Nile monitors (Varanus niloticus), a large carnivorous lizard, are established in the C-51 Basin in Palm Beach County in close proximity to the Artur R. Marshall Loxahatchee National Wildlife Refuge (Lox NWR, Figure 1). They were first sighted in 2007 and breeding was confirmed in 2011 (Ketterlin-Eckles et al. 2017). They have been confirmed as far east as I-95 along the C-51 and west to within 2 kilometers of Stormwater Treatment Area (STA) 1E. Nile Monitors are semi-aquatic habitat generalists and in their native range of sub-Saharan Africa are found in both freshwater and estuaries. In Florida, they are most often found along networks of vegetated canal banks. They are diet generalists consuming invertebrates, fish, reptiles, amphibians, [...]
Summary
Nile monitors (Varanus niloticus), a large carnivorous lizard, are established in the C-51 Basin in Palm Beach County in close proximity to the Artur R. Marshall Loxahatchee National Wildlife Refuge (Lox NWR, Figure 1). They were first sighted in 2007 and breeding was confirmed in 2011 (Ketterlin-Eckles et al. 2017). They have been confirmed as far east as I-95 along the C-51 and west to within 2 kilometers of Stormwater Treatment Area (STA) 1E. Nile Monitors are semi-aquatic habitat generalists and in their native range of sub-Saharan Africa are found in both freshwater and estuaries. In Florida, they are most often found along networks of vegetated canal banks. They are diet generalists consuming invertebrates, fish, reptiles, amphibians, mammals, eggs, and carrion (Campbell 2005, Enge et al. 2004, Engeman et al. 2011, F. Mazzotti, University of Florida, Davie, Florida 2016, unpubl. data). Possible threats to native species by Nile monitors include predation and competition for resources (Campbell 2005, Enge et al. 2004, Gore et al. 2003).
Because of their potential to significantly impact Florida wildlife, the Florida Fish and Wildlife Conservation Commission (FWC) listed Nile monitors as a conditional species in 2010, meaning they can no longer be sold or acquired as a personal pet in Florida, limiting the likelihood of new introductions. In addition, monthly surveys for removal were initiated in 2012, primarily on the East transect of the C-51. Data from surveys conducted in 2012 – 2014 were analyzed to determine detection probability, occupancy, and trend in occupancy to assess effectiveness of removal efforts (Ketterlin-Eckles et al. in prep). In addition, the data were used to conduct a power analysis to determine the number of surveys necessary to detect a 50% decline in occupancy. Overall the average detection probability was 0.058 (95% Credible interval 0.034–0.091) at the East transect. Site occupancy rate declined from 0.82 to 0.51 from 2012–2014 at the East transect. The power analysis indicated that with 36 or 48 surveys per season there was a high power (>90%) to detect a 50% decline in Nile monitor occurrence at the C-51 canal when detection probability is 0.05 and if detection probability could be raised to as low as 0.1, only 24 surveys per year were needed (Ketterlin-Eckles et al. in prep). Since 2014, additional surveys and removal efforts have been conducted at a rate of a minimum of two per month (24 per year) primarily by FWC and augmented by surveys by University of Florida.
The objectives of this project are to:
• Analyze all data from 2012-2019 to determine if there has been a decline in Nile monitor site occupancy which will allow for assessment of the effectiveness of control efforts.
• Conduct additional survey and removal efforts in the C-51 East, C-51 West, and E2 canals to ensure data are adequate to detect trends. These surveys will augment surveys being conducted by FWC.
• Assess how covariates such as canal width, vegetation, temperature, and time of year affect detection probability for the purpose of refining survey efforts.
