| Abstract/Description or Keywords |
The white sturgeon, Acipenser transmontanus, is the largest freshwater fish in North America, and one of five sturgeon species in Canada. White sturgeon occur in three large river systems on the west coast: the Fraser, Columbia and Sacramento drainages. In British Columbia they occur in the Fraser River system from the estuary upstream past the Morkill River, northwest of McBride; in the upper Columbia system in Arrow and Slocan lakes and in the mainstem downstream of Hugh L. Keenleyside Dam; and in the Kootenay River from Kootenay Lake upstream to the U.S. border. The most distinguishing features of white sturgeon are a long scale-less body, with rows of large bony plates, called scutes, along the back and sides (Figure 1). Also conspicuous are the shark-like tail, and long snout. Sturgeon have no teeth but can extend their mouth to engulf food, detection of which is aided by four barbels in front of the mouth. Young white sturgeon feed on a variety of foods, including benthic invertebrates and small fish; larger fish (e.g., salmon and eulachon) can be important in the diets of older white sturgeon, although this may vary among populations. Figure 1. The white sturgeon, Acipenser transmontanus. (Drawing by Loucas Raptis of a specimen from the Nechako River.) White sturgeon are slow-growing, take a long time to reach sexual maturity, and live a long time. In the Fraser River, some individuals have been aged at more than 100 years. Age of reproductive maturity for females may be 26 years or more, although it can be half this for males. Spawning occurs at intervals of up to 10 years. The record white sturgeon was caught in the Columbia River, at Astoria, and weighed approximately 1900 pounds. Specimens exceeding 1300 pounds and 6 m have been caught in the Fraser River. White sturgeon are one of the few fish species in British Columbia that spawn during the peak freshet period in the spring, typically May and June. The number of eggs released by a female during spawning may vary from about 700,000 in a medium-sized female to more than four million in a very large one. The eggs are sticky and attach to the rocky bottom or vegetation. Embryos hatch into larvae with an attached yolk sac, then metamorphose to look like miniature adults within 30 days. In British Columbia, white sturgeon habitat has declined in both quality and quantity. The regulation of river flows has had a large influence, particularly on the Columbia, Kootenay and Nechako systems. The effects of dams are numerous, including changes to water quality, streamflow patterns, water temperature, physically suitable habitat, and potentially changes in species composition. Dredging, gravel extraction, dyking and channelization have also been common practices throughout the province, and may be especially important on the lower Fraser River. Population declines have occurred in many parts of the Canadian range, particularly in the lower Fraser, Nechako, Columbia and Kootenay rivers. The abundance of sturgeon in the Fraser River mainstem upstream of Hell’s Gate may be naturally low but stable. Conservation planning efforts have been initiated and are mostly complete for the Columbia, Kootenay, and Nechako Rivers. White sturgeon were uplisted by COSEWIC in November 2003, from a “species of management concern” to “endangered,” although legal listing under SARA has not yet occurred. The Conservation Plan.— Development of a Fraser River White Sturgeon Conservation Plan (referred to henceforth as the “Plan”) has recently been initiated, and a Working Group has been assembled to oversee development of a draft Plan. The Plan will be a high-level planning document that provides information on white sturgeon biology and conservation, identifies information gaps, and sets priorities for action by government and non-government organizations. Development of the Plan requires an understanding of the threats to long-term persistence of white sturgeon in the Fraser River. This document attempts to summarize the issues facing conservation of Fraser River white sturgeon stocks. The document is meant as a discussion paper rather than a final conclusion; the intent is for the Working Group, technical experts, and stakeholders to review the contents so that a set of priorities for action can emerge as part of the Plan. A separate document will be prepared to capture the input received from the Working Group and others. Fraser River white sturgeon are divided into four distinct stock groups (Figure 2); the challenges facing the species vary among these different stock groups (Ptolemy and Vannesland 2003). For the most part, the various threats can be described but not quantified. Despite difficulties with quantification, in many cases there may be considerable evidence that a specific threat is real. The threats are presented and discussed here as “impact hypotheses,” hypothesized mechanisms that influence abundance, distribution and health of white sturgeon. The intent is to focus attention first on the underlying mechanisms influencing white sturgeon (e.g., water temperature) before assessing the causal agents controlling the mechanism (e.g., river regulation). Our aim in doing this is to focus attention on available data and uncertainties as a first step, rather than foster immediate arguments about which cause is most important. |
