|Scientific Name:||Acipenser transmontanus (Fraser Regional subpopulation)|
|Species Authority:||Richardson, 1836|
|Red List Category & Criteria:||Vulnerable A2abc ver 3.1|
|Assessor/s:||Down, T. & Ptolemy, J. (Ministry of Water, Land & Air Protection, Canada)|
|Reviewer/s:||St. Pierre, R. & Pourkazemi, M. (Sturgeon Red List Authority)|
The three white sturgeon groups in the mainstem of the lower Fraser River up to the Nechako River are considered together as the Fraser River regional subpopulation.
In the lower Fraser recreational angler catch-per-unit effort of sub-legal size fish (50–100 cm) fell from 0.34 to 0.17 fish per trip between 1985 and 1990 (Inglis and Rosenau 1994). In another study standardized multi-panel gill nets set at the same site at the same time of year showed a similar reduction from 1985–87 to 1992–93 (Lane et al. 1994). A comparison of the fish community in the lower Fraser between 1972–73 and 1993–94 also showed an apparent decrease in white sturgeon abundance (Richardson et al. 2000). The catch-per-effort, for assessment sampling in the Nechako River, declined significantly between 1982 and 1999 (Korman and Walters 2000).
During the summer/fall period of 1993 and 1994 there was an unexplained die-off of adult white sturgeon in the lower Fraser River (McAdam 1995). These episodes are worrisome, as all fish observed were large adults. The recovered carcasses (38) ranged in size from 2.16 to 3.86 m total length (mean = 3.18) and were primarily female. The age of the smallest fish was estimated at 27–30 years.
Area of occupancy has no doubt been reduced in the lower mainstem due to the alienation of side channels from dyking activity, the infolding of sloughs and wetlands, development and industrial activity. The loss of sloughs, side channels and other low velocity backwater areas has decreased available juvenile rearing habitat. Loss of side channels may reduce spawning habitat availability as well.
|Range Description:||At least two groups of white sturgeon occur in the lower Fraser between Mission and Hell's Gate and another in the middle Fraser between Hell’s Gate and the mouth of the Nechako River.
Fraser River subpopulations do not mix with the U.S. Regional population. Although it is known that some sub-adults spend time in the estuary (Veinott et al. 1999), Fraser River white sturgeon are not known to migrate further into the marine environment. There are no reports of white sturgeon in the Strait of Georgia off the Fraser River (Lane 1991).
Native:Canada (British Columbia)
|Range Map:||Click here to open the map viewer and explore range.|
Good information documenting historic population or subpopulation size decline does not exist. Records prior to 1900 (Semakula and Larkin 1968, Echols 1995) indicate annual sturgeon catches in the commercial fishery on the lower Fraser peaked at about 454,000 kg in 1897. The fishery collapsed in 1900, revived slightly in 1907, and collapsed again in 1917. Since then the commercial harvest has rarely exceeded 22,000 kg and during the 1965–75 period was about 12,000 kg per annum. Much of the commercial sturgeon catch was incidental to the salmon fishery although there may have been a directed fishery at the turn of the 20th century. This makes it difficult to compare the historical catch to more recent catches due to the changes in fishing patterns that have occurred.
Mark recapture estimates for the subpopulation (R.L. & L Environmental Services Ltd. 2000) show a population size of 22,000 (95% CI = 9,800–70,700). Length frequency and age distribution in the mainstem subpopulation appears relatively normal with most fish younger than age 20 (R.L. & L. Environmental Services Ltd. 2000). Fish
RL&L used a size of > 150 cm (called oversize) to separate adult individuals from sub-adults and juveniles. On this basis, 45% of the fish sampled in the lower Fraser were estimated to be adult fish; 37% in the canyon section were adults; and 20% of the subpopulation between Hell’s Gate and the Nechako. Overall, total number of adult white sturgeon in the lower Fraser River is estimated to be 8,876 fish or about 40% of the subpopulation.
RL&L found the sex ratio was skewed to males and varied from 4–4.5:1 below Hell’s Gate, to 7.6:1 in the middle Fraser. Fewer than 10% of the females and 12% of the males examined in the adult size class were in the late reproductive stages, indicating that the proportion of reproductively mature individuals in a given year is quite low. Limited data from an earlier study based on analysis of pectoral fin rays indicated intervals between spawning in the lower Fraser vary from 4–9 years (Semakula and Larkin 1968).
|Habitat and Ecology:||
Although it is known that some sub-adults spend time in the estuary (Veinott et al. 1999), Fraser River white sturgeon are not known to migrate further into the marine environment. There are no reports of white sturgeon in the Strait of Georgia off the Fraser River (Lane 1991).
In the river below Hell’s Gate some females may spawn as young as 18 and males at 14 years of age. Generation length in the regional subpopulation downstream of the Nechako appears to be in the range of 35–40 years of age.
|Major Threat(s):||Area of occupancy has no doubt been reduced in the lower mainstem due to the alienation of side channels from dyking activity, the infolding of sloughs and wetlands, development and industrial activity. The loss of sloughs, side channels and other low velocity backwater areas has decreased available juvenile rearing habitat. Loss of side channels may reduce spawning habitat availability as well.|
|Citation:||Down, T. & Ptolemy, J. (Ministry of Water, Land & Air Protection, Canada) 2004. Acipenser transmontanus (Fraser Regional subpopulation). In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 25 May 2013.|
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