Mertens' water monitor (''Varanus mertensi''), also called commonly Mertens's water monitor, and often misspelled Mertin's water monitor, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia altho ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Varanidae The Varanidae are a family of lizards in the superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely rel ...

. The species is

endemic Endemism is the state of a species being found 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 found else ...

to northern

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

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

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...

of aquatic and

riparian A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...

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''. Baltimor ...

Description

''Varanus mertensi'' 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.

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 and Tanami deserts in the region of the Pilbara, an ...

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...

, 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 ra ...

of the

Northern Territory The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia. The Northern Territory shares its borders with Western Aust ...

and the

Gulf Country The Gulf Country 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 called the Gulf Savannah. It ...

, to the western side of the

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

Far North Queensland Far North Queensland (FNQ) is the northernmost part of the Australian state of Queensland. Its largest city is Cairns and it is dominated geographically by Cape York Peninsula, which stretches north to the Torres Strait, and west to the Gulf Co ...

Behaviour

''Varanus mertensi'' is

semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...

, 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 ...

s, and waterways throughout its range. When disturbed, it drops into the water, where it can stay submerged for long periods.

Feeding

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

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...

s, and carrion, also taking terrestrial vertebrates and

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

s when available. It has a good sense of smell and may dig up prey when foraging, including the eggs of freshwater

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

Breeding

''Varanus mertensi'' lays eggs in a

burrow 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 locomotion. Burrows provide a form of s ...

, 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 true toad native to South and mainland Central America, but which has been introduced to various islands throughout Oceania ...

s through its range, 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 ''Varanus mertensi'' 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, on the Great Northern Highway, northeast of Perth. It was established in 1886 to service a new goldfield at Halls Creek, and it is now a port and service centre for ...

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:Mertens' Water Monitor (Varanus mertensi) (10096243733).jpg,

Australia Zoo Australia Zoo is a zoo located in the Australian state of Queensland on the Sunshine Coast near Beerwah/Glass House Mountains. It is a member of the Zoo and Aquarium Association (ZAA), and is owned by Terri Irwin, the widow of Steve Irwin, wh ...

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. It is one of the largest zoos in the United States by area and is the largest metropolitan zoo in ...

File:Washington DC Zoo - Varanus mertensi 2.jpg, Smithsonian National Zoological Park 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 one ...

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