Trends in Abundance: In California, green sturgeon have been collected in small numbers in marine waters from the Mexican border to the Oregon border. They have been noted in a number of rivers, but spawning populations are known only in the Rogue, Sacramento and Klamath Rivers (see below). The following distributional information on green sturgeon in California waters was compiled by Patrick Foley (University of California, Davis, 1992) and updated from information in Adams et al. (2007)
North Coast. From the Eel River northward, it is likely that most records of sturgeon caught in rivers and estuaries refer to north coast green sturgeon. However, most early references regarding sturgeon from the north coast did not identify the species and some reports indicated white sturgeon to be more abundant (Fry 1979). While white sturgeon do occur on occasion in the Klamath and other rivers, it is highly likely that most historic records are for north coast green sturgeon. Accounts from 19th century newspapers (The Humboldt Times) report sturgeon from the mainstem Eel River, South Fork of Eel River and the Van Duzen River (Wainwright 1965). Length and weights given in these newspaper accounts are most consistent with those of adult green sturgeon.
In the middle part of this century, two young green sturgeon were collected in the mainstem Eel River and large sturgeon were observed jumping in tidewater (Murphy and DeWitt 1951). Two additional young green sturgeon were taken from the Eel River in 1967 and are in the fish collection at Humboldt State University. Substantial numbers of juveniles were caught by CDFG in the mainstem Eel River during trapping operations in 1967-1970 (O'Brien et al. 1976): 22 at Eel Rock in 1967, 53 at McCann in 1967 and 161 in 1969, 221 at Fort Seward in 1968, and smaller numbers at other localities. Green sturgeon have been included in lists of natural resources found in the Eel River Delta (Monroe and Reynolds 1974, Blunt 1980). However, CDFG biologists D. McCleod and L. Preston observed a 1+ m long sturgeon, most likely a green sturgeon, in a gravel extraction trench in the mainstem Eel upstream of the Blue Lake Bridge (river mile 16) on May 20, 1992. Green sturgeon are still occasionally seen in the Eel River (Adams et al. 2007). One green sturgeon was detected near Cock Robin Island in the Eel River estuary in 2008 (S. Lindley, pers. comm.).
Records of sturgeon in the Humboldt Bay system, comprising Arcata Bay to the north and Humboldt Bay to the south, are almost exclusively green sturgeon. Ten years of trawl investigations in South Humboldt Bay produced three green sturgeon (Samuelson 1973). Records from Arcata Bay are more numerous. On August 6 and 7, 1956, 50 green sturgeon were tagged in Arcata Bay by CDFG biologist Ed Best (D. Kohlhorst, pers. comm.). Total length ranged from 57.2 cm to 148.6 cm with a mean TL of 87.0 cm (± 20.6 cm SD). In 1974, nine green sturgeon were collected over a two-month period in Arcata Bay (Sopher 1974). Total length of these fish ranged between 73-112 cm. The Coast Oyster Company, Eureka, pulls an annual series of trawls in Arcata Bay in order to decrease the abundance of bat rays, Myliobatis californica. Green sturgeon are incidentally taken in this operation. Eight green sturgeon collected for parasite evaluation in 1988 and 1989 had total lengths ranging between 78-114 cm. One large individual, 178 cm TL and 18.2 kg, was returned to the bay.
Green sturgeon have been reported from the Mad River (Fry 1979), but recent evidence of their presence is scant (Bruce Barngrover, pers. comm. 1992).
An occasional green sturgeon is encountered in the coastal lagoons of Humboldt County (Terry Roelofs, pers. comm. 1992). Big Lagoon and Stone Lagoon are connected to the ocean during part of the year and migrating sturgeon may gain entry at this time. In June 1991, a 120-cm green sturgeon was gillnetted in Stone Lagoon (Terry Roelofs, pers. comm. 1992). In 2007, green sturgeon tagged with sonic tags were detected moving in and out of Humboldt Bay in array set up to study the movements of coho salmon (S. Lindley, USFWS, unpublished). Both the northern and southern DPS use Humboldt Bay during the spring and fall (S. Lindley, pers. comm.).
Klamath and Trinity Rivers. The largest spawning population of green sturgeon in California is in the Klamath River Basin. Both green sturgeon and white sturgeon have been found in the Klamath River estuary (Snyder 1908a, USFWS 1980-91) but white sturgeon are taken infrequently, in very low numbers, and are presumed to be coastal migrants (USFWS 1982). A sturgeon investigation program, initiated in 1979 by USFWS, found that almost all sturgeon occurring above the estuary were green sturgeon (USFWS 1980-83). The sturgeon primarily use the mainstem Klamath River and mainstem Trinity River, but have also been seen in the lower portion of the Salmon River as well (Adams et al. 2007).
