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Green Sturgeon (Acipenser medirostris)

Status | Species Description | Habitat | Distribution | Population Trends | Threats | Conservation Efforts | Regulatory Overview | Taxonomy | Key Documents | More Info

Status

ESA Threatened - Southern DPS
ESA Species of Concern - Pacific-northern DPS (including coastal spawning populations from the Eel River north to the Klamath and Rogue rivers)
CITES Appendix II - throughout its range

Species Description

Weight:
up to 350 pounds (160 kg)
Length:
average 4.5-6.5 feet (1.5-2 m), can be as long at 7 feet
Appearance:
they have no scales, but they have five rows of characteristic bony plates on their body called "scutes"
Lifespan:
60-70 years
Diet:
shrimp, mollusks, amphipods, and small fish
Behavior:
anadromous; they live primarily in the sea and breed in fresh water

Green sturgeon are long-lived, slow-growing fish, and are the most marine-oriented of the sturgeon species. Mature males range from 4.5-6.5 feet (1.4-2 m) in "fork length" and do not mature until they are at least 15 years old (Van Eenennaam, 2002), while mature females range from 5-7 feet (1.6-2.2 m) fork length and do not mature until they are at least 17 years old. They can weigh up to 350 pounds (160 kg). Maximum ages of adult green sturgeon are likely to range from 60-70 years (Moyle, 2002).

Although they are members of the class of bony fishes, the skeleton of sturgeons is composed mostly of cartilage. Sturgeon don't have scales, but they have five rows of characteristic bony plates on their body called "scutes". The backbone of the sturgeon curves upward into the caudal fin, forming their shark-like tail. On the ventral, or underside, of their flattened snouts are sensory barbels and a siphon-shaped, toothless mouth.

Green sturgeon are believed to spend the majority of their lives in nearshore oceanic waters, bays, and estuaries. Younger green sturgeon reside in fresh water, with adults returning to freshwater to spawn when they are about 15 years of age and more than 4 feet (1.3 m) in size. Spawning is believed to occur every 2-5 years (Moyle, 2002). Adults typically migrate into fresh water beginning in late February, and spawning occurs from March-July, with peak activity from April-June (Moyle et al., 1995). Females produce 60,000-140,000 eggs (Moyle et al., 1992). Juvenile green sturgeon spend a few years in fresh and estuarine waters before they leave for saltwater. They then disperse widely in the ocean.

The only feeding data we have on adult green sturgeon shows that they are eating "benthic" invertebrates including shrimp, mollusks, amphipods, and even small fish (Moyle et al., 1992).

Habitat

Green sturgeon utilize both freshwater and saltwater habitat. Green sturgeon spawn in deep pools or "holes" in large, turbulent, freshwater river mainstems (Moyle et al., 1992). Specific spawning habitat preferences are unclear, but eggs likely are broadcast over large cobble substrates, but range from clean sand to bedrock substrates as well (Moyle et al., 1995). It is likely that cold, clean water is important for proper embryonic development.

Adults live in oceanic waters, bays, and estuaries when not spawning. Green sturgeon are known to forage in estuaries and bays ranging from San Francisco Bay to British Columbia.

Critical Habitat
In October 2009, NMFS designated critical habitat for the Southern DPS [pdf].

Distribution

This species is found along the west coast of Mexico, the United States, and Canada. Green sturgeon are the most broadly distributed, wide-ranging, and most marine-oriented species of the sturgeon family. The green sturgeon ranges from Mexico to at least Alaska in marine waters, and is observed in bays and estuaries up and down the west coast of North America (Moyle et al., 1995).

The actual historical and current distribution of where this species spawns is unclear as green sturgeon make non-spawning movements into coastal lagoons and bays in the late summer to fall, and because their original spawning distribution may have been reduced due to harvest and other anthropogenic effects.

Green sturgeon are believed to spawn in the Rogue River, Klamath River Basin, and the Sacramento River. Spawning appears to rarely occur in the Umpqua River. Green sturgeon in the South Fork of the Trinity River were thought extirpated (Moyle, 2002), but juveniles captured at Willow Creek on the Trinity River (Scheiff et al., 2001) suggest that the fish could be coming from either the South Fork or the Trinity River (Adams et al., in press). Green sturgeon appear to occasionally occupy the Eel River.

Population Trends

No good data on current population sizes exists and data on population trends is lacking. Tagging experiments have been conducted irregularly since 1954, though regular tagging did not occur until 1990. Over 500 green sturgeon have been captured and over 200 have been tagged.

Threats

The principal factor in the decline of the Southern DPS is:

Other threats to the Southern DPS include:

Conservation Efforts

Fishing regulations and conservation measures represent a reduction in risk to green sturgeon. California, Oregon, Washington (United States) and British Columbia (Canada) have restricted commercial and sport fisheries where green sturgeon occur (IUCN Red List of Threatened Species ). Recent implementation of sturgeon fishing restrictions in Oregon and Washington and protective efforts put in place on the Klamath, Trinity, and Eel Rivers in the 1970s, 1980s, and 1990s may offer protection to the Southern DPS. The recent closure of the California recreational fishery may also provide beneficial to this species. The most important conservation currently occurring is the change in operations of Red Bluff Diversion dam (open from mid September to mid May) allowing access to spawning areas above the dam. Originally, the dam was closed year around.

Regulatory Overview

After completion of a study of its status (Adams et al., 2002) in 2002, NMFS determined that the green sturgeon is comprised of two DPSs that qualify as species under the ESA, but that neither warranted listing as threatened or endangered [pdf] (68 FR 4433). Uncertainties in the structure and status of both DPSs led NMFS to add them to the Species of Concern List [pdf] (69 FR 19975).

The "not warranted" determination was challenged in April 2003. NMFS produced an updated status review in February 2005 and proposed that the Southern DPS should be listed as threatened under the ESA. NMFS published a final rule in April 2006 listing the Southern DPS as threatened [pdf] (71 FR 17757).

In September 2008, NMFS proposed critical habitat for the Southern DPS [pdf]. In October 2009, NMFS published the final rule to designate critical habitat [pdf].

In May 2009, NMFS proposed a 4(d) rule [pdf] to apply ESA take prohibitions to the Southern DPS. NMFS published the final 4(d) rule in June 2010.

Taxonomy

Kingdom: Animalia
Phylum: Chordata
Class: Osteichthyes
Order: Acipenseriformes
Family: Acipenseridae
Genus: Acipenser
Species: smedirostris

Key Documents

(All documents are in PDF format.)
Title Federal Register Date
5-Year Status Review n/a 08/25/2015
Species of concern status review Pacific-Northern Green Sturgeon DPS n/a 11/20/2014
Initiation of 5-Year Review for the Southern DPS 77 FR 64959 10/24/2012
Final 4(d) Rule to Establish Take Prohibitions 75 FR 30714 06/02/2010
Critical Habitat for the Southern DPS Final Rule 74 FR 52300 10/09/2009
Proposed 4(d) Rule to Establish Take Prohibitions 74 FR 23822 05/21/2009
Proposed Critical Habitat for the Southern DPS 73 FR 52084 09/08/2008
Species of Concern Fact Sheet: Detailed n/a 11/02/2007
n/a 05/17/2007
Final ESA Listing Rule for Southern DPS 71 FR 17757 04/07/2006
Proposed ESA Listing for Southern DPS 70 FR 17386 04/06/2005
Status Review Update (2005) n/a 02/2005
n/a 06/2002

More Information

References

Updated: August 25, 2015