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North American Green Sturgeon (Acipenser medirostris)
Sturgeons are among the largest and most ancient of cartilaginous fishes. They are placed, along with paddlefishes and numerous fossil groups, in the infraclass Chondrostei, which also contains the ancestors of all other bony fishes. The sturgeons themselves are not ancestral to modern bony fishes but are a highly specialized and successful offshoot of ancestral chondrosteans, retaining such ancestral features as a heterocercal tail, fin structure, jaw structure, and spiracle. They have replaced a bony skeleton with one of cartilage and possess a few large bony plates instead of scales. Sturgeons are highly adapted for preying on bottom animals, which they detect with a row of extremely sensitive barbells on the underside of their snouts. They protrude their extraordinarily long and flexible “lips” to suck up food. Sturgeons are confined to temperate waters of the Northern Hemisphere. Of 25 extant species, only two live in California, the green sturgeon and the white sturgeon (A. transmontanus). (Moyle 2002)
Green sturgeon is similar in appearance to white sturgeon, except the barbels are closer to the mouth than the tip of the long, narrow snout. The dorsal row of bony plates numbers 8-11, lateral rows, 23-30, and bottom rows, 7-10; there is one large scute behind the dorsal fin as well as behind the anal fin (both lacking in white sturgeon). The scutes also tend to be sharper and more pointed than in white sturgeon. The dorsal fin has 33-36 rays, the anal fin, 22-28. The body color is olive green with an olivaceous stripe on each side; the scutes are paler than the body. (Moyle 2002)
Green sturgeon can reach 7 feet (210 cm) in length and weigh up to 350 pounds (159 kg).
On April 7, 2006, the National Marine Fisheries Service (NMFS) issued a final rule listing the Southern distinct population segment (DPS) of North American green sturgeon (Acipenser medirostris)(green sturgeon) as a threatened species under the United States Endangered Species Act. Included in the listing is the green sturgeon population spawning in the Sacramento River and living in the Sacramento River, the Sacramento-San Joaquin Delta, and the San Francisco Bay Estuary. This threatened determination was based on the reduction of potential spawning habitat, the severe threats to the single remaining spawning population, the inability to alleviate these threats with the conservation measures in place, and the decrease in observed numbers of juvenile Southern DPS green sturgeon collected in the past two decades compared to those collected historically (NMFS 2006).
Critical habitat under the United States Endangered Species Act has not been designated for the Southern DPS of green sturgeon.