The Green Sturgeon and Its Environment: Introduction
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Environ Biol Fish DOI 10.1007/s10641-006-9155-8 GREEN STURGEON The green sturgeon and its environment: introduction A. Peter Klimley Æ Peter J. Allen Æ Joshua A. Israel Æ John T. Kelly Received: 10 August 2006 / Accepted: 26 September 2006 Ó Springer Science+Business Media B.V. 2006 The green sturgeon, Acipenser medirostris, is one distinctly olive-green body color, with olivaceous of two acipenserid fishes native to the temperate stripes usually present on its sides and ventral waters of the Pacific coast of North America. surface. Originally, three species of sturgeon were de- Green sturgeon are currently thought to be scribed from this region, and this one named comprised of two genetically distinct breeding ‘‘medirostris’’ or ‘‘middle snout’’ based on the populations (Israel et al. 2004): a northern dis- length of its rostrum relative to the other tinct population segment (DPS) consisting of fish purported species (Ayers 1854), both of which that spawn in the Rogue River, Oregon (Erickson were later determined to be white sturgeon, et al. 2002), and the Klamath River, California Acipenser transmontanus (Moyle 2002). The (Van Eenennaam et al. 2001), and a southern green sturgeon is similar in appearance to the DPS that spawns in the Sacramento River, congeneric white sturgeon, with which it co- California. Increasingly, many fish species are occurs, except that its barbels are usually closer being recognized as consisting of multiple, genet- to the mouth than to the tip of the snout. Green ically distinct stocks. In many cases, these stocks sturgeon are heavily armored, possessing one are managed separately because of distinctive dorsal, two lateral and two bottom rows of scutes phenotypic, physiological, and behavioral charac- or bony plates (Moyle 2002). In addition, there teristics representative of the unique adaptations are often one or two large scutes behind the each stock has to the environmental conditions in dorsal fin, as well as one behind the anal fin, a particular habitat (Waples 1995). Although little which are both lacking in the white sturgeon. The is known about what distinguishes these green common name of the species is apt due its sturgeon populations biologically, several unique physical characteristics differentiate the river systems in which they occur. Tidal flows in an A. P. Klimley (&) Á P. J. Allen Á J. T. Kelly expansive estuary, voluminous flows, long river Department of Wildlife, Fish & Conservation length, and multiple tributaries in an extensive Biology, University of California, One Shields Avenue, Davis, CA 95616, USA watershed distinguish the Sacramento River from e-mail: [email protected] the Rogue and Klamath Rivers with their small estuaries, relatively short length, and smaller J. A. Israel watersheds. Based on the best information avail- Department of Animal Science, University of California, One Shields Avenue, Davis, CA 95616, able to the National Marine Fisheries Service USA (Adams et al. in press), the southern DPS was 123 Environ Biol Fish listed as ‘‘threatened’’ on April 8, 2006 under the birth to only 12–40 pups every other year, but can U.S. Endangered Species Act. live up to 35 years (Klimley 1999). The amount of rainfall in the watersheds on the Aspects of the reproductive biology of the western coast of North America that are inhab- green sturgeon resemble those of K-selected ited by green sturgeon varies greatly between species inhabiting stable environments. Females years, and this affects what reaches of these rivers spawn at an advanced age and infrequently. Adult sturgeon can utilize on successive years. Further- females captured during their spawning migration more, the timing of the rainfall influences the in the Klamath River ranged from 16 to 40 years environmental conditions under which the eggs old (Van Eenennaam et al. 2006). Based on their and juveniles develop within the river through taxonomic affinity, spawning is thought to occur changes in flow timing and volume, and the every 5 years (Tracy 1990), though individuals resulting differences in temperatures and dis- tagged with coded ultrasonic transmitters have solved oxygen concentration. Green sturgeon been found to return after 2–4 years to upstream appear to be adapted to this level of natural pools in the Rogue River, Oregon, where they environmental variability. Individuals of the spe- were believed to be spawning (Erickson and cies migrate extensive geographic distances over Webb in press). Assuming an age at first spawning the continental shelf (Moyle 2002; Erickson and of 16 years, and using conservative estimates of Hightower in press; Lindley, personal communi- both life-span and average spawning periodicity, cation), always returning to their natal rivers to 50 years (Nakamoto 1995) and 4 years, respec- spawn, although they would appear to be capable tively, the oldest females of the species might be of occupying other rivers that may be more expected to spawn only eight times within