Mertens’ Water Monitor

Appearance

The monitor grows to a length of about one metre. 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

The 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.

Status

Mertens’ Water Monitors are threatened by the spread of Cane Toads through their range, through poisoning after eating them. Because of this they are listed as Vulnerable under Northern Territory legislation.

Behavior

The monitor is semi-aquatic, a strong swimmer and seldom far from water. It is often seen basking on mid-stream 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.

Habitat

The 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.

Reproduction

The monitor 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.

Food

The monitor feeds both on land and in the water, mainly on fish, frogs and carrion, also taking terrestrial vertebrates and insects when available. It has a good sense of smell and may dig up prey when foraging, including the eggs of freshwater turtles.