 In the case of the Mertens ' water monitor , more commonly known as Merten 's water monitor , there was only one region that was monitored , but over the course of 18 months . This region is located 70 kilometers south of Darwin , at the Manton Dam Recreation Area . Within the Manton Dam Recreation Area , there were 14 sites set up to survey the population of water monitors , measuring abundance and site occupancy at each one . Seven surveys were conducted , each of which ran for four weeks and included 16 site visits , where each site was sampled twice per day for two consecutive days throughout the 4 weeks . Each site visit occurred between 7 : 30 -10 : 30 AM , and 4 : 00- 7 : 00 PM , when Varanus mertensi can be viewed sunbathing on the shore or wrapped around a tree branch close to shore . The whole project lasted from December 2004 to May 2006 , and unveiled a total of 194 sightings of Varanus mertensi in 1568 site visits . Of the seven surveys , abundance was highest during the second survey , which took place in February 2005 , two months into the project . Following this measurement , the abundance declined in the next 4 surveys , before declining sharply after the second to last survey in February 2006 . In the final survey taken in May 2006 , there were only two Varanus mertensi observed . Cane toads were first recorded in the region of study during the second survey during February 2005 , also when the water monitor abundance was at its highest over the course of the study . Numbers of the cane toad population stayed low for the next year after introduction , and then skyrocketed to its peak in the last survey during May 2006 . When you compare the two populations side by side one can see clearly that the onset of the cane toads had an immediate negative impact on the Varanus mertensi , as their population began to drop in February 2005 , which was when the first cane toads entered the Manton Dam Recreation Area . At the end of the study , some scattered population of water monitors remained in the upper sites of the Manton Dam , which suggests that local extinctions occurred at certain shoreline sites within Manton Dam , but a complete extinction of the population did not occur . 
