Ecology and Control of an Introduced Population of Southern Watersnakes (Nerodia fasciata) in Southern California

Abstract

Native to the southeastern United States, Southern Watersnakes (Nerodia fasciata) are known from two sites in California, but their ecological impacts are poorly understood. We investigated the ecology of Southern Watersnakes in Machado Lake, Harbor City, Los Angeles County, California, including an assessment of control opportunities. We captured 306 watersnakes as a result of aquatic trapping and hand captures. We captured snakes of all sizes (162-1063 mm snout-vent length [SVL], 3.5-873.3 g), demonstrating the existence of a well-established population. The smallest reproductive female was 490 mm SVL and females contained 12-46 postovulatory embryos (mean 5 21). Small watersnakes largely consumed introduced Western Mosquitofish (Gambusia affinis), while larger snakes specialized on larval and metamorph American Bullfrogs (Lithobates catesbeianus) and Green Sunfish (Lepomis cyanellus). Overall capture per unit effort (CPUE) in traps declined with time during an intensive 76-d trapping bout, but CPUE trends varied considerably among traplines and it is unlikely that the overall decline in CPUE represented a major decrease in the snake population size. Although we found no direct evidence that Southern Watersnakes are affecting native species in Machado Lake, this population may serve as a source for intentional or unintentional transportation of watersnakes to bodies of water containing imperiled native prey species or potential competitors.

Size distribution and reproductive phenology of the invasive Burmese python (Python molurus bivittatus) in the Greater Everglades Ecosystem, Florida, USA

“…Additionally, inconsistent methods across studies and over time exacerbate issues with defining species size-stage classes through size at maturity or identifying phenotypic variation (Feldman and Meiri 2012). For example, snake studies often measure animal body size using total length (tip of snout to tip of tail; e.g., Burger et al 1987;Snow et al 2007b) while others use snout-vent length (SVL; tip of snout to vent; e.g., Reed et al 2016;. This difference is important to note when attempting to understand or compare morphologies between the sexes because male squamates store their hemipenes, inverted, in the ventral tail base, causing males to have generally longer tails (and therefore relatively longer total lengths) than females of the same SVL (Fitch 1960;Shine et al 1999).…”

Hidden in Plain Sight: Detecting Invasive Species When They Are Morphologically Similar to Native Species

“…Currently, the CFP is home to at least 11 established species of non-native lizards and three species of non-native snakes, most of which are found in urbanized areas (Palmer and Fisher, 2010;Pauly and Borthwick, 2015;Reed et al, 2016;Fisher et al, 2020Fisher et al, , 2021Putman et al, 2020). In contrast there are ∼45 species of native lizards and snakes in the CFP, with only a few species occurring in urban areas (Fisher, 2016a,b).…”

Targeting eradication of introduced watersnakes using integral projection models

“…Watersnakes of the genus Nerodia have established multiple non-native populations in California, USA since 1992 (Balfour et al, 2007a(Balfour et al, , 2007bReed et al, 2016), and provide an opportunity to use IPMs to target eradication effort in an incipient invasion. Eradication of watersnakes before they become widespread is desirable given concerns about impacts to native species (Rose & Todd, 2014).…”