Both adults and juveniles have been identified in the mainstem Klamath River. Adults are taken annually, spring and summer, by an in-river Native American gillnet fishery. The numbers average around 500 fish per year (see below). They have also been taken by sport fishermen as far inland as Happy Camp (river km 172) (unpubl. CDFG Tagging Data 1969-73, Fry 1979, USFWS 1981). However, the apparent limit for the spawning migration is Ishi Pishi Falls, upriver from Somes Bar, Siskiyou County (approximately river km 113). A few juveniles have been taken as high up as Big Bar (river km 81) (Tom Kisanuki, pers. comm.), but most have been recovered by seining operations directed at salmonids in the tidewater (USFWS, CDFG). Sampling by the USFWS captured 7 juveniles in (June) 1991 and 23 in (June-July) 1992 (T. Kisanuki, pers. comm.1995). Catch data from six outmigrant traps placed in the Klamath River reported that juvenile green sturgeon were caught every year (2000-2005) during trap operations (unpubl. Cunanan and Hines 2006, USFWS). The number of green sturgeon captured each year varied from one (2005) to 775 (2003). The total number of juvenile green sturgeon captured over the six years of operation was 1599. The size of captured green sturgeon varied from a minimum of 20 mm to a maximum of 252 mm and averaged 68.5 mm. Green sturgeon captured by the traps were most likely juveniles ranging in age from a couple of weeks to less than two years old, based on growth curves developed by Nakamato et al. (1995) and Van Eenennamm et al. (2001). However, the average size (68.5 mm) was similar to the size of artificially reared Klamath River green sturgeon at 35 days old (66.4 mm; Van Eenennaam et al. 2001).
The Trinity River enters the Klamath River at Weitchpec (river km 70). The earliest green sturgeon described from the Klamath Basin came from the Trinity River (Gilbert 1897). Both adults and juveniles have been identified; 211 sturgeon, between 7-29 cm TL, were captured near Willow Creek, Humboldt County, incidental to a salmonid migration study in July-September, 1968 (Healey 1970). The USFWS has collected juvenile green sturgeon in recent years from the Trinity River, as far up as Big Bar: 2 (in 1989), 0 (1990), 6 (1991) and 36 (1992) (T. Kisanuki, pers. comm.). Adults are caught yearly in a Native American gillnet fishery (USFWS 1980), a traditional fishery with a long history (Kroeber and Barrett 1960). Spawning migrants penetrate the mainstem Trinity River up to about Grays Falls, Burnt Ranch, Trinity County (river km 72).
Sturgeon have also been reported to use the South Fork Trinity River, a third-order stream entering above Willow Creek (river km 51) (USFWS 1981). Oral histories from old-time residents confirm this. However, a large flood in 1964 had devastating effects on anadromous fish habitat in this subbasin (U.S. Department of the Interior 1985). Millions of cubic yards of soil were moved into South Fork Trinity River and its tributaries. Channel widening and loss of depth resulted. This event, along with other changes in basin morphology, has apparently resulted in the loss of suitable sturgeon habitat. There are no recent sightings from this watershed.
The Salmon River is a fourth-order stream entering the Klamath River at Somes Bar (river km 106). The water in this river is generally clear and becomes turbid only during high run-off periods. Adult sturgeon have been seen swimming in this river by observers standing on bluffs overhead. The approximate limit to upriver migration is at the mouth of Wooley Creek (river km 8), a third-order stream.
Del Norte County. Green sturgeon have been taken during gillnet sampling in Lake Earl (D. McCloud, pers. comm.). Lake Earl is located along the coast of Del Norte County, 8 km north of Crescent City and 11 km south of the mouth of Smith River. It is connected by a narrow channel to Lake Talawa, a smaller lake directly to the west. A sand spit separates Lake Talawa from the ocean and is occasionally breached by winter storms or by human activities. Coastal migrant green sturgeon enter at this time and become trapped after the sand spit is rebuilt (Monroe et al. 1975).
The Smith River is the northernmost river along the California coast, entering the ocean approximately 5 km south of the Oregon border. Blunt (1980) included green sturgeon in an inventory of anadromous species found in the Smith River. They occasionally enter the estuary and have been observed in Patrick's Creek, an upstream tributary 53 km from the ocean (Monroe et al. 1975). Juveniles have not been found.
Overall, north coast green sturgeon are apparently occur in fewer streams than they did historically and presumably are also in reduced numbers, although evidence is limited. The only time series data available of green sturgeon abundance in the Klamath River comes from tribal catch data (see below). The number of females spawning in the Klamath River is estimated at 760-1500 per year. The population of subadults-adults is estimated at tens of thousands, with no clear evidence of population decline (Adams et al. 2002).