocodiles (Crocodylus porosus) by differences in the number of belly scales and the arrangement of scales on the nape of the neck. Furthermore, these species tend to prefer different (but overlapping) habitats, with saltwater crocodiles occupying deep freshwater pools and fast-flowing, rocky streams up to 700 miles inland, as well as brackish and coastal areas, and New Guinea crocodiles being found mainly in inland river systems and freshwater swamps and marshes. (Burgin and Pernetta, 1983; Hall, 1989)

  • Sexual Dimorphism
  • male larger
  • Range length
    3.0 to 3.5 m
    9.84 to 11.48 ft

Development

Eggs are laid approximately two weeks after mating and incubation typically lasts for 12-13 weeks. Although the mode of gender determination has not been studied in this species specifically, it is nearly certain that they exhibit temperature-dependent sex determination, as do other crocodylians. In the closely related freshwater crocodile (Crocodylus porosus), intermediate incubation temperatures produce males, while lower and higher temperatures produce females. ("The management of crocodiles in captivity: 1. Captive breeding and the management of adult crocodiles", 1989; Britton, 2012; Burgin and Pernetta, 1983; Hall, 1991; Heiser, et al., 2012; Lang and Andrews, 1994)

  • Development - Life Cycle
  • temperature sex determination

Reproduction

Courtship behavior of New Guinea crocodiles seems to be triggered by the onset of the rainy season. Courtship and mating has not been observed in the wild, but observations under captivity report that mating individuals display head contact, a submissive display by a male to a female. A male may also blow bubbles underneath a female's body. If a female is willing to mate, she will lift her snout out of the water. A male will then circle and swim over her, pushing her into the water, where mating takes place. Size-specific dominance breeding hierarchies have been observed in captivity. (Burgin and Pernetta, 1983)

Reproductive activities occur throughout the year, with most breeding occurring from September to December. Northern populations form their nests during the dry season (June-October), while southern populations nest during the wet season (November-May). All New Guinea crocodiles form mound nests. Eggs are deposited in a central chamber, with a constant temperature maintained by the decomposition of surrounding organic materials. The majority of nests are constructed on land, above the previous year's high water mark and under the protection of overhanging vegetation, although some are built on floating masses of vegetation. Clutch and egg sizes vary depending on the population, with southern individuals laying fewer, larger eggs that hatch into larger juveniles. Clutch sizes can range from 10 to 48 eggs, with an average incubation time of 83 to 91 days. Egg mass averages 19.8-150.5 g, with a length of 60.0-116.0 mm and a diameter of 37.5-52.3 mm. Eggs exhibit high levels of mortality, due in large part to the high risk of nest flooding, as well as predation. The exact age at which New Guinea crocodiles reach sexual maturity is unknown, but measurements of sexually active individuals have been recorded. Females reach reproductive maturity once they have achieved 55-60% of their total length (1.4-2.0 m snout-vent length), while males reach sexual maturity at around 2.4 m snout-vent length. (Britton, 2012; Burgin and Pernetta, 1983; Cox, 2010; Hall and Johnson, 1987; Hall, 1991)

Hatchling size differs between southern and northern populations. Southern hatchlings range from 26-32 cm in length, about 5 cm longer than hatchlings from the northern population. (Cox, 2010; Hall, 1989)

  • Breeding interval
    New Guinea crocodiles are assumed to produce one clutch of eggs per breeding season.
  • Breeding season
    Most breeding occurs from September to December. Southern population breed in the wet season (December to March), while northern populations breed in the dry season (June to September).
  • Range number of offspring
    10 to 48
  • Average number of offspring
    27
  • Range gestation period
    83 to 91 days

Like most crocodiles, New Guinea crocodiles exhibit parental care. Females construct nests from surface litter, soil, and plant debris near mixed swamp woodland-forest, providing shelter and food for hatchlings. These crocodiles do reuse nests, but it is not known if the same females return to the same specific nests. Females remain near the nest while eggs are incubating, although it is unknown if they defend their nests as aggressively as other species. It is assumed that hatchlings of this species use vocalization to stimulate one or both of the parents to excavate the nest, after which they guide the hatchlings to the water. Adults of both sexes typically defend their young, both from potential predators and other adults. ("The management of crocodiles in captivity: 1. Captive breeding and the management of adult crocodiles", 1989; Britton, 2012; Burgin and Pernetta, 1983; Hall and Johnson, 1987; Heiser, et al., 2012)

