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).
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Non-breeding
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: Coastal areas of North Pacific from Gulf of Alaska to southern California and Ensenada, Mexico; currently known to spawn only in the Sacramento and Klamath river systems in California and the Rogue River in Oregon (Houston 1988, Berstein and Bemis 1997, NMFS 2001). The possibility of current spawning in the Umpqua River, Oregon, is under investigation. There is recent evidence of limited green sturgeon spawning in the Eel River based on the collection of both adult and juvenile fish in the mid-1990s (see NMFS 2003). The species formerly spawned in the San Joaquin River in California (NMFS 2001). Green sturgeons are reported to spawn in the Feather River, but this has not been substantiated. The northern distinct population segment (DPS) ranges northward from the Eel River, California; the southern DPS includes drainages whose estuaries are south of the Eel River (NMFS 2003).
The largest spawning population is thought to occur in the Klamath River on the north coast of California (NMFS 2003). Juveniles are captured each year in the Klamath River and have also been found in the lower portion of the Salmon River (a tributary to the Klamath River). Adults occur in the Trinity River, a major tributary to the Klamath River, to Gray's Falls (rkm 69), but spawning can be confirmed only up to the Willow Creek trap (rkm 40).
In the Sacramento river system, spawning occurs predominantly in the upper Sacramento River, above Hamilton City and perhaps as far upstream as Keswick Dam (see NMFS 2003). Juveniles are found throughout the Delta and San Francisco Bay. Adults and juveniles occur throughout the upper Sacramento River (NMFS 2003).
The Rogue River recently was confirmed as a third spawning area; radio-tagged spawners moved upriver as far as rkm 39 (see NMFS 2003); juveniles are taken in beach seining efforts in the Rogue River estuary, and adults are taken in almost all of the Oregon coastal estuaries from the Chetco River to Nehalem Bay (see NMFS 2003).
In the mid-1930s, before Bonneville dam, green sturgeons were found in the Columbia River up to the Cascade Rapids; today they occur up river to the Bonneville Dam (rkm 235) but predominately in the lower 60 rkm. Tagging studies indicate a substantial exchange of fish between the Columbia River and Willapa Bay. The estuaries of Willapa Bay, the Columbia River, and Grays Harbor are late summer concentration areas. The reasons for these concentrations are unclear, but they do not appear to be related to spawning or feeding (NMFS 2003).
Small numbers have been taken in both Tomales Bay and Bodega Bay and a single fish has been taken from the Noyo River. Green sturgeons are regularly taken in small numbers in Humboldt Bay and have been caught in coastal waters and in estuaries from Arcata Bay to the Oregon border. Small numbers of both adult and juvenile green sturgeons have been observed in the Eel River (NMFS 2003). Green sturgeons occur in small numbers along the western coast of Vancouver Island and the Skeena River. Historically, they were not uncommon in the Fraser River. There is no evidence of historical or recent spawning in Canada (Trevor Davies, draft COSEWIC report, 2003).
U.S.A. (CA) Southern Distinct Population Segment, which includes all spawning populations south of the Eel River (exclusive), principally including the Sacramento River spawning population.
Length: 213 cm
Amur River Demersal Habitat
This taxon is one of a number of demersal species in the Amur River system. Demersal river fish are found at the river bottom, feeding on benthos and zooplankton
The persistence of mercury contamination in Amur River bottom sediments is a major issue, arising from historic cinnabar mining in the basin and poor waste management practises, especially in the communist Soviet era, where industrial development was placed ahead of sound conservation practises.
The largest native demersal fish species in the Amur River is the 560 centimeter (cm) long kaluga (Huso dauricus); demersal biota are those that inhabit the bottom of a surface water body. Another large demersal fish found in the Amur is the 300 cm Amur sturgeon (Acipenser schrenckii), a taxon which is endemic to the Amur basin.
Other demersal endemic fish species (all in the concubitae family) of the Amur Basin are Iksookimia longicorpa, I. koreensis, I. hugowolfeldi, Cobitis melanoleuca melanoleuca and the Puan spine loach (Iksookimia pumila).
Habitat and Ecology
Green Sturgeon are oviparious broadcast spawners and adult Green Sturgeon typically migrate into freshwater beginning in late February and spawning occurs in April to June in deep, turbulent river mainstems (Moyle et al. 1995). Klamath and Rogue River populations appear to spawn within 160 km of the ocean while the Sacramento population may travel over 320 km upriver. Green Sturgeon eggs and larvae are comparatively larger than those of other sturgeon species. For example, Cech et al. (2000) reported a egg diameter of 4.34, 3.40 and 2.62 mm for green, white, and Atlantic Sturgeon (A. oxyrinchus) respectfully indicating that Green Sturgeon have eggs which have a volume twice that of white and over four times that of Atlantic Sturgeon. Consequently, Green Sturgeon have a relatively lower fecundity in comparison to other similar sized sturgeon species as reproductive energy is more heavily invested in egg size rather than egg number (Van Eenennaam et al. 2001b, Cech et al. 2000). Fecundity varies with age and size, but has been estimated to be in the order of 2,800 eggs per kilogram bodyweight; approximately half that of White Sturgeon (Acipenser transmontanus) at 5,648 eggs per kilogram bodyweight (Moyle 2002).
