Green Sturgeon (Acipenser medirostris )

Green Sturgeon
Sturgeon
Courtesy of Harry Morse, CDFW
Juvenile Green Sturgeon
Juvenile Green Sturgeon
Courtesy of DWR
Green Sturgeon
Green Sturgeon
Courtesy of Daniel W. Gotshall

Protection Status

There are two populations of green sturgeon in California, a northern Distinct Population Segment (nDPS) and a southern Distinct Population Segment (sDPS). The sDPS green sturgeon spawn in the Sacramento, Feather, and possibly the Yuba rivers. The nDPS green sturgeon spawn in the Rogue, Klamath, and historically in the Eel and Umpqua rivers.

State Listings
California state species protection status listings are governed by the California Endangered Species Act (CESA).
-Green Sturgeon are not listed under the California Endangered Species Act.

Federal Listings
Federal species protection status listings are governed by the Endangered Species Act (ESA).
- Green sturgeon - southern DPS: THREATENED (2006)
- Green sturgeon - northern DPS: species of concern (2006)


Critical Habitat
The Endangered Species Act (ESA) requires the federal government to designate critical habitat for any species it lists under the ESA.
- In October 2009, NMFS designated critical habitat for the Southern DPS (pdf).

Life History

Green sturgeon are a prehistoric cartilaginous fish that inhabit the waters along the west coast of North America, from Alaska to Baja California. By comparing the DNA and movement patterns of tagged fish, researchers identified two genetically Distinct Population Segments (DPS) of green sturgeon. Although these fish may look identical, their genetic makeup is very different. This distinction allows these populations to be effectively managed to preserve diversity.

Green sturgeon that spawn in the Klamath River in northern California and the Rogue River in southern Oregon belong to the northern DPS (nDPS) and are listed by NOAA Fisheries as a Species of Concern. Historically, this population has also spawned in the Umpqua and Eel rivers and research currently being conducted on the Eel River may discover that spawning is still occurring there. A total population of approximately 1000 adult sDPS green sturgeon has been estimated using DIDSON technology during surveys on the spawning grounds on the mainstem Sacramento River.

Green sturgeon reach maturity at around 15 years of age and can live to be 70 years old. Unlike salmon, they may spawn several times during their long lives, returning to their natal rivers every 3-5 years. During spawning runs, adult sDPS fish enter San Francisco Bay between mid-February and early May and migrate rapidly up the Sacramento River. Spawning mainly occurs in cool sections of the upper Sacramento River with deep, turbulent flows. Green sturgeon spawn when water temperature is between 12-15 degrees Celsius. In the fall, these post spawn adults move back down the river and re-enter the ocean. After hatching, larvae and juveniles migrate downstream toward the Sacramento-San Joaquin Delta and estuary. After rearing in the delta and estuary for several years, they move out to the ocean. As adults, both sDPS and nDPS green sturgeon migrate seasonally within the nearshore waters along the west coast, congregating in bays and estuaries in Washington, Oregon, and California during the summer and fall months. During winter and spring months they congregate off of northern Vancouver Island, British Columbia, Canada."

Habitat

Adult and subadult nDPS and sDPS green sturgeon spend most of their lives coexisting in marine and estuarine waters from the Bering Sea, Alaska (Colway and Stevenson 2007) to El Socorro, Baja California, Mexico (Rosales-Casian and Almeda-Juaregui 2009). Although the two DPSs coexist in the marine environment, the two species do not appear to enter the freshwater of each other’s natal rivers. Lindley et al. (2011) found that green sturgeon tagged in the Klamath or Rogue rivers were not detected near the Golden Gate Bridge, and green sturgeon tagged in San Pablo Bay/Sacramento River area were not detected in the Rogue or Klamath rivers.

Based on tag detections at fixed monitor arrays, subadult (ocean entry to age of first spawning) and adult sDPS green sturgeon can be found in transit within nearshore coastal waters from Monterey Bay, California, to Graves Harbor, Alaska (Moser and Lindley 2007; Lindley et al. 2008; Lindley et al. 2011). In the summer and fall, large concentrations of these fish are observed within coastal bays and estuaries, including the Columbia River estuary, Willapa Bay, Winchester Bay, and Grays Harbor (Moser and Lindley 2007, Lindley et al. 2008, Lindley et al. 2011). It is likely that these areas are used for feeding and possibly for thermal refugia due to the presence of cold, upwelled water along the west coast in the summer (Moser and Lindley 2007). During winter and spring, many of these fish migrate north to the nearshore marine waters from southern Vancouver Island to Graves Harbor, Alaska (Erickson and Hightower 2007, Lindley et al. 2008, Lindley et al. 2011).

