Transcontinental Introductions of Watersnakes (Nerodia) into California

Abstract

Author(s): Balfour, Peter S.; Stitt, Eric W. | Abstract: The watersnakes (Nerodia) are a group of semi-aquatic snakes native to North America, primarily east of the Rocky Mountains. Five populations of 3 watersnake species have become established in California. In the northern Sacramento area, more than 100 southern watersnakes (N. fasciata), including numerous gravid females, have been captured since their discovery in 1992. Thus far, this population is known from two tributaries of the American River. In southern California, another southern watersnake population is known from Harbor Park Lake, a semi-isolated urban lake in Los Angeles County. A population of northern watersnakes (N. sipedon) has become established in Roseville, CA, and until the mid-1990s a dense population of diamondbacked watersnakes (N. rhombifer) flourished at Lafayette Reservoir in Contra Costa County. These are potentially worrisome introductions because watersnakes share numerous traits with other invasive aquatic species, including a wide breadth of physiological tolerances, large native distributional ranges, and they occur in many different freshwater types. Watersnakes can be highly fecund, are viviparous, and readily disperse. They are generalist predators that coevolved with many of the aquatic vertebrates now inhabiting western waters. As such, introduced Nerodia pose potential threats to native wildlife, including special status species such as the federally-listed threatened giant gartersnake. To address issues surrounding the management, eradication, or control of Nerodia populations in the western states, concerned biologists formed the multi-agency Nerodia Working Group. Short-term goals of the group include experimental eradication/control of the southern California population, listing Nerodia as a restricted genus under Section 671 of Title 14 of California’s Code of Regulations, and conducting outreach to the pet trade and other groups to raise awareness about these potentially invasive species.