The eggs do not form a thick jelly coat as do those of other North American sturgeon and exhibit poor adhesion to substrate (Deng 2000, Cech et al. 2000), which would indicate sensitivity to turbidity loading (Moyle et al. 1994, Moyle 2002). Furthermore, the larger eggs and higher growth rates of developing Green Sturgeon in comparison to other North American sturgeons suggests that a higher oxygen demand may be required for proper embryonic development; thus Green Sturgeon may require colder, cleaner water for spawning. (USFWS 1995).
Eggs hatch in 7 to 9 days at 15°C (Van Eenennaam et al. 2001). Cech et al. (2000) reported that temperatures above 20°C are lethal to embryos and temperatures above 24°C significantly reduce five-day larval growth rates. Larvae begin to feed at 10 days post hatch and complete metamorphosis into juveniles at 45 days (Adams et al. 2002). Juvenile Green Sturgeon grow rapidly reaching 60 cm within 2–3 years and they spend 1–4 years in fresh and estuarine waters before dispersal to saltwater (Beamsesderfer and Webb 2002). Green Sturgeon are commonly observed in bays and estuaries up and down the coast and large concentrations enter the Columbia River estuary, and Washington's Grays Harbor and Willapa Bay during late summer (Moyle et al. 1995). Limited tagging studies show that tagged individuals from the Columbia River have been recaptured off the west coast of Vancouver Island (Adams et al. 2002).
During the 1 to 4 years of freshwater residence, juveniles gradually move to deeper and more saline areas as they grow (Beamesderfer and Webb 2002). As juveniles grow, they exhibit greater tolerance to salinity and achieve seawater tolerance at seven months or sooner (Allen and Cech 2003). Adults return to freshwater to spawn, and Green Sturgeon have been reported to spawn up to 160 km upstream in the Klamath and Rogue rivers, and over 300 km upstream in the Sacramento River (Beamesderder and Webb 2002). After spawning, they to sea in late autumn to early winter when temperatures drop below 10°C and flows increased above 100 m3s-1 (Erickson et al. 2002).
Juveniles are opportunistic benthic feeders with a diet consisting of various invertebrates and fish (EPIC 2001, Moyle 2002). Stomach content analysis indicates that adult Green Sturgeon have a marine diet consisting of various benthic invertebrates including shrimp, crabs, worms, amphioids, and isopods (EPIC 2001), but have also been observed feeding on sand lances (Ammodytes hexapterus) and other fish.
Habitat Type: Freshwater
Comments: Green sturgeons spend most of their lives in coastal marine waters, estuaries, and the lower reaches of large rivers. They ascend rivers to spawn, but specific spawning and rearing habitats are poorly known.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Tagged green sturgeons from the Sacramento and Columbia Rivers are primarily captured to the north in coastal and estuarine waters, with some fish tagged in the Columbia being recaptured as far north as British Columbia; while there is some bias associated with recovery of tagged fish through commercial fishing, the pattern of a northern migration is supported by the large concentration of green sturgeon in the Columbia River estuary, Willapa Bay, and Grays Harbor which peaks in August. These fish tend to be immature; however, mature fish and at least one ripe fish have been found in the lower Columbia River. Genetic evidence suggests that Columbia River green sturgeon are a mixture of fish from at least the Sacramento, Klamath, and Rogue Rivers. The reasons for the concentration of green sturgeon in Oregon and Washington estuaries during the summer are unknown as there is no known spawning in these rivers and all stomachs examined to date have been empty. See NMFS (2003) for specific sources of this information.
Comments: Adults feed on bottom invertebrates and small fish.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 1 - 5
Comments: Wide-ranging migrant, but only 3 known spawning rivers (Klamath River, California; Sacramento River system, California; Rogue River, Oregon (Moyle et al. 1995). Juveniles have been found in several additional coastal rivers in Oregon, but spawning in these areas has not been confirmed (Moyle et al. 1995).
250 - 2500 individuals
Comments: Each of the known or suspected spawning populations presently contain at most a few hundred mature females (Musick et al. 2000). Coded population size is based on this information.
Very little is known about habits and life history, probably similar to those of white sturgeon.
Life History and Behavior
Apparently spawning occurs in the spring. Individuals become sexually mature at about 17 years (males) or approximately 21 years (females) (NMFS 2001). Females spawn at intervals of 3-7 years (NMFS 2001). Individuals live up to several decades.
Molecular Biology and Genetics
Barcode data: Acipenser medirostris
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Acipenser medirostris
Public Records: 7
Specimens with Barcodes: 17
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
Green Sturgeon are not subjected to overfishing and habitat fragmentation that have affected other sturgeon species. There are active fisheries restrictions in place throughout the species’ range in the U.S. and Canada.
The current adult–subadult population size is estimated at least in the tens of thousands and there is no evidence of overall population decline, although four of the seven known spawning locations may have been lost. Considerable research is underway or planned to fill in information gaps on stock structure, abundance and migrations. Although Green Sturgeon currently does not warrant "threatened" status under U.S. Endangered Species Act, concerns remain about the limited number of spawning rivers, potential growth of fisheries, and persistent habitat threats from water withdrawals and agricultural pesticides. Given the species’ life history characteristics and limited number of spawning sites, it is considered likely that the species would quickly move into a threatened category if current conservation efforts were withdrawn. It is therefore assessed as Near Threatened.
