GREEN STURGEON The green sturgeon and its environment: introduction

The green sturgeon, Acipenser medirostris, is one of two acipenserid fishes native to the temperate waters of the Pacific coast of North America. Originally, three species of sturgeon were described from this region, and this one named ‘‘medirostris’’ or ‘‘middle snout’’ based on the length of its rostrum relative to the other purported species (Ayers 1854), both of which were later determined to be white sturgeon, Acipenser transmontanus (Moyle 2002). The green sturgeon is similar in appearance to the congeneric white sturgeon, with which it cooccurs, except that its barbels are usually closer to the mouth than to the tip of the snout. Green sturgeon are heavily armored, possessing one dorsal, two lateral and two bottom rows of scutes or bony plates (Moyle 2002). In addition, there are often one or two large scutes behind the dorsal fin, as well as one behind the anal fin, which are both lacking in the white sturgeon. The common name of the species is apt due its distinctly olive-green body color, with olivaceous stripes usually present on its sides and ventral surface. Green sturgeon are currently thought to be comprised of two genetically distinct breeding populations (Israel et al. 2004): a northern distinct population segment (DPS) consisting of fish that spawn in the Rogue River, Oregon (Erickson et al. 2002), and the Klamath River, California (Van Eenennaam et al. 2001), and a southern DPS that spawns in the Sacramento River, California. Increasingly, many fish species are being recognized as consisting of multiple, genetically distinct stocks. In many cases, these stocks are managed separately because of distinctive phenotypic, physiological, and behavioral characteristics representative of the unique adaptations each stock has to the environmental conditions in a particular habitat (Waples 1995). Although little is known about what distinguishes these green sturgeon populations biologically, several unique physical characteristics differentiate the river systems in which they occur. Tidal flows in an expansive estuary, voluminous flows, long river length, and multiple tributaries in an extensive watershed distinguish the Sacramento River from the Rogue and Klamath Rivers with their small estuaries, relatively short length, and smaller watersheds. Based on the best information available to the National Marine Fisheries Service (Adams et al. in press), the southern DPS was A. P. Klimley (&) P. J. Allen J. T. Kelly Department of Wildlife, Fish & Conservation Biology, University of California, One Shields Avenue, Davis, CA 95616, USA e-mail: [email protected]