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US Fish & Wildlife Service FieldNotes

STOCKTON FWO: Snake Wrangling Biologists

Region 8, August 9, 2011
Ron Smith, USFWS R8 Aquatic Invasive Species Program Coordinator, holding a Nerodia sipedon.
Ron Smith, USFWS R8 Aquatic Invasive Species Program Coordinator, holding a Nerodia sipedon. - Photo Credit: n/a

By Louanne McMartin, Stockton FWO

During a searing hot September day in the Sacramento Valley, U.S. Fish and Wildlife Service Aquatic Invasive Species biologists Ron Smith and Louanne McMartin, waded through an urban wetland choked with invasive plants following University of California, Davis PhD student, Jonathan Rose, to capture invasive watersnakes in Roseville, California.

Native to North America east of the Rocky Mountains, three watersnake species of Nerodia are now found in California. Though their ill temperament and foul smell make them unsuitable pets, Nerodia are occasionally captured and sold in the pet trade and it is likely that the Nerodia populations found in California are the result of released or escaped pets.

Snake wrangling is exactly what the name implies; capturing wild snakes by either an “advanced” technique of grabbing them by the tail, (the likes of what you may have seen on TV) or by a more arcane method of using traps to corral them before reaching down and securing them behind the head. Although nonvenomous, Nerodia can defend themselves by delivering a series of rapid bites while smearing feces and musk onto anyone attempting to capture them. Other than that unpleasant aspect, these nonnative watersnakes are no real threat to humans.

If the snakes do not pose a direct threat to humans, what is the problem? Nerodia pose a credible threat to Endangered Species Act listed vertebrates, including the Giant Gartersnake (Thamnophis gigas), primarily through direct competition and predation and possible transmission of disease and parasites. The Folsom population of Nerodia is directly upstream from gartersnake habitat via the American River and its tributaries, while the Roseville population of Nerodia is within the boundaries of the American Basin of the Southern Sacramento Valley Recovery Unit for the Giant Gartersnake. In addition, other species of concern, such as the Red-legged Frog (Rana draytonii) which occupies the area once infested by Nerodia in Lafayette Reservoir, could be prey if the watersnake populations rebound. Should Nerodia expand further, they would come in contact with a wider range of listed species suitable as snake prey.

A coalition of biologists from state and federal agencies, academia, and private consultants formed the Nerodia Work Group (NWG) to direct management efforts of four known populations of Nerodia from California waterways. To address the introduction pathway, an initial (and successful) goal was to have watersnakes listed as a restricted genus under Section 671 of Title 14 of California’s Code of Regulations and conduct outreach to the pet trade to prevent future introductions.

Through the Science Support Partnership Program, U.S. Geological Survey Research Wildlife Biologist, Dr. Robert Reed, an expert in brown tree snake and python capture methods and Dr. Brian D. Todd, Assistant Professor of the Department of Wildlife, Fish, and Conservation Biology at the University of California, Davis, conducted research to assist the NWG with: trap development, proof-of-concept eradication, post-control monitoring, demographic analysis to estimate success, and recommendations on how to proceed with eradication of Nerodia populations in California (research results are expected in early 2012).

Transferring the methods learned from the research, Dr. Todd and a team of students placed 156 aquatic funnel traps and 7 large single funnel box traps at the Roseville site this past summer. Although data has not been analyzed, Jonathan Rose indicated that as the number of captured Nerodia fell due to the removals, sightings of the native gartersnake species had increased. With fewer Neroida around, native species stand a better chance of survival. For more information please click on the Research link at: http://wfcb.ucdavis.edu/people/faculty/btodd/

Contact Info: Louanne McMartin, 209-946-6400 X 337, louanne_mcmartin@fws.gov