Green sturgeon (Acipenser medirostris) COSEWIC assessment and status report: chapter 6

Species information

Update
COSEWIC Status Report
on the
Green sturgeon
Acipenser medirostris
in Canada
2004

Name and classification

Class:
Actinopterygii
Order:
Acipenseriformes
Family:
Acipenseridae
Genus:
Acipenser
Scientific name:
Acipenser medirostris Ayers 1854
Common names
  English:
Green sturgeon
  French Canada/France:
Esturgeon vert
  Salish First Nations:
K’toyethen
  Mexico:
Esturión verde
  Japan:
Chôzame
  Russian Federation:
Sterlyad
  Asia:
Sakhalin Sturgeon
Synonyms:
A. medirostris mikado, A. acutirostris (Froese and Pauly 2003)


Sturgeons are classified in the family Acipenseridae which consists of four genera: Acipenser, Huso, Scaphirhynchus, and Pseudoscaphirhynchus (Helfman et al. 1997). The green sturgeon (A. medirostris) was first described in 1854 from a specimen caught in San Francisco Bay (Ayres 1854, Adams et al. 2002). Asian populations (regionally named “Sakhalin” sturgeon) were initially considered to be conspecifics due to meristic count overlap to North American populations and were classified as either A. mikadoi or A. medirostris mikado. Zhang et al. (2001) and Fain et al. (2000) both conducted genetic analysis examining mitochondrial DNA sequences of Asian and North American green sturgeon and determined that the two forms of green sturgeon should be considered a single species. However, other genetic evidence (Birstein et al. 1993, 1997; Birstein and DeSalle 1998) and morphometric studies (North et al. 2002) suggest that the Asian and North American forms should be considered separate species (A. mikadoi and A. medirostris respectively). Further work is required to address this disagreement.

Description

Sturgeon are easily distinguished from other families of fish by a combination of features including four barbels in front of a subterminal mouth, five rows of bony scutes, a heterocercal tail, an elongate snout, a single fleshy dorsal fin located near the caudal peduncle, and a largely cartilaginous endoskeleton, including an unconstricted notochord that extends into the tail (Figure 1; Helfman et al. 1997; Echols 1995). 

The green sturgeon is anadromous but spends more time in the marine environment than any other species of sturgeon (Adams et al. 2002). The first record of green sturgeon captured in Canada was on August 30th, 1908. The specimen was 34 cm in length and was caught near Victoria, British Columbia (BC) (Clemens and Wilby, 1961). Green sturgeon can reach a maximum length and weight of 2.3 m and 159 kg (Scott and Crossman 1973).


Figure 1. Illustration of a green sturgeon (Acipenser medirostris ), 107 cm. Alaska.

Figure 1. Illustration of a green sturgeon (Acipenser medirostris ), 107 cm. Alaska.

BC 63-1064 (from Scott and Crossman 1973, art 1973).


Green sturgeon have a dark olive green dorsal surface and a white ventral surface with longitudinal and olive-green stripes between the lateral and ventrolateral plates and on the midventral surface extending the length of the body (Scott and Crossman 1973). The colouration pattern on its ventral surface resembles an arrow pointing towards its snout terminating anterior to its pectoral fins (Figure 2). There is anecdotal evidence that a colour variant of the species may exist. There have been reports of brown to golden coloured green sturgeon captured in San Francisco Bay and the Sacramento River. However, no “golden sturgeon” have been reported in Canada and whether this second morphotype is due to genetic or environmental influences is currently unknown (CDFG 2000 cited in EPIC 2001).


Figure 2. Photo of ventral surface of green sturgeon showing the arrow pattern terminating anterior to the pectoral fins

Figure 2. Photo of ventral surface of green sturgeon showing the arrow pattern terminating anterior to the pectoral fins (Photo courtesy Terry Slack).

Photo courtesy Terry Slack.


Due to range overlap and morphometric similarity, the green sturgeon can be confused with the white sturgeon (A. transmontanus), however they can be easily distinguished by a lateral line scute count; green sturgeon having 23-30 bony plates and the white sturgeon 38-48 (Scott and Crossman 1973). In addition, the position of the anal vent differs between the species, with the anal vent of the green sturgeon located directly between the posterior insertions of the pelvic fins compared to the white sturgeon where it is found posterior to the pelvic fins (Slack and Stace-Smith 1996;). Furthermore, the green sturgeon has two rows of 4 to 8 post vent scutes while the white sturgeon has a single row of 1 to 4 scutes extending from the pelvic fins to the anal fin (Figure 3).


Figure 3. Differences between green and white sturgeon vent location, and placement and number of ventral scutes

Differences between green and white sturgeon (see long description below).

Adapted from Eddy and Underhill 1978.

Description of Figure 3

Figure 3 shows differences between green and white sturgeon.

Green sturgeon

  • Vent located on imaginary line between insertions of the pelvic fins
  • One row of 1 – 4 scutes between pelvic and anal fins

White sturgeon

  • Vent caudal to imaginary line drawn between insertions of pelvic fins
  • Two rows of 4 – 8 scutes each between pelvic and anal fins


Unlike all other sturgeon species, green sturgeon larvae lack a direct swim-up or post-hatching stage (Deng 2000; Cech et al. 2000). They can also be distinguished from white sturgeon larvae by their larger size, lighter pigmentation, and size and shape of yolk sac (Adams et al. 2002; Cech et al. 2000).

North et al. (2002) conducted a study examining meristic and morphometric characteristics of green sturgeon captured in the Columbia River (Table 1). These individuals are likely representative of green sturgeon found in Canadian waters due to geographic proximity, and there is no evidence that morphometrics significantly vary between Distinct Population Segments (DPS).

Designatable units

Within North America, the National Marine Fishery Service (NMFS) has identified northern and southern Discrete Population Segments (DPS) for green sturgeon with the latitudinal boundary located at Eel River, CA (40º 42’N) (Adams et al. 2002). Israel et al. (2002) conducted a preliminary population genetic study indicating that green sturgeon found in the Rogue River, Oregon, and the Klamath River are distinct from those from San Pablo Bay, California. However, green sturgeon collected from the Columbia River appeared to be a mixture of other populations suggesting that there are currently unknown spawning populations or this result may be an artifact of low sample sizes and differences among years of specimen collection. As the specimens from the Columbia River and the northern DPS are closest to Canada, there is a greater likelihood that individuals found in Canadian waters are from these populations.

 

Table 1. Comparison of selected meristic characteristics (mean ± standard deviation) from 50 green sturgeon collected from the Columbia River in August 1999 and white sturgeon (North et al. 2002).
Character Green Sturgeon White Sturgeon
Mean Range S.D. Range
Total Length (cm) 148 125-170   n.a.
Dorsal Scutes 9.4 7-12 ± 1.1 11-14
Lateral Scutes 28.5 22-33 ± 2.8 36-48
Ventral Scutes 9.2 7-12 ± 1.1 9-12
Gill Rakers 19 15-26 ± 2.5 23-36

Values for white sturgeon are absolute ranges cited in North et al. (2002) from Scott and Crossman (1973), Schreiber (1959), Miller and Lea (1972) and Hart (1973).

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