their favorable depending on the rainfall in a given lifetime. Despite these K-selected traits, the green year. Once spawning has occurred, the large size sturgeon also resembles an r-selected species of the eggs, demersal behavior of the larvae adapted to variable environments, in that females (Kynard et al. 2005), rapid growth of the young produce many eggs per spawn. Their fecundity (Deng et al. 2002), and early seawater tolerance increases with the size of the mature female, (Allen and Cech 2007) appear to be adaptations ranging from 59,000 to 242,000 eggs (Van Een- for life in short, coastal river systems (Artyukhin ennaam et al. 2006). Compared with other stur- and Andronov 1990). geon species, though, the number of eggs Green sturgeon possess a reproductive strategy produced per spawning event relative to body intermediate to the two conventionally opposing weight is quite low due to the large egg size, ‘‘r-selected’’ and ‘‘K-selected’’ life history types which is second in size only to Chinese sturgeon, (Pianka 1970). A classical r-selected species grows Acipenser sinensis (Van Eenennaam et al. 2006). rapidly, reaches maturity early, reproduces often, Such a life history strategy suggests that green and produces many eggs, but is short lived—adap- sturgeon have evolved to tolerate short-term tations that promote success in variable environ- stochasticity in their environment resulting from ments. The Pacific sardine, Sardinops sagax,isa annual variability in weather and river conditions, good example of a coastal pelagic species with r- yet the species may be highly sensitive to larger selected traits, growing to maturity within 2 years, scale changes such as habitat loss or permanent reproducing multiple times each year, producing alteration of flow regime. In its combination of up to 2 million eggs per year, but typically living for life history characteristics, the green sturgeon less than 8 years. In contrast, K-selected species would be classified as a ‘‘periodic strategist’’ in grow slowly, reach maturity at an advanced age, the more diverse classifications of Winemiller and and have few young, but are long lived—adapta- Rose (1992) and King and McFarlane (2003). tions that result in greater success in stable Given the current conservation interest in this environments where competition is greater among species, basic biological studies of the kind species. For example, the scalloped hammerhead, presented herein are of timely importance. Sphyrna lewini, is an archetypal K-selected spe- This special issue of Environmental Biology of cies. It takes up to 15 years to reach maturity, gives Fishes is largely comprised of articles with results 123 Environ Biol Fish Fig. 1 Evgenii Artyukhin (left) shown in 1998 at a hatchery in Astrakhan in the Volga Delta where he was artificially spawning beluga sturgeon presented at a symposium on the biology of the he died of cancer a month after the meeting. Paul green sturgeon held at the 39th Annual Meeting Vecsei bore the daunting task of converting of the California-Nevada chapter of the Ameri- Evgenyi’s notes and presentation into an article can Fisheries Society in March 2005. Funding for for the volume. As Paul indicated in correspon- this symposium was provided by CalFed contract dence, some of the information that we would ERP-02D-P57. We have organized the articles have hoped be in the article was unfortunately under four subjects: physiology, movements, lost with him upon his untimely death in Russia. population biology, and distribution. The articles present new observations that provide a greater understanding of the relationship between this References species and its environment. Adams PB, Grimes C, Hightower J, Lindley ST, Moser We appreciate the continued assistance of ML, Parsley MJ (in press) Population status of North Lynn Bouvier, Assistant to the Editor of Envi- American green sturgeon, Acipenser medirostris. ronmental Biology of Fishes, and Suzanne Mek- Environ Biol Fish king, Publishing Editor for Aquatic Sciences at Allen PJ, Cech JJ Jr (2007) Age/size effects on juvenile green sturgeon, Acipenser medirostris, oxygen con- Springer, in producing this Special Issue. Also sumption, growth, and osmoregulation in saline critical was David Noakes, the Editor-in-Chief of environment. Environ Biol Fish (in press) the journal, who showed keen interest in publish- Artyukhin N, Andronov AE (1990) A morphobiological ing the materials of the green sturgeon sympo- study of the green sturgeon Acipenser medirostris (Chondrostei, Acipenseridae), from the Tumnin (Dat- sium as a dedicated issue of the journal. ta) River and some aspects of the ecology and We dedicate this volume to Evgenyi Artyukhin zoogeography of Acipenseridae. J Ichthyol 30:11–21 of the Central Laboratory of Fish Reproduction Artyuhkhin EN, Vecsei P (in press) Morphology and in Saint Petersburg, Russia (Fig. 1). Evgenyi gave ecology of Pacific sturgeons. Environ Biol Fish Ayers WO (1854) Descriptions of new species of fish from a well-organized and polished presentation about San Francisco Bay.