NORTH AMERICAN GREEN STURGEON } Acipenser medirostris
DESCRIPTION: Green sturgeon are large with shark-like tails, sandpaper-textured skin, and five widely separated rows of bony plates called scutes. Adults have long, narrow, shovel-like snouts with whisker-like sensory organs called barbels on the undersides, and toothless “vacuum cleaner” mouths with no teeth. They are generally olive green in color, with a stripe down each side.
HABITAT: A bottom-dwelling species, green sturgeon are mostly seen from inshore waters to 200 feet, primarily in the seawater and mixing zones of bays and estuaries. In estuaries, they concentrate in deep areas with soft bottoms and move into intertidal areas to feed at high tides. Adults travel as far as 93 miles upstream to spawn in rivers and need good water quality and specific temperatures to spawn and hatch their eggs.
RANGE: Green sturgeon are found in the ocean from the Bering Sea, Alaska, as far south as Ensenada, Mexico; they frequent estuaries and bays from British Columbia, Canada, to Monterey Bay, California, and river mouths from the Skeena River, British Columbia, to the Sacramento River, California, but are only found significant distances inland in a handful of rivers in Oregon and California. They spawn only in Oregon’s Rogue River and the Klamath and Sacramento river systems in California.
MIGRATION: Both juveniles and adults move extensively up and down the coast to take advantage of scattered food resources. Juveniles stay in freshwater for one to four years before heading for estuaries, where they remain for up to four to six years more, migrating considerable distances along the coast as they grow larger.
BREEDING: Green sturgeon spawn during late spring and early summer in the mainstem of large river systems, in relatively fast water flows and probably in deep holes greater than three meters. It can take over a decade for green sturgeon to reach breeding maturity, and adults have infrequent reproductive success.
LIFE CYCLE: After spawning, the adhesive eggs settle to the river bottom and attach to cobblestones, hatching around eight days later. Larvae are less than an inch long. Green sturgeon life can be divided into three phases: freshwater juveniles (under three years old); coastal migrants (three to thirteen for females, three to nine for males); and adults (more than thirteen for females or nine for males).
FEEDING: Opportunistic predators that eat a variety of prey according to availability, sturgeon generally feed on invertebrates like shrimp, crabs, worms, amphipods, and isopods. Large sturgeon will eat fish, but mainly fish that are small, disabled, or dead.
THREATS: Sturgeons are imperiled by water withdrawals from rivers, dams blocking access to spawning habitat, habitat alteration, overfishing, poaching for caviar, pesticides, and pollutants.
POPULATION TREND: The southern population has been reduced to about 50 spawning-age fish, while the northern population has been extirpated from at least four former spawning rivers.
|Photo © Dan W. Gotshall||HOME / DONATE NOW / SIGN UP FOR E-NETWORK / CONTACT US / PHOTO USE /|