Distribution, Habitat, and Future of Harter's Water Snake, Nerodia harteri, in Texas

Abstract

Detailed studies of the distribution and habitat use of the endemic Texas snake Nerodia harteri were conducted from 1979 to 1987. The Brazos water snake N. h. harteri is restricted to the upper Brazos River drainage; it is found in about 303 km of stream plus two reservoirs, Possum Kingdom Lake and Lake Granbury. The Concho water snake, N. h. paucimaculata occupies 396 stream-km in the ConchoColorado River drainage, and about 25 km of lake. As such, Harter's water snake has one of the smallest ranges of any North American snake species. Medium to large, flat rocks on an unshaded shore for hiding places and rocky shallows for feeding grounds appear to be important for juveniles. There is an ontogenetic habitat shift in N. harteri that may also be common in many other Nerodia. We found that adult N. harteri are not restricted to rocky riffles in flowing rivers but can inhabitat a much wider range of habitats in pools and lakes. Several sections of both the Brazos and Colorado rivers are uninhabited by N. harteri, apparently because juvenile habitat is lacking or scarce. Riffles are more isolated on the uninhabited stretches, and they may be too far apart to recolonize after catastrophic local population extinctions. Past dam projects have eliminated populations of Nerodia harteri through habitat destruction by inundation and siltation. Fragmentation of populations may also prevent recolonization after local extinctions. A major dam being constructed on the Colorado River near Stacy, McCullough County, will inundate about 18% of the known habitat of Nerodia h. paucimaculata and perhaps degrade another 8% or more. A unique agreement whereby the dam-constructing authority will construct artificial habitats and fund biological studies could ameliorate the negative effects of the dam and reservoir on populations of the Concho water snake. al of Herpet logy, Vol. 23, No. 4, pp. 373-38 , 1989 ibution, Habitat, and F ture of Ha ter's Water Snake, dia harteri, in Texas AN J. SCO T, JR.,1 TERRY C. MAXWELL,2 OKLA W. THORNTON, JR.,3 . FITZGERALD,4 AND JOHN W. FLURY2 ional Ecology R search Center, U.S. Fish and Wildlife S rvice, Museum of Southwestern Biology, i ersity of New Mexico, Alb querque, New Mexico 87131, USA art ent of Bi logy, Angelo State University, San Angelo, Texas 76909, USA lorado River Mun cipal Water District, Big Spring, Texas 79721, USA art ent of Bi logy, University of New Mexico, Albu uerque, N w Mexico 87131, USA The only endemic Texas snake, Harter's water snake (Nerodia harteri), is known from the upper reaches of two river basins in the center of the state. Two subspecies are recognized: the Brazos water snake (Nerodia harteri harteri) in the upper Brazos River drainage, and the Concho water snake (Nerodia harteri paucimaculata) in the upper Concho-Colorado River drainage. The species was discovered in 1936 in the Brazos River in Palo Pinto County, Texas, and described in 1941 (Trapido, 1941; Fig. 1). The Colorado-Concho form of N. harteri was found ' in 1942 (Marr, 1944) and described as N. h. paucimaculata by Tinkle and Conant (1961) from Robert Lee, Coke County, Texas (Fig. 2). Few collections were made of either subspecies, and little was known of the species until Williams (1969) completed an ecological study of N. harteri in the Colorado River at Robert Lee. Although knowledge of the total distribution and population status was sketchy, a general concern for the survival of the species developed among several Texas biologists. Formal concern was expressed in 1975 when the Texas ) a escribed as N. h. paui l a onant (1961) from t , exas (Fig. 2). Few e o either subspecies, and t e species until i liams c lo ical study of N. har373 This content downloaded from 207.46.13.48 on Thu, 02 Feb 2017 20:19:11 UTC All use subject to http://about.jstor.org/terms N. J. SCOTT, JR., ET AL.