National NatureServe Conservation Status
Rounded National Status Rank: N1N - Critically Imperiled
Rounded National Status Rank: N3 - Vulnerable
NatureServe Conservation Status
Rounded Global Status Rank: G3 - Vulnerable
Reasons: Large marine range along North Pacific Ocean of North America, but only a few known spawning rivers; threats include commercial and sport fisheries, modification of spawning habitats, entrainment in water project diversions, and pollution; appears not to be greatly threatened, but better information on abundance and trends is needed.
Date Listed: 06/06/2006
Lead Region: National Marine Fisheries Service (Region 11)
Where Listed: U.S.A. (CA) Southern Distinct Population Segment
Population location: U.S.A. (CA) Southern Distinct Population Segment
Listing status: T
For most current information and documents related to the conservation status and management of Acipenser medirostris , see its USFWS Species Profile
The National Marine Fisheries Service (NMFS 2003) has determined that, based on genetic evidence of discreteness, there are two Distinct Population Segments (DPS's) for Green Sturgeon. The northern population ranges from the Eel River, California, to at least the Rogue River, Oregon. The southern population is principally comprised of the Sacramento River spawning stock.
Their wide distribution, large numbers observed seasonally in some areas, and projections based on demographic rates suggest that total Green Sturgeon numbers are at least in the tens of thousands (Beamesderfer and Webb 2002). The largest known spawning stock of Green Sturgeon is that of the Klamath River and its tributary, the Trinity River. The Klamath River population is estimated to number up to 66,000 individuals of which 3,000 would be mature adults. Actual spawner numbers in the Klamath were estimated at 760–1,500 females per year based on average harvest and total mortality rates (Beamesderfer and Webb 2002).
Based on a review of recent tagging studies, harvest analyses, and stock assessments from many locations, Beamesderfer and Webb (2002) estimated that the total adult and subadult population size of Green Sturgeon is within the range of 34,000 to 160,000 fish. Of these, greatest abundance was recorded for the Columbia River estuary, and ocean and bay waters of Oregon and Washington.
Attempts to determine trends in sturgeon abundance in the northern DPS have been inconclusive regarding the status of Green Sturgeon, and the status of the northern Green Sturgeon population is unknown (NMFS 2002, Davies 2004).
Similar attempts to determine the status of Green Sturgeon in the southern DPS were also inconclusive, and with the exception of anecdotal evidence of a reduction of Green Sturgeon entrainment at water export facilities indicative of a population decline, the status of the southern DPS is also unknown (NMFS 2002, Davies 2004).
Global Short Term Trend: Relatively stable (=10% change)
Comments: The available population information for green sturgeon in the northern DPS does not provide any evidence that the abundance of green sturgeon in this DPS is declining (NMFS 2003). In particular, the fishery-dependent harvest data from the Yurok tribal fishery show no evidence that catch or CPUE are declining, or that large fish are being removed from that spawning population. Despite this information, NMFS was uncertain about the status of green sturgeon in this DPS because no direct fisheries-independent population estimates were available.
There is no evidence from the available San Pablo Bay population information that green sturgeon abundance in the southern DPS is declining (NMFS 2003). Nevertheless, NMFS (2003) was uncertain about the status of
green sturgeon in this DPS because the method of deriving population estimates involves numerous assumptions and there are no direct measures of population abundance.
The long life span and late age of maturity makes sturgeon vulnerable to chronic and acute effects of bioaccumulation. White Sturgeon, for example have been found to have the greatest contaminant concentrations compared to salmonids, suckers, Walleye (Sander vitreus), Pacific Lamprey (Lampetra tridentata), and Eulachon (Thaleichthys pacificus), [USEPA 1999]. Whole body concentrations of hexachlorobenzene (19 ųg/kg), DDT (787 ųg/kg), p,p’DDE (620 ųg/kg), Aroclors (173 ųg/kg), and dioxins were an order of magnitude higher in concentration than all other species tested. Although Green Sturgeon are less exposed to anthropogenic contaminants due to their marine migratory phase, there is the potential for exposure when entering freshwater to spawn and during estuarine concentrations.
Marine and estuarine environments in Canada are of concern as they are heavily impacted by a number of activities including logging, aquaculture, agriculture and urbanization, and can be the eventual sinks to freshwater pollutants. However, a 1994 assessment of the quality of the lower Fraser River ecosystem indicated that no dramatic changes in species assemblages were determined to have occurred since the previous study in 1974 (Healey et al. 1994) despite an increase in usage. Area managed for conservation also increased from 23 to 69% over the same time period with 80% of the increase being accounted for by conservation efforts on the Fraser River estuary (MWLAP 2002). The increase in estuary protection and the results from Healey et al. (1994) suggests that estuarine habitat loss that may effect Green Sturgeon is likely not substantial in Canada.
In the US, where all known spawning populations occur, Green Sturgeon have lost spawning habitat to poor land use practices and habitat alteration through water management projects (EPIC 2001). This has caused a decline in general water quality in some areas through increased sedimentation as well as the loss of deep pools which Green Sturgeon are known to prefer. Furthermore, damming of river systems can block previously available spawning habitat, affect natural flow regimes, potentially reduce areas of thermal refugia, and change sediment transport characteristics of the river which may cascade and impact sturgeon by modifying ecosystem community structure (EPIC 2001). 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).