Lifespan/Longevity

There is little information available regarding the lifespan of this species. In general, mortality is greatest during the early life stages, with adults suffering little mortality outside of predation by humans. There is a record of this crocodile reaching 24.6 years of age in captivity. (Burgin and Pernetta, 1983; de Magalhaes, 2013)

  • Range lifespan
    Status: captivity
    24.6 (high) years

Behavior

These crocodiles are semi-aquatic, with well-developed limbs that allow them to move easily through the water and over land. They thermoregulate by seeking shade, submerging in water, elevating their head above the substrate, and gaping their mouths. They are primarily nocturnal, tending to remain in covered, protected areas during the day, and are rarely found basking. (Britton, 2012; Johnson, 1973)

Home Range

There is no reported information on the home range of the species. They are not known to defend specific territories, outside of nests while eggs are incubating. (Britton, 2012; Hall and Johnson, 1987)

Communication and Perception

While this species' methods of communication have not been specifically studied, it is likely that they employ similar communication methods to other crocodiles. In general, crocodiles communicate through vocalization, using sound extensively in their social behavior. Male crocodiles emit a variety of sounds during courtship and territorial displays. They also slap their heads and tail against the water as territorial displays. Hatchlings emit calls to stimulate adults to excavate nests, and juveniles may use distress calls to attract adult protection. Crocodiles also have musk glands beneath their throats and inside the cloaca, likely used for communication via scent. Their eyes, protected by a nictitating membrane, allow a wide field of binocular vision. ("The management of crocodiles in captivity: 1. Captive breeding and the management of adult crocodiles", 1989; Heiser, et al., 2012)

Food Habits

New Guinea crocodiles are opportunistic feeders. Hatchlings feed on mosquitos, grasshoppers, water bugs, and other aquatic invertebrates, and small juveniles feed heavily on schools of small fish. Adults have been reported to eat insects, fish, frogs, turtles, water snakes and lizards, rails, grebes, and ducks. (Britton, 2012; Burgin and Pernetta, 1983; Montague, 1983)

  • Animal Foods
  • birds
  • amphibians
  • reptiles
  • fish
  • insects
  • other marine invertebrates

Predation

Adult New Guinea crocodiles have no predators other than humans; however, they are vulnerable to predation from a number of sources before they reach maturity. Eggs are at risk of predation from wild pigs, monitor lizards, and humans. Meanwhile, juveniles may suffer harassment from larger conspecifics and even cannibalism. Other predators of young crocodiles include accipitrid birds of prey and sharks. (Burgin and Pernetta, 1983; Hall and Johnson, 1987; Montague, 1983)

Ecosystem Roles

New Guinea crocodiles are considered apex predators and therefore are important in maintaining ecological balance. As juveniles, it is likely they help regulate insect populations and as adults, they help regulate populations of fishes, waterfowls, and amphibians. These crocodiles may serve as a host to a number of parasites. Animals in captivity are particularly susceptible to bacterial and parasitic infections. (Britton, 2012; Junker and Boomker, 2006)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There is a large industry for crocodile skin in Papua New Guinea and crocodile hunting is a major source of income in small villages. (Montague, 1983)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no adverse effects of New Guinea crocodiles on humans.

