Green Sturgeon
Acipenser medirostris
Profile / Morphology 2
Green sturgeon are large bottom oriented anadromous fish. Their snout is elongated and bladelike with 4 barbels (sensory “whiskers”) in front of the mouth. The upper lobe of the tail is longer than the lower lobe, similar to most sharks. Like most sturgeon, they are characterized by unique arrangements of armored plates called scutes, which are located along their back and sides. They can be distinguished from white sturgeon (with which they co-occur) by the number of scutes along the side of the body. Green sturgeon have 23 to 30 scutes, compared to over 38 for white sturgeon. Green sturgeon also have 1-2 scutes behind the dorsal fin (white sturgeon have none), and a relatively long snout with barbels (whisker like appendages) closer to the mouth than the tip of the snout. While many green sturgeon are olive-green on their dorsal side, they can be gray or golden brown.
Diet 3
They eat burrowing shrimps like Upogebia and Neotrypaea ghost shrimp as well as mollusks, amphipods, and even small fishes.
Average lifespan in the wild 3
over 40 years
Size / Weight 3
7 feet (adult female maximum) / 350 lb (maximum)
Habitat 3
Green sturgeon are generally found over soft bottomed estuarine and river habitats where they feed on burrowing shrimps and other invertebrates. Green sturgeon are euryhaline, since they do not spend a large part of their life in estuaries, and migrate between the sea and freshwater.
Range 3
Baja Mexico to Canada along the Pacific coast. They are rare south of Point Conception, California. Two distinct population segments (DPS) under the Endangered Species Act have been defined for green sturgeon - a northern DPS (spawning populations in the Klamath and Rogue rivers) and a southern DPS (spawners in the Sacramento River) (Adams et al. 2002).
Range description 4
Green Sturgeon is an anadromous species that spend most of their life in near-shore marine and estuarine waters from Mexico to southeast Alaska (Houston 1988, Moyle et al. 1995, Davies 2004).
Large concentrations of Green Sturgeon are still found in coastal estuaries, but their range in freshwater has been restricted by damming in some rivers. For example, Green Sturgeon were historically observed hundreds of kilometers upstream in the Sacramento and Columbia rivers, but are currently restricted in the Columbia River to the lower 60 km downstream of the Bonneville Dam (Moyle 2002). Spawning is presently known to occur in only three rivers in North America, all of which are in the United States: the Rogue River in Oregon (Erickson et al. 2001, Rien et al. 2001), and the Klamath and Sacramento river systems in California (EPIC 2001, Adams et al. 2002, CDFG 2002, Moyle et al. 1992,1994). Spawning populations have been extirpated from the San Joaquin, Eel, South Fork, and Trinity rivers, and possibly the Umpqua River (EPIC 2001, NMFS 2002). Seasonal concentrations occur in several estuaries including the Sacramento-San Joaquin, Eel, Columbia, Willapa Bay, Grays Harbor and the Fraser River (Beamesderfer and Webb 2002).
Reproductive / Life Span 3
They spawn in the Sacramento, Klamath and Rogue rivers in the spring and early summer, with a peak in mid-April to mid-June (Adams et al. 2002). Spawning occurs in deep pools or “holes” in large, turbulent river mainstreams. Specific spawning habitat preferences are unclear, most likely large cobbles, yet can range from clean sand to bedrock. Individuals spawn every 3 to 5 years beginning about age 15. Green sturgeon females produce 60,000-140,000 eggs, producing the largest egg diameter (1/5th of an inch or 4.3 mm) of any sturgeon. The large egg size provides larger yolk stores for the nourishment of embryos, resulting in more successful young. Juveniles appear to spend one to three years in freshwater before they enter the ocean. Adults migrate to the north in spring (generally north of Vancouver Island Canada) and return south in the fall.
The green sturgeon can live for over 40 years.
Relatives 3
Green sturgeon are members of the sturgeon family, which contains over 30 similar looking species throughout the Northern hemisphere. The sturgeon group dates back over 200 million years in the fossil record. Sturgeons are famous for their eggs, which are called caviar and can vary in value according to species of origin.
Found in the following Estuarine Reserves 3
South Slough (OR), San Francisco (CA), Elkhorn Slough (CA), Tijuana River (CA).
Water quality factors needed for survival 3
•Water Temperature: spawning occurs in temps of 8 to 14 °C, optimal larval growth is at 15 °C
•Turbidity: moderate
•Water Flow: spawning occurs in relatively high flow
•Salinity: euryhaline - spawn in freshwater streams, adults live in ocean and estuaries
•Dissolved Oxygen: adults have been found in 6.5 to 9 mg/L
Threats 3
For the 1887-1901 period, an 88% decline is recorded from commercial fishery landings of sturgeon (mostly white sturgeon) on the west coast (Cech 1992). No distinction was made in those years between the similar white and green sturgeon.
Identified threats include: •Green sturgeon characteristics that make them vulnerable to habitat degradation and overexploitation include large size, late maturity, low productivity, long life span, and an anadromous life style.
•Freshwater habitat used for spawning has been affected by habitat alteration from water development and land-use practices causing sedimentation, especially in the Klamath, Rogue, and Eel rivers.
•Exotic species are a problem for the southern population, where an exotic clam is out competing prey the sturgeon are adapted to and feed upon.
•Introduced striped bass may feed on young green sturgeon (NMFS 2005).
•Recent habitat evaluations in the upper Sacramento River have shown significant green sturgeon habitat was probably altered or made inaccessible by dam construction over the years (NMFS 2005).
•High water temperatures created by the changes to water flow from dams may be a problem for the southern population (NMFS 2005).
Green sturgeon congregate in coastal waters and estuaries, including non-birth estuaries, where they are vulnerable to capture in salmon gillnet and other fisheries (Moser and Lindley 2007). They enter estuaries, in Washington at least, during the summer when estuary water temperatures are more than 2°C (4°F) warmer than adjacent coastal waters (Moser and Lindley 2007).
Conservation notes 3
Importance to Humans and Estuaries
Green sturgeon were once common enough to support commercial and recreational fisheries throughout their range. This is no longer the case. As large, long-lived predators, and because of their migratory lifestyle, they were a significant source of nutrients being brought into and out of estuaries.
How to Help Protect This Species
Since green sturgeon use estuaries and freshwater areas, they are susceptible to water pollution, plus damage to and alteration of stream channels and riparian zones. Suggested methods to protect Green sturgeon include:
•Efforts to minimize runoff of neighborhood pollutants, fertilizer, and sediment into local streams are helpful to this species or other stream and estuary dwelling species.
•Join a stream or watershed advocacy group in your area to protect your local estuary ecosystems.
•Advocate implementation of effective fish passage solutions so fish can bypass dams and artificial barriers.
•Support restoration of more natural water flow regimes.
•Support conservation programs like the Species of Concern program and other non governmental organization programs that work to protect the endangered population.
•Support research into the ecology of the species including the need to understand how the different populations mix in the open ocean and to make better population size and biomass estimates. Better data on other spawning sites and the Trinity and Eel River animals are needed.
Sources and Credits
- (c) CAFS, some rights reserved (CC BY-NC), http://d1iraxgbwuhpbw.cloudfront.net/images/species/acmed_u1.jpg
- Adapted by GTMResearchReserve from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Acipenser_medirostris
- (c) GTMResearchReserve, some rights reserved (CC BY-SA)
- (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/30916250