Beamesderfer and Webb (2002 suggest that habitat conditions throughout the Green Sturgeon range have stabilized or are improving, but the results of spawning surveys have yet to substantiate that (NMFS 2002). Most of the northern population segment spawns in the Klamath River. Potential threats to this population include concentration of spawning, harvest (especially in mixed-stock estuarine fisheries), and loss of spawning habitat such as the Columbia River, and the Eel and South Fork, and Trinity Rrivers in California (Adams et al. 2002).
The southern population segment (south of the Eel River) is more of a concern because it has fewer spawners (limited to the Sacramento-San Joaquin system), which makes it more susceptible to catastrophic events. These fish also face potentially lethal temperature limits, entrainment by water projects, and may be adversely affected by pesticides and other toxic substances and exotic species (Adams et al. 2002). It is probable that Green Sturgeon spawning habitat has been lost behind dams and water diversions throughout the Central Valley (e.g., Red Bluff Diversion Dam and Glenn-Colusa Irrigation District pumping plant).
Green Sturgeon harvest is all bycatch in Green Sturgeon harvest is all bycatch in two three fisheries. The smaller bycatch occurs in Klamath River Tribal salmon gill net fisheries while the larger portion is in the White Sturgeon commercial and sport fisheries (Adams et al. 2002). Total annual harvest of Green Sturgeon declined substantially to 1,192 fish in 1999–2001 from 6,871 fish in 1985–1989. Most of this earlier harvest came from the Columbia River (51%) and Washington coastal fisheries (28%). In recent years, Columbia and Washington coastal harvest was substantially reduced and in 2001 these two bycatch fisheries and that of the Klamath River tribes were about equal in number. Catch reduction in the Columbia River is a result of increasingly restrictive regulations. For the sturgeon sport fishery, slot limits prohibit retention of fish (white or green) less than 107 cm (42 inches) or more than 152 cm (60 inches). Green Sturgeon retained as bycatch in the commercial fishery must be between 122 and 168 cm (48-66 inches).
Klamath Tribal fisheries (Yurok and Hoopa) accounted for an average 266 adult fish annually from 1986–2001 with no apparent trend. This fishery is monitored but not regulated. California sport catch of Green Sturgeon, primarily in San Pablo Bay, is not monitored, but is thought to be only a few fish each year (Adams et al. 2002). California slot size limits for both sturgeon species is 117–183 cm (46–72 inches).
There is also a bycatch in the domestic trawl fishing industry in B.C., which takes about 171 Green Sturgeon annually (Davis 2004).
There is no information on the extent of illegal exploitation of Green Sturgeon, but poaching activity on White Sturgeon in the lower Fraser River is a concern (Ptolemy and Vennesland 2003).
Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable
Comments: Threats include commercial and sport fisheries (including bycatch in white sturgeon fishery), modification of spawning habitats (e.g., as a result of logging, agriculture, mining, road construction, and urban development in coastal watersheds), entrainment in water project diversions, and pollution (see Moyle et al. 1995 for further details). All known spawning rivers have flow regimes affected by water projects (Moyle et al. 1995).
There is no documentation of green sturgeon spawning in the San Joaquin River at present, but there may have been spawning there before construction of large-scale hydropower and irrigation development (NMFS 2003).
Green sturgeons reportedly spawned in the South Fork Trinity River but apparently no longer do so in areas affected by extensive sedimentation from the 1964 flood (see NMFS 2003).
Spawning populations are highly vulnerable to over-fishing because individuals tend to hold and concentrate in deep, cold pools in rivers.
There are some risk factors of potential concern for the northern DPS, most notably bycatch harvest in various fisheries; however, there is uncertainty about the overall level of risk facing this DPS (NMFS 2003). In the case of harvest bycatch for which there is the most information, it is not possible to directly assess the impact of harvest on green sturgeon in this DPS. Nevertheless, the available data shows that overall green sturgeon harvest has declined substantially since the mid-1980s due to increasingly restrictive harvest management measures, suggesting that risk from harvest has been also reduced. Although the risk to green sturgeon from harvest bycatch may be declining, NMFS (2003) believed that it may be prudent for fisheries managers to continue recent conservative management measures as well as consider additional harvest protections until population monitoring information can be obtained to assess the status of this DPS with greater certainty. Based on a review of the best available information, NMFS (2003) concluded that the northern green sturgeon DPS is not presently in danger of extinction nor is it likely to become so in the foreseeable future.
There is a great deal of uncertainty regarding the effects of potential risk factors on green sturgeon in the southern DPS (NMFS 2003). While there is some information on harvest bycatch impacts, it appears most of the identified risk factors are not well documented or are only suspected to be risk factors. Examples of the latter include entrainment at the Delta water export facilities, impacts from exotic species introductions, impacts from contaminants, and lethal water temperatures. In the case of harvest bycatch for which there is the most information and perhaps the greatest concern, it is not possible to directly assess the impact of harvest on green sturgeon in this DPS. Nevertheless, direct harvest appears to be limited in California and harvest from fisheries in Oregon and Washington has declined substantially since the mid-1980s and even more so since the mid-1990s due to increasingly restrictive harvest management measures. These harvest reductions and associated restrictive management measures suggest that risk to green sturgeon from harvest bycatch has been reduced. Although the risk to green sturgeon from bycatch harvest may be declining, NMFS (2003) believed that it may be prudent to consider additional harvest protections until population monitoring information can be obtained to assess the status of this DPS with greater certainty. Based on a review of the best available information, NMFS (2003) concluded that the southern green sturgeon DPS is not presently in danger of extinction nor is it likely to become so in the foreseeable future.