Spawning of sDPS green sturgeon primarily occurs in the mainstem Sacramento River although a spawning event was documented in 2011 in the lower Feather River at the Thermalito Afterbay Outlet (Seesholtz 2012). On both of these rivers, dams currently prevent adult green sturgeon from reaching upstream areas that likely supported spawning historically (Mora et al. 2009). Although spawning has not been documented, adult green sturgeon have been observed during the spawning season in the lower Yuba River downstream of Daguerre Point Dam (Cramer Fish Sciences 2011), suggesting that green sturgeon may have spawned historically in those rivers.

The Sacramento River is an important migratory corridor for larval and juvenile sturgeon during their downstream migration to the San Francisco Bay Delta and Estuary. The San Francisco Bay Delta and Estuary provides year-round rearing habitat for juveniles, as well as foraging habitat for non-spawning adults and subadults in the summer months (NMFS 2008).

Given the lack of credible evidence, it does not appear that green sturgeon historically utilized the San Joaquin River (Biological Review Team (BRT) 2005; Beamesderfer et al. 2007), although modeling studies (Mora et al. 2009) suggest that spawning could have been supported by habitat that existed in that system historically. Although there is evidence of sturgeon presence in the Russian River, which flows into the Pacific Ocean north of San Francisco Bay, the only known photo is of a white sturgeon.

References:
Beamesderfer, R.C.P., M.L. Simpson, and G.J. Kopp. 2007. Use of life history information in a population model for Sacramento green sturgeon. Env. Biol. Fish. 79:315-337.

BRT. 2005. Green sturgeon (Acipenser medirostris) status review update. Prepared for the National Marine Fisheries Service. 36 pp.

Colway, C. and D.E. Stevenson. 2007. Confirmed records of two green sturgeon from the Bering Sea and Gulf of Alaska. Northwestern Naturalist 88(3):188-192.

Cramer Fish Sciences. 2011. Memo: Green Sturgeon Observations at Daguerre Point Dam, Yuba River, CA. Paul Bergman. June 7, 2011.

Erickson, D.L., and J.E. Hightower. 2007. Oceanic distribution and behavior of green sturgeon (Acipenser medirostris). In Munro, J., J.E. Hightower, K. McKown, K.J. Sulak, A.W. Kahnle, and F. Caron, eds. Anadromous sturgeons: habitats, threats, and management. AFS Symposium 56: 197-211.

Lindley, S.T., M.L. Moser, D.L. Erickson, M. Belchik, D.W. Welch, E. Rechisky, J.T. Kelly, J. Heublein, and A.P. Klimley. 2008. Marine migration of North American green sturgeon. Trans. Am. Fish. Soc. 137:182-194.

Lindley, S.T., D.L. Erickson, M.L. Moser, G. Williams, O.P. Langness, B.W. McCovey, M. Belchik, D. Vogel, W. Pinnix, J.T. Kelly, J.C. Heublein, and A.P. Klimley. 2011. Electronic tagging of green sturgeon reveals population structure and movement among estuaries. Trans. Am. Fish. Soc. 140:108-122.

Mora, E.A., S.T. Lindley, D.L. Erickson, and A.P. Klimley. 2009. Do impassable dams and flow regulation constrain the distribution of green sturgeon in the Sacramento River, California? J. Applied Ichthyology 25:39-47.

Moser, M.L., and S.T. Lindley. 2007. Use of Washington estuaries by subadult and adult green sturgeon. Env. Biol. Fish. 79:243-253.

NMFS. 2008. Draft Biological Report, Proposed Designation of Critical Habitat for the Southern Distinct Population Segment of North American Green Sturgeon. September 2008.

Rosales-Casian, J.R. and C. Almeda-Juaregui. 2009. Unusual occurrence of a green sturgeon (Acipenser medirostris) at El Socorro Bay, Baja California, Mexico. California Cooperative Fisheries Investigations, CalCoFI Reports 50:169-171.

Seesholtz, A.M., Manuel, M.J., and J.P. Van Eenennaam. 2014. First documented spawning and associated habitat conditions for green sturgeon in the Feather River, California. Env. Biol. Fish. DOI 10.1007/s10641-014-0325-9

Identification

Juvenile green sturgeon
Figure 1. Juvenile green sturgeon. (source: Beamesderfer and Gray 2009).
Sturgeon are among the largest and most ancient of bony fishes. They are highly specialized, containing such features as a heterocercal tail, fin structure, jaw structure, spiral valve intestine, and spiracle. They have a cartilaginous skeleton and possess several rows of large ossified plates, called scutes, instead of scales (Figure 1). Sturgeon are highly adapted for feeding on bottom-dwelling animals, which they detect using a row of extremely sensitive barbels on the underside of their snouts. Sturgeons also have electrical sensory organs on their snout, called Ampullae of Lorenzini, that help them detect prey in murky waters and perhaps guide them during their coastal migrations, as observed in hammerhead sharks (Klimley 1993). They can protrude their long and flexible mouths (similar to the lake sturgeon shown in Figure 2) into the substrate to slurp up food.

lake sturgeon
Figure 2. Photo of the tubular mouth of a
lake sturgeon (source: http://dnr.wi.gov/)
Only two sturgeon species reside on the west coast of North America, the green sturgeon, Acipenser medirostris, and the white sturgeon, A. transmontanus (Moyle 2002). Green sturgeon were first described by Ayres (1854) from San Francisco Bay. Green sturgeon may be distinguished from the sympatric white sturgeon (Figure 3) by their olive green color, their barbells (which are closer to the mouth than the tip of their snout), a prominent green stripe on the lateral and ventral sides of their abdomen, the presence of relatively sharp scutes, differences in number of lateral scutes, the presence of one large scute behind the dorsal and anal fins (which is absent in white sturgeon), and the location of the vent (North et al. 2002).

