Mertens' water monitor (''Varanus mertensi''), often misspelled Mertin's water monitor, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

monitor lizard Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and West African Nile monitor, one species is also found in south America as an invasive species. A ...

. The species is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to northern

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, and is a wide-ranging, actively foraging, opportunistic

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

of aquatic and

riparian A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripar ...

habitats. It is named after German herpetologist

Robert Mertens Robert Friedrich Wilhelm Mertens (1 December 1894 – 23 August 1975) was a German herpetologist. Several taxa of reptiles are named after him.Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). ''The Eponym Dictionary of Reptiles''. Baltimore ...

Description

Mertens' water monitor grows to a total length (including tail) of about . 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. Varanus mertensi-Wyndham-WA

Amongst all monitor species, including even the water monitors of '' Soterosaurus'', Mertens' water monitor is morphologically the most well adapted to an aquatic lifestyle, being able to seal its upwards facing nostrils when underwater. It is capable of swallowing prey underwater, which is an ability not reported in any other monitor species other than the Borneo earless monitor (''Lanthanotus borneensis''). It is also the only monitor species reported capable of using its sense of smell to locate and capture prey underwater.

Distribution and habitat

Mertens' water monitor is found in coastal and inland waters across much of northern Australia, from the

Kimberley region The Kimberley is the northernmost of the nine regions of Western Australia. It is bordered on the west by the Indian Ocean, on the north by the Timor Sea, on the south by the Great Sandy Desert, Great Sandy and Tanami Desert, Tanami deserts in t ...

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

, across the

Top End The Top End of Australia's Northern Territory is a geographical region encompassing the northernmost section of the Northern Territory, which aside from the Cape York Peninsula is the northernmost part of the Australian continent. It covers a ...

of the

Northern Territory The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an states and territories of Australia, Australian internal territory in the central and central-northern regi ...

and the

Gulf Country The Gulf Country or North West Queensland is the region of woodland and savanna grassland surrounding the Gulf of Carpentaria in north western Queensland and eastern Northern Territory on the north coast of Australia. The region is also ca ...

, to the western side of the

Cape York Peninsula The Cape York Peninsula is a peninsula located in Far North Queensland, Australia. It is the largest wilderness in northern Australia.Mittermeier, R.E. et al. (2002). Wilderness: Earth's last wild places. Mexico City: Agrupación Sierra Madre, ...

Far North Queensland Far North Queensland (FNQ) is the northernmost part of the States and territories of Australia, Australian state of Queensland. Its largest city is Cairns, Queensland, Cairns and it is dominated geographically by Cape York Peninsula, which stret ...

Behaviour

Mertens' water monitor is

semiaquatic In biology, being semi-aquatic refers to various macroorganisms that live regularly in both aquatic and terrestrial environments. When referring to animals, the term describes those that actively spend part of their daily time in water (in ...

, a strong swimmer, and seldom far from water. It is often seen basking on midstream rocks and logs, and on branches overhanging

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

s, and waterways throughout its range. When disturbed, it drops into the water, where it can stay submerged for long periods. It has been observed sleeping underwater.

Feeding

Mertens' water monitor feeds both on land and in the water, mainly on

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

frog A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

crayfish Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some spe ...

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

amphipod Amphipoda () is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphipod species cur ...

s, and carrion, also taking terrestrial vertebrates,

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

s, and human rubbish when available. It's diet consists mainly of freshwater '' Holthuisana'' crabs, which are reported to make up 29-83.7% of the biomass found in gut and scat samples. 11.5% of prey biomass was found to be fish. While eggs and frogs are infrequently eaten, large amounts of them are eaten when found. Arthropods including spiders, beetles and water bugs, while frequently eaten, make up a small proportion of ingested prey biomass. It has a good sense of smell and may dig up prey when foraging, including the

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...

s of freshwater

turtle Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

Breeding

Mertens' water monitor lays eggs in a

burrow file:Chipmunk-burrow (exits).jpg, An eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of Animal lo ...

, 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.OzAnimals.com: Mertens’ Water Monitor.

Conservation and status

Mertens’ water monitor is threatened by the spread of

cane toad The cane toad (''Rhinella marina''), also known as the giant neotropical toad or marine toad, is a large, Terrestrial animal, terrestrial true toad native to South America, South and mainland Central America, but which has been Introduced spe ...

s through its

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

, through poisoning after eating them. Because of this ''V. mertensi'' is listed as Vulnerable under Northern Territory legislation.

Gallery

File:Varanus mertensi 3238.jpg, Portrait of Mertens' water monitor in the Northern Territory File:Varanus mertensi - Wyndham WA.jpg, Mertens' water monitor at the Grotto waterhole near

Wyndham, Western Australia Wyndham is the northernmost town in the Kimberley region of Western Australia, northeast of Perth via the Great Northern Highway. It was established in 1886 to service a new goldfield at Halls Creek, and it is now a port and service centre fo ...

File:Mertens' Water Monitor (Varanus mertensi) (10096243733).jpg, Australia Zoo File:Varanus mertensi.jpg, Australia Zoo File:(1)Mertens water monitor.jpg,

Featherdale Wildlife Park Featherdale Wildlife Park is a zoo located in Doonside, Sydney, Australia. The park is located in Sydney's west, approximately from Sydney's CBD. The park contains various species native to Australia, and is known to be one of the world's larg ...

File:Varanus mertensi 2zz.jpg,

Bronx Zoo The Bronx Zoo (also historically the Bronx Zoological Park and the Bronx Zoological Gardens) is a zoo within Bronx Park in the Bronx, New York City. It is one of the largest zoos in the United States by area and the largest Metropolis, metropol ...

File:Mertens' water monitor 01.jpg,

Healesville Sanctuary Healesville Sanctuary, formally known as the Sir Colin MacKenzie Sanctuary, is a zoo specialising in native Australian animals. It is located at Healesville in rural Victoria, Australia, and has a history of breeding native animals. It is on ...

References

External links

Monitor Lizards: ''Varanus mertensi'' (includes notes on keeping and breeding in captivity)
{{Taxonbar, from=Q1819998 Varanus Monitor lizards of Australia Endemic fauna of Australia Reptiles of Queensland Reptiles of the Northern Territory Reptiles of Western Australia Taxa named by Ludwig Glauert Reptiles described in 1951