Due to life history characteristics that make it particularly sensitive to human activities or natural events Green Sturgeon has a designation of "Special Concern" in Canada (Houston 1988, Davies 2004), and no harvest is allowed in Canadian waters.
In response to a petition to list Green Sturgeon under the U.S. Endangered Species Act, the National Marine Fisheries Service (NMFS) completed a status review for this species (Adams et al. 2002). NMFS determined that the species is comprised of two distinct population segments (DPS) but that neither warrants listing as a threatened or endangered species at this time (NMFS 2003). However, because of remaining uncertainties about their population structure and status, both DPS populations were added to the agency's list of candidate species and will be reevaluated in five years provided sufficient new information becomes available.
It is listed on CITES Appendix II.
Management Requirements: See recovery plan for Sacramento-San Joaquin Delta native fishes (USFWS 1995).
Biological Research Needs: Current research needs include: 1. Detailed studies on life history and ecological requirements. 2. Population assessment and monitoring.
It is essential that immediate efforts be undertaken to implement direct monitoring of green sturgeon in both the northern and southern DPSs (NMFS 2003).
Global Protection: Unknown whether any occurrences are appropriately protected and managed
Comments: Fisheries along Pacific coast are managed by each state (e.g., California, Oregon, and Washington).
Needs: 1. Fisheries that target green sturgeon should be limited until more is learned about the biology and abundance of the species. 2. Implement regulations to reduce the catch of large reproductive females. See recovery plan for Sacramento-San Joaquin Delta native fishes (USFWS 1995).
Relevance to Humans and Ecosystems
The Green sturgeon (Acipenser medirostris) is a species of sturgeon native to the Pacific Ocean, from China and Russia, over into Canada and the United States.
Sturgeons are among the largest and most ancient of ray finned 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 sensitive barbels on the underside of their snouts. They protrude their very 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 to 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 colour of the white sturgeon is yellow with some pink instead of the green of the green sturgeon.
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 was proposed under the United States Endangered Species Act in September 2008 for the Southern DPS of green sturgeon.
The northern DPS of the green sturgeon (which spawn in the Rogue River, Klamath River, and Umpqua River) is a U.S. National Marine Fisheries Service Species of Concern. Species of Concern are those species about which the U.S. Government’s National Oceanic and Atmospheric Administration, National Marine Fisheries Service, has some concerns regarding status and threats, but for which insufficient information is available to indicate a need to list the species under the U.S. Endangered Species Act.
Life history and habitat requirements
Sturgeons have adopted a temporal strategy to controlling risks. Sturgeons live a long time, delay maturation to large sizes, and spawn multiple times over their lifespan. The sturgeon’s long life span and repeat spawning in multiple years allows them to outlast periodic droughts and environmental catastrophes. The high fecundity that comes with large size allows them to produce large numbers of offspring when suitable spawning conditions occur and to make up for years of poor conditions. Adult green sturgeon do not spawn every year and only a fraction of the population enters freshwater where they might be at risk of a catastrophic event in any year. The widespread ocean distribution of green sturgeon ensures that most of the population at any given time is dispersed among areas where they are not vulnerable to catastrophic losses.
The ecology and life history of green sturgeon have received little study, evidently because of the generally low abundance, limited spawning distribution, and low commercial and sport fishing value of the species (Moyle 2002). Green sturgeon is the most marine species of sturgeon, coming into rivers mainly to spawn (Moyle 2002). Green sturgeons do not spawn every year, and it is believed that the majority of adult green sturgeons are in the ocean at any given time.
The United States Fish and Wildlife Service (USFWS) reported in 1995 that for the Klamath River, green sturgeon life history could be divided into three phases: 1) freshwater juveniles (<3 years old); 2) coastal migrants (3–13 years old for females and 3–9 years for males); and 3) adults (>13 years old for females and > 9 years old for males).
Northern DPS green sturgeon migrate up the Klamath River between late February and late July (Moyle 2002). The spawning period is March–July, with a peak from mid-April to mid-June (Moyle 2002). Spawning takes place in deep, fast water (Moyle 2002). Preferred spawning substrate is likely large cobble, but it can range from clean sand to bedrock (Moyle 2002). Eggs are broadcast and externally fertilized in relatively fast water and probably in depths greater than 3 m (Moyle 2002). Female green sturgeon produce 59,000-242,000 eggs, about 4.34 millimeters (mm) in diameter (Van Eenennaam et al. 2001 and 2006).
