Mertens' water monitor

Mertens' water monitor (Varanus mertensi), also called commonly Mertens's water monitor, and often misspelled Mertin's water monitor, is a species of lizard in the family Varanidae. The species is endemic to northern Australia, and is a wide-ranging, actively foraging, opportunistic predator of aquatic and riparian habitats.[2] It is named after German herpetologist Robert Mertens.[3]

Mertens' water monitor
Mertens' water monitor at Australia Zoo
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Varanidae
Genus: Varanus
Subgenus: Varanus
Species:
V. mertensi
Binomial name
Varanus mertensi
Glauert, 1951

Description

Varanus mertensi grows to a total length (including tail) of about 2.0 m (6.6 ft). It is dark brown to black above, with many cream to yellow spots. The underparts are paler – white to yellowish – with grey mottling on the throat and blue-grey bars on the chest. The tail is strongly compressed laterally, with a high median dorsal keel, and is about 1.5 times the length of head and body.[4]

Distribution and habitat

Mertens' water monitor is found in coastal and inland waters across much of northern Australia, from the Kimberley region of Western Australia, across the Top End of the Northern Territory and the Gulf Country, to the western side of the Cape York Peninsula in Far North Queensland.[4]

Behaviour

Varanus mertensi is semiaquatic, a strong swimmer, and seldom far from water. It is often seen basking on midstream rocks and logs, and on branches overhanging swamps, lagoons, and waterways throughout its range. When disturbed, it drops into the water, where it can stay submerged for long periods.[4]

Feeding

Mertens' water monitor feeds both on land and in the water, mainly on fish, frogs, crabs, crayfish, shrimps, amphipods, and carrion, also taking terrestrial vertebrates, insects, spiders, and human rubbish when available.[4][5] It has a good sense of smell and may dig up prey when foraging, including the eggs of freshwater turtles.[6]

Breeding

Varanus mertensi lays eggs in a burrow, usually with egg-laying taking place early in the dry season and hatching in the following wet season. The eggs hatch within 200–300 days after laying, depending on temperature, with the hatchlings able to enter the water and swim immediately.[6][7]

Conservation and status

Mertens’ water monitor is threatened by the spread of cane toads through its range, through poisoning after eating them. Because of this V. mertensi is listed as Vulnerable under Northern Territory legislation.[6]

References
  1. Shea, G.; Woinarski, J.C.Z.; Macdonald, S.M.; Cogger, H. (2018). "Varanus mertensi". IUCN Red List of Threatened Species. 2018: e.T83778246A101752340. doi:10.2305/IUCN.UK.2018-1.RLTS.T83778246A101752340.en. Retrieved 19 November 2021.
  2. Mayes, Phillip James (2006). The ecology and behaviour of Varanus mertensi (Reptilia: Varanidae) (Dissertation submitted for the Degree of Doctor of Philosophy). Perth, Western Australia: Faculty of Natural Sciences, Edith Cowan University.
  3. Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. ISBN 978-1-4214-0135-5. (Varanus mertensi, p. 176).
  4. Cogger HG (1979). Reptiles and Amphibians of Australia. Sydney: Reed. p. 257. ISBN 0-589-50108-9.
  5. "Varanus Mertensi".
  6. "Threatened Species of the Northern Territory: Mertens Water Monitor" (PDF). Simon Ward, John Woinarski, Tony Griffiths and Lindley McKay (compilers). Department of Natural Resources, Environment and the Arts, Northern Territory. November 2006. Archived from the original (PDF) on 9 October 2009. Retrieved 10 January 2010.
  7. OzAnimals.com: Mertens’ Water Monitor.
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