Juvenile green sturgeon
Figure 3. Lateral and ventral morphological differences
between green sturgeon (a-b) and white sturgeon (c-d).
The two DPSs inhabit similar estuarine and marine waters along the west coast and are morphologically similar; therefore genetic analysis must be conducted to identify them to their associated DPS.

References
Ayres, W. O. 1854. Descriptions of three new species of sturgeon San Francisco. Proceedings of the California Academy of Natural Sciences 1:14-15.

Klimley, A. P. 1993. Highly directional swimming by scalloped hammerhead sharks, Sphyrna lewini, and subsurface irradiance, temperature, bathymetry, and geomagnetic field. Marine Biology. 117:1-22.

Moyle, P.B. 2002. Inland Fishes of California. University of California Press, Berkeley, CA. 502 pp.

North, J.A., R.A. Farr, and P. Vescei. 2002. A comparison of meristic and morphometric characters of green sturgeon Acipenser medirostris. J. Applied Ichthyology 18:234-239.

Research

Research through both collaborative and independent efforts has been conducted on such topics as distribution, migration, spawning and feeding habitat utilization, adult abundance estimates, and genetic research. Some examples of this research include:

UC Davis conducts habitat assessments, genetic analysis, adult spawning abundance estimates, habitat partitioning between green and white sturgeon, and telemetry studies in the Sacramento River and the San Francisco Bay Delta Estuary. Within its laboratories, research (e.g., temperature, salinity, contaminants, entrainment risk, etc.) is conducted on the early life stages;

USBR conducts telemetry studies of adult green sturgeon in the upper Sacramento River;

USFWS conducts habitat assessments and egg and larval/juvenile green sturgeon research in the upper Sacramento River;

Corps is conducting Population Viability Analysis;

CDWR conducts telemetry and DIDSON studies of adults and egg/larvae sampling in the Feather River;

CDFW annually tags green sturgeon in Suisun and San Pablo bays and collects and analyzes data from angler report cards;

WDFW and ODFW conducts a coastwide green sturgeon monitoring program to assess population viability and gather information on how to better manage anthropogenic threats. They were awarded three years (2010-2012) of funding through the ESA section 6 recovery grant program and several hundred green sturgeon were tagged and detected using arrays of monitors in various coastal bays and estuaries;

NMFS conducts genetic analysis and maintains an array of monitors near the Golden Gate Bridge and off Pt. Reyes;

Cramer Fish Sciences conducts research on green sturgeon in the Yuba River;

CVPIA has invested in two green sturgeon research projects that have helped improve our understanding of the life history requirements and temporal patterns of sDPS green sturgeon habitat use; and

Consultants are tracking green sturgeon at various locations in California.

Recovery Plan

A Green Sturgeon Recovery Plan is currently being developed by NOAA Fisheries. The Recovery Team consists of the following scientists from many agencies and distributed along the west coast.

David Woodbury
NMFS Green Sturgeon Recovery Coordinator

Ray Beamesderfer
R2 Resource Consultants

Russ Bellmer
California Department of Fish and Wildlife

Richard Corwin
U.S. Bureau of Reclamation (retired)

Daniel Erickson
Oregon Department of Fish and Wildlife

Marty Gingras
California Department of Fish and Wildlife

Josh Israel
U.S. Bureau of Reclamation

Steve Lindley
NMFS Southwest Fisheries Science Center

Mary Moser
NMFS Northwest Fisheries Science Center

Mike Parsley (retired)
U.S. Geological Survey

Bill Poytress
U.S. Fish and Wildlife Service

Alicia Seesholtz
California Department of Water Resources

Fishing Regulations

See Sturgeon fishing regulations effective Jan.1, 2013

Green sturgeon may not be taken or possessed within California

Green sturgeon may not be removed from the water and shall be released immediately

It is unlawful to take any sturgeon from January 1 to December 31 on the Sacramento River from Keswick Dam (Shasta County) downstream to the Highway 162 Bridge (Glenn County). In addition, wire leaders and lamprey or shrimp baits are prohibited in that stretch of river.

Green sturgeon taken and released incidentally to white sturgeon fishing shall be reported on a Sturgeon Fishing Report Card issued by the department, in accordance with procedures defined in CCR Sections 1.74 and 5.79.