Temperatures of 23–26 °C affected cleavage and gastrulation of green sturgeon embryos and all died before hatch (Van Eenennaam et al. 2005). Temperatures of 17.5–22 °C were suboptimal as an increasing number of green sturgeon embryos developed abnormally and hatching success decreased at 20.5–22 °C, although the tolerance to these temperatures varied between progenies (Van Eenennaam et al. 2005). The lower temperature limit was not evident from the Van Eenennaam et al. 2005 study, although hatching rate decreased at 11 °C and hatched green sturgeon embryos were shorter, compared to 14 °C. The mean total length of hatched green sturgeon embryos decreased with increasing temperature, although their wet and dry weight remained relatively constant (Van Eenennaam et al. 2005). Van Eenennaam et al. 2005 concluded that temperatures 17–18 °C may be the upper limit of the thermal optima for green sturgeon embryos. Growth studies on younger juvenile green sturgeon determined that cyclical 19-24 °C water temperature was optimal (Allen et al. 2006).
Green sturgeon fertilization and hatching rates are 41.2% and 28.0%, compared with 95.4% and 82.1% for the white sturgeon (Deng et al. 2002). However, the survival of green sturgeon larvae is very high (93.3%) (Deng et al. 2002). Female green sturgeon invest a greater amount of their reproductive resources into maternal yolk for nourishment of the embryo, which results in larger larvae (Van Eenennaam et al. 2001). Five-day-old green sturgeon larvae have almost twice the weight of white sturgeon larvae (65 versus 34 milligrams (mg)) (Van Eenennaam et al. 2001). This greater reserve of maternal yolk and larger larvae could provide an advantage in larval feeding and survival (Van Eenennaam et al. 2001). Compared with other acipenserids, green sturgeon larvae appear more robust and easier to rear (Van Eenennaam et al. 2001). Juveniles continue to grow rapidly, reaching 300 mm in 1 year and over 600 mm within 2–3 years for the Klamath River (USFWS 1995). Juveniles spend from 1–4 years in fresh and estuarine waters and disperse into salt water at lengths of 300–750 mm (USFWS 1995).
A conceptual model of early behavior and migration of green sturgeon early life intervals based on the Kynard et al. 2005 study follows: Females deposit eggs at sites with large rocks and moderate or eddy water flow that keeps the large, dense, poorly adhesive eggs from drifting, so eggs sink deep within the rocks. CH2M Hill (2002) assumed that hatchling green sturgeon embryos drift downstream like hatchling white sturgeon embryos. This was incorrect. Hatchling green sturgeon embryos seek nearby cover, and remain under rocks, unlike white sturgeon which drift downstream as embryos (i.e. newly hatched green sturgeon do not exhibit pelagic behavior like newly hatched white sturgeon) (Deng et al. 2002). After about 9 days fish develop into larvae and initiate exogenous foraging up- and downstream on the bottom (they do not swim up into the water column, unlike white sturgeon). After a day or so, larvae initiate a downstream dispersion migration that lasts about 12 days (peak, 5 days). At the age of ten days, when exogenous foraging begins, green sturgeons are 19 to 29 mm in length (mean 24 mm) (Deng et al. 2002). At the age of 15 to 21 days, green sturgeon are 30 mm or greater in length (Deng et al. 2002). At the age of 45 days, metamorphosis is complete and green sturgeon are 70 to 80 mm in length (Deng et al. 2002). All migration and foraging during the migration period is nocturnal, unlike white sturgeon. During the first 10 months of life, green sturgeon are the most nocturnal of any North American sturgeon yet studied, and this was the case for all life intervals during any activity (migration, foraging, or wintering). Post-migrant larvae are benthic, foraging up- and downstream diurnally with a nocturnal activity peak. Foraging larvae select open habitat, not structure habitat, but continue to use cover in the day. When larvae develop into juveniles, there is no change in response to bright habitat, and no preference or avoidance of bright habitat. In the fall, juveniles migrate downstream mostly at night to wintering sites, ceasing migration at 7–8 °C. During winter, juveniles select low light habitat, likely deep pools with some rock structure. Wintering juveniles forage actively at night between dusk and dawn and are inactive during the day, seeking the darkest available habitat.
For the Klamath River green sturgeon, an average length of 1.0 m is attained in 10 years, 1.5 m by age 15, and 2.0 m by 25 years of age (USFWS 1993). The largest reported green sturgeon weighed about 159 kg and was 2.1 m in length (USFWS 1993). The largest green sturgeon have been aged at 42 years, but this is probably an underestimate, and maximum ages of 60–70 years or more are likely (Moyle 2002).
Little is known about green sturgeon feeding at sea, but it is clear they behave quite differently than white sturgeon (CDFG 2005a). Green sturgeons are probably found in all open Oregon estuaries, with a lot of movement in and out of estuaries and up and down the coast (ODFW 2005a). Adults feed in estuaries during the summer (ODFW 2005a). Stomachs of green sturgeons caught in Suisun Bay contained Corophium sp. (amphipod), Crago franciscorum (bay shrimp), Neomysis awatchensis (Opossum shrimp) and annelid worms (Ganssle 1966). Stomachs of green sturgeon caught in San Pablo Bay contained Crago franciscorum (bay shrimp), Macoma sp. (clam), Photis californica (amphipod), Corophium sp. (amphipod), Synidotea laticauda (isopod), and unidentified crab and fish (Ganssle 1966). Stomachs of green sturgeons caught in Delta contained Corophium sp. (amphipod), Neomysis awatchensis (Opossum shrimp) (Radtke 1966). Radtke 1966 also reported that while the Asiatic clam (Corbicula fluminea) was abundant throughout the Delta, Suisun Bay and San Pablo Bay, it was not utilized as a food source by green sturgeons.