Conservation Status

There are worldwide pressures on crocodiles from hunting and displacement by humans. Crocodile hunting is the only means of income for many villages in Papua New Guinea and the majority (75-95%) of the crocodiles being hunted are New Guinea crocodiles. While crocodiles in Papua New Guinea are plentiful and play an important role in the economy, increasing rates of crocodile harvesting could diminish population densities. There are many government regulations in place that help to protect this species of from overhunting. (Bolton and Laufa, 1982; Britton, 2012; Cox, 2010)

Contributors

Vi Tran (author), Indiana University-Purdue University Fort Wayne, Mark Jordan (editor), Indiana University-Purdue University Fort Wayne, Jeremy Wright (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

insectivore

An animal that eats mainly insects or spiders.

island endemic

animals that live only on an island or set of islands.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

male parental care

parental care is carried out by males

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

terrestrial

Living on the ground.

visual

uses sight to communicate

References

Food and Agriculture Organization. The management of crocodiles in captivity: 1. Captive breeding and the management of adult crocodiles. FAO Conservation Guide 22. Rome, Italy: Food and Agriculture Organization of the United Nations. 1989. Accessed June 19, 1913 at http://www.fao.org/docrep/006/t0226e/t0226e00.htm.

Bolton, M., M. Laufa. 1982. The crocodile project in Papua New Guinea. Biological Conservation, 22/3: 169-179.

Britton, A. 2012. "Crocodylus novaeguineae (Schmidt, 1928)" (On-line). Crocodilian species list. Accessed June 17, 2013 at http://crocodilian.com/cnhc/csp_cnov.htm.

Burgin, S., J. Pernetta. 1983. The status and ecology of crocodiles in the Purari. Monographiae biologicae, 51: 409-428.

Cox, J. 2010. New Guinea Freshwater Crocodile Crocodylus novaeguineae. Pp. 90-93 in S Manolis, C Stevenson, eds. Crocodiles: Status Survey and Conservation Action Plan, Third Edition. Darwin, Australia: Crocodile Specialist Group. Accessed June 17, 2013 at http://www.iucncsg.org/365_docs/attachments/protarea/16_C-9056770a.pdf.

Hall, P. 1991. Estimation of nesting female crocodilian size from clutch characteristics: correlates of reproductive mode, and harvest implications. Journal of Herpetology, 25/2: 133-141. Accessed June 17, 2013 at http://www.jstor.org/stable/1564639.

Hall, P. 1989. Variation in geographic isolates of the New Guinea crocodile (Crocodylus novaeguineae Schmidt) compared with the similar, allopatric, Philippine crocodile (C. mindorensis Schmidt). Copeia, 1: 71-80. Accessed June 17, 2013 at http://www.jstor.org/stable/1445607.

Hall, P., D. Johnson. 1987. Nesting biology of Crocodylus novaeguineae in Lake Murray District, Papua New Guinea. Herpetologica, 43/2: 249-258. Accessed June 17, 2013 at http://www.jstor.org/stable/3892058.

Heiser, J., C. Janis, F. Pough. 2012. Vertebrate life. United States of America: Pearson Education.

Johnson, C. 1973. Thermoregulation in crocodilians - I. head-body temperature control in the Papuan-New Guinean crocodiles, Crocodylus novaeguineae and Crocodylus porosus. Comparative biochemistry and physiology, 49/1: 3-28.

Junker, K., J. Boomker. 2006. A check-list of the pentastomid parasites of crocodilians and freshwater chelonians. Onderstepoort Journal of Veterinary Research, 73: 27-36. Accessed June 19, 2013 at http://ojvr.org/index.php/ojvr/article/viewFile/167/161.

Ladds, P., L. Sims. 1990. Diseases of young captive crocodiles in Papua New Guinea. Australian Veterinary Journal, 67/9: 323-330. Accessed June 19, 2013 at http://www.ncbi.nlm.nih.gov/pubmed/2264804.

Lang, J., H. Andrews. 1994. Temperature-dependent sex determination in crocodilians. Journal of Experimental Zoology, 270/1: 28-44.

Montague, J. 1983. Influence of water level, hunting pressure and habitat type on crocodile abundance in the Fly River drainage, Papua New Guinea. Biological Conservation, 26/4: 309-339.

de Magalhaes, J. 2013. "AnAge entry for Crocodylus novaeguineae" (On-line). The Animal Ageing and Longevity Database. Accessed June 19, 2013 at http://genomics.senescence.info/species/entry.php?species=Crocodylus_novaeguineae.

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