This chapter examines the geomorphic role of fish, amphibians, and reptiles. As stated in Chapter 1, I must regrettably ignore the geomorphic effects of dinosaurs, Permian–era mega–amphibians, and other geologically distant effects of the ectothermic (cold–blooded) vertebrates. Each of the groups of modern ectothermic animals does induce geomorphic change; however, the bulk of these changes are either transitory or aquatic in nature, and are therefore only briefly described.

The geomorphic role of fish

The geomorphic work of fish can be categorized into three major efforts: nest building/digging, disturbances associated with feeding, and burrowing. Nest creation is a relatively simple affair, in which a fish prepares a nest by cutting into the gravel of a coarse streambed with downward beats of the tail (Hansell 1984). The salmonids – that is, salmon and trout – are probably the best known of such nest builders. Von Frisch (1983), Chapman (1988), Crisp and Carling (1989), and Kondolf et al. (1993) describe the typical salmon nest, or “redd,” as a hollow pit 10–20 cm deep and 1–2 m long, oriented in the direction of the stream current. The base of the pit, also called the “pot” (Crisp and Carling 1989), is comprised of coarser lag gravels (typical particle size for a brown trout redd in California was 45–64 mm, whereas cutthroat trout in Idaho spawn in gravel with particles up to 100 mm in diameter; Kondolf et al. 1993; Thurow and King 1994), and a “tailspill” of finer–grained material forms a low mound immediately downstream of the pit (Lisle 1989; Kondolf et al. 1993).