Threats to the green sturgeon include being taken as bycatch in salmon gillnet and other fisheries, water development projects that affect migration or decrease habitat quality, and other land use stressors that affect habitat quality. Exotic species may negatively affect the southern DPS. Commercial fisheries have been prohibited in the Columbia River and Willapa Bay since 2001. Harvest of green sturgeon in California has been prohibited since March 2007. Beginning in March 2010 and to protect green sturgeon on their spawning grounds, the Sacramento River sturgeon fishery was closed year-round between the Keswick Dam and Hwy 162 bridge (approximately 90 miles).
Current and historical distribution
Prehistoric fish distributions have been mapped by Gobalet et al. 2004 based on bones at Native American archaeological sites. Data were reported on dozens of sites throughout California and summarized by county. Sturgeon remains were observed in 12 counties, all in the Central Valley. Observations were concentrated at San Francisco Bay and Sacramento-San Joaquin and delta sites (Contra Costa, Alameda, San Francisco, Marin, Napa, San Mateo and Santa Cruz counties). Historical 18th-century accounts report the aboriginal gillnetting and use of tule balsa watercraft for the capture of sturgeon, and fishing weirs were also likely employed on bay tidal flats (Gobalet et al. 2004). Most sturgeons were unidentified species but green sturgeons were specifically identified from Contra Costa and Marin County sites. Sturgeon remains (unidentified species) were also identified from lower Sacramento River counties (Sacramento, Yolo, Colusa, Glenn, and Butte counties). No sturgeon remains were found in samples from the upper Sacramento River although other fish species including salmonids were reported in those areas.
Green sturgeons which spawn in the Rogue River, Klamath River, and Umpqua River are the Northern DPS green sturgeon, while the green sturgeons which spawn in the Sacramento River system are Southern DPS green sturgeon (NMFS 2005). Both the Northern DPS green sturgeon and Southern DPS green sturgeon occur in large numbers in the Columbia River estuary, Willapa Bay, and Grays Harbor, Washington (NMFS 2005).
A number of presumed spawning populations (Eel River and South Fork Trinity River) have been lost in the past 25–30 years (Moyle 2002). Moyle 1976 reported green sturgeon spawning in the Mad River, but does not mention the Mad River in 2002. Scott and Crossman 1973 reported potential spawning in the Fraser River in Canada, but Moyle 2002 reported that there was no evidence of green sturgeon spawning in Canada or Alaska. Green and white sturgeon enter the Feather River system annually and spawning of green sturgeon was documented for the first time in 2011(Seesholtz et al. 2014). No current use by sturgeon of Sacramento River tributaries, other than the Feather River system, has been reported (Beamesderfer et al. 2004, Moyle 2002). No evidence was found to indicate that green sturgeons were historically present, are currently present, or were historically present and have been extirpated from the San Joaquin River upstream from the Delta (Beamesderfer et al. 2004). There is no evidence of green sturgeon spawning in the Columbia River or other rivers in Washington (Moyle 2002, ODFW 2005a and 2005b). In contrast to those studies, samples from green sturgeon collected in the Columbia River suggest the existence of one or more spawning populations in addition to the Sacramento system, Klamath, and Rogue populations, suggesting not all spawning populations have been identified (Israel et al. 2004).
The green sturgeon is the most widely distributed member of the sturgeon family Acipenseridae, and is also the most marine-oriented of the sturgeon species. Green sturgeon are known to range in nearshore marine waters from Mexico to the Bering Sea, with a general tendency to head North after their out-migration from freshwater (NMFS 2005). They are commonly observed in bays and estuaries along the western coast of North America, with particularly large concentrations entering the Columbia River estuary, Willapa Bay, and Grays Harbor during the late summer (Moyle 2002, NMFS 2005). While there is some bias associated with recovery of tagged fish through commercial fishing, the pattern of a northern migration is supported by the large concentration of green sturgeon in the Columbia River estuary, Willapa Bay, and Grays Harbor, which peaks in August (NMFS 2005).
Individual Southern DPS green sturgeon tagged by the California Department of Fish and Game (CDFG) in the San Francisco Estuary have been recaptured off Santa Cruz, California; in Winchester Bay on the southern Oregon coast; at the mouth of the Columbia River; and in Gray’s Harbor, Washington (USFWS 1993 and Moyle 2002). Most tags for Southern DPS green sturgeon tagged in the San Francisco Estuary have been returned from outside that estuary (Moyle 2002). Green sturgeons remain present in all documented historic habitats and ranges in Oregon (ODFW 2005b).
White and green sturgeon juveniles, subadults, and adults are widely distributed in the Sacramento-San Joaquin Delta and estuary areas including San Pablo (Beamesderfer et al. 2004). White sturgeon historically ranged into upper portions of the Sacramento system including the Pit River and a substantial number were trapped in and above Lake Shasta when Shasta Dam was closed in 1944 and successfully reproduced until the early 1960s (Beamesderfer et al. 2004). Landlocked white sturgeon populations have been widely observed in the Columbia and Fraser systems but no landlocked green sturgeon populations have ever been documented in any river system (Beamesderfer et al. 2004), indicating that green sturgeon likely did not historically spawn in the upper reaches of rivers prior to the construction of large dams as NMFS 2005 has assumed.
