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Green Sturgeon (Acipenser medirostris)

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

  Green Sturgeon
Green Sturgeon
(Acipenser medirostris)
Photo: Toz Soto,
Karuk Tribe Fisheries Dept.



green sturgeon range map
Green Sturgeon Range Map
(click for larger view PDF)


 

 

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

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

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).

 
green sturgeon critical habitat map
Green Sturgeon Critical Habitat
(click for larger view PDF)


  Green Sturgeon DPS Map. The Northern DPS includes populations from the Rogue, Klamth-Trinty, and Eel rivers. The Southern DPS includes a single population in the Sacramento River.
Green Sturgeon DPS Map
Image: NOAA
(click for larger image)


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. Since 1990, tagging has been conducted on a regular basis. 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:

  • reduction of the spawning area to a limited section of the Sacramento

Other threats to the Southern DPS include:

  • insufficient freshwater flow rates in spawning areas,
  • contaminants (e.g., pesticides)
  • bycatch of green sturgeon in fisheries
  • potential poaching (e.g., for caviar)
  • entrainment by water projects
  • influence of exotic species
  • small population size
  • impassable barriers
  • elevated water temperatures

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 This link is an external site.). 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.

Key Documents
(All documents are in PDF format.)

Title Federal Register Date

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

  • Adams, P.B., C.B. Grimes, J.E. Hightower, S.T. Lindley, and M.L. Moser. 2002. Status Review for the North American green sturgeon. NOAA, National Marine Fisheries Service, Southwest Fisheries Science Center, Santa Cruz, CA. 49 p.
  • Adams, P.B., C.l. Grimes, J.E. Hightower, S.T. Lindley, M.L. Moser, and M.J. Parsley. In Press. "Population Status of North American Green Sturgeon, Acipenser medirostris" Environmental Biology of Fishes.
  • Beamesderfer, R.C.P. and M.A.H. Webb. 2002 Green sturgeon status review information. S.P. Cramer and Associates, Gresham, Oregon, U.S.
  • Moyle, P.B., P.J. Foley, and R.M. Yoshiyama. 1992. Status of green sturgeon, Acipensermedirostris, in California. Final Report submitted to National Marine Fisheries Service. 11 p. University of California, Davis, CA 95616.
  • Moyle, P.B., R.M. Yoshiyama, J.E. Williams, and E.D. Wikramanayake. 1995. Fish Species of Special Concern in California. Second edition. Final report to CA Department of Fish and Game, contract 2128IF.
  • Moyle, P.B. 2002. Inland fishes of California. University of California Press, Berkeley, CA. 502 pp.
  • Scheiff, A.J., J.S. Lang, W.D. Pinnix. 2001. Juvenile salmonid monitoring on the mainstem Klamath River at Big Bar and mainstem Trinity River at Willow Creek 1997-2000. USFWS, AFWO, Arcata, CA 95521, 114 pp.
  • Van Eenennaam, J. P. 2002. Personnel Communication. In Adams, P.B., C.B. Grimes, J.E. Hightower, S.T. Lindley, and M.L. Moser. 2002. Status Review for the North American green sturgeon. NOAA, National Marine Fisheries Service, Southwest Fisheries Science Center, Santa Cruz, CA. 49 p.

Updated: June 2, 2014

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