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Allen, P. J., M. Nicholl, S. Cole, A. Vlazny, and J.J. Cech, Jr. 2006. Growth of Larval to Juvenile Green Sturgeon in Elevated Temperature Regimes. Transactions of the American Fisheries Society 135:89-96.
Beamesderfer, R., M. Simpson, G. Kopp, J. Inman, A. Fuller and D. Demko. 2004. Historical and Current Information on Green Sturgeon Occurrence in the Sacramento and San Joaquin Rivers and Tributaries. S.P. Cramer and Associates, Inc. 46 p.
California Department of Fish and Game. 2005. White Sturgeon Population Estimate. Email from Marty Gingras, Senior Biologist Supervisor, California Department of Fish and Game. 1 p.
CH2M Hill, Inc. 2002. Environmental Impact Statement/Environmental Impact Report for Fish Passage Improvement Project at the Red Bluff Diversion Dam. Prepared by CH2MHill, Inc. for the Tehama-Colusa Canal Authority and the U.S. Bureau of Reclamation.
Deng, X., J.P. Van Eenennaam, and S.I. Doroshov. 2002. Comparison of Early Life Stages and Growth of Green and White Sturgeon. American Fisheries Society Symposium 28:237-248.
Gobalet, K.W., P.D. Schultz, T.A. Wake, and N. Siefkin. 2004. Archaeological perspectives on Native American fisheries of California, with emphasis on steelhead and salmon. Transactions of the American Fisheries Society 133:801-833.
Ganssle, D. 1966. Fishes and Decapods of San Pablo and Suisun Bays. In: D.W. Kelley (ed.) Ecological Studies of the Sacramento San Joaquin Estuary: Part I; Zooplankton, Zoobenthos, and Fishes of San Pablo and Suisun Bays, Zooplankton and Zoobenthos of the Delta. California Department of Fish and Game. Fish Bulletin 133.
Israel, J.A., J.F. Cordes, M.A. Blumberg and B. May. 2004. Geographic Patterns of Genetic Differentiation among Collections of Green Sturgeon. North American Journal of Fisheries Management 24:922-931.
Kynard, B., E. Parker and T. Parker. 2005. Behavior of early life intervals of Klamath River green sturgeon, Acipenser medirostris, with a note on body color. Environmental Biology of Fishes 72:85-97.
Moyle, P.B. 2002. Inland Fishes of California. University of California Press, Berkeley, California. 106-113 p.
Oregon Department of Fish and Wildlife. 2005a. Wildfish: Chapter 6. http://www.dfr.state.or.us/ODFWhtml/Research&Reports/WildFish/Chapter6.html.
Oregon Department of Fish and Wildlife. 2005b. Oregon Native Fish Status Report. Salem, Oregon. 491 p.
National Marine Fisheries Service. 2005. Endangered and Threatened Wildlife and Plants: Proposed Threatened Status for Southern Distinct Population Segment of North American Green Sturgeon. April 6, 2005. Federal Register 70(65):17386-17401.
National Marine Fisheries Service. 2006. Endangered and Threatened Wildlife and Plants: Threatened Status for Southern Distinct Population Segment of North American Green Sturgeon. April 7, 2006. Federal Register 71(67):17757-17766.
Seesholtz, A.M., M.J. Manuel, and J.P. Van Eenennaam. 2014. First documented spawning and associated habitat conditions for green sturgeon in the Feather River, California. Environmental Biology of Fishes 97(9)
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Names and Taxonomy
Comments: Based on genetic data, NMFS (2003) identified two distinct population segments (DPSs). The geographic range of the northern DPS occurs largely within the Coastal Range ecoregion which extends from the Olympic Peninsula southward through the Coast Range and Klamath Mountains to and including the Eel River. The southern DPS occurs south of the Eel River, largely within the Central California Valley ecoregion which includes the Sacramento and San Joaquin rivers. NMFS stated that further research may revise these ranges and that additional DPSs could be recognized in the future.
ACIPENSER MIKADOI of eastern Asia formerly was included in this species. Chromosomal and molecular data support the recognition of A. MEDIROSTRIS and A. MIKADOI as distinct species (Birstein 1993, Birstein et al. 1993, Birstein and Bemis 1997, Birstein and DeSalle 1998).
Gene sequencing data of Birstein and DeSalle (1998) indicate that there are least three main clades within ACIPENSER: A. STURIO-A. OXYRINCHUS, A. SCHRENCKII-A. TRANSMONTANUS, and all Ponto-Caspian species plus A. DABRYSNUS and A. BREVIROSTRUM.
Krieger et al. (2000) examined phylogenetic relationships of North American sturgeons based on mtDNA sequences and found that (1) nucleotide sequences for all four examined genes for the three SCAPHIRHYNCHUS species were identical; (2) the two ACIPENSER OXYRINCHUS subspecies were very similar in sequence; (3) A. TRANSMONTANUS and A. MEDIROSTRIS were sister taxa, as were A. FULVESCENS and A. BREVIROSTRUM (in constrast to Birstein and